From: LARRY KLAES (ljk4_at_msn.com)
Date: Thu Sep 15 2005 - 16:17:29 UTC
Paper: astro-ph/0509359
Date: Tue, 13 Sep 2005 20:15:35 GMT (71kb)
Title: All quiet in Globular Clusters
Authors: Andrej Dobrotka (Slovak Univ. of Technology, IAP), Jean-Pierre
Lasota
(IAP), Kristen Menou (Columbia Univ.)
Comments: 10 pages, 6 figures
\\
Cataclysmic Variables (CVs) should be present in large numbers in Globular
Clusters (GCs). Numerous low-luminosity X-ray sources identified over the
past
few years as candidate CVs in GCs support this notion. Yet, very few
"cataclysms," the characteristic feature of this class of objects in the
field,
have been observed in GCs. We address this discrepancy here, within the
framework of the standard Disk Instability Model for CV outbursts. We argue
that the paucity of outbursts in GCs is probably not a direct consequence of
the donors' low metallicities. We present diagnostics based on outburst
properties allowing tests of the hypothesis that rare cataclysms are
entirely
due to lower mass transfer rates in GCs relative to the field, and we argue
against this explanation. Instead, we propose that a combination of low mass
transfer rates (>~ 10^14-15 g/s) and moderately strong white dwarf magnetic
moments (>~ 10^30 G cm^3) stabilize CV disks in GCs and thus prevent most of
them from experiencing frequent outbursts. If it is so, rare cataclysms in
GCs
would signal important evolutionary differences between field and cluster
CVs.
\\ ( http://arXiv.org/abs/astro-ph/0509359 , 71kb)
Paper: astro-ph/0509372
Date: Wed, 14 Sep 2005 06:28:31 GMT (378kb)
Title: Photometric study of the variable star population in the globular
cluster NGC 6397
Authors: J. Kaluzny, I.B. Thompson, W.Krzeminski
Comments: 8 pages, 9 figures, submitted to MNRAS on 21 April 2005
\\
We present the results of a photometric survey for variable stars in the
central region of the nearby globular cluster NGC 6397.Time series
photometry
was obtained for 30 variable objects. The sample includes 12 new objects, of
which 6 show periodic lightcurves and 2 are eclipsing binaries of unknown
period. Six variables possess certain and three possess likely X-ray
counterparts detected with the Chandra observatory. Among them four are
cataclysmic variables and one is a foreground eclipsing binary. The
cataclysmic
variable CV2 exhibited a likely dwarf nova type outburst in May 2003. The
cataclysmic variable CV3 was observed at 18.5<V<20.0 during 5 observing
runs,
but went into a low state in May 2003 when it reached V>22. We have found
that
thelight curve of the optical companion to the millisecond pulsar
PSRJ1740-5340
exhibits noticeable changes of its amplitude on a time scale of a few
months. A
shallow eclipse with Delta_V=0.03 mag was detected in one of the cluster
turnoff stars suggesting the presence of a large planet or brown dwarf in
orbit.
\\ ( http://arXiv.org/abs/astro-ph/0509372 , 378kb)
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