2,402 research outputs found
An empirical initial-final mass relation from hot, massive white dwarfs in NGC 2168 (M35)
The relation between the zero-age main sequence mass of a star and its
white-dwarf remnant (the initial-final mass relation) is a powerful tool for
exploration of mass loss processes during stellar evolution. We present an
empirical derivation of the initial-final mass relation based on spectroscopic
analysis of seven massive white dwarfs in NGC 2168 (M35). Using an internally
consistent data set, we show that the resultant white dwarf mass increases
monotonically with progenitor mass for masses greater than 4 solar masses, one
of the first open clusters to show this trend. We also find two massive white
dwarfs foreground to the cluster that are otherwise consistent with cluster
membership. These white dwarfs can be explained as former cluster members
moving steadily away from the cluster at speeds of <~0.5 km/s since their
formation and may provide the first direct evidence of the loss of white dwarfs
from open clusters. Based on these data alone, we constrain the upper mass
limit of WD progenitors to be >=5.8 solar masses at the 90% confidence level
for a cluster age of 150 Myr.Comment: 14 pages, 3 figures. Accepted for publication in the Astrophysical
Journal Letters. Contains some acknowledgements not in accepted version (for
space reasons), otherwise identical to accepted versio
Agricultural Transition in the New Federal States of Germany
International Development,
The White Dwarf Population in NGC 1039 (M34) and the White Dwarf Initial-Final Mass Relation
We present the first detailed photometric and spectroscopic study of the
white dwarfs (WDs) in the field of the ~225 Myr old (log tau_cl = 8.35) open
cluster NGC 1039 (M34) as part of the ongoing Lick-Arizona White Dwarf Survey.
Using wide-field UBV imaging, we photometrically select 44 WD candidates in
this field. We spectroscopically identify 19 of these objects as WDs; 17 are
hydrogen-atmosphere DA WDs, one is a helium-atmosphere DB WD, and one is a cool
DC WD that exhibits no detectable absorption lines. We find an effective
temperature (T_eff) and surface gravity (log g) for each DA WD by fitting
Balmer-line profiles from model atmospheres to the observed spectra. WD
evolutionary models are then invoked to derive masses and cooling times for
each DA WD. Of the 17 DAs, five are at the approximate distance modulus of the
cluster. Another WD with a distance modulus 0.45 mag brighter than that of the
cluster could be a double-degenerate binary cluster member, but is more likely
to be a field WD. We place the five single cluster member WDs in the empirical
initial-final mass relation and find that three of them lie very close to the
previously derived linear relation; two have WD masses significantly below the
relation. These outliers may have experienced some sort of enhanced mass loss
or binary evolution; however, it is quite possible that these WDs are simply
interlopers from the field WD population. Eight of the 17 DA WDs show
significant CaII K absorption; comparison of the absorption strength with the
WD distances suggests that the absorption is interstellar, though this cannot
be confirmed with the current data.Comment: 24 pages, 13 figures. Accepted for publication in the Astronomical
Journal. Figures 1, 2 and 3 reduced in resolutio
Model atmosphere analysis of the extreme DQ white dwarf GSC2U J131147.2+292348
A new model atmosphere analysis for the peculiar DQ white dwarf discovered by
Carollo et al. (2002) is presented. The effective temperature and carbon
abundance have been estimated by fitting both the photometric data
(UBJ,VRF,IN,JHK) and a low resolution spectrum (3500<lambda<7500 A) with a new
model grid for helium-rich white dwarfs with traces of carbon (DQ stars). We
estimate Teff ~ 5120 +/- 200 K and log[C/He] ~ -5.8 +/- 0.5, which make GSC2U
J131147.2+292348 the coolest DQ star ever observed. This result indicates that
the hypothetical transition from C2 to C2H molecules around Teff = 6000 K,
which was inferred to explain the absence of DQ stars at lower temperatures,
needs to be reconsidered.Comment: 4 pages, 2 figures, accepted for publication in Astronomy and
Astrophysics Letter
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