Ellipsoidal Variability and the Difference between Sequence D and E Red Giants

Abstract

We have studied a sample of Large Magellanic Cloud red giant binaries that lie on sequence E in the period--luminosity plane. We show that their combined light and velocity curves unambiguously demonstrate that they are binaries showing ellipsoidal variability. By comparing the phased light and velocity curves of both sequence D and E variables, we show that the sequence D variation -- the Long Secondary Period -- is not caused by ellipsoidal variability. We also demonstrate several further differences between stars on sequences D and E. These include differences in velocity amplitude, in the distribution of eccentricity, and in the correlations of velocity amplitude with luminosity and period. We also show that the sequence E stars, unlike stars on sequence D, do not show any evidence of a mid-infrared excess that would indicate circumstellar dust.

7 pages, 5 figures. Accepted to MNRAS 2010 February 18

References in corpus (4)

• Spitzer SAGE survey of the Large Magellanic Cloud II: Evolved Stars and Infrared Color Magnitude Diagrams
• Long Secondary Periods in Variable Red Giants
• Ellipsoidal Variability and Long Secondary Periods in MACHO Red Giant Stars
• Evidence for mass ejection associated with long secondary periods in red giants

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• Period-luminosity relations in evolved red giants explained by solar-like oscillations
• A newly discovered stellar type: dusty post-red giant branch stars in the Magellanic Clouds
• Infrared Period-Luminosity Relations of Evolved Variable Stars in the Large Magellanic Cloud
• Predicting the Fate of Binary Red Giants Using the Observed Sequence E Star Population: Binary Planetary Nebula Nuclei and Post-RGB Stars
• Binarity as the Origin of Long Secondary Periods in Red Giant Stars
• The Light Curve Shapes as a Key to Resolving the Origin of Long Secondary Periods in Red Giant Stars
• Semiregular variables with periods lying between the period-luminosity sequences C', C and D
• Eccentric Ellipsoidal Red Giant Binaries in the LMC: Complete Orbital Solutions and Comments on Interaction at Periastron
• Long Period Variables in the Large Magellanic Cloud from the EROS-2 survey
• On the pulsation modes of OGLE small amplitude red giant variables in the LMC
• The Orbital Nature of 81 Ellipsoidal Red Giant Binaries in the Large Magellanic Cloud
• Long-period variables in NGC147 and NGC185
• Photometric Analysis of the OGLE Heartbeat Stars
• Radial Velocity Curves of Ellipsoidal Red Giant Binaries in the Large Magellanic Cloud