J/ApJ/931/157 UV-to-NIR spectra of 8 Wolf-Rayet stars in LMC (Aadland+, 2022)
WO-type Wolf-Rayet stars: the last hurrah of massive star evolution.
Aadland E., Massey P., John Hillier D., Morrell N.I., Neugent K.F.,
Eldridge J.J.
<Astrophys. J., 931, 157 (2022)>
=2022ApJ...931..157A 2022ApJ...931..157A
ADC_Keywords: Spectra, ultraviolet; Spectra, optical; Spectra, infrared;
Stars, Wolf-Rayet; Magnitudes, absolute; Spectral types;
Magellanic Clouds
Keywords: Massive stars ; Wolf-Rayet stars ; Stellar evolution ; WC stars
Abstract:
Are WO-type Wolf-Rayet (WR) stars in the final stage of massive star
evolution before core-collapse? Although WC- and WO-type WRs have very
similar spectra, WOs show a much stronger OVIλλ3811,34
emission-line feature. This has usually been interpreted to mean that
WOs are more oxygen rich than WCs, and thus further evolved. However,
previous studies have failed to model this line, leaving the relative
abundances uncertain, and the relationship between the two types
unresolved. To answer this fundamental question, we modeled six WCs
and two WOs in the LMC using UV, optical, and NIR spectra with the
radiative transfer code cmfgen in order to determine their physical
properties. We find that WOs are not richer in oxygen; rather, the OVI
feature is insensitive to the abundance. However, the WOs have a
significantly higher carbon and lower helium content than the WCs, and
hence are further evolved. A comparison of our results with
single-star Geneva and binary BPASS evolutionary models show that,
while many properties match, there is more carbon and less oxygen in
the WOs than either set of evolutionary model predicts. This
discrepancy may be due to the large uncertainty in the
12C+4He->16O nuclear reaction rate; we show that if the
Kunz+ 2002ApJ...567..643K 2002ApJ...567..643K rate is decreased by a factor of 25%-50%,
then there would be a good match with the observations. It would also
help explain the LIGO/VIRGO detection of black holes whose masses are
in the theoretical upper mass gap.
Description:
The first part of this study was described by A22b
(Aadland+ 2022ApJ...924...44A 2022ApJ...924...44A), where we analyzed high-quality UV,
optical, and near-IR (NIR) data on four WC4 stars.
Here we complete our study by providing an analysis of two WO-type
stars, as well as two additional WC4s.
For the four A22b stars:
The UV observations, obtained with the Faint Object Spectrograph (FOS)
on the Hubble Space Telescope (HST), covered the wavelength region of
1140-3300Å at a resolving power R of 1100-1600. The observations
were obtained on UT 1995-11-16 (data set Y2JE0403-7T), 1994-09-26
(data set Y2A10203-6T), 1996-04-15 (data set Y21E0105-8T), and
1995-11-21 (data set Y2JE0203-8T) for the stars BAT99-8, 9, 11, and
52, respectively. These UV observations were obtained as part of
GO-5460 (PI: D.J. Hillier).
The optical data were collected using the Magellan Echellette (MagE)
on the 6.5m Magellan Baade Telescope at Las Campanas Observatory,
covering the wavelength range 3150-9300Å with R=4100. The BAT99-8
observations were taken on UT 2016-02-21; BAT99-9 was taken on UT
2016-01-11; BAT99-11 was taken on UT 2016-02-21 and BAT99-52 was taken
on 2015-11-26.
The NIR spectra were taken using the Folded port InfraRed Echellette
(FIRE) on the Magellan Baade Telescope, for a wavelength range
8300-25000Å with R∼5000. BAT99-8, BAT99-9, and BAT99-52 were all
observed on UT 2016 February 20, with BAT99-11 being observed the
following night.
All four stars analyzed in this paper were observed in the UV with
HST, either with the Faint Object Spectrograph (FOS) or the Space
Telescope Imaging Telescope (STIS). In addition, the two WO stars were
also observed with the Cosmic Origins Spectrograph (COS) on
2015-07-16,17. The four stars were also observed on the 6.5m Magellan
telescopes at Las Campanas Observatory in Chile, in the optical with
the Magellan Echellette (MagE) on 2020-12-01 and 2015-01-09, and in
the NIR with FIRE on 2020-11-29 and 2017-02-09.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
sample.dat 75 8 *Our sample (including data from the first paper:
Aadland+ 2022ApJ...924...44A 2022ApJ...924...44A --added here by CDS)
sp/* . 8 Individual spectra in ASCII format
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Note on sample.dat: Data in this table comes from the fifth catalog of LMC
Wolf-Rayet stars (Neugent+ 2018, J/ApJ/863/181) and references therein,
except as noted.
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See also:
III/136 : Optical spectrophotometry of WR C and O Stars (Torres+ 1987)
III/215 : 7th Catalog of Galactic Wolf-Rayet stars (van der Hucht, 2001)
J/AJ/119/2214 : Photometry of Magellanic OB associations (Massey+, 2000)
J/ApJ/611/452 : Evolution of massive stars (El Eid+, 2004)
J/A+A/537/A146 : Stellar models with rot. 0.8<M<120, Z=0.014 (Ekstrom+, 2012)
J/ApJ/748/96 : Massive binaries in the LMC (Massey+, 2012)
J/ApJ/863/181 : The fifth catalog of LMC Wolf-Rayet stars (Neugent+, 2018)
J/AJ/158/192 : HeII em. from Wolf-Rayet stars in MW & LMC (Leitherer+, 2019)
J/ApJ/888/54 : Sp. of a rare low-mass Wolf-Rayet star in LMC (Margon+, 2020)
J/ApJ/898/85 : CII emission-line stars in LMC with MagE sp. (Margon+, 2020)
J/ApJ/922/177 : 2MASS red supergiants in the SMC (Massey+, 2021)
Byte-by-byte Description of file: sample.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name Star name
12- 14 A3 --- SpT Spectral type
16 A1 --- f_SpT Flag on SpT (1)
18- 19 I2 h RAh Hour of right ascension (J2000)
21- 22 I2 min RAm Minute of right ascension (J2000)
24- 28 F5.2 s RAs Second of right ascension (J2000)
30 A1 --- DE- Sign of declination (J2000)
31- 32 I2 deg DEd Degree of declination (J2000)
34- 35 I2 arcmin DEm Arcminute of declination (J2000)
37- 40 F4.1 arcsec DEs Arcsecond of declination (J2000)
42- 46 F5.2 mag Vmag [12.6/15.2] V magnitude
48- 51 F4.1 mag VMag [-6/-3.8] Absolute V magnitude, MV (2)
53- 70 A18 --- AName Alternative IDs (for objects from this paper)
72- 75 A4 --- Ref Reference paper; column added by CDS (3)
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Note (1): Flag as follows:
b = Subtype WO2 is from Massey+ (2014ApJ...788...83M 2014ApJ...788...83M) and confirmed here.
Note that it is incorrectly listed as "WO3" in the Fifth
Catalog through an oversight on the part of P.M.
Note (2): VMag has been computed using the small color excess given in
Section 4, assuming AV=3.1E(B-V), and adopting a true distance
modulus to the LMC of 18.50 (50kpc, van den Bergh 2000glg..book.....V 2000glg..book.....V &
Pietrzynski+ 2019Natur.567..200P 2019Natur.567..200P).
Note (3): Reference as follows:
A22b = Aadland+ 2022ApJ...931..157A 2022ApJ...931..157A (This catalog)
A22a = Aadland+ 2022ApJ...924...44A 2022ApJ...924...44A (data from Table 1)
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Byte-by-byte Description of file: sp/*
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Bytes Format Units Label Explanations
-------------------------------------------------------------------------------
1- 10 F10.4 0.1nm lambda [0/24936.6] Vacuum wavelength, Angstroms
12- 24 E13.6 cW/m2/nm Flux [-9.2e-15/4] Flux, erg/s/cm2/Å
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 18-Apr-2024