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J/MNRAS/301/640 Ultracompact H II regions studies. II. (Walsh+, 1998)
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Studies of ultracompact H II regions -
II. High-resolution radio continuum and methanol maser survey.
Walsh A.J., Burton M.G., Hyland A.R., Robinson G.
<Mon. Not. R. Astron. Soc. 301, 640 (1998)>
=1998MNRAS.301..640W
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ADC_Keywords: H II regions ; Masers ; Radial velocities
Keywords: masers - stars: formation - ISM: general - H II regions -
radio continuum: ISM - radio lines: ISM
Abstract:
High spatial resolution radio continuum and 6.67-GHz methanol spectral
line data are presented for methanol masers previously detected by
Walsh et al. (1997, Cat. <J/MNRAS/291/261>). Methanol maser and/or
radio continuum emission is found in 364 cases towards IRAS-selected
regions. For those sources with methanol maser emission, relative
positions have been obtained to an accuracy of typically 0.05arcsec,
with absolute positions accurate to around 1arcsec. Maps of selected
sources are provided. The intensity of the maser emission does not
seem to depend on the presence of a continuum source. The coincidence
of water and methanol maser positions in some regions suggests there
is overlap in the requirements for methanol and water maser emission
to be observable. However, there is a striking difference between the
general proximity of methanol and water masers to both cometary and
irregularly shaped ultracompact (UC) HII regions, indicating that, in
other cases, there must be differing environments conductive to
stimulating their emission. We show that the methanol maser is most
likely present before an observable UC HII region is formed around a
massive star and is quickly destroyed as the UC HII region evolves.
There are 36 out of 97 maser sites that are linearly extended. The
hypothesis that the maser emission is found in a circumstellar disc is
not inconsistent with these 36 maser sites, but is unlikely. It
cannot, however, account for all other maser sites. An alternative
model which uses shocks to create the masing spots can more readily
reproduce the maser spot distributions.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 126 1003 List of the UC HII regions detected
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See also:
J/A+A/336/339 : VLA observations of ultracompact HII regions (Molinari+ 1998)
J/A+AS/133/29 : Molecular line survey towards UC HII (Hatchell+ 1998)
J/MNRAS/291/261 : Methanol maser of IRAS-selected sources (Walsh+ 1997)
J/ApJS/91/659 : Ultracompact HII regions radio images (Kurtz+ 1994)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- IRAS Name of IRAS source, used for the pointing
centre
13- 18 A6 --- Obs Date of Observation (either Aug/94 or Jan/95)
20- 21 I2 h RAh ? 8.64GHz radio continuum
right ascension (J2000)
23- 24 I2 min RAm ? 8.64GHz radio continuum
right ascension (J2000)
26- 30 F5.2 s RAs ? 8.64GHz radio continuum
right ascension (J2000)
32 A1 --- DE- 8.64GHz radio continuum
declination sign (J2000)
33- 34 I2 deg DEd ? 8.64GHz radio continuum declination (J2000)
36- 37 I2 arcmin DEm ? 8.64GHz radio continuum declination (J2000)
39- 42 F4.1 arcsec DEs ? 8.64GHz radio continuum declination (J2000)
43 A1 --- n_RAh [nc] Note (1) (2)
44 A1 --- l_S8.64GHz [~] Limit flag on S8.64GHz
45- 51 F7.2 mJy S8.64GHz ? 8.64GHz radio continuum integrated
flux density
53- 54 I2 h RA1h ? 6.67GHz methanol maser
right ascension (J2000)
56- 57 I2 min RA1m ? 6.67GHz methanol maser
right ascension (J2000)
59- 64 F6.3 s RA1s ? 6.67GHz methanol maser
right ascension (J2000)
66 A1 --- DE1- 6.67GHz methanol maser
declination sign (J2000)
67- 68 I2 deg DE1d ? 6.67GHz methanol maser declination (J2000)
70- 71 I2 arcmin DE1m ? 6.67GHz methanol maser declination (J2000)
73- 77 F5.2 arcsec DE1s ? 6.67GHz methanol maser declination (J2000)
78 A1 --- n_RA1h [nc] Note (1) (3)
79- 84 F6.1 Jy S6.67GHzm ? 6.67GHz methanol maser peak flux density
(in Janskys per beam)
87- 92 F6.1 km/s RV ? Radial velocity of the methanol maser
component, with respect to the local
standard of rest (LSR)
95- 96 I2 h RA2h ? 6.67GHz radio continuum
right ascension (J2000)
98- 99 I2 min RA2m ? 6.67GHz radio continuum
right ascension (J2000)
101-105 F5.2 s RA2s ? 6.67GHz radio continuum
right ascension (J2000)
107 A1 --- DE2- 6.67GHz radio continuum
declination sign (J2000)
108-109 I2 deg DE2d ? 6.67GHz radio continuum declination (J2000)
111-112 I2 arcmin DE2m ? 6.67GHz radio continuum declination (J2000)
114-117 F4.1 arcsec DE2s ? 6.67GHz radio continuum declination (J2000)
120 A1 --- n_RA2h [nc] Note (2) (1)
121-126 F6.1 mJy S6.67GHzr ? 6.67GHz radio continuum integrated flux
density
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Note (1): n: non detection
c: can't locate
Note (2): A non detection implies that the flux dentity is value is one
{sigma} upper limit.
Note (3): A non detection implies that the peak flux value is the three
{sigma} upper limit.
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Acknowledgements: Andrew Walsh <ajw@phys.unsw.edu.au>
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(End) Patricia Bauer [CDS] 29-Apr-1999