505 research outputs found
Stellar populations in the Carina region: The Galactic plane at l = 291
Previous studies of the Carina region have revealed its complexity and
richness as well as a significant number of early-type stars. In many cases,
these studies only concentrated on the central region or were not homogeneous.
This latter aspect, in particular, is crucial because very different ages and
distances for key clusters have been claimed in recent years. The aim of this
work is to study in detail an area of the Galactic plane in Carina. We analyze
the properties of different stellar populations and focus on a sample of open
clusters and their population of YSOs and highly reddened early stars. We also
studied the stellar mass distribution in these clusters and the possible
scenario of their formation. Finally, we outline the Galactic spiral structure
in this direction. We obtained photometric data for six young open clusters
located in Carina at l = 291, and their adjacent stellar fields, which we
complemented with spectroscopic observations of a few selected targets. We also
culled additional information from the literature. Our results provide more
reliable estimates of distances, color excesses, masses, and ages of the
stellar populations in this direction. We estimate the basic parameters of the
studied clusters and find that they identify two overdensities of young stellar
populations. We find evidence of PMS populations inside them, with an apparent
coeval stellar formation in the most conspicuous clusters. We also discuss
apparent age and distance gradients in the direction NW-SE. We study the mass
distributions of several clusters in the region. They consistently show a
canonical IMF slope. We discover and characterise an abnormally reddened
massive stellar population. Spectroscopic observations of ten stars of this
latter population show that all selected targets were massive OB stars. Their
location is consistent with the position of the Car-Sag spiral arm.Comment: 15 pages, 13 figure
Extended star formation history of the star cluster NGC 2154 in the Large Magellanic Cloud
The colour-magnitude diagram (CMD) of the intermediate-age Large Magellanic Cloud star cluster NGC 2154 and its adjacent field has been analysed using Padova stellar models to determine the clusterÂŽs fundamental parameters and its star formation history. Deep BR CCD photometry, together with synthetic CMDs and integrated luminosity functions, has allowed us to infer that the cluster experienced an extended star formation period of about 1.2 Gyr, which began approximately 2.3 Gyr ago and ended 1.1 Gyr ago. However, the physical reality of such a prolonged period of star formation is questionable, and could be the result of inadequacies in the stellar evolutionary tracks themselves. A substantial fraction of binaries (70 per cent) seems to exist in NGC 2154.Fil: Baume, Gustavo Luis. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica La Plata; ArgentinaFil: Carraro, Giovanni. UniversitĂ di Padova; ItaliaFil: Costa, E.. Universidad de Chile; ChileFil: Mendez, R. A.. Universidad de Chile; ChileFil: Girardi, L.. Osservatorio Astronomico di Padova; Itali
Spiral structure of the Third Galactic Quadrant and the solution to the Canis Major debate
With the discovery of the Sagittarius dwarf spheroidal (Ibata et al. 1994), a
galaxy caught in the process of merging with the Milky Way, the hunt for other
such accretion events has become a very active field of astrophysical research.
The identification of a stellar ring-like structure in Monoceros, spanning more
than 100 degrees (Newberg et al. 2002), and the detection of an overdensity of
stars in the direction of the constellation of Canis Major (CMa, Martin et al.
2004), apparently associated to the ring, has led to the widespread belief that
a second galaxy being cannibalised by the Milky Way had been found. In this
scenario, the overdensity would be the remaining core of the disrupted galaxy
and the ring would be the tidal debris left behind. However, unlike the
Sagittarius dwarf, which is well below the Galactic plane and whose orbit, and
thus tidal tail, is nearly perpendicular to the plane of the Milky Way, the
putative CMa galaxy and ring are nearly co-planar with the Galactic disk. This
severely complicates the interpretation of observations. In this letter, we
show that our new description of the Milky Way leads to a completely different
picture. We argue that the Norma-Cygnus spiral arm defines a distant stellar
ring crossing Monoceros and the overdensity is simply a projection effect of
looking along the nearby local arm. Our perspective sheds new light on a very
poorly known region, the third Galactic quadrant (3GQ), where CMa is located.Comment: 5 pages, 2 figures. Quality of Fig 1 has been degraded to make it
smaller. Original fig. available on request. accepted for publication in
MNRAS letter
Luminosity and mass functions of galactic open clusters: II. NGC 4852
e present wide field deep UBVI photometry for the previously unstudied open
cluster NGC 4852 down to a limiting magnitude , obtained from
observations taken with the Wide Field Imager camera on-board the MPG/ESO 2.2m
telescope at La Silla (ESO, Chile). These data are used to obtain the first
estimate of the cluster basic parameters, to study the cluster spatial
extension by means of star counts, and to derive the Luminosity (LF) and Mass
Function (MF). The cluster radius turns out to be arcmin. The
cluster emerges clearly from the field down to V=20 mag. At fainter magnitud
es, it is completely confused with the general Galactic disk field. The stars
inside this region define a young open cluster (200 million years old) 1.1 kpc
far from the Sun (m-M = 11.60, E(B-V) = 0.45). The Present Day Mass Functions
(PDMF) from the photometry is one of the most extended in mass insofar
obtained, and can be represented as a power-law with a slope and (the Salpeter (1955) MF in this notation has a slope ), in the mass range . Below this
mass, the MF cannot be considered as representative of the cluster MF, as the
cluster merges with the field and therefore the MF is the result of the
combined effect of strong irregularities in the stellar background and
interaction of the cluster with the dense Galactic field. The cluster total
mass at the limiting magnitude results to be 2570210 M.Comment: 9 pages, 10 eps figures (some degraded in resolution), accepted for
publication in A&
NGC 2401: A template of the Norma-Cygnus Arm's young population in the Third Galactic Quadrant
Based on a deep optical CCD (UBV(RI)_C) photometric survey and on the
Two-Micron All-Sky-Survey (2MASS) data we derived the main parameters of the
open cluster NGC 2401. We found this cluster is placed at 6.3 0.5 kpc
(V_O - M_V = 14.0 \pm 0.2) from the Sun and is 25 Myr old, what allows us to
identify NGC 2401 as a member of the young population belonging to the
innermost side of the extension of the Norma-Cygnus spiral--arm in the Third
Galactic Quadrant. A spectroscopic study of the emission star LSS 440 that lies
in the cluster area revealed it is a B0Ve star; however, we could not confirm
it is a cluster member. We also constructed the cluster luminosity function
(LF) down to and the cluster initial mass function (IMF) for all
stars with masses above M \sim 1-2 M_{\sun}. It was found that the slope of
the cluster IMF is . The presence of a probable PMS star
population associated to the cluster is weakly revealed.Comment: 10 paginas, 11 eps figures, accepted for publication in MNRA
Luminosity and mass functions of galactic open clusters II: NGC 4852
We present wide-field deep UBVI photometry for the previously unstudied open cluster NGC 4852 down to a limiting magnitude I ⌠24, obtained from observations taken with the Wide Field Imager camera on-board the MPG/ESO 2.2 m telescope at La Silla (ESO, Chile). These data are used to obtain the first estimate of the cluster basic parameters, to study the cluster spatial extension by means of star counts, and to derive the Luminosity (LF) and Mass Function (MF). The cluster radius turns out to be 5.0 ±1.0 arcmin. The cluster emerges clearly from the field down to V = 20 mag. At fainter magnitudes, it is completely confused with the general Galactic disk field. The stars inside this region define a young open cluster (200 million years old) 1.1 kpc far from the Sun (m - M = 11.60, E(B - V) = 0.45). The Present Day Mass Functions (PDMF) from the V photometry is one of the most extended in mass obtained to date, and can be represented as a power-law with a slope α = 2.3 ± 0.3 and (the Salpeter MF in this notation has a slope α = 2.35), in the mass range 3.2 †m/mâ †0.6. Below this mass, the MF cannot be considered as representative of the cluster MF, as the cluster merges with the field and therefore the MF is the result of the combined effect of strong irregularities in the stellar background and interaction of the cluster with the dense Galactic field. The cluster total mass at the limiting magnitude results to be 2570 ±210 Mâ.Facultad de Ciencias AstronĂłmicas y GeofĂsica
Extended star formation history of the star cluster NGC 2154 in the large magellanic cloud
The colour-magnitude diagram (CMD) of the intermediate-age Large Magellanic Cloud star cluster NGC 2154 and its adjacent field has been analysed using Padova stellar models to determine the cluster's fundamental parameters and its star formation history. Deep BR CCD photometry, together with synthetic CMDs and integrated luminosity functions, has allowed us to infer that the cluster experienced an extended star formation period of about 1.2 Gyr, which began approximately 2.3 Gyr ago and ended 1.1 Gyr ago. However, the physical reality of such a prolonged period of star formation is questionable, and could be the result of inadequacies in the stellar evolutionary tracks themselves. A substantial fraction of binaries (70 per cent) seems to exist in NGC 2154.Facultad de Ciencias AstronĂłmicas y GeofĂsica
Open clusters in the Third Galactic Quadrant. II. The intermediate age open clusters NGC 2425 and NGC 2635
We analyse CCD broad band (UBV(RI)c) photometric data obtained in the fields
of the poorly studied open clusters NGC 2425 and NGC 2635. Both clusters are
found to be of intermediate age thus increasing the population of open clusters
known to be of the age of, or older than, the Hyades. More explicitly, we find
that NGC 2425 is a 2.2 Gyr old cluster, probably of solar metallicity, located
at 3.5 kpc from the Sun. NGC 2635 is a Hyades age (600 Myr) cluster located at
a distance of 4.0 kpc from the Sun. Its Colour Magnitude Diagram reveals that
it is extremely metal poor for its age and position, thus making it a very
interesting object in the context of Galactic Disk chemical evolution models.Comment: 10 pages, 13 figures. Figure quality has been quiet degraded.
Accepted by A&
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