J/A+A/631/A58 Oph A mosaic image (Coutens+, 2019)
VLA cm-wave survey of young stellar objects in the Oph A cluster:
constraining extreme UV- and X-ray-driven disk photoevaporation.
A pathfinder for Square Kilometre Array studies.
Coutens A., Liu H.B., Jimenez-Serra I., Bourke T.L., Forbrich J., Hoare M.,
Loinard L., Testi L., Audard M., Caselli P., Chacon-Tanarro A., Codella C.,
Di Francesco J., Fontani F., Hogerheijde M., Johansen A., Johnstone D.,
Maddison S., Panic O., Perez L.M., Podio L., Punanova A., Rawlings J.M.C.,
Semenov D., Tazzari M., Tobin J.J., van der Wiel M.H.D.,
van Langevelde H.J., Vlemmings W., Walsh C., Wilner D.
<Astron. Astrophys. 631, A58 (2019)>
=2019A&A...631a..58C 2019A&A...631a..58C (SIMBAD/NED BibCode)
ADC_Keywords: Protostars ; YSOs ; Radio continuum ; Stars, radio ;
Interstellar medium; Interferometry
Keywords: stars: formation - protoplanetary disks - radio continuum: stars -
stars: activity
Abstract:
Observations of young stellar objects (YSOs) in centimeter bands can
probe the continuum emission from growing dust grains, ionized winds,
and magnetospheric activity, which are intimately connected to the
evolution of protoplanetary disks and the formation of planets. We
have carried out sensitive continuum observations toward the Ophiuchus
A star-forming region using the Karl G. Jansky Very Large Array (VLA)
at 10GHz over a field-of-view of 6' with a spatial resolution of
θmajxθmin∼0.4"x0.2". We achieved a 5µJy/beam
root-mean-square noise level at the center of our mosaic field of
view. Among the eighteen sources we detected, sixteen are YSOs (three
Class 0, five Class I, six Class II, and two Class III) and two are
extragalactic candidates.We find that thermal dust emission generally
contributes less that 30% of the emission at 10GHz. The radio
emission is dominated by other types of emission such as
gyro-synchrotron radiation from active magnetospheres, free-free
emission from thermal jets, free-free emission from the outflowing
photo-evaporated disk material, and/or synchrotron emission from
accelerated cosmic-rays in jet or protostellar surface shocks. These
different types of emission could not be clearly disentangled. Our
non-detections towards Class II/III disks suggest that extreme
UV-driven photoevaporation is insufficient to explain the disk dispersal,
assuming that the contribution of UV photoevaporating stellar winds to
radio flux does not evolve with time. The sensitivity of our data
cannot exclude photoevaporation due to X-ray photons as an efficient
mechanism for disk dispersal. Deeper surveys with the Square Kilometre
Array will be able to provide strong constraints on disk
photoevaporation.
Description:
This mosaic image of the Oph A YSO cluster was obtained with the VLA
in most extended A array configuration, which provides a projected
baseline range from 310m to 34300m. It is the result of the
combination of five epochs of observations between 2 December 2016 and
22 January 2017
This mosaic image of the Oph A YSO cluster was obtained with the VLA
in most extended A array configuration, which provides a projected
baseline range from 310m to 34300m. It is the result of the
combination of five epochs of observations between 2 December 2016 and
22 January 2017. We used the 3-bit samplers and configured the
correlator to have 4GHz of continuous bandwidth coverage centered on
the sky frequency of 10GHz (X band) divided into 32 contiguous
spectral windows. The pointing centers of our observations are given
in Table 2. They are separated by 2.6', while the primary beam FWHM is
4.2'. In each epoch of observation, the total on-source observing time
for each pointing was 312 seconds. The quasar J1625-2527 was observed
approximately every 275 seconds for complex gain calibration. We
observed 3C286 as the absolute flux reference. The joint imaging of
these mosaic fields forms an approximately parallelogram-shaped,
mosaic field of view, of which the width and height are ∼6'. We
calibrated the data manually using the CASA software package,
following standard data calibration procedures. The imaging was done
with Briggs robust = 2.0 weighting, gridder='mosaic', specmode='mfs',
and nterms=1. At the average observing frequency, we obtained a
synthesized θmaxxθmin∼0.4"x0.2" and a maximum
detectable angular scale of ∼5"'(or ∼700au). After primary beam
correction, we achieved a root-mean-square (RMS) noise level of
∼5µJy/beam at the center of our mosaic field, degraded to
∼28µJy/beam toward the edges of the mosaic. The flux calibration
uncertainty is expected to be about 5%.
Objects:
-----------------------------------------
RA (2000) DE Designation(s)
-----------------------------------------
16 28 06 -24 32.5 Oph A = LDN 1688
-----------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 120 1 Information on fits imae
fits/* . 1 fits image
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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- 24 I5 --- Nx Number of pixels along X-axis
26- 30 I5 --- Ny Number of pixels along Y-axis
32- 53 A22 "datime" Obs.Date Observation date
55- 65 E11.6 Hz Freq Observed frequency
67- 72 I6 Kibyte size Size of FITS file
74-101 A28 --- FileName Name of FITS file, in subdirectory fits
103-120 A18 --- Title Title of the FITS file
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Acknowledgements:
Audrey Coutens, audrey.coutens(at)u-bordeaux.fr
(End) Patricia Vannier [CDS] 24-Sep-2019