J/A+AS/120/283 Water maser features in ultracompact HII regions (Hofner+ 1996)
A survey of water maser emission toward ultracompact HII regions
Hofner P., Churchwell E.
<Astron. Astrophys. Suppl. Ser. 120, 283 (1996)>
=1996A&AS..120..283H 1996A&AS..120..283H (SIMBAD/NED BibCode)
ADC_Keywords: Masers ; Radio lines
Keywords: masers - ISM: HII regions - radio lines: ISM
Abstract:
In this paper we present high resolution images and spectra toward 21
H2O maser sources in the vicinity of ultracompact (UC) HII regions.
This survey provides the basis for future studies with milli-arcsecond
resolution, utilizing very long baseline interferometry (VLBI)
techniques. Emission from the 616-523 masing transition of
interstellar H2O is observed in the close vicinity of UC HII regions
with a median angular distance of 2.9" and a median linear projected
distance of 0.1pc from the continuum peak. We find that for UC HII
regions with cometary morphology the water maser emission is located
in front of the cometary arc whereas for non-cometary UC HII regions
the water masers are often observed projected onto the contours of the
ionized gas. Due to the large median distance of the water masers from
the I-front of the UC HII region, it is unlikely, that the water
masers are formed in the shocked layer of warm molecular gas in the
interface between the ionized gas of the UC HII region and surrounding
molecular gas which is predicted by the Bow Shock theory of UC HII
regions. A comparison with maps in the NH3 inversion transitions
shows that in at least 7 cases, the water masers are associated with
hot (T>100K), dense (n(H2)≃107cm-3) molecular clumps. For the
UC HII regions G5.89-0.38 and G45.07+0.13 we find spatial and velocity
correspondence between water masers and outflowing molecular gas. It
is thus likely, that for these sources the H2O masers are taking
part in the bipolar outflow.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3 65 109 Observed water maser features
table3.tex 85 347 TeX version of table3
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See also:
J/A+AS/133/29 : Molecular line survey towards UC HII (Hatchell+ 1998)
Byte-by-byte Description of file: table3
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Bytes Format Units Label Explanations
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1- 11 A11 --- Source Source name
14- 15 I2 --- No Number of maser cluster
16 A1 --- m_No Multiplicity index on No
18- 19 I2 h RAh Right ascension (1950)
21- 22 I2 min RAm Right ascension (1950)
24- 29 F6.3 s RAs Right ascension (1950)
31 A1 --- DE- Declination sign
32- 33 I2 deg DEd Declination (1950)
35- 36 I2 arcmin DEm Declination (1950)
38- 42 F5.2 arcsec DEs Declination (1950)
44- 48 F5.1 km/s Vlsr LSR velocity of feature
52- 56 F5.1 Jy Inu Intensity of feature (Jy/beam)
61- 64 F4.1 km/s DeltaV Velocity range over which emission is observed
in the cluster
65 A1 --- n_DeltaV [ab] Note (1)
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Note (1): a: Full Width at Zero Power for single features
b: Distance to UC HII region >20"
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Acknowledgements: P. Hofner
(End) Patricia Bauer [CDS] 09-May-1996