65 research outputs found
The 2XMMi/SDSS Galaxy Cluster Survey. III. Clusters associated with spectroscopically targeted luminous red galaxies in SDSS-DR10
We present a sample of 383 X-ray selected galaxy groups and clusters with
spectroscopic redshift measurements (up to z ~ 0.79) from the 2XMMi/SDSS Galaxy
Cluster Survey. The X-ray cluster candidates were selected as serendipitously
detected sources from the 2XMMi-DR3 catalogue that were located in the
footprint of the Sloan Digital Sky Survey (SDSS-DR7). The cluster galaxies with
available spectroscopic redshifts were selected from the SDSS-DR10. We
developed an algorithm for identifying the cluster candidates that are
associated with spectroscopically targeted luminous red galaxies and for
constraining the cluster spectroscopic redshift. A cross-correlation of the
constructed cluster sample with published optically selected cluster catalogues
yielded 264 systems with available redshifts. The present redshift measurements
are consistent with the published values. The current cluster sample extends
the optically confirmed cluster sample from our cluster survey by 67 objects.
Moreover, it provides spectroscopic confirmation for 78 clusters among our
published cluster sample, which previously had only photometric redshifts. Of
the new cluster sample that comprises 67 systems, 55 objects are newly X-ray
discovered clusters and 52 systems are sources newly discovered as galaxy
clusters in optical and X-ray wavelengths. Based on the measured redshifts and
the fluxes given in the 2XMMi-DR3 catalogue, we estimated the X-ray
luminosities and masses of the cluster sample.Comment: A&A in press, 12 pages, 15 figures, 1 table,
http://www.aanda.org/index.php?option=com_article&access=doi&doi=10.1051/0004-6361/20132297
The 2XMMi/SDSS Galaxy Cluster Survey. II. The optically confirmed cluster sample and the L_X-T relation
We compile a sample of X-ray-selected galaxy groups and clusters from the
XMM-Newton serendipitous source catalogue (2XMMi-DR3) with optical confirmation
and redshift measurement from the Sloan Digital Sky Survey (SDSS). The X-ray
cluster candidates were selected from the 2XMMi-DR3 catalogue in the footprint
of the SDSS-DR7. We developed a finding algorithm to search for overdensities
of galaxies at the positions of the X-ray cluster candidates in the photometric
redshift space and to measure the redshifts of the clusters from the SDSS data.
The detection algorithm provides the photometric redshift of 530 galaxy
clusters. Of these, 310 clusters have a spectroscopic redshift for at least one
member galaxy. About 75 percent of the optically confirmed cluster sample are
newly discovered X-ray clusters. Moreover, 301 systems are known as optically
selected clusters in the literature while the remainder are new discoveries in
X-ray and optical bands. The optically confirmed cluster sample spans a wide
redshift range 0.03-0.70 (median z=0.32). In this paper, we present the
catalogue of X-ray-selected galaxy groups and clusters from the 2XMMi/SDSS
galaxy cluster survey. The catalogue has two subsamples: (i) a cluster sample
comprising 345 objects with their X-ray spectroscopic temperature and flux from
the spectral fitting, and (ii) a cluster sample consisting of 185 systems with
their X-ray flux from the 2XMMi-DR3 catalogue, because their X-ray data are
insufficient for spectral fitting. The updated L_X-T relation of the current
sample with X-ray spectroscopic parameters is presented. We see no evidence for
evolution in the slope and intrinsic scatter of the L_X-T relation with
redshift when excluding the low-luminosity groups.Comment: A&A in press, 18 pages, 25 figures, 3 tables (revised version after
language editing
The 3XMM/SDSS Stripe 82 Galaxy Cluster Survey: Cluster catalogue and discovery of two merging cluster candidates
We present a galaxy cluster survey based on XMM-Newton observations that are
located in Stripe 82 of the Sloan Digital Sky Survey (SDSS). The survey covers
an area of 11.25 deg. The X-ray cluster candidates were selected as
serendipitously extended detected sources from the third XMM-Newton
serendipitous source catalogue (3XMM-DR5). A cross-correlation of the candidate
list that comprises 94 objects with recently published X-ray and optically
selected cluster catalogues provided optical confirmations and redshift
estimates for about half of the candidate sample. We present a catalogue of
X-ray cluster candidates previously known in X-ray and/or optical bands from
the matched catalogues or NED. The catalogue consists of 54 systems with
redshift measurements in the range of 0.05-1.19 with a median of 0.36. Of
these, 45 clusters have spectroscopic confirmations as stated in the matched
catalogues. We spectroscopically confirmed another 6 clusters from the
available spectroscopic redshifts in the SDSS-DR12. The cluster catalogue
includes 17 newly X-ray discovered clusters, while the remainder were detected
in previous XMM-Newton and/or ROSAT cluster surveys. Based on the available
redshifts and fluxes given in the 3XMM-DR5 catalogue, we estimated the X-ray
luminosities and masses for the cluster sample. We also present the list of the
remaining X-ray cluster candidates (40 objects) that have no redshift
information yet in the literature. Of these candidates, 25 sources are
considered as distant cluster candidates beyond a redshift of 0.6. We also
searched for galaxy cluster mergers in our cluster sample and found two strong
candidates for newly discovered cluster mergers at redshifts of 0.11 and 0.26.
The X-ray and optical properties of these systems are presented.Comment: 17 pages, 12 figures, accepted for publication in A&A, revised
version after language editin
Photometric and Spectroscopic Analysis of the SX Phe Star BL Cam
In the present paper, we report the photometric and spectroscopic
observations obtained by the 1.88 m telescope at the Kottamia astronomical
observatory of the pulsating star BL Cam. Fourier analysis of the light curves
reveals that the fundamental mode has two harmonics. The O-C method is used to
establish the period changes. So far, the analysis has been very successful in
mapping the pulsation amplitude of the star across the instability strip. By
using the formalism of Eddington and Plakidis (1929), we found significant
results and strong indications of the evolutionary period change. A total of 55
new maximum light timings are reported. New values of (1/P) dP/dt are estimated
using the O-C diagram based on all newly obtained times of maximum light
combined with those taken from the literature, assuming the periods are
decreasing and changing smoothly. To compute the effective temperature and
surface gravity of the star, we performed model atmosphere analysis on its
spectra. The physical parameters of the star are calculated and compared with
the evolutionary models
Optical intra-day variability of the blazar S5 0716+714
We present an extensive recent multi-band optical photometric observations of
the blazar S5 0716+714 carried out over 53 nights with two telescopes in India,
two in Bulgaria, one in Serbia, and one in Egypt during 2019 November -- 2022
December. We collected 1401, 689, 14726, and 165 photometric image frames in B,
V, R, and I bands, respectively. We montiored the blazar quasi-simultaneously
during 3 nights in B, V, R, and I bands; 4 nights in B, V, and R; 2 nights in
V, R, and I; 5 nights in B and R; and 2 nights in V and R bands. We also took
37 nights of data only in R band. Single band data are used to study intraday
flux variability and two or more bands quasi-simultaneous observations allow us
to search for colour variation in the source. We employ the power-enhanced
F-test and the nested ANOVA test to search for genuine flux and color
variations in the light curves of the blazar on intraday timescales. Out of 12,
11, 53, and 5 nights observations, intraday variations with amplitudes between
~3% and ~20% are detected in 9, 8, 31 and 3 nights in B, V, R, and I bands,
respectively, corresponding to duty cycles of 75%, 73%, 58% and 60%. These duty
cycles are lower than those typically measured at earlier times. On these
timescales color variations with both bluer-when-brighter and
redder-when-brighter are seen, though nights with no measurable colour
variation are also present. We briefly discuss possible explanations for this
observed intraday variability.Comment: 19 pages, 5 figures, 4 tables, Accepted for Publication in MNRA
The 2XMMi/SDSS Galaxy Cluster Survey I. The first cluster sample and X-ray luminosity-temperature relation
We present a catalogue of X-ray selected galaxy clusters and groups as a
first release of the 2XMMi/SDSS Galaxy Cluster Survey. The survey is a search
for galaxy clusters detected serendipitously in observations with XMM-Newton in
the footprint of the Sloan Digital Sky Survey (SDSS). The main aims of the
survey are to identify new X-ray galaxy clusters, investigate their X-ray
scaling relations, identify distant cluster candidates and study the
correlation of the X-ray and optical properties. In this paper we describe the
basic strategy to identify and characterize the X-ray cluster candidates that
currently comprise 1180 objects selected from the second XMM-Newton
serendipitous source catalogue (2XMMi-DR3). Cross-correlation of the initial
catalogue with recently published optically selected SDSS galaxy cluster
catalogues yields photometric redshifts for 275 objects. Of these, 182 clusters
have at least one member with a spectroscopic redshift from existing public
data (SDSS-DR8). Here we present the X-ray properties of the first cluster
sample which comprises 175 clusters, among which 139 objects are new X-ray
discoveries while the others were previously known as X-ray sources. The first
cluster sample from the survey covers a wide range of redshifts from 0.09 to
0.61, bolometric luminosities L_500 = 1.9 x 10^42 - 1.2 x 10^45 erg/s, and
masses M_500 = 2.3 x 10^13 - 4.9 x 10^14 Msun. We extend the relation between
the X-ray bolometric luminosity L_500 and the X-ray temperature towards
significantly lower T and L and still find that the slope of the linear L-T
relation is consistent with values published for high luminosities.Comment: A&A accepted, 14 pages, 17 figures, 2 tables. The first cluster
catalogue with the X-ray-optical overlay and fitted spectra for each cluster
is publicly available from http://www.aip.de/groups/xray/XMM_SDSS_CLUSTER
The changing material around (2060) Chiron from an occultation on 2022 December 15
We could accurately predict the shadow path and successfully observe an
occultation of a bright star by Chiron on 2022 December 15. The Kottamia
Astronomical Observatory in Egypt did not detect the occultation by the solid
body, but we detected three extinction features in the light curve that had
symmetrical counterparts with respect to the central time of the occultation.
One of the features is broad and shallow, whereas the other two features are
sharper with a maximum extinction of 25 at the achieved spatial
resolution of 19 km per data point. From the Wise observatory in Israel, we
detected the occultation caused by the main body and several extinction
features surrounding the body. When all the secondary features are plotted in
the sky plane we find that they can be caused by a broad 580 km disk with
concentrations at radii of 325 \pm 16 km and 423 \pm 11 km surrounding Chiron.
At least one of these structures appears to be outside the Roche limit. The
ecliptic coordinates of the pole of the disk are = 151
8 and = 18 11, in agreement with previous
results. We also show our long-term photometry indicating that Chiron had
suffered a brightness outburst of at least 0.6 mag between March and September
2021 and that Chiron was still somewhat brighter at the occultation date than
at its nominal pre-outburst phase. The outermost extinction features might be
consistent with a bound or temporarily bound structure associated with the
brightness increase. However, the nature of the brightness outburst is unclear,
and it is also unclear whether the dust or ice released in the outburst could
be feeding a putative ring structure or if it emanated from it.Comment: 6 pages, 4, figure
The XMM Cluster Survey: evolution of the velocity dispersionâtemperature relation over half a Hubble time
We measure the evolution of the velocity dispersionâtemperature (ÏvâTX) relation up to z = 1 using a sample of 38 galaxy clusters drawn from the XMM Cluster Survey. This work improves upon previous studies by the use of a homogeneous cluster sample and in terms of the number of high-redshift clusters included. We present here new redshift and velocity dispersion measurements for 12 z > 0.5 clusters observed with the Gemini Multi Object
Spectographs instruments on the Gemini telescopes. Using an orthogonal regression method,we find that the slope of the relation is steeper than that expected if clusters were self-similar, and that the evolution of the normalization is slightly negative, but not significantly different from zero (Ïv âT0.86±0.14E(z)â0.37±0.33). We verify our results by applying our methods to cosmological hydrodynamical simulations. The lack of evolution seen in our data is consistent with simulations that include both feedback and radiative cooling
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