219 research outputs found
Probing the dusty stellar populations of the Local Volume Galaxies with JWST/MIRI
The Mid-Infrared Instrument (MIRI) for the {\em James Webb Space Telescope}
(JWST) will revolutionize our understanding of infrared stellar populations in
the Local Volume. Using the rich {\em Spitzer}-IRS spectroscopic data-set and
spectral classifications from the Surveying the Agents of Galaxy Evolution
(SAGE)-Spectroscopic survey of over a thousand objects in the Magellanic
Clouds, the Grid of Red supergiant and Asymptotic giant branch star ModelS
({\sc grams}), and the grid of YSO models by Robitaille et al. (2006), we
calculate the expected flux-densities and colors in the MIRI broadband filters
for prominent infrared stellar populations. We use these fluxes to explore the
{\em JWST}/MIRI colours and magnitudes for composite stellar population studies
of Local Volume galaxies. MIRI colour classification schemes are presented;
these diagrams provide a powerful means of identifying young stellar objects,
evolved stars and extragalactic background galaxies in Local Volume galaxies
with a high degree of confidence. Finally, we examine which filter combinations
are best for selecting populations of sources based on their JWST colours.Comment: 16 pages, 7 figures, 2 online tables; accepted for publication in Ap
Current and Future Space and Airborne Observatories for ISM Studies
A tremendous amount of radiation is emitted by the Interstellar Medium in the
mid- and far-infrared (3-500 {\mu}m) that represents the majority of the light
emitted by a galaxy. In this article we motivate ISM studies in the infrared
and the construction of large specialized observatories like the Stratospheric
Observatory For Infrared Astronomy (SOFIA), which just concluded its mission on
a scientific high note, and the newly launched James Webb Space Telescope
(JWST) that just begun its exciting scientific mission. We introduce their
capabilities, present a few examples of their scientific discoveries and
discuss how they complemented each other. We then consider the impact of the
conclusion of SOFIA for the field in a historic context and look at new
opportunities specifically for far-infrared observatories in space and in the
stratosphere
Westbrook's Molecular Gun: Discovery of Near-IR Micro-Structures in AFGL 618
We present high-sensitivity near-IR images of a carbon-rich proto-planetary
nebula, AFGL 618, obtained with the Subaru Telescope. These images have
revealed ``bullets'' and ``horns'' extending farther out from the edges of the
previously known bipolar lobes. The spatial coincidence between these near-IR
micro-structures and the optical collimated outflow structure, together with
the detection of shock-excited, forbidden IR lines of atomic species, strongly
suggests that these bullets and horns represent the locations from which
[\ion{Fe}{2}] IR lines arise. We have also discovered CO clumps moving at km s at the positions of the near-IR bullets by re-analyzing the
existing CO interferometry data. These findings indicate that
the near-IR micro-structures represent the positions of shocked surfaces at
which fast-moving molecular clumps interface with the ambient circumstellar
shell.Comment: 2 figures. To appear in the ApJ Letter
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
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