COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2523 Konkoly Observatory Budapest 21 May 1984 HU ISSN 0374-0676 SOME PECULIARITIES OF NINE DELTA SCUTI STARS On the basis of observational data published by Breger (1979), we have investigated various physical characteristics of 89 Delta Scuti stars. Several variables exhibit some peculiarities; these are considered in the present note. 1. The mode of radial pulsations was estimated in two ways by using both the absolute bolometric magnitude Mbol and the pulsation "constant" Q (Tsvetkov, 1982). It was difficult, however, to estimate the mode of six of the variables considered. a. By comparison of the observed absolute bolometric magnitude Mbol (= Mv + B.C.) with a known set of absolute bolometric magnitudes Mbol,n we estimated the mode of each star. Mbol,n were calculated from theoretical period-effective temperature-luminosity relations for the four lowest modes by using the observed period and effective temperature(n = 0,1,2,3 corresponds to mode F, 1H, 2H, 3H, respectively, Mbol,0 > Mbol,1 > Mbol,2 > Mbol,3). The difference between the two kinds of luminosities of a given star estimated in this way does not exceed 0.2-0.3 mag but for the six variables mentioned above, this difference is too large (see Table I). b. We also estimated the modes by comparison of the observed pulsation "constant" Q with the mean values of the pulsation "constants" Qn for the four lowest modes: 0.033, 0.025, 0.020, 0.017 days for mode F, 1H, 2H, 3H, respectively. The difference between the two kinds of pulsation "constants" for these six variables is also too large (Table I). 2. Three kinds of masses (in solar masses) are also listed in Table I: evolutionary masses Me,I and Me,P, interpolated from the evolutionary tracks of Iben (1967) and Paczynski (1970), respectively, masses Mg = g R^2 /G, computed from the stellar radii R and surface gravities g (G denotes the gravitational constant); pulsation masses MQ, calculated by means of Faulkner's (1977) fitting formulae for a chemical composition (X,Y,Z) = (0.70, 0.28, 0.02). Table I Peculiar Delta Scuti variables Star Mbol Mbol,0 Q Me,I Me,P Mg MQ or (days) HR HD Name Mbol,3 238 4818 V 526 Cas 2.32 1.02 0.072 - 1.70 1.56 0.35 515 10845 VY Psc 0.83 0.09 0.052 2.03 2.18 2.09 0.90 3662 79439 18 UMa 2.02 0.82 0.065 1.72 1.84 1.54 0.42 4746 108506 FT Vir 1.56 2.34 0.010 1.72 1.85 1.37 ? 7020 172748 delta Sct 1.51 0.61 0.055 1.72 1.86 1.71 0.65 7859 195961 rho Pav 2.43 1.81 0.045 - 1.64 1.28 0.72 1225 24832 DL Eri 1.29 0.82 0.045 1.81 1.96 2.00 1.09 3185 67523 rho Pup 1.70 1.37 0.040 1.65 1.77 1.67 1.16 5017 115604 20 CVn 1.42 0.97 0.041 1.75 1.90 1.70 1.09 Note (according to Tsvetkov, 1982). For the first six stars without mode estimate: Mbol - Mbol,0 > 0.5 and Q > 0.045 or (for FT Vir only) Mbol-Mbol,3 < - 0.5 and Q < 0.012. For the three last stars with a doubtful estimate of fundamental mode (F?): 0.3 < Mbol-Mbol,0<= 0.5 and 0.037 < Q <= 0.045. It is evident from Table I that the pulsation masses MQ are too small in comparison with the other two masses (the difference varies from about 2 to 5 times). One gets for FT Vir an abnormally large mass MQ (not given in Table I). We note that for the "normal" Delta Scuti stars there is an agreement(within the limits of the accuracy of determination) between the estimates of these three kinds of masses. Data for three variables with a doubtful estimate of fundamental mode (F?) are also listed in Table I. For these stars, the above considered peculiarities are smaller but yet considerable. Because of the indicated peculiarities, the nine variables in Table I have been excluded from our investigations of various semiempirical relations for Delta Scuti stars. Thus, we confirm and extend our results from an earlier note (Tsvetkov, 1979), in which the variables delta Sct and rho Pup were considered. The former star has been discussed time and again (see, e.g., references in the cited note). As to rho Pup, a transient Ca II K chromospheric emission at a phase of maximum outward acceleration as well as a bump in the radial velocity curve were observed in this star (Dravins et al., 1977). The variables FT Vir and rho Pup are situated outside the instability strip (towards the lower effective temperature), the latter star has an unreliable absolute visual magnitude Mv (Breger, 1979). Five of the six variables (excepting FT Vir) without a mode estimate have very low luminosity for their period. VY Psc and DL Eri pulsate with more than one period (Breger, 1979). The indicated peculiarities of the variables in Table I may be due to various causes: the observational data are not accurate, the ordinary photometric calibrations are not applicable to these stars; the considered variables may belong to another type of variable stars, nonradial oscillations may be excited in them, etc. The star FT Vir is a special case. Its very low Q value of 0.010 day may be due to nonradial pulsations in a high overtone pk. From Tables 17.2 of Cox (1980) for linear, adiabatic, nonradial oscillations of polytropes with a polytropic index 2 <= nu <=4 (l = 2), one may estimate a mode p7 for FT Vir. It is interesting to note that Kurtz (1982) estimated a similar mode (p6) from the value of Q = 0.011 day for the "rapidly oscillating Ap star" 21 Com (Kurtz, 1982, Musielok and Kozar, 1982, Garrido and Sanchez-Lavega, 1983). Moreover, Kurtz suggests that perhaps many B, A, F, G stars oscillate in p modes of low l, high k as does the Sun. One can note in this context that both radial and nonradial oscillations may be excited in models of Delta Scuti stars (Dziembowski, 1977). Some sort of made coupling might account for the complicated observed behaviour of many of these objects. From the observational point of view, some real Delta Scuti variables (in particular, 1 Mon = HR 2107 = HD 40535) perform probably. nonradial pulsation (see Section III and Table III in Breger, 1979). New detailed observations and theoretical investigations are required in order to understand the peculiarities of the stars considered in this note. TS.G. TSVETKOV Department of Astronomy University of Sofia Anton Ivanov Street 5 1126 Sofia, Bulgaria References: Breger, M.: 1979, Publ.Astron.Soc.Pacif. 91, 5 [BIBCODE 1979PASP...91....5B ] Cox, J.P.: 1980, "Theory of Stellar Pulsation", Princeton University Press. [BIBCODE 1980tsp..book.....C ] Dravins, D., Lind, J. and Sarg, K.: 1977, Astron.Astrophys. 54, 381 [BIBCODE 1977A&A....54..381D ] Dziembowski, W.: 1977, Acta Astron. 27, 95 [BIBCODE 1977AcA....27...95D ] Faulkner, D.J,: 1977, Astrophys.J. 218, 209 [BIBCODE 1977ApJ...218..209F ] Garrido, R. and Sanchez-Lavega, A.: 1983, Inf.Bull.Var. Stars, No. 2368 Iben, I.: 1967, Ann.Rev.Astron.Astrophys. 5, 571 [BIBCODE 1967ARA&A...5..571I ] Kurtz, D.W.: 1982, Monthly Notices Roy.Astr.Soc. 200, 807 [BIBCODE 1982MNRAS.200..807K ] Musielok, B. and Kozar, T.: 1982, Inf.Bull.Var. Stars, No. 2237 Paczynski, B: 1970, Acta Astron. 20, 49 [BIBCODE 1970AcA....20...47P ] Tsvetkov, Ts.G.: 1979, Inf.Bull.Var. Stars, No. 1548 Tsvetkov, Ts.G.: 1982, Soviet Astron.J. (Astron. Zh.) 59, 1103 [BIBCODE 1982AZh....59.1103T ] CORRECTION TO I.B.V.S. No. 2489 "In the discussion of FT Ori I should have noted that J. Tomkin was, in fact, the first to observe line doubling in that system. I am collaborating with him in the analysis of our spectroscopic material." C.H. LACY