98 research outputs found
Near-Infrared Photometric Study of the Old Open Cluster Trumpler 5
We present JHK near-infrared photometric study for the old open cluster (OC)
Trumpler 5 (Tr 5), based on the 2MASS data. From the color-magnitude diagrams
of Tr 5, we have located the position of the red giant clump (RGC) stars, and
used the mean magnitude of the RGC stars in K-band to estimate the distance to
Tr 5, d = 3.1 +/- 0.1 kpc ((m-M)_0 = 12.46 +/- 0.04). From fitting the
theoretical isochrones of Padova group, we have estimated the reddening,
metallicity, and age : E(B-V) = 0.64 +/- 0.05, [Fe/H] = -0.4 +/- 0.1 dex, and t
=2.8 +/- 0.2 Gyr (log t=9.45 +/- 0.04), respectively. These parameters
generally agree well with those obtained from the previous studies on Tr 5 and
confirms that this cluster is an old OC with metallicity being metal-poorer
than solar abundance, located in the anti-Galactic center region.Comment: JKAS (J. of the Korean Astron. Soc.) in press (2009 Dec issue), page
numbers will be change
UBVI CCD Photometry of the Old Open Cluster NGC 1193
We present UBVI photometry of the old open cluster NGC 1193. Color-magnitude
diagrams (CMDs) of this cluster show a well defined main sequence and a sparse
red giant branch. For the inner region of r<50 arcsec, three blue straggler
candidates are newly found in addition to the objects Kaluzny (1988) already
found. The color-color diagrams show that the reddening value toward NGC 1193
is E(B-V) =0.19 +/- 0.04. From the ultraviolet excess measurement, we derived
the metallicity to be [Fe/H]=-0.45 +/- 0.12. A distance modulus of (m-M)_0
=13.3 +/- 0.15 is obtained from zero age main sequence fitting with the
empirically calibrated Hyades isochrone of Pinsonneault et al. (2004). CMD
comparison with the Padova isochrones by Bertelli et al. (1994) gives an age of
log t =9.7 +/- 0.1.Comment: JKAS (J. of the Korean Astron. Soc.) in press (Dec 2008 issue
The properties of early-type galaxies in the Ursa Major cluster
Using SDSS-DR7 and NASA/IPAC Extragalactic Database spectroscopic data, we
identify 166 galaxies as members of the Ursa Major cluster with Mr < -13.5 mag.
We morphological classify all galaxies by means of carefully inspecting g-, r-,
i-band colour and monochromatic images. We show that the Ursa Major cluster is
dominated by late-type galaxies, but also contains a significant number of
early- type galaxies, particularly in the dwarf regime. We present further
evidence for the existence of several subgroups in the cluster, consistent with
previous findings. The early-type fraction is found to correlate with the mass
of the subgroup. We also investigate environmental effects by comparing the
properties of the Ursa Major early-type dwarf galaxies to those of the Virgo
cluster. In contrast to the Virgo, the red sequence of the Ursa Major cluster
is only sparsely populated in the optical and ultraviolet colour-magnitude
relations. It also shows a statistically significant gap between -18 < Mr < -17
mag, i.e. the Ursa Major cluster lacks early-type dwarf galaxies at the bright
end of their luminosity function. We discover that the majority of early-type
dwarf galaxies in the Ursa Major cluster have blue cores with hints of recent
or ongoing star formation. We suggest that gravitational tidal interactions can
trigger central blue star forming regions in early-type dwarfs. After that,
star formation would only fade completely when the galaxies experience ram
pressure stripping or harassment, both of which are nearly absent in the Ursa
Major cluster.Comment: 19 pages, 18 figures, 2 tables, Accepted for publication in MNRA
HI properties and star formation history of a fly-by pair of blue compact dwarf galaxies
A fly-by interaction has been suggested to be one of the major explanations
for enhanced star formation in blue compact dwarf (BCD) galaxies, yet no direct
evidence for this scenario has been found to date. In the HI Parkes all-sky
survey (HIPASS), ESO 435-IG 020 and ESO 435- G 016, a BCD pair were found in a
common, extended gas envelope of atomic hydrogen, providing an ideal case to
test the hypothesis that the starburst in BCDs can be indeed triggered by a
fly-by interaction. Using high-resolution data from the Australia Telescope
Compact Array (ATCA), we investigated HI properties and the spectral energy
distribution (SED) of the BCD pair to study their interaction and star
formation histories. The high-resolution HI data of both BCDs reveal a number
of peculiarities, which are suggestive of tidal perturbation. Meanwhile, 40% of
the HIPASS flux is not accounted for in the ATCA observations with no HI gas
bridge found between the two BCDs. Intriguingly, in the residual of the HIPASS
and the ATCA data, 10% of the missing flux appears to be located between the
two BCDs. While the SED-based age of the most dominant young stellar population
is old enough to have originated from the interaction with any neighbors
(including the other of the two BCDs), the most recent star formation activity
traced by strong H emission in ESO 435-IG 020 and the shear motion of
gas in ESO 435- G 016, suggest a more recent or current tidal interaction.
Based on these and the residual emission between the HIPASS and the ATCA data,
we propose an interaction between the two BCDs as the origin of their recently
enhanced star formation activity. The shear motion on the gas disk, potentially
with re-accretion of the stripped gas, could be responsible for the active star
formation in this BCD pair.Comment: 10 pages, 8 figures, 3 tables, accepted for publication in A&
Near-Infrared Photometry of the Star Clusters in the Dwarf Irregular Galaxy IC 5152
We present JHK-band near-infrared photometry of star clusters in the dwarf
irregular galaxy IC 5152. After excluding possible foreground stars, a number
of candidate star clusters are identified in the near-infrared images of IC
5152, which include young populations. Especially, five young star clusters are
identified in the (J-H, H-K) two color diagram and the total extinction values
toward these clusters are estimated to be A_V =2 - 6 from the comparison with
the theoretical values given by the Leitherer et al. (1999)'s theoretical star
cluster model.Comment: Accepted by the Journal of the Korean Astronomical Society, 2006
December issue (Vol. 39, No. 4
The Extended Virgo Cluster Catalog
We present a new catalog of galaxies in the wider region of the Virgo
cluster, based on the Sloan Digital Sky Survey (SDSS) Data Release 7. The
Extended Virgo Cluster Catalog (EVCC) covers an area of 725 deg^2 or 60.1
Mpc^2. It is 5.2 times larger than the footprint of the classical Virgo Cluster
Catalog (VCC) and reaches out to 3.5 times the virial radius of the Virgo
cluster. We selected 1324 spectroscopically targeted galaxies with radial
velocities less than 3000 kms^-1. In addition, 265 galaxies that have been
missed in the SDSS spectroscopic survey but have available redshifts in the
NASA Extragalactic Database are also included. Our selection process secured a
total of 1589 galaxies of which 676 galaxies are not included in the VCC. The
certain and possible cluster members are defined by means of redshift
comparison with a cluster infall model. We employed two independent and
complementary galaxy classification schemes: the traditional morphological
classification based on the visual inspection of optical images and a
characterization of galaxies from their spectroscopic features. SDSS u, g, r,
i, and z passband photometry of all EVCC galaxies was performed using Source
Extractor. We compare the EVCC galaxies with the VCC in terms of morphology,
spatial distribution, and luminosity function. The EVCC defines a comprehensive
galaxy sample covering a wider range in galaxy density that is significantly
different from the inner region of the Virgo cluster. It will be the foundation
for forthcoming galaxy evolution studies in the extended Virgo cluster region,
complementing ongoing and planned Virgo cluster surveys at various wavelengths.Comment: 69 pages, 29 figures, 4 tables, accepted for publication in the ApJ
Large-scale filamentary structures around the Virgo cluster revisited
We revisit the filamentary structures of galaxies around the Virgo cluster,
exploiting a larger dataset based on the HyperLeda database than previous
studies. In particular, this includes a large number of low-luminosity
galaxies, resulting in better sampled individual structures. We confirm seven
known structures in the distance range 4~~Mpc~ SGY~ 16~
Mpc, now identified as filaments, where SGY is the axis of the supergalactic
coordinate system roughly along the line of sight. The Hubble diagram of the
filament galaxies suggests they are infalling toward the main-body of the Virgo
cluster. We propose that the collinear distribution of giant elliptical
galaxies along the fundamental axis of the Virgo cluster is smoothly connected
to two of these filaments (Leo~II~A and B). Behind the Virgo cluster
(16~~Mpc~ SGY~ 27~~Mpc), we also identify a new filament
elongated toward the NGC 5353/4 group ("NGC 5353/4 filament") and confirm a
sheet that includes galaxies from the W and M clouds of the Virgo cluster ("W-M
sheet"). In the Hubble diagram, the NGC 5353/4 filament galaxies show infall
toward the NGC 5353/4 group, whereas the W-M sheet galaxies do not show hints
of gravitational influence from the Virgo cluster. The filamentary structures
identified can now be used to better understand the generic role of filaments
in the build-up of galaxy clusters at z~~0.Comment: 8 pages, 4 figures, accepted for publication in Ap
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