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

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

Oct 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985apj...297..206s&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 297, Oct. 1, 1985, p. 206-232.

Other

57

Binary Stars, Pulsars, Stellar Oscillations, Stellar Spectrophotometry, Abundance, Angular Momentum, Line Shape, Radial Velocity, Radiant Flux Density, Silicon, Stellar Models, Stellar Rotation, Vibration Mode

Scientific paper

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.

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