CDROM/APJS/V99/P135 Rotation and Spectral Peculiarities (Abt & Morrell 1995) ================================================================================ The Relation Between Rotational Velocities and Spectral Peculiarities Among A-Type Stars Helmut A. Abt & Nidia I. Morrell <1995, ApJS, 99, 135> =1995ApJS...99..135A ================================================================================ Abstract: We obtained new data to determine whether the spectral appearance of A-type stars is entirely determined by their rotational velocities. For this purpose we derived rotational velocities for 1700 northern A-type stars from CCD coude spectra, calibrated with the new Slettebak et al. system, and new MK classifications based on wide photographic Cassegrain spectra for 2000 northern and some southern stars in the Bright Star Catalogue. In addition we determined the equivalent widths of the lambda 4481 Mg II lines in the coude spectra. Tables and graphs show variations of rotational velocities and lambda 4481 line strengths as functions of type and luminosity, and frequencies of the normal and abnormal stars. After deconvolutions of the rotational velocities, assuming random orientations of rotational axes, we find that all rapid rotators have normal spectra and nearly all slow rotators have abnormal spectra (Ap or Am). Those abnormalities are generally attributed to diffusion and can occur only with little rotational mixing. However at all types there are overlaps of these distributions, implying that a given intermediate rotational velocity is insufficient to determine whether the star should have a normal or abnormal spectrum. However, we realized that (1) some of our "standards," such as Vega and Alpha Dra, are really abnormal, causing us to classify similar peculiar stars as "normal," (2) many of the "normal" stars near A2 IV have the characteristics of peculiar stars such as low rotational velocities and weak 4481 Mg II and K lines, and (3) the mean rotational velocities of "normal" stars are depressed just at those types where the Ap and Am stars are most frequent. Therefore we conclude that the overlaps are due to our failure to detect all the abnormal stars and that a specific rotational velocity is probably enough to determine whether a star will have a normal or abnormal spectrum. Keywords: stars: chemically peculiar -- stars: early-type -- stars: fundamental parameters -- stars: rotation File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- table2.dat 56 2092 Summary of Stellar Data -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 6 A6 --- HR *Bright Star Catalogue number 7-15 A9 --- HD *Henry Draper or Aitken Double Star number 16 1X --- --- Blank 17-43 A27 --- MK *MK classification 44 A1 --- l_Vsini Limiting character on Vsini 45-47 I3 km/s Vsini []? Vsini, rotational velocity 48-49 A2 --- u_Vsini *[:?pst] Vsini uncertainty flag 50-51 2X --- --- Blank 52-55 F4.2 0.1nm W4481 []? Equivalent width for 4481 A line 56 A1 --- u_W4481 *[:pst] W4481 uncertainty flag -------------------------------------------------------------------------------- Notes for file: table2.dat -------------------------------------------------------------------------------- HR, HD: If both the HR and HD fields are blank, the remaining fields are continuations of the previous record. MK: Explanation of the Classification Terminology (from Table 1): (standard) Classification standard star s Sharp lined n Broad lined nn Very broad lined ksn The Ca II K line has both sharp and broad components st Strong wk Weak v. Very Lam Boo A star in which many of the metals are weak, indicating underabundances 4481 weak The 4481 Mg II line is weak. Measures may indicate that other lines are also weak. This may be a mild version of the Lambda Boo stars. Am(A3/A7/F0) A metallic line star in which the spectral type based on the Ca II K line is A3, on the Balmer lines is A7, and on the metallic lines is F0. This is an abbreviation of the form Am(K/H/M=A3/A7/F0). p(SrEuCr st, CaMg wk) An Ap star in which the Sr is strongest relative to the standards, Eu is next strongest, etc.; the lines of Ca and Mg are weak relative to those in standards. The type is based on the hydrogen lines. shell(Ti,Ca) A shell spectrum that has sharp Ti and Ca absorption lines. (:) Uncertainty in the previous symbol. u_Vsini, u_W4481: Uncertainty flag, or indication if this is a program star (p) or a star from Slettebak et al. 1975, ApJS, 29, 137 -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 02-Aug-95