Access to Astronomical Catalogues

← Click to display the menu
J/A+A/291/261       H2O masers in HII regions                   (Cadella+, 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
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:
FileName Lrecl Records Explanations
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
Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
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)
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)
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
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 FH2O ? Integrated flux 105-111 E7.1 solLum LH2O ? Water maser luminosity
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
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

catalogue service