30 research outputs found
An Infrared Color-Magnitude Relationship
We have investigated a sample of dusty supergiants and Mira variables and have found a roughly linear relationship between the absolute magnitude at 12 mum and the [l2]-[25] color. Both samples follow the same infrared color-magnitude relationship, whic
High spatial-resolution IRAS images of M51
High spatial-resolution (approx. equal to 30 seconds) images of M51 in the four Infrared Astronomy Satellite (IRAS) bands (12, 25, 60, and 100 microns) have been obtained. The spatial variation in flux in all four bands is coincident with the spiral features seen in H alpha and 6 cm with a few exceptions. In the nuclear region (4 minutes) the position of the peak of maximum intensity shifts in relation to the visual nucleus: it is coincident with the nucleus at 12 microns, shifts approximately 45 seconds to south-southwest, and is 45 seconds northwest of the nucleus at 60 and 100 microns
High spatial resolution restoration of IRAS images
A general technique to improve the spatial resolution of the IRAS AO data was developed at The Aerospace Corporation using the Maximum Entropy algorithm of Skilling and Gull. The technique has been applied to a variety of fields and several individual AO MACROS. With this general technique, resolutions of 15 arcsec were achieved in 12 and 25 micron images and 30 arcsec in 60 and 100 micron images. Results on galactic plane fields show that both photometric and positional accuracy achieved in the general IRAS survey are also achieved in the reconstructed images
Statistics of Stellar Populations of Star Clusters and Surrounding Fields in the Outer Disk of the Large Magellanic Cloud
A comparative analysis of Washington color-magnitude diagrams (CMDs) for 14
star clusters and respective surrounding fields in the Large Magellanic Cloud
(LMC) outer disk is presented. Each CCD frame including field and respective
cluster covers an area of 185 arcmin^2. The stellar population sampled is of
intermediate age and metallicity. CMD radial analysis involving star count
ratios, morphology and integrated light properties are carried out. Luminosity
functions (LFs) are also presented. Two main results are: (i) Within the range
4<R(kpc)<8, the distance from the LMC center is well correlated with the
average age in the sense that inner fields are younger and; (ii) Beyond
approximately 8kpc the outer fields do not show evidence of a significant
intermediate-age component in their stellar populations, as inferred from red
giant clump star counts.Comment: 27 pages, 4 tables, 11 figures; accepted by the A
The Search for High-Mass X-ray Binaries in the Phoenix Dwarf Galaxy
We report on the first X-ray images of the Phoenix dwarf galaxy, taken with
\emph{XMM-Newton} in July 2009. This local group dwarf galaxy shares
similarities with the Small Magellanic Cloud (SMC) including a burst of star
formation 50 Myr ago. The SMC has an abundance of High Mass X-ray
Binaries (HMXBs) and so we have investigated the possibility of an HMXB
population in Phoenix with the intention of furthering the understanding of the
HMXB-star formation rate relation. The data from the combined European Photon
Imaging Cameras (EPIC) were used to distinguish between different source
classes (foreground stars, background galaxies, AGN and supernova remnants)
using EPIC hardness ratios and correlations with optical and radio catalogues.
Of the 81 X-ray sources in the field of view, six are foreground stars, four
are galaxies and one is an AGN. The remaining sources with optical counterparts
have log() consistent with AGN in the local universe.
Further investigation of five sources in the field of view suggests they are
all background AGN. Their position behind the gas cloud associated with Phoenix
makes them a possible tool for further probing the metallicity of this region.
We find no evidence for any HMXBs in Phoenix at this time. This rules out the
existence of the X-ray persistent supergiant X-ray binary systems. However the
transient nature of the Be/X-ray binaries means we cannot rule out a population
of these sources but can conclude that it is not extensive.Comment: 13 pages, 4 figures, 4 tables, Accepted for publication in MNRA
On the relationship between the Delta Scuti and Gamma Doradus pulsators
We searched for Delta Scuti-type pulsations amongst known and candidate Gamma
Doradus stars. We acquired 270 h of observations and monitored a total of 26
stars. One target, HD 209295, turned out to be a member of both classes of
pulsating star. We classify six of our targets as new bona fide Gamma Doradus
stars, nine more as good Gamma Doradus candidates, and three as ellipsoidal
variables. The remainder comprise one Delta Scuti star and five unexplained
variables.
We revise the blue border of the Gamma Doradus phenomenon towards cooler
temperatures. This new blue edge extends from a temperature of about 7550 K on
the ZAMS to 7400 K one magnitude above it. Five bona fide Gamma Doradus stars
we observed are located inside the Delta Scuti instability strip, but none of
them exhibited observable Delta Scuti pulsations. We therefore suggest that
Gamma Doradus stars are less likely to be Delta Scuti pulsators compared to
other normal stars in the same region of the lower instability strip. In
addition, we show that there is a clear separation between the pulsation
constants Q of Delta Scuti and Gamma Doradus stars. The Gamma Doradus stars
known to date all have Q>0.23 d.Comment: 12 pages, 9 figures. MNRAS, in pres
Discovery of a New Low-Latitude Milky Way Globular Cluster using GLIMPSE
Spitzer Space Telescope imaging as part of the Galactic Legacy Mid-Plane
Survey Extraordinaire (GLIMPSE) reveals a previously unidentified low-latitude
rich star cluster near l=31.3 degrees, b=-0.1 degrees. Near-infrared JHK'
photometry from the Wyoming Infrared Observatory indicates an extinction of A_V
~ 15+/-3 mag for cluster members. Analysis of 13CO features along the same
sightline suggests a probable kinematic distance of 3.1 -- 5.2 kpc. The new
cluster has an angular diameter of ~1-2 pc, a total magnitude m_{K_0}=2.1
corrected for extinction, and a luminosity of M_K ~ -10.3 at 3.1 kpc. In
contrast to young massive Galactic clusters with ages <100 Myr, the new cluster
has no significant radio emission. Comparison to theoretical K-band luminosity
functions indicates an age of at least several Gyr and a mass of at least 10^5
solar masses. Unlike known old open clusters, this new cluster lies in the
inner Galaxy at R_{GC} ~ 6.1 kpc. We designate this object ``GLIMPSE-C01'' and
classify it as a Milky Way globular cluster passing through the Galactic disk.
We also identify a region of star formation and fan-shaped outflows from young
stellar objects in the same field as the cluster. The cluster's passage through
the Galactic molecular layer may have triggered this star formation activity.Comment: Accepted for Publication in AJ Report with full resolution images
available at http://physics.uwyo.edu/~chip/Glo
The evolution of lithium depletion in young open clusters: NGC 6475
We have carried out a high resolution spectroscopic survey of the 220-250 Myr
old cluster NGC 6475: our main purpose is to investigate Li evolution during
the early stages of the Main Sequence. We have determined Li abundances for 33
late F to K-type X-ray selected cluster candidates, extending the samples
already available in the literature; for part of the stars we obtained radial
and rotational velocities, allowing us to confirm the membership and to check
for binarity. We also estimated the cluster metallicity which turned out to be
over-solar ([Fe/H]=+0.14 +/-0.06). Our Li analysis evidenced that (i) late
F-type stars (Teff > 6000 K) undergo a very small amount of Li depletion during
the early phases on the ZAMS; (ii) G-type stars (6000 > Teff > 5500 K) instead
do deplete lithium soon after arrival on the ZAMS. Whereas this result is not
new, we show that the time scale for Li depletion in these stars is almost
constant between 100 and 600 Myr; (iii) we confirm that the spread observed in
early K-type stars in younger clusters has converged by 220 Myr. No constraints
can be put on later-type stars. (iv) Finally, we investigate the effect of
metallicity on Li depletion by comparing NGC 6475 with the similar age cluster
M 34, but we show that the issue remains open, given the uncertain metallicity
of the latter cluster. By using the combined NGC 6475 + M 34 sample together
with the Hyades and the Pleiades, we compare quantitatively Li evolution from
the ZAMS to 600 Myr with theoretical predictions of standard models.Comment: to appear in A&
Galaxy populations in the Antlia cluster. II. Compact elliptical galaxy candidates
We present a photometric analysis of four galaxies classified as compact
elliptical (cE) galaxies in the FS90 Antlia Group catalogue. Only 6 members of
this rare type of galaxies are known until now. Using data in various
photometric systems, we measured brightness and colour profiles, as well as
structural parameters. By comparing them with those of other galaxies in the
Antlia cluster, as well as with confirmed cE galaxies from the literature, we
found that two of the FS90 cE candidates, albeit being spectroscopically
confirmed Antlia members, are not cE galaxies. However, one of these objects
presents strong ellipticity and position angle variations that resemble those
already reported for M32, leading us to speculate about this kind of objects
being progenitors of cE galaxies. The other two FS90 cE candidates, for which
radial velocities are not available, match some features typical of cE galaxies
like being close in projection to a larger galaxy, displaying flat colour
profiles, and having a high degree of compactness. Only one of the remaining cE
candidates shows a high central surface brightness, two components in its
brightness profile, distinct changes in ellipticity and position angle where
the outer component begins to dominate, and seems to follow the same trend as
other confirmed cE galaxies in a luminosity versus mean effective surface
brightness diagram. Moreover, it shows a distorted inner structure with similar
characteristics to those found by simulations of interacting galaxies, and an
extremely faint structure that seems to link this object with one of the Antlia
dominant galaxies, has been detected in MOSAIC-CTIO, FORS1-VLT, and ACS-HST
images. The cE nature of this galaxy as well as the possible interaction with
its bright companion, still have to be confirmed through spectroscopy.Comment: 15 pages, 8 figures, accepted for publication in MNRA
Lithium abundances and extra mixing processes in evolved stars of M67
Aims. We present a spectroscopic analysis of a sample of evolved stars in M67
(turn-off, subgiant and giant stars) in order to bring observational
constraints to evolutionary models taking into account non-standard transport
processes. Methods. We determined the stellar parameters (Teff, log g, [Fe/H]),
microturbulent and rotational velocities and, Lithium abundances (ALi) for 27
evolved stars of M67 with the spectral synthesis method based on MARCS model
atmospheres. We also computed non-standard stellar evolution models, taking
into account atomic diffusion and rotation-induced transport of angular
momentum and chemicals that were compared with this set of homogeneous data.
Results. The lithium abundances that we derive for the 27 stars in our sample
follow a clear evolutionary pattern ranging from the turn-off to the Red Giant
Branch. Our abundance determination confirms the well known decrease of lithium
content for evolved stars. For the first time, we provide a consistent
interpretation of both the surface rotation velocity and of the lithium
abundance patterns observed in an homogeneous sample of TO and evolved stars of
M67. We show that the lithium evolution is determined by the evolution of the
angular momentum through rotation-induced mixing in low-mass stars, in
particular for those with initial masses larger than 1.30 M_\odot at solar
metallicity.Comment: 13 pages, 8 figure