J/A+A/694/A26 Radio flux variability in UCHII regions (Yang+, 2025)
Dynamic massive star formation: Radio flux variability in UCHII regions.
Yang A.Y., Thompson M.A., Urquhart J.S., Brunthaler A., Menten K.M.,
Gong Y., Tsai C.-W., Patel A.L., Li D., Cotton W.D.
<Astron. Astrophys. 694, A26 (2025)>
=2025A&A...694A..26Y 2025A&A...694A..26Y (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; H II regions ; Radio continuum
Keywords: instrumentation: interferometers - stars: formation - HII regions -
radio continuum: general
Abstract:
Theoretical models of early accretion during the formation process of
massive stars have predicted that HII regions exhibit radio
variability on timescales of decades. However, large-scale searches
for such temporal variations with sufficient sensitivity have not yet
been carried out.
We aim to identify HII regions with variable radio wavelength fluxes
and to investigate the properties of the identified objects,
especially those with the highest level of variability.
We compared the peak flux densities of 86 ultracompact HII (UCHII)
regions measured by the GLOSTAR and CORNISH surveys and identified
variables that show flux variations higher than 30% over ∼8yr
timespan between these surveys.
We found a sample of 38 variable UCHII regions, which is the largest
sample identified to date. The overall occurrence of variability is
44±5%, suggesting that variation in UCHII regions is significantly
more common than prediction. The variable UCHII regions are found to
be younger than non-variable UCHII regions, with over 50% of them
meeting the size criterion of hypercompact (HC) HII regions. We
studied the 7 UCHII regions (the "Top7") that show the highest
variability with variations >100%. The Top7 variable UCHII regions
are optically thick at 4-8GHz and compact, suggesting they are in a
very early evolutionary stage of HCHII or UCHII regions. There is a
significant correlation between variability and the spectral index of
the radio emission. No dependence is observed between the variations
and the properties of the sources' natal clumps traced by
submillimeter continuum emission from dust, although variable HII
regions are found in clumps at an earlier evolutionary stage.
Description:
Both GLOSTAR and CORNISH observations were made in the C-band (4-8GHz)
in the B and BnA configurations of the classic VLA (or the upgraded
JVLA in the case of GLOSTAR).
Table1 contains the sample of the 38 variable UCHII regions that we
have identified in the GLOSTAR and CORNISH at 5GHz for the region
between 10<l<40 and 56<l<60.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 117 38 The sample of 38 UCHII with radio flux variations
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See also:
J/A+A/627/A175 : GLOSTAR. Radio Source Catalogue I (Medina+ 2019)
J/A+A/670/A9 : GLOSTAR. Radio Source Catalogue. II. (Dzib+, 2023)
J/A+A/680/A92 : GLOSTAR. Radio Source Catalogue. III. (Yang+, 2023)
J/ApJS/205/1 : CORNISH project II. Source catalog (Purcell+, 2013)
J/A+A/615/A103 : A catalogue of northern ultra-compact H II regions
(Kalcheva+, 2018)
J/MNRAS/473/1059 : Complete sample of Galactic clumps (Urquhart+, 2018)
J/ApJS/235/3 : Massive outflows associated with ATLASGAL clumps
(Yang+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- Name Galactic name (GLLL.llll+BB.bbbb)
19- 26 F8.5 deg GLON Galactic longitude
28- 35 F8.5 deg GLAT Galactic latitude
37- 45 F9.5 deg RAdeg Right Ascension (J2000)
47- 55 F9.5 deg DEdeg Declination (J2000)
57- 61 F5.2 mJy/beam SpeakG Peak flux density GLOSTAR at 5GHz
63- 66 F4.2 mJy/beam e_SpeakG Uncertainty in SpeakG at 5GHz
68- 72 F5.2 mJy/beam SpeakC Peak flux density CORNISH at 5GHz
74- 77 F4.2 mJy/beam e_SpeakC Uncertainty in SpeakC at 5GHz
79- 82 F4.2 arcsec thetaS Angular scale (geometric average)
84- 87 F4.2 arcsec thetadcon Deconvolved angular scale
88 A1 --- n_thetadcon [*] Note on thetadcon (1)
90- 95 F6.3 pc Diam []?=- Linear diameter of the source
97-100 F4.1 pc Dist []?=- Heliocentric distance
102-106 F5.1 pc fvar ?=- Flux variation fraction
108-112 F5.2 --- alpha ?=- Spectral index fitted from the
sub-images of GLOSTAR (2)
114-117 F4.2 --- e_alpha ?=- Uncertainty of the spectral index from
the fitting process of the sub-images of
GLOSTAR
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Note (1): * refers to unresolved sources that have angular sizes <1.5" and
their thetadcon are considered the upper-limit values. The upper-limit of
thetadcon is set to be 0.32", which corresponds to one standard deviation of
the distribution of beam sizes from the CORNISH survey.
Note (2): "---" means that the alpha is unreliable and not adopted.
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Acknowledgements:
Aiyuan Yang, ayyang(at)mpifr-bonn.mpg.de
(End) Patricia Vannier [CDS] 29-Nov-2024