88 research outputs found
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
An Erupting Classical Nova in a Globular Cluster of M87
Only one certain classical nova eruption has ever been detected inside a
globular cluster - nova 1860 A.D. (T Sco) in M80. During a survey of M87 we
have detected an erupting star coincident (to within 0.08 pixels) with a
globular cluster of that giant elliptical galaxy. We are able to discount
variables in the foreground or background of M87. The light curve and color of
the erupting star match those expected for a nova at the distance of M87. The
chance superposition of an M87 field nova on the globular cluster is very
unlikely but cannot be completely ruled out.Our detection hints at a globular
cluster nova frequency novae/cluster/year, much higher than
previous observations have suggested
The Measurement of Solar Diameter and Limb Darkening Function with the Eclipse Observations
The Total Solar Irradiance varies over a solar cycle of 11 years and maybe
over cycles with longer period. Is the solar diameter variable over time too?
We introduce a new method to perform high resolution astrometry of the solar
diameter from the ground, through the observations of eclipses by reconsidering
the definition of the solar edge. A discussion of the solar diameter and its
variations must be linked to the Limb Darkening Function (LDF) using the
luminosity evolution of a Baily's Bead and the profile of the lunar limb
available from satellite data. This approach unifies the definition of solar
edge with LDF inflection point for eclipses and drift-scan or heliometric
methods. The method proposed is applied for the videos of the eclipse in 15
January 2010 recorded in Uganda and in India. The result shows light at least
0.85 arcsec beyond the inflection point, and this suggests to reconsider the
evaluations of the historical eclipses made with naked eye.Comment: 16 pages, 11 figures, accepted in Solar Physics. arXiv admin note:
text overlap with arXiv:astro-ph/0601109 by other author
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