33 research outputs found
A Sodium laser guide star coupling efficiency measurement method
Large telescope's adaptive optics (AO) system requires one or several bright
artificial laser guide stars to improve its sky coverage. The recent advent of
high power sodium laser is perfect for such application. However, besides the
output power, other parameters of the laser also have significant impact on the
brightness of the generated sodium laser guide star mostly in non-linear
relationships. When tuning and optimizing these parameters it is necessary to
tune based on a laser guide star generation performance metric. Although return
photon flux is widely used, variability of atmosphere and sodium layer make it
difficult to compare from site to site even within short time period for the
same site. A new metric, coupling efficiency is adopted in our field tests. In
this paper, we will introduce our method for measuring the coupling efficiency
of a 20W class pulse sodium laser for AO application during field tests that
were conducted during 2013-2015
Multicolor photometry of the galaxies in the central region of Abell 2634
An optical photometric observation with the BATC multicolor system is carried
out for the central 56' x 56' region of the nearby cluster of galaxies, Abell
2634. We achieved the spectral energy distributions (SEDs) of 5572 sources
detected down to mag, including 178 previously known galaxies, with
fourteen filters covering a wavelength range from 3600 \AA\ to 10000 \AA. After
excluding the foreground and background galaxies, a sample of 124 known members
is formed for an investigation of the SED properties. Based on the knowledge of
SED properties of member galaxies, we performed the selection of faint galaxies
belonging to Abell 2634. The color-color diagrams are powerful in the
star/galaxy separation, and 359 faint galaxies are selected by their color
features. The technique of photometric redshift and color-magnitude correlation
for the early-type galaxies are applied for these faint galaxies, and a list of
74 faint member galaxies is achieved. Basis on the enlarged sample of member
galaxies, the spatial distribution and color-magnitude relation of the galaxies
in core region of Abell 2634 are discussed. We find a tendency that the color
index dispersion of the early-type members is larger for the outer region,
which might reflect some clues about the environmental effect on the evolution
of galaxies in a cluster.Comment: 35 pages, 21 Postscript figures and tables, LaTeX, using aasms4.st
Chandra X-ray Analysis of Galaxy Cluster A168
We present Chandra X-ray observations of galaxy cluster A168 (z=0.045). Two
X-ray peaks with a projected distance of 676 kpc are found to be located close
to two dominant galaxies, respectively. Both peaks are significantly offset
from the peak of the number density distribution of galaxies. This suggests
that A168 consists of two subclusters, a northern subcluster (A168N) and a
southern subcluster (A168S). Further X-ray imaging analysis reveals that (1)
the X-ray isophotes surrounding the two X-ray peaks are heavily distorted, (2)
an elongated and ontinuous filament connects the two X-ray peaks. These suggest
that strong interactions have occurred between the two subclusters. Spectral
analysis shows that A168 has a mean temperature of 2.53 +/- 0.09 keV and a mean
metallicity of 0.31 +/- 0.04 Z_{solar}. The metallicity is roughly a constant
across the cluster but the temperature shows some systematic variations. Most
X-ray, optical and radio properties of A168 are consistent with it being an
off-axis merger several Gyrs after a core passage, although detailed numerical
simulations are required to see whether the observed properties, in particular
the significant offset between the optical and X-ray centers, can be reproduced
in such a scenario.Comment: 17 pages, 7 figures, to be published in ApJ. When this paper was
being refereed, Eric Hallman and Maxim Markevitch carried out a similar work
(astro-ph/0406322); our results are in broad agreemen