J/ApJ/700/1216 Spectroscopy of Be stars in open clusters (McSwain+, 2009)
Variability of Be stars in southern open clusters.
McSwain M.V., Huang W., Gies D.R.
<Astrophys. J., 700, 1216-1232 (2009)>
=2009ApJ...700.1216M 2009ApJ...700.1216M
ADC_Keywords: Clusters, open ; Stars, Be ; Stars, B-type ; Spectra, red ;
Rotational velocities ; Effective temperatures ; Stars, masses
Keywords: open clusters and associations: individual (NGC 3293, NGC 3766,
NGC 4755, NGC 6231) - stars: emission-line, Be
Abstract:
We recently discovered a large number of highly active Be stars in the
open cluster NGC 3766, making it an excellent location to study the
formation mechanism of Be star disks. To explore whether similar disk
appearances and/or disappearances are common among the Be stars in
other open clusters, we present here multiple epochs of Hα
spectroscopy for 296 stars in eight open clusters. We identify 12 new
transient Be stars and confirm 17 additional Be stars with relatively
stable disks. By comparing the Hα equivalent widths to the
photometric y-Hα colors, we present a method to estimate the
strength of the Hα emission when spectroscopy is not available.
For a subset of 128 stars in four open clusters, we also use blue
optical spectroscopy and available Stromgren photometry to measure
their projected rotational velocities, effective temperatures, and
polar surface gravities. We combine our Be star detections from these
four clusters to investigate physical differences between the
transient Be stars, stable Be stars, and normal B-type stars with no
line emission. Both types of Be stars are faster rotating populations
than normal B-type stars, and we find no significant physical
differences between the transient and stable Be stars in our sample.
Description:
We obtained red optical spectra of 296 Be and B-type stars in eight
open clusters during observing runs in 2005 February, 2006 May, and
2007 May using the Cerro Tolo Inter-American Observatory (CTIO) Blanco
4-m telescope with the Hydra multi-fiber spectrograph. For a subset of
four open clusters, we also obtained blue optical spectra during the
2006 and 2007 runs.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 55 296 Hα equivalent widths
table5.dat 115 128 Physical parameters of cluster members
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See also:
J/MNRAS/386/447 : RV catalogue of O-type stars in NGC 6231 (Sana+, 2008)
J/A+A/457/265 : The VLT-FLAMES Survey of Massive Stars (Dufton+, 2006)
J/ApJS/161/118 : byHα photometry in open clusters (McSwain+, 2005)
J/ApJ/622/1052 : byHα photometry of NGC 3766 (McSwain+, 2005)
J/A+A/402/549 : UBVRIHalpha photometry of NGC 3293 (Baume+, 2003)
J/A+A/395/823 : CCD Δa-photometry of 5 open clusters (Paunzen+, 2002)
J/A+A/369/511 : Open star clusters. III. NGC 4103, 5281, 4755 (Sanner+, 2001)
J/AJ/115/734 : NGC 6231 UBVRI and Hα photometry (Sung+ 1998)
J/A+A/315/384 : Binarity among B-stars in NGC 6231 (Raboud, 1996)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Cl Cluster identification (1)
15- 17 I3 --- MG Star identification in cluster
19- 24 F6.2 0.1nm WHa05 ? Hα equivalent width in 2005 Feb (2)
26- 31 F6.2 0.1nm WHa06 ? Hα equivalent width in 2006 May (2)
33- 38 F6.2 0.1nm WHa07 ? Hα equivalent width in 2007 May (2)
40- 42 A3 --- Em2 Be stars and candidates found in our
photometry (Paper II, Cat. J/ApJS/161/118)
44- 55 A12 --- Em Be star status based upon our red
spectroscopic observations only; in this work
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Note (1): WHα may be contaminated by nebular emission in NGC 3293 and
IC 2581.
Note (2): HJD(t-2450000) for the different clusters as follows:
--------------------------------------------
Cluster 2005 Feb 2006 May 2007 May
--------------------------------------------
Collinder 272 3404.832 3870.178 4225.757
Hogg 16 3404.832 3870.178 4225.757
IC 2581 3404.708 --- 4225.5494
NGC 3293 3404.772 3870.506 4223.321
NGC 3766 3403.790 3870.224 4225.662
NGC 4755 3403.863 --- 4223.717
NGC 6231 --- 3869.828 4223.813
NGC 6664 --- 3870.933 4223.930
--------------------------------------------
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- sp [Be ] Spectral class: B or Be star
4- 11 A8 --- Cl Cluster identification ( in Simbad)
13- 15 I3 --- MG Star identification in cluster
17- 19 I3 km/s vsini ? Rotational velocity
21- 22 I2 km/s e_vsini ? vsini uncertainty
24- 28 I5 K Teff ? Effective temperature
30- 33 I4 K e_Teff ? Teff uncertainty
35- 38 F4.2 [cm/s2] logg ? Surface gravity
40- 43 F4.2 [cm/s2] e_logg ? logg uncertainty
45- 48 F4.2 [cm/s2] loggP ? Polar surface gravity
50- 53 F4.1 Msun Mass ? Mass (M*)
55- 57 F3.1 Msun e_Mass ? Mass uncertainty
59- 62 F4.1 Rsun Rad ? Radius (R*)
64- 66 F3.1 Rsun e_Rad ? Rad uncertainty
68- 70 I3 km/s Vc ? Critical velocity (1)
72- 75 A4 --- SB? Binarity comment
77- 95 A19 --- Aut Author's name for SB? remark
97-115 A19 --- BibCode Bibcode for SB? remark
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Note (1): The critical velocity is given in equation (5):
Vcrit=(GM*/Re)0.5 where the equatorial radius Re=1.5Rp. For
simplicity, we assume the polar radius of the star, Rp, is equal to
R* (Rad). See section 4.2 for further details.
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Nomenclature note: Stars are <Cl* {Cl} MG NNN> for Simbad.
History:
From electronic version of the journal
23-Sep-2011: Insert into VizieR
27-Sep-2011: Table 2 modified according to PDF version to include NGC 3766
which is missing in HTML version.
References:
McSwain & Gies. Paper I. 2005ApJ...622.1052M 2005ApJ...622.1052M Cat. J/ApJ/622/1052
McSwain & Gies. Paper II. 2005ApJS..161..118M 2005ApJS..161..118M Cat. J/ApJS/161/118
McSwain et al. Paper III. 2008ApJ...672..590M 2008ApJ...672..590M
(End) Emmanuelle Perret [CDS] 27-Jul-2011