27 research outputs found
Submillimeter Imaging of NGC 891 with SHARC
The advent of submillimeter wavelength array cameras operating on large
ground-based telescopes is revolutionizing imaging at these wavelengths,
enabling high-resolution submillimeter surveys of dust emission in star-forming
regions and galaxies. Here we present a recent 350 micron image of the edge-on
galaxy NGC 891, which was obtained with the Submillimeter High Angular
Resolution Camera (SHARC) at the Caltech Submillimeter Observatory (CSO). We
find that high resolution submillimeter data is a vital complement to shorter
wavelength satellite data, which enables a reliable separation of the cold dust
component seen at millimeter wavelengths from the warmer component which
dominates the far-infrared (FIR) luminosity.Comment: 4 pages LaTeX, 2 EPS figures, with PASPconf.sty; to appear in
"Astrophysics with Infrared Surveys: A Prelude to SIRTF
Recommended from our members
High-Frequency Measurements Of The Spectrum Of Sagittarius A*
We report near-simultaneous interferometric measurements of the spectrum of Sagittarius A* over the 5-354 GHz range and single-dish observations that have yielded the first detection of Sgr A* at 850 GHz. We confirm that Sgr A*'s spectrum rises more steeply at short millimeter wavelengths than at centimeter wavelengths, leading to a near-millimeter/submillimeter excess that dominates its luminosity. Below 900 GHz, Sgr A*'s observed luminosity is 70 +/- 30 L.. A new upper limit to Sgr A*'s 24.3 mu m flux, together with a compilation of other extant IR data, imply a far-infrared spectral turnover, which can result from either an intrinsic synchrotron cutoff or excess extinction near Sgr A*. If the former applies, Sgr A*'s total synchrotron luminosity is <10(3) L., while in the latter case it is <3 x 10(4) L. if spherical symmetry also applies.NSF AST96-15025, AST96-13717Astronom
G34.24+0.13MM: A Deeply Embedded ProtoâB Star
By means of millimeter and submillimeter imaging, we have identified a massive protostellar object that coincides with a methanol maser and is not detectable in the continuum at centimeter wavelengths. Located 84" (1.5 pc) southeast of the ultracompact H II (UCHII) region G34.26+0.15, the new object G34.24+0.13MM was discovered in a wide-field 350 ÎŒm continuum image obtained with the Submillimeter High Angular Resolution Camera (SHARC) at the Caltech Submillimeter Observatory (CSO). Interferometric imaging at 225.7 and 110.7 GHz continuum has determined more precisely the position and angular diameter (2".0, or 7600 AU) of the object. No source was detected at that position in 1.2-3.7 ÎŒm imaging or 10 and 20 ÎŒm photometry. Our observations are consistent with a cool dust core with temperature ~50 K, total gas mass 100 M_â, and total luminosity in the range of 1600-6300 L_â. Considering the high luminosity and lack of compact radio continuum emission, we conclude that this core probably contains a deeply embedded proto-B star
Characterization of a submillimeter high-angular-resolution camera with a monolithic silicon bolometer array for the Caltech Submillimeter Observatory
We constructed a 24-pixel bolometer camera operating in the 350- and 450-”m atmospheric windows for the Caltech Submillimeter Observatory (CSO). This instrument uses a monolithic silicon bolometer array that is cooled to approximately 300 mK by a single-shot 3 He refrigerator. First-stage amplification is provided by field-effect transistors at approximately 130 K. The sky is imaged onto the bolometer array by means of several mirrors outside the Dewar and a cold off-axis elliptical mirror inside the cryostat. The beam is defined by cold aperture and field stops, which eliminates the need for any condensing horns. We describe the instrument, present measurements of the physical properties of the bolometer array, describe the performance of the electronics and the data-acquisition system, and demonstrate the sensitivity of the instrument operating at the observatory. Approximate detector noise at 350 ”m is 5 x 10^-15 W/âHz, referenced to the entrance of the Dewar, and the CSO system noise-equivalent flux density is approximately 4 Jy/âHz. These values are within a factor of 2.5 of the background limit
Radial Distribution of Dust Grains Around HR 4796A
We present high-dynamic-range images of circumstellar dust around HR 4796A
that were obtained with MIRLIN at the Keck II telescope at lambda = 7.9, 10.3,
12.5 and 24.5 um. We also present a new continuum measurement at 350 um
obtained at the Caltech Submillimeter Observatory. Emission is resolved in Keck
images at 12.5 and 24.5 um with PSF FWHM's of 0.37" and 0.55", respectively,
and confirms the presence of an outer ring centered at 70 AU. Unresolved excess
infrared emission is also detected at the stellar position and must originate
well within 13 AU of the star. A model of dust emission fit to flux densities
at 12.5, 20.8, and 24.5 um indicates dust grains are located 4(+3/-2) AU from
the star with effective size, 28+/-6 um, and an associated temperature of
260+/-40 K.
We simulate all extant data with a simple model of exozodiacal dust and an
outer exo-Kuiper ring. A two-component outer ring is necessary to fit both Keck
thermal infrared and HST scattered-light images. Bayesian parameter estimates
yield a total cross-sectional area of 0.055 AU^2 for grains roughly 4 AU from
the star and an outer-dust disk composed of a narrow large-grain ring embedded
within a wider ring of smaller grains. The narrow ring is 14+/-1 AU wide with
inner radius 66+/-1 AU and total cross-sectional area 245 AU^2. The outer ring
is 80+/-15 AU wide with inner radius 45+/-5 AU and total cross-sectional area
90 AU^2. Dust grains in the narrow ring are about 10 times larger and have
lower albedos than those in the wider ring. These properties are consistent
with a picture in which radiation pressure dominates the dispersal of an
exo-Kuiper belt.Comment: Accepted by Astrophysical Journal (Part1) on September 9, 2004. 13
pages, 10 figures, 2 table
Interstellar gas within pc of Sgr A
We seek to obtain a coherent and realistic three-dimensional picture of the
interstellar gas out to about 10 pc of the dynamical center of our Galaxy,
which is supposed to be at Sgr A. We review the existing observational
studies on the different gaseous components that have been identified near Sgr
A, and retain all the information relating to their spatial configuration
and/or physical state. Based on the collected information, we propose a
three-dimensional representation of the interstellar gas, which describes each
component in terms of both its precise location and morphology and its
thermodynamic properties. The interstellar gas near Sgr A can represented
by five basic components, which are, by order of increasing size: (1) a central
cavity with roughly equal amounts of warm ionized and atomic gases, (2) a ring
of mainly molecular gas, (3) a supernova remnant filled with hot ionized gas,
(4) a radio halo of warm ionized gas and relativistic particles, and (5) a belt
of massive molecular clouds. While the halo gas fills of the
studied volume, the molecular components enclose of the
interstellar mass.Comment: 21 pages, 7 figure
Fourier Transform Spectroscopy of the submillimetre continuum emission from hot molecular cores
We have used a Fourier Transform Spectrometer on the James Clerk Maxwell
Telescope to study the submillimetre continuum emission from dust in three hot
molecular cores (HMC). The spectral index beta of the dust emission for these
sources has been determined solely within the 30 GHz wide 350 GHz (850 micron)
passband to an accuracy comparable to those determined through multi-wavelength
observations. We find an average beta = 1.6, in agreement with spectral indices
determined from previous submillimetre observations of these sources and with
those determined for HMC in general. The largest single source of uncertainty
in these results is the variability of the atmosphere at 350 GHz, and with
better sky subtraction techniques we show that the dust spectral index can
clearly be determined within one passband to high accuracy with a submillimetre
FTS. Using an imaging FTS on SCUBA-2, the next generation wide-field
submillimetre camera currently under development to replace SCUBA at the JCMT
in 2006, we calculate that at 350 GHz it will be possible to determine beta to
+/- 0.1 for sources as faint as 400 mJy/beam and to +/- 0.3 for sources as
faint as 140 mJy/beam.Comment: 11 pages, 5 figures, accepted for publication in MNRA