271 research outputs found
The Mass-Loss Return From Evolved Stars to The Large Magellanic Cloud VI: Luminosities and Mass-Loss Rates on Population Scales
We present results from the first application of the Grid of Red Supergiant
and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved
stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed
grid of 80,843 radiative transfer (RT) models of evolved stars and
circumstellar dust shells composed of either silicate or carbonaceous dust. We
fit GRAMS models to ~30,000 Asymptotic Giant Branch (AGB) and Red Supergiant
(RSG) stars in the LMC, using 12 bands of photometry from the optical to the
mid-infrared. Our published dataset consists of thousands of evolved stars with
individually determined evolutionary parameters such as luminosity and
mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate
discriminating between Oxygen- and Carbon-rich chemistry. The global dust
injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB
stars is on the order of 1.5x10^(-5) solar masses/yr, equivalent to a total
mass injection rate (including the gas) into the ISM of ~5x10^(-3) solar
masses/yr. Carbon stars inject two and a half times as much dust into the ISM
as do O-rich AGB stars, but the same amount of mass. We determine a bolometric
correction factor for C-rich AGB stars in the K band as a function of J - K
color, BC(K) = -0.40(J-K)^2 + 1.83(J-K) + 1.29. We determine several IR color
proxies for the dust mass-loss rate (MLR) from C-rich AGB stars, such as log
(MLR) = (-18.90)/((K-[8.0])+3.37)-5.93. We find that a larger fraction of AGB
stars exhibiting the `long-secondary period' phenomenon are O-rich than stars
dominated by radial pulsations, and AGB stars without detectable mass-loss do
not appear on either the first-overtone or fundamental-mode pulsation
sequences.Comment: 19 pages, 19 figure
CO J = 2 - 1 Emission from Evolved Stars in the Galactic Bulge
We observe a sample of 8 evolved stars in the Galactic Bulge in the CO J = 2
- 1 line using the Submillimeter Array (SMA) with angular resolution of 1 - 4
arcseconds. These stars have been detected previously at infrared wavelengths,
and several of them have OH maser emission. We detect CO J = 2 - 1 emission
from three of the sources in the sample: OH 359.943 +0.260, [SLO2003] A12, and
[SLO2003] A51. We do not detect the remaining 5 stars in the sample because of
heavy contamination from the galactic foreground CO emission. Combining CO data
with observations at infrared wavelengths constraining dust mass loss from
these stars, we determine the gas-to-dust ratios of the Galactic Bulge stars
for which CO emission is detected. For OH 359.943 +0.260, we determine a gas
mass-loss rate of 7.9 (+/- 2.2) x 10^-5 M_Sun/year and a gas-to-dust ratio of
310 (+/- 89). For [SLO2003] A12, we find a gas mass-loss rate of 5.4 (+/- 2.8)
x 10^-5 M_Sun/year and a gas-to-dust ratio of 220 (+/- 110). For [SLO2003] A51,
we find a gas mass-loss rate of 3.4 (+/- 3.0) x 10^-5 M_Sun/year and a
gas-to-dust ratio of 160 (+/- 140), reflecting the low quality of our tentative
detection of the CO J = 2 - 1 emission from A51. We find the CO J = 2 - 1
detections of OH/IR stars in the Galactic Bulge require lower average CO J = 2
- 1 backgrounds.Comment: 40 pages, 16 figures, appeared in the 1 March 2013 issue of the
Astrophysical Journa
Asymptotic Giant Branch Variables in the Galaxy and the Local Group
AGB variables, particularly the large amplitude Mira type, are a vital step
on the distance scale ladder. They will prove particularly important in the era
of space telescopes and extremely large ground-based telescopes with adaptive
optics, which will be optimized for infrared observing. Our current
understanding of the distances to these stars is reviewed with particular
emphasis on improvements that came from Hipparcos as well as on recent work on
Local Group galaxies. In addition to providing the essential calibration for
extragalactic distances Gaia may also provide unprecedented insight into the
poorly understood mass-loss process itself.Comment: Accepted for publication in Astrophysics and Space Science. From a
presentation at the conference "The Fundamental Cosmic Distance Scale: State
of the Art and Gaia Perspective, Naples May 2011. 8 Pages, 9 Figure
Oxygen-rich dust production in IC 10
We report the detection of oxygen-rich circumstellar envelopes in stars of
the nearby (700 kpc) starburst galaxy IC 10. The star formation history and the
chemical environment of this galaxy makes it an ideal target to observe dust
production by high-mass stars in a low-metallicity environment. The goal of
this study is to identify oxygen-rich stars in IC 10 and to constrain their
nature between asymptotic giant branch stars (AGBs), red supergiants (RSGs),
and other infrared bright sources. We examine the mass-loss rate of the stars
and compare to results obtained for the Magellanic Clouds. Our objectives are
to (1) assess whether RSGs can be significant dust producers in IC 10, and (2),
solve the discrepancy between the star formation history of IC 10 and the
relatively low number of RSGs detected in the optical. We search for silicate
dust in emission by using the spectral map observed with the Infrared
Spectrograph on board the Spitzer Space Telescope. The optical (UBVRI) and
infrared (JHK, Spitzer/IRAC and Spitzer/MIPS) photometry is used to assert the
membership of the stars to IC 10 and disentangle between AGBs and RSGs.
Radiative models are used to infer mass-loss rates and stellar luminosities.
The luminosity and colors of at least 9 silicate emission sources are
consistent with stars within IC 10. Furthermore, the photometry of 2 of these
sources is consistent with RSGs. We derive dust mass-loss rates similar to the
values found in the Magellanic Clouds. Accounting for the sample completeness,
RSGs are not important contributors to the dust mass budget in IC 10.Comment: Accepted for publication in A&
Evidence for Pre-Existing Dust in the Bright Type IIn SN 2010jl
SN 2010jl was an extremely bright, Type IIn SNe which showed a significant IR
excess no later than 90 days after explosion. We have obtained Spitzer 3.6 and
4.5 \mum and JHK observations of SN 2010jl \sim90 days post explosion. Little
to no reddening in the host galaxy indicated that the circumstellar material
lost from the progenitor must lie in a torus inclined out of the plane of the
sky. The likely cause of the high mid-IR flux is the reprocessing of the
initial flash of the SN by pre-existing circumstellar dust. Using a 3D Monte
Carlo Radiative Transfer code, we have estimated that between 0.03-0.35 Msun of
dust exists in a circumstellar torus around the SN located 6 \times 10 ^17 cm
away from the SN and inclined between 60-80\cdot to the plane of the sky. On
day 90, we are only seeing the illumination of approximately 5% of this torus,
and expect to see an elevated IR flux from this material up until day \sim 450.
It is likely this dust was created in an LBV-like mass loss event of more than
3 Msun, which is large but consistent with other LBV progenitors such as {\eta}
Carinae.Comment: Accepted in A
Expanding the set of rhodococcal Baeyer–Villiger monooxygenases by high-throughput cloning, expression and substrate screening
To expand the available set of Baeyer–Villiger monooxygenases (BVMOs), we have created expression constructs for producing 22 Type I BVMOs that are present in the genome of Rhodococcus jostii RHA1. Each BVMO has been probed with a large panel of potential substrates. Except for testing their substrate acceptance, also the enantioselectivity of some selected BVMOs was studied. The results provide insight into the biocatalytic potential of this collection of BVMOs and expand the biocatalytic repertoire known for BVMOs. This study also sheds light on the catalytic capacity of this large set of BVMOs that is present in this specific actinomycete. Furthermore, a comparative sequence analysis revealed a new BVMO-typifying sequence motif. This motif represents a useful tool for effective future genome mining efforts.
Cold Dust in Three Massive Evolved Stars in the LMC
Massive evolved stars can produce large amounts of dust, and far-infrared
(IR) data are essential for determining the contribution of cold dust to the
total dust mass. Using Herschel, we search for cold dust in three very dusty
massive evolved stars in the Large Magellanic Cloud: R71 is a Luminous Blue
Variable, HD36402 is a Wolf-Rayet triple system, and IRAS05280-6910 is a red
supergiant. We model the spectral energy distributions using radiative transfer
codes and find that these three stars have mass-loss rates up to 10^-3 solar
masses/year, suggesting that high-mass stars are important contributors to the
life-cycle of dust. We found far-IR excesses in two objects, but these excesses
appear to be associated with ISM and star-forming regions. Cold dust (T < 100
K) may thus not be an important contributor to the dust masses of evolved
stars.Comment: accepted to A&A as part of the Herschel first results special issu
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