The Trans-Antarctic Mountain range behind BTN
 
 
     

Science Projects for Pilot

   

   


Read the PILOT science paper
(now published in PASA, 2005, 22, 199-235)

Listed below are some sample science projects that could be conducted with PILOT. We invite you to add to this list. Please email your ideas, following the format below, to jacara@phys.unsw.edu.au.

 

Title Survey for Supernovae in Starbursts
Submitted by Stuart Ryder (AAO)
Outline of Science

Core-collapse supernovae (CCSNe) are responsible for generating, then liberating, the bulk of the light metals in the Universe. As such, all models for the chemical evolution of galaxies have the CCSNe rate as a fundamental input parameter. Despite the number of amateur and robotic supernova searches now underway, these can only deliver a lower limit to the actual rate.

The CCSNe rate will of course be greatest in the regions where the star formation rate is high, i.e. starbursts, and Ultra-Luminous IRAS Galaxies (ULIRGs). Unfortunately, these regions are also heavily obscured by dust, and crowded with young star clusters, making early detection of CCSNe in these regions extremely difficult. Near-infrared, diffraction-limited observations with PILOT could reveal 5-10 new CCSNe per year in 15 starbursts/ULIRGs that would be missed by existing searches.

Antarctic Advantages Near-IR diffraction limited imaging yields the spatial resolution required (~100 pc at 100 Mpc) to detect new CCSNe against a crowded and dusty background. The ability to re-visit each galaxy at any time during the 4 month winter increases the odds of a discovery, as well as enabling a light curve to be built up. Adaptive optics systems such as NAOS/Conica don't perform as well as had been hoped when guiding on the bright, but partly-resolved ULIRG nucleus, so truly diffraction-limited imaging with a 2-metre telescope in Antarctica is easily competitive with NACO on the VLT.
Wavelengths or Filters K band (2 microns) necessary. J through K (1-2.5 microns) would be useful.
Spatial Resolution 0.2" (100pc @ 100Mpc)
Area of Sky All southern sky monitoring
Frequency / Number of Samples Observing just 15 ULIRGs 3 times per year for 10 minutes each is expected to yield 9 CCSNe discoveries, based on current models.
Individual Observations 10 minutes is fine. Discovery opportunity increase with frequency of visits.
Light curves of SN2001lg in the Radio SN Detection Rates

 

Title Star Formation in the Thermal Infrared
Submitted by Michael Burton (UNSW)
Outline of Science

There are three principal regimes for star formation studies that PILOT would greatly facilitate:

  • The Galactic ecology. Examining the environment around star formation complexes, through the comparison of the emission from three spectral features: the H2 emission at 2.4um in the 1-0 Q-branch lines, the 3.3um PAHs emission feature and the Br-alpha emission at 4.05um. These allow the conditions and extent of the molecular, neutral (i.e. the PDR interface) and the ionized gas to be probed, respectively. For example, see the SPIREX image of NGC 6334 (below), showing the shells of fluoresently excited molecular gas around the sites of massive star formation, with the complex PAH organic molecules pervading the region.
  • The presence and evolution of disks during star formation. The IR excess emission from the disk around young stellar sources is readily detectable at 3.5um (L-band), and the colour (H-K) can easily be distinguished from the reddening vector. See the colour-colour diagrams below for NGC 6334 which show that the IR excess is hard to identify if observations are confined to just the J, H and K wavebands (1-2.4um).
  • The massive embedded stellar content, and its evolutionary state. All but the very coldest massive protostars are visible in the mid-IR, and the spectral features (particularly the silicate dust feature) measure the column density. The colour variations across the mid-IR window, from 8-25um, indicates the evolutionary state of the sources (i.e. how far embedded they are). See model SEDs below.
Antarctic Advantages
  • Background reduced by ~20 times from temperate sites.
  • Improved sky stability.
  • Improved sky transmission, especially from 20-30 microns.
  • Diffraction limited observations using only tip-tilt correction.

The 'Antarctic advantage' has already been demonstrated through the operation, in 1998-99, of the 60 cm SPIREX telescope at the South pole, equipped with a 1024x1024 IR array, operating from 2.4-5 microns.

Wavelengths or Filters Imaging through filters (broad and narrow band) from 2.3 to 30 microns.
Spatial Resolution Diffraction limit (0.25" at 2.3 microns to 3" at 30 microns)
Area of Sky Generally such observations are confined to individual sources or star forming complexes. However a thermal IR sky survey (2.4um + 3.5um), 4-5 magnitudes deeper than 2MASS, and with 5-10x higher spatial resolution, could be undertaken.
Frequency / Number of Samples

For a sky-survey, PILOT could achieve the following:

  • At 3.6um, to 0.001 Jy/arcsec^2: 2000 square degrees in a month, to all-sky in a year.
  • At 11um, to 0.01 Jy/arcsec^2: 400 square degrees in a month, to 4000 square degrees in a year.
Individual Observations  
NGC 6334, as imaged by SPIREX (B=PAHs, G=L-band, R=Br alpha)

NGC 6334, SPIREX/MSX composite (B=PAHs, G=8um, R=21um)s

NGC 6334 Colour-colour diagram using just JHK data. The disks are hard to find! The reddening vector and the infrared excess are degenerate. From Rathborne, 2003, PhD thesis, UNSW.
NGC 6334 Colour-Colour diagram now using HK and L band data. Notice how the IR excess sources, those presumed to have disks around them, are now readily identified.
Model spectral energy distributions representative of embedded massive protostars, as a function of the optical depth of the obscuring material to the central star (tau_V = 100, 500 & 1000). These have been calculated using the DUSTY code (Ivezic & Elitzur, 1997, MN, 287, 799), for a central source temperature of 30,000K and an r^-1.5 density distribution. The features in the spectrum are due to absorption from silicates. The shaded overlays are the windows that are accessible from Dome C, and at top from Mauna Kea. This illustrates the new windows that open at Dome C in the mid-IR and sub-mm which will facilitate the study of such objects.
Illustrative sketches show the evolution of the spectral energy distribution during low mass star formation. Initially the core is cold, 20-30K, peaking in the sub-millimetre (Class 0). An infrared excess appears and first peaks in the far-IR, emission from a warm envelope heated by the accretion luminosity (Class I). The peak shifts to the mid- and near-IR as a disk forms. (Class II). Its spectral shape depends on whether the disk is passive (merely re-processing the radiation from the central star) or active (also kept hot by ongoing accretion). Finally, the disk dissipates (Class III). As is apparent, all stages of disk evolution are best studied at by observations at wavelengths longer than 3um - ie in the thermal infrared.
An illustration of the stellar energy distribution for a 3 LSun system surrounded by a circumstellar disk at a distance of 400 pc. The excess from the disk is only weakly discerned at K-band, but clearly distinguished for observations in L-band. From Lada, 1999, in NATO ASIC Proc. 540, The Origin of Stars and Planetary Systems, p143.

 

Title Imaging and Photometric follow-up of Transiting Planet Candidates
Submitted by Marton Hidas (UNSW)
Outline of Science

Transit searches attempt to detect close-orbiting extrasolar planets by detecting the periodic dip in the host star's lightcurve as the planet transits it. They are generally performed with wide-field cameras looking at crowded fields. However, ~90% of candidates detected by such searches will actually be eclipsing binary stars, either undergoing grazing eclipses, or with the depth of the eclipse diluted by a third, blended star (Brown 2003, astro-ph/0307256).

High spatial resolution imaging and multi-colour photometry provides efficient ways to determine the nature of the transiting system:

  • Stars blended in the wide-field search images can be resolved.
  • The star hosting the transiting object can be identified and the true (undiluted) transit depth measured.
  • The host star's colours yield estimates of its size and mass, and thus constrain models of the transiting system (Drake & Cook, 2004 ApJ 604, 379)
  • Many binary systems can be identified by the colour dependence of the eclipse shape, even when diluted (Tingley 2004, astro-ph/0406201).
Antarctic Advantages
  • High spatial resolution
  • Provide guaranteed follow-up of candidates with periods up to a few weeks.
  • The low scintillation and small variation in airmass improves the photometric precision. It should be possible to improve from the current 2-5 milli-magnitude rms errors of wide-field transit searches to significantly better than 1 milli-magnitude precision. The scintillation and Poisson-noise limits for a 1-minute exposure on a V=13 star with PILOT are each ~0.3 mmag (based on equations in Kjeldsen & Frandsen, 1992, PASP, 104, 413). The higher S/N of light curves thus obtained would provide tighter constraints on the physical properties of the transiting system.
  • Good access to Galactic plane (where many transit searches are looking).
  • Candidates will generally be bright enough to be used as AO reference stars
Filters V, I, possibly J, H, K to constrain stellar types.
Spatial Resolution This project will use the highest possible spatial resolution that can be achieved (in the visible). To be truly advantageous over other telescopes, PILOT will need to do considerably better than 0.5 arcsec.
Area of Sky A field of view at lest 1-2 arcmin across around each candidate star will be needed. Candidates will generally be near the Galactic plane or in other crowded fields, such as clusters.
Individual Observations For each candidate, a minimum of two complete transit events would need to be observed. Observation at half-period intervals also used for shallow secondary eclipses. A transit event typically lasts 2-5 hours, and typical periods will be 1-7 days. Thus, a total of ~10-20 hours of observing per candidate will be needed, over a few days to weeks. The target stars will be relatively bright (V<~14), so individual exposures will not need to be longer than a few minutes.
How long for the project? It would be an on-going project (as long as transit searches in the southern hemisphere are on-going).
Related projects

There are several transit search programs currently underway which are ideally located to provide candidates for follow-up by PILOT:

  • Vulcan-South, at the South Pole.
  • The UNSW/APT Planet Search, at Siding Spring Observatory.
  • The All-Sky Automated Survey at Las Campanas, Chile.

 

Title Cosmic Shear Experiments
Submitted by Chris Blake and David Woods (UNSW)
Outline of Science

Light rays follow geodesics, which bend in the presence of matter. It follows that a coherent shape distortion is imprinted in the distribution of distant background galaxies by mass fluctuations in the intervening cosmic web. This pattern of cosmic shear is a powerful cosmological probe. It is directly sensitive to the dark matter distribution predicted by theory, and does not depend on the details of how galaxy light traces mass.

The most serious limitation for ground-based optical cosmic shear experiments is the systematic variation in the point-spread function (psf) due to atmospheric seeing. These psf distortions are typically an order of magnitude larger than the cosmological shear that we wish to measure. The outstanding natural seeing performance (i.e. stable atmosphere) obtainable at Dome C (~0.1'') is therefore extremely advantageous for controlling systematic psf variability and, equally importantly, resolving high-redshift galaxy shapes.

In addition to excellent image quality, cosmic shear surveys demand high galaxy surface density (10-100 per square arcmin) to reduce statistical noise. This requirement is much more important than measuring accurate shapes for individual galaxies, because there is an irreducible experimental scatter in the shape information owing to the unknown galaxy ellipticity before shear. Galaxy shapes must be resolved, but are not required to be measured at high signal-to-noise.

Cosmic shear experiments may be broadly divided into two categories (for useful reviews see Hoekstra, Yee & Gladders 2002; Refregier 2003):

  1. Experiments mapping 'blank fields' to detect the shear pattern resulting from gravitational lensing by the cosmic web of large-scale structure. Current state-of-the-art surveys cover a few square degrees and have measured the amplitude of mass fluctuations (called sigma_8) to 10% (e.g. Bacon et al. 2003). In 10-15 years, cosmic shear surveys will cover the whole sky and will have the power to characterize the properties of the dark energy as a function of redshift.
  2. Experiments targeting the most massive clusters (where the shear distortions will be largest). The shear pattern can be used to re-construct the cluster gravitational potential (Kaiser & Squires 1993), which can be compared with CDM theory. Currently this has been performed for tens of clusters (and also from space using the HST).

PILOT could also make a valuable contribution in the regime of strong gravitational lensing, via observations of lensed arcs in the vicinity of high-redshift clusters. It has been shown that the probability of giant arc formation due to galaxy clusters is a sensitive measure of global cosmic parameters, particularly for the dark energy model (Bartelmann et al. 1998). Intriguingly, numerical simulations of clusters in the currently-favoured cosmological constant model fall short by an order of magnitude in reproducing the observed abundance of large gravitational arcs (Bartelmann et al. 2003, 1998). However, another study suggests that simulations using realistic redshift distributions for background galaxies resolves this discrepancy in the observed arc statistics (Wambsganss et al. 2004). Also, possible modifications to our current understanding of cluster sub-structure and evolution may be necessary to help resolve this difference in theory and observation.

A recent project addressing these issues is the 'Red-Sequence Cluster Survey', which mapped 90 deg^2 in R and z-bands, discovering 8 strong gravitational arcs (Gladders et al. 2003). Near-infrared imaging is a prerequisite for pursuing these studies to higher redshift.

Observing Projects

Let us assess the competitiveness of some specific cosmic shear observational programmes possible with PILOT:

'Blank-field' cosmic shear survey over ~100 square degrees. This would be competitive if completed within ~5 years (the CFHT Legacy 'wide' survey is intending to map ~170 square degrees). PILOT can reach the required detection sensitivity of K ~21 in a ~1 hr pointing; the 20' field-of-view of the near-IR wide-field imager implies that 100 square degrees can be mapped in ~900 hr. The planned optical imager has a much smaller field-of-view (2') and would not be competitive for this type of survey.

Survey for strongly lensed gravitational arrcs in galaxy clusters. A 100 deg^2 survey to K ~2$ would yield 100-500 clusters with velocity dispersions in excess of 700 km s^-1 in the interval 1.0 < z < 1.5. Doing this type of wide-field, near-IR 'arc survey' of galaxy clusters would address the above questions and obtain an accurate, independent measurement of cosmological parameters.

Targeted observations of the outskirts of galaxy clusters. PILOT could map the outer regions of clusters (or bright galaxies) where cosmic shear observations can discriminate between different dark matter halo profiles (see Hoekstra et al. 1998; Hoekstra, Yee & Gladders 2004). The viability of the cluster shear observational technique in infrared wavebands has recently been demonstrated by King et al. (2002).

Targeted observations of superclusters. By mapping known superclusters, a cosmic shear survey can quantify the degree of filamentary structure present in the web of dark matter (see Gray et al. 2002), a critical observable discriminating between theories of structure formation.

Observing Issues

The required magnitude limits in optical or near-infrared wavebands to deliver the minimum source density of 10 per square arcmin (of galaxies that are usable for lensing studies) are R ~ 24 or K ~21 mags. To date, most cosmic shear experiments have been performed in the optical: with existing facilities, the attainable surface density of background galaxies (in a fixed integration time) is roughly an order of magnitude higher with optical observations than with near-IR imaging. Moreover, advances in infrared detector technology have lagged significantly in terms of the available field-of-view. However, given the dramatically reduced near-IR background available in Antarctica, it is timely to reassess this situation. Mapping cosmic shear in infrared wavebands offers a number of advantages:

  • galaxy shapes are smoother, tracing older stellar populations rather than knots of star formation, thus ellipticities are easier to measure;
  • background galaxies at high redshift (z > 1) are more readily detected;
  • the availability of infrared colours greatly enhances the efficacy of photometric redshifts, allowing a more accurate determination of the redshift distribution of the background galaxies;
  • for observations targeting cosmic shear behind galaxy clusters, the availability of K-band imaging enables the 'contamination' from foreground objects and cluster members to be greatly reduced (e.g. King et al. 2002);
  • combining the K-band luminosity of such clusters with the weak lensing mass estimate yields a mass-to-light ratio.
References
  • Bacon D.J., Massey R.J., Refregier A.R., Ellis R.S., 2003, MNRAS, 344, 673
  • Bartelmann, M., Huss, A., Colberg, J.M., Jenkins, A., Pearce, F.R. 1998, A\&A, 330, 1
  • Bartlemann, M., Meneghetti, M., Perrotta, F., Baccigalupi, C., Moscardini, L. 2003, A&A, 409, 449
  • Gladders, M.D., Hoekstra, H., Yee, H.K.C., Hall, P.B., Barrientos, L.F. 2003, ApJ, 593, 48
  • Gray M.E. et al., 2002, ApJ, 568, 141
  • Hoesktra H., Franx M., Kuijken K., Squires G., 1998, ApJ, 504, 636
  • Hoesktra H., Yee H.K.C., Gladders M.D., 2002, NewAR, 46, 767
  • Hoesktra H., Yee H.K.C., Gladders M.D., 2004, ApJ, 606, 67
  • Kaiser N., Squires G., 1993, ApJ, 404, 441
  • Refregier A., 2003, ARA&A, 41, 645
  • Wambsganss, J., Bode, P., Ostriker, J.P. 2004, ApJ, 606, 93

 

Title Gravitational Microlensing Towards the Galactic Centre
Submitted by Michael Burton (UNSW)
Outline of Science

Gravitational microlensing occurs if the geodesic from a star passes sufficiently close to a massive foreground object so that its path is lensed, splitting the light into multiple images. If there is a planet near one of the image an additional lensing effect can occur (Gould & Loeb 1992). The amplitude and light curve of the event depend on the geometry of the orbit and the mass of the planet. Typically it will result in a perturbation on the microlensing light curve of a few percent, lasting for a few hours. If there is a planet already present in the lensing system the probability of detecting a lensing signature from it is reasonably high if the sampling frequency is frequent and the photometric accuracy high (Albrow et al 1999).

To maximise the probability of finding such events a telescope should continuously monitor a region of sky where the stellar density is high. Nowhere is this more so than towards the Galactic Centre, which lies at 29S and so is well suited for viewing from Dome C. Furthermore, the Galactic centre is readily seen at 2.4 microns (extinction obscures the Galactic centre shortward of 1.6 microns), the very waveband where the sky background is lowest in Antarctica. Imaging with the JHK camera covers a 40’ field of view, achieving a sensitivity of 20.7 magnitudes (SNR=10) in 5 minutes. Alternating with images in H-band (sensitivity limit 21.4 magnitudes in 5 minutes), would enable the colour of the light curve to be measured, and so distinguish from non-lensing light variations. Towards the Galactic centre every pixel would contain at least one star! As calculated by Gould (1995), the optical depth for lensing is then unity; i.e. we would always be able to find at least one event underway. Such a tool would provide a powerful too for exploring the incidence of planetary systems through the secondary lensing signature imposed on the microlensing light curve.

Antarctic Advantages High sensitivity in K-dark window, where Galactic centre readily observed through extinction. Diffraction-limited imaging across wide-field readily obtained with just tip-tilt at 2.4 microns, so facilitating accurate photometry. Galactic centre well-placed for viewing in mid-winter, and its position facilitates long-time period monitoring, being accessible for ~14 hours per day.
Wavelength or Filters K-band (2.4 microns), with H-band (1.65 microns) to facilitate identification of type of light-curve variation.
Spatial Resolution 0.2" at K-band, across field of view.
Area of Sky Field of camera (40') centred on Galactic centre.
Frequency of sampling. Every 15 minutes
Individual Observations 5 minutes in K-band, then 5 minutes in H-band. Repeat continuously while Galactic centre accessible (above 25 degree elevation) - for ~14 hours each transit.
References
  • Albrow, M. et al., 1999. ApJ, 512, 673.
  • Gould, A., 1995. ApJ, 446, L71.
  • Gould, A. & Loeb, A., 1992, ApJ, 396, 104
  • Paczynski, B., 1986, ApJ, 301, 503.

 

Title Planetary Microlensing in the Inner Galaxy

Submitted by

 

Ian Bond (Massey University), Phil Yock (University of Auckland)
Outline of Science

The conditions at Dome C provide opportunities for studies in planetary microlensing that are not possible at any other site on the globe. By working in conjunction with the existing OGLE-III and MOA-II telescopes in Chile and New Zealand that are dedicated to gravitational microlensing, the PILOT telescope at Dome C would provide the opportunity to determine approximate abundancies of gas-giant and ice-giant planets in the Galaxy, and to obtain a useful limit on the abundance of terrestrial planets. Approximately 300 hours of telescope time on PILOT would be required per annum for 3 to 4 years. A telescope purpose built for microlensing at Dome C could determine the abundance of terrestrial planets in a similar period.

Gravitational microlensing occurs if the light ray from a star passes sufficently close to a massive foreground object so that it's path is bent, or lensed, into multiple images (see figure below). These images cannot be directly resolved but, as the lensing star moves across the line of sight, the total amplified light from the background star can be measured and this generates a symmetrical light curve profile that is now well recognized (Paczynski 1986). If the lens star has a planetary companion, additional lensing may occur, producing a perturbation in the light curve (Mao and Paczynski 1991, Gould and Loeb 1992). A positive demonstration of this effect was recently reported by the OGLE and MOA groups, where an observed 7 day perturbation in the light curve of a microlensing event was attributed to a 1.5 Jupiter mass planet in an orbit around a 0.3 solar mass main sequence star with an orbital radius of ~3 AU (Bond et al 2004).

Planetary microlensing is extremely difficult to detect in practice. In general, the planetary perturbations in the light curve are very short lived (occuring on timescales ranging from a few days to a few hours), and can occur anytime during the typically 40 day timescale of a microlensing event. The chances of catching these perturbations can be improved by focussing on the the special class of events where the lens star moves into near perfect alignment with the background star resulting in very high magnifications in excess of 50. In these events, the planetary perturbations will occur within a 24-48 hour period centred on the time of peak amplification (Griest and Safizadeh 1998). Furthermore the sensitivity to planets is greatly enhanced as was demonstrated in actual observations of high magnification events. In MACHO 1998-BLG-35, which peaked at an amplification of 80, a small perturbation was observed just on the threshold of detectability, possibly due a planet of between 0.5 and 1.5 Earth masses (Rhie et al 2000, Bond et al 2002). More recent observations of the event MOA 2003-BLG-32, which peaked at an extremely high magnification of more than 500, also demonstrated the high planetary sensitivity in these events (Abe et al 2004). In this case, no planetary perturbations were seen, but very strong constraints on the planetary configuration of the lensing system were obtained with substantial exclusion regions of 0.9-8.7 AU for Neptune mass planets and 2.3-3.6 AU for terrestrial mass planets. The exclusion regions for Jupiter mass planets were so large that they were effectively ruled out for any orbital radius.

To fully realize the sensitivity to planets in high magnification events, it is necessary to obtain densely sampled uninterrupted observations during a 24-48 hour period. This is currently attempted using a network of collaborating telescopes around the globe. The microlensing survey groups, MOA and OGLE, find around 6-12 high magnification events each year. However, most of these do not receive the required dense sampling - usually due to a combination of unfavourable weather and the lack of a telescope at a suitable longitude at the critical time. The PILOT telescope at Dome C would be ideally suited as a follow-up telescope for high magnification events. The excellent clear skies opportunities would greatly improve the "catchment" of high magnification events alerted by the survey groups. Over a 3-4 year period, 30-40 high magnification events could be monitored at sensitivities comparable to or better than in MOA 2003-BLG-32. This would provide good statistics on the abundances of gas giants and ice giants, as well as rough statistics on terrestrial planets, that would not be possible with telescopes elsewhere on the globe.

In order to determine the abundances of all types of planets with good statistical precision, a dedicated wide-field telescope at Dome C and a large camera would be required. An aperture of approximately 1.5 m and a camera with about 1 Gpixels would enable a sufficient number of main sequence stars to be monitored in 3 to 4 years for this purpose (Bennett et al 2002).

 

References

Abe, F. et al (2004). Science, 305, 1264.

Bennett, D.P. & Rhie, S.H. (2002). ApJ, 574, 985.

Bond, I.A. et al (2002). MNRAS, 333, 71.

Bond, I.A. et al (2004). ApJ, 606, L155.

Gould, A. & Loeb, A. (1992). ApJ, 396, 104.

Griest, K. & Safizadeh, N. (1998). ApJ, 500, 37.

Mao, S. & Paczynski, B. (1991). ApJ, 374, L37.

Paczynski, B. (1986). ApJ, 304, 1.

Rhie, S.H. et al (2000). ApJ, 533, 378.

Gravitational microlensing occurs if the light ray from a star passes sufficently close to a massive foreground object so that it's path is bent, or lensed, into multiple images.

 

Title High Resolution Planetary Imaging
Submitted by Jeremy Bailey (AAO / Macabre University)
Outline of Science

By using the selective imaging (or lucky imaging) technique it should be possible to take diffraction limited planetary images at any wavelength using a 2m telescope and thus obtain results comparable with the Hubble Space Telescope. The images can be used for general monitoring of changes to planetary atmospheres and surfaces. Some specific projects that could be carried out are:

  1. Studies of the atmospheric circulation of Venus at the lower cloud layer. By observing Venus at 1.7 or 2.2-2.4 microns we see the cloud structure silhouetted against the thermal radiation from the lower atmosphere. Continuous monitoring of the cloud motions at high spatial resolution would provide valuable data that can be compared with the predictions of atmospheric general circulation models (GCMs).
  2. Studies of the Venus oxygen airglow. Imaging of Venus at 1.27 microns enables one to observe the strong (mega-Rayleigh) and highly variable molecular oxygen airglow emission from the Venus upper atmosphere. Continuous monitoring of variations in its intensity and spatial structure would place constraints on the dynamics and chemistry of the upper atmosphere.
  3. Mars surface pressure imaging. By observing Mars in narrow band filters that isolate the 2 micron CO2 bands it is possible to take images of the surface pressure distribution. These should allow monitoring of weather systems on Mars and provide data that can be used to test Mars atmosphere GCMs.
Antarctic Advantages
  • Good seeing
  • Slow seeing timescale
  • 24 hour coverage
  • Low daylight sky brightness especially near the Sun (as Venus must be observed in daylight).
  • Low water vapour
Wavelengths or Filters Broadband filters from 0.3 to 2.5 microns, plus selected narrow band IR filters.
Spatial Resolution Diffraction limited (0.06 arcsec at 0.5 micron, 0.25 arcsec at 2 micron)
Area of Sky 50 arcseconds.
Frequency of Sampling Continuous short (10-50ms) exposures with real time processing to select and stack frames.
Individual Observations
  • Continuous monitoring for many days at time resolutions of around a minute.
  • For Mars and Venus, in particular, observations are restricted to favourable opportunities when the planets are in the south and close to conjunction / opposition.
  • Venus has to be observed in daylight (summer).
  • This project is likely to require a specially designed instrument that can provide short exposure times and fast frame rates.

 

Title Resolved Stellar Populations in Nearby Galaxies
Submitted by Joss Bland-Hawthorn (AAO)
Outline of Science

Our understanding of galaxy formation and evolution has largely rested to date on global quantities like galaxy luminosity, mass, colour and type. But very deep optical and near infrared imaging of stellar populations in a few nearby galaxies have begun to reveal how global estimates hide a richer past.

In the Local Group, there are two dominant galaxies (M31 and the Milky Way) and more than 40 (mostly dwarf) galaxies. The star formation histories of all dwarfs reveals an old stellar population followed by a complex and chequered history. Van den Bergh has stated that there may be some dependence on the radial distance to the nearest large galaxy, but the existing data are barely good enough to support this observation.

For the Galaxy, we know a great deal. The figure shows the age-metallicity distribution for all components of the Galaxy. This complex plot defies any simple interpretation. The stellar bulge, halo and thick disk are all dominated by old stellar components.

The deepest colour-magnitude diagram to date has come from the Hubble Space Telescope (Brown et al 2003). A small patch of the outer M31 halo was imaged in two bands (check) for a total of 100 orbits. The data reach down to V=31 (50% completeness), well below the main sequence turn off at the distance of M31. These data clearly demonstrate the important contribution of an intermediate age 7-9 Gyr population, something that is not seen in the Galactic halo. This emphasizes the different accretion histories that are possible within two neighbouring galaxies. Unfortunately, the HST is likely to be decommissioned before this important work can be completed.

The PILOT telescope can do important work at V and K on resolved stellar populations. We need to study a handful of galaxies in very different local (group) density fields in order to see how the accretion histories depend on either the halo or local density field. Important inroads into this issue can be made out to 2 Mpc with PILOT working at V and K. In V, we need reach below the main sequence turn off for an old stellar population (V=29). Equivalently, we need to reach K=25 or J=25 although it may be possible to soften this requirement. The main source confusion comes from signal fluctuations due to unresolved stars. Thus, a 0.2” PSF will be adequate for the proposed work.

We will need the power of an ELT to reach Virgo, particularly in V band.

Antarctic Advantages

  • High angular resolution, at both V and K.
  • Wide field.
  • High sensitivity at K.
Filters Two bands. V & K best, I & K good, J & K OK. Must measure colours.
Spatial Resolution 0.1" pixels in 0.2" seeing. 5' field of view.
Area of Sky Within Local Group. Distance limit 2 Mpc (ie m-M = 26.5 magnitudes).
Individual Observations Need to achieve K=25 (=20 hours for S/N=5) or J=25 (=20 hours for S/N=10) and V=29 magnitudes (100 hrs for S/N=10).
How long for the project? 20 galaxies (4 group densities x 5 per group)
References

Brown et al, 2003, ApJL, 592, L17

Freeman & Bland-hawthorn, 2002, ARAA, 40, 487

van der Bergh, ??.

The age-metallicity relation of the Galaxy for its different component: TDO = thin disk open clusters; TDG = thick disk globular clusters; B = bulge; YHG = young halo globular clusters; OHG = old halo globular clusters. The blue corresponds to think disk field stars, the green to thick disk field stars and the black shows the distribution of halo field stars extending down to [Fe/H] = -5. From Freeman & Bland-Hawthorn, 2002, ARAA, 40, 487-537.
Colour Magnitude Diagram of M31's halo, from Brown et al. This is the deepest CMD ever obtained, and is illustrative of the kind of work that could be tackled by PILOT on account of the good seeing at Dome C. Ridge lines (coloured curves) and Horizontal Branch stars (coloured points) of four Globular Clusters overplotted. The GCs have been shifted only by the differences in distance and reddening. Note that much of the M31 subgiant branch is brighter than those of the clusters, indicating that M31's halo is predominantly younger than Galactic GCs. To bottom right is the best fit achieved using old (11-13.5 Gyr) isochrones spanning a range in metallicity (-2.31 < [Fe/H] < 0). The two dominant components to the fit are a majority population of intermediate-age (6-11 Gyr) metal-rich ([Fe/H] > -0.5) stars and a smaller population of old (10-13.5 Gyr) metal-poor ([Fe/H] < -0.5) stars. It is colour-coded to highlight the intermediate-age metal-rich (red) and old metal-poor (blue) components.

 

 

 

Title Studies of Pulsar Wind Nebulae
Submitted by Matthew Whiting (UNSW)
Outline of Science

A pulsar wind nebula (PWN) represents the interaction of the electromagnetic wind from a young pulsar with the surrounding environment. Some 99% of the pulsar's spin-down energy is carried away in this electromagnetic wind, which is only seen through the shock features resulting from the interaction. One of the features that are seen are unequal bipolar jets, extending along the inferred pulsar spin axis. These jets often terminate in one or more bright knots of emission. Other features seen are the fibrous arcs, or wisps as they are often called, which are cylindrically symmetric about the spin axis.

Furthermore, these features are dynamic. The Crab Pulsar Nebula is the prototypical example of an active PWN. The knots, wisps and jets have been observed (Hester et al 2002) to vary on timescales of a month at both optical and X-ray energies, and a good correspondence has been found between images in both energy ranges (with HST and Chandra). Faster variability, on timescales of days, has also been observed in the near-infrared by Melatos et al (2004) with adaptive optics on Gemini. The latter images also allowed a good determination of the spectral slopes of the different features, and found good evidence for different emission processes in the wisps compared to the knot at the base of the jet.

The most promising advantage offered by PILOT is the possibility of doing high-angular resolution imaging at optical wavelengths, allowing one to probe physical scales previously only achievable with HST. An interesting possibility would be to examine variability of both the non-thermal shock-related features and the emission-line features, such as the H-alpha filaments in the surrounding environment.

Diffraction-limited imaging in the NIR over a full field, without the distortions introduced by AO systems would also be desirable. One of the problems encountered by Melatos et al (2004) was good characterisation of the changing PSF over the AO-corrected field, a problem what would be mitigated somewhat by the large isoplanatic angle available at Dome C.

There are two approaches that could be taken for an observing scheme:

  • One would be to take high-resolution images through a range of filters, from optical to near-infrared, to determine the spectral shapes, and hence the emission processes.
  • A second would be too look for variability in the features over a period of months. This would require imaging at a frequency of approximately once per week (this would depend on the individual PWN being studied) for several months, building up a lightcurve and looking for movement of features. If done at NIR wavelengths, the frequency may need to be shorter, due to potentially faster variability (Melatos et al 2004).

 

References

Hester et al. (2002), ApJ 577, L49

Melatos et al. (2004), ApJ, Submitted

 

Title Time Delays in Gravitational Lenses
Submitted by Matthew Whiting (UNSW)
Outline of Science

One of the more elegant ways to measure the Hubble Constant H0 is to utilise strongly-lensed quasars. When a quasar is lensed by intervening matter into two or more images, the distance that the light travels to form each image is different. This pathlength difference will translate into a time delay measured by the observer between the images. If the quasar shows significant photometric variations, the light curves for each image will be shifted relative to one another. One can obtain a measurement of H0 as the time delay depends on the geometric distances to the lens and the source, which in turn depend on the value of H0. Such a measurement of H0 is independent of systematics found in determinations that use the "cosmic distance ladder". Recent reviews of the topic can be found in Kochanek & Schechter (2004) and Kochanek (2002).

In practice, things are more complicated than simply measuring a time delay. One also needs good astrometry of the lensed images, and good quality imaging of the entire system. The former is required as one needs to know exactly how much the images have been deflected. The latter, however, is very important for the construction of the lens model, as one needs to know what the nature of the lensing object (ie. is it a galaxy or a cluster?) as well as simply the location of the lensed images. Images with good spatial resolution are thus crucial for accurate measurements. Studies are done currently with ground-based telescopes but often require some degree of deconvolution, which will carry potential systematic effects.

Recent measurements of H0 from gravitational lenses give values consistent with the HST Key Project only if the lensing galaxies have constant M/L (71 +/- 3 km/s/Mpc cf. 73 +/- 8 km/s/Mpc respectively) (Kochanek & Schechter 2004). The more likely case of an isothermal density profile results in a significantly lower value of 48 +/- 3 km/s/Mpc, raising the possibility that local determinations of H0 are too high. These results are based on just four systems, however, so more lensed systems need to be investigated. A telescope such as PILOT provides an opportunity to address this problem, and offers two important advantages over other telescopes:

  • High spatial resolution at optical and near-infrared wavelengths. Working at close to the diffraction limit in the optical (and at it in the near-IR) makes PILOT comparable to HST. The good angular resolution will enable accurate modelling of the lens system, crucial for correct interpretation of the time-delays and a measurement of H0.

However, diffraction-limited imaging in the near-infrared with PILOT offers a niche that is not exploited elsewhere. As well as high angular resolution, K band imaging will be important for studies of dusty, reddened lensed systems, where extinction in the lensing galaxy makes the quasar images fainter, increasing the photometric errors for a given exposure time. Additionally, near-infrared light is more representative of the total stellar mass of a galaxy, so K band imaging of the lens galaxy will allow better mass density determination.

  • Ability to monitor continuously for long periods is an advantage. For good determination of the time-delay, good temporal sampling is necessary, particularly when the time-scale of photometric variations is not known a priori. Furthermore, these time-scales can range from days to months, and so a long baseline may well be needed to determine the delays.

A typical observing scheme that can be envisaged would be a "snapshot"-style program of relatively short exposures, repeated regularly to build up a light curve. These exposures could thus fit into other scheduled programs being executed on the telescope. An example program would be an image every 12-24 hrs, over the winter. This would build up a dense light-curve that would enable a quite precise time-delay measurement.

Known quasar lenses are rarely more than a few arcseconds in size (given by the separation of the images), but the lensing system will often be larger. The field of view of an AO-corrected optical imager, or a high-resolution K-band imager will be sufficient.

References

Kochanek, C. & Schechter, P., Measuring and Modeling the Universe, from the Carnegie Observatories Centennial Symposia. Published by Cambridge University Press, as part of the Carnegie Observatories Astrophysics Series. Ed: W. L. Freedman, 2004, p. 117.

Kochanek, C., 2004, ApJ 578, 25

 

Title of Project Deep Near-IR Extra-galactic Surveys
Submitted by Rob Sharp (AAO)
Outline of Science

This program addresses three key areas studied extensively with recent HST deep field observations.

  1. The nature of galaxy evolution. Galaxy morphological evolution studies are always hampered by the simple fact that at higher redshifts (z>1) optical observations sample the rest frame UV flux. A quick census of relatively normal galaxies in the rest frame UV shows that even these classical systems show strange morphologies in the UV, with images dominated by small scale phenomenon, often of little significance in terms of the overall galaxy structure. Ideally we wish to study galaxies in the rest frame H or K band, since this is the wavelength which traces the peak emission from the underlying stellar populations. However, until high resolution mid-IR cameras become routinely available (an opening for PILOT in another mode is clear here) we must learn what we can from the rest frame optical bands which are shifted into the IR at z>1. The proposed PILOT survey will allow, for the first time, the morphological study of a large sample of galaxies at high redshift in the rest frame optical bands. Such a study would give vital information on the structural evolution of galaxies and the nature of there formation (hierarchical modals verse down-sizing).
  2. Search for I-band drop-outs. The current hot topic in high redshift galaxy populations is the search for i' band drop out galaxies, at z>6. With the release of the HST UDF attention has focused on the possibility of z' drop outs and higher redshift objects. However, such work require IR photometry in order for candidates to 'drop out' of the z' band. The scarcity of such objects requires wider field observations than are practical with HST/NICMOS or 8m class telescopes. The PILOT near IR camera would allow one to push this technique onto the next level, with observations in the ZYJHK bands replacing the classical Lyman break selection using UBVRI at lower redshifts (z<4). The wide field of the PILOT telescope means one can be competitive in this field with a modest investment of telescope time.
  3. New Classes of Objects. Dickinson et al (2000 ApJ 531 624) discovered a quite extraordinary objects (HDF-N J123656.3+621322) in the NICMOS observations of the HDF-N. The object is detected only in the NICMOS H band image and follow-up ground based K band imaging. Recently, Yan et al. (2004 ApJ 612 93) reported several similar extremely red objects in the NICMOS UDF observations. However, their nature and space density is currently unknown, with plausible explanations ranging form z>10 galaxies to extreme carbon stars. The potential field of view and wavelength coverage of the proposed survey will allow one to address the problems associated with small number statistics and define a plausible SED for this class of object.
Antarctic Advantages

PILOT offers a critical combination of depth and area. The deep optical HST surveys (HDF-N/S, GOODS, UDF) have shown what can be achieved with excellent quality data. While a 2m PILOT telescope cannot match the resolution or sensitivity of the optical HST data, it represents a great leap forwards in comparison to the HST/NICMOS camera. A diffraction limited Antarctic telescope would seem to be able to deliver images to depths and resolutions, on a par with NICMOS, over fields of view greater than the GOODS survey fields. The extension to the K band has not been performed before.

Unfortunately, the Antarctic location means that PILOT will struggle to observe the southern HST GOODS field center ed on the Chandra Deep Field South but the HDF-S is well placed for study, providing excellent optical data to use in tandem with the PILOT observations.

One could envisage a series of survey projects, with different depths and area coverage, to address complementary science goals. An excellent model for the survey aims would seem to be the UKIDSS DXS and UDXS surveys. PILOT can most likely not compete with UKIDSS in terms of raw sensitivity and area (the smaller telescope inevitable reducing the 'survey power' of the instrument) the key opening for PILOT is the improved resolution, which will uniquely allow morphological studies, for a large sample of galaxies, in the rest frame optical bands over the redshift range 1-3.

Observations

The needs, in terms of camera specification, depend subtly on which aspects of any such survey program one wishes to tackle. For a preliminary deep survey, along the lines of the deep HST surveys, I propose the following, center ed on the HDF-S:

  • 2Kx2K IR camera. A larger array size, while desirable, would increase cost. However, the survey area at high resolution is PILOTs unique capability in this wavelength range.
  • 0.1arcsec pixel scale to adequately sample the PSF at the shortest wavelengths. Filter set to include ZYJH and K.

This gives a field of view of 3.3x3.3arcmin, or 0.003deg^2, well matched the HST/WFPC2 camera field of view for HDF-S.

Based on the predicted sensitivity information, it is suggested that within 10 hours of exposure, on a single telescope pointing, such a camera would reach sensitivities on a par with those of the NICMOS HDF-S surveys. The resolution and area combination will allow ground breaking studies even if current observational depth estimates prove to be a little optimistic.

The Basic program therefore requires 50hours observation (10hours in each of 5 filters), plus overheads associated with calibration of the camera and atmospheric absorption.

Future Expansion Several options present them selves as obvious routes for expansion of the project based on assessment of the initial modest investment of telescope time. A camera upgrade, to 4Kx4K quadruples the survey power of the instrument, allowing increasing survey efficiency. An initial assessment of the data from the current proposed program would indicate whether a future strategy would be to cover a wider area to shallower survey depths or to enlarge the deep survey modestly, to account for the effects of cosmic variance.

 

Title A wide-field survey of star-forming regions: from low-mass prestellar cores to the progenitors of OB stars
Submitted by Vincent Minier (CEA Centre d’Etudes de Saclay)
Outline of Science

Star formation is a key astrophysical mechanism in the Galactic ecology and evolution. To date, major progress has been achieved in understanding the formation of low- to intermediate-mass stars. These stars form from the collapse of dense cloud cores in the molecular interstellar medium (GMCs) of the Galaxy. Two very early evolutionary stages have recently been identified:

  1. the formation of a gravitationally-bound, starless, prestellar cores;
  2. the formation of a cold protostar (class 0 protostar), following the collapse of a prestellar core, that accretes material from the surrounding envelope of molecular gas and dust.

Yet, several fundamental questions remain open:

  • What determines the distribution of the initial mass function?
  • How do prestellar cores form in the molecular clouds and what governs their collapse and evolution to protostars?

The formation of high-mass (M>8 M_Sun) stars is in contrast less understood. Massive stars are born in very obscured regions (A_v >20 mag) of cold molecular gas and dust, far away from us (typically a few kpc) and within dense stellar clusters (~10^4 stars pc-3). They also experience short lives (10^6-10^7 years). These observational constraints are the main reasons of our limited knowledge of high-mass star formation (HMSF). An empirical evolutionary sequence has been proposed.

Massive stars form in hot molecular cores and then evolve to ZAMS stars that ionises their environment to produce several classes of HII regions (hyper compact, ultra compact, etc.). Recent (sub)millimetre observations also claim the discovery of high-mass protostars, which are likely protoclusters of embedded young stellar object, given the spatial resolution (~0.5 pc).

Theoretically, high-mass star formation is problematic: the outward radiative acceleration becomes important for high-mass stars and will ultimately stop accretion. The infall accretion rate must then exceed the outflow rate to produce a high-mass star, i.e. the gravity must overcome the radiative pressure. Two scenarios have then been proposed. HMSF could proceed either through protostellar mergers (Bonnell & Bate 2002) or through the collapse of a supersonically turbulent core with a sufficiently large accretion rate (McKee & Tan 2003). High-mass prestellar cores are only expected in the second scenario.

The main physical processes leading to high-mass stars are still unclear. We might then ask whether massive stars also form through the collapse of a pre-stellar core? Do "Class 0" high-mass protostars exist?

Objectives: A census of the earliest stages of star formation. Unbiased surveys of GMCs in the FIR/sub mm continuum is necessary to take a complete census of the pre- and proto-stellar population within star-forming regions because prestellar cores,Class 0 protostars and HMSF protoclusters emit the bulk of their luminosity between 60 and 400um. The coldest objects have their SED peak around 200um.

An unbiased and wide-field survey at 200, 350, 450um of nearby regions of star formation will allow us to potentially detect all the prestellar cores and protostars in a given star-forming region, then derive their mass and luminosity via SED fitting and modelling, and finally obtain the early stellar population (i.e. IMF). To do so, a sample of low-mass star-forming regions (e.g. Corona Australis) to OB star progenitor complexes (e.g. NGC6334) is needed.

Antarctic Advantages Observations at 200, 350 and 450 um will be possible from Antarctica. The 200um is an exceptional feature of Antarctic Astronomy as this wavelength is generally unobservable from ground. The ESA Herschel Space Observatory will observe in the continuum at 250um with SPIRE.
Wavelengths 200, 350, 450 microns.
Spatial Resolution

2-m telescope: 20" at 200um

  • 20" = 20000 AU = 0.1 pc at 1 kpc
  • 20" = 2000 AU = 0.01 pc at 100 pc
Area of sky Large GMCs and star forming regions in the Southern Hemisphere at distance < 2 kpc. (e.g. NGC6334; NIR extinction map; and GMCs from the Delta Quadrant Survey (DQS)).
Sensitivity Need to reach 0.1 M_sun at 0.5 kpc at 200 microns.

 

Title Probing the First Light of the Universe with Gamma Ray Bursts
Submitted by Karl Glazebrook (John Hopkins)
Outline of Science

Gamma Ray Bursts (GRBs) are the most powerful, energetic explosions in the Universe. For a period of a few days they are 100-1000 times more luminous than Quasars. Current satellite missions are capable of detecting the gamma ray flux of GRBs to z=20 and the forthcoming SWIFT mission (launching Oct 2004) will be able to reach z=70 (Lamb & Reichart 2001). Note z=20 is 180 Myr after the Big Bang (1% of the current age), z=70 is 28 Myr (0.2% of now!).

We now know GRBs are associated with star-formation in galaxies, they occur in off-nuclear star-forming disks and spectra have been obtained to redshifts as high as z~4. The best theoretical model is they represent a 'hypernova' associated with the collapse of a super-massive star directly in to a black hole.

However 20-40% of GRBs are "dark bursts", i.e. they have no optical counterpart. Given GRBs are detectable to very high-redshifts the natural conclusion is these dark bursts have z>7, at these redshifts all optical light (< Lyman alpha in the rest frame) is removed by neutral Hydrogen absorption in the IGM.

This would imply a lot of star-formation occurred in the Universe at z>7, an epoch not yet probed by any observations whether from ground or space. This would in fact solve a key problem in cosmology: the re-ionization of the Universe.

After it's early fireball phase the Universe consisted of neutral Hydrogen until the first stars were formed at some now unknown time. This is often referred to as the time of 'First Light'. These early stars would produce ultraviolet radiation which would ionize the Universe some time between z=20 and z=7. Observations of galaxies and quasars at z=6 show the amount of ultraviolet produced at this 'late' time is insufficient to ionize the Universe and further that the Universe is already almost completely ionized so it must have happened earlier. Observations of the Cosmic Microwave Background are consistent with a range of z=7 - 20.

The early universe contained no heavy elements - these are made in stars. Calculations of likely modes of star-formation in pristine material shows that we expect the very first generation of stars to be different to those that form today in the 'dirty' interstellar medium. We expect them to be much more massive, on average, this is known as 'Population III'. Being massive they would produce lots of ultraviolet and hence be capable of ionizing the Universe. Many models predict an early peak of star-formation due to this Pop III at z>10.

Because GRBs are ultra-luminous and trace massive star-formation they can be used to trace Pop III and re-ionization. The opportunity is timely with the imminent launch of SWIFT, which will be rapidly followed by further more powerful gamma-ray satellites.

PILOT can provide rapid JHKLM imaging of GRB locations to search for afterglows, the position of the break will be revealed by colours and hence the redshift can be determined. z>20 can be probed. The M band can reach z=35 if star-formation ever occurred back then - only 80 Myr after the Big Bang! Studying the redshift distribution of GRBs will reveal any Pop III and the epoch of 'First Light.

Antarctic Advantages
  • The LM bands can only be probed at cosmological distances in the Antarctic where the sky is uniquely dark, This only PILOT can probe the z>20 regime where GRBs are only bright in LM.
  • The K-band is also enormously more sensitive in the Antarctic giving us a window on 10<z<15 GRBs.
  • The regime where the Antarctic has a huge advantage is EXACTLY the redshift range we wish to probe.
  • GRBs are point sources which means the good seeing is a huge advantage.
  • The long polar night means any rapid response is not going to be interrupted by any untimely daylight! GRB light-curves could be followed for a long time.
Instrument Requirements We need a 1 arcmin FOV and KLM capability, JH in addition would be useful. (SWIFT will produce 10 arcsec positions form the XRT, about 100-200 per year so 10-80 at z>7). If the FOV was ~ 10 arcmin one could even work with the +/- 4 arcmin gamma ray positions!
Observations

Gamma ray bursts remain bright to very high-redshifts, Lamb & Reichart 2001 calculate L=M=15 microJy for a z>20 GRB. One beautiful reason for this is the time dilation makes the fading slower at high-redshift, so if one observes at a fixed time after the event the time dilation effect approximately cancels the cosmological dimming.

The Lamb & Reichart number refers to 24 hrs post-burst. A typical afterglow fades at t^-4/3 so one hour after the burst these would be 70x brighter! (~1000 microJy)

These fluxes are detectable easily with PILOT - a 5 min exposure reaches a noise limit of 300 microJy in L, if it is not detected a 1 hr M exposure would reach 200 microJy. This would correspond to a z=36 object!

Note for the 'easy' z=10 case, we find the GRB = 700 microJy in K whereas a 1 min K exposure reaches 17 microJy!

Note there is a lot of variation in GRB properties - many would be a lot brighter and some fainter. Part of the science is to pin down in detail their elusive properties.

Obviously one would want a JHKLM sequence of observations, such a project is perfectly suited to a robot telescope.

Future Developments

An obvious upgrade would be a spectrograph working in the KL bands. This will allow us to probe the gas in the universe and the host galaxies at z>10. We could measure the elemental abundances, the large-scale structure of the early Universe from metal forest absorption lines, the amount of re-ionization from the shape of the Ly-alpha edge.

Given the above numbers for K-imaging sensitivity spectroscopy at R=100-300 is possible even on a 2m telescope.

A NIR spectrograph could be quite inexpensive due to the natural environment eliminating the need for expensive cryogenics.

This is an obvious pathfinder for an Antarctic ELT - extremely high spectral and spatial resolution observations would be possible at z>10.

 

Title The evolution of galaxy mass and morphology: high resolution imaging beyond the Hubble Limit - A PILOT Ultra Deep Field.
Submitted by Karl Glazebrook (JHU)
Outline of Science

The Hubble Space Telescope has revolutionized our view of the high-redshift Universe with it's deep, high-resolution images. Galaxies paint the sky in numbers up to 10^7 per deg^2 and star-formation rates are much higher than they are today. The picture of the 1<z<4 Universe is of great disturbance: many anomalous looking galaxies abound with little sign of the regular Hubble sequence.

However HST Deep Fields (HDFs) are inherently biased: they are predominantly taken in the optical and have very tiny fields of view of only a few arcmin. At z>1 the optical samples the rest-frame ultraviolet - in such pictures only the scattered star-forming regions containing young UV luminous OB stars can be seen. Young 'Lyman-break galaxies' (LBGs) with prodigious star-formations rates dominate our picture. Older, redder more regular stellar components can not be seen. HST does have JH imaging with NICMOS but here the field is even smaller and no large surveys are possible.

To truly characterise the high-redshift Universe we need ultra-deep surveys in the near-infrared, ideally in the reddest possible band to pick up more normal galaxies at high-redshift. And we need to cover much larger areas - typical cosmic variance on the scale of the Hubble Deep Fields is 100% leading to large uncertainties in measurements.

Tantalizing results from deep ground near-IR surveys have revealed populations of massive galaxies beyond z>1 with much more regular morphologies. The Gemini Deep Deep Survey has shown spectroscopically that massive, old galaxies exist to z=2 at K~20 (Glazebrook et al., 2004, Nature, 430, 181), and ACS images reveal regular elliptical and spiral galaxies. Franx et al have found a substantial population of 'Distant Red Galaxies' (DRGs) with J-K > 2.3, z>2 and K<22.5, these appear to be massive and much redder/less UV luminous than LBGs. One has an HST NICMOS image showing a classical bulge+disk.

Why is the near-IR so important? This is where the bulk of the light from old stars come out, if one wants to weigh a galaxy by stellar mass then one needs light > 4000Å break. For z>2 this means the K-band is absolutely essential to measure stellar mass at high-redshift rather than the transient UV bright episodes of star-formation. Massive galaxies tend to be highly clustered as well, there are zero at z>2 in the HDF-N and 3 in the HDF-S. (As determined from deep VLT K-band imaging).

I propose ultra-deep wide-area K-band imaging to secure resolved imaging over substantial areas. Our goal is to image large numbers of z>2 red galaxies and measure there morphologies. Are they ancestors to spiral galaxies? Do they have disks? How far back in time can we see disks or genuine elliptical galaxies? (This record is currently held by GDDS, the highest redshift spectroscopic early type (i.e. the spectrum shows an old stellar population) is z=2.1 and the high-redshift with also an ACS image is z=1.5). Such galaxies are the most interesting: galaxies which are already old and z=3-4 constrain the epoch of first star-formation in the Universe pushing it back to z>>6.

Quantitative morphological measures (bulge/disk decomposition, concentration, asymmetry, 'Gini' coefficients) will be applied. Comparison with deep optical images will establish photometric redshifts. Stellar mass functions will be established as f(redshift, morphology), which will measure the nature of the growth of galaxies ('hierarchical assembly' or 'down-sizing'?) and hence test galaxy formation models. By covering large areas we will be able to measure clustering and hence obtain constraints on the dark mass of their halos.

Antarctic Advantages
  • This takes advantage of the unique Antarctic 2-2.5 micron 'cosmological window' where the sky is very dark to enable ultra deep fields.
  • This takes advantage of the wide diffraction limited field due to the very good Dome C seeing.
  • The southern latitude means most of the southern sky is circumpolar and visible all winter, there is no daylight to interrupt observing. This is ideal for the accumulation of long exposures on deep fields.
  • PILOT is the only facility conceived which can go to the required depth, over a large enough area.
Instrument Requirements Wide field (40' diameter ) K band imaging with a resolution of 0.3" or better. JH are also desirable and perhaps V,I (though these could be obtained elsewhere albeit not in as good seeing). This remains TBD.
Observations

To study rare bright objects as well as more common fainter objects we need a two-tier approach.

  1. A 100 hour exposure will reach K=23.5 for extended sources, thus K<22.5 galaxies will have S/N > 25, suitable for morphology of resolved objects with 0.3" resolution. A 40' diameter FOV will contain 4000 galaxies of the type studied by GDDS and Franx et al and an unknown number of fainter objects yet to be studied. The field would represent a 300 fold improvement in cosmological volume on any comparable large telescope imaging (e.g. the FIRES VLT field).
  2. A 10 hour exposure reaches K=22.3, a 3x3 pattern of such fields will cover 2 deg x 2 deg on the sky. A 2 deg scale corresponds to a transverse size of 220 comoving Mpc at z=3, this field will be ample for studying the clustering and large-scale structure of 1<z<5 red galaxies (correlation lengths ~ 10 Mpc).
Synergy & Serendipity

The brightest galaxies (K<21) found at high-redshift would be followed up spectroscopically with Gemini (FLAMINGOS-2, GNIRS) to study stellar populations and velocity dispersions.

Such a uniquely wide-area deep K survey has the potential to detect new populations of objects at very high redshift (z>13 which are invisible at shorter wavelengths). There is likely a 2nd epoch of star-formation in Pop III objects at these redshifts (see associated GRB science case), if there are the number that would be bright enough to be seen is unknown. The K=23.5 limit corresponds to a rest frame unobscured UV luminosity from a SFR of 50 Msun/yr at z=15 and would be a factor 2-3 times more luminous than the brightest LBGs at z=3. Of course the abundance of z=15 objects is a subject of educated speculation, for example these UV luminosities assume a Salpeter IMF, a Pop III IMF would result in even more UV output.

These deep fields would lay the ground work for the cosmological science case for any future Antarctic ELT.

Other Thoughts The dark, broad window in the K-band is a unique advantage. A wide K filter seems like a poor choice given the thermal background is zooming up at the red end. I'd also get 3 filters of width ~ 1500 Å to cover the 2-2.5 micron range, so we can get colour information as well in this unique window.

 

 

 

Title of Project The complete star-formation history of the early Universe
Submitted by Karl Glazebrook (JHU)
Outline of Science

The rise of the Universal star-formation rate (SFR) from z=0 to z=1 is well established from a variety of indicators (ultraviolet, Balmer lines,. far-IR emission). The history of Universal SFR for z>1 is poorly determined, it appears to peak and decline from z=1 to z=6 (the infamous 'Madau-Lilly diagram'). However this result comes from the measured ultraviolet light of high-redshift star-forming galaxies ('Lyman Break Galaxies' or LBGs) and there is a big problem: dust.

Interstellar grains are thick in star-forming regions and are very effective at absorbing ultraviolet (UV) light from young stars. For example typical visual extinctions OBSERVED in star-forming galaxies locally predict large extinctions (>2 mags) in the UV. In fact we now have extensive evidence that this is also true at high-redshift. The slopes of the UV spectra of LBGs are consistent with around 2 mags of extinction, we also find a population of sub-mm sources (the 'SCUBA galaxies') which can only be explained by very dusty starbursts. Typically when plotting a SFR-z diagram constant extinction is assume for lack of anything better. The majority - 90% - of the UV light is absorbed!

Paradoxically it turns out that the best place to measure the SFR of a galaxy is in the deep red. This is because this is where the Halpha emission line comes out. The Halpha line strength is a direct measure of the number of ionizing photons in a galaxy and hence the number of young stars. But because it comes out at 6563Å it is little affected by dust. At z>1 Halpha is observed in the near-IR, some limited spectroscopy has been done of z=1 galaxies (Glazebrook et al. 1998) and z=3 LBGs (Erb et al. 2003). These typically show the SFRs several times larger than was calculated from the UV, consistent with most of it being absorbed by dust. However only handfuls of galaxies have been studied due to the extreme difficulties of near-IR spectroscopy even on 8m telescopes.

To truly measure the evolution of the cosmological SFR we need deep Halpha-selected samples to allow the construction of the Halpha luminosity function from z=1 to z=4. The only dataset to do this is from HST using the NICMOS camera in a slitless grism mode in J & H. Because of the low space background slitless images can be used to directly search for lines down to a limiting Halpha flux, the resulting Halpha LF is measured at z=1.5 (Yan et al., Hopkins et al. 2000) from only dozens of objects over tens of arcmin^2.

The 'cosmologically dark' K-band window from PILOT would allow us to extend this to high-redshift and backwards in time - in particular to z=3 and the era of Lyman break galaxies. I propose deep imaging in the K-band at a series of redshifts from z=2.0 to z=3.0 with narrow band filters. In conjunction with deep broad-K images narrow-line excess objects can be identified using standard techniques.

Is star-formation really declining from z=1 to z=3? Such a long baseline (2-6 Gyr after the Big Bang) will reveal the epoch of peak galaxy formation. The measured SFR-distribution function will tell us how it depends on galaxy size, and combined with the deep broad-K observations proposed on mass. In fact the combination of direct SFR measurements and stellar mass measures of the same galaxies has proved powerful at 1<z<2 in the Gemini Deep Deep Survey - direct evidence for 'downsizing' - the motion of peak SFR to smaller mass galaxies with time - is seen. (Juneau et al. 2004). Both these measurements at z>2 are ideally suited to deep K-band observations.

Antarctic Advantages
  • Narrow-band observations are most sensitive in the darkest windows, the dark K window is ideal and confers a huge advantage for this work.
  • The diffraction limited imaging (0.3") over the wide 40' FOV only possible from the Antarctic allows us to search for extremely compact dwarf star-forming galaxies at these redshifts.
  • The number of galaxies is the determining factor for luminosity calculations, the uniquely wide field is an advantage.
Instrument Requirements Wide field imaging with special narrow band 2-2.6 micron filters. (Typically 1%, 3-5 of them covering the wavelength range).
Observations

A 10 hour exposure through a 1% (200A wide) filter at 2.2 microns will reach a line flux of 10^-17 ergs/cm2/s for PILOT parameters (taking a sky background of 150 microJy/arcsec^2 at 2.2 microns as I have to do my own S/N calc for narrow band). At z=2.35 this is L(Ha) = 4*10^41 ergs/s or a SFR of 2.8 Msun/yr. Very low! Note the z=1.5 Ha LF from Hopkins et al 2000 imply this is a 0.04 L* object!! (L* is 10^43 ergs/s or 71 Msun/yr)

Observing 5 filters would then take 50 hours.

The line limit corresponds to an equivalent width of 20A in the REST FRAME if we match the galaxies detected through their emission lines in the narrow band filter to those that would be seen in a deep (i.e. 100 hour, K<23.5) broad band image, as proposed separately in the "galaxy mass evolution" project above.. Even locally this would detect 80% of star-forming galaxies, thus we expect to be able to match with the broad band and get photometric redshifts.

We can estimate the number of objects expected using the luminosity function of Hopkins et al. and transposing it to z=2.35 (i.e. no evolution). For S>10^-17 ergs/cm^2/s we calculate a Ha source density of 1200 per 40' diameter PILOT field, an ample number for eliminating cosmic variance which plagues smaller surveys. [At z=2.35 the survey size is ~ 40x70x70 comoving Mpc which is many clustering scales.]

One might also want to cover a larger area (3x3 pointing) grid with shallower surveys as in the 'galaxy stellar mass' survey I proposed. This two tier approach would better sample rare, brighter objects as well as the more common, fainter ones.

Synergy and Serendipity

With such deep narrow-band observations there might be many unidentified lines, some with objects too faint for reliable photo-z's and some which only appear in the line (i.e. no continuum). These would be excellent candidates for follow-up mutil-object spectroscopy - the flux limit of 10^-17 ergs/cm^2/s is easily in reach of telescopes such as Gemini. (A typical calculation shows S/N=5 at the limit in 10 hrs). An Antarctic ELT would do even better. Spectroscopy at moderate resolution (R=3000) could distinguish between various possibilities: one would observe Ha+[NII] or Hb+[OIIII] or the [OII] doublet or the asymmetric LyA line (at z=17!)

Is the last possibility even reasonable? The other proposals I have written have all emphasised the serendipitous potential of really high-redshift searches (z>10) from ANY deep K-band observations. The Ly-alpha luminosity at z=17 would be > 4x10^43 ergs/s, this is a few times that of the z=6.5 object of Rhoads et al. (2004) found in a narrow band optical search in a survey of comparable sky area. Of course the SFR at z>10 is unknown, it's measurement is a powerful test of the hypothetical Population III and re-ionization. One point to bear in mind is low-metallicity Pop-III galaxies would have much higher Ly-alpha equivalent widths than their low-z counterparts. One might want to pursue this with a deeper narrow-band survey of > 100 hours exposure.

Other Issues Is it useful to do narrow filters in J & H too? We can pick OH free windows - there might be more at Dome C than from Mauna Kea.

 

 

 

Title Stellar Streams and Dark Matter Halos
Submitted by Geraint Lewis (University of Sydney)
Outline of Science

A fundamental prediction of cold dark matter (CDM) cosmologies is that the dark matter halos of massive galaxies, like our own Milky Way, should be significantly flattened. The shape of the dark matter halo influences the motion of orbiting satellites, with asphericies introducing strong torques which act to precess the orbit. Until recently, testing this has proven to be very problematic due to the lack of suitable kinematic tracers beyond the Galactic disk.

The Sagittarius dwarf galaxy is being slowly dismembered by the tidal forces of the Milky Way. Throughout its demise, stars have been torn from the body of the dwarf and now litter the orbit, and this tidal stream of stars now completely encircles the Galaxy. With its extensive range through the dark matter halo, it was realised that the morphology and kinematics of this stream provided an ideal tracer of the underlying mass distribution of the halo. Several analyses of the stream, however, have concluded that the dark matter must be essentially spherical, at odds with theoretical expectation.

While not completely ruled out by CDM, the apparent spherical form of the halo of the Milky Way raises questions on the nature of dark matter in general. Clearly, it is important to determine the shapes of the halos of other galaxies. While tidal streams tend to be extremely faint (~29-30 mag/sq.arc), and hence difficult to detect when unresolved, they stand out morphologically when considering the distribution of individual stars (Ibata et al. 2001; McConnachie et al. 2004). As pointed out by Bland-Hawthorn in this document, the PILOT program can play an important role in the detection of resolved stellar populations within the Local Group. Fitting PILOT with a wide-field camera will allow an expansion of this program, allowing global stellar population properties to be determined (Ferguson et al. 2002). Mapping the halos of Local Group galaxies and nearby groups (such as the Sculptor Group) will clearly reveal any tidal streams associated with disrupting systems, calibrating the current rate of accretion. The morphology of any tidal streams will provide a measure of the mass and shape of the dark matter halo, allowing a catalogue of halo shapes to be determined.

To fully characterise the shape of the dark matter halo, the detailed orbital properties of a dwarf undergoing disruption is needed. For this, the kinematic properties of the stellar streams are required. Current studies of the extensive stellar stream discovered in M31 reveal that, with the 10-m Keck telescope, stellar kinematics can be determined to an accuracy of 10 km/s for a star with I band magnitude of ~21 with a 1 hr integration (Ibata et al. 2004); given orbital velocities are of the order 250km/s, this velocity resolution is sufficient to accurately determine the kinematics of the stream. While PILOT may be too small to compete with this, the lower sky background and higher angular resolution afforded to Dome C suggests that a larger antarctic telescope (8m+) would provide kinematic measurements of tidal stream stars in various galaxies, and hence significant constraints on the shape of dark matter halos.

AntarcticAdvantage
  • High angular resolution
  • Low background

 

Area of Sky Local Group Galaxies (ie out to ~3 Mpc)
Filters Two bands to determine colours (e.g. V & K)
Spatial Resolution 0.1" pixels, wide field of view for mapping halos.
Individual Observations Mapping of the halos of galaxies within ~3Mpc
References
  • Ferguson et al. (2002), AJ, 124, 1452
  • Ibata et al. (2001), Nature, 412 49
  • Ibata et al. (2004), MNRAS, 351, 117
  • McConnachie et al. (2004), MNRAS, 351, 94

 

Title Emission-line mapping of the high redshift universe
Submitted by Geraint Lewis (University of Sydney)
Outline of Project

While classical imaging and long-slit spectroscopy have provided a wealth of astronomical data, our understanding of the detailed properties of objects in the high redshift universe requires spatially resolved spectroscopy. The excellent seeing and low sky background available in antarctica immediately lends itself to integral field spectroscopy. Two potential astrophysical studies (although there many more) include;

a) Gravitational lensing: Massive galaxies can split the light from distant quasars into a number of images, separated by 0.5-1" on the sky. As well as producing multiple images, these gravitational lenses can also induce signficant magnification, producing gross distorted images of normally unresolved features, such as the Broad Emission Line Region (BLR; Mediavilla et al. 1998; Mott et al. 2004). With gravitational lens inversion, the fine detail of such emission regions can be exquisitely mapped (see Wayth et al 2004 for an example). Furthermore, additional differential magnfication effects are expected to occur, resulting in differing variability for continuum and emission sources (Lewis et al. 1998). For such a study, spectroscopic monitoring is required, but it is vital the emission from various lens images is clearly separated. Hence, an integral field unit with the superb seeing afforded by an antarctic telescope is ideal.

b) Star-forming galaxies: In recent years, the submm/IR view of the high redshift universe has revealed that much of the star formation in young systems was hidden, buried in dust cocoons that reradiate the intense UV of young stars at much longer wavelengths. SCUBA studies have uncovered a substantial population of these galaxies at at z>1, and integral field spectroscopy of the brightest examples have revealed complex structure and dynamics, interpreted as violent interactions and star burst induced superwinds (Swinbank et al. 2004). Furthermore, similar star forming populations in the early universe have now been uncovered by Spitzer, and integral field spectroscopy will be vital in uncovering the physical properties driving star formation in these young systems.

Of these two studies, gravitational lens systems provide an simpler observational challenge, require integration times of order ~1hr with current integral field spectrographs on 4-m class telescopes to obtain detailed maps. The high angular resolution, however, is needed to ensure the resultant continuum subtracted images reflect real emission features, rather than poor PSF subtraction (Wayth private communication). The study of star forming galaxies is more technically challenging, with Ly_a imaging of the brighter Spitzer sources requiring 8-hrs on current 8-m class telescopes. Both Ly_a imaging and H_B imaging will take advantage of significantly lower sky background available at antarctica, bringing this proposal into the grasp of PILOT.

 

Antatctic Advantage High angular resolution, Low background
Observation Details
  • Targeted gravitational lenses, Spitzer selected sources etc
  • Spatial Resolution: 0.1" lenslets
  • Spectral Resolution: Line widths 500-5000 km/s, targeting Ly_a at z>2.2 (>3900A) or H_B in the IR (z>1)
References

Lewis et al (1998, MNRAS, 295, 573)

Lewis & Belle (1998, MNRAS, 297, 69)

Mediavilla et al (1998, ApJ, 503, 27)

Motta et al (2004, ApJ, 613, 86)

Swinbank et al (2004, in preparation)

Wayth et al. (2004, MNRAS, submitted)

   

 

Title A Survey for Cool Brown Dwarfs and Extrasolar Giant Planets
Submitted by Michael Burton (UNSW)
Outline of Project

Brown dwarfs are sub-stellar mass objects, whose mass is too low for the nuclear fusion of hydrogen to sustain its luminosity over the bulk of its lifetime (though fusion can play a role in brown dwarfs, however, with the fusion of lithium, of deuterium and of hydrogen possible, depending on the mass of the object and its age). Brown Dwarfs are born hot, shining primarily through the release of gravitational potential energy and accretion luminosity, and spend the rest of their lives cooling, emitting in the infrared (Burrows et al. 2001). As they cool, their spectra change radically, quite unlike stars. Spectroscopically, they can at first look similar to late-type M dwarfs, then pass through a L dwarf stage where warm (~1300-2100 K) dust emission dominates, and finally end in the T dwarf stage where absorption bands from methane, water and ammonia (c.f. Jupiter) dominate as they cool further. This means that the spectral type of a brown dwarf depends on both its mass and the age, unlike a main sequence star. Modelling is needed to separate the degeneracy between mass and age for a brown dwarf of a given surface temperature. Infrared colours (JHKL) can be used to spectrally identify brown dwarfs, though the presence of strong methane absorption bands means that while the K-L colour is red (as expected from a cool object), the near-infrared colours of T dwarfs (e.g. H-K) may be neutral or even blue (as the radiation is forced to shorter wavelengths to escape through spectral windows in the brown dwarf atmospheres). Before such identifications can be made, however, the challenge is in finding brown dwarfs for, after their first few million years, they have cooled so much that they are both faint and emit the bulk of their radiation in thermal infrared wavelengths, and hence are difficult to detect.

Giant extrasolar planets also fall into the same class of objects as brown dwarfs. While their origins are likely quite different (formed in the disk surrounding a young stellar object vs. a separate gravitational condensation site), physically they are identical objects (although environmental differences, e.g. proximity to a star that provides an external heating source, may result in some different observational characteristics). The study of brown dwarfs thus overlaps with that of planetary science, and will provide insight into the latter.

The study of brown dwarfs is thus a fundamental part of the study of stars, since they can be formed by the same processes with the only difference being the mass of the resulting object. The future evolution of brown dwarfs is, however, radically different to that of stars, being that of a degenerate body without a central fusion luminosity source. It is less than a decade since the first clear evidence of a brown dwarf was reported (Gliese 229B; Oppenheimer et al. 1995) and there remains much to be learnt about their properties and evolution. While it is now clear that brown dwarfs do not provide for the missing mass needed to account for galactic rotation curves, it is also clear that their number density in the solar neighbourhood is comparable to that of M dwarfs. The initial mass function is still rising as the mass falls below the fusion-edge defining the main sequence. Isolated brown dwarfs have also been found to be numerous in several galactic clusters. Of particular interest is the occurrence of brown dwarfs in binary systems, for which only limited information is available. Binary frequency decreases with stellar mass, from ~60% for solar-type stars to ~35% for M-dwarfs. Furthermore, there are few sub-stellar mass companions found to solar-type stars in radial velocity surveys targeting planets (the so-called “brown dwarf desert”; Marcy & Butler 1998). Understanding why this is the case is important for the theory of star formation, and the cause of the initial mass function, but the there are limited statistics so far to provide a clear picture of the degree of binarity that results in the low mass end. Brown dwarfs also display weather – the atmospheric chemistry in their photospheres, which is a strong function of temperature, and changes radically during evolution as the brown dwarf cools. Photometric and spectroscopic variations can be expected due to presence of cloud systems as the sources rotate. Such changes will also be a function of spectral type.

All these facets of brown dwarf behaviour are little understood, as there are still relatively few sources known (a few hundred, dominated by the hotter and younger sources). PILOT, with its sensitivity in the thermal-IR L and M bands, is well suited to extend the current surveys, both to greater distances and to the detection of cooler (and thus older, and presumably far more common) brown dwarfs. In particular, a survey to depth at L band (3.8um) of 14.8 mags. (as could be reached in 1 minute with PILOT) would provide a similar sensitivity to that reached by the 2MASS survey (Kirkpatrick et al. 1999) in K band, but be capable of detecting cooler and redder sources. The Table below (adapted from Burrows et al. 2001) gives an indication as to how far away a 15 MJupiter brown dwarf could be found, as a function of its age, in the K, L and M bands. While such an object can readily be detected when it is young, by the time it has reached 1 Gyear in age it can only be found relatively close to the Sun. Note, however, that with PILOT we are actually more sensitive to detecting such objects in the M band than at L band, despite the reduced sensitivity, because brown dwarfs of this age are so cool. PILOT could thus be used to conduct the first extensive survey for old, cool brown dwarfs within a few tens of parsecs of the Sun.

Antarctic Advantage The primary advantage of Antarctic for this experiment is the high sensitivity in the L (3.8µm) and M (4.6µm) bands compared to temperate sites.
Observation Details This is a survey project. To survey a 1 square degree area to the depths in the Table would take 1 month per filter (assuming a 25% efficiency over that time). It is necessary to survey in at least 3 filters (K, L, M) and ideally also in methane on-band and off-band filters (the methane bands are at 1.7 and 3.3µm). Thus this project would benefit greatly from the use of a dichroic beamsplitter, and multiple arrays.
References

Burrows, A., Hubbard, W.B., Lunine, J.I. & Liebert, J., 2001, Rev. Mod. Phys., 73, 719

Kirkpatrick, J.D. et al., 1999, ApJ, 519, 802.

Marcy, G.W. & Butler, R.P., 1998, Ann. Rev. A&A, 36, 57

Oppenheimer, B.R., Kulkarni, S.R., Matthews, K. & van Kerkwijk, M.H., 1995, Science, 270, 1478

   
Age
Eff. Temp
Spectral
K (2.2µm)
L (3.8µm)
M (4.6µm)
Distance (pc)
(yrs)
(K)
Class
(Jy)
(Jy)
(Jy)
K
L
M
1 (7)
2,225
M
3 (-1)
3 (-2)
3 (-2)
6,000
300
200
1 (8)
1,437
L
5 (-3)
1 (-3)
5 (-3)
700
50
70
1 (9)
593
T
1 (-5)
1 (-5)
5 (-4)
30
5
20
Fluxes (in Jy) of a15 MJupiter object at 10 pc distance, as a function of waveband (2.2, 3.8 and 4.6µm, respectively) and age (from Burrows et al. 2001). The effective surface temperature is also indicated, as is the spectral class, which passes from M to L to T as the brown dwarf ages. The distance away that PILOT could detect such an object (5 sigma, 1 hour) is also indicated. The brown dwarfs themselves can be identified through their colours, though additional filters for on and off the methane bands, at 1.7 and 3.3µm, would be required for a clear spectral classification.

 

Title Stellar Oscillations
Submitted by Tim Bedding (University of Sydney)
Outline of Science

Measuring stellar oscillations is a beautiful physics experiment. A star is a gaseous sphere and will oscillate in many different modes when suitably excited. The frequencies of these oscillations depend on the sound speed inside the star, which in turn depends on properties such as density, temperature and composition. The Sun oscillates in many modes simultaneously and comparing the mode frequencies with theoretical calculations (helioseismology) has led to significant revisions to solar models (e.g., Christensen-Dalsgaard, J., 2002). In particular: the Sun's convection zone has turned out to be 50% deeper than previously thought; the helium abundance cannot be as low as is required to reproduce the apparent neutrino flux (a result vindicated by recent evidence from SNO for neutrino flavour oscillations); the angular velocity does not increase rapidly with depth, fortunately removing the inconsistency between planetary orbits and General Relativity; and the opacities had been underestimated immediately beneath the convection zone. Measuring oscillation frequencies in other stars (asteroseismology) will allow us to probe their interiors in exquisite detail and study phenomena that do not occur in the Sun. We expect asteroseismology to produce major advances in our understanding of stellar structure and evolution, and of the underlying physical processes.

Thanks to the steadily improving Doppler precision provided by modern spectrographs, the field of asteroseismology has finally become a reality. For a recent review, see Bedding & Kjeldsen (2003). However, to make further gains we require that stars be observed as continuously as possible and with extremely high photometric precision. Antarctica offers both of these features and is second only to space as the site for an asteroseismology program. The low scintillation at Dome C, combined with its location near the South Pole, presents an unrivalled opportunity to carry out asteroseismology on solar-like stars and achieve a breakthrough in our understanding of the role played in stellar evolution by processes such as convection, rotation and mixing.

Antarctic Advantages
  • High photometric precision due to low scintillation.
  • Long-time period observations.
References

Bedding & Kjeldsen, 2003, PASA 20, 203

Christensen-Dalsgaard, J., 2002, Rev. Modern Phys. 74, 1073

   

 

Title Searching for Obscured AGB Stars in the Magellanic Clouds
Submitted by Tony Wong (UNSW/ATNF)
Outline of Science

The chemical enrichment of the ISM is largely provided by mass loss from evolved asymptotic giant branch (AGB) stars. Though many such stars have been identified in optical and near-infrared sky surveys, those with the highest mass loss rates (> ~10^-5 Msun/yr) are often too obscured to be seen optically. In many ways these are the most interesting sources, yet because they are only bright in the infrared and in molecular lines, they remain a poorly studied population. This is especially the case in the Magellanic Clouds (MCs), due to their greater distance and the limited sensitivity and resolution of IRAS. However, the well-constrained distances to the MCs, and the relative lack of Galactic foreground absorption or emission, provide a key advantage: stellar luminosities can be determined more accurately. This has been used, for example, to demonstrate differences in the period-luminosity relation between obscured and optically visible AGB stars (Wood 1998). In addition, the low metallicity of the MCs provides a unique environment in which to study the process of "early" metal enrichment as would have occurred in the young Universe (see e.g. van Loon 2000).

However, small sample size and selection effects are still a problem for these studies. PILOT will be able to substantially increase the number of known obscured AGB stars in the MCs by going deeper than IRAS in the mid-infrared and also providing the angular resolution needed to identify optical and near-infrared counterparts. This enlarged sample can then be followed up with near-infrared photometry to obtain light curves, searches for molecular masers and thermal lines with radio telescopes, and spectroscopy by 8m class telescopes to compare with chemical models.

Antarctic Advantage

Antarctica is the best place on Earth to view the Magellanic Clouds. Around latitude -30, where most southern telescopes are located, the MCs reach only moderate elevations of 40-50 degrees, and then only in the summer if one must observe at night. In Antarctica the MCs can be observed continuously at high elevation. Other advantages of PILOT for this work:

  • wide field of view to conduct blind surveys of the MCs for sources missed by IRAS,
  • angular resolution, needed to resolve sources in star clusters and crowded fields,
  • coverage from the visible into the thermal infrared, for detailed spectral typing.
References

van Loon, J. Th. 2000, A&A, 354, 125

Wood, P. R. 1998, A&A, 338, 592