165 research outputs found
Modeling and Analysis of a Spectrum of the Globular Cluster NGC 2419
NGC 2419 is the most distant massive globular cluster in the outer Galactic
halo. It is unusual also due to the chemical peculiarities found in its red
giant stars in recent years. We study the stellar population of this unusual
object using spectra obtained at the 1.93-m telescope of the Haute-Provence
Observatory. At variance with commonly used methods of high-resolution
spectroscopy applicable only to bright stars, we employ spectroscopic
information on the integrated light of the cluster. We carry out population
synthesis modeling of medium-resolution spectra using synthetic stellar
atmosphere models based on a theoretical isochrone corresponding accurately to
the observed color-magnitude diagram. We study the influence of non-Local
Thermodynamic Equilibrium for some chemical elements on our results. The
derived age (12.6 Gyr), [Fe/H]=-2.25 dex, helium content Y=0.25, and abundances
of 12 other chemical elements are in a good qualitative agreement with
published high-resolution spectroscopy estimates for red giant members in the
cluster. On the other hand, the derived element abundance, [alpha/Fe]=0.13 dex
(the mean of [O/Fe], [Mg/Fe] and [Ca/Fe]), differs from the published one
([alpha/Fe] =0.4 dex) for selected red giants in the cluster and may be
explained by a large dispersion in the alpha-element abundances recently
discovered in NGC2419. We suggest that studies of the {\it integrated} light in
the cluster using high-resolution spectrographs in different wavelength regions
will help to understand the nature of these chemical anomalies.Comment: 19 pages, 6 figures, accepted for publication in the journal
"Astronomy Reports". This work was presented in a poster at IAU General
Assembly XXVIII, Beijing 2012 (Special Session 1 "Origin and Complexity of
Massive Star Clusters"). Four sentences were added thanks comments of Th. H.
Puzi
Surface photometry of dwarf irregular galaxies in different environments
Surface photometry data on 90 dwarf irregular galaxies (dIrrs) in a wide
vicinity of the Virgo cluster and 30 isolated dIrrs are presented. Images from
the Sloan Digital Sky Survey (SDSS) are used. The following mean photometric
characteristics (color and central surface brightness) are obtained for objects
in the two samples:(V-I)o=0.75 mag (sigma=0.19 mag), (B-V)o=0.51 mag
(sigma=0.13 mag), SBv=22.16 mag/sq.arcsec (sigma=1.02 mag/sq.arcsec) for the
dIrrs in the vicinity of the Virgo cluster and (V-I)o=0.66 mag (sigma=0.43
mag), (B-V)o=0.57 mag (sigma=0.16 mag), SBv=22.82 mag/sq.arcsec (sigma=0.73
mag/sq.arcsec) for the isolated galaxies. The mean central surface brightnesses
for the isolated galaxies in this sample is lower than for the dIrrs in a
denser environment. The average color characteristics of the dIrrs in the
different environments are the same to within ~0.2 mag.Comment: 14 pages, 3 figures, 2 table
6-meter telescope observations of three dwarf spheroidal galaxies with very low surface brightness
Dwarf spheroidal galaxies (dSphs) are mostly investigated in the Local Group.
DSphs are difficult targets for observations because of their small size and
very low surface brightness. Here we measure spectroscopic and photometric
parameters of three candidates for isolated dSphs, KKH65=BTS23, KK180, and
KK227, outside the Local Group. The galaxies are found to be of low metallicity
and low velocity dispersion. They are among the lowest surface brightness
objects in the Local Universe. According to the measured radial velocities,
metallicities, and structural and photometric parameters, KKH65 and KK227 are
representatives of the ultra-diffuse quenched galaxies. KKH65 and KK227 belong
to the outer parts of the groups NGC3414 and NGC5371, respectively. KK180 is
located in the Virgo cluster infall region.Comment: 4 pages, 3 figures, 3 tables, 3 Appendices with 5 figures and 3
table
Gemini spectroscopy of the outer disk star cluster BH176
BH176 is an old metal-rich star cluster. It is spatially and kinematically
consistent with belonging to the Monoceros Ring. It is larger in size and more
distant from the Galactic plane than typical open clusters, and it does not
belong to the Galactic bulge. Our aim is to determine the origin of this unique
object by accurately determining its distance, metallicity, and age. The best
way to reach this goal is to combine spectroscopic and photometric methods. We
present medium-resolution observations of red clump and red giant branch stars
in BH176 obtained with the Gemini South Multi-Object Spectrograph.We derive
radial velocities, metallicities, effective temperatures, and surface gravities
of the observed stars and use these parameters to distinguish member stars from
field objects. We determine the following parameters for BH176:
km/s, , age Gyr, , distance
kpc, -element abundance dex (the
mean of [Mg/Fe], and [Ca/Fe]). BH176 is a member of old Galactic open clusters
that presumably belong to the thick disk. It may have originated as a massive
star cluster after the encounter of the forming thin disk with a high-velocity
gas cloud or as a satellite dwarf galaxy.Comment: 15 pages, 7 fufures, Accepted for publication in Astronomy &
Astrophysic
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