1,501 research outputs found
Probing The Lower Mass Limit For Supernova Progenitors And The High-Mass End Of The Initial-Final Mass Relation From White Dwarfs In The Open Cluster M35 (NGC 2168)
We present a photometric and spectroscopic study of the white dwarf (WD) population of the populous, intermediate-age open cluster M35 (NGC 2168); this study expands upon our previous study of the WDs in this cluster. We spectroscopically confirm 14 WDs in the field of the cluster: 12 DAs, 1 hot DQ, and 1 db star. For each DA, we determine the WD mass and cooling age, from which we derive each star's progenitor mass. These data are then added to the empirical initial-final mass relation (IFMR), where the M35 WDs contribute significantly to the high-mass end of the relation. The resulting points are consistent with previously published linear fits to the IFMR, modulo moderate systematics introduced by the uncertainty in the star cluster age. Based on this cluster alone, the observational lower limit on the maximum mass of WD progenitors is found to be similar to 5.1M(circle dot) - 5.2M(circle dot) at the 95% confidence level; including data from other young open clusters raises this limit to as high as 7.1M(circle dot), depending on the cluster membership of three massive WDs and the core composition of the most massive WDs. We find that the apparent distance modulus and extinction derived solely from the cluster WDs ((m-M)(V) = 10.45 +/- 0.08 and E(B-V) = 0.185 +/- 0.010, respectively) is fully consistent with that derived from main-sequence fitting techniques. Four M35 WDs may be massive enough to have oxygen - neon cores; the assumed core composition does not significantly affect the empirical IFMR. Finally, the two non-DA WDs in M35 are photometrically consistent with cluster membership; further analysis is required to determine their memberships.NSF AST-0397492, AST-0602288Astronom
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
SDSS J142625.71+575218.3: A Prototype for A New Class of Variable White Dwarf
We present the results of a search for pulsations in six of the recently discovered carbon-atmosphere white dwarf ("hot DQ") stars. On the basis of our theoretical calculations, the star SDSS J142625.71 + 575218.3 is the only object expected to pulsate. We observe this star to be variable, with significant power at 417.7 s and 208.8 s ( first harmonic), making it a strong candidate as the first member of a new class of pulsating white dwarf stars, the DQVs. Its folded pulse shape, however, is quite different from that of other white dwarf variables and shows similarities with that of the cataclysmic variable AM CVn, raising the possibility that this star may be a carbon-transferring analog of AM CVn stars. In either case, these observations represent the discovery of a new and exciting class of object.NSF AST-0507639, AST-0602288, AST-0607480, AST-0307321Astronom
A Spectroscopic Survey of the Fields of 28 Strong Gravitational Lenses: The Group Catalog
With a large, unique spectroscopic survey in the fields of 28 galaxy-scale
strong gravitational lenses, we identify groups of galaxies in the 26
adequately-sampled fields. Using a group finding algorithm, we find 210 groups
with at least five member galaxies; the median number of members is eight. Our
sample spans redshifts of 0.04 0.76 with a median of 0.31,
including 174 groups with . Groups have radial velocity
dispersions of 60 1200 km s with a median of 350
km s. We also discover a supergroup in field B0712+472 at 0.29
consisting of three main groups. We recover groups similar to 85% of
those previously reported in these fields within our redshift range of
sensitivity and find 187 new groups with at least five members. The properties
of our group catalog, specifically 1) the distribution of , 2)
the fraction of all sample galaxies that are group members, and 3) the fraction
of groups with significant substructure, are consistent with those for other
catalogs. The distribution of group virial masses agrees well with theoretical
expectations. Of the lens galaxies, 12 of 26 (46%) (B1422+231, B1600+434,
B2114+022, FBQS J0951+2635, HE0435-1223, HST J14113+5211, MG0751+2716,
MGJ1654+1346, PG 1115+080, Q ER 0047-2808, RXJ1131-1231, and WFI J2033-4723)
are members of groups with at least five galaxies, and one more (B0712+472)
belongs to an additional, visually identified group candidate. There are groups
not associated with the lens that still are likely to affect the lens model; in
six of 25 (24%) fields (excluding the supergroup), there is at least one
massive ( 500 km s) group or group candidate projected
within 2 of the lens.Comment: 87 pages, 8 figures, a version of this was published in Ap
Serendipitous discovery of a cluster of galaxies with a peculiar central galaxy
We report the serendipitous discovery of a cluster of galaxies at z=0.369.
Thirty-eight candidate members were identified based on rough broad-band
photometric redshifts, and three members were confirmed spectroscopically. The
brightest cluster galaxy (BCG) is exceptionally blue, with B-V=0.12 and
V-I=1.02. The surface-brightness profile of the BCG follows an r^(1/4)-law
profile out to 3" in all three bands. The effective radius is significantly
smaller in bluer bandpasses, resulting in a blue core and a color gradient
opposite to the metallicity-induced color gradient observed in typical
elliptical galaxies. Beyond 3" an extended envelope of emission in excess of
the r^(1/4)-law profile is observed, the position angle of which coincides with
the major axis of the galaxy cluster. The spectrum of the BCG contains strong
Balmer absorption, a minimal 4000 A break, and a broad Mg II emission line,
suggesting that the galaxy has undergone recent star formation and may harbor a
central AGN. The presence of numerous nearby bright stars makes this cluster an
interesting target for next-generation adaptive optics using natural guide
stars.Comment: 21 pages, 8 figures, accepted for publication in the Astronomical
Journa
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