COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2603 Konkoly Observatory Budapest 15 October 1984 HU ISSN 0374 - 0676 SEARCH FOR B-TYPE VARIABLE STARS IN OPEN CLUSTERS The search for beta Cephei stars in open clusters and OB associations can provide valuable information, in order to get a reliable observational definition for this type of variable stars. After the pioneer work of Hill (1967), some astronomers have pointed out the significance of these searches, which have been up to now mostly restricted to clusters in the southern hemisphere. We have started an observational program for northern clusters, which has already produced the first results (Delgado et al., 1984). The clusters listed in the table deserve a particular attention in this respect. They have been selected from the catalogues of Becker and Fenkart (1971), Mermilliod (1976) and Lynga (1981), according to the following criteria: - Observable from our latitude (37d N) - Magnitude of brightest star <10 - Earliest spectral type between O6 and B4 -Included in one of those age groups of Mermilliod (1981), containing clusters with already detected B-type variable members The second criterium is imposed by our instrumental capabilities. However, a number of clusters large enough can be selected. The table contains the number of the cluster in the NGC or IC catalogues, the coordinates (equinox 1950.0), the youngest spectral type, the magnitude of the brightest member and the logarithm of the age in years. An asterisk indicates that some members of the cluster are confirmed or suspected variables. Number Alpha Delta ST m Log age Ref. ------------------------------------------------------ NGC 457 01 15.9 +58 04 B1 6 7.40 581 01 29.9 +60 27 B2 9 7.35 637 01 39.4 +63 55 B0 8 654 01 40.6 +61 38 B0 10 7.18 663 01 42.6 +61 00 B0 9 7.35 869(*) 02 15.5 +56 55 B0 7 6.75 1,2,3 884(*) 02 18.9 +56 53 B0 7 6.50 1,2,3 1502(*) 04 03.3 +62 12 B0 7 7.30 1 1960 05 32.8 +34 06 B3 9 7.40 2169(*) 06 05.6 +13 58 B1 7 7.70 1 2244 06 29.7 +04 54 O5 7 6.48 2264 06 38.3 +09 56 08 5 7.30 6823 19 41.0 +23 11 O7 9 6.30 6830 19 48.9 +22 56 B0 10 8.0 6871(*) 20 04.0 +35 58 O6 7 7.0 4 6883 20 09.4 +35 42 B3 8 7.17 6910 20 21.3 +40 37 B0 7 7.0 6913 20 22.1 +38 22 B0 9 7.0 7160(*) 21 52.3 +62 22 B2 7 7.0 1 7235 22 10.8 +57 02 B0 9 6.3 7380 22 45.0 +57 50 O9 10 6.58 7510 23 09.4 +60 18 O9 10 7.0 7788 23 54.2 +61 07 B1 10 7.2 7790 23 55.9 +60 56 B4 10 7.82 IC 1805 02 28.9 +61 14 O6 9 6.12 4996(*) 20 14.6 +37 29 B0 8 7.0 5 ------------------------------------------------ 1.- G. Hill, 1967: Astrophys. J. Suppl., 14, 237 2.- J.R. Percy, 1972: Pub. Astron. Soc. Pacific, 84, 420 3.- R. Garrido and A.J. Delgado, 1982: IBVS, No. 2080 4.- A.J. Delgado et al., 1984: Astron. Astrophys. Suppl. In press 5.- A. J. Delgado et al., 1984: In preparation In our opinion, the systematic performance of such observations should clarify two main problems related to beta Cephei stars: 1/ Precise determination of the zone in the HR diagram, in which B-type variable stars are found. This obviously leads to the knowledge of the evolutionary status of the beta Cephei stars and to defining the limits of the instability strip or box, if any. 2/ Possibility of establishing a period - luminosity or period - luminosity - colour relation for stars of the same age and chemical composition and of testing the possible dependence of this relation on the parameters of the cluster. As mentioned before, we are presently carrying out observations on the clusters listed in the Table. Any information concerning the member stars of these clusters should be acknowledged by the authors. A.J. DELGADO, E.J. ALFARO, R. GARRIDO and J.M. GARCIA-PELAYO Instituto de Astrofisica de Andalucia C.S.I.C., Apdo. 2144, 18080 Granada Spain References: Becker, W., and Fenkart, R.P., 1971: Astron. Astrophys. Suppl. Ser., 4, 241. [BIBCODE 1971A&AS....4..241B ] Delgado, A.J., Alfaro, E.J., Garcia-Pelayo, J.M., Garrido, R., and Vidal, S:, 1984: Astron. Astrophys. Suppl. Ser., in press. [BIBCODE 1984A&AS...58..447D ] Hill, G., 1967: Astrophys. J. Suppl., 14, 237. [BIBCODE 1967ApJS...14..263H ] Lynga, G., 1981: Catalogue of open cluster data; Stellar Data Center. Observatoire de Strasbourg. [BIBCODE 1981ADCBu...1...90L ] Mermilliod, J.C., 1976: Astron. Astrophys. Suppl. Ser., 24, 159. [BIBCODE 1976A&AS...24..159M ] Mermilliod, J.C., 1981: Astron. Astrophys. Suppl. Ser., 44, 467. [BIBCODE 1981A&AS...44..467M ]