COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3460 Konkoly Observatory Budapest 11 May 1990 HU ISSN 0374 - 0676 ROTATIONAL VELOCITIES OF G AND K GIANTS Rotational velocities, vsini, are often helpful in determining the properties of ellipsoidal variables and other rapidly rotating stars by providing a measurement of the absolute radius (e.g., Hall 1990). With this in mind, I have obtained high-dispersion spectra for a large number of late-type stars during 6-11 February 1990 (UT) with the stellar spectrograph of the National Solar Observatory's McMath Solar Telescope on Kitt Peak in Arizona. While moat of these stars were slowly rotating giants observed for another purpose, a number of known or suspected rapid rotators and binaries containing a cool giant were included in the program as ancillary targets. The spectra covered the range 6520- 6600 A, at 0.09 A/pixel, and were taken with an 800x800 pixel TI CCD. All the data were reduced with the standard computer programs available at the telescope. Rotational velocities were determined by artificially broadening spectra of slowly rotating comparison stars of appropriate spectral type by various amounts and comparing such spectra calculated for a range of vsini with a spectrum of the star in question. This technique can be quite accurate because rotational broadening has pronounced, characteristic effects on the many line blends in the H-alpha region. Results are given in Table 1. The numbers in parentheses refer to the references listed below the table. References to existing rotational velocities are generally to Uesugi and Fukuda, who gave much more extensive information than I can justify including here. Most of the spectral types have been taken from the Bright Star Catalogue. Unfortunately, it was impossible to classify the stars with these H-alpha spectra, since the metallic lines seem to be only mildly dependent on T_eff but are more sensitive to differences in abundance and turbulence. There are caveats to be applied to the results of this technique. First, we must not apply spectra for giants to supergiants, which have such intrinsically broad line profiles that they would all be thought rapidly rotating. Several of the stars in Table 1 (notably 5 Cet, zeta And, and UU Cnc, which are ellipsoidal binaries) have sizes rather large for K giants and might be expected to have greater turbulence than in normal giants. This effect is generally not a problem, however: for the strengths of the broad shallow lines of these Table 1. Rotational Velocities and Spectral Types Star No.of Spectral Comparison vsini Other Values Spectra Type Star (km/s) (km/s) 5 Cet HD 352 2 K3 III (1) alpha Tau 23+/1 22+/-3(1) alpha Cas HD 3712 1 K0 III delta CrB