J/A+A/660/A89 Massive binaries in Westerlund 1. VIII. (Ritchie+, 2022)
A VLT/FLAMES survey for massive binaries in Westerlund 1.
VIII. Binary systems and orbital parameters.
Ritchie B.W., Clark J.S., Negueruela I., Najarro F.
<Astron. Astrophys., 660, A89 (2022)>
=2022A&A...660A..89R 2022A&A...660A..89R (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Stars, double and multiple ; Radial velocities ; Optical
Keywords: stars: evolution - supergiants - binaries: general -
techniques: radial velocities
Abstract:
The galactic cluster Westerlund 1 contains a rich population of
evolved, massive stars. A high binary fraction has been inferred from
previous multi-wavelength observations. Aims. We use multi-epoch
spectroscopy of a large sample of early-type stars in Westerlund 1 to
identify new binaries and binary candidates in the cluster.
VLT/FLAMES was used with the GIRAFFE spectrograph in HR21 mode to
obtain spectra of ∼100 OB stars over a 14-month baseline in 2008 and
2009, supplemented with follow-up observations in 2011 and 2013.
Radial velocities were obtained from strong Paschen series absorption
lines in the I-band.
We identify 20 new OB I-III binaries, a WN9h binary, and a WC9d
binary, greatly increasing the number of directly confirmed binary
systems in Westerlund 1, while 12 O9-9.5 Iab-III stars are identified
as candidate binaries based on radial velocity changes that are
inconsistent with photospheric variability. The 173.9 day SB1 W1030
represents the first longer-period system identified in the cluster,
while the determination of a 53.95 day period for W44 (WR L) makes it
the first Wolf-Rayet binary in Westerlund 1 with a confirmed orbital
period greater than ten days. Our results suggest the binary fraction
in the OB population is at least ∼40%, and may be significantly
higher.
These results demonstrate that binary systems can be effectively
identified in the population of OB I-III stars evolving off the main
sequence in Westerlund 1. Future multi-epoch surveys will be able to
fully characterise this population.
Description:
The VLT/FLAMES survey for massive binaries in Westerlund 1 carried out
observations in 2008, 2009, 2011, and 2013, using the FLAMES-GIRAFFE
multi-fibre spectrograph on VLT UT2 Kueyen with setup HR21 covering
the 8484-9001Å range with R=λ/Δλ∼16200. The
FLAMES-GIRAFFE pipeline was used to bias subtract, flat-field, and
wavelength calibrate the data, while subsequent processing made use of
IRAF for the extraction of individual spectra as well as rectification
and heliocentric velocity correction. Full details of target
selection, fibre prioritisation, and data reduction are given in Paper
I (Ritchie et al., 2009A&A...507.1585R 2009A&A...507.1585R), with additional discussion in
Clark et al., 2020A&A...635A.187C 2020A&A...635A.187C, Cat. J/A+A/635/A187.
We present multi-epoch observations of more than 100 OB and Wolf-Rayet
stars in the massive Galactic cluster Westerlund 1. Tables 5 and 6
list the known binaries and candidate binaries identified in this work.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 86 28 Binaries in Westerlund 1
table6.dat 45 33 Candidate binaries in Westerlund 1
tablea1.dat 72 119 Summary of radial velocity observations
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See also:
J/A+A/635/A187 : Massive binaries in Westerlund 1. VII. (Clark+, 2020)
Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- ID Name
6- 9 A4 --- OName Other name
11- 15 A5 --- n_ID Notes on ID (1)
17- 33 A17 --- SpType Spectral type
35- 43 A9 --- Type Type (2)
44- 49 F6.2 d P ?=- Period
50- 51 A2 --- u_P [? ] Uncertainty flag on P (3)
53- 57 F5.1 km/s K1 ?=- K1 velocity
58 A1 --- u_K1 [?] Uncertainty flag on K1 (3)
60- 64 F5.1 km/s K2 ?=- K2 velocity
65 A1 --- u_K2 [?] Uncertainty flag on K2 (3)
67- 71 F5.1 km/s gamma ?=- Mass center of the system velocity
72 A1 --- u_gamma [?] Uncertainty flag on gamma (3)
74- 75 A2 --- l_e [~<≥ ] Limit flag on e
76- 79 F4.2 --- e ?=- Eccentricity
80 A1 --- u_e [?] Uncertainty flag on e (3)
82 A1 --- l_omega [~] Limit flag on omega
83- 85 I3 deg omega ?=- Perioastron
86 A1 --- u_omega [?] Uncertainty flag on omega (3)
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Note (1): References as follows:
a = Bonanos (2007AJ....133.2696B 2007AJ....133.2696B, Cat. J/AJ/133/2696)
b = Koumpia & Bonanos (2012A&A...547A..30K 2012A&A...547A..30K)
c = Ritchie et al. (2010A&A...520A..48R 2010A&A...520A..48R)
d = Clark et al. (2011A&A...531A...2S 2011A&A...531A...2S)
Note (2): The type column indicates single or double lined systems (SB1/SB2)
and Eclipsing or Periodic photometric variables. Strong X-ray sources are
also noted (Clark et al., 2019A&A...623A..83C 2019A&A...623A..83C).
An asterisk marks SB1s with anomalous C III λ8500 absorption that
implies the presence of a luminous O9 secondary.
Note (3): Targets that require confirmation of the orbital period are marked
with one (candidate) or two (tentative) question marks, while other parameters
with errors ≥20% are also highlighted with a question mark.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- ID Name
8- 27 A20 --- SpType Spectral type from Clark et al.
(2020A&A...635A.187C 2020A&A...635A.187C, Cat. J/A+A/635/A187)
29 A1 --- RVflag [o±] Radial velocity changes flag (1)
31 A1 --- X-rayflag [o±] X-ray luminosity flag from
Clark et al., 2019A&A...626A..59C 2019A&A...626A..59C (1)
33 A1 --- IRflag [o±] Infrared excess flag (1)
35 A1 --- r_IRflag Reference for IRflag (2)
38 A1 --- radioflag [o±] Non-thermal radio emission flag (1)
40 A1 --- r_radioflag Reference for radioflag (2)
43 A1 --- Morphflag Spectral morphology flag (1)
45 A1 --- r_Morphflag Reference for Morphflag (2)
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Note (1): Indicators of binarity are listed as RV changes, X-ray luminosity,
an infra-red excess, non-thermal radio emission, and spectral morphology
(e.g. double lines, broad lines, or anomalously weak lines).
Objects are listed if they
(a) display substantial RV changes (ΔRV>25km/s),
(b) display any secondary indicator that is strongly inconsistent with a
single star, or
(c) display two or more indicators that individually suggest binarity.
Flag as follows:
+ = indicators that are strongly inconsistent with a single star
o = indicators that suggest a binary interpretation
- = none
Note (2): References as follows:
c = Clark et al. (2013A&A...560A..11C 2013A&A...560A..11C)
d = Dougherty et al. (2010A&A...511A..58D 2010A&A...511A..58D)
e = Andrews et al. (2019A&A...632A..38A 2019A&A...632A..38A, Cat. J/A+A/632/A38)
f = Crowther et al. (2006MNRAS.372.1407C 2006MNRAS.372.1407C)
g = Clark et al., Paper III, 2020A&A...635A.187C 2020A&A...635A.187C, Cat. J/A+A/635/A187
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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 Name
7- 10 A4 --- OName Other name
12 A1 --- n_ID Note on ID (1)
15- 33 A19 --- SpType Spectral Type
35- 36 I2 --- Nobs Observations
38- 42 F5.3 --- P(null) ?=- null probability
44- 49 F6.2 km/s RVmean Mean RV (1)
51- 56 F6.2 km/s RVrange ?=- RV Range
58- 61 F4.2 km/s e_RVmean Mean error on RV
63- 68 F6.2 --- sigmadet ?=- Maximum significance of RV differences
between any two epochs of observation
70 I1 --- T5 [5]? 5 when sources in table5.dat
(Binaries in Westerlund 1)
72 I1 --- T6 [6]? 6 when sources in table6.dat
(Candidate binaries in Westerlund 1)
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Note (1): RVs are measured from the Paschen series, unless noted as:
a = RVs measured from CaII λλ8542,8662
b = RVs measured from CaII λλ8912,8927
(see Ritchie et al., 2009A&A...507.1597R 2009A&A...507.1597R),
c = RVs measured from the CIII λ8664 emission line
(see Clark et al., 2011A&A...531A..28C 2011A&A...531A..28C),
d = RVs measured from HeI λ8845.
Values presented for 2011 and 2013 FLAMES observations only.
For W13, values are given for the more massive absorption-line component
(Ritchie et al., 2010A&A...520A..48R 2010A&A...520A..48R).
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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
Clark et al., Paper VII 2020A&A...635A.187C 2020A&A...635A.187C, Cat. J/A+A/635/A187
(End) Patricia Vannier [CDS] 23-Aug-2022