J/ApJ/789/10 M33 WR and Of-type Stars (Neugent+, 2014)
The close binary frequency of Wolf-Rayet stars as a function of metallicity
in M31 and M33.
Neugent K.F., Massey P.
<Astrophys. J., 789, 10 (2014)>
=2014ApJ...789...10N 2014ApJ...789...10N (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, Wolf-Rayet ; Stars, double and multiple
Equivalent widths ; Magnitudes
Keywords: galaxies: individual: M31, M33 - galaxies: stellar content -
Local Group - binaries: close - stars: Wolf-Rayet
Abstract:
Massive star evolutionary models generally predict the correct ratio
of WC-type and WN-type Wolf-Rayet stars at low metallicities, but
underestimate the ratio at higher (solar and above) metallicities. One
possible explanation for this failure is perhaps single-star models
are not sufficient and Roche-lobe overflow in close binaries is
necessary to produce the "extra" WC stars at higher metallicities.
However, this would require the frequency of close massive binaries to
be metallicity dependent. Here we test this hypothesis by searching
for close Wolf-Rayet binaries in the high metallicity environments of
M31 and the center of M33 as well as in the lower metallicity
environments of the middle and outer regions of M33. After identifying
∼100 Wolf-Rayet binaries based on radial velocity variations, we
conclude that the close binary frequency of Wolf-Rayets is not
metallicity dependent and thus other factors must be responsible for
the overabundance of WC stars at high metallicities. However, our
initial identifications and observations of these close binaries have
already been put to good use as we are currently observing additional
epochs for eventual orbit and mass determinations.
Description:
Our ability to undertake this project was in a large part due to the
existence of the multi-object fiber-fed spectrograph Hectospec
(Fabricant et al. 2005PASP..117.1411F 2005PASP..117.1411F) on the 6.5 m MMT. Its large
field of view (1° in diameter) was well matched to our survey
areas of M31 and M33. Hectospec's 300 fibers and their allowed close
spacing (20'') let us observe a multitude of candidates using only
four pointing configurations. We were assigned 2.5 nights of dark time
in the Fall of 2012 through NOAO (2012B-0129). When designing the
fiber configurations, we were able to assign 71% of our M31 WRs using
two configurations and 77% of our M33 WRs using an additional two
configurations, making a total of four configurations. We were able to
observe five of the remaining M33 candidates as part of the present
study, and recently obtained spectra of the sixth star as part of our
follow-up study of the binaries we identify here.
Objects:
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RA (ICRS) DE Designation(s)
----------------------------------------------------------
00 42 44.33 +41 16 07.5 M31 = NAME Andromeda
01 33 50.90 +30 39 35.8 M33 = NAME Triangulum Galaxy
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 77 6 Newly Found M33 WR and Of-type Stars
table3.dat 34 250 E/I Values for the 250 observed candidates
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See also:
J/ApJ/505/793 : New WR star in M33 (Massey+, 1998)
J/AJ/131/2478 : M31 and M33 UBVRI photometry (Massey+, 2006)
J/AJ/133/2393 : UBVRI phot. in seven Local Group dwarfs galaxies
(Massey+, 2007)
J/ApJ/733/123 : The Wolf-Rayet content of M33 (NGC 598) (Neugent+, 2011)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- Star Star ([NM2011] JHHMMSS.ss+DDMMSS.s
in Simbad)
21- 24 F4.2 --- rho Distance from the center within the
plane of M33 normalized to D25 (1)
26- 35 A10 --- Type Type of star
37- 39 F3.1 [0.1nm] log(-EW)HeII ?=- Log(-EW) of He II lambda4686
41- 42 I2 0.1nm FWHMHeII ?=- FWHM of He II lambda4686
44- 46 F3.1 [0.1nm] log(-EW)CIV ?=- Log(-EW) of C IV lambda5606
48- 49 I2 0.1nm FWHMCIV ?=- FWHM of C IV lambda5606
51- 55 F5.2 mag Vmag V-band magnitude (2)
57- 61 F5.2 mag m4750 lambda4750 Å AB magnitude (3)
63- 66 F4.1 mag VMag V-band Absolute magnitudes (4)
68- 71 F4.1 mag M4750 lambda4750 Å Absolute magnitudes (4)
73- 77 A5 --- OBassoc OB association (5)
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Note (1): Distance from the center within the plane of M33, normalized to the
D25 isophotal radius of 30.8' assuming α2000 = 01h33m50.89s,
δ2000 = 30°39'36.8'', an inclination of 56°, and a position
angle of the major axis of 23°, following Kwitter & Aller
(1981MNRAS.195..939K 1981MNRAS.195..939K) and Zaritsky et al. (1989AJ.....97...97Z 1989AJ.....97...97Z).
Note (2): From Massey et al. (2006, J/AJ/131/2478).
Note (3): AB magnitude through CT filter centered at 4750 Å and calibrated
using the values from Massey & Johnson (1998, J/ApJ/505/793).
Note (4): Absolute magnitudes computed assuming a true distance modulus of
24.60 (830 Mpc) and adopting an average reddening of E(B - V) = 0.12 based on
Massey et al. (2007, J/AJ/133/2393). Adopting RV = 3.1 leads to an
AV = 0.37 mag and Am4750=0.45 mag.
Note (5): OB association as defined by Humphreys & Sandage
(1980ApJS...44..319H 1980ApJS...44..319H). Parenthesis means the star is just outside the
boundaries of the association, while "Fld" implies it is a field star,
not in a cataloged OB association.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 17 A17 --- ID Star name (JHHMMSS.ss+DDMMss)
19- 22 I4 0.1nm Wave Wavelength; Angstroms
24- 27 F4.1 --- E/Ifxcor External scatter to internal error ratio
from fxcor
29- 32 F4.1 --- E/Ihand External scatter to internal error ratio by
hand
34 I1 --- Num Number of lines used
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 14-Mar-2017