J/A+A/624/A100 HII region G24.78+0.08 A1 images (Cesaroni+, 2019)
In-depth study of the hypercompact H II region G24.78+0.08 A1.
Cesaroni R., Beltran, M.T., Moscadelli L., Sanchez-Monge A., Neri R.
<Astron. Astrophys. 624, A100 (2019)>
=2019A&A...624A.100C 2019A&A...624A.100C (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; Radio continuum ; Radio lines
Keywords: stars: early-type - H II regions -
ISM individual objects: G24.78+0.08 - stars: winds, outflows
Abstract:
The earliest phases of the evolution of a massive star are closely
related to the developement of an HII region. Hypercompact HII
regions are the most interesting in this respect because they are very
young, and hence best suited to study the beginning of the expansion
of the ionised gas inside the parental core.
We have analysed the geometrical and physical structure of the
hypercompact HII region G24.78+0.08 A1, making use of new continuum
and hydrogen recombination line data (H41α, H63α,
H66α, H68α) and data from the literature (H30α,
H35α).
We fit the continuum spectrum with a homogenous, isothermal shell of
ionised gas at 104K and derive the size of the HII region and the
Lyman continuum luminosity of the ionising star. We also fit the
recombination line spectra emitted from the same shell with a model
taking into account expansion at constant speed.
The best fits to the continuum and line spectra allow the derivation
of the Lyman continuum luminosity of the ionising star, HII region
size, geometrical thickness of the shell, and expansion velocity.
Comparison between the 5cm and 7mm brightness temperature
distributions demonstrates that a thin layer of ionised gas of a few
1000K at the surface of the HII region is necessary to reproduce
the morphology of the continuum emission at both wavelengths.
We confirm that the G24 A1 hypercompact HII region consists of a
thin shell ionised by an O9.5 star. The shell is expanding at a speed
comparable to the sound speed in the ionised gas. The radius of the
HII region exceeds the critical value needed to trap the ionised
gas by the gravitational field of the star, consistent with the
observed expansion.
Description:
We make observations of G24 A1 with the VLA, the IRAM/Plateau de Bure
Interferometer, and the e-MERLIN.
Maps presented in Figs. 1, 3, and 4 of the article.
Objects:
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RA (2000) DE Designation(s)
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18 36 12.56 -07 13 10.8 G24.78+0.08 A = [FC2000] G024.79+0.08 A
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 142 12 List of fits images
fits/* . 12 Individual fits images
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 37 F8.4 km/s RV ? Radial velocity
39- 45 F7.4 GHz Freq ? Observed frequency
47- 51 I5 Kibyte size Size of FITS file
53- 97 A45 --- FileName Name of FITS file, in subdirectory fits
99-142 A44 --- Title Title of the FITS file
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Acknowledgements:
Riccardo Cesaroni, cesa(at)arcetri.inaf.it
(End) Patricia Vannier [CDS] 13-Feb-2019