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Title:
Time-dependent structure in ultraviolet absorption lines of the rapid rotators HD 64760 (B0Ib) and HD 93521 (O9.5V)
Authors:
Howarth, Ian D.; Townsend, R. H. D.; Clayton, M. J.; Fullerton, A. W.; Gies, D. R.; Massa, D.; Prinja, R. K.; Reid, A. H. N.
Affiliation:
AA(Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT), AB(Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT), AC(Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT), AD(Center for Astrophysical Sciences, Department of Physics & Astronomy, The Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, USA), AE(Center for High Angular Resolution Astronomy, Georgia State University, Atlanta, GA 30303, USA), AF(Hughes STX, 7701 Greenbelt Road, Greenbelt, MD 20770, USA), AG(Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT), AH(Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 296, Issue 4, pp. 949-960. (MNRAS Homepage)
Publication Date:
06/1998
Origin:
MNRAS
MNRAS Keywords:
STARS: EARLY-TYPE, STARS: OSCILLATIONS, ULTRAVIOLET: STARS
DOI:
10.1046/j.1365-8711.1998.01437.x
Bibliographic Code:
1998MNRAS.296..949H

Abstract

Cross-correlation provides an effective line-averaging function for spectra containing many line features, a result which can be exploited in order to perform time-series and spatial-domain analyses of absorption-line variability in data of (relatively) poor quality. We apply this method to high-resolution IUE spectra. For the known non-radial pulsator HD 93521 (O9.5V), time-series analysis of the cross-correlation function recovers two periods that are confirmed in independent optical data (P_1=1.77 h, P_2=2.90 h); there is no statistically significant excess power at these frequencies in lines formed in the stellar wind. By comparing phase information from the time-series analysis with results from pulsation models we estimate l~=10+/-1 and 6+/-1 as the harmonic degrees for P_1 and P_2, respectively, with l+m<~2 for each mode (where m is the azimuthal order of the mode). We also present evidence for absorption-line variability in HD 64760 (HR3090 B0.5 Ib), finding marginally significant signals with P_1=8.9 h (or, possibly, 14.2 h) and P_2=29 h. The longer period is present, with a strong signal, in wind-formed lines. We consider possible circumstellar and (quasi-)photospheric origins for P_2, and conclude that this signal probably does not arise through rotational modulation (with the corollary that the stellar-wind signal also does not arise in corotating structures, contrary to previous suggestions). The phase behaviour of the signals is consistent with non-radial pulsation models characterized by l=5+/-1 (P_1) and 2+/-1 (P_2), with l+m<=1, supporting a previous suggestion by Baade that both low- and higher-order modes are present; the wind modulation at P_2 may then result from leakage of pulsation energy into the supersonic outflow. The lack of significant photometric variability is a serious difficulty for this model (any sinusoidal photometric variability at P_2 has semiamplitude <2 mmag at lambda_eff=1575Angstroms, with 95 per cent confidence), but this may itself be a consequence of wave leakage.

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