Cool white dwarfs in the Sloan & SuperCOSMOS Sky Surveys

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

2. 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

3. 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.

4. 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.

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

6. 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

7. (work by Andrew Digby: MNRAS, 2003, 344, 583) 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)

8. 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 SuperCOSMOS Science Archive: features

9. 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) http://surveys.roe.ac.uk/ssa

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

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

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

16. 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: • - 15.0 < r < 20.0 • - 40.0 < mu < 600.0 (mas/yr) • see also: • Gould & Kolmeier, ApJS, 152, 103 (2004) • Munn et al., AJ, 127, 3034 (2004) • (both using USNOB) • ~1000 new cool WDs;

17. 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)

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

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

20. 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