1994A&A...291..261C


C.D.S. - SIMBAD4 rel 1.7 - 2020.01.21CET17:41:42

1994A&A...291..261C - Astronomy and Astrophysics, volume 291, 261-270 (1994/11-1)

The occurrence of H2O masers in HII regions.

CODELLA C., FELLI M., NATALE V., PALAGI F. and PALLA F.

Abstract (from CDS):

The results of a survey of 22.2 GHz 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 δ=-30deg) 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.

Abstract Copyright:

Journal keyword(s): masers - stars: formation - HII regions - radio lines: interstellar

Nomenclature: [CFN94] HHMMSS.s+DDMMSS N=17 among 68

Simbad objects: 38

goto View the reference in ADS

Number of rows : 38

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NAME W 3 OH HII 02 27 04.1 +61 52 22           ~ 933 2
2 NAME Orion-KL SFR 05 35 14.16 -05 22 21.5           ~ 1960 1
3 PMN J1759-2345 HII 17 59 53.4 -23 45 31           ~ 7 0
4 [CFN94] 175650.3-234524 Mas 17 59 53.5 -23 45 31           ~ 2 1
5 [L89b] 10.314-00.262 HII 18 09 23.2 -20 08 33           ~ 3 0
6 [CFN94] 180625.0-200908 Mas 18 09 23.3 -20 08 33           ~ 1 1
7 [KC97c] G017.0+00.9 HII 18 18 20.9 -13 42 49           ~ 7 0
8 [CFN94] 181530.9-134403 Mas 18 18 21.0 -13 42 49           ~ 2 2
9 [L89b] 22.982-00.356 HII 18 34 25.3 -09 00 36           ~ 4 0
10 [CFN94] 183141.1-090300 Mas 18 34 25.4 -09 00 36           ~ 2 1
11 [KC97c] G023.9+00.1 HII 18 34 38 -07 59.8           ~ 5 0
12 [CFN94] 183155.1-080200 Mas 18 34 38.2 -07 59 35           ~ 1 1
13 [KC97c] G024.7-00.2a HII 18 36 52.2 -07 24 54           ~ 4 0
14 [CFN94] 183409.9-072729 Mas 18 36 52.3 -07 24 54           ~ 1 1
15 GAL 025.38-00.18 HII 18 38 14 -06 47.6           ~ 37 0
16 [CFN94] 183532.6-065028 Mas 18 38 14.3 -06 47 47           ~ 1 1
17 [CFN94] 184020.3-033724 Mas 18 42 58.2 -03 34 23           ~ 1 1
18 [KC97c] G028.8+00.3 HII 18 42 58.2 -03 34 23           ~ 4 0
19 [KC97c] G031.0+00.5 SR? 18 46 17.6 -01 27 20           ~ 5 0
20 [CFN94] 184342.2-013036 Mas 18 46 17.7 -01 27 20           ~ 2 1
21 [CFN94] 185808.7+040954 Mas 19 00 37.7 +04 14 11           ~ 1 1
22 [KJB2003] G37.749-0.109 HII 19 00 37.7 +04 14 11           ~ 5 0
23 SSTGLMC G037.7632-00.2151 HII 19 01 02.1 +04 12 00           ~ 12 0
24 [CFN94] 185833.1+040741 Mas 19 01 02.2 +04 12 00           ~ 1 1
25 [KB94] 38 HII 19 01 53.2 +04 12 43           ~ 8 0
26 [CFN94] 185924.2+040821 Mas 19 01 53.3 +04 12 43           ~ 2 1
27 [CFN94] 190044.7+053121 Mas 19 03 12.2 +05 35 49           ~ 1 1
28 [KB94] 40 HII 19 03 12.2 +05 35 49           ~ 4 0
29 [CFN94] 190439.1+073415 Mas 19 07 04.3 +07 38 59           ~ 1 1
30 [KB94] 43 HII 19 07 04.3 +07 38 59           ~ 6 0
31 [KC97c] G039.9-01.3 HII 19 08 57.4 +05 35 24           ~ 3 0
32 [CFN94] 190629.9+053032 Mas 19 08 57.5 +05 35 24           ~ 1 1
33 [KJB2003] G48.929-0.281 HII 19 22 16.3 +14 03 50           ~ 14 0
34 [CFN94] 191958.2+135803 Mas 19 22 16.3 +14 03 50           ~ 1 1
35 GAL 048.99-00.29 HII 19 22 26.0 +14 07 08           ~ 12 0
36 [CFN94] 192008.0+140120 Mas 19 22 26.1 +14 07 08           ~ 2 1
37 NAME Cyg X FIR 33 Y*O 20 38 35.9 +42 37 22           B1.5 359 1
38 GRS G081.70 +00.50 SFR 20 39 01.6 +42 19 38           O4.5 935 0

    Equat.    Gal    SGal    Ecl

To bookmark this query, right click on this link: simbad:objects in 1994A&A...291..261C and select 'bookmark this link' or equivalent in the popup menu


2020.01.21-17:41:42

© Université de Strasbourg/CNRS

    • Contact