The nonradial oscillations of Spica. I - Two commensurable modes. II - A 'quasi-toroidal' mode

Abstract

view Abstract Citations (66) References (59) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The nonradial oscillations of Spica. I. Two commensurable modes. Smith, M. A. Abstract Spica (B1 III-IV) is the primary of a detached 4.01 day binary in which a 4 hr pulsation mode died out a decade ago. Its spectral line profiles still exhibit a complicated traveling pattern of line profile "bumps", characteristic of nonradial pulsation (NRP). The author obtained high-resolution Reticon observations of the Si III λλ4552 - 4574 triplet of this star over 4 1/4 nights and has been able to ascribe these variations to four sectorial, equatorial nonradial modes: (1) an l = m = +2 "equilibrium" tidal mode with a period of 48.2 hr; (2) a tidally forced quasi-toroidal mode; (3) an l = m = -8 mode with an apparent period of 6.52±0.08 hr, and (4) an l = m = -16 mode with an apparent period of 3.20±0.016 hr. The ratio of the periods for the latter two modes is almost exactly equal to the ratio of their l-values, 2.0. This "commensurability" of modes is discussed within the context of a differential rotation model for Spica. The picture is that the two nonradial modes are in resonance with the interior rotation rate, the orbital rate, and one another. Publication: The Astrophysical Journal Pub Date: October 1985 DOI: 10.1086/163517 Bibcode: 1985ApJ...297..206S Keywords: Binary Stars; Pulsars; Stellar Oscillations; Stellar Spectrophotometry; Abundance; Angular Momentum; Line Shape; Radial Velocity; Radiant Flux Density; Silicon; Stellar Models; Stellar Rotation; Vibration Mode; Astrophysics full text sources ADS | data products SIMBAD (5)