J/A+A/635/A187 Massive binaries in Westerlund 1. VII. (Clark+, 2020)
A VLT/FLAMES survey for massive binaries in Westerlund 1. VII. Cluster census.
Clark J.S., Ritchie B.W., Negueruela I.
<Astron. Astrophys., 635, A187 (2020)>
=2020A&A...635A.187C 2020A&A...635A.187C (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Populations, stellar ; Photometry ;
Spectral types
Keywords: stars: early-type - stars: evolution -
open clusters and associations: individual: Westerlund 1
Abstract:
Context. The formation, properties, and evolution of massive stars
remain subject to considerable theoretical and observational
uncertainty. This impacts on fields as diverse as galactic feedback,
the production of cosmic rays, and the nature of the progenitors of
both electromagnetic and gravitational wave transients. Aims. The
young massive clusters many such stars reside within provide a unique
laboratory for addressing these issues. In this work we provide a
comprehensive stellar census of Westerlund 1 in order to to underpin
such efforts. Methods. We employed optical spectroscopy of a large
sample of early-type stars to determine cluster membership for
photometrically-identified candidates, characterise their spectral
type, and identify new candidate spectroscopic binaries. Results.
Sixty nine new members of Westerlund 1 are identified via I-band
spectroscopy. Together with previous observations, they illustrate a
smooth and continuous morphological sequence from late-O giant through
to OB supergiant. Subsequently, the progression bifurcates, with one
branch yielding mid-B to late-F hypergiants, and cool supergiants, and
the other massive blue stragglers prior to a diverse population of
H-depleted WRs. We identify a substantial population of O-type stars
with very broad Paschen series lines, a morphology that is directly
comparable to known binaries in the cluster. In a few cases additional
low-resolution R-band spectroscopy is available, revealing
double-lined He I profiles and confirming binarity for these objects;
suggesting a correspondingly high binary fraction amongst relatively
unevolved cluster members.Conclusions. Our current census remains
incomplete, but indicates that Westerlund 1 contains at least 166
stars with initial masses estimated to lie between ∼25M☉ and
∼50M☉, with more massive stars already lost to supernova. Our
data is consistent with the cluster being co-eval, although binary
interaction is clearly required to yield the observed stellar
population, which is characterised by a uniquely rich cohort of
hypergiants ranging from spectral type O to F, with both mass-stripped
primaries and rejuvenated secondaries or merger products present.
Future observations of Wd1 and similar stellar aggregates hold out the
prospect of characterising both single- and binary- evolutionary
channels for massive stars and determining their relative
contributions. This in turn will permit the physical properties of
such objects at the point of core-collapse to be predicted, which is
of direct relevance for understanding the formation of relativistic
remnants such as the magnetars associated with Wd1 and other young
massive clusters.
Description:
We present classifications of a further 69 members of Wd1, producing a
current census of 166 massive, evolved stars.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 112 166 Stellar population of Westerlund 1
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See also:
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)
J/A+A/477/147 : X-ray sources in Westerlund 1 (Clark+, 2008)
J/A+A/623/A83 : Blue stragglers Wd1-27 and Wd1-30a spectra (Clark+, 2019)
J/A+A/632/A38 : Westerlund 1 reduced images of radio emission (Andrews+, 2019)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- ID Primary optical identifier for the sources
7- 8 I2 h RAh Right ascension (J2000)
10- 11 I2 min RAm Right ascension (J2000)
13- 17 F5.2 s RAs Right ascension (J2000)
19 A1 --- DE- Declination sign (J2000)
20- 21 I2 deg DEd Declination (J2000)
23- 24 I2 arcmin DEm Declination (J2000)
26- 29 F4.1 arcsec DEs Declination (J2000)
31- 34 F4.1 mag Bmag ? B magnitude (1)
36- 40 F5.2 mag Vmag ? V magnitude (1)
42- 46 F5.2 mag Rmag ? R magnitude (1)
48- 52 F5.2 mag Imag ? I magnitude (1)
54- 70 A17 --- SpType Spectral type
73-112 A40 --- Notes Notes (2)
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Note (1): B-, V-, R- and I-band photometry derived from the dataset described in
Clark et al. (2005A&A...434..949C 2005A&A...434..949C) and, if not available,
Bonanos (2007, Cat. J/AJ/133/2696).
Note (2): other designations (including the W2xxx and W3xxx designations
previously employed but superseded by this work) and notes regarding spectral
appearance and variability,
with Eclipsing (E) and Periodic (P) photometric variables and
Radial Velocity (RV) spectroscopic variables listed with their relevant
periods.
The vast majority of classifications derive from this work,
Clark et al. (2005A&A...434..949C 2005A&A...434..949C), Crowther et al. (2006MNRAS.372.1407C 2006MNRAS.372.1407C),
and Negueruela et al. (2010A&A...516A..78N 2010A&A...516A..78N), with exceptions highlighted.
References. Additional data used in the construction of this table from
(1) = Bonanos (2007, Cat. J/AJ/133/2696)
(2) = Ritchie et al. (2009A&A...507.1585R 2009A&A...507.1585R)
(3) = Ritchie et al. (2010A&A...520A..48R 2010A&A...520A..48R)
(4) = Ritchie et al. (2011BSRSL..80..628R 2011BSRSL..80..628R)
(5) = Clark et al. (2010A&A...514A..87C 2010A&A...514A..87C)
(6) = Clark (2011A&A...531A..28C 2011A&A...531A..28C)
(7) = Koumpia & Bonanos (2012A&A...547A..30K 2012A&A...547A..30K)
(8) = Clark et al. (2013A&A...560A..11C 2013A&A...560A..11C)
(9) = Clark et al. (2014A&A...565A..90C 2014A&A...565A..90C)
(10) = Clark et al. (2019A&A...623A..83C 2019A&A...623A..83C)
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History:
From electronic version of the journal
References:
Ritchie et al., Paper I 2009A&A...507.1585R 2009A&A...507.1585R
Ritchie et al., Paper II 2010A&A...520A..48R 2010A&A...520A..48R
Clark et al., Paper III 2011A&A...531A..28C 2011A&A...531A..28C
Clark et al., Paper IV 2014A&A...565A..90C 2014A&A...565A..90C
Clark et al., Paper V 2019A&A...623A..83C 2019A&A...623A..83C
Clark et al., Paper VI 2019A&A...626A..59C 2019A&A...626A..59C
(End) Patricia Vannier [CDS] 15-Jun-2020