Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981apj...245..960v&link_type=abstract
Astrophysical Journal, Part 1, vol. 245, May 1, 1981, p. 960-976.
Astronomy and Astrophysics
Astrophysics
189
Main Sequence Stars, Radial Velocity, Star Clusters, Stellar Evolution, Stellar Rotation, Stellar Spectra, A Stars, Angular Momentum, B Stars, Emission Spectra, Fourier Transformation, H Alpha Line, Hertzsprung-Russell Diagram, K Lines, Line Spectra, Power Spectra, T Tauri Stars
Scientific paper
Rotational velocities for 64 pre-main-sequence (PMS) stars in NGC 2264 and Taurus-Auriga have been derived using two Fourier transform techniques. The velocities are not randomly distributed on the H-R diagram: for radiative track stars the 1.5 Msun evolutionary track conveniently separates regimes of high and low υ sin i. Stars of mass less than 1.5 Msun generally rotate at less than 25km , whereas well over half the higher mass stars rotate in the range 25-150 km s-1 Most stars on convective tracks and most Hα emission stars have υ sin i < 35 km s-1, suggesting that most of the angular momentum loss has occurred before the PMS stars show a photospheric spectrum and that rotation is not the primary determinant of emission-line activity. Specific angular momentum on the zero-age main sequence probably increases more steeply with mass than M2/3. The Skumanich relation between velocity and age does not hold for PMS stars but can be reformulated to be consistent with the observations by using angular momentum instead of rotational velocity and correcting for changes in the internal structure of the contracting star. It is speculated that the rapid rotators expected from theoretical considerations may reside among the strong emission-line stars which, because of a lack of absorption lines, could not be measured for rotational velocities. Angular momentum loss is likely to occur during initial evolution on convective tracks; no conclusions may be drawn as to the existence of angular momentum loss on radiative tracks. The angular momentum problem has been solved for most stars by the time they reveal photo spheric spectra, since all velocities measured lie well below break-up velocity.
Kuhi Leonard V.
Vogel Stuart N.
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