J/A+A/291/261 H2O masers in HII regions (Codella+, 1994)
The occurrence of H2O masers in HII regions
Codella C., Felli M., Natale V., Palagi F., Palla F.
<Astron. Astrophys. 291, 261 (1994)>
=1994A&A...291..261C 1994A&A...291..261C
ADC_Keywords:Masers; H II regions
Keywords: maser - stars: formation - HII regions - radio lines: interstellar
Abstract:
The results of a survey of 22.2GHz H2O maser emission towards a large
sample of HII regions (427) detected in hydrogen recombination lines
(Lockman) are presented. The sample favours classical HII regions with
large excitation parameter. We found 68 water maser sources, 17
of which are new detections. Adding the detections found in the
literature, the total number of masers associated with the sample
is 80. The overall maser percentage is low (19%), much less than what
found in samples of ultracompact (UC) HII regions. The percentage
changes if we divide our sample into two sub-classes: HII regions
known to have ultracompact components (i.e. where a younger generation
of star formation is also present) and the rest. In the first
sub-class the maser percentage is 28%, in the second 15%. The total
number of masers in HII regions where no UC component has been (so
far) reported is 43. This value is greater than that expected from the
ratio between the lifetime of the HII region (106yr) and that of the
maser phase, even assuming a maser lifetime as long as 105yr. This
implies that maser excitation (and star formation) occurs several
times in the lifetime of the same star forming complex. From 410
positions observed, 230 can be associated with a high degree of
confidence to an IRAS Point Source. We expect that most of the HII
regions not associated with IRAS PS are diffuse regions in the last
phases of their evolution. The percentage of water masers in this
sub-class is very low: 8%. The number of masers with no counterpart in
the Lockman sample (and above Dec=-30°) is very large: 334. This
number most probably reflects the extreme high density conditions
known to exist in the earliest phases of an HII region, which strongly
reduce its radio continuum and line emission. The analysis of a
homogeneous sample of classical HII regions allows to confirm in a
quantitative fashion the well known result that the maser phenomenon
occurs during the earliest phase of the evolution of a massive star
and that it fades away as the HII region evolves into the diffuse
stage.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 78 410 Summary of the observed sources
table1.tex 103 662 LaTeX version of table1
table2.dat 111 129 Derived parameters of the detected maser sources
table2.tex 129 296 LaTeX version of table2
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension 1950
4- 5 I2 min RAm Right ascension 1950
7- 10 F4.1 s RAs Right ascension 1950
12 A1 --- DE- Declination sign
13- 14 I2 deg DEd Declination 1950
16- 17 I2 arcmin DEm Declination 1950
19- 20 I2 arcsec DEs Declination 1950
26- 32 F7.3 deg GLON Galactic longitude
34- 40 F7.3 deg GLAT Galactic latitude
49- 53 F5.2 kpc d ? Distance
55- 65 A11 --- IRAS IRAS name
66- 69 F4.1 Jy Dl ? Detection limit (3 r.m.s.)
70 A1 --- Mas [M] A 'M' indicates that maser is detected
72- 78 A7 --- Rem Remarks (1)
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Note (1): the following abbreviations are used:
D = double position
nd = maser known but not detected in this survey
N = new detection
K = kinematic distance
P = photometric distance
S = source associated with Sharpless regions
(see the description of table1 in the paper)
* = a problem in the position was detected at CDS (see the
"History" section below)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension 1950
4- 5 I2 min RAm Right ascension 1950
7- 10 F4.1 s RAs Right ascension 1950
13 A1 --- DE- Declination sign
14- 15 I2 deg DEd Declination 1950
17- 18 I2 arcmin DEm Declination 1950
20- 21 I2 arcsec DEs Declination 1950
23- 30 A8 "DD/MM/YY" Date Observation date
32 A1 --- l_Fpeak limit flag on Fpeak
34- 39 I6 Jy Fpeak Flux of the strongest component
43- 46 I4 Jy e_Fpeak ? Noise of the spectrum (r.m.s.)
50- 54 F5.3 km/s FWHM ? FWHM of the strongest component
58- 62 F5.1 km/s Vpeak ? Velocity of the strongest component
67- 71 F5.1 km/s Vmin ? Lower extreme of the emission interval
76- 80 F5.1 km/s Vmax ? Upper extreme of the emission interval
84- 88 F5.3 km/s Vres Spectral resolution
96-101 I6 Jy.km/s FH2O ? Integrated flux
105-111 E7.1 solLum LH2O ? Water maser luminosity
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History:
* 16-Jun-1994: Original version
* 20-Jan-2010: [Francois Ochsenbein, CDS]
errors in source positions detected
-- In table1 an '*' was added for the 2 masers:
#8: the B1950 and galactic positions are not compatible.
If the galactic position (151.594-00.228) is correct,
the B1950 position would be 04 07 19 +51 03.0, close
to the source IRAS 04073+5102
#295: the Declination was corrected from +00 02 into +10 02
(compatible with the IRAS name)
-- In table2, the Declination sign was changed (from '+' to '-')
at RA=18 47 56.8 to be compatible with table1
(End) Patricia Bauer [CDS] 16-Jun-1994