228 research outputs found
The Contribution of Thermally-pulsing Asymptotic Giant Branch and Red Supergiant Stars to the Luminosities of the Magellanic Clouds at 1-24 μm
We present the near-through mid-infrared flux contribution of thermally-pulsing asymptotic giant branch (TP-AGB) and massive red supergiant (RSG) stars to the luminosities of the Large and Small Magellanic Clouds (LMC and SMC, respectively). Combined, the peak contribution from these cool evolved stars occurs at ~3-4 μm, where they produce 32% of the SMC light, and 25% of the LMC flux. The TP-AGB star contribution also peaks at ~3-4 μm and amounts to 21% in both galaxies. The contribution from RSG stars peaks at shorter wavelengths, 2.2 μm, where they provide 11% of the SMC flux, and 7% for the LMC. Both TP-AGB and RSG stars are short lived, and thus potentially impose a large stochastic scatter on the near-IR derived mass-to-light (M/L) ratios of galaxies at rest-frame 1-4 μm. To minimize their impact on stellar mass estimates, one can use the M/L ratio at shorter wavelengths (e.g., at 0.8-1 μm). At longer wavelengths (≥8 μm), emission from dust in the interstellar medium dominates the flux. In the LMC, which shows strong polycyclic aromatic hydrocarbon (PAH) emission at 8 μm, TP-AGB and RSG contribute less than 4% of the 8 μm flux. However, 19% of the SMC 8 μm flux is from evolved stars, nearly half of which is produced by the rarest, dustiest, carbon-rich TP-AGB stars. Thus, star formation rates of galaxies, based on an 8 μm flux (e.g., observed-frame 24 μm at z = 2), may be biased modestly high, especially for galaxies with little PAH emission
The Contribution of Thermally-Pulsing Asymptotic Giant Branch and Red Supergiant Starts to the Luminosities of the Magellanic Clouds at 1-24 micrometers
We present the near-through mid-infrared flux contribution of thermally-pulsing asymptotic giant branch (TP-AGB) and massive red supergiant (RSG) stars to the luminosities of the Large and Small Magellanic Clouds (LMC and SMC, respectively). Combined, the peak contribution from these cool evolved stars occurs at approx 3 - 4 micron, where they produce 32% of the SMC light, and 25% of the LMC flux. The TP-AGB star contribution also peaks at approx 3 - 4 micron and amounts to 21% in both galaxies. The contribution from RSG stars peaks at shorter wavelengths, 2.2 micron, where they provide 11% of the SMC flux, and 7% for the LMC. Both TP-AGB and RSG stars are short lived, and thus potentially impose a large stochastic scatter on the near-IR derived mass-to-light (M/L) ratios of galaxies at rest-frame 1 - 4 micron. To minimize their impact on stellar mass estimates, one can use the M/L ratio at shorter wavelengths (e.g., at 0.8 - 1 micron). At longer wavelengths (much > 8 micron), emission from dust in the interstellar medium dominates the flux. In the LMC, which shows strong polycyclic aromatic hydrocarbon (PAH) emission at 8 micron, TP-AGB and RSG contribute less than 4% of the 8 micron flux. However, 19% of the SMC 8 micron flux is from evolved stars, nearly half of which is produced by the rarest, dustiest, carbon-rich TP-AGB stars. Thus, star formation rates of galaxies, based on an 8 micron flux (e.g., observed-frame 24 micron at z = 2), may be biased modestly high, especially for galaxies with little PAH emission
Near-Infrared Stellar Populations in the metal-poor, Dwarf irregular Galaxies Sextans A and Leo A
We present JHK observations of the metal-poor ([Fe/H] -1.40)
Dwarf-irregular galaxies, Leo A and Sextans A obtained with the WIYN
High-Resolution Infrared Camera at Kitt Peak. Their near-IR stellar populations
are characterized by using a combination of colour-magnitude diagrams and by
identifying long-period variable stars. We detected red giant and asymptotic
giant branch stars, consistent with membership of the galaxy's intermediate-age
populations (2-8 Gyr old). Matching our data to broadband optical and mid-IR
photometry we determine luminosities, temperatures and dust-production rates
(DPR) for each star. We identify 32 stars in Leo A and 101 stars in Sextans A
with a DPR , confirming that metal-poor
stars can form substantial amounts of dust. We also find tentative evidence for
oxygen-rich dust formation at low metallicity, contradicting previous models
that suggest oxygen-rich dust production is inhibited in metal-poor
environments. The total rates of dust injection into the interstellar medium of
Leo A and Sextans A are (8.2 1.8) and (6.2 0.2) ,
respectively. The majority of this dust is produced by a few very dusty evolved
stars, and does not vary strongly with metallicity.Comment: 21 pages, 11 figures, 10 tables; accepted for publication in Ap
Dust Destruction Rates and Lifetimes in the Magellanic Clouds
The nature, composition, abundance, and size distribution of dust in galaxies
is determined by the rate at which it is created in the different stellar
sources and destroyed by interstellar shocks. Because of their extensive
wavelength coverage, proximity, and nearly face-on geometry, the Magellanic
Clouds (MCs) provide a unique opportunity to study these processes in great
detail. In this paper we use the complete sample of supernova remnants (SNRs)
in the MCs to calculate the lifetime and destruction efficiencies of silicate
and carbon dust in these galaxies. We find dust lifetimes of 22 +- 13 Myr (30
+- 17 Myr) for silicate (carbon) grains in the LMC, and 54 +- 32 Myr (72 +- 43
Myr) for silicate (carbon) grains in the SMC. The significantly shorter
lifetimes in the MCs, as compared to the Milky Way, are explained as the
combined effect of their lower total dust mass, and the fact that the
dust-destroying isolated SNe in the MCs seem to be preferentially occurring in
regions with higher than average dust-to-gas (D2G) mass ratios. We also
calculate the supernova rate and the current star formation rate in the MCs,
and use them to derive maximum dust injection rates by asymptotic giant branch
stars and core collapse supernovae. We find that the injection rates are an
order of magnitude lower than the dust destruction rates by the SNRs. This
supports the conclusion that, unless the dust destruction rates have been
considerably overestimated, most of the dust must be reconstituted from
surviving grains in dense molecular clouds. More generally, we also discuss the
dependence of the dust destruction rate on the local D2G mass ratio, the
ambient gas density and metallicity, as well as the application of our results
to other galaxies and dust evolution models.Comment: 15 pages, 8 figures, 5 tables, accepted to Ap
Spitzer Space Telescope evidence in NGC 6791: no super-mass-loss at super-solar metallicity to explain helium white dwarfs?
We use archival Spitzer Space Telescope photometry of the old, super-solar
metallicity massive open cluster NGC 6791 to look for evidence of enhanced mass
loss, which has been postulated to explain the optical luminosity function and
low white dwarf masses in this benchmark cluster. We find a conspicuous lack of
evidence for prolificacy of circumstellar dust production that would have been
expected to accompany such mass loss. We also construct the optical and
infrared luminosity functions, and demonstrate that these fully agree with
theoretical expectations. We thus conclude that there is no evidence for the
mass loss of super-solar metallicity red giants to be sufficiently high that
they can avoid the helium flash at the tip of the red giant branch.Comment: accepted for publication in ApJ Letter
An Optical and Infrared Time-Domain Study of the Supergiant Fast X-ray Transient Candidate IC 10 X-2
We present an optical and infrared (IR) study of IC 10 X-2, a high-mass X-ray
binary in the galaxy IC 10. Previous optical and X-ray studies suggest X-2 is a
Supergiant Fast X-ray Transient: a large-amplitude (factor of 100),
short-duration (hours to weeks) X-ray outburst on 2010 May 21. We analyze R-
and g-band light curves of X-2 from the intermediate Palomar Transient Factory
taken between 2013 July 15 and 2017 Feb 14 show high-amplitude ( 1
mag), short-duration ( d) flares and dips ( 0.5 mag).
Near-IR spectroscopy of X-2 from Palomar/TripleSpec show He I,
Paschen-, and Paschen- emission lines with similar shapes and
amplitudes as those of luminous blue variables (LBVs) and LBV candidates
(LBVc). Mid-IR colors and magnitudes from Spitzer/IRAC photometry of X-2
resemble those of known LBV/LBVcs. We suggest that the stellar companion in X-2
is an LBV/LBVc and discuss possible origins of the optical flares. Dips in the
optical light curve are indicative of eclipses from optically thick clumps
formed in the winds of the stellar counterpart. Given the constraints on the
flare duration ( d) and the time between flares ( d),
we estimate the clump volume filling factor in the stellar winds, , to be
, which overlaps with values measured from massive star
winds. In X-2, we interpret the origin of the optical flares as the accretion
of clumps formed in the winds of an LBV/LBVc onto the compact object.Comment: 15 pages, 4 figures. Submitted to ApJ on Sep 26 201
Identification of a Class of Low-Mass Asymptotic Giant Branch Stars Struggling to Become Carbon Stars in the Magellanic Clouds
We have identified a new class of Asymptotic Giant Branch (AGB) stars in the
Small and Large Magellanic Clouds (SMC/LMC) using optical to infrared
photometry, light curves, and optical spectroscopy. The strong dust production
and long-period pulsations of these stars indicate that they are at the very
end of their AGB evolution. Period-mass-radius relations for the
fundamental-mode pulsators give median current stellar masses of 1.14 M_sun in
the LMC and 0.94 M_sun in the SMC (with dispersions of 0.21 and 0.18 M_sun,
respectively), and models suggest initial masses of <1.5 M_sun and <1.25 M_sun,
respectively. This new class of stars includes both O-rich and C-rich
chemistries, placing the limit where dredge-up allows carbon star production
below these masses. A high fraction of the brightest among them should show S
star characteristics indicative of atmospheric C/O ~ 1, and many will form
O-rich dust prior to their C-rich phase. These stars can be separated from
their less-evolved counterparts by their characteristically red J-[8] colors.Comment: 16 pages, 18 figures, accepted for publication in Ap
The first 8-13 micron spectra of globular cluster red giants: circumstellar silicate dust grains in 47 Tucanae (NGC 104)
We present 8-13 micron spectra of eight red giants in the globular cluster 47
Tucanae (NGC 104), obtained at the European Southern Observatory 3.6m
telescope. These are the first mid-infrared spectra of metal-poor, low-mass
stars. The spectrum of at least one of these, namely the extremely red,
large-amplitude variable V1, shows direct evidence of circumstellar grains made
of amorphous silicate.Comment: Accepted for publication in Astronomy and Astrophysics, 5 page
The LF of TP-AGB stars in the LMC/SMC
We show that Monte Carlo simulations of the TP-AGB stellar population in the LMC and SMC galaxies using the CB. models produce LF and color distributions that are in closer agreement with observations than those obtained with the BC03 and CB07 models. This is a progress report of work that will be published elsewhere
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