COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2330 Konkoly Observatory Budapest 9 May 1983 HU ISSN 0374 - 0676 RADIAL VELOCITY MEASUREMENTS OF alpha Pyx AND zeta CMa In 1980 a spectroscopic monitoring of bright southern B stars using the 90cm telescope of Manuel Foster Observatory, Santiago de Chile, was started (Sterken and Vogt, 1982). The programme consists of systematic observations of southern early-type B stars which are too bright to be observed photometrically. During the first months of operation a one-prism spectrograph with a dispersion of 36 A/mm at Hgamma was used. Zeta Canis Majoris (HR 2282, B2.5V, V=3.02, B-V=-.19) is known since long as a long-period spectroscopic binary (Curtis, 1908). Many radial velocities have been published since then, but the star has never been monitored for short-term variability. Its spectral type and luminosity class locates its position in the H-R diagram close to the locus of the beta Cep stars. zeta CMa was monitored during 4 nights in December 1980 and January 1981. From the large scatter in radial velocities obtained on a night-to-night basis, and considering the fact that alpha Pyxidis (HR 3468, B1.5III, V=3.68, B-V=-.18) has the right spectral type and luminosity class for being a beta Cep star, Van Hoof (1973) concluded that it is probably a beta Cephei variable. Balona (1977) pointed out that the published radial velocities indicate variation, but he found the star constant in V. We monitored the star during 5 nights in December 1980 and March 1981. Kodak IIa-O emulsion has been used; all plates were measured with the Grant Spectrocomparator at the headquarters of ESO in Garching. The table gives the plate numbers as listed in the logbook of the Manuel Foster Institute, heliocentric date and heliocentric velocity. For ----------------------------------------------------------- Heliocentric radial velocities alpha Pyx=HR 3468 Plate nr JD-2440000 RV Plate nr JD-2440000 RV ----------------------------------------------------------- 65 4589.623 5.9 308 4680.745 29.1 66 .648 12.4 309 .758 27.8 68 .686 14.3 310 .773 20.8 74 .807 17.7 311 .784 20.7 75 .818 12.2 312 4682.602 24.4 170 4614.577 12.5 313 .614 23.2 171 .590 14.4 314 .626 20.4 172 .606 16.6 315 .638 23.6 173 .616 21.2 316 .650 23.7 174 .628 15.3 317 .660 20.6 175 .640 19.1 318 .676 10.6 176 .656 21.9 319 .687 19.4 177 .670 19.0 320 .698 19.2 178 .680 22.0 321 .710 18.5 179 .689 14.2 322 .723 23.5 180 .700 30.1 323 .738 25.1 181 .710 20.6 324 .750 21.2 182 .724 20.2 325 .762 16.9 183 .738 52.1 326 .773 24.3 184 .748 19.5 327 .788 25.0 185 .759 6.4 332 4683.561 23.2 290 4677.647 16.8 333 .578 23.1 291 .658 25.2 334 .593 21.2 292 .671 35.1 335 .606 18.6 293 .685 24.0 336 .621 11.5 296 4680.595 26.4 337 .626 18.5 297 .606 13.0 340 .666 31.7 298 .619 7.4 341 .678 23.5 299 .631 8.1 342 .690 21.1 300 .644 13.6 343 .705 17.3 301 .658 19.8 344 .719 19.4 302 .669 16.4 345 .731 10.8 303 .682 9.4 346 .744 21.3 304 .695 24.2 347 .756 27.1 305 .708 16.6 348 .768 7.3 306 .713 37.7 349 .779 24.0 307 .734 23.2 350 .791 45.5 ----------------------------------------------------------- ----------------------------------------------------------- Heliocentric radial velocities zeta CMa = HR 2282 Plate nr JD-2440000 RV Plate nr JD-2440000 RU ----------------------------------------------------------- 46 4590.330 50.3 109 4611.447 78.2 47 .339 39.6 111 .457 26.0 48 .362 25.4 112 .471 16.0 49 .371 33.2 113 .477 21.2 50 .386 31.0 114 .487 19.6 54 .463 42.0 116 .504 23.2 55 .470 33.1 117 .511 27.7 56 .479 31.8 118 .517 35.6 58 .516 20.9 119 .525 59.8 59 .529 25.7 132 4614.319 51.7 61 .545 45.9 133 .327 62.4 78 4595.316 24.9 134 .338 46.5 79 .325 26.8 135 .342 48.4 80 .347 34.8 136 .349 28.6 81 .356 8.2 137 .358 33.7 82 .373 38.0 139 .373 36.7 83 .382 0.7 140 .381 35.6 84 .390 17.7 141 .388 33.7 85 .400 45.7 142 .398 19.0 86 .413 27.7 143 .409 30.9 88 .432 13.0 144 .424 26.3 89 .463 36.1 146 .440 25.7 90 .487 23.5 147 .449 16.2 91 .512 29.5 148 .456 29.2 92 .518 30.5 149 .469 30.6 97 4611.318 22.7 150 .494 16.8 98 .329 41.1 151 .501 41.4 99 .337 32.6 152 .510 35.1 100 .346 53.9 153 .519 10.9 101 .360 47.0 154 .527 35.5 102 .369 45.1 155 .537 28.7 105 .398 38.1 156 .544 38.9 107 .431 34.4 ----------------------------------------------------------- zeta CMa the radial velocities are the means of the velocities of the He I 4388 and 4471 lines; in the case of alpha Pyx the He I 4144, 4388 and 4471 lines were used. The mean error on one velocity determination is estimated as 6-8 km s^-1. On JD 244-4595, -4611 and -4614 the radial velocity range of zeta CMa is definitely larger than the inaccuracy of the measurements, but the form of the radial velocity curve is too irregular to draw any conclusion regarding the nature of the variations. The measurements of alpha Pyx yield a relatively well defined sinusoidal velocity curve on JD 2444680, with a probable period of about 5 hours and a range of nearly 20 km s^-1. On the other nights the variations were more erratic, but with a smaller amplitude. The presence of this short-term variability makes alpha Pyx a suitable target for a more elaborate study using a larger telescope equipped with a grating spectrograph. The authors are indebted to Mrs. E.M. Acuna and Mr. G. Le-Cerf for taking a number of plates, and to the European Southern Observatory for donating the plate material. Financial support was provided by the National Foundation for Collective Fundamental Research (FKFO 2.0028.79) and by the National Science Foundation (NFWO) of Belgium. C. STERKEN and D. VANDER LINDEN Astrophysical Institute, Vrije Universiteit Brussel Pleinlaan 2, B-1050 Brussels References: Balona, L.A., 1977, Mem.R.astr.Soc. 84, 101 [BIBCODE 1977MmRAS..84..101B ] Curtis, H.D., 1908, Lick Obs.Bull. 5, 60 [BIBCODE 1908LicOB...5...60C ] Sterken, C., Vogt, N., 1982, The Messenger 28, 12 [BIBCODE 1982Msngr..28...12S ] van Hoof, A., 1973, Med.Kon.Vl.Ac.Wet. XXXV, 4.