12 research outputs found
Spectroscopic analysis of DA white dwarfs from the McCook & Sion catalog
For some years now, we have been gathering optical spectra of DA white dwarfs
in an effort to study and define the empirical ZZ Ceti instability strip.
However, we have recently expanded this survey to include all the DA white
dwarfs in the McCook & Sion catalog down to a limiting visual magnitude of
V=17.5. We present here a spectroscopic analysis of over 1000 DA white dwarfs
from this ongoing survey. We have several specific areas of interest most
notably the hot DAO white dwarfs, the ZZ Ceti instability strip, and the DA+dM
binary systems. Furthermore, we present a comparison of the ensemble properties
of our sample with those of other large surveys of DA white dwarfs, paying
particular attention to the distribution of mass as a function of effective
temperature.Comment: 8 pages, 7 figures, to appear in Journal of Physics Conference
Proceedings for the 16th European White Dwarf Worksho
Radial velocity measurements of white dwarfs
We present 594 radial velocity measurements for 71 white dwarfs obtained
during our search for binary white dwarfs and not reported elsewhere. We
identify three excellent candidate binaries, which require further observations
to confirm our preliminary estimates for their orbital periods, and one other
good candidate. We investigate whether our data support the existence of a
population of single, low mass (<~0.5 solar masses) white dwarfs (LMWDs). These
stars are difficult to explain in standard models of stellar evolution. We find
that a model with a mixed single/binary population is at least ~20 times more
likely to explain our data than a pure binary population. This result depends
on assumed period distributions for binary LMWDs, assumed companion masses and
several other factors. Therefore, the evidence in favour of the existence of a
population of single LMWDs is not sufficient, in our opinion, to firmly
establish the existence of such a population, but does suggest that extended
observations of LMWDs to obtain a more convincing result would be worthwhile .Comment: 14 pages, 4 Figures. Accepted for publication in MNRAS. Added
Institutio
Multiwavelength Observations of the Hot DB Star PG 0112+104
We present a comprehensive multiwavelength analysis of the hot DB white dwarf
PG 0112+104. Our analysis relies on newly-acquired FUSE observations, on
medium-resolution FOS and GHRS data, on archival high-resolution GHRS
observations, on optical spectrophotometry both in the blue and around Halpha,
as well as on time-resolved photometry. From the optical data, we derive a
self-consistent effective temperature of 31,300+-500 K, a surface gravity of
log g = 7.8 +- 0.1 (M=0.52 Msun), and a hydrogen abundance of log N(H)/N(He) <
-4.0. The FUSE spectra reveal the presence of CII and CIII lines that
complement the previous detection of CII transitions with the GHRS. The
improved carbon abundance in this hot object is log N(C)/N(He) = -6.15 +- 0.23.
No photospheric features associated with other heavy elements are detected. We
reconsider the role of PG 0112+104 in the definition of the blue edge of the
V777 Her instability strip in light of our high-speed photometry, and contrast
our results with those of previous observations carried out at the McDonald
Observatory.Comment: 10 pages in emulateapj, 9 figures, accepted for publication in Ap