COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1807 Konkoly Observatory Budapest 1980 June 18 RADIUS VARIATION OF TEN CLASSICAL CEPHEIDS In a recent paper by Caccin et al. (1980) a method has been presented which, under essentially the same physical assumptions than the Baade-Wesselink one (Wesselink, 1946),allows a more accurate and unique determination of the mean radius of classical cepheids, through a global treatment of light, colour and velocity curves. We have used this method to determine the radii of ten well observed cepheids of various period. For the light and colour curves we have used the V and B-V data from the Tonantzintla Catalogue by Mitchell et al. (1964), whereas for the radial velocity u we used data from different authors (see note). Following the procedure described by Caccin et al., Fourier series have been fitted to these data, and the radius R_o at the phase phi_o of minimum radial velocity has come out from numerical solution of the equation 2.1715+integral_0^1 ({log_10 {R_o-KP integral_phi0^phi (u(phi') d phi')} d(B-V)/d phi} d(phi)) - integral_0^1 dV(phi)/d phi (B-V) d phi = 0 using the value K = 1.31 (Parsons, 1972) for the conversion factor from radial to pulsational velocity. The mean radius then comes out from numerical integration of the radial velocity curve: = - KP*integral_0^1 u(phi) d phi We have also computed the slope "b" of the relation surface brightness vs. colour index. In Table I we give, for each star, the ephemeris used for reducing the observations (P, T0); the mean radius ; the order N1, N2, N3 of the Fourier series for light, colour and velocity curves, respectively; the area B of the loop (V,B-V) and the coefficient b defined [FIGURE 1a] [FIGURE 1b] above. In Figure 1 we present, for each star, the function R(phi). The radius determination presented here have been used in the paper by Caccin et al.(1980) to determine a new period-radius relation, whose slope seems in agreement with theoretical computations by Cogan (1978). Table I Name TO Period N1 N2 N3 B b RT Aur 20957.466 3.728261 36.2 3 4 4 0.047 2.113 U Sgr 36761.956 6.744925 45.7 5 5 3 0.057 2.283 Eta Aql 33292.574 7.176641 53.3 4 4 4 0.067 2.106 S Nor 36849.51 9.75494 56.5 5 5 3 0.048 1.858 Beta Dor 26013.93 9.844235 63.9 5 5 7 0.051 2.040 Zeta Gem 33442.665 10.153507 67.6 6 6 6 0.036 2,050 X Cyg 32573.990 16.3861 97.0 4 4 7 0.159 1.874 T Mon 28193.08 27.018 146.8 5 7 7 0.174 2.221 l Car 35619.7 35.5412 163.2 5 5 3 0.124 2.121 SV Vul 29020.87 45.145 170.0 4 4 3 0.262 1.949 Note: the sources of radial velocity. RT Aur - Bappu, M.K.W. and Raghavan, N.: 1969, M.N.R.astr.Soc.142,245. U Sgr - Jacobsen, T.S.: 1970, Ap.J. 159,569. eta Aql - Schwarzschild, M., Schwarzschild, B. and Adams, W.S.: 1948, Ap.J.,108,207 S Nor - Breger, M.: 1970, A.J., 75,239. Beta Dor - Parsons, S.B.: 1970, A.J., 76,562. zeta Gem - Scarfe, C.D.: 1976, Ap.J., 209,141. X Cyg - Becker, W. and Strohmeier, W.: 1942, Zeit.Astr.,21,295. T Mon - Sanford, R.F.: 1956, Ap.J., 123,201. l Car - Dawe, J.A.: 1969, M.N.R. astr.Soc.145,377. SV Vul - Sanford, R.F.: 1956, Ap.J. 123,201. G. RUSSO and C. SOLLAZZO Capodimonte Astronomical Observatory Via Moiariello, 16 I-80231 Napoli - Italy References: Caccin,B., Onnembo,A., Russo,G. and Sollazzo,C.: 1980, Astr.Astrophys., submitted Cogan,B.C.: 1978, Ap.J. 221,635 [BIBCODE 1978ApJ...221..635C ] Mitchell,R-I., Iriarte,B., Steinmetz,D. and Johnson, H.L.: 1964, Bol. Obs. Tonantzintla Tacubaya, 3,153 [BIBCODE 1964BOTT....3..153M ] Parsons S.B.: 1972, Ap.J. 1974,57 [BIBCODE 1972ApJ...174...57P ] Wesselink, A.J.: 1946, Bull. Astr.Inst.Netherl. 10,468