707 research outputs found
Hubble Space Telescope Photometry of Hodge 301: An "Old" Star Cluster in 30 Doradus
We present Hubble Space Telescope Planetary Camera UVI data for the
little-studied cluster Hodge 301 3' northwest of 30 Doradus' central ionizing
cluster R136. The average reddening of Hodge 301 is found to be =
(0.28+-0.05) mag from published infrared and ultraviolet photometry. Using two
different sets of evolutionary models, we derive an age of ~ 20-25 Myr for
Hodge 301, which makes it roughly 10 times as old as R136. Hodge 301 is the
most prominent representative of the oldest population in the 30 Dor starburst
region; a region that has undergone multiple star formation events. This range
of ages is an important consideration for the modelling of starburst regions.
Hodge 301 shows a widened upper main sequence largely caused by Be stars. We
present a list of Be star candidates. The slope of the initial mass function
for intermediate-mass main sequence stars ranging from 10 to 1.3 solar masses
is found to be -1.4+-0.1 in good agreement with a Salpeter law. There is no
indication for a truncation or change of slope of the IMF within this mass
range. In accordance with the age of Hodge 301 no obvious pre-main-sequence
stars are seen down to 1 solar mass. We estimate that up to 41+-7 stars with
more than 12 solar masses may have turned into supernovae since the formation
of the cluster. Multiple supernova explosions are the most likely origin of the
extremely violent gas motions and the diffuse X-ray emission observed in the
cluster surroundings.Comment: To appear in the Astronomical Journal (Feb 2000 issue). 16 pages in
two-column style. 9 separate figures, in part in significantly reduced
resolution for space reasons (bitmapped postscript or jpg
Mean age gradient and asymmetry in the star formation history of the Small Magellanic Cloud
We derive the star formation history in four regions of the Small Magellanic
Cloud (SMC) using the deepest VI color-magnitude diagrams (CMDs) ever obtained
for this galaxy. The images were obtained with the Advanced Camera for Surveys
onboard the Hubble Space Telescope and are located at projected distances of
0.5-2 degrees from the SMC center, probing the main body and the wing of the
galaxy. We derived the star-formation histories (SFH) of the four fields using
two independent procedures to fit synthetic CMDs to the data. We compare the
SFHs derived here with our earlier results for the SMC bar to create a deep
pencil-beam survey of the global history of the central SMC. We find in all the
six fields observed with HST a slow star formation pace from 13 to 5-7 Gyr ago,
followed by a ~ 2-3 times higher activity. This is remarkable because dynamical
models do not predict a strong influence of either the LMC or the Milky Way
(MW) at that time. The level of the intermediate-age SFR enhancement
systematically increases towards the center, resulting in a gradient in the
mean age of the population, with the bar fields being systematically younger
than the outer ones. Star formation over the most recent 500 Myr is strongly
concentrated in the bar, the only exception being the area of the SMC wing. The
strong current activity of the latter is likely driven by interaction with the
LMC. At a given age, there is no significant difference in metallicity between
the inner and outer fields, implying that metals are well mixed throughout the
SMC. The age-metallicity relations we infer from our best fitting models are
monotonically increasing with time, with no evidence of dips. This may argue
against the major merger scenario proposed by Tsujimoto and Bekki 2009,
although a minor merger cannot be ruled out.Comment: 30 pages, 16 figures, accepted for publication in Ap
The luminosity function of Palomar 5 and its tidal tails
We present the main sequence luminosity function of the tidally disrupted
globular cluster Palomar 5 and its tidal tails. For this work we analyzed
imaging data obtained with the Wide Field Camera at the INT (La Palma) and data
from the Wide Field Imager at the MPG/ESO 2.2 m telescope at La Silla down to a
limiting magnitude of approximately 24.5 mag in B. Our results indicate that
preferentially fainter stars were removed from the cluster so that the LF of
the cluster's main body exhibits a significant degree of flattening compared to
other GCs. This is attributed to its advanced dynamical evolution. The LF of
the tails is, in turn, enhanced with faint, low-mass stars, which we interpret
as a consequence of mass segregation in the cluster.Comment: 4 pages, 3 figures, to be published in the proceedings of the
conference "Satellites and tidal streams" held at La Palma, Canary Islands,
May 26 - 30, 200
Relations between abundance characteristics and rotation velocity for star-forming MaNGA galaxies
We derive rotation curves, surface brightness profiles, and oxygen abundance
distributions for 147 late-type galaxies using the publicly available
spectroscopy obtained by the MaNGA survey. Changes of the central oxygen
abundance (O/H)_0, the abundance at the optical radius (O/H)_R25, and the
abundance gradient with rotation velocity V_rot are examined for galaxies with
rotation velocities from 90 km/s to 350 km/s. We found that each relation shows
a break at V_rot^* ~200 km/s. The central (O/H)_0 abundance increases with
rising V_rot and the slope of the (O/H)_0 - V_rot relation is steeper for
galaxies with V_rot < V_rot^*. The mean scatter of the central abundances
around this relation is 0.053 dex. The relation between the abundance at the
optical radius of a galaxy and its rotation velocity is similar; the mean
scatter in abundances around this relation is 0.081 dex. The radial abundance
gradient expressed in dex/kpc flattens with the increase of the rotation
velocity. The slope of the relation is very low for galaxies with V_rot >
V_rot^*. The abundance gradient expressed in dex/R25 is rougly constant for
galaxies with V_rot < V_rot^*, flattens towards V_rot^*, and then again is
roughly constant for galaxies with V_rot > V_rot^*. The change of the gradient
expressed in terms of dex/h_d (where h_d is the disc scale length) with
rotation velocity is similar to that for gradient in dex/R25. The relations
between abundance characteristics and other basic parameters (stellar mass,
luminosity, and radius) are also considered.Comment: Accepted for publication in the Astronomy and Astrophysic
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