91 research outputs found
Addendum: "The Dynamics of M15: Observations of the Velocity Dispersion Profile and Fokker-Planck Models" (ApJ, 481, 267 [1997])
It has recently come to our attention that there are axis scale errors in
three of the figures of Dull et al. (1997, hereafter D97). D97 presented
Fokker-Planck models for the collapsed-core globular cluster M15 that include a
dense, centrally concentrated population of neutron stars and massive white
dwarfs, but do not include a central black hole. In this Addendum, we present
corrected versions of Figures 9, 10, and 12, and an expanded version of Figure
6. This latter figure, which shows the full run of the velocity dispersion
profile, indicates that the D97 model predictions are in good agreement with
the moderately rising HST-STIS velocity dispersion profile for M15 reported by
Gerssen et al. (2002, astro-ph/0209315). Thus, a central black hole is not
required to fit the new STIS velocity measurements, provided that there is a
sufficient population of neutron stars and massive white dwarfs. This
conclusion is consistent with the findings of Gerssen et al. (2002,
astro-ph/0210158), based on a reapplication of their Jeans equation analysis
using the corrected mass-to-light profile (Figure 12) for the D97 models.Comment: 4 pages, 4 figures, submitted to Ap
Chandra X-ray Sources in the Collapsed-Core Globular Cluster M30 (NGC 7099)
We report the detection of six discrete, low-luminosity (Lx < 10^33 erg/s)
X-ray sources, located within 12 arcsec of the center of the collapsed-core
globular cluster M30 (NGC 7099), and a total of 13 sources within the half-mass
radius, from a 50 ksec Chandra ACIS-S exposure. Three sources lie within the
very small upper limit of 1.9 arcsec on the core radius. The brightest of the
three core sources has a luminosity of Lx (0.5-6 keV) = 6x10^32 erg/s and a
blackbody-like soft X-ray spectrum, which are both consistent with it being a
quiescent low-mass X-ray binary (qLMXB). We have identified optical
counterparts to four of the six central sources and a number of the outlying
sources, using deep Hubble Space Telescope and ground-based imaging. While the
two proposed counterparts that lie within the core may represent chance
superpositions, the two identified central sources that lie outside of the core
have X-ray and optical properties consistent with being CVs. Two additional
sources outside of the core have possible active binary counterparts. We
discuss the X-ray source population of M30 in light of its collapsed-core
status.Comment: 18 pages, 13 figures (8 color), resubmitted to ApJ after
incorporating referee comment
Faint X-ray Sources in the Globular Cluster Terzan 5
We report our analysis of a Chandra X-ray observation of the rich globular
cluster Terzan 5, in which we detect 50 sources to a limiting 1.0-6 keV X-ray
luminosity of 3*10^{31} ergs/s within the half-mass radius of the cluster.
Thirty-three of these have L_X>10^{32} ergs/s, the largest number yet seen in
any globular cluster. In addition to the quiescent low-mass X-ray binary (LMXB,
identified by Wijnands et al.), another 12 relatively soft sources may be
quiescent LMXBs. We compare the X-ray colors of the harder sources in Terzan 5
to the Galactic Center sources studied by Muno and collaborators, and find the
Galactic Center sources to have harder X-ray colors, indicating a possible
difference in the populations. We cannot clearly identify a metallicity
dependence in the production of low-luminosity X-ray binaries in Galactic
globular clusters, but a metallicity dependence of the form suggested by Jordan
et al. for extragalactic LMXBs is consistent with our data.Comment: 15 pages, 10 figures (3 color). Resubmitted to ApJ after
incorporating referee comments. v2: Added references to introductio
New Cataclysmic Variables and other Exotic Binaries in the Globular Cluster 47 Tucanae
We present 22 new (+3 confirmed) cataclysmic variables (CVs) in the non
core-collapsed globular cluster 47 Tucanae (47 Tuc). The total number of CVs in
the cluster is now 43, the largest sample in any globular cluster so far. For
the identifications we used near-ultraviolet (NUV) and optical images from the
Hubble Space Telescope, in combination with X-ray results from the Chandra
X-ray Observatory. This allowed us to build the deepest NUV CV luminosity
function of the cluster to date. We found that the CVs in 47 Tuc are more
concentrated towards the cluster center than the main sequence turnoff stars.
We compared our results to the CV populations of the core-collapsed globular
clusters NGC 6397 and NGC 6752. We found that 47 Tuc has fewer bright CVs per
unit mass than those two other clusters. That suggests that dynamical
interactions in core-collapsed clusters play a major role creating new CVs. In
47 Tuc, the CV population is probably dominated by primordial and old
dynamically formed systems. We estimated that the CVs in 47 Tuc have total
masses of approx. 1.4 M_sun. We also found that the X-ray luminosity function
of the CVs in the three clusters is bimodal. Additionally, we discuss a
possible double degenerate system and an intriguing/unclassified object.
Finally, we present four systems that could be millisecond pulsar companions
given their X-ray and NUV/optical colors. For one of them we present very
strong evidence for being an ablated companion. The other three could be CO- or
He-WDs.Comment: Published on MNRAS. 31 Pages, 23 Figures, 5 Tables. Minor changes
with respect to previous arXiv versio
A Chandra X-ray Study of the Globular Cluster M80
We report our analysis of a Chandra X-ray observation of the rich globular
cluster M80, in which we detect some 19 sources to a limiting 0.5-2.5 keV X-ray
luminosity of 7*10^30 ergs/s within the half-mass radius. X-ray spectra
indicate that two of these sources are quiescent low-mass X-ray binaries
(qLMXBs) containing neutron stars. We identify five sources as probable
cataclysmic variables (CVs), one of which seems to be heavily absorbed,
implying high inclination. The brightest CV may be the X-ray counterpart of
Nova 1860 T Sco. The concentration of the X-ray sources within the cluster core
implies an average mass of 1.2+/-0.2 Msun, consistent with the binary nature of
these systems and very similar to the radial distribution of the blue
stragglers in this cluster. The X-ray and blue straggler source populations in
M80 are compared to those in the similar globular cluster 47 Tuc.Comment: Submitted to ApJ. 15 pages, 6 figure
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