123 research outputs found
Masers and the Massive Star Formation Process: New Insights Through Infrared Observations
Our mid-infrared and near-infrared surveys over the last five years have
helped to strengthen and clarify the relationships between water, methanol, and
OH masers and the star formation process. Our surveys show that maser emission
seems to be more closely associated with mid-infrared emission than cm radio
continuum emission from UC HII regions. We find that masers of all molecular
species surveyed trace a wide variety of phenomena and show a proclivity for
linear distributions. The vast majority of these linear distributions can be
explained by outflows or shocks, and in general do not appear to trace
circumstellar disks as was previously thought. Some water and methanol masers
that are not associated with radio continuum emission appear to trace
infrared-bright hot cores, the earliest observable stage of massive stellar
life before the onset of a UC HII region.Comment: 6 pages, 3 figures, to appear in the proceedings of IAU Symposium
227: "Massive Star Birth: A Crossroads of Astrophysics", version with
full-resolution images available at http://www.ctio.noao.edu/~debuize
12 and 18 micron images of dust surrounding HD 32297
We present the first subarcsecond-resolution images at multiple mid-IR
wavelengths of the thermally-emitting dust around the A0 star HD 32297. Our
observations with T-ReCS at Gemini South reveal a nearly edge-on resolved disk
at both 11.7 microns and 18.3 microns that extends ~150 AU in radius. The
mid-IR is the third wavelength region in which this disk has been resolved,
following coronagraphic observations by others of the source at optical and
near-IR wavelengths. The global mid-IR colors and detailed consideration of the
radial color-temperature distribution imply that the central part of the disk
out to ~80 AU is relatively deficient in dust.Comment: 4 pages, 3 figures; accepted for publication in ApJ
Surveying the Giant HII Regions of the Milky Way with SOFIA: IV. Sgr D, W42, and a Reassessment of the Giant HII Region Census
This is the fourth paper exploring the infrared properties of giant HII
regions with the FORCAST instrument on the Stratospheric Observatory For
Infrared Astronomy (SOFIA). Our survey utilizes the census of 56 Milky Way
giant HII regions identified by Conti & Crowther (2004), and in this paper we
present the 20 and 37 micron imaging data we have obtained from SOFIA for
sources Sgr D and W42. Based upon the SOFIA data and other multi-wavelength
data, we derive and discuss the detailed physical properties of the individual
compact sources and sub-regions as well as the large scale properties of Sgr D
and W42. However, improved measurements have revealed much closer distances to
both regions than previously believed, and consequently both sources are not
powerful enough to be considered giant HII regions any longer. Motivated by
this, we revisit the census of giant HII regions, performing a search through
the last two decades of literature to update each source with the most recent
and/or most accurate distance measurements. Based on these new distance
estimates, we determine that 14 sources in total (25%) are at sufficiently
reliable and closer distances that they are not powerful enough to be
considered giant HII regions. We briefly discuss the observational and physical
characteristics specific to Sgr D and W42 and show that they have properties
distinct from the giant HII regions previously studied as a part of this
survey.Comment: 31 pages, 8 figures, 7 tables; accepted for publication in Ap
High-Resolution Mid-Infrared Morphology of Cygnus A
We present subarcsecond resolution mid-infrared images at 10.8 and 18.2
microns of Cygnus A. These images were obtained with the University of Florida
mid-IR camera/spectrometer OSCIR at the Keck II 10-m telescope. Our data show
extended mid-IR emission primarily to the east of the nucleus with a possible
western extension detected after image deconvolution. This extended emission is
closely aligned with the bi-conical structure observed at optical and near-IR
wavelengths by the HST. This emission is consistent with dust heated from the
central engine of Cygnus A. We also marginally detect large-scale low level
emission extending > 1.5 kpc from the nucleus which may be caused by in-situ
star formation, line emission, and/or PAH contamination within the bandpass of
our wide N-band filter.Comment: 20 pages, 8 figures, accepted for publication in the Astrophysical
Journa
Subaru Spectroscopy and Spectral Modeling of Cygnus A
We present high angular resolution (0.5) MIR spectra
of the powerful radio galaxy, Cygnus A, obtained with the Subaru telescope. The
overall shape of the spectra agree with previous high angular resolution MIR
observations, as well as previous Spitzer spectra. Our spectra, both on and off
nucleus, show a deep silicate absorption feature. The absorption feature can be
modeled with a blackbody obscured by cold dust or a clumpy torus. The deep
silicate feature is best fit by a simple model of a screened blackbody,
suggesting foreground absorption plays a significant, if not dominant role, in
shaping the spectrum of Cygnus A. This foreground absorption prevents a clear
view of the central engine and surrounding torus, making it difficult to
quantify the extent the torus attributes to the obscuration of the central
engine, but does not eliminate the need for a torus in Cygnus A
Mid-Infrared Imaging of NGC 6334 I
We present high-resolution (<0.5") mid-infrared Keck II images of individual
sources in the central region of NGC 6334 I. We compare these images to images
at a variety of other wavelengths from the near infrared to cm radio continuum
and speculate on the nature of the NGC 6334 I sources. We assert that the
cometary shape of the UCHII region here, NGC 6334 F, is due to a champagne-like
flow from a source on the edge of a molecular clump and not a due to a bow
shock caused by the supersonic motion of the UCHII region through the
interstellar medium. The mid-infrared emission in concentrated into an arc of
dust that define the boundary between the UCHII region and the molecular clump.
This dust arc contains a majority of the masers in the region. We discuss the
nature of the four near-infrared sources associated with IRS-I 1, and suggest
that one of the sources, IRS1E, is responsible for the heating and ionizing of
the UCHII region and the mid-infrared dust arc. Infrared source IRS-I 2, which
has been thought to be a circumstellar disk associated with a linear
distribution of methanol masers, is found not to be directly coincident with
the masers and elongated at a much different position angle. IRS-I 3 is found
to be a extended source of mid-infrared emission coming from a cluster of young
dusty sources seen in the near-infrared.Comment: Accepted for publication by the Astrophysical Journal, 27 pages, 9
figure
Understanding the 8 micron vs. Pa-alpha relationship on sub-arcsecond scales in Luminous Infrared Galaxies
This work explores in detail the relation between the 8 micron and the
Pa-alpha emissions for 122 HII regions identified in a sample of 10 low-z LIRGs
with nearly constant metallicity (12 + log (O/H) ~ 8.8). We use Gemini/T-ReCS
high-spatial resolution (<~ 0.4" ~ 120 pc for the average distance of 60 Mpc of
our sample) mid-infrared imaging (at 8.7 micron or 10.3 micron) together with
HST/NICMOS continuum and Pa-alpha images. The LIRG HII regions extend the
L_8micron vs. L_Pa-alpha relation found for HII knots in the high-metallicity
SINGS galaxies by about two orders of magnitude to higher luminosities. Since
the metallicity of the LIRG sample is nearly constant, we can rule out this
effect as a cause for the scatter seen in the relationship. In turn, it is
attributed to two effects: age and PAH features. The L_8micron/L_Pa-alpha
ratio, which varies by a factor of ten for the LIRG HII regions, is reproduced
by a model with instantaneous star formation and ages ranging from ~ 4 to 7.5
Myr. The remaining dispersion around the model predictions for a given age is
probably due to differential contributions of the PAH features (the 8.6 micron,
in our case) to the 8 micron emission from galaxy to galaxy.Comment: 16 pages, 9 figures, accepted for publication in ApJ; paper with
full-resolution figures can be found at:
http://damir.iem.csic.es/extragalactic
Crystalline Silicate Emission in the Protostellar Binary Serpens--SVS20
We present spatially resolved mid-infrared spectroscopy of the class
I/flat-spectrum protostellar binary system SVS20 in the Serpens cloud core. The
spectra were obtained with the mid-infrared instrument T-ReCS on Gemini-South.
SVS20-South, the more luminous of the two sources, exhibits a mid-infrared
emission spectrum peaking near 11.3 \micron, while SVS20-North exhibits a
shallow amorphous silicate absorption spectrum with a peak optical depth of
. After removal of the the line-of-sight extinction by the
molecular common envelope, the ``protostar-only'' spectra are found to be
dominated by strong amorphous olivine emission peaking near 10 \micron. We also
find evidence for emission from crystalline forsterite and enstatite associated
with both SVS20-S and SVS20-N. The presence of crystalline silicate in such a
young binary system indicates that the grain processing found in more evolved
HAeBe and T Tauri pre-main sequence stars likely begins at a relatively young
evolutionary stage, while mass accretion is still ongoing.Comment: Accepted for publication by The Astrophysical Journa
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