8 research outputs found
Trap Target Studies
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
CE-30 - Toward a Trapped Particle Target
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
A Hot DQ White Dwarf in the Open Star Cluster M35
We report the discovery of a hot DQ white dwarf, NGC 2168:LAWDS 28, that is a
likely member of the 150-Myr old cluster NGC 2168 (Messier 35). The spectrum of
the white dwarf is dominated by CII features. The effective temperature is
difficult to estimate but likely > 20,000 K based on the temperatures of hot
DQs with similar spectra. NGC2168:LAWDS 28 provides further evidence that hot
DQs may be the ``missing'' high-mass helium-atmosphere white dwarfs. Based on
published studies, we find that the DBA WD LP 475-242 is likely a member of the
Hyades open cluster, as often assumed. These two white dwarfs are the entire
sample of known He-atmosphere white dwarfs in open clusters with turnoff masses
>2 solar masses. Based on the number of known cluster DA white dwarfs and a
redetermination of the H-atmosphere:He-atmosphere ratio, commonly known as the
DA:DB ratio, we re-examine the hypothesis that the H- to He-atmosphere ratio in
open clusters is the same as the ratio in the field. Under this hypothesis, we
calculate that five He-atmosphere WDs are expected to have been discovered,
with a probability of finding fewer than three He-atmosphere white dwarfs of
0.08, or at the ~ 2-sigma level.Comment: 9 pages with 2 figures, uses LaTeX/AASTeX 5.2. Accepted for
publications in ApJ Letter
WIYN Open Cluster Study. XIX. Main Sequence Fitting Distances to Open Clusters Using V-K Color-Magnitude Diagrams
We have combined existing optical magnitudes for stars in seven open clusters
and 54 field stars with the corresponding JHKs photometry from the Two Micron
All Sky Survey (2MASS). Combining optical with near-IR photometry broadens the
color baseline minimizing the influence of photometric errors and allows better
discrimination between cluster stars and contaminating foreground and
background populations. The open clusters in this study include NGC 2516, M35,
M34, NGC 3532, M37, M67, and NGC 188. The field stars we are using possess high
quality Hipparcos parallaxes and well-determined metal abundances allowing us
to empirically determine the dependence of (V-K) color on metal abundance in
the range -0.45<=[Fe/H]<=+0.35. Using this relation along with the parallaxes
of the field stars, we are able to construct an unevolved main sequence in the
[Mv,(V-K)o] diagram for a specific abundance. These diagrams are then used to
fit to the cluster main sequences in the [V,V-K] color-magnitude diagram in
order to estimate a distance for each open cluster. We find that the resultant
distances are within the range of distances found in the literature via the
main sequence fitting technique. It is hoped that this will spur an expansion
of the current (limited) database of star clusters with high quality (V-K)
photometry down to the unevolved main sequence.Comment: 17 pages, 7 figures, to appear in The Astronomical Journal - February
200
From the Top to the Bottom of the Main Sequence: A Complete Mass Function of the Young Open Cluster M35
We present very deep and accurate photometry of the open cluster M35 (VRIc
filters). We have covered a region of 27.5x27.5 square arcmin.
The data range from Ic=12.5 to 23.5 mag, and the color intervals are
0.4\le(V-I)c\le3.0, 0.5\le(R-I)c\le2.5. Roughly, these values span from 1.6
M_\odot down to the substellar limit. By using the location of the stars on
color-magnitude and color-color diagrams, we have selected candidate members of
this cluster. We have merged our sample with previously published data and
obtained a color-magnitude diagram for the complete stellar population of the
cluster, covering the spectral range early B - mid M. The Mass Function
increases monotonically, when plotted in a log-log form, until it reaches ~0.8
M_\odot (\alpha=2.59). It remains shallower for less massive stars (\alpha=0.81
for 0.8-0.2 M_\odot), whereas a decrease ins observed for stars close to the
substellar regime. The total mass of the cluster is ~1600 M_\odot in the area
covered by this study.Comment: Accepted ApJ (Jan 10, 2001 issue
The CFHT Open Star Cluster Survey. IV. Two Rich, Young Open Star Clusters: NGC 2168 (M35) and NGC 2323 (M50)
We continue our study of rich Galactic clusters by presenting deep CCD
observations of both NGC 2168 (M35) and NGC 2323 (M50). Both clusters are found
to be rich (NGC 2168 contains at least 1000 stars brighter than V = 22 and NGC
2323 contains approximately 2100 stars brighter than our photometric limit of V
= 23) and young (age of NGC 2168 = 180 Myrs, age of NGC 2323 = 130 Myrs). The
color-magnitude diagrams for the clusters exhibit clear main sequences
stretching over 14 magnitudes in the V, B-V plane. Comparing these long main
sequences with those of earlier clusters in the survey, as well as with the
Hyades, has allowed for accurate distances to be established for each cluster
(dist. of NGC 2168 = 912 +/- 70/65 pc, dist. of NGC 2323 = 1000 +/- 81/75 pc).
Analysis of the luminosity and mass functions suggest that despite their young
ages, both clusters are somewhat dynamically relaxed exhibiting signs of
mass-segregation. This is especially interesting in the case of NGC 2323, which
has an age of only 1.3 times the dynamical relaxation time. The present
photometry is also deep enough to detect all of the white dwarfs in both
clusters. We discuss some interesting candidates which may be the remnants of
quite massive (M > 5 Mo) progenitor stars. The white dwarf cooling age of NGC
2168 is found to be in good agreement with the main-sequence turn-off age.
These objects are potentially very important for setting constraints on the
white dwarf initial-final mass relationship and upper mass limit for white
dwarf production.Comment: 34 pages, including 12 diagrams and 5 tables. Accepted for
publication in AJ. Minor typos correcte