Cool white dwarfs in the Sloan & SuperCOSMOS Sky Surveys Nigel Hambly, Wide Field Astronomy Unit, IfA, University of Edinburgh

Why study cool white dwarfs? most numerous remnants of their progenitor population mass-to-light ratio >10,000 makes truly “dark” matter WD LFs can be employed in cosmochronometry individual cool WDs can be very interesting

Multicolour imaging surveys yield stellar CMDs hot (blue) WDs relatively easily identified in sparsely populated regions of colour space cool WDs unidentifiable by colour alone (although …)  would ideally like HR diagram to determine luminosity class of all stars to identify the WDs.

Multi-epoch data provide the means via proper motions Following Hertzsprung: where constant c is a function of tangential velocity. The quantity on the RHS is called H, the Hertzsprung parameter or ‘reduced proper motion’. A plot of H versus colour yields an HR-ish diagram.

SuperCOSMOS high mechanical stability controlled environment fast  enables a whole-sky multi-epoch digitisation programme: SuperCOSMOS Sky Survey

SuperCOSMOS Sky Survey: Hambly et al., 2001, MNRAS, 326, 1279 et seq. Schmidt photographic imaging survey B,R,I (22.0, 20.5, 18.5); R at second epoch Currently Dec < +3.0; whole sky end 2005 Absolute calibrations: m +/- 0.3; RA, Dec +/- 0.3” typically Relative calibrations: m +/- 0.05; RA, Dec +/- 0.03” at best Proper motions: typically < +/- 10 mas/yr

eg. SSS astrometry and SDSS photometry very clear separation of different populations, even with a small colour baseline this work accomplished by wholesale download of EDR data and heavy processing by user entire SSS & DR1 now incorporated in one-stop shop: the SuperCOSMOS Science Archive (SSA) (work by Andrew Digby: MNRAS, 2003, 344, 583)

SuperCOSMOS Science Archive: features catalogue data in a commercial DBMS: - SQL interface ( + JDBC/ODBC, …) - highly flexible and configurable - ease of indexing (eg. spatial & other) to expedite common queries high performance hardware - trawl 1 billion merged records in 15min - trawl at the server side; ship results only Virtual Observatory compatibility: - output formats include XML VOTable - Unified Content Descriptors (UCDs) basic interfaces with push-button functionality as well as generalised SQL

SSA: homepage ~4 TB catalogue data, including SSS, DR1, EDR 2MASS & USNOB comprehensive online documentation flexible user interface - basic (eg. cone search) - advanced (eg. free-form SQL for datamining)

SSA : schema browser

extragalactic example: “select top 5 * from ReliableGalaxies where gCorMagB < 16.5”  bright galaxy catalogue made to order.

Flexible, (relatively!) simple SQL syntax: process (~10 min) at the server (no large downloads reqd.)

Combine SSS astrometry and SDSS DR1 photometry from the SSA: very clear separation of different populations, even with a small colour baseline high degree of completeness: < r < < mu < (mas/yr) see also: Gould & Kolmeier, ApJS, 152, 103 (2004) Munn et al., AJ, 127, 3034 (2004) (both using USNOB)  ~1000 new cool WDs;

very clear separation of different populations, even with a small colour baseline see also Gould et al. astro-pa/04???? thousands of new, cool white dwarfs combined selection using Hr, (g-r) and (r-i)

Further analysis: two-colour diagrams very clear separation latest cool WD models from Didier Saumon & colleagues

Further analysis: model atmosphere fits only pure H fits done at this preliminary stage

Future work: DR2 … expand comparison with model atmospheres decomposition of sample into different kinematic populations computation of LFs with strict selection and precise analysis  eg. Digby et al. subdwarf LF calculations