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The B and Be star population of NGC 3766

McSwain, M. Virginia and Huang, Wenjin and Gies, Douglas R. and Grundstrom, Erika D. and Townsend, Richard H.D. (2008) The B and Be star population of NGC 3766. Astrophysical Journal, 672 (1). pp. 590-603. ISSN 0004-637X. doi:10.1086/523934. https://resolver.caltech.edu/CaltechAUTHORS:MCSWapj08

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Abstract

We present multiple epochs of Hα spectroscopy for 47 members of the open cluster NGC 3766 to investigate the long-term variability of its Be stars. Sixteen of the stars in this sample are Be stars, including one new discovery. Of these, we observe an unprecedented 11 Be stars that undergo disk appearances and/or near disappearances in our Hα spectra, making this the most variable population of Be stars known to date. NGC 3766 is therefore an excellent location to study the formation mechanism of Be star disks. From blue optical spectra of 38 cluster members and existing Strömgren photometry of the cluster, we also measure rotational velocities, effective temperatures, and polar surface gravities to investigate the physical and evolutionary factors that may contribute to the Be phenomenon. Our analysis also provides improvements to the reddening and distance of NGC 3766, and we find E(B - V ) = 0.22 ± 0.03 and (V - MV )₀ = 11.6 ± 0.2, respectively. The Be stars are not associated with a particular stage of main-sequence evolution, but they are a population of rapidly rotating stars with a velocity distribution generally consistent with rotation at 70%-80% of the critical velocity, although systematic effects probably underestimate the true rotational velocities, so that the rotation is much closer to critical. Our measurements of the changing disk sizes are consistent with the idea that transitory, nonradial pulsations contribute to the formation of these highly variable disks.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1086/523934DOIArticle
http://www.iop.org/EJ/abstract/0004-637X/672/1/590/PublisherArticle
ORCID:
AuthorORCID
Townsend, Richard H.D.0000-0002-2522-8605
Additional Information:© 2008 American Astronomical Society. Print publication: Issue 1 (2008 January 1); received 2007 July 18; accepted for publication 2007 September 26. We thank the referee, Phil Massey, for providing comments that improved this work. Also, we are grateful to Giovanni Carraro, Mark Pinsonneault, and Swetlana Hubrig for helpful discussions that contributed to this work. We are grateful to Yale University and the SMARTS Consortium for providing observing time at the CTIO 1.5 mtelescope. This research hasmade use of the WEBDA database, operated at the Institute for Astronomy of the University of Vienna. M. V. M. was supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST 04-01460. This work was also supported by the National Science Foundation under grant AST 06-06861 (D. R. G) and by NASA under grant LTSA/NNG05GC36G (R. H. D. T.).
Funders:
Funding AgencyGrant Number
NSF Astronomy and Astrophysics Postdoctoral FellowshipAST 04-01460
NSFAST 06-06861
NASALTSA/NNG05GC36G
Subject Keywords:open clusters and associations: individual (NGC 3766); stars: emission-line, Be
Issue or Number:1
DOI:10.1086/523934
Record Number:CaltechAUTHORS:MCSWapj08
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:MCSWapj08
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13798
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:14 Jul 2009 20:26
Last Modified:08 Nov 2021 22:40

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