564 research outputs found
Automated search for star clusters in large multiband surveys: II. Discovery and investigation of open clusters in the Galactic plane
Automated search for star clusters in J,H,K_s data from 2MASS catalog has
been performed using the method developed by Koposov et. al (2008). We have
found and verified 153 new clusters in the interval of the galactic latitude
-24 < b < 24 degrees. Color excesses E(B-V), distance moduli and ages were
determined for 130 new and 14 yet-unstudied known clusters. In this paper, we
publish a catalog of coordinates, diameters, and main parameters of all the
clusters under study. A special web-site available at http://ocl.sai.msu.ru has
been developed to facilitate dissemination and scientific usage of the results.Comment: 9 pages, 3 tables, 5 figures, accepted to Astronomy Letter
Automated search for galactic star clusters in large multiband surveys: I. Discovery of 15 new open clusters in the Galactic anticenter region
Aims: According to some estimations, there are as many as 100000 open
clusters in the Galaxy, but less than 2000 of them have been discovered,
measured, and cataloged. We plan to undertake data mining of multiwavelength
surveys to find new star clusters. Methods: We have developed a new method to
search automatically for star clusters in very large stellar catalogs, which is
based on convolution with density functions. We have applied this method to a
subset of the Two Micron All Sky Survey catalog toward the Galactic anticenter.
We also developed a method to verify whether detected stellar groups are real
star clusters, which tests whether the stars that form the spatial density peak
also fall onto a single isochrone in the color-magnitude diagram. By fitting an
isochrone to the data, we estimate at the same time the main physical
parameters of a cluster: age, distance, color excess. Results: For the present
paper, we carried out a detailed analysis of 88 overdensity peaks detected in a
field of degrees near the Galactic anticenter. From this analysis,
15 overdensities were confirmed to be new open clusters and the physical and
structural parameters were determined for 12 of them; 10 of them were
previously suspected to be open clusters by Kronberger (2006) and Froebrich
(2007). The properties were also determined for 13 yet-unstudied known open
clusters, thus almost tripling the sample of open clusters with studied
parameters in the anticenter. The parameters determined with this method showed
a good agreement with published data for a set of well-known clusters.Comment: accepted to A&
Ages and abundances in large-scale stellar disks of nearby S0 galaxies
By undertaking deep long-slit spectroscopy with the focal reducer SCORPIO of
the Russian 6m telescope, we studied stellar population properties and their
variation with radius in 15 nearby S0 galaxies sampling a wide range of
luminosities and environments. For the large-scale stellar disks of S0s, we
have measured SSP-equivalent metallicities ranging from the solar one down to
[Z/H]=-0.4 - -0.7, rather high magnesium-to-iron ratios, [Mg/Fe] > +0.2, and
mostly old SSP-equivalent ages. Nine of 15 (60%) galaxies have large-scale
stellar disks older than 10 Gyr, and among those we find all the galaxies which
reside in denser environments. The isolated galaxies may have intermediate-age
stellar disks which are 7-9 Gyr old. Only two galaxies of our sample, NGC 4111
and NGC 7332, reveal SSP-equivalent ages of their disks of 2-3 Gyrs. Just these
two young disks appear to be thin, while the other, older disks have scale
heights typical for thick stellar disks. The stellar populations in the bulges
at radii of 0.5r_eff are on the contrary more metal-rich than the solar
metallicity, with the ages homogeneously distributed between 2 and 15 Gyr,
being almost always younger than the disks. We conclude that S0 galaxies could
not form in groups at z=0.4 as is thought now; a new scenario of the general
evolution of disk galaxies is proposed instead.Comment: Accepted to the MNRA
Chemodynamic subpopulations of the Carina dwarf galaxy
We study the chemodynamical properties of the Carina dwarf spheroidal by
combining an intermediate spectroscopic resolution dataset of more than 900 red
giant and red clump stars, with high-precision photometry to derive the
atmospheric parameters, metallicities and age estimates for our targets. Within
the red giant branch population, we find evidence for the presence of three
distinct stellar sub-populations with different metallicities, spatial
distributions, kinematics and ages. As in the Fornax and Sculptor dwarf
spheroidals, the subpopulation with the lowest average metallicity is more
extended and kinematically hotter than all other populations. However, we
identify an inversion in the parallel ordering of metallicity, kinematics and
characteristic length scale in the two most metal rich subpopulations, which
therefore do not contribute to a global negative chemical gradient. Contrary to
common trends in the chemical properties with radius, the metal richest
population is more extended and mildly kinematically hotter than the main
component of intermediate metallicity. More investigations are required to
ascertain the nature of this inversion, but we comment on the mechanisms that
might have caused it.Comment: 9 pages, 9 figures, accepted for publication in MNRA
Gaia 1 and 2. A pair of new Galactic star clusters
We present the results of the very first search for faint Milky Way
satellites in the Gaia data. Using stellar positions only, we are able to
re-discover objects detected in much deeper data as recently as the last couple
of years. While we do not identify new prominent ultra-faint dwarf galaxies, we
report the discovery of two new star clusters, Gaia 1 and Gaia 2. Gaia 1 is
particularly curious, as it is a massive (2.210 M), large
(9 pc) and nearby (4.6 kpc) cluster, situated 10' away from the brightest
star on the sky, Sirius! Even though this satellite is detected at significance
in excess of 10, it was missed by previous sky surveys. We conclude that Gaia
possesses powerful and unique capabilities for satellite detection thanks to
its unrivalled angular resolution and highly efficient object classification.Comment: 9 pages, accepted to MNRA
Nine tiny star clusters in Gaia DR1, PS1 and DES
We present the results of a systematic Milky Way satellite search performed
across an array of publicly available wide-area photometric surveys. Our aim is
to complement previous searches by widening the parameter space covered.
Specifically, we focus on objects smaller than and include old, young,
metal poor and metal rich stellar population masks. As a result we find 9 new
likely genuine stellar systems in data from GAIA, DES, and Pan-STARRS, which
were picked from the candidate list because of conspicuous counterparts in the
cut-out images. The presented systems are all very compact () and faint
(), and are associated either with the Galactic disk, or the
Magellanic Clouds. While most of the stellar systems look like Open Clusters,
their exact classification is, as of today, unclear. With these discoveries, we
extend the parameter space occupied by star clusters to sizes and luminosities
previously unexplored and demonstrate that rather than two distinct classes of
Globular and Open clusters, there appears to be a continuity of objects,
unmarked by a clear decision boundary.Comment: 17 pages, 13 figures, accepted in MNRAS. v1 submitted version; v2
accepted Versio
Leo V: A Companion of a Companion of the Milky Way Galaxy
We report the discovery of a new Milky Way dwarf spheroidal galaxy in the
constellation of Leo identified in data from the Sloan Digital Sky Survey. Leo
V lies at a distance of about 180 kpc, and is separated by about 3 degrees from
another recent discovery, Leo IV. We present follow-up imaging from the Isaac
Newton Telescope and spectroscopy from the Hectochelle fiber spectrograph at
the Multiple Mirror Telescope. Leo V's heliocentric velocity is 173.4 km/s,
which is offset by about 40 km/s from that of Leo IV. A simple interpretation
of the kinematic data is that both objects may lie on the same stream, though
the implied orbit is only modestly eccentric (e = 0.2)Comment: Submitted to ApJ (Letters
The PPMXL catalog of positions and proper motions on the ICRS. Combining USNO-B1.0 and 2MASS
USNO-B1.0 and 2MASS are the most widely used full-sky surveys. However, 2MASS
has no proper motions at all, and USNO-B1.0 published only relative, not
absolute (i.e. on ICRS) proper motions. We performed a new determination of
mean positions and proper motions on the ICRS system by combining USNO-B1.0 and
2MASS astrometry. This catalog is called PPMXL {VO-access to the catalog is
possible via http://vo.uni-hd.de/ppmxl}, and it aims to be complete from the
brightest stars down to about full-sky. PPMXL contains about 900
million objects, some 410 million with 2MASS photometry, and is the largest
collection of ICRS proper motions at present. As representative for the ICRS we
chose PPMX. The recently released UCAC3 could not be used because we found
plate-dependent distortions in its proper motion system north of -20
declination. UCAC3 served as an intermediate system for . The resulting typical individual mean errors of the proper motions
range from 4 mas/y to more than 10 mas/y depending on observational history.
The mean errors of positions at epoch 2000.0 are 80 to 120 mas, if 2MASS
astrometry could be used, 150 to 300 mas else. We also give correction tables
to convert USNO-B1.0 observations of e.g. minor planets to the ICRS system.Comment: 9 pages, 9 figure
SMASH 1 : A VERY FAINT GLOBULAR CLUSTER DISRUPTING in the OUTER REACHES of the LMC?
We present the discovery of a very faint stellar system, SMASH 1, that is potentially a satellite of the Large Magellanic Cloud. Found within the Survey of the Magellanic Stellar History (SMASH), SMASH 1 is a compact (rh=9.1-3.4+5.9pc) and very low luminosity (Mv=-1.0±0.9,Lv=102.3±0.4L⊙ ) stellar system that is revealed by its sparsely populated main sequence and a handful of red giant branch candidate member stars. The photometric properties of these stars are compatible with a metal-poor ([Fe/H]=-2.2) and old (13 Gyr) isochrone located at a distance modulus of ∼18.8, i.e., a distance of . Situated at 11.°3 from the LMC in projection, its three-dimensional distance from the Cloud is 13 kpc, consistent with a connection to the LMC, whose tidal radius is at least . Although the nature of SMASH 1 remains uncertain, its compactness favors it being a stellar cluster and hence dark-matter free. If this is the case, its dynamical tidal radius is only ≲19 pc at this distance from the LMC, and smaller than the system's extent on the sky. Its low luminosity and apparent high ellipticity (ϵ=0.62-0.21+0.17) with its major axis pointing toward the LMC may well be the tell-tale sign of its imminent tidal demise.Peer reviewe
Are group- and cluster-scale dark matter halos over-concentrated?
We investigate the relationship between the halo mass, M_200, and
concentration, c, for a sample of 26 group- and cluster-scale strong
gravitational lenses. In contrast with previous results, we find that these
systems are only ~ 0.1 dex more over-concentrated than similar-mass halos from
dark matter simulations; the concentration of a halo with M_200 = 10^14 M_sun
is log c = 0.78\pm0.05, while simulations of halos with this mass at similar
redshifts (z ~ 0.4) predict log c ~ 0.56 - 0.71. We also find that we are
unable to make informative inference on the slope of the M_200-c relation in
spite of our large sample size; we note that the steep slopes found in previous
studies tend to follow the slope in the covariance between M_200 and c,
indicating that these results may be measuring the scatter in the data rather
than the intrinsic signal. Furthermore, we conclude that our inability to
constrain the M_200-c slope is due to a limited range of halo masses, as
determined by explicitly modelling our halo mass distribution, and we suggest
that other studies may be producing biased results by using an incorrect
distribution for their halo masses.Comment: 8 pages; accepted to MNRA
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