7 research outputs found
A census with ROSAT of low-luminosity X-ray sources in globular clusters
I analyze 101 observations from the ROSAT archive to search for X-ray sources
in or near 55 globular clusters. New sources are found in the cores of NGC362
(a double source), NGC6121 (marginally significant), NGC6139, and NGC6266; and
outside the cores of NGC6205, NGC6352 and NGC6388. More accurate positions are
determined for the X-ray sources in some ten clusters. The improved position
for the source in NGC6341 excludes the suggested ultraviolet counterpart. It is
shown that one of the two sources reported near the core NGC6626 is spurious,
as is the detection of a pulsar period in the PSPC data of this cluster; the
central source is resolved in three sources. One source reported previously in
NGC6304 is demoted to an upper limit. For 20 cluster cores better upper limits
to the X-ray luminosity are obtained.
From a statistical analysis I argue that several sources outside the cluster
cores may well belong to the clusters. All spectral energy distributions
observed so far are relatively soft, with bremsstrahlung temperatures =~0.9keV;
there is evidence however that bremsstrahlung spectra do not correctly describe
the spectra. The X-ray luminosity per unit mass for the cluster as a whole does
not depend on the concentration; the luminosity per unit mass for the core may
increase with the cluster concentration.Comment: 24 pages, 8 figures, 5 tables, accepted for publication in Astronomy
and Astrophysic
Ground and space-based study of two globular cluster CVs: M22 CV1 and M5 V101
As a class of compact binaries with large binding energy, cataclysmic
variables formed through close encounters play an important role in the
dynamical evolution of globular clusters. As part of a systematic search for
CVs undergoing dwarf nova eruptions in globular clusters, our 2004 monitoring
programme of M22 detected an outburst of the dwarf nova candidate CV1 during
May. We implement the ISIS image subtraction routine to obtain a light curve
for an outburst of CV1. We present the outburst light curve as well as
HST/WFPC2 photometry in the V, U and near ultra-violet (nUV) bands and a
Chandra/ACIS-S spectrum of the object. Our results confirm the DN nature of the
outburst and the CV status of the object. We also present the results of a
ground-based study of another globular cluster CV, M5 V101 - including
quiescent medium-resolution WHT/ISIS spectroscopy in the B and R bands,
displaying prominent Balmer and HeI emission, and R-band photometry.Comment: 12 pages, 11 figures. Accepted for publication in MNRA