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MACHO observations of LMC red giants: Mira and semi-regular pulsators, and contact and semi-detached binaries

Published online by Cambridge University Press:  25 May 2016

P.R. Wood ,
C. Alcock ,
R.A. Allsman ,
D. Alves ,
T.S. Axelrod ,
A.C. Becker ,
D.P. Bennett ,
K.H. Cook ,
A.J. Drake  and
K.C. Freeman
...Show all authors
P.R. Wood
Affiliation:
Mount Stromlo and Siding Spring Observatories, Australian National University
C. Alcock
Affiliation:
Center for Particle Astrophysics, University of California, Berkeley Lawrence Livermore National Laboratory
R.A. Allsman
Affiliation:
Supercomputing Facility, Australian National University
D. Alves
Affiliation:
Department of Physics, University of California, Davis Lawrence Livermore National Laboratory
T.S. Axelrod
Affiliation:
Mount Stromlo and Siding Spring Observatories, Australian National University
A.C. Becker
Affiliation:
Center for Particle Astrophysics, University of California, Berkeley Departments of Astronomy and Physics, University of Washington
D.P. Bennett
Affiliation:
Center for Particle Astrophysics, University of California, Berkeley Lawrence Livermore National Laboratory Department of Physics, University of Notre Dame
K.H. Cook
Affiliation:
Lawrence Livermore National Laboratory
A.J. Drake
Affiliation:
Mount Stromlo and Siding Spring Observatories, Australian National University
K.C. Freeman
Affiliation:
Mount Stromlo and Siding Spring Observatories, Australian National University
K. Griest
Affiliation:
Center for Particle Astrophysics, University of California, Berkeley Department of Physics, University of California, San Diego
L.J. King
Affiliation:
Center for Particle Astrophysics, University of California, Berkeley Department of Physics, University of Notre Dame
M.J. Lehner
Affiliation:
Department of Physics, University of Sheffield
S.L. Marshall
Affiliation:
Lawrence Livermore National Laboratory
D. Minniti
Affiliation:
Lawrence Livermore National Laboratory Departamento de Astronomia, P. Universidad Católica, Santiago
B.A. Peterson
Affiliation:
Mount Stromlo and Siding Spring Observatories, Australian National University
M.R. Pratt
Affiliation:
Center for Space Research, MIT
P.J. Quinn
Affiliation:
European Southern Observatory
C.W. Stubbs
Affiliation:
Center for Particle Astrophysics, University of California, Berkeley Departments of Astronomy and Physics, University of Washington
W. Sutherland
Affiliation:
Department of Physics, University of Oxford
A. Tomaney
Affiliation:
Departments of Astronomy and Physics, University of Washington
T. Vandehei
Affiliation:
Center for Particle Astrophysics, University of California, Berkeley Department of Physics, University of California, San Diego
D.L. Welch
Affiliation:
Department of Physics and Astronomy, McMaster University

Abstract

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The MACHO data base has been used to examine light curves of all red giant stars brighter than Mbol ∼ −2 in a 0.5° × 0.5° area of the LMC bar. Periods, often multiple, have been searched for in all stars found to be variable. Five distinct period-luminosity sequences have been found on the low mass (M ≲ 2.25M⊙) giant branch. Comparison of observed periods, luminosities and period ratios with theoretical models identifies Miras unambiguously as radial fundamental mode pulsators, while semi-regular variables can be pulsating in the 1st, 2nd or 3rd overtone, or even the fundamental. All these variables lie on just 3 of the 5 distinct sequences, and they all appear to be on the AGB.

The fourth sequence contains red giants on the first giant branch (FGB) or at the red end of the core-helium burning loops of intermediate mass stars (M ≳ 2.25M⊙). The light curves of these stars strongly suggest that they are contact binaries, and they make up ∼0.5% of stars within 1 mag. of the FGB tip. Stars on the fifth sequence show semi-regular, eclipse-like light curves. The light curves and periods of these stars suggest that they are in semi-detached binaries, transfering mass to an invisible companion via a stellar wind or Roche lobe overflow. They make up ∼25% of AGB stars. If the existence of these red giant contact and semi-detached binaries is confirmed, then extant theories of binary star evolution will require substantial modification.

Type
Part 2. Pulsation, Mass Loss, Cool Envelopes
Information
Symposium - International Astronomical Union , Volume 191: Asymptotic Giant Branch Stars , 1999 , pp. 151 - 158
Copyright
Copyright © Astronomical Society of the Pacific 1999 

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