COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1831 Konkoly Observatory Budapest 1980 August 25 HU ISSN 0374-0676 VARIABILITY OF COOL CARBON STARS SITUATED NEAR OR IN INTERMEDIATE-AGE OPEN CLUSTERS Absolute magnitudes and masses of carbon stars are still very poorly known. Individual parallaxes of carbon stars - members of double or multiple systems or stellar clusters might substantially improve the situation. To get more reliable photometric data for carbon stars situated near or in open clusters, photographic monitoring of these stars have been carried out at Baldone with the Schmidt telescope (80/120/240 cm) of the Radioastrophysical Observatory. The observations have been made in three passbands: R(0.63) - ORWO ZPI plates + Schott RG1 filter, V - A 600 films + ZHS 17 filter, B - ZU2 or ZU21 plates + GG13 filter. Summary of the photometry of the carbon stars - apparently associated with the intermediate-age (10^9-0.4x10^8 years) open clusters are presented in Table I. Of the eleven carbon stars studied eight are named variable stars, the other three have also shown definite light variations. Some additional information for all of the stars follow. V532 Cas = CCS 3210 = MSB 75 - stable cycle length and light amplitude. V533 Cas = BC 38 - stable cycle length and light amplitude. CCS 414 - irregular light variations. CCS 184 - the interval of observations is too short to determine the type of variability. FR Per = CCS 183 = neither R(0.63)- nor V- and B-magnitudes showed variations during the observing interval. Only on one plate taken much earlier than others (in the year 1968) the B-magnitude was 0m6 fainter. This result does not contradict the statement that light variations of the star have long waves (1). SY Per =CCS 194 = IRC+50115 = AFGL 558. The elements of semiregular light variations in Table I are given according to the GCVS (7). Our observations confirm them. HN Aur =CCS 252 - semiregular light variations, average cycle length about 165 days superimposed on very slow variations with the cycle length of about 1400 days. VZ Per =CCS 112 - nonvariable according to (7). Our photometry, however, indicates light variations with a small amplitude. To get a definite conclusion photoelectric observations are necessary. DY Per =CCS 107 - in accordance with the GCVS (7) the star had semiregular light variations with a large amplitude and a long period. OQ Aur = CC5339 - irregular or semiregular light variations. BC 89 - extremely red star. Light cycles are rather stable, but maximum (or minimum) magnitude is very different for different cycles. In Table II some characteristics of the observed carbon stars and related open clusters are presented which might give evidence on cluster membership of the stars. Of the eleven stars six are included in the membership classes 1 and 2. Three of these six stars have large amplitude long-period variations, two - semiregular variation with smaller amplitudes and one - irregular variations. According to Eggen (5), Hartwick and Hesser (6), two further irregular variable carbon stars with small amplitudes are probable members of clusters of similar age with those discussed here. Thus there are eight photometrically studied carbon stars - probable members of intermediate-age open clusters. They are practically equally distributed among the types of variability M, SR, and Lb. It would be of importance to improve the statistics by studying the variability of carbon stars in intermediate-age clusters of southern sky, for example, in NGC 5822 and NGC 3114. The photometric data obtained from our earlier observations have been published for some of the stars (2,4). Additional data on the photometry of carbon stars near the clusters NGC 7789, NGC 2099, NGC 1528, NGC 1664, and NGC 744 will appear in papers submitted for publication in the serial editions:"Investigations of the Sun and Red Stars" and "Nautchnije Informacii". Table I Photometric data and spectra of the observed carbon stars 1 2 3 4 5 6 7 8 Star Obs.time V B-V V-R Max.JD24... P Sp V532 Cas 1968-80 9m9-11m1 5m1 1m5 41238 450d Ne;C6,3e V533 Cas " 12.1-14.3 3.6: 1.4 41250 305 N* CCS 414 1972-80 12.2-13.0 5.4: 1.7 - - N* CCS 184 1977-80 13.5-14.1 5: 1.9 - - - FR Per " 10.3 3.0 1.4 - - R3;C3,3 SY Per " 9.1-10.2 5.0 1.6 30525 476 Ne;C4,6 HN Aur 1971-80 11.2-11.7 4.4 1.4 - 165: N5 VZ Per 1975-78 10.6-10.8 2.2 - - - R4,C4,5J DY Per " 10.6-13.2 2.2 - - 800: RBiC4,5 OQ Aur 1969-75 14.6-15.3 3.7: 1.6 - - - BC 89 1975-79 11.4-14.4 6: 2.0 42800 470 N* 1. Name of the star in the General Catalogue of Variable Stars (7), or, if the star is not named as a variable, its number in the General. Catalogue of Cool Carbon Stars (CCS)(11) or in the lists of carbon stars found at Baldone (BC). 2. Time interval of photometric observations. 3. The range of V-magnitude according to observations made at Baldone. 4. Mean colour index B-V, for fainter stars it refers to the maximum light (symbol :). 5. Mean colour index V-R(0.63). 6. Time of light maximum in Julian days for periodic variable stars. 7. Length of the period or cycle of light variations in days. 8. Spectral class from CCS (11), Larsson-Leander (8) and Yamashita (12,13) or from objective prism spectra taken at Baldone (*). Table II Data on the observed carbon stars and related clusters 1 2 3 4 5 6 7 8 Star Cluster Age rho rho/r V_r M_ V(max) Mbsh. 10^8y V532Cas NGC 7789 9.1 22' 2.3 -46+-3 -2.3 1 V533Cas " " 28 2.9 - -0.1 2 CCS 414 NGC 2099 1.6 20 1.7 - +0.6 3 CCS 184 NGC 1528 1.0 29 2.6 - +3.0 4 FR Per " " 37 3.3 -11+-3 -0.3 2 SY Per " " 39 3.5 - 1+-8 -1.5 2 HN Aur NGC 1664 0.89 1 0.2 - -0.3 2 VZ Per Tr 2 0.5 17 1.9 -16+-5 +0.8 3 DY Per " " 22 2.4 -39+-5 +0.8 4 OQ Aur NGC 1912 0.43 20 2.3 - +3.0 4 BC 89 NGC 744 0.39 15 2.2 - -0.7 2 1.Name of the star as in Table I. 2.Name of the related cluster. 3.Age of the cluster according to Lindoff (9),in 10^8years. 4.Angular distance between the star and the cluster centre,in arc minutes. 5.The same distance expressed in angular diamater (according to Trumpler) of the cluster. 6.Radial velocity of the star according to Stanford (10) or Dean (3). 7.Visual magnitude of the carbon star at maximum light, assuming that the star belongs to the cluster. For this estimation the data from col. 3 Table I and published data on the distance of the cluster are used. 8.Membership class, estimated from rho/r, the place of the star in H-R diagram relative to the observed or expected red giant sequence of the cluster, and the data on radial velocities. Class 1 corresponds to the most probable cluster members, class 4- to likely nonmembers. Z. ALKSNE A. ALKSNIS Radioastrophysical Observatory Latvian Academy of Sciences Riga, U.S.S.R. References: 1. Ahnert, P., Hoffmeister, C., Rohlfs, E., van de Voorde,A., 1947, Veroff.Sternw.Sonneberg, 1, 156 2. Alksnis, A., Alksne, Z., Daube,I.,1973, in Photometric Investigations of Red Stars, Riga, "Zinatne",7 3. Dean, C.A., 1976, Astron.J., 81, 364 [BIBCODE 1976AJ.....81..364D ] 4. Duncans, L., 1974, Investigations of the Sun and Red Stars, No.1, 23 5. Eggen, O.J., 1974, Publ. A.S.P., 86, 960 [BIBCODE 1974PASP...86..960E ] 6. Hartwick, F.D.A., Hesser J.E.,1974.Astrophys.J., 192, 391 [BIBCODE 1974ApJ...192..391H ] 7. Kukarkin, B.V.,Kholopov, P.N., Efremov, Yu.N., Kukarkina,N.P., Kurochkin, N.E., Medvedeva, G.I., Perova, N.B., Fedorovich, V.P., Frolov, M.S.,t969-71, General Cat. of Var.Stars. Vol.1-3 (and Supplements) 8. Larsson-Leander, G., 1954, Arkiv for Astron.,1, 417 [BIBCODE 1954ArA.....1..417L ] 9. Lindoff U., 1968, Arkiv for Astron., 5,1 [BIBCODE 1968ArA.....5....1L ] 10. Sanford, R.F., 1944, Astrophys. J., 99, 145 [BIBCODE 1944ApJ....99..145S ] 11. Stephenson, C.B., 1973,Publ.Warner and Swasey Obs.,1, No. 4 [BIBCODE 1973gcss.book.....S ] 12. Yamashita, Y., 1972,Ann.Tokyo Astr.Obs.,Sec.Ser., 13, 169 [BIBCODE 1972AnTok..13..169Y ] 13. Yamashita, Y., 1975,Ann.Tokyo Astr.Obs.,Sec.Ser., 15, 47 [BIBCODE 1975AnTok..15...47Y ]