24 research outputs found
Radial Velocity Studies of Close Binary Stars.IV
Radial-velocity measurements and sine-curve fits to the orbital velocity
variations are presented for the fourth set of ten close binary systems: 44
Boo, FI Boo, V2150 Cyg, V899 Her, EX Leo, VZ Lib, SW Lyn, V2377 Oph, Anon Psc
(GSC 8-324), HT Vir. All systems are double-lined spectroscopic binaries with
only two of them not being contact systems (SW Lyn and GSC 8-324) and with five
(FI Boo, V2150 Cyg, V899 Her, EX Leo, V2377 Oph) being the recent photometric
discoveries of the Hipparcos satellite project. Five of the binaries are
triple-lined systems (44 Boo, V899 Her, VZ Lib, SW Lyn, HT Vir). Three (or
possibly four) companions in the triple-lined systems show radial-velocity
changes during the span of our observations suggesting that these are in fact
quadruple systems. Several of the studied systems are prime candidates for
combined light and radial-velocity synthesis solutions.Comment: aastex5.0, 5 figures in PS; submitted to Astron.
Spectral Energy Distributions and Age Estimates of 172 Globular Clusters in M31
In this paper we present CCD multicolor photometry for 172 globular clusters
(GCs), taken from the Bologna catalog (Battistini et al. 1987), in the nearby
spiral galaxy M31. The observations were carried out by using the National
Astronomical Observatories 60/90 cm Schmidt Telescope in 13 intermediate-band
filters, which covered a range of wavelength from 3800 to 10000A. This provides
a multicolor map of M31 in pixels of 1.7"*1.7". By aperture photometry, we
obtain the spectral energy distributions (SEDs) for these GCs. Using the
relationship between the BATC intermediate-band system used for the
observations and the UBVRI broad-band system, the magnitudes in the B and V
bands are derived. The computed V and B-V are in agreement with the values
given by Battistini et al. (1987) and Barmby et al. (2000). Finally, by
comparing the photometry of each GC with theoretical stellar population
synthesis models, we estimate ages of the sample GCs for different
metallicities. The results show that nearly all our sample GCs have ages more
than 10^{9} years, and most of them are around 10^{10} years old. Also, we find
that GCs fitted by the metal-poor model are generally older than ones fitted by
the metal-rich model.Comment: 38 pages, 7 figures will appear in the February 2003 issue of A
Globular Cluster and Galaxy Formation: M31, the Milky Way and Implications for Globular Cluster Systems of Spiral Galaxies
The globular cluster (GC) systems of the Milky Way and of our neighboring
spiral galaxy, M31, comprise 2 distinct entities, differing in 3 respects. 1.
M31 has young GCs, ages from ~100 Myr to 5 Gyr old, as well as old globular
clusters. No such young GCs are known in the Milky Way. 2. We confirm that the
oldest M31 GCs have much higher nitrogen abundances than do Galactic GCs at
equivalent metallicities. 3. Morrison et al. found M31 has a subcomponent of
GCs that follow closely the disk rotation curve of M31. Such a GC system in our
own Galaxy has yet to be found. These data are interpreted in terms of the
hierarchical-clustering-merging (HCM) paradigm for galaxy formation. We infer
that M31 has absorbed more of its dwarf systems than has the Milky Way. This
inference has 3 implications: 1. All spiral galaxies likely differ in their GC
properties, depending on how many companions each galaxy has, and when the
parent galaxy absorbs them. The the Milky Way ties down one end of this
spectrum, as almost all of its GCs were absorbed 10-12 Gyr ago. 2. It suggests
that young GCs are preferentially formed in the dwarf companions of parent
galaxies, and then absorbed by the parent galaxy during mergers. 3. Young GCs
seen in tidally-interacting galaxies might come from dwarf companions of these
galaxies, rather than be made a-new in the tidal interaction. There is no ready
explanation for the marked difference in nitrogen abundance for old M31 GCs
relative to the oldest Galactic GCs. The predictions made by Li & Burstein
regarding the origin of nitrogen abundance in globular clusters are consistent
with what is found for the old M31 GCs compared to that for the two 5 Gyr-old
M31 GCs.Comment: to be published in ApJ, Oct 2004; 13 pages of text, 2 tables, 7
postscript figure
The M31 Globular Cluster Luminosity Function
We combine our compilation of photometry of M31 globular cluster and probable
cluster candidates with new near-infrared photometry for 30 objects. Using
these data we determine the globular cluster luminosity function (GCLF) in
multiple filters for the M31 halo clusters. We find a GCLF peak and dispersion
of V_0^0=16.84 +/-0.11, sigma_t=0.93 +/- 0.13 (Gaussian sigma = 1.20 +/- 0.14),
consistent with previous results. The halo GCLF peak colors (e.g., B^0_0 -
V^0_0) are consistent with the average cluster colors. We also measure V-band
GCLF parameters for several other subsamples of the M31 globular cluster
population. The inner third of the clusters have a GCLF peak significantly
brigher than that of the outer clusters (delta V =~ 0.5mag). Dividing the
sample by both galacticentric distance and metallicity, we find that the GCLF
also varies with metallicity, as the metal-poor clusters are on average 0.36
mag fainter than the metal-rich clusters. Our modeling of the catalog selection
effects suggests that they are not the cause of the measured differences, but a
more complete, less-contaminated M31 cluster catalog is required for
confirmation. Our results imply that dynamical destruction is not the only
factor causing variation in the M31 GCLF: metallicity, age, and cluster initial
mass function may also be important.Comment: AJ, in press. 36 pages, including 7 figure
Wide-Field Survey of Globular Clusters in M31. I. A Catalog of New Clusters
We present the result of a wide-field survey of globular clusters (GCs) in
M31 covering a 3deg x 3deg field c. We have searched for GCs on CCD images
taken with Washington CMT1 filters at the KPNO 0.9 m telescope using steps: (1)
inspection of morphological parameters given by the SExtractor package such as
stellarity, full maximum, and ellipticity; (2) consulting the spectral types
and radial velocities obtained from spectra takena spectrograph at the WIYN 3.5
m telescope; and (3) visual inspection of the images of each object. We have
and GC candidates, of which 605 are newly found GCs and GC candidates and 559
are previously known GCs. Amoects there are 113 genuine GCs, 258 probable GCs,
and 234 possible GCs, according to our classification critee known objects
there are 383 genuine GCs, 109 probable GCs, and 67 possible GCs. In total
there are 496 genprobable GCs and 301 possible GCs. Most of these newly found
GCs have T1 magnitudes of 17.5 - 19.5 mag, [17.9 < V < 19.9 mag assuming (C-T1)
~ 1.5], and (C-T1) colors in the range 1 - 2.Comment: accepted by AJ, using emulateapj.cl
The Kinematics and Metallicity of the M31 Globular Cluster System
With the ultimate aim of distinguishing between various models describing the
formation of galaxy halos (e.g. radial or multi-phase collapse, random
mergers), we have completed a spectroscopic study of the globular cluster
system of M31. We present the results of deep, intermediate-resolution,
fibre-optic spectroscopy of several hundred of the M31 globular clusters using
the Wide Field Fibre Optic Spectrograph (WYFFOS) at the William Herschel
Telescope in La Palma, Canary Islands. These observations have yielded precise
radial velocities (+/-12 km/s) and metallicities (+/-0.26 dex) for over 200
members of the M31 globular cluster population out to a radius of 1.5 degrees
from the galaxy center. Many of these clusters have no previous published
radial velocity or [Fe/H] estimates, and the remainder typically represent
significant improvements over earlier determinations. We present analyses of
the spatial, kinematic and metal abundance properties of the M31 globular
clusters. We find that the abundance distribution of the cluster system is
consistent with a bimodal distribution with peaks at [Fe/H] = -1.4 and -0.5.
The metal-rich clusters demonstrate a centrally concentrated spatial
distribution with a high rotation amplitude, although this population does not
appear significantly flattened and is consistent with a bulge population. The
metal-poor clusters tend to be less spatially concentrated and are also found
to have a strong rotation signature.Comment: 33 pages, 20 figure
Interstellar Polarization in M31
The wavelength dependence of interstellar polarization due to dust in M31 has
been observed along four sightlines. Only one sightline had been measured
previously.The globular clusters, S78, S150, S233 and Baade 327 were used as
point sources to probe the interstellar dust in M31. The Serkowski law produces
good fits for all the sightlines although the relationship between K and
lambda(max) may be different from that found in the Galaxy. The results of this
study imply that the slope K/lambda(max) may be significantly larger in M31.
The Serkowski curves are significantly narrower than those of the same
lambda(max) in the Galaxy and may require extreme modifications to the size
distributions of silicate particles. The fits for the four sightlines reveal
values of lambda(max) ranging from 4800 to 5500 A. These are consistent with
average values of lambda(max) measured in the Galaxy and the Magellanic Clouds.
The range measured for M31 corresponds to R(V) values of 2.7 to 3.1. The range
in R(V) seen in the Galaxy is 2.5 to 5.5 implying, for this small sample, that
the average size ofinterstellar grains in M31 is typically smaller than that
seen for Galactic grains if the nature of the grains is the same. Also, the
polarization efficiency for these sightlines is large although some bias is
expected since sightlines known to have significant interstellar polarization
were selected for the sample.Comment: 13 pages, 2 figures, AJ in press (June
A HST/WFPC2 survey of bright young clusters in M31. I. VdB0, a massive star cluster seen at ~= 25 Myr
{Aims.} We introduce our imaging survey of possible young massive globular
clusters in M31 performed with the Wide Field and Planetary Camera 2 (WFPC2) on
the Hubble Space Telescope (HST). We present here details of the data reduction
pipeline that is being applied to all the survey data and describe its
application to the brightest among our targets, van den Bergh 0 (VdB0), taken
as a test case. {Methods.} The reddening, the age and the metallicity of the
cluster are estimated by comparison of the observed Color Magnitude Diagram
(CMD) with theoretical isochrones. {Results.} Under the most conservative
assumptions the stellar mass of VdB0 is M > 2.4 x 10^4 M_sun, but our best
estimates lie in the range ~ 4-9 x 10^4 M_sun. The CMD of VdB0 is best
reproduced by models having solar metallicity and age = 25 Myr. Ages smaller
than = 12 Myr and larger than = 60 Myr are clearly ruled out by the available
data. The cluster has a remarkable number of Red Super Giants (> 18) and a CMD
very similar to Large Magellanic Cloud clusters usually classified as young
globulars such as NGC 1850, for example. {Conclusions.} VdB0 is significantly
brighter (>~ 1 mag) than Galactic open clusters of similar age. Its present-day
mass and half-light radius (r_h=7.4 pc) are more typical of faint globular
clusters than of open clusters. However, given its position within the disk of
M31 it is expected to be destroyed by dynamical effects, in particular by
encounters with giant molecular clouds, within the next ~ 4 Gyr.Comment: 18 pages, 16 figures (quality of Figures 1,2,3 and 4 reduced).
Accepted for publication in Astronomy & Astrophysics. Minor revisions to
sect. 1.
HST/WFPC2 Color-Magnitude Diagrams for Globular Clusters in M31
We report new HST/WFPC2 photometry for 10 globular clusters (GC) in M31
observed in F5555W(V) and F814W(I). Additionally we have reanalyzed HST
archival data of comparable quality for 2 more GCs. Extraordinary care is taken
to account for the effects of blended stellar images and required field
subtraction. We thus reach 1 mag fainter than the horizontal branch (HB) even
in unfavorable cases. We present the color-magnitude diagrams (CMDs) and
discuss their main features also in comparison with the properties of the
Galactic GCs. This analysis is augmented with CMDs previously obtained and
discussed by Fusi Pecci et al. (1996) on 8 other M31 clusters. We report the
following significant results: 1. The locus of the red giant branches give
reliable metallicity determinations which compare generally very well with
ground-based integrated spectroscopic and photometric measures, as well as
giving good reddening estimates. 2. The HB morphologies show the same behavior
with metallicity as the Galactic GCs, with indications that the 2nd-parameter
effect can be present in some GCs of our sample. However, at [Fe/H] ~ -1.7 we
observe a number of GCs with red HB morphology such that the HB type versus
[Fe/H] relation is offset from the MW and resembles that of the Fornax dwarf
spheroidal galaxy. One explanation for the offset is that they are younger than
their MW counterparts by 1-2 Gyr. 3. The Mv(HB)-[Fe/H] relationship has been
determined and the slope (~0.20) is very similar to the values derived from RR
Lyrae stars in the MW and the LMC. The zero-point of this relation based on the
assumed distance modulus (m-M)o(M31)=24.47+/-0.03 is consistent with
(m-M)o(LMC)=18.55.Comment: 50 pages, 12 figures (one in jpeg format), 8 tables, accepted for
publication in The A