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Mass-Loss During the RR Lyrae Phase of the HB: Mass Dispersion on the HB and RR Lyrae Period Changes

Published online by Cambridge University Press:  15 February 2018

Rebecca A. Koopmann ,
Young-Wook Lee ,
Pierre Demarque  and
Jamie M. Howard
Rebecca A. Koopmann
Affiliation:
Department of Astronomy, Yale University, New Haven, CT, USA
Young-Wook Lee
Affiliation:
Department of Astronomy, Yale University, New Haven, CT, USA
Pierre Demarque
Affiliation:
Department of Astronomy, Yale University, New Haven, CT, USA
Jamie M. Howard
Affiliation:
Department of Astronomy, Yale University, New Haven, CT, USA

Extract

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Horizontal branch (HB) models were evolved using the Yale stellar evolution code, YREC, to test the possibility that mass loss during the RR Lyrae phase is able to produce the observed color (mass) dispersion on the HB (Willson and Bowen 1984) and the anomalous period changes in RR Lyrae stars (Laskarides 1974). Models of total mass 0.64, 0.66, 0.68, 0.70, and 0.72 M⊙ (YMS = 0.23, Z = 0.001) were evolved with constant mass loss rates of 0, 10-10, and 10-9 M⊙ yr-1. Mass loss was assumed to occur only in the RR Lyrae phase, and the instability strip was defined by 3.800 < log Teff < 3.875.

HB stars which lose mass evolve further to the blue. Low mass loss rates do not affect the shape of the tracks significantly. Stars, which without mass loss could not become blue HB stars, were able to emerge from the instability strip on the blue side.

Type
Theoretical Breakthroughs
Information
International Astronomical Union Colloquium , Volume 139: New Perspectives on Stellar Pulsation and Pulsating Variable Stars , 1993 , pp. 312
Copyright
Copyright © Cambridge University Press 1993

References

Laskarides, P. G. 1974, Astrophys.&Sp.Science, 27, 485 Google Scholar
van Albada|T. S. & Baker, N. 1971, Ap.J., 169, 311 Google Scholar
Willson, L. A. & Bowen, G. H. 1984, Nature, 312, 429 Google Scholar