J/A+A/632/A38 Westerlund 1 reduced images of radio emission (Andrews+, 2019)
A radio census of the massive stellar cluster Westerlund 1.
Andrews H., Fenech D., Prinja R.K., Clark J.S., Hindson L.
<Astron. Astrophys. 632, A38 (2019)>
=2019A&A...632A..38A 2019A&A...632A..38A (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Stars, radio ; Radio continuum
Keywords: stars: massive - stars: mass loss - stars: wind, outflows -
supergiants - stars: Wolf-Rayet - binaries: general
Abstract:
Massive stars and their stellar winds are important for a number of
feedback processes. The mass lost in the stellar wind can help
determine the end-point of the star as a neutron star (NS) or a black
hole (BH). However, the impact of mass loss on the post-main sequence
evolutionary stage of massive stars is not well understood. Westerlund
1 is an ideal astrophysical laboratory in which to study massive stars
and their winds in great detail over a large range of different
evolutionary phases. We aim to study the radio emission from
Westerlund 1, in order to measure radio fluxes from the population of
massive stars, and determine the mass-loss rates and spectral indices
where possible. Observations were carried out in 2015 and 2016 with
the Australia Telescope Compact Array (ATCA) at 5.5 and 9GHz using
multiple configurations, with maximum baselines ranging from 750m to
6km. Thirty stars are detected in the radio from the fully
concatenated dataset, ten of which are Wolf Rayet stars (WRs)
(predominantly late type WN stars), five yellow hypergiants (YHGs),
four red supergiants (RSGs), one luminous blue variable (LBV), the
sgB[e] star W9, and several OB supergiants. New source detections in
the radio are found for the WR stars, and five OB supergiants. These
detections lead to evidence for three new OB supergiant binary
candidates, which is inferred from derived spectral index limits.
Spectral indices and index limits were determined for massive stars in
Westerlund 1. For cluster members found to have partially optically
thick emission, mass-loss rates were calculated. Under the
approximation of a thermally emitting stellar wind and a steady
mass-loss rate, clumping ratios were then estimated for eight WRs.
Diffuse radio emission was detected throughout the cluster. Detections
of knots of radio emission with no known counterparts indicate the
highly clumped structure of this intra-cluster medium, likely shaped
by a dense cluster wind.
Description:
Radio continuum observations centred on the massive stellar cluster
Westerlund 1 were taken at two spectral windows, centered at 5.5 and
9GHz, over 4 different array configurations, with varying resolutions
due to the different maximum baselines of the array for each, at 6km,
1.5km and 750m. Source images of the 30 radio sources detected with
known stellar counterparts and images representing different data
combinations of continuum observations of the total field of view
containing the stellar cluster are presented.
Objects:
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RA (2000) DE Designation(s)
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16 47 04.00 -45 51 04.9 Westerlund 1 = Cl Westerlund 1
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 172 17 List of fits images
fits/* . 17 Individual fits images
figs/* . 45 Individual fits images presented in the
figures of the paper
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See also:
J/A+A/477/147 : X-ray sources in Westerlund 1 (Clark+, 2008)
J/A+AS/127/423 : VI photometry of Westerlund 1 and 2 (Piatti+ 1998)
J/AJ/133/2696 : BVRI light curves of Westerlund 1 stars (Bonanos, 2007)
J/AJ/145/46 : UBVIc photometry in Westerlund 1 (Lim+, 2013)
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- 36 F7.5 GHz Freq ? Observed frequency
38- 47 A10 "date" Obs.date Observation date
49- 53 I5 Kibyte size Size of FITS file
55- 68 A14 --- FileName Name of FITS file, in subdirectory fits
70-172 A103 --- Title Title of the FITS file
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Acknowledgements:
Holly Andrews, holly.andrews.16(at)ucl.ac.uk
(End) Holly Andrews [UCL, UK], Patricia Vannier [CDS] 07-Nov-2019