J/A+A/620/A31 ALMA maps of G17.64+0.16 (Maud+, 2018)
Chasing discs around O-type (proto)stars:
ALMA evidence for an SiO disc and disc wind from G17.64+0.16.
Maud L.T., Cesaroni R., Kumar M.S.N, van der Tak F.F.S, Allen V.,
Hoare M.G., Klaassen P.D., Harsono D., Hogerheijde M.R.,
Sanchez-Monge A., Schilke P., Ahmadi A., Beltran M.T., Beuther H.,
Csengeri T., Etoka S., Fuller G., Galvan-Madrid R., Goddi C., Henning T.,
Johnston K.G., Kuiper R., Lumsden S., Moscadelli L., Mottram J.C.,
Peters T., Rivilla V.M., Testi L., Vig S., de Wit W.J., Zinnecker H.
<Astron. Astrophys. 620, A31 (2018)>
=2018A&A...620A..31M 2018A&A...620A..31M (SIMBAD/NED BibCode)
ADC_Keywords: Infrared sources ; Millimetric/submm sources ; Interferometry;
YSOs
Keywords: stars: formation - stars: protostars - stars: massive -
stars: winds, outflows - stars: pre-main sequence -
submillimeter: stars
Abstract:
We present high angular resolution (∼0.2") continuum and molecular
emission line Atacama Large Millimeter/sub-millimeter Array (ALMA)
observations of G17.64+0.16 in Band 6 (220-230GHz) taken as part of a
campaign in search of circumstellar discs around (proto)-O-stars. At a
resolution of ∼400au the main continuum core is essentially unresolved
and isolated from other strong and compact emission peaks. We detect
SiO (5-4) emission that is marginally resolved and elongated in a
direction perpendicular to the large-scale outflow seen in the 13CO
(2-1) line using the main ALMA array in conjunction with the Atacama
Compact Array (ACA). Morphologically, the SiO appears to represent a
disc-like structure. Using parametric models we show that the
position-velocity profile of the SiO is consistent with the Keplerian
rotation of a disc around an object between 10-30M☉ in mass,
only if there is also radial expansion from a separate structure. The
radial motion component can be interpreted as a disc wind from the
disc surface. Models with a central stellar object mass between 20 and
30M☉ are the most consistent with the stellar luminosity
1x105L☉) and indicative of an O-type star. The H30α
millimetre recombination line (231.9GHz) is also detected, but
spatially unresolved, and is indicative of a very compact, hot,
ionised region co-spatial with the dust continuum core. The broad
line-width of the H30α emission
(Full-Width-Half-Maximum=81.9km/s is not dominated by
pressure-broadening but is consistent with underlying bulk motions.
These velocities match those required for shocks to release silicon
from dust grains into the gas phase. CH3CN and CH3OH thermal
emission also shows two arc shaped plumes that curve away from the
disc plane. Their coincidence with OH maser emission suggests that
they could trace the inner working surfaces of a wide-angle wind
driven by G17.64 which impacts the diffuse remnant natal cloud before
being redirected into the large-scale outflow direction. Accounting
for all observables, we suggest that G17.64 is consistent with a
O-type young stellar object in the final stages of protostellar
assembly, driving a wind, but that has not yet developed into a
compact HII region. The existence and detection of the disc in G17.64
is likely related to its isolated and possibly more evolved nature,
traits which may underpin discs in similar sources.
Description:
We observed G17.64+0.16 (AFGL 2136) with the 12m array of ALMA during
cycle 2 in July and September 2015 (2013.1.00489.S). With baselines
between 40 to 1500m the typical resulting resolution was ∼0.2". We
covered a board continuum band (bandwidth=1.875GHz) and also had many
higher frequency resolution, narrow bandwidth spectral windows
targetting lines. Here we provide continuum maps, and the data cubes
of 13CO, SiO, CH3CN K=3 and K=4, CH3OH and H30α. Continuum
images as presented in the paper are mode with a briggs robust 0.5 and
1.5, whereas all data cubes for the molecular lines use robust 0.5
only. The data from the 12m observations were all self-calibrated
using the strong point-like continuum source. In addition we provide
ACA data that was taken on 27 November 2016 of the 13CO line. This
data is calibrated by the standard ALMA pipeline.
Objects:
------------------------------------------------------------------------
RA (2000) DE Designation(s)
------------------------------------------------------------------------
18 22 26.385 -13 30 11.97 AFGL 2136 IRS 1 = MSX6C G017.6380+00.1566
------------------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 151 9 List of fits files
fits/* . 9 Individual fits files
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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- 2 I2 h RAh Right ascension (J2000.0)
4- 5 I2 min RAm Right ascension (J2000.0)
7- 12 F6.3 s RAs Right ascension (J2000.0)
14 A1 --- DE- Declination sign (J2000.0)
15- 16 I2 deg DEd Declination (J2000.0)
18- 19 I2 arcmin DEm Declination (J2000.0)
21- 25 F5.2 arcsec DEs Declination (J2000.0)
27- 30 I4 --- Nx Number of pixels along X-axis
32- 35 I4 --- Ny Number of pixels along Y-axis
37- 39 I3 --- Nz ? Number of slices
41- 63 A23 "datime" Obs.date Observation date (YYYY-MM-DDThh:mm:ss.sss)
65- 71 F7.3 GHz RefFreq Reference frequency of the cube at Nz=0
73- 78 F6.1 kHz dFreq ? Frequency resolution for datacubes
80- 86 I7 --- Kibyte size Size of FITS file
88-112 A25 --- FileName Name of FITS file, in subdirectory fits
114-151 A38 --- Title Description of FITS image
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Acknowledgements:
Luke Maud, maud(at)strw.leidenuniv.nl
(End) Patricia Vannier [CDS] 11-Oct-2018