The rotation of α Oph investigated using polarimetry

Jeremy Bailey, Daniel V. Cotton, Ian D. Howarth, Fiona Lewis, Lucyna Kedziora-Chudczer

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)

Abstract

Recently we have demonstrated that high-precision polarization observations can detect the polarization resulting from the rotational distortion of a rapidly rotating B-type star. Here, we investigate the extension of this approach to an A-type star. Linear-polarization observations of α Oph (A5IV) have been obtained over wavelengths from 400 to 750 nm. They show the wavelength dependence expected for a rapidly rotating star combined with a contribution from interstellar polarization. We model the observations by fitting rotating-star polarization models and adding additional constraints including a measured vesin i. However, we cannot fully separate the effects of rotation rate and inclination, leaving a range of possible solutions. We determine a rotation rate (ω = Ω/Ωc) between 0.83 and 0.98 and an axial inclination i > 60◦. The rotation-axis position angle is found to be 142 ± 4◦, differing by 16◦ from a value obtained by interferometry. This might be due to precession of the rotation axis due to interaction with the binary companion. Other parameters resulting from the analysis include a polar temperature Tp = 8725 ± 175 K, polar gravity log gp = 3.93 ± 0.08 (dex cgs), and polar radius Rp = 2.52 ± 0.06 R. Comparison with rotating-star evolutionary models indicates that α Oph is in the later half of its main-sequence evolution and must have had an initial ω of 0.8 or greater. The interstellar polarization has a maximum value at a wavelength (λmax) of 440 ± 110 nm, consistent with values found for other nearby stars.
Original languageEnglish
Pages (from-to)2254-2267
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Volume494
Issue number2
DOIs
Publication statusPublished - 2020

Keywords

  • polarimetry
  • polarization (light)
  • stars

Fingerprint

Dive into the research topics of 'The rotation of α Oph investigated using polarimetry'. Together they form a unique fingerprint.

Cite this