2005A&A...431..183A


Query : 2005A&A...431..183A

2005A&A...431..183A - Astronomy and Astrophysics, volume 431, 183-195 (2005/2-3)

Dust content in compact HII regions (NGC 7538-IRS1, IRS2, and IRS3).

AKABANE K. and KUNO N.

Abstract (from CDS):

The luminosity of the central star of the compact HII regions of NGC 7538 was estimated from the solid angle of the IR sources subtended relative to the central star, and was found to be 5∼10 times as intense as that of IR sources. Under the single central star approximation, the luminosity gives a stellar UV photon rate NU(*) (s–1) of ∼3.0x1048, ∼1.5x1049, ∼5.1x1049, and ∼1.7x1047 for the compact HII regions of NGC 7538-IRS1(A/2), B, IRS2, and IRS3, respectively. NU (*) and the observed electron density, ne, provide the dust opacity of the ionizing photon, τSd, for the optical path out to the Stroemgren sphere radius rS, assuming a gas with standard dust content. Ionizing photon opacity over the same optical path but with the actual dust content τSda is also derived from ri/rS, where ri is the radius of the ionized sphere, which is estimated from NU(*) and the observed volume emission measure ne2 (4πri3/3) (Spitzer, Physical Processes in the Interstellar Medium (New York: John Wiley and Sons, Inc.), 103]). An observational trend of γ{NU(*)/4πri2}1/2∼constant, where γ=τSdaSd, was obtained for the 4 compact HII regions of the NGC 7538(N). Fourteen selected compact HII regions from data catalogued by VLA observations were examined for this trend, and a similar result was obtained. A limit of γ as 15≥γ≥0.1 was given for the 14 selected sources. The size of the dust-depleted cavity of the NGC 7538(N) suggested by Chini et al. (1986A&A...167..315C) coincides with that of the ionized sphere of the IRS2 of the region.

Abstract Copyright:

Journal keyword(s): HII regions - infrared: ISM - radio continuum: ISM - dust, extinction

CDS comments: Table 3: IRAS1 not identified.

Simbad objects: 8

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Number of rows : 8
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 NGC 7538 OpC 23 13 37 +61 30.0           ~ 873 1
2 [WBN74] NGC 7538 IRS 3 Y*? 23 13 43.646 +61 28 14.02           ~ 65 0
3 NAME NGC 7538 IRS 1-3 reg 23 13 45 +61 28.3           ~ 26 1
4 [WBN74] NGC 7538 IRS 1 Y*O 23 13 45.318 +61 28 11.69           ~ 411 3
5 [WBN74] NGC 7538 IRS 1S Rad 23 13 45.382 +61 28 10.53           ~ 5 0
6 [WBN74] NGC 7538 IRS 1N Rad 23 13 45.382 +61 28 10.70           ~ 7 0
7 [WBN74] NGC 7538 IRS 2 Y*? 23 13 45.4691116296 +61 28 19.985984832           ~ 74 0
8 IRAS 23118+6110 Y*O 23 14 02.09473 +61 27 18.8460           ~ 373 0

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