J/ApJ/826/224 RSG and foreground candidates in M31 (Massey+, 2016)
The red supergiant content of M31*.
Massey P., Evans K.A.
<Astrophys. J., 826, 224-224 (2016)>
=2016ApJ...826..224M 2016ApJ...826..224M (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, supergiant ; Radial velocities ;
Spectral types ; Effective temperatures ; Photometry, infrared
Keywords: galaxies: individual: M31 - galaxies: stellar content - Local Group -
stars: massive - supergiants
Abstract:
We investigate the red supergiant (RSG) population of M31, obtaining
the radial velocities of 255 stars. These data substantiate membership
of our photometrically selected sample, demonstrating that Galactic
foreground stars and extragalactic RSGs can be distinguished on the
basis of B-V, V-R two-color diagrams. In addition, we use these
spectra to measure effective temperatures and assign spectral types,
deriving physical properties for 192 RSGs. Comparison with the solar
metallicity Geneva evolutionary tracks indicates astonishingly good
agreement. The most luminous RSGs in M31 are likely evolved from
25-30 M☉ stars, while the vast majority evolved from stars with
initial masses of 20 M☉ or less. There is an interesting
bifurcation in the distribution of RSGs with effective temperatures
that increases with higher luminosities, with one sequence consisting
of early K-type supergiants, and with the other consisting of M-type
supergiants that become later (cooler) with increasing luminosities.
This separation is only partially reflected in the evolutionary
tracks, although that might be due to the mis-match in metallicities
between the solar Geneva models and the higher-than-solar metallicity
of M31. As the luminosities increase the median spectral type also
increases; i.e., the higher mass RSGs spend more time at cooler
temperatures than do those of lower luminosities, a result which is
new to this study. Finally we discuss what would be needed
observationally to successfully build a luminosity function that could
be used to constrain the mass-loss rates of RSGs as our Geneva
colleagues have suggested.
Description:
In selecting targets to observe, we used the 437 photometrically
selected red supergiant (RSG) candidates given in Table 1 of Massey et al.
(2009, J/ApJ/703/420). The observations were all made with Hectospec,
a 300-fiber spectrometer on the 6.5 m MMT (Fabricant et al.
2005PASP..117.1411F 2005PASP..117.1411F). The 270 lines/mm grating was used, providing a
reciprocal dispersion of 1.2 Å/pixel, and a spectral resolution of
4.5-5.2 Å from 3650-9200 Å in first order. Since no blocking
filter is used, there is some contamination from second-order blue in
the far red, but given the colors of these stars, this is pretty
minimal; the grating is blazed at 5000 Å. The six "WR configurations"
were observed for 90 minutes each (UT 2014 September 24, September 26,
November 21, November 22, November 26, and November 28); the one "red star"
configuration was observed for 60 minutes (UT 2014 October 1). The
observations were made in a self-staffed queue; P. M. and collaborator
Kathryn Neugent were present for the November observing.
Objects:
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RA (ICRS) DE Designation(s)
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00 42 44.33 +41 16 08.4 M31* = NAME M31*
00 42 44.33 +41 16 07.5 M31 = NAME Andromeda
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 94 354 Radial Velocities RSG and Foreground Candidates
table2.dat 58 255 Physical Properties
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See also:
II/145 : Brightest stars in a foreground field of M31
(Berkhuijsen+, 1988)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/AJ/96/1884 : BVRJHK photometry of M31 red supergiants (Humphreys+ 1988)
J/ApJ/501/153 : VRB photometry of red supergiants (Massey 1998)
J/ApJ/703/420 : Red supergiants in M31 (Massey+, 2009)
J/ApJ/825/50 : Variable stars in M31 + M33. III. YSGs + RSGs (Gordon+, 2016)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- ID Stellar identifier (JHHMMSS.SS+DDMMSS.S)
21- 26 F6.3 --- X/R Ratio (1)
28- 33 F6.1 km/s RV-M31 M31 radial velocity
35- 40 F6.1 km/s RV-Obs Observed radial velocity
42- 44 F3.1 km/s e_RV-Obs Uncertainty in RV-Obs
46 I1 --- Nobs [1/6] Number of observations
48- 51 F4.1 --- TDR Tonry & Davis (1979AJ.....84.1511T 1979AJ.....84.1511T) r-parameter
53- 58 F6.1 --- RV-M09 ? Old Massey et al. (2009, J/ApJ/703/420) radial
velocity
60- 62 A3 --- PType [RSG fgd] Photometric type (2)
64- 94 A31 --- Com Additional comment
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Note (1): Where X is the distance along the semi-major axis, and R is the
galactocentric radius within the plane of M31.
Note (2): Based upon B-V vs V-R.
Photometric type as follows:
fgd = Foreground;
RSG = Red supergiant.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- ID Stellar identifier (JHHMMSS.SS+DDMMSS.S)
21- 27 A7 --- SpType Spectral type
29- 32 I4 K Teff ? Effective temperature
34- 38 F5.2 mag Ksmag ? Apparent Ks band magnitude
39 A1 --- u_Ksmag [:] Uncertainty flag on Ksmag
41 A1 --- Source [MFX] Data source code (1)
43- 48 F6.2 mag KMag ? Absolute K band magnitude
50- 53 F4.2 [Lsun] logL ? Log luminosity relative to solar
55- 58 I4 Rsun Rad ? Radius relative to solar
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Note (1): Code as follows:
M = 2MASS (Cutri et al. 2003, Cat. II/246);
F = FLAMINGOS (Massey et al. 2009, J/ApJ/703/420);
X = No data.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 02-Mar-2018