Cool white dwarfs in the Sloan Super COSMOS

Cool white dwarfs in the Sloan & Super. COSMOS Sky Surveys Nigel Hambly, Wide Field Astronomy Unit, If. A, 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 …) Þ 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.

Super. COSMOS • high mechanical stability • controlled environment • fast Þ enables a whole-sky multi-epoch digitisation programme: Super. COSMOS Sky Survey

Super. COSMOS 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 (work by Andrew Digby: MNRAS, 2003, 344, 583) • 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 & DR 1 now incorporated in one-stop shop: the Super. COSMOS Science Archive (SSA)

Super. COSMOS 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 15 min - 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, DR 1, EDR 2 MASS & USNOB • comprehensive online documentation • flexible user interface - basic (eg. cone search) - advanced (eg. free-form SQL for datamining) http: //surveys. roe. ac. uk/ssa

SSA : schema browser http: //surveys. roe. ac. uk/ssa

• extragalactic example: “select top 5 * from Reliable. Galaxies where g. Cor. Mag. B < 16. 5” Þ 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 DR 1 photometry from the SSA: • very clear separation of different populations, even with a small colour baseline • high degree of completeness: - 15. 0 < r < 20. 0 - 40. 0 < mu < 600. 0 (mas/yr) • see also: Gould & Kolmeier, Ap. JS, 152, 103 (2004) Munn et al. , AJ, 127, 3034 (2004) (both using USNOB) Þ ~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: • DR 2 … • expand comparison with model atmospheres • decomposition of sample into different kinematic populations • computation of LFs with strict selection and precise analysis Þ eg. Digby et al. subdwarf LF calculations