96 research outputs found
Massive Star Formation in the Molecular Ring Orbiting the Black Hole at the Galactic Center
A ring of dense molecular gas extending 2-7 pc orbits the supermassive black
hole Sgr A* at the center of our Galaxy. Using the Green Bank Telescope, we
detected water maser lines and both narrow (0.35 km/s) and broad (30 - 50 km/s)
methanol emission from the molecular ring. Two of the strongest methanol lines
at 44 GHz are confirmed as masers by interferometric observations. These class
I methanol masers are collisionally excited and are signatures of early phases
of massive star formation in the disk of the Galaxy, suggesting that star
formation in the molecular ring is in its early phase. Close inspection of the
kinematics of the associated molecular clumps in the HCN (J=1-0) line reveals
broad red-shifted wings indicative of disturbance by protostellar outflows from
young (few times 10^4 yr), massive stars embedded in the clumps. The thermal
methanol profile has a similar shape, with a narrow maser line superimposed on
a broad, red-shifted wing. Additional evidence for the presence of young
massive protostars is provided by shocked molecular hydrogen and a number of
striking ionized and molecular linear filaments in the vicinity of methanol
sources suggestive of 0.5-pc scale protostellar jets. Given that the
circumnuclear molecular ring is kinematically unsettled and thus is likely be
the result of a recent capture, the presence of both methanol emission and
broad, red-shifted HCN emission suggests that star formation in the
circumnuclear ring is in its infancy.Comment: 13 pages, 4 figures, ApJ Letters (in press
New Molecular Species In Comet C/1995 (Hale-Bopp) Observed with the Caltech Submillimeter Observatory
We present millimeter-wave observations of HNCO, HC3N, SO, NH2CHO, H(13)CN, and H3O(+) in comet C/1995 O1 (Hale-Bopp) obtained in February-April, 1997 with the Caltech Submillimeter Observatory (CSO). HNCO, first detected at the CSO in comet C/1996 B2 (Hyakutake), is securely confirmed in comet Hale-Bopp via observations of three rotational transitions. The derived abundance with respect to H2O is (4-13) x 10(exp -4). HC3N, SO, and NH2CHO are detected for the first time in a comet. The fractional abundance of HC3N based on observations of three rotational lines is (1.9 +/- 0.2) x 10(exp -4). Four transitions of SO are detected and the derived fractional abundance, (2-8) x 10(exp -3), is higher than the upper limits derived from UV observations of previous comets. Observations of NH2CHO imply a fractional abundance of (1-8) x 10(exp -4). H3O(+) is detected for the first time from the ground. The H(13)CN (3-2) transition is also detected and the derived HCN/H(13)CN abundance ratio is 90 +/- 15, consistent with the terrestrial C-13/C-12 ratio. in addition, a number of other molecular species are detected, including HNC, OCS, HCO(+), CO(+), and CN (the last two are first detections in a comet at radio wavelengths)
A Submillimeter HCN Laser in IRC+10216
We report the detection of a strong submillimeter wavelength HCN laser line
at a frequency near 805 GHz toward the carbon star IRC+10216. This line, the
J=9-8 rotational transition within the (04(0)0) vibrationally excited state, is
one of a series of HCN laser lines that were first detected in the laboratory
in the early days of laser spectroscopy. Since its lower energy level is 4200 K
above the ground state, the laser emission must arise from the inner part of
IRC+10216's circumstellar envelope. To better characterize this environment, we
observed other, thermally emitting, vibrationally excited HCN lines and find
that they, like the laser line, arise in a region of temperature approximately
1000 K that is located within the dust formation radius; this conclusion is
supported by the linewidth of the laser. The (04(0)0), J=9-8 laser might be
chemically pumped and may be the only known laser (or maser) that is excited
both in the laboratory and in space by a similar mechanism.Comment: 11 pages, 3 figure
Masers and Outflows in the W3(OH)/W3(H2O) region
Methanol masers and molecular shock tracers were observed in the
W3(OH)/W3(HO) region with the BIMA array and the Onsala 20m radiotelescope.
Characteristics of the outflows in the region are discussed. A model of the
W3(OH) methanol maser formation region is constructed.Comment: 4 pages, 2 figures, numerous journal misprints are correcte
A search for 85.5- and 86.6-GHz methanol maser emission
We have used the Australia Telescope National Facility Mopra 22m millimetre
telescope to search for emission from the 85.5-GHz and 86.6-GHz transitions of
methanol. The search was targeted towards 22 star formation regions which
exhibit maser emission in the 107.0-GHz methanol transition, as well as in the
6.6-GHz transition characteristic of class II methanol maser sources. A total
of 22 regions were searched at 85.5 GHz resulting in 5 detections, of which 1
appears to be a newly discovered maser. For the 86.6-GHz transition
observations were made of 18 regions which yielded 2 detections, but no new
maser sources. This search demonstrates that emission from the 85.5- and
86.6-GHz transitions is rare. Detection of maser emission from either of these
transitions therefore indicates the presence of special conditions, different
from those in the majority of methanol maser sources. We have observed temporal
variability in the 86.6-GHz emission towards 345.010+1.792, which along with
the very narrow line width, confirms that the emission is a maser in this
source. We have combined our current observations with published data for the
6.6-, 12.1-, 85.5-, 86.6-, 107.0-, 108.8- and 156.6-GHz transitions for
comparison with the maser model of Sobolev & Deguchi (1994). This has allowed
us to estimate the likely ranges of dust temperature, gas density, and methanol
column density, both for typical methanol maser sources and for those sources
which also show 107.0-GHz emission.Comment: 11 pages, accepted for publication in MNRAS, Latex, mn2e.cl
Perspective from a Younger Generation -- The Astro-Spectroscopy of Gisbert Winnewisser
Gisbert Winnewisser's astronomical career was practically coextensive with
the whole development of molecular radio astronomy. Here I would like to pick
out a few of his many contributions, which I, personally, find particularly
interesting and put them in the context of newer results.Comment: 14 pages. (Co)authored by members of the MPIfR (Sub)millimeter
Astronomy Group. To appear in the Proceedings of the 4th
Cologne-Bonn-Zermatt-Symposium "The Dense Interstellar Medium in Galaxies"
eds. S. Pfalzner, C. Kramer, C. Straubmeier, & A. Heithausen (Springer:
Berlin
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