Extremely metal-poor stars in the Galactic bulge

Martin Asplund (RSAA), Louise Howes (RSAA), Stefan Keller (RSAA), David Yong (RSAA), David Nataf (RSAA)

The very oldest as well as the most metal-poor stars are predicted to now reside in the central regions of galaxies such as the Milky Way bulge. The Galactic bulge is however in general metal-rich and very crowded, making an unbiased survey for such first stars candidates highly inefficient: only 0.1% of bulge stars have [Fe/H]<-2. We are using SkyMapper uvgriz photometry to pre-select metal-poor star candidates that are subsequently follow-up spectroscopically with AAOmega/AAT to confirm their metal-poor nature. The most interesting extremely metal-poor stars are then observed with 8-10m telescopes such as VLT and Magellan to determine the chemical compositions in detail to enable a comparison with Galactic metal-poor halo stars.

Super-metal rich stars in the solar neighbourhood

Martin Asplund (RSAA), Luca Casagrande (RSAA), David Nataf (RSAA), Jane Lin (RSAA)

How metal-rich can stars become? In the solar neighbourhood there are frequent claims that some stars have as high [Fe/H] as +0.5 or even higher. Such extremely high metallicities in even quite old stars is very difficult to explain given that the present-day interstellar medium only has solar metallicity. One possibility is that these stars have migrated radially from the inner Galactic disk or even the bulge due to transient interactions with spiral arms or the bar. These stars thus trace a critical, until recently overlooked, process for understanding the evolution of galaxies like the Milky Way. Super-metal rich stars are readily identifiable through their SkyMapper colours and we intend to compile a complete census of such stars in the solar neighbourhood. These will be observed spectroscopically both with GALAH and dedicated programs with HERMES/AAT and other telescopes, including high-resolution infrared spectroscopy (the optical spectra of these metal-rich stars are severely blended, making an accurate analysis difficult while the infrared regions contain numerous clean lines for parameter and abundance purposes). We will also investigate the possibility of using SkyMapper colours to identify alpha-enhanced metal-rich stars that may have a particular origin distinct from other metal-rich stars. Identifying metal-rich stars is helpful to guide exoplanet searches as the frequency of close-in giant planets increase rapidly with stellar metallicity.

Characterising Transiting Exoplanet Candidates from HATSouth

Daniel Bayliss (Geneva), Gaspar Bakos (Princeton), Joel Hartman (Princeton), Brian Schmidt (RSAA)

HATSouth is world's largest ground-based transit survey. We operate a dedicated network of fully autonomous telescopes that continuously search large fields in the southern hemisphere for transiting exoplanets. In order to characterise the exoplanet candidates we find, we need to accurately characterise the properties of the host star - most importantly their temperature and log(g). This helps us rule out false positives such as giant stars and rapidly rotating hot stars. It also allows us to prioritise interesting candidates (such as exoplanets transiting m-dwarfs). Currently we rely on 2MASS and APASS colours, but the SkyMapper Short Survey will greatly enhance our characterisation of host stars. This is becoming increasingly important as we now have over 700 HATSouth candidates - too many to follow-up all individually with spectroscopy.

Primordial Gaseous Seeds

Joss Bland-Hawthorn (U. Syd), Matthew Nichols (EPFL), Mary Putman (Columbia)

Dwarf galaxies represent some of the earliest formed structures and reflect the conditions of the early universe in which larger structures formed. Due to their proximity, most of the smallest dwarf galaxies known have been found in the vicinity of the Milky Way and Andromeda, where they have already been affected by the hot halo and potential of a larger galaxy. Unmolested versions of these dwarfs are likely to larger distances and still contain substantial quantities of gas which is fuelling ongoing star formation. We will use the main SkyMapper Survey to examine a population of HI clouds which show dwarf galaxy-like properties and could be host to these untouched galaxies which are potentially similar to the recently discovered dwarfs Leo P and Leo T that appear as faint smudges in SDSS. The southern sky provides many valuable targets for these systems with several surveys having found compact high velocity HI clouds that provide good dwarf galaxy candidates (Putman et al. 2002; Moss et al. 2013), and additional high resolution and sensitivity data will become available with ASKAP.
We will perform a systematic search in SkyMapper of the HI cloud candidates for resolved and unresolved stellar systems. Based on pre-existing techniques (e.g. Kniavez et al. 2004) we should easily detect HI seeds like Leo P at 2.3 Mpc and due to the nature of the search potentially detect Leo T like follow up candidates at 2.5 Mpc and Leo P like ones out to 6 Mpc.

Hypervelocity Stars

Warren R. Brown (CfA), Brian Schmidt (RSAA), Stefan Keller (RSAA), Margaret Geller (CfA), Scott Kenyon (CfA)

Hypervelocity stars travel with such extreme velocities that dynamical ejection involving a massive black hole is their most likely origin. Observers have discovered about two dozen unbound main sequence stars since the first in 2005, and their anisotropic spatial distribution is puzzling. Interestingly, different predicted ejection mechanisms yield different spatial and flight time distributions of unbound stars. SkyMapper is crucial for understanding what is going on. SkyMapper uvgri-band photometry will enable us to efficiently identify short-lived main sequence stars at faint magnitudes, stars that should not exist in the outer halo unless they were ejected there. Spectroscopy of these targets will yield a large and complete sample of unbound stars over the southern sky, and thereby provide a strong constraint on hypervelocity star origin. Hypervelocity stars are important because their properties probe the nature and environment of the Milky Way's massive black hole, and, with future Gaia proper motions measurements, their trajectories may provide unique tracers of the dark matter halo that surrounds the Milky Way.

Exploring the Halo of the Galaxy with SkyMapper

Gary Da Costa (RSAA), Andy Casey (Cambridge), Ken Freeman (RSAA), Stefan Keller (RSAA), Dougal Mackey (RSAA), Chris Owen (RSAA student, current PhD thesis using BHB stars identified in SkyMapper commissioning data as halo tracers)

In the current cosmological paradigm large galaxies like the Milky Way are built-up through the merger and accretion of lower mass systems, predominantly at early epochs. In the inner parts of the Galaxy the spatial and kinematic signatures of this process have been erased by the relatively short dynamical timescales but in the outer parts of the Galactic halo, where dynamical timescales are long, there is considerable evidence that supports the hierarchical assembly picture. The outstanding unresolved question, however, is what fraction of the stars in the halo today originated in the tidal disruption of satellite galaxies. The SDSS results indicate that this fraction is probably quite high but additional constraints from the southern hemisphere sky are needed. The SkyMapper filter system is designed for optimal use in stellar programs, providing information on stellar gravities and metal abundances. Coupled with multi-epoch imaging, SkyMapper photometry will allow us to isolate particular types of halo tracers, which can then be used to investigate the stellar distribution, and the degree of sub-structure, in the Galactic halo. The halo tracers include RRL variables and blue horizontal branch stars, which can function as standard candles, and metal-poor red giants which potentially sample distances to ~100 kpc. The program will use Main Survey data.

Mapping the Structure of the Outer Parts of the Magellanic Clouds

Gary Da Costa (RSAA), Ken Freeman (RSAA), Stefan Keller (RSAA), Dougal Mackey (RSAA)

The Small and Large Magellanic Clouds are our nearest significant galaxy neighbours. But have they always been our neighbours? What are their true extents on the sky? And how strongly have gravitational interactions between the Clouds and the Milky Way, and between the Clouds themselves, influenced their evolution? These are important questions and remarkably, they lack clear answers. We intend to use SkyMapper imaging of the full area of the periphery of the Magellanic Clouds to construct detailed 2-dimensional maps of the stellar distribution. With these data we will study the underlying density profile in the extreme outer parts of these galaxies. We shall also investigate the extent and location of any deviations from the underlying profile, seeking particularly possible sub-structures. Such features may be signatures of gravitational interactions, and their orientation and location will indicate whether the primary interaction is between the Clouds themselves or with the Galaxy. Our results will complement and extend those of the ESO VISTA near-IR (Y, J and Ks bands) survey of the Magellanic Clouds (VMC) as the area covered by the SkyMapper imaging is much more extensive - the VMC survey reaches only to ~7deg from the LMC centre. In our analysis of the SkyMapper data we will use matched-filter techniques in which only those stars that fall in particular regions of the multi-dimensional colour-magnitude space dominated by LMC (SMC) members are used in the analysis. In this way we can achieve much improved signal-to-noise over stellar densities derived from single band data. We will also investigate the stellar populations of the extreme outskirts - an old metal-poor halo population should be readily distinguished in the SkyMapper survey photometric bands from an extension of the younger (age ~ few Gyr) more metal-rich population that dominates the inner regions of both Clouds (and from foreground dwarf stars). We will also study the stellar populations in the region between the Clouds where the Magellanic Stream appears to originate. The program requires Main Survey data.

The SkyMapper Survey Search for Extremely Metal-Poor Stars

Gary Da Costa (RSAA), Martin Asplund (RSAA), Michael Bessell (RSAA), Andy Casey (Cambridge), Anna Frebel (MIT), Alex Heger (Monash), Heather Jacobson (MIT), Stefan Keller (RSAA), Karin Lind (Uppsala), Fabiola Marino (RSAA), John Norris (RSAA), Brian Schmidt (RSAA), David Yong (RSAA)

SkyMapper uvgi photometry is used to select candidate Extremely Metal-Poor (EMP) stars using the metallicity sensitivity provided by the SkyMapper v filter. Candidates brighter than g ~ 15.5 are followed-up spectroscopically at the 2.3m with the resulting high probability candidates then observed at high dispersion using facilities at Magellan and Keck. The program has already resulted in the discovery of the most iron-poor star known (Keller et al., 2014, Nature, 506, 463). The ultimate aims of the program are a much improved characterisation of the Metallicity Distribution Function at the lowest metallicities, a more complete understanding of the role of carbon enhancement in the formation of the most metal-poor stars, and improved constraints on the mass function of the first generation of metal-free stars. The program will also provide much new information on the formation of the chemical elements. The survey will use both Short Survey and Main Survey data.

The Halos of nearby Globular Clusters

Ken Freeman (RSAA), Gary Da Costa (RSAA), Dougal Mackey (RSAA)

The goal of the project is to discover stars in the outer parts of nearby Galactic globular clusters, at and beyond their tidal radii. These rare stars are valuable tracers of the formation and evolution of the clusters. Because they are so rare, wide field imaging in several bands is needed to find them, and thus the project is well suited to the SkyMapper survey. The regions of globular clusters beyond their tidal radii are populated by stars from several possible sources. These include: (a) stars that have evaporated from the cluster through two-body relaxation, mass loss driven by early stellar evolution, or through tidal shocking as the cluster crosses the Galactic disk or passes near the Galactic Centre; (b) stars that belong to a tidally stripped parent dwarf galaxy of which the cluster was the nucleus (e.g., omega Cen, M54) or a former member; and, (c) for globular clusters that may have formed in a local starburst in the manner of NGC2070 in the LMC, the stars that formed in the vicinity of the cluster might still be moving along with the cluster, although not part of it. Such stars may be of interest in the context of current work on the multiple stellar populations present in most globular clusters. In each case the stars may form a halo around the cluster or show leading and trailing tidal tails as is observed in clusters such as Pal 5. The observational aim is to identify stars that are photometrically like the cluster members, using all the SkyMapper band passes for which the photometry is accurate enough to detect cluster-like stars. The analysis templates will come from the distribution of cluster stars in the multi-colour, magnitude space provided by the SkyMapper data. The target list will include relatively nearby clusters to permit spectroscopic follow-up of the extra-tidal population to learn more about their origin. The program will use Main Survey data.

Compact and Ultracompact binaries in the Milky Way Galaxy

Paul Groot (Radboud), Danny Steeghs (Warwick), Lilia Ferrario (ANU), Tom Marsh (Warwick), Philipp Podsiadlowski (Oxford), Gijs Nelemans (Radboud), Lars Bildsten (UCSB), Patrick Woudt (UCT), David Buckley (SAAO), Steven Bloemen (Radboud), Gavin Ramsay (Armagh), Ben Stappers (Manchester), P. Jonker (SRON/Radboud), Brian Warner (UCT), Boris Gäsicke (Warwick), Stephane Vennes (CAS), Adela Kawka (CAS)

Compact and Ultracompact binary systems consist of at least one stellar remnant in a very close orbit, with periods less than ~1-6 hours. They can either be detached or semi-detached, and the primary star can be a white dwarf or a neutron star. Depending on the exact binary constellation they are called double degenerates, post common-envelope binaries, AM CVn stars, Cataclysmic Variables, Ultracompact X-ray binaries or recycled pulsars.
The astrophysical significance of these systems is multifold:

• a) they probe the final stages of binary evolution and their absolute and relative abundance in the Milky Way Galaxy allows us to understand the physics of binary evolution.
• b) they are the main source population for low-frequency gravitational wave emission.
• c) they allow an understanding of the occurrence and physics of gravitational tides, which in turn are a probe of the equation of state of dense, cold matter.
• d) they are probes of accretion physics, in particular the effect of chemical composition
• e) they are the source population of supernovae Type Ia, which are not only used to trace the accelerated expansion of the Universe, but also the main source of iron in the Universe.

In the last decade our teams have opened up the study of these objects, both theoretically as well as observationally. The known source populations have doubled to tripled over this period, in particular through the availability of large scale (Northern) optical photometric surveys, radio surveys and the combination of the two. As an example, in the transition radio pulsar systems the combination of having optical and radio data at the same time has been vital in understanding the evolution of these objects. Population numbers are often still low due to their intrinsic rarity, severely limiting population studies. The Southern Hemisphere is virtually unexplored. SkyMapper offers unprecedented opportunities for the detection of new systems in the South. Our aim is to, at least, double the number of known systems and then use them to understand the Galactic population of (ultra)compact binaries as well as the final stages of binary stellar evolution. The SkyMapper sample will complement the study of these systems using the VPHAS+ ESO Public Survey and the GBS Survey, both led by our team. Selection of candidates from SkyMapper will be based on source colours, as well as variability (outbursts/eclipses).
Detailed (high-speed) photometric and spectroscopic optical and radio follow-up is, and will be, obtained with the suite of observational resources to our disposal (ESO, SAAO, MeerKAT+MeerLICHT, Parkes, La Palma and AAO). We will combine these observational studies with detailed population synthesis modelling (Nelemans; Podsiadlowski) as well as in depth modelling of individual systems (e.g. using the MESA code developed by Bildsten et al.).

The Stromlo Milky Way Satellite Survey

Helmut Jerjen (RSAA), Gary Da Costa (RSAA), John Norris (RSAA), Antonino Milone (RSAA), Dongwon Kim (RSAA), Martin Asplund (RSAA), Anna Frebel (CfA), Marla Geha (Yale), Andres Jordan (Catolica), Renee Kraan-Korteweg (UCT), Pavel Kroupa (Bonn), Mario Mateo (Michigan), Se-Heon Oh (UCT), Ed Olszewski (Arizona), Patrick Tisserand (IAP), Matthew Walker (Cambridge), Shane Walsh (Curtin), Beth Willman (Haverford), Manuela Zoccali (Catolica)

Our team will pursue the search for optically elusive, dark matter-dominated satellite galaxies and other stellar overdensities in the halo of the Milky Way. We employ our own, highly efficient data-mining algorithms to scrutinise Terabyte size imaging sets that are flowing from the SkyMapper Southern Sky Survey. Newly discovered stellar systems will be systematically analysed by means of deep follow-up observations (imaging and spectroscopy) with telescope facilities worldwide. Fundamental properties are determined including spatial coordinates, size, stellar and dark matter contents, star density and presence of extra-tidal stars. Chemical abundance measurements of the stellar populations are compared with our team's latest results on Galactic halo stars, the multi-populations in globular clusters and galaxy formation models. The physical parameters we derive for Milky Way satellite galaxies represent important empirical input to constrain the process of galaxy formation on small (satellites) and large (Milky Way) scales. At the later stage of the program they will enable us to conduct a comparative statistical study for testing key predictions of the currently best theoretical model for structure formation and evolution in the universe. These research activities will be the most comprehensive in the Southern hemisphere and highly competitive to ongoing US-lead studies with Pan-STARRS and the Dark Energy Survey, both probing only half of the southern sky.

Exploring Supernovae through light echoes

Wolfgang Kerzendorf (ESO), Armin Rest (STScI)

Supernovae are the brilliant explosive death throes of stars. They are one of the most energetic events in the Universe and thus are excellent laboratories to explore high energy physics. Furthermore, a subclass of these objects - namely Type Ia supernovae - can be calibrated to serve as cosmic distance probes, enabling the discovery of the accelerated expansion of the Universe. Transient surveys, targeting extragalactic supernovae, supply a wealth of information about the early phase (to a maximum of a couple years post-explosion), while close-by Galactic supernovae are studied hundreds of years post-explosion through their remnants, but in much greater detail than is possible for their extragalactic counterparts. Linking the studies of remnants and early-time observations is essential to combine the unique information about supernovae coming from each of these disparate measurements. Light echoes are the most direct way of connecting a remnant to its early-time spectra which can then be used for classification. This technique has successfully been applied to a handful of supernovae, most notably classifying Tycho's supernova as Type Ia and Cas A as Type IIb.
We will use Skymapper to survey large areas of the southern sky in order to detect light echo systems associated with historical supernovae (including Kepler (SN 1604), SN 1006, RCW86, Crab Nebula, and W49B). Once detected we will obtain follow-up spectra using 8-m class telescopes and hope that in some favourable cases we will not only provide a classification spectrum, but also a three dimensional view of the event by observing different light echoes.

The Interstellar Extinction Curve for 2.2 < R_V < 2.9

David Nataf (RSAA), Luca Casagrande (RSAA), Martin Asplund (RSAA)

The interstellar extinction toward the inner Galaxy is known to be steeper-than-standard (Udalski 2003; Zasowski et al. 2009), to be very high (Gonzalez et al. 2013) and to be spatially variable on very small scales in both its normalisation and in its wavelength-dependence (Nataf et al. 2013). As the extinction curve in the case of steep extinction is poorly-constrained empirically, systematic errors remain outstanding in either interpreting data toward the inner Galaxy, let alone applying steeper-than-standard extinction to extragalactic observations. We will exploit SkyMapper photometry in its unique filter combination - the filters are somewhat distinct from Sloan and DECam filters of the same name - to precisely calibrate the shape of the extinction curve in this low R_V regime.

Finding the Galactic Population of Symbiotic Binary Stars

Jeno Sokoloski (Columbia), Juan Luna (IAFE/Conicet)

Symbiotic systems are interacting binary stars in which a compact object (usually a white dwarf) accretes material from a red-giant companion. Some symbiotic stars appear to end their lives as type Ia supernovae. But the Galactic population of symbiotic stars, and the way in which symbiotics can evolve to become type Ia supernovae, are poorly understood. One of the reasons is that standard spectroscopic methods of identifying symbiotic stars lead to strong selection biases. SkyMapper can overcome these biases. We will use the SkyMapper photometric survey to identify new symbiotic stars and to estimate how many of these systems exist in our Galaxy. Symbiotics will stand out because of their distinctive colour signature - red at the red end of the optical spectrum (due to the red giant mass-donor star) and blue at the blue end of the optical spectrum (due to the accreting WD) - and their variability. The broad spectral coverage of the SkyMapper filters are perfect for our project, and we will use optical spectroscopy of early candidates to refine the region of colour-colour space where symbiotic systems reside. This research has implications for the progenitors of type Ia supernovae and binary stellar evolution.

RCorBor stars

Patrick Tisserand (IAP)

1800 candidates of R Coronae Borealis stars (RCBs) were found using the WISE and 2MASS all sky infrared surveys (Tisserand, P. 2012, 2014). Photometric monitoring of those candidates using the SkyMapper's g, r, i, and z filters would be useful to detect the typical signature of RCBs: unpredictable large and fast photometric declines (up to 9 mag in 1 week). With a maximum magnitudes ranging between 14 and 16 mags, RCBs would appeared either bright (close to saturation) down to undetected on a single SkyMapper photometric epoch during the 5 years survey. Those photometric measurements can mainly be used to discriminate between RCB stars and Carbon Miras as the latest present large periodic pulsations.

Search for high redshift QSOs (5.8<z<6.7)

Patrick Tisserand (IAP), Brian Schmidt (RSAA), Christopher Onken (RSAA), Christian Wolf (RSAA)

Using a i-drop out selection technique with the SkyMapper i and z filters, we can expect to find up to 30 high redshift quasars (5.8<z<6.7) brighter than Z<20 mag in the entire SkyMapper southern sky survey. We would be able to increase by more than a factor two the numbers of bright high redshift QSOs known in this range of redshift and therefore obtain better constraint on the period of reionisation of our Universe.

Photometry of flat-spectrum radio sources

Oleg Titov (Geoscience Australia), Richard Hunstead (U. Syd), Helen Johnston (U. Syd), David Jauncey (CSIRO/RSAA), Laura Stanford (GA), Tapio Pursimo (NOT), Sandor Frey (FÖMI SGO), Leonid Gurvits (JIVE)

About 3000 radio quasars are observed regularly by the International VLBI Service, IVS, to define and maintain the International Celestial Reference Frame, ICRF. We have presented evidence for large scale systematic proper motions, dipole and quadrupole effects, at a level in excess of 10 microarcsec/year. This result presents a serious challenge to the standard cosmologies. High redshifts are of particular interest because the systematic proper motions are expected to increase with redshift. However, due to the north-south imbalance in the distribution and spectroscopic completeness of the reference radio sources, the statistical analysis meets serious difficulties. To improve the statistics in the South we began a spectroscopic program in 2010 (NTT, Gemini South), but the number of high-redshift quasars is limited due to lack of modern digital sky surveys for efficient preselection of the targets. We need accurate photometric magnitudes in different optical colours to identify the strong flat-spectrum radio sources at redshifts z>3 for further observation with international VLBI networks. The SkyMapper data will be used in the same way as SDSS DR9 in the northern hemisphere to identify the stellar-like radio source identifications with large colour dropouts, e.g., g-r > 3. Based on the experience with SDSS we expect these colour dropouts to be caused by the combination of the Ly-alpha emission line at z>3 and the Ly-alpha forest absorption blueward of the emission line. The targets selected using this scheme will be proposed for spectroscopic observations at other large optical facilities.

Investigating the Galactic White Dwarf Population with SkyMapper

Stephane Vennes (Czech Academy of Sciences), Adela Kawka (CAS), Lilia Ferrario (ANU), Stefan Keller (RSAA), Mike Bessell (RSAA), David Buckley (SAAO), Gary Da Costa (RSAA)

Using SkyMapper multi-band photometry supplemented with ultraviolet and infrared archival data as well as astrometric data products (proper motion) we will extract the first deep-sky catalogue of white dwarfs covering all Galactic latitudes from the Southern Cap to the Galactic plane. In a first step, we will develop the colourimetric criteria based on new model atmospheres that are necessary to discriminate white dwarfs from other populations (e.g., cool subdwarf stars). Next, with SkyMapper team members we will initiate the spectroscopic investigation. The first phase of the programme will exploit existing preliminary data to train our models and selection criteria, and in the second phase we will gradually build a catalogue of white dwarf and other subluminous stars (e.g., EHB) concurrently with the survey build-up. The spectroscopic follow-up will be initiated as soon as practical using world-class facilities such as ESO. The full data set will allow us to constrain white dwarf formation scenarios in the disc and halo of the Galaxy. In addition, a large hidden population of double degenerate stars should emerge from follow-up spectroscopic investigations, which, combined with the WD+MS binary population, will allow us to conduct population synthesis calculations leading to a definitive population census and tight constraints of the white dwarf space distribution and formation rate (luminosity function).

Classification and photo-z catalogue, faint end of galaxy luminosity function

Christian Wolf (RSAA), Brian Schmidt (RSAA), Christopher Onken (RSAA)

We use statistical classification methods to derive a star/galaxy/QSO/white-dwarf classification including photometric redshifts for galaxies and QSOs. In the short survey this will allow photo-z preselection of spectroscopic surveys such as TAIPAN. In the main survey we hope to achieve a 0.01 RMS redshift precision for objects at r<19 and z<0.2, so as to define the deepest all-sky z<0.2 galaxy catalogue and investigate the faint end of the galaxy luminosity function, split by galaxy types (SED, surface brightness, light profile). Dr Wolf is currently running activities within the new 2dFLenS survey that will extend the GAMA survey as a training sample and improve on its weakest characteristics for this purpose. He is also accomplished with both galaxy and QSO photo-z's.

Optical counterparts of radio source population in ASKAP pilot surveys

Christian Wolf (RSAA), Julie Banfield (CSIRO), Brian Schmidt (RSAA), Bäbel Koribalski (CSIRO), Ray Norris (CSIRO) and the ATLAS team

We investigate the optical counterpart identification of radio sources discovered in the existing pilot surveys to the forthcoming ASKAP surveys EMU, POSSUM and WALLABY, including a radio-optical classification and photo-z estimation. We want to characterise the optical properties of the radio source populations and the properties of the SkyMapper-based identification to provide a reference for the ASKAP surveys. Dr Banfield is deeply involved in the radio survey ATLAS and the ASKAP activities.

Optical counterparts of X-ray source population in ROSAT and eROSITA

Christian Wolf (RSAA), Mara Salvato (MPE), CAASTRO and the German eROSITA team

We investigate the optical counterpart identification of X-ray sources found in the existing ROSAT catalogue and the forthcoming eROSITA survey, including an Xray-optical classification and photo-z estimation. We want to characterise the optical properties of the X-ray source populations and the properties of the SkyMapper-based identification. This project is part of a collaboration between CAASTRO and the German eROSITA team. Dr Salvato is already set up for X-ray/optical cross-matching and experienced from the Northern Sky.

The QSO luminosity function and using QSOs as local probes

Christian Wolf (RSAA), Christopher Onken (RSAA), Patrick Tisserand (IAP), Brian Schmidt (RSAA)

QSOs are to be identified at all redshifts and magnitude levels where it is possible with high confidence (see Wolf et al. photo-z program). The brightest QSOs in the Southern Sky are yet to be identified, and so far only ~3000 sq.deg have been searched by the Hamburg-ESO-survey. These will be interesting targets for absorption-line follow-up studies. The whole range of z<2.5 QSOs will be used for cross-checking the calibration and dust correction over the survey area. The faintest QSOs will be used for a study of the QSO luminosity function and its evolution. Large QSO groups will be selected for follow-up high-cadence monitoring.

Ultra-Cool White Dwarfs in the Southern Sky

Christian Wolf (RSAA), Mike Bessell (RSAA)

Ultra-cool white dwarfs (UCWDs) are rare and physically unexplained. Their SEDs are highly "non-Planckian", with very steep spectral slopes on either side of a maximum between g and r-band. The favoured physical explanation for these objects and their SEDs is that they are almost pure He white dwarfs with low-mass (0.2-0.3 M_sol) and T<3500 K, where collisionally-induced absorption (CIA) suppresses the far-red and NIR flux to produce extremely blue optical-NIR colours from spectral slopes that are much steeper than any Planck law can produce. They are thus potentially cooler than even the oldest CO white dwarfs, and might be the leftover He cores of former red giants that lost their envelopes by binary interaction (Justham, Wolf et al. 2009). Ten such UCWDs are known across the sky, of which six were found in SDSS (Gates et al. 2004). Only two are known in the Southern Sky, the relatively bright LHS 1402 and a faint specimen found by Wolf (2005). With SkyMapper we want to find all UCWDs in the Southern Sky, which should be possible using the SkyMapper filters even in the Galactic plane, as the survey sensitivity will limit us to a distance of ~100 parsec and thus dust extinction won't be a major factor. At 100 pc distance significant dust extinction would make them too faint to be found anyway. We expect to find 20-30 objects and will use the two known ones for verification of our search method.

SkyMapper Transient Search

Fang Yuan (RSAA), Richard Scalzo (RSAA), Brian Schmidt (RSAA)

The SkyMapper Transient (SMT) search is a rolling search of the southern and equatorial sky utilizing the SkyMapper Telescope. The search is designed to ulitize the poor seeing nights at SSO, covering approximately 1000 sq.deg per full night with an expected cadence of 3-4 nights. The SkyMapper Transients survey will provide a new capability to identify and study transient object in great details. As one of the flagship missions of the ARC Centre for Excellence in All-Sky Astrophysics (CAASTRO), SkyMapper transients will contribute signicantly to the study of both the Dynamic Universe and the Dark Universe. While 70% of the SkyMapper SN discoveries will be Type Ia supernovae (SNe Ia) useful for probing Dark Energy, the remainder of these dynamic events will probe the diversity of explosions throughout the Universe.