Anomalous Orbital Characteristics of the AQ Col (EC 05217-3914) System

Tomomi Otani, Anthony E Lynas-Gray, David Kilkenny, Chris Koen, Ted von Hippel, Murat Uzundag, Maja Vuckovic, Clara Pennock, Roberto Silvotti

Research output: Contribution to journalArticlepeer-review

Abstract

AQ Col (EC 05217-3914) is one of the first detected pulsating subdwarf B (sdB) stars and has been considered to be a single star. Photometric monitoring of AQ Col reveals a pulsation timing variation with a period of 486 days, interpreted as time delay due to reflex motion in a wide binary formed with an unseen companion with expected mass larger than 1.05 Msun. The optical spectra and color–magnitude diagram of the system suggested that the companion is not a main-sequence star but a white dwarf or neutron star. The pulsation timing variation also shows that the system has an eccentricity of 0.424, which is much larger than any known sdB long period binary system. That might be due to the existence of another short period companion to the sdB star. Two optical spectra obtained on 1996 December 5 show a radial velocity change of 49.1 km s−1 in 46.1 minutes, which suggests the hot subdwarf in the wide binary is itself a close binary formed with another unseen white dwarf or neutron star companion; if further observations show this interpretation to be correct, AQ Col is an interesting triple system worthy of further study.

Original languageAmerican English
JournalAstrophysical Journal
Volume926
DOIs
StatePublished - Feb 1 2022

Keywords

  • Multiple stars
  • Variable stars
  • Subdwarf stars
  • Extreme horizontal branch stars
  • Stellar evolution
  • Timing variation methods
  • Pulsation frequency method
  • White dwarf stars

Disciplines

  • Stars, Interstellar Medium and the Galaxy

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