1998A&A...336..339M

Query : 1998A&A...336..339M

1998A&A...336..339M - Astronomy and Astrophysics, volume 336, 339-351 (1998/8-1)

A search for precursors of ultracompact HII regions in a sample of luminous IRAS sources. II. VLA observations.

MOLINARI S., BRAND J., CESARONI R., PALLA F. and PALUMBO G.G.C.

Abstract (from CDS):

We have used the Very Large Array (VLA) to search for radio continuum emission towards a sample of 67 IRAS sources selected from a previous study. All observed sources are associated with high density molecular gas, exhibit an infrared spectral energy distribution characteristic of very cold young stellar objects and many of them are associated with H2O masers. The observed sample is divided into two groups of sources: High, with IRAS spectral energy distributions resembling those of ultracompact HII regions, and Low, for which previously collected evidence suggests that they may contain a higher fraction of protostellar objects than the High group; such objects might not have started hydrogen burning yet. Radio continuum emission was detected towards 37 sources (55%), although only in 22 cases an association with the IRAS source is established. Of the latter, 9 (24%) objects belong to the Low type and 13 (43%) to the High type. Thus, we find that 76% of Low and 57% of High sources are not associated with a radio counterpart. Because the majority of the sources have luminosities above ∼104L☉, corresponding to central stars of spectral type between B2 and O7, the lack of radio emission is interpreted as being due to the action of accreting matter that chokes off the expansion of the ionised gas. We show that this requires only moderate mass accretion rates, below ∼10–4M☉/yr. Alternatively, dust absorption can also effectively absorb UV photons and the gas column density implied by our observations indicates values in excess of 1022cm–2. The physical properties of IRAS sources with associated radio counterpart derived from the present observations do not distinguish between High and Low sources. These sources are likely to be ZAMS stars with variable amounts of dust within the ionised region which acts as UV field absorber. The large majority of detected sources (75%) have spherical or unresolved morphology, while 15% are irregular or multiply peaked and only 10% have a core-halo structure. These results agree with the known properties of ultracompact HII regions, even though the average luminosity of the present sample is an order of magnitude lower than that in previous studies.

Abstract Copyright: ∼

Journal keyword(s): stars: formation - stars: pre-main sequence - stars: circumstellar matter - ISM: HII regions - sources as a function of wavelength: radio continuum: ISM

VizieR on-line data: <Available at CDS (J/A+A/336/339): fig.dat note1a.dat note1b.dat table1a.dat table1b.dat table2a.dat>

Nomenclature: Tables 1a, 1b: Mol NNNW, Mol NNNWNN, Mol NNNWN/NN, N=44.

Simbad objects: 116

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Number of rows : 116
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024 		#notes
1 IRAS 00420+5530 Y*? 00 44 57.31 +55 47 18.1           ~ 58 0
2 IRAS 04579+4703 Y*O 05 01 39.661 +47 07 21.92           ~ 50 0
3 IRAS 05137+3919 Cld 05 17 13.3 +39 22 14           ~ 65 0
4 IRAS 05168+3634 mul 05 20 16.2 +36 37 21           ~ 46 0
5 GAL 174.20-00.08 Cld 05 30 45.9 +33 47 56           ~ 205 2
6 NGC 1985 RNe 05 37 47.8 +31 59 24           ~ 136 2
7 IRAS 05373+2349 Y*O 05 40 24.2280641304 +23 50 54.705306336           ~ 61 1
8 Mol 12 Rad 05 40 24.4 +23 50 54           ~ 49 0
9 IRAS 06584-0852 Y*O 07 00 50.94192 -08 56 30.1812           ~ 36 0
10 3C 286 Sy1 13 31 08.2883506368 +30 30 32.960091564   17.51 17.25     ~ 4341 2
11 Mol 30 Rad 17 48 09.3 -27 43 21           ~ 6 0
12 M 8 OpC 18 03 37 -24 23.2           ~ 614 1
13 IRAS 18014-2428 IR 18 04 29.6 -24 28 47           ~ 14 0
14 IRAS 18024-2231 IR 18 05 30.6 -22 31 36           ~ 9 0
15 LBN 008.55-00.88 HII 18 06.4 -21 39           ~ 12 0
16 IRAS 18144-1723 IR 18 17 24.4 -17 22 13           ~ 34 0
17 AGAL G014.891-00.404 Y*O 18 19 07.4495 -16 11 34.047           ~ 40 0
18 IRAS 18256-0742 IR 18 28 20.5 -07 40 22           ~ 13 0
19 JCMTSF J183035.5-100709 Rad 18 30 36 -10 07.2           ~ 22 0
20 LBN 028.77+03.43 HII 18 31 26.5 -02 04 22           ~ 230 2
21 IRAS 18363-0554 Rad 18 39 03.7 -05 52 15           ~ 9 0
22 IRAS 18396-0431 Rad 18 42 18.8 -04 28 37           ~ 13 0
23 IRAS 18424-0329 Rad 18 45 03.3 -03 26 49           ~ 11 0
24 GAL 034.4+00.23 HII 18 53 17.4 +01 24 55           ~ 82 1
25 RAFGL 5542 Y*O 18 53 37.88832 +01 50 30.5844           ~ 70 0
26 IRAS 18517+0437 SFR 18 54 13.8 +04 41 32           ~ 74 0
27 [ERG2015] 6375 smm 18 55 16.778 +03 05 07.47           ~ 26 0
28 IRAS 18532+0047 Rad 18 55 50.6 +00 51 22           ~ 17 0
29 Mol 78N Rad 18 55 51.132 +00 51 25.77           ~ 1 0
30 Mol 78S Rad 18 55 51.393 +00 51 18.28           ~ 1 0
31 Mol 81 Rad 18 57 42.1 +03 06 04           ~ 4 1
32 IRAS 18565+0349 Rad 18 59 03.4 +03 53 22           ~ 15 0
33 AGAL G040.121+01.500 HII 18 59 14 +07 04.9   13.60 12.74     ~ 33 0
34 IRAS 18571+0349 Rad 18 59 40.0 +03 53 35           ~ 14 0
35 IRAS 18586+0106 Rad 19 01 10.6 +01 11 16           ~ 18 0
36 IRAS 19012+0505 mul 19 03 43.5 +05 09 49           ~ 30 0
37 Mol 91C4 HII 19 03 46.328 +05 10 06.18           ~ 1 0
38 Mol 91C3 HII 19 03 46.512 +05 09 58.78           ~ 1 0
39 Mol 91C1 HII 19 03 46.898 +05 09 52.43           ~ 1 0
40 Mol 91C2 HII 19 03 46.952 +05 09 58.91           ~ 1 0
41 [CPA2006] N75 bub 19 03 47.1 +05 09 27           ~ 40 0
42 Mol 91C5 HII 19 03 47.974 +05 09 57.60           ~ 1 0
43 IRAS 19043+0726 Rad 19 06 47.7 +07 31 38           ~ 15 0
44 Mol 93S4 Rad 19 06 47.779 +07 31 33.14           ~ 1 0
45 Mol 93S3 Rad 19 06 48.330 +07 31 36.64           ~ 1 0
46 Mol 93S1 Rad 19 06 48.345 +07 31 40.30           ~ 1 0
47 Mol 93N2 Rad 19 06 48.449 +07 31 51.56           ~ 1 0
48 Mol 93S5 Rad 19 06 48.570 +07 31 34.94           ~ 1 0
49 Mol 93N1 Rad 19 06 48.627 +07 31 49.62           ~ 1 0
50 IRAS 19088+0902 Rad 19 11 15.9 +09 07 27           ~ 21 0
51 IRAS 19092+0841 Rad 19 11 37.4 +08 46 30           ~ 28 0
52 IRAS 19094+0944 mul 19 11 52.0 +09 49 46           ~ 17 0
53 Mol 102 Rad 19 22 07.7 +14 29 20           ~ 4 0
54 Mol 103C5 Rad 19 23 36.868 +17 29 15.30           ~ 1 0
55 Mol 103 Rad 19 23 37.0 +17 28 59           ~ 9 0
56 Mol 103C3 Rad 19 23 37.157 +17 28 58.50           ~ 2 0
57 Mol 103C6 Rad 19 23 37.236 +17 29 21.94           ~ 1 0
58 Mol 103C1 Rad 19 23 37.392 +17 29 09.59           ~ 1 0
59 Mol 103C2 Rad 19 23 37.440 +17 29 05.82           ~ 1 0
60 Mol 103C4 Rad 19 23 37.664 +17 29 00.86           ~ 1 0
61 LBN 053.54+00.04 HII 19 30 14.9 +18 17 30           ~ 36 0
62 Mol 108 Rad 19 38 58.1 +22 46 32           ~ 5 0
63 Mol 109 Rad 19 39 33.2 +23 59 55           ~ 7 0
64 Mol 110 Rad 19 40 59.4 +24 04 39           ~ 10 0
65 Mol 114N Rad 20 06 59.954 +27 30 22.85           ~ 1 0
66 Mol 114S Rad 20 06 59.999 +27 30 18.13           ~ 1 0
67 Mol 114 Rad 20 07 06.7 +27 28 53           ~ 7 0
68 Mol 115 Rad 20 07 31.5 +33 59 39           ~ 6 0
69 Mol 116 Rad 20 08 09.8 +35 59 20           ~ 7 0
70 Mol 117C8 Rad 20 11 46.053 +36 49 39.23           ~ 1 0
71 Mol 117C9 Rad 20 11 46.072 +36 49 44.50           ~ 1 0
72 Mol 117C8/10 Rad 20 11 46.269 +36 49 41.08           ~ 1 0
73 Mol 117C11 Rad 20 11 46.389 +36 49 25.76           ~ 1 0
74 Mol 117 Rad 20 11 46.4 +36 49 37           ~ 7 0
75 Mol 117C10 Rad 20 11 46.451 +36 49 41.85           ~ 1 0
76 Mol 117C3 Rad 20 11 46.502 +36 49 35.74           ~ 1 0
77 Mol 117C7 Rad 20 11 46.536 +36 49 30.67           ~ 1 0
78 Mol 117C2/4 Rad 20 11 46.537 +36 49 40.19           ~ 1 0
79 Mol 117C2 Rad 20 11 46.584 +36 49 39.02           ~ 1 0
80 Mol 117C1 Rad 20 11 46.622 +36 49 38.16           ~ 1 0
81 Mol 117C1/3 Rad 20 11 46.702 +36 49 37.25           ~ 1 0
82 Mol 117C5 Rad 20 11 46.866 +36 49 33.46           ~ 1 0
83 Mol 117C6 Rad 20 11 46.890 +36 49 29.76           ~ 1 0
84 Mol 117C4 Rad 20 11 46.915 +36 49 36.13           ~ 1 0
85 Mol 118 Rad 20 12 31.3 +35 54 46           ~ 8 0
86 IRAS 20126+4104 Y*O 20 14 25.8816769656 +41 13 36.879427236           B2.5-B0.5 441 0
87 Mol 121S Rad 20 20 39.244 +39 37 50.98           ~ 1 0
88 LBN 077.61+01.59 HII 20 20 39.3 +39 37 52           ~ 78 0
89 Mol 121N Rad 20 20 39.470 +39 38 12.74           ~ 1 0
90 Mol 122 Rad 20 23 31.7 +39 57 23           ~ 5 0
91 Mol 123C2 Rad 20 23 55.015 +37 38 07.78           ~ 1 0
92 Mol 123C1 Rad 20 23 55.155 +37 38 13.00           ~ 1 0
93 IRAS 20220+3728 Y*O 20 23 55.2 +37 38 12           ~ 49 3
94 Mol 123C3 Rad 20 23 55.342 +37 38 10.52           ~ 1 0
95 Mol 125 Rad 20 29 46.9 +35 31 39           ~ 6 0
96 Mol 126 Rad 20 30 27.9 +41 15 48           ~ 7 0
97 Mol 129 Rad 20 35 09.5 +41 13 18           ~ 5 0
98 IRAS 20444+4629 MoC 20 45 59.64 +46 40 06.2           ~ 23 0
99 IRAS 21078+5211 HII 21 09 31.03 +52 24 16.1           ~ 56 0
100 IRAS 21307+5049 Y*O 21 32 30.59280 +51 02 16.0368           ~ 46 0
101 [BGE2002] BIMA 2 Y*O 21 40 42.36 +58 16 09.7           ~ 119 0
102 NAME IC 1396 North CGb 21 40 42.6537 +58 16 01.882           ~ 189 1
103 IRAS 21519+5613 HII 21 53 38.8 +56 27 53           ~ 38 0
104 LBN 102.79-00.92 HII 22 19 09.0 +56 04 45           ~ 104 0
105 IRAS 22172+5549 Y*O 22 19 09.14787 +56 05 00.0380           ~ 104 0
106 LDN 1204A HII 22 21 26.68 +63 51 38.2           ~ 110 0
107 IRAS 22305+5803 Y*O 22 32 23.972 +58 18 57.91           ~ 37 0
108 IRAS 22506+5944 Y*O 22 52 38.09760 +60 01 01.1928           ~ 58 0
109 IRAS 23026+5948 IR 23 04 45.4557529824 +60 04 37.582742172           ~ 21 0
110 Mol 155N Rad 23 16 10.819 +61 39 12.19           ~ 1 0
111 Mol 155S3 Rad 23 16 11.170 +61 37 52.76           ~ 1 0
112 Mol 155S2 Rad 23 16 11.448 +61 37 50.35           ~ 1 0
113 IRAS 23140+6121 IR 23 16 11.7 +61 37 45           ~ 33 0
114 Mol 155S1 Rad 23 16 11.768 +61 37 48.57           ~ 1 0
115 IRAS 23314+6033 HII 23 33 43.8650890512 +60 50 26.959478136           ~ 29 0
116 Mol 160 Rad 23 40 54.5 +61 10 28           ~ 105 0

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