2001ApJ...553..254O


Query : 2001ApJ...553..254O

2001ApJ...553..254O - Astrophys. J., 553, 254-266 (2001/May-3)

High-resolution mid-infrared imaging and spectroscopic observations of a massive star forming region W51 IRS 2.

OKAMOTO Y.K., KATAZA H., YAMASHITA T., MIYATA T. and ONAKA T.

Abstract (from CDS):

Mid-infrared (7.8-13.5µm) imaging and low-resolution spectroscopic observations were made for the massive star-forming region W51 IRS 2 with spatial resolution of 1". IRS 2 was resolved into seven sources based on the continuum and the emission line maps. The nature of these sources was investigated using their thermal dust emission, the 9.7 µm absorption feature, and/or three fine-structure emission lines of [Ne II] at 12.8 µm, [Ar III] at 8.99 µm, and [S IV] at 10.51 µm. Four of the sources were identified as ultracompact H II regions and one as an embedded protostar candidate. The spectral types of the ionizing sources are derived from the line ratios to be all around O9, which is much later than those (O5.5 and O7.5) derived from the radio continuum fluxes. The observed line ratios of (ultra-)compact H II regions in IRS 2 and in the literature follow a single excitation track, but it is different from that predicted from model calculations. We propose two possible resolutions for the discrepancy: (1) the employed models for the stellar atmosphere are not sufficiently accurate in the UV range, or (2) the (ultra-)compact H II regions are ionized by stellar clusters.

Abstract Copyright:

Journal keyword(s): ISM: Dust, Extinction - ISM: H II Regions - Infrared: ISM: Continuum - Infrared: ISM: Lines and Bands - ISM: individual (W51) - Stars: Formation

Nomenclature: Fig.1, Table 2: OKYM W51 IRS 2 N (Nos 1-7).

Simbad objects: 41

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Number of rows : 41
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 IC 1795 HII 02 25 43.5 +62 06 13           ~ 236 0
2 [RLK73] IRc 2 IR 05 35 14.51548 -05 22 30.5943           ~ 619 1
3 NGC 2170 RNe 06 07 48 -06 23.1           ~ 41 0
4 NGC 3576 HII 11 11 49.8 -61 18 14           ~ 234 2
5 [GS70] 298.2-00.3 HII 12 10 01.886 -62 50 00.46           ~ 66 1
6 * alf Her ** 17 14 38.85818 +14 23 25.2262   4.51 3.06     M5Ib-II+G5III+F2V: 195 0
7 M 8 HII 18 03 37 -24 23.2           ~ 598 1
8 NAME W 33-Met HII 18 14 12.5 -17 55 44           ~ 28 0
9 MSX6C G025.3953+00.0336 Y*O 18 37 30.58 -06 41 19.6           ~ 41 2
10 GAL 025.38-00.18 HII 18 38 14 -06 47.6           ~ 37 0
11 GAL 029.9-00.0 HII 18 46 08.0 -02 40 41           ~ 34 0
12 GAL 045.1+00.1 HII 19 13.4 +10 51           ~ 13 0
13 GRS G045.50 +00.06 HII 19 14.4 +11 12           ~ 3 0
14 [WBN74] W 51 IRS 2W Y*O 19 23 39.787 +14 31 07.46           ~ 16 0
15 OKYM W51 IRS 2 6 IR 19 23 39.816 +14 31 05.07           ~ 24 0
16 [WBN74] W 51 IRS 2 PCG 19 23 39.93 +14 31 09.4           ~ 277 0
17 [WBN74] W 51 IRS 2E Y*O 19 23 40.167 +14 31 06.63           ~ 22 0
18 W 51 SNR 19 23 50 +14 06.0           ~ 1242 1
19 SH 2-88 B HII 19 46 47.32920 +25 12 45.6230           ~ 156 2
20 GAL 075.84+00.4 HII 20 22 +37.6           ~ 2 0
21 SH 2-106 HII 20 27 26.8 +37 22 49           ~ 432 2
22 [IF78] S106 C HII 20 27 27.4 +37 23 06           ~ 5 0
23 DR 22 HII 20 39 16.67 +41 18 44.7           ~ 47 1
24 * bet Peg LP* 23 03 46.45746 +28 04 58.0336 6.05 4.09 2.42 0.92 -0.40 M2.5II-III 586 0
25 [WBN74] NGC 7538 IRS 2 Y*? 23 13 45.4691116296 +61 28 19.985984832           ~ 73 0
26 SH 2-159 Y*O 23 15 31.27440 +61 07 10.4450           ~ 179 2
27 OKYM W51 IRS 2 1 IR ~ ~           ~ 2 0
28 NAME NGC 2170 IRS 1 IR ~ ~           ~ 2 0
29 W 51d1 Rad ~ ~           ~ 12 0
30 OKYM W51 IRS 2 7 IR ~ ~           ~ 1 0
31 [LBG82] G298.2-0.3 W IR ~ ~           ~ 2 0
32 [LBG82] NGC 3576 7 IR ~ ~           ~ 2 0
33 [LBG82] NGC 3576 6 IR ~ ~           ~ 2 0
34 [LBG82] NGC 3576 5 IR ~ ~           ~ 2 0
35 [LBG82] NGC 3576 3 IR ~ ~           ~ 2 0
36 [LBG82] NGC 3576 2 IR ~ ~           ~ 2 0
37 [LBG82] NGC 3576 1 IR ~ ~           ~ 2 0
38 [LBG82] G298.2-0.3 E IR ~ ~           ~ 2 0
39 OKYM W51 IRS 2 5 HII ~ ~           ~ 2 0
40 OKYM W51 IRS 2 4 IR ~ ~           ~ 2 0
41 OKYM W51 IRS 2 2 HII ~ ~           ~ 1 0

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2023.02.06-07:02:08

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