COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2504 Konkoly Observatory Budapest 18 April 1984 HU ISSN 0374-0676 ON THE PERIOD-LUMINOSITY RELATION FOR DELTA SCUTI STARS In our previous paper (Frolov, Irkaev, 1982) different parameters for Delta Scuti stars in open clusters were given, in particular, reliable luminosities based only on cluster membership. In Table I we give for each variable the Table I Praesepe (Av=0) lg P Mv B-V (B-V)0 b-y (b-y)0 BR Cnc = KW 45 -1.420 2.06 0.231 0.131 BS Cnc = KW 154 -1.292 2.31 0.251 0.149 BU Cnc = KW 207 -1.276 1.48 0.197 0.104 BN Cnc = KW 323 -1.409 1.60 0.224 0.130 BQ Cnc = KW 292 -1.131 1.98 0.304 0.198 BW Cnc = KW 340 -1.143 2.28 0.259 0.147 BX Cnc = KW 445 -1.276 1.77 0.208 0.120 BY Cnc = KW 449 -1.237 1.72 0.201 0.115 Pleiades (Av=0.06) V 534 Tau=HII 1266 -1.495 2.57 0.36 0.34 0.229 0.214 V 624 Tau=HII 158 -1.699 2.80 0.235 0.215 0.149 0.134 V 647 Tau=HII 1362 -1.328 2.40 0.26 0.24 0.153 0.138 V 650 Tau=HII 1425 -1.509 2.08 0.153 0.133 0.090 0.075 Coma (Av=0) FM Com=HR 4684. -1.260 1.89 0.181 0.099 Hyades (Av=0) upsilon Tau=VB 60 -0.876 1.00 0.268 0.165 theta2 Tau=VB 72 -1.097 1.56 0.179 0.099 rho Tau=VB 95 -1.174 1.37 0.240 0.144 V 480 Tau=VB 123 -1.377 1.81 0.21 0.122 V 483 Tau=VB 30 -1.268 2.29 0.278 0.170 V 696 Tau=VB 33 -1.444 1.94 0.223 0.126 V 775 Tau=VB 38 -1.208 2.43 0.320 0.196 V 777 Tau=VB 141 -0.790 1.19 0.253 0.150 alpha Per (Av=0.30) V 459 Per=H 501 -1.432 2.90 0.351 0.251 0.212 0.138 V 461 Per=H 606 -1.456 2.74 0.330 0.230 0.207 0.133 V 465 Per=H 906 -1.523 2.54 0.276 0.176 0.167 0.093 NGC 7789 (Av=0.84) V 521 Cas=K 573 -0.833 1.56 0.64 0.36 colour-indices (B-V) and (b-y) from various sources and reddening free ones, Mv and P values were taken from our cited paper, (B-V)_0 and (b-y)_0 were calculated on the basis of absorption values Av for each cluster according to our cited paper and the following relations: E(B-V) = 1/3 Av, E(b-y) = 0.74 E(B-V) (Crawford, Mandwewala, 1976). Using the least squares solution we have calculated both the PL and the PLC relations for cluster Delta Scuti stars. Two unusual variables in NGC 2264, V 588 Mon = W2 (A7 III-IV) and V 589 Mon = W 20 (F2 III), may still be at gravitational. contraction phase, and the evolved giant BT Cnc=KW 204 (F0 III) in Praesepe were not used either. Therefore, these relations were obtained practically only for main-sequence variables of the Delta Scuti- type: Mv = -1.66 lg P - 0.11, sigma_0 = +/-0.37, +/-0.34 +/-0.44 Mv = -2.06 lg P + 4.14 (B-V)_0 -1.61, sigma_0 = +/-0.31, +/-0.32 +/-1.32 +/-0.61 Mv = -2.02 lg P + 5.39 (b-y)_0 -1.33, sigma_0 = +/-0.33. +/-0.35 +/-2.09 +/-0.60 [FIGURE 1] For V 521 Cas = K 573 in NGC 7789 Mv = +1.56 and P = 0.147d were taken from Breger (1983), this star was not used for the P-L-(b-y)_0 relation due to absence of (b-y) -observations. The second relation is shown in Figure 1. We note that co-efficients for lg P in all our relations are much smaller than the co-efficient -3.052 of the Breger's PLC relation (Breger, 1979), which was derived by the maximum - likelihood method. Our coefficients for (b-y)_0 and (B-V)_0 are also smaller compared with 8.456 (Breger, 1979) and 5.285 (Halprin, Moon, 1983), correspondingly. We feel that the reason for this difference is not only an effect of different method used but it indicates the reality of a smaller slope of the PL and PLC relations for main-sequence pulsators compared with the bulk of Delta Scuti variables. We have calculated the value of sigma_0 = +-0.40 for open cluster Delta Scuti stars with the Breger's PLC relation which is indeed larger than that for our relations. It is of interest to note that all the a Per cluster variables, i.e. the youngest objects, lie below the line of our PL and PLC relations (these stars are marked in the Figure 1 by symbols "alpha"). M.S. FROLOV Astronomical Council of the USSR Academy of Sciences 48, Pjatnitskaja str. Moscow 109017, USSR B.N. IRKAEV Dushanbe Astrophysical Institute of Tadjik Academy of Sciences 22, Sviridenko Str. Dushanbe 734670, USSR References: Breger, M. 1979, Publ.Astron.Soc.Pacif., vol. 91, p. 5. [BIBCODE 1979PASP...91....5B ] Breger, M. 1983, I.B.V.S., No. 2393 Crawford, D.L., Mandwewala, N. 1976, Publ.Astron.Soc.Pacif., vol. 88, p. 917 [BIBCODE 1976PASP...88..917C ] Frolov, M.S., Irkaev, B.N. 1982, I.B.V.S., No. 2249 Halprin, L., Moon, T.T. 1983, Astrophys, and Space Sci., vol. 91, p. 43 [BIBCODE 1983Ap&SS..91...43H ]