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Time-Series Spectroscopy of ζ Ophiuchi

Published online by Cambridge University Press:  15 February 2018

A.H.N. Reid ,
C.T. Bolton ,
R.A. Crowe ,
M.S. Fieldus ,
A.W. Fullerton ,
D.R. Gies ,
I.D. Howarth ,
D. McDavid ,
R.K. Prinja  and
K.C. Smith
A.H.N. Reid
Affiliation:
Dept. of Physics & Astronomy, University College London, Gower St., London, WC1E 6BT, England, U. K.
C.T. Bolton
Affiliation:
Dept. of Physics & Astronomy, University College London, Gower St., London, WC1E 6BT, England, U. K.
R.A. Crowe
Affiliation:
Dept. of Physics & Astronomy, University College London, Gower St., London, WC1E 6BT, England, U. K.
M.S. Fieldus
Affiliation:
Dept. of Physics & Astronomy, University College London, Gower St., London, WC1E 6BT, England, U. K.
A.W. Fullerton
Affiliation:
Dept. of Physics & Astronomy, University College London, Gower St., London, WC1E 6BT, England, U. K.
D.R. Gies
Affiliation:
Dept. of Physics & Astronomy, University College London, Gower St., London, WC1E 6BT, England, U. K.
I.D. Howarth
Affiliation:
Dept. of Physics & Astronomy, University College London, Gower St., London, WC1E 6BT, England, U. K.
D. McDavid
Affiliation:
Dept. of Physics & Astronomy, University College London, Gower St., London, WC1E 6BT, England, U. K.
R.K. Prinja
Affiliation:
Dept. of Physics & Astronomy, University College London, Gower St., London, WC1E 6BT, England, U. K.
K.C. Smith
Affiliation:
Dept. of Physics & Astronomy, University College London, Gower St., London, WC1E 6BT, England, U. K.

Abstract

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We have undertaken a multi-site, multi-wavelength observing campaign on the archetypal O stars ζ Puppis (O4 I(n)f) and ζ Ophiuchi (O9.5 V). Both stars are well known for the strength of their line profile variations (lpv's), and represent extremes of O spectral type and luminosity class. UV time-series spectroscopy of ζ Pup and ζ Oph is described by Prinja et al. (Ap.J. 1992, 390, 266), and Howarth et al. (Ap.J. 1992, submitted) respectively. The optical spectroscopic results of ζ Oph are reported by Reid et al. (1992, ApJ submitted), of which some of the principal results are given here.

During late April, and early May, 1989, we obtained high-resolution, high signal-to-noise optical spectra of the late O-type, rapid rotator ζ Oph. Time-series analysis, using the CLEAN algorithm, has shown that the characteristic lpv seen in HeI λ447lÅ, Si III λλ4552, 4567, 4575Å, and MgII λ448lÅ can be satisfactorily represented as a set of 4 sinusoids. No substantial variation is observed in HeII λ4541, or NIII λ4517Å. We attribute this behaviour to a combination of equatorial gravity-darkening and a latitudinally-confined origin for the lpv.

The phase changes over the line profiles indicate repetitive patterns of axial symmetry, rotating prograde in the co-rotating frame of the star. The periods are 3.339 hours (-m = 4), 2.435 hours (-m = 5 or -m = 6), 1.859 hours (-m = 9 ± 1), and either 1.366 hours or 1.292 hours (-m = 11 ± 1); -m represents the spatial frequency around the stellar equator. The first three periods confirm those found at earlier epochs, and we conclude that some lpv characteristics are reproduced over at least a 2-year interval.

Since no commensurate superperiod (|m|P) exists, and since the super-periods are less than our estimated minimum rotation period for ζ Oph (> 18 hours), we reject a rotational modulation origin for the lpv and conclude that the star is undergoing multi-mode, sectorial, non-radial pulsations.

Type
Beyond the Classical Instability Strip
Information
International Astronomical Union Colloquium , Volume 139: New Perspectives on Stellar Pulsation and Pulsating Variable Stars , 1993 , pp. 190
Copyright
Copyright © Cambridge University Press 1993