Cool Customers in the Stellar Graveyard. II. Limits to Substellar Objects around Nearby DAZ White Dwarfs

Results from a concerted Hubble Space Telescope (HST) survey of nearby whitedwarfs for substellar objects is presented. A total of 7 DAZ white dwarfs withdistances of $<$ 50 pc had high contrast and high spatial resolution NICMOScoronagraphic images taken to search for candidate substellar objects atseparations $\ltorder$10\arcsec away. Limits to unresolved companions arederived through analysis of 2MASS photometry of the white dwarfs compared toexpected fluxes based on the WDs effective temperature, distance, and gravity. From our survey with HST we find several candidate companions, which havebeen or will be followed up with second epoch observations. We find that forfour of the white dwarfs we are sensitive to planetary companions $\gtorder$10M$_{Jup}$, and sensitive to companions $>$ 18 M$_{Jup}$ for all of the targets.The lack of significant near infrared excesses for our targets limits any kindof unresolved companions present to be substellar. In light of these results wemake several comments on the possibility of determining the origin of whitedwarfs with metals in their atmospheres.Comment: 11 pages, 7 figures, emulateapj, revisions to figures and text, to appear in September A