COMMISSION 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3841 Konkoly Observatory Budapest 11 February 1993 HU ISSN 0374 - 0676 SIMULTANEOUS PHOTOMETRY AND RADIAL VELOCITIES OF DELTA SCUTI It is well known that for some types of pulsating variable stars the application of the Baade-Wesselink method is connected with serious difficulties. Nevertheless, when applicable, this method is a good source of luminosities, radii etc. for pulsating variables. If we want to try to apply the Baade-Wesselink method to stars varying their light curves from one cycle to another and having not quite stable periods (like Delta Scuti stars), we need to obtain photometric data and radial velocities practically simultaneously. In the literature such material is sparse. During the recent years we are measuring radial velocities of pulsating variables using the CORAVEL-type spectrophotometer ILS designed by Tokovinin (1987). Delta Scuti stars are on the boundary of the possibilities of this device: for main sequence stars we can measure velocities in the spectral type range F5-M5, it being possible to measure somewhat earlier type giants. On July 26/27,1992 we tried to measure the radial velocity of the prototype star, Delta Sct, at the 1-m reflector of the Simeiz International Observatory (Crimea, the Ukraine). The attempt was quite successful, so on July 31/August 1 we organized simultaneous photometric and spectroscopic observations at two telescopes of the Simeiz Observatory. The same 1-m reflector was used for radial velocities, and the photometric observations were done at the 60-cm reflector. The photometric conditions, rather typical for Simeiz, were far from being excellent, and we estimate the real accuracy of our results as +-0.02m-0.03m filters. Table 1 Radial velocities of Delta Scuti JD hel V_r_sun Sigma JD hel V_r_sun Sigma 2448.. 2448... 830.289 -37.8 0.4 835.282 -40.9 0.4 830.293 -31.9: 0.5 835.284 -39.0 0.4 830.296 -37.8 0.4 835.286 -39.2 0.4 830.301 -37.7 0.2 835.308 -39.2 0.4 830.304 -38.2 0.4 835.311 -38.3 0.4 830.307 -38.9 0.3 835.325 -38.4 0.3 830.332 -43.0 0.9 835.328 -38.3 0.5 830.335 -44.2 0.7 835.345 -39.8 0.7 830.339 -44.4 0.9 835.348 -39.7 0.7 830.354 -57.1: 2.0 835.361 -46.6 0.8 830.354 -52.2: 2.3 835.364 -43.5 0.5 830.357 -52.2: 2.2 835.368 -48.6 0.5 830.357 -57.1: 2.0 835.384 -45.7 1.0 830.375 -47.6: 0.9 835.386 -48.1 0.7 830.378 -51.3: 1.0 835.388 -50.5 0.8 830.380 -48.4: 1.1 835.407 -43.0 0.7 830.398 -44.6 0.7 835.409 -47.2 0.8 830.401 -47.0 0.5 835.411 -46.3 0.7 830.404 -47.2 0.5 835.432 -43.9 0.9 835.434 -43.1 0.8 835.448 -42.1 1.3 835.450 -42.3 0.9 Table 2 Photometry of Delta Scuti JD hel V B-V V-R 2448... 835.2941 4.75 0.39 0.32 835.3028 4.77 0.39 0.35 835.3104 4.77 0.40 0.32 835.3173 4.79 0.40 0.35 835.3269 4.79 0.39 0.34 835.3348 4.79 0.39 0.34 835.3381 4.79 0.38 0.34 835.3429 4.74 0.37 0.31 835.3516 4.76 0.35 0.35 835.3582 4.69 0.37 0.33 835.3635 4.66 0.37 0.30 835.3690 4.65 0.36 0.30 835.3772 4.62 0.32 0.29 835.3854 4.62 0.34 0.30 835.3907 4.60 0.33 0.28 835.3960 4.62 0.33 0.30 835.4043 4.59 0.35 0.29 835.4105 4.56 0.32 0.28 835.4167 4.62 0.36 0.29 835.4244 4.64 0.37 0.31 835.4322 4.62 0.35 0.31 835.4377 4.70 0.34 0.35 Table 1 contains the radial velocities measured during the two nights, Table 2 the results of photometry during the second night. We have covered with simultaneous photometric and spectroscopic observations practically a complete cycle of delta Sct (P=0.194d). Then we have undertaken an attempt to use the Baade-Wesselink method (in its "maximum likelihood" version suggested by Balona, 1977, with subsequent iterations described by Coulson et al., 1986). In minor variance with the traditional approach, we approximated with trigonometric polynomials only the radial velocity curve, and then computed the radial velocity integral for the moments when the photometry had been acquired. It seems to us that this modification allows us to reduce the number of avoidable approximations, this being of particular importance for not strictly periodic variables. The unknown (5 log e/R_0) in Balona's method (before iterations) for our observations is determined with rather poor accuracy (40 to 59 per cent for different combinations of magnitudes and colours), but the final results are in good agreement, their average being =1.9+-0.1 R_sun. Though a somewhat larger radius would seem preferable, this value does not disagree too much with expectations for an F3III star. Frolov (1970) derived for delta Sct =2.9 R_sun from its atmospheric parameters and quoted the value 3.7 R_sun from Bessell (1967). Estimates based on the star's luminosity (M_v=~+1.5) and effective temperature lead to radius values about 3 R_sun the contrary, the value 8.4 R_sun from Rachkovskaya (1986), based on model atmospheres, is unexpectedly large. It seems to us that, provided one obtains more accurate photometry, it is possible to use ILS radial velocities with simultaneous photometry for Baade-Wesselink determinations of radii for the large amplitude subgroup of Delta Scuti variables. The authors are grateful to the administration and the staff of the Simeiz International Observatory for the possibility to use the telescopes and for excellent hospitality and help. Thanks are due to Mr. O. Ugolnikov for his assistance during spectroscopic observations, and to Dr. M. Frolov for valuable discussion. L.N. BERDNIKOV Yu.V. KULAGIN A.S. RASTORGOUEV Sternberg Astronomical Institute 13, University Avenue, Moscow 119899, Russia N.N. SAMUS Institute for Astronomy, Russian Acad. Sci. 48, Pyatnitskaya Str., Moscow 109017, Russia References: Balona, L.A., 1977, Mon. Notic. R.A.S., 178, 231. [BIBCODE 1977MNRAS.178..231B ] Bessell, M.S., 1967, Proc. Astr. Soc. Austral., 1, 14. [BIBCODE 1967PASAu...1...14B ] Coulson, I.M., Caldwell, J.A R., Gieren, W.P., 1986, Astrophys. J., 303, 273. [BIBCODE 1986ApJ...303..273C ] Frolov, M.S., 1970, in "Pulsating Stars", ed. B.V. Kukarkin, "Nauka" Publishers, Moscow, p. 240 (in Russian) Rachkovskaya, T.M., 1986, Izv. Crim. Obs., 75, 149. Tokovinin, A.A., 1987, Soviet Astronomy, 31, 98. [BIBCODE 1987SvA....31...98T ]