SDSS ultracool and halo WD candidates

A new catalogue of ~4 million light-motion curves, together with over 200 derived statistical quantities, for objects in Stripe 82 brighter than r~21.5 has been constructed by combining these data by Bramich et al. (2008MNRAS.386..887B). This catalogue is at present the deepest catalogue of its kind.

Extracting ~130000 objects with highest signal-to-noise ratio proper motions, we build a reduced proper motion diagram to illustrate the scientific promise of the catalogue. In this diagram, disc and halo subdwarfs are well-separated from the cool white dwarf sequence. Our sample of 1049 cool white dwarf candidates includes at least eight and possibly 21 new ultracool H-rich white dwarfs (Teff<4000K) and one new ultracool He-rich white dwarf candidate identified from their SDSS optical and UKIDSS infrared photometry.