J/A+A/616/A66 6.7GHz CH3OH maser in G24.78+0.08 (Moscadelli+, 2018)
The feedback of an HC HII region on its parental molecular core.
The case of core A1 in the star-forming region G24.78+0.08.
Moscadelli L., Rivilla V.M., Cesaroni R., Beltran M.T., Sanchez-Monge A.,
Schilke P., Mottram J.C., Ahmadi A., Allen V., Beuther H., Csengeri T.,
Etoka S., Galli D., Goddi C., Johnston K.G., Klaassen P.D., Kuiper R.,
Kumar M.S.N., Maud L.T., Moller T., Peters T., Van der Tak F., Vig S.
<Astron. Astrophys., 616, A66 (2018)>
=2018A&A...616A..66M 2018A&A...616A..66M (SIMBAD/NED BibCode)
ADC_Keywords: Star Forming Region ; Masers
Keywords: techniques: interferometric - masers - ISM: jets and outflows -
ISM: molecules - radio continuum: ISM
Abstract:
G24.78+0.08 is a well known high-mass star-forming region,
where several molecular cores harboring OB young stellar objects are
found inside a clump of size ~=1pc. This article focuses on the most
prominent of these cores, A1, where an intense hypercompact (HC) HII
region has been discovered by previous observations.
Our aim is to determine the physical conditions and the kinematics of
core A1, and study the interaction of the HII region with the parental
molecular core.
We combine ALMA 1.4mm high-angular resolution (~=0.2'') observations
of continuum and line emission with multi-epoch Very Long Baseline
Interferometry data of water 22GHz and methanol 6.7GHz masers. These
observations allow us to study the gas kinematics on linear scales
from 10 to 104au, and to accurately map the physical conditions of
the gas over core A1.
The 1.4mm continuum is dominated by free-free emission from the
intense HC HII region (size~=1000au) observed to the North of core A1
(region A1N). Analyzing the H30α line, we reveal a fast bipolar
flow in the ionized gas, covering a range of LSR velocities (VLSR) of
~=60km/s. The amplitude of the VLSR gradient, 22km/s/mpc, is one of
the highest so far observed towards HC HII regions. Water and methanol
masers are distributed around the HC HII region in A1N, and the maser
three-dimensional (3D) velocities clearly indicate that the ionized
gas is expanding at high speed (≥200km/s) into the surrounding
molecular gas. The temperature distribution (in the range 100-400K)
over core A1, traced with molecular (CH3OCHO, 13CH3CN,
13CH3OH, and CH3CH2CN) transitions with level energy in the
range 30K≤Eu/k≤300K, reflects the distribution of shocks produced
by the fast-expansion of the ionized gas of the HII region. The
high-energy (550K≤Eu/k≤800K) transitions of vibrationally excited
CH3CN are likely radiatively pumped, and their rotational
temperature can significantly differ from the kinetic temperature of
the gas. Over core A1, the VLSR maps from both the 1.4mm molecular
lines and the 6.7GHz methanol masers consistently show a VLSR gradient
(amplitude ~=0.3km/s/mpc) directed approximately S-N. Rather than
gravitationally supported rotation of a massive toroid, we interpret
this velocity gradient as a relatively slow expansion of core A1.
Description:
We observed G24.78+0.08 (tracking center: RA=18:36:12.55 (J2000),
DE=-07:12:10.9) with the European VLBI Network3 (EVN) in the 51-60
A+ CH3 OH transition (rest frequency 6.668519GHz). Data were taken
at three epochs: 2007, March 20 (program code: EM064B), 2009, March 12
(EM064F), and 2012, November 3 (EM099B).
Objects:
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RA (2000) DE Designation(s)
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18 36.2 -07 13 G24.78+0.08 = GAL 024.78+00.08
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 76 60 6.7GHz CH3OH maser parameters for G24.78+0.08 A1
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- Cluster [A1N A1SW CM] Cluster name or
CM for Centers of Motion
6- 11 A6 --- Feat Feature label number
12 A1 --- n_Feat [b] Note (1)
14- 18 A5 --- Epochs Observing epochs at which the feature was
detected (2)
21- 25 F5.2 Jy/beam Ipeak ?=- Intensity of the strongest spot,
averaged over the observing epochs
at restfreq=6.668519GHz
27- 31 F5.1 km/s VLSR Intensity-weighted LSR velocity,
averaged over the observing epochs
33- 39 F7.2 mas oRA Position offset along RA (3)
41- 44 F4.2 mas e_oRA rms uncertainty on oRA (3)
46- 52 F7.2 mas oDE Position offset along DE (3)
54- 57 F4.2 mas e_oDE rms uncertainty on oDE (3)
59- 62 F4.1 km/s Vx ?=- Component of the relative proper motion
along RA (4)
64- 66 F3.1 km/s e_Vx ? rms uncertainty on Vx (4)
68- 72 F5.1 km/s Vy ?=- Component of the relative proper motion
along DE (4)
74- 76 F3.1 km/s e_Vy ? rms uncertainty on Vy (4)
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Note (1): b: Feature with not reliable proper motion, even if observed at
three epochs.
Note (2): The three observing epochs are as follows:
1 = 2007 March 20
2 = 2009 March 12
3 = 2012 November 3
Note (3): Position offsets along the RA and Dec axes, relative to the persistent
feature #1 of cluster A1N, measured at the first epoch of detection
he absolute position of the reference feature #1 in cluster A1N at the
observing epoch on March 20, 2007, is:
RA=18:36:12.5625 (J2000), DE=-7:12:10.811, with an accuracy of ±1mas.
Note (4): Components of the relative proper motion along the RA and Dec axes,
measured with respect to the reference feature #0-A1N
(the "center of motion" of cluster A1N).
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 14-Nov-2018