COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 162 Konkoly Observatory 10 October 1966 DETERMINATION OF THE MASS AND THE MODEL OF THE VARIABLES: RT AURIGAE, ETA AQUILAE, X CYGNI, MIRA CETI AND BM CASSIOPEIAE OF POP. I, AND RR LYRAE AND TWO TYPICAL VARIABLES OF POP. II. The authors, prosecuting a work started with the study of the internal constitution of Eta Aquilae, published in the Combined Colloquium of the Commissions 27 and 42, Bamberg 1965(1), have applied the same computational scheme to study the following stars: RT Aurigae, X Cygni, Mira Ceti, of Population I, and RR Lyrae and two typical variables of Pop. II. Assuming the radius and the effective temperature derived from the observations, they compute for each of these stars a set of models with different masses, and the characteristic frequency of: the adiabatic oscillation for every model; then they choose the model, and therefore the mass, for which the frequency so calculated equals the observed one. The authors put in evidence that for each of the studied stars the mass so chosen is nearly coincident with the one corresponding to the minimum of the graph sigma = sigma (M), which can be made for each star, likewise to that noticed for Eta Aquilae in the previously mentioned paper. Moreover, the authors applied this method to the star BM Cassiopeiae, the mass of which has been determined in a different way (M = 14.3)(2), and they found a very remarkable agreement, as shown in Table 1, where the results for each star are referred. (1) A. Masani, A. Martini, M. Nelli, E. Albino - Study of the Constitution of Eta Aquilae - Astronomisches Institut der Universitat, Erlangen- Nurnberg, Bd. IV, Nr. 40. - IAU Coll. on Var. Stars p. 255. [BIBCODE 1965VeBam..27..255M ] (2) Thiessen - Zeitschr. fur Astr. - 39. 65, 1956. [BIBCODE 1956ZA.....39...65T ] Table 1 Star Pop. R(cm) Teff(degK) sigma_obs M x_i X_e M_e sigma_calc.ad lambda (cm^-1) RT Aur I 9.6 (11) 6.0 (3) 1.95(-5) 0.806 .008 .0059 0.707 1.9 (-5) -1.5 (-5)+3.05(-5)i Eta Aqu I 4.0 (12) 5.12(3) 1.03(-5) 5.35 .0084 .0032 1.29 1.06(-5) -2.14(-6)+9.11(-6)i X Cyg I 4.77(12) 5.0 (3) 4.43(-6) 3. .0046 .0033 1.73 4.16(-6) -2.93(-6)+3.46(-6)i Mira I 2.73(13) 2.3 (3) 2.14(-7) 0.6 .00005 .00003 0.338 2.03(-7) -7.52(-11)+2.82(-7)i RR Lyr II 3.75(11) 8.0 (3) 1.32(-4) 1.75 .0568 .0228 0.776 1.3 (-4) -7.59(-7)+1.3 (-4)i - II 5.5 (11) 8.0 (3) 5.1 (-5) 1.5 .022 .013 0.655 5.47(-5) -2.08(-5)+4.58(-5)i - II 1.92(12) 5.9 (3) 4.88(-6) 2. .0098 .004 0.664 5.12(-6) -4.42(-7)+7.57(-6)i BM Cas I 1.56(13) 4.41(3) 2.69(-6) 14.3 .0014 .0082 0.35 2.56(-6) -2.46(-8)+2.59(-6)i x_i = value of x=r/R in the point where L (luminosity) starts decreasing x_e = value of x=r/R in the point whee L = 0 M_e = mass of the nucleus, (in solar units), in x=x_e lambda = damping + sigma_calc._non_adiab. i. The authors continued the computation for each mass so determined, also for the non adiabatic approximation, as it is shown in Table 1. The small mass deduced for Mira Ceti is interesting: it must be underlined that, for this star, the fitting with the internal partially degenerate nucleus occurs in a satisfactory way. This fact assumes great importance to understand the evolutive process that brings to the formation of such stars. The authors give in Table 2, for its peculiar importance, the model they obtained for the variable Mira Ceti. Table 2 Model of Mira Ceti x= r/R y= m(r)/M log rho log P log K log T L(r)/L(R) 0.961 1. - 10.296 0.739 - 4.732 3.27 1. 0.814 0.907 - 8.0255 3.21 - 3.244 3.474 1. 0.675 0.774 - 8.078 3.818 1.69 4.016 1. 0.396 0.602 - 8.016 4.425 1.174 4.369 1. 0.0177 0.562 - 7.447 6.246 - 0.124 5.162 1. 0.0000493 0.5615 0.678 16.564 - 0.514 7.652 0.999 0.0000333 0.56149 1.322 17.32 - 0.536 7.808 0. Psi_1= -6.2 Psi_2= -7.2 Psi_c= 25 0. 0. 6.795 22.446 -- 7.808 0. A. MASANI, A. MARTINI, M. NELLI, Astronomical Observatory of Milano-Merate E. ALBINO Centro di Calcolo della Universita di Genova DS CYGNI L'examen de 66 cliches obtenus avec une chambre photographique Dogmar Goerz (O =113 mm, F = 494 mm ) entre juillet 1945 et janvier 1959 moritre que l'etoile DS Cygni a varie le plus souvent entre la 13e et la 14e grandeur mais aucun maximum ayant l'importance de celui du mois d'aout dernier n'a ete decele. Trois cliches du telescope Schmidt de 400 mm d'ouverture pris ulterieurement ont donne les magnitudes suivantes: T. U. m_p 1962 octobre 21,885 12,75 1966 septembre 23,890 13,2 1966 septembre 23,915 13,2 26 Septembre 1966 CH. BERTAUD Observatoire de Meudon Comme suite a la note concernant DS Cyg publiee dans le no 151 de l'IBVS, j'ai examine cette etoile sur 20 plaques de ma collection, depuis 1942. Sur 8 de ces plaques donnant la mp-limite 13,5, DS Cyg est invisible. Sur 12 autres plaques, la variable est visible: la maximum observe (24 Avril 1963) est mp 13,2 d'apres les etoiles de la S.A. 40 Mt. Wilson dans le champ de laquelle DS Cyg est se trouve egalement situee. Mais je dois faire remarquer que, selon ce qu'indique M. A. Koeckelenbergh dans sa note, les trois cliches ou l'augmentation d'eclat de la variable a ete remarquee ont ete obtenus sur des plaques Ilford HPS qui sont des plaques panchromatiques. DS Cyg etant une variable irreguliere nettement rouge (spectre N), l'augmentation d'eclat apparente peut trouver sa cause dans la nature des plaques utilisees par l'observateur. Paris, 9 Octobre 1966 R. WEBER