Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-08-07
Astrophys.J.601:1075-1087,2004
Astronomy and Astrophysics
Astrophysics
Accepted to ApJ. New version contains some additional data. Results unchanged
Scientific paper
10.1086/380581
In this paper we present new and improved data on 38 cool white dwarfs identified by Oppenheimer et al. 2001 (OHDHS) as candidate dark halo objects. Using the high-res spectra obtained with LRIS, we measure radial velocities for 13 WDs that show an H alpha line. We show that the knowledge of RVs decreases the UV-plane velocities by only 6%. The radial velocity sample has a W-velocity dispersion of sig_W = 59 km/s--in between the values associated with the thick disk and the stellar halo. We also see indications for the presence of two populations by analyzing the velocities in the UV plane. In addition, we present CCD photometry for half of the sample, and with it recalibrate the photographic photometry of the remaining WDs. Using the new photometry in standard bands, and by applying the appropriate color-magnitude relations for H and He atmospheres, we obtain new distance estimates. New distances of the WDs that were not originally selected as halo candidates yield 13 new candidates. On average, new distances produce velocities in the UV plane that are larger by 10%, with already fast objects gaining more. Using the new data, while applying the same UV-velocity cut (94 km/s) as in OHDHS, we find a density of cool WDs of 1.7e-4 pc^-3, confirming the value of OHDHS. In addition, we derive the density as a function of the UV-velocity cutoff. The density (corrected for losses due to higher UV cuts) starts to flatten out at 150 km/s (0.4e-4 pc^-3), and is minimized (thus minimizing a possible non-halo contamination) at 190 km/s (0.3e-4 pc^-3). These densities are in a rough agreement with the estimates for the stellar halo WDs, corresponding to a factor of 1.9 and 1.4 higher values.
Blandford Roger. D.
Hansen Brad M.
Koopmans Leon V. E.
Oppenheimer Ben R.
Rich Robert Michael
No associations
LandOfFree
Cool White Dwarfs Revisited -- New Spectroscopy and Photometry does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Cool White Dwarfs Revisited -- New Spectroscopy and Photometry, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cool White Dwarfs Revisited -- New Spectroscopy and Photometry will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-616807