144 research outputs found
Hubble Space Telescope imaging of the compact elliptical galaxy M32 reveals a dearth of carbon stars
We present new {\em Hubble Space Telescope} WFC3/IR medium-band photometry of
the compact elliptical galaxy M32, chemically resolving its thermally pulsating
asymptotic giant branch stars. We find 2829 M-type stars and 57 C stars. The
carbon stars are likely contaminants from M31. If carbon stars are present in
M32 they are so in very low numbers. The uncorrected C/M ratio is 0.020
0.003; this drops to less than 0.007 after taking into account contamination
from M31. As the mean metallicity of M32 is just below solar, this low ratio of
C to M stars is unlikely due to a metallicity ceiling for the formation of
carbon stars. Instead, the age of the AGB population is likely to be the
primary factor. The ratio of AGB to RGB stars in M32 is similar to that of the
inner disc of M31 which contain stars that formed 1.5--4 Gyr ago. If the M32
population is at the older end of this age then its lack of C-stars may be
consistent with a narrow mass range for carbon star formation predicted by some
stellar evolution models. Applying our chemical classifications to the dusty
variable stars identified with {\em Spitzer}, we find that the x-AGB candidates
identified with {\em Spitzer} are predominately M-type stars. This
substantially increases the lower limit to the cumulative dust-production rate
in M32 to 1.97 .Comment: 10 pages, 7 figures, submitted MNRAS 7/12/2
On testing the violation of the Clausius inequality in nanoscale electric circuits
The Clausius inequality, one of the classical formulations of the second law,
was recently found to be violated in the quantum regime. Here this result is
formulated in the context of a mesoscopic or nanoscale linear RLC circuit
interacting with a thermal bath. Previous experiments in this and related
fields are analyzed and possibilities of experimental detection of the
violation are pointed out. It is discussed that recent experiments reached the
range of temperatures, where the effect should be visible, and that a part of
the proposal was already confirmed.Comment: 5 pages revtex 4. No figure
Infrared properties of Active OB stars in the Magellanic Clouds from the Spitzer SAGE Survey
We present a study of the infrared properties of 4922 spectroscopically
confirmed massive stars in the Large and Small Magellanic Clouds, focusing on
the active OB star population. Besides OB stars, our sample includes yellow and
red supergiants, Wolf-Rayet stars, Luminous Blue Variables (LBVs) and
supergiant B[e] stars. We detect a distinct Be star sequence, displaced to the
red, and find a higher fraction of Oe and Be stars among O and early-B stars in
the SMC, respectively, when compared to the LMC, and that the SMC Be stars
occur at higher luminosities. We also find photometric variability among the
active OB population and evidence for transitions of Be stars to B stars and
vice versa. We furthermore confirm the presence of dust around all the
supergiant B[e] stars in our sample, finding the shape of their spectral energy
distributions (SEDs) to be very similar, in contrast to the variety of SED
shapes among the spectrally variable LBVs.Comment: 5 pages, 1 figure, to appear in the proceedings of the IAUS 272 on
"Active OB stars: structure, evolution, mass loss and critical limits"
(Paris, July 19-23, 2010), Cambridge University Press. Editors C. Neiner, G.
Wade, G. Meynet and G. Peter
Dust in the bright supernova remnant N49 in the LMC
We investigate the dust associated with the supernova remnant (SNR) N49 in
the Large Magellanic Cloud (LMC) as observed with the Herschel Space
Observatory. N49 is unusually bright because of an interaction with a molecular
cloud along its eastern edge. We have used PACS and SPIRE to measure the far IR
flux densities of the entire SNR and of a bright region on the eastern edge of
the SNR where the SNR shock is encountering the molecular cloud. Using these
fluxes supplemented with archival data at shorter wavelengths, we estimate the
dust mass associated with N49 to be about 10 Msun. The bulk of the dust in our
simple two-component model has a temperature of 20-30 K, similar to that of
nearby molecular clouds. Unfortunately, as a result of the limited angular
resolution of Herschel at the wavelengths sampled with SPIRE, the uncertainties
are fairly large. Assuming this estimate of the dust mass associated with the
SNR is approximately correct, it is probable that most of the dust in the SNR
arises from regions where the shock speed is too low to produce significant
X-ray emission. The total amount of warm 50-60 K dust is ~0.1 or 0.4 Msun,
depending on whether the dust is modeled in terms of carbonaceous or silicate
grains. This provides a firm lower limit to the amount of shock heated dust in
N49.Comment: accepted by the Astronomy & Astrophysics Lette
The youngest massive protostars in the Large Magellanic Cloud
We demonstrate the unique capabilities of Herschel to study very young
luminous extragalactic young stellar objects (YSOs) by analyzing a central
strip of the Large Magellanic Cloud obtained through the HERITAGE Science
Demonstration Program. We combine PACS 100 and 160, and SPIRE 250, 350, and 500
microns photometry with 2MASS (1.25-2.17 microns) and Spitzer IRAC and MIPS
(3.6-70 microns) to construct complete spectral energy distributions (SEDs) of
compact sources. From these, we identify 207 candidate embedded YSOs in the
observed region, ~40% never-before identified. We discuss their position in
far-infrared color-magnitude space, comparing with previously studied,
spectroscopically confirmed YSOs and maser emission. All have red colors
indicating massive cool envelopes and great youth. We analyze four example
YSOs, determining their physical properties by fitting their SEDs with
radiative transfer models. Fitting full SEDs including the Herschel data
requires us to increase the size and mass of envelopes included in the models.
This implies higher accretion rates (greater than or equal to 0.0001 M_sun/yr),
in agreement with previous outflow studies of high-mass protostars. Our results
show that Herschel provides reliable longwave SEDs of large samples of
high-mass YSOs; discovers the youngest YSOs whose SEDs peak in Herschel bands;
and constrains the physical properties and evolutionary stages of YSOs more
precisely than was previously possible.Comment: Main text: 4 pages, 3 figures, 1 table; Online material: 3 figures, 1
table; to appear in the A&A Herschel Special Issu
Herschel Observations of a Newly Discovered UX Ori Star in the Large Magellanic Cloud
The LMC star, SSTISAGE1C J050756.44-703453.9, was first noticed during a
survey of EROS-2 lightcurves for stars with large irregular brightness
variations typical of the R Coronae Borealis (RCB) class. However, the visible
spectrum showing emission lines including the Balmer and Paschen series as well
as many Fe II lines is emphatically not that of an RCB star. This star has all
of the characteristics of a typical UX Ori star. It has a spectral type of
approximately A2 and has excited an H II region in its vicinity. However, if it
is an LMC member, then it is very luminous for a Herbig Ae/Be star. It shows
irregular drops in brightness of up to 2 mag, and displays the reddening and
"blueing" typical of this class of stars. Its spectrum, showing a combination
of emission and absorption lines, is typical of a UX Ori star that is in a
decline caused by obscuration from the circumstellar dust. SSTISAGE1C
J050756.44-703453.9 has a strong IR excess and significant emission is present
out to 500 micron. Monte Carlo radiative transfer modeling of the SED requires
that SSTISAGE1C J050756.44-703453.9 has both a dusty disk as well as a large
extended diffuse envelope to fit both the mid- and far-IR dust emission. This
star is a new member of the UX Ori subclass of the Herbig Ae/Be stars and only
the second such star to be discovered in the LMC.Comment: ApJ, in press. 9 pages, 5 figure
Spitzer View of Massive Star Formation in the Tidally Stripped Magellanic Bridge
The Magellanic Bridge is the nearest low-metallicity, tidally stripped
environment, offering a unique high-resolution view of physical conditions in
merging and forming galaxies. In this paper we present analysis of candidate
massive young stellar objects (YSOs), i.e., {\it in situ, current} massive star
formation (MSF) in the Bridge using {\it Spitzer} mid-IR and complementary
optical and near-IR photometry. While we definitely find YSOs in the Bridge,
the most massive are , found in the Large
Magellanic Cloud (LMC). The intensity of MSF in the Bridge also appears
decreasing, as the most massive YSOs are less massive than those formed in the
past. To investigate environmental effects on MSF, we have compared properties
of massive YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge
are apparently less embedded than in the LMC: 81% of Bridge YSOs show optical
counterparts, compared to only 56% of LMC sources with the same range of mass,
circumstellar dust mass, and line-of-sight extinction. Circumstellar envelopes
are evidently more porous or clumpy in the Bridge's low-metallicity
environment. Second, we have used whole samples of YSOs in the LMC and the
Bridge to estimate the probability of finding YSOs at a given \hi\ column
density, N(HI). We found that the LMC has higher probability than
the Bridge for N(HI) cm, but the trend reverses at
lower N(HI). Investigating whether this lower efficiency relative to HI is due
to less efficient molecular cloud formation, or less efficient cloud collapse,
or both, will require sensitive molecular gas observations.Comment: 41 pages, 20 figures, 6 tables; accepted for publication in ApJ;
several figures are in low resolution due to the size limit here and a high
resolution version can be downloaded via
http://www.astro.virginia.edu/~cc5ye/ms_bridge20140215.pd
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