COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2249 Konkoly Observatory Budapest 1982 December 15 HU ISSN 0374-0676 ON DELTA SCUTI STARS IN OPEN CLUSTERS 29 Delta Scuti stars are already known as members of different open clusters. Data for these variables are given in Table I. Table I Praesepe m0 - M = 6.20 Av = 0.0 log t = 8.54 P = 0.055d (BT, BV Cnc excluded) Mv = +2.0 (BT Cnc excluded) 1. BT Cnc = KW 204 P = 0.102d F0III V = 6.68 Mv = +0.5 2. BR Cnc = KW 45 0.038 F0Vn 8.26 +2.1 3. BS Cnc = KW 154 0.051 A9Vn 8.51 +2.3 4. BU Cnc = KW 207 0.053 A7Vn 7.68 +1.5 5. BN Cnc = KW 323 0.039 A8V 7.80 +1.6 6. BQ Cnc = KW 292 0.074 F2Vn 8.18 +2.0 7. BV Cnc = KW 318 5h:: F0V 8.66 +2.5 8. BW Cnc = KW 340 0.072 F0Vn 8.48 +2.3 9. BX Cnc = KW 445 0.053 A7V 7.97 +1.8 10. BY Cnc = KW 449 0.058 A7Vn 7.92 +1.7 Pleiades m0 - M = 5.64 Av = 0.06 log t = 7.2 P = O 032 Mv = +2.5 1. V 539 Tau = HII 1266 P = 0.032d A9V V = 8.27 Mv = +2.6 2. V 624 Tau = HII 158 0.020 A7V 8.50 +2.8 3. V 647 Tau = HII 1362 0.047 A7V 8.10 +2.4 4. V 650 Tau = HII 1425 0.031 A3V 7.78 +2.1 Coma m0 - M = 4.55 Av = 0.0 log t ~ 8.6 P = 0.055d Mv = +1.9 1. FM Com = HR 4684 P = 0.05515028d A7V V = 6.44 Mv = +1.9 Hyades m0 - M = 3.29 Av = 0.0 log t = 8.83 P = 0.080d Mv = +1.7 1. nu2 Tau = VB 60 P = 0.133d A8Vn V = 4.29 Mv = +1.0 2. Theta2 Tau = VB 72 0.080 A5V 4.85 +1.6 3. rho Tau = VB 95 0.067 A8Vn 4.66 +1.4 4. V 480 Tau = VB 123 0.042 A7IV 5.10 +1.8 5. V 483 Tau = VB 30 0.054 F0V 5.58 +2.3 6. V 696 Tau = VB 33 0.036 A9V 5.23 +1.9 7. V 775 Tau = VB 38 0.062 F0m 5.72 +2.4 8. V 777 Tau = VB 141 0.162 A8Vn 4.48 +1.2 alpha Per m0 - M = 5.94 Av = 0.30 log t = 7.1 P = 0.034 Mv = +2.7 1. V 459 Per = H 501 P = 0.037d F0IV V = 9.14 Mv = +2.9 2. V 461 Per = H 606 0.035 A8 V 8.98 +2.7 3. V 465 Per = H 906 0.030 A6Vn 8.78 +2.5 Table I (cont.) NGC 2264 m0 - M = 9.10 Av = 0.21 log t ~ 6 P = 0.117d: Mv = +0.7 1. V 588 Mon = W 2 P = 0.11d: A7III-IV V = 9.68 Mv = +0.4 2. V 589 Mon = W 20 0.124 F2III 10.27 +1.0 NGC 7789 m0 - M = 12.20 Av = 0.89 log t ~ 9.7 P = 0.17d: = +0.7 1: V 521 Cas P = 0.17d: Mv = +0.7 V = 13.76 Distance moduli (m0 -M),for Pleiades, Praesepe, Hyades, alpha Per and NGC 2264 are from Kholopov (1980); those for Coma cluster and NGC 7789 are from Becker and Fenkart (1971); ages of the clusters are directly from Lindoff, (1968) or in the same system of ages; spectral types, V-magnitudes, periods for individual variables are from different modern sources; absolute magnitudes Mv are based on adopted values of distance moduli, V and interstellar absorption Av. In the case of Theta2 Tau V, Sp and Mv are given for companion (Peterson et al., 1981) though it is unknown which star is unstable. It is interesting to note that two stars in the Hyades cluster, V 775 Tau and V 777 Tau are X-ray sources, according to recent published data. There is a difference between the known open cluster variables and field stars: Delta Scuti stars having large light amplitudes (more than about 0.1mag) are absent in the clusters, excluding only one possible outlying (about 10deg from the cluster) member of the Hyades cluster VZ Cnc (Eggen, 1979). Besides 29 small amplitude variables which are all Delta Scuti type stars, one can find five more suspected open cluster variables of this type in Rufener (1981). These stars are probably also small amplitude variables. Therefore, about one sixth of all known Delta Scuti stars are small amplitude members of different open clusters. Two correlations for open cluster Delta Scuti stars are shown in Figure 1 and Figure 2: mean period and mean Mv of the cluster variables versus the age of the cluster; NGC2264 was omitted by the reason of its extremely young age and peculiar evolutionary status of its two known Delta Scuti stars. The two Figures show that, the greater the age, the longer the mean period of cluster variables and the higher their mean luminosity. The present statistics unfortunately holds almost fully on dwarf Delta Scuti stars, which themselves cannot have large pulsational amplitudes. More statistics on giant stars is needed to confirm (or disprove) the result on small amplitudes of open cluster members. It is interesting to note here that several large amplitude Delta Scuti stars along with short- periodic SX Phe type variable (Jorgensen, 1982) can be typical for globular clusters with different metal abundances (RS Gru, XX Cyg). [FIGURE 1] [FIGURE 2] More serious attention must be paid to the search for these variables in open clusters, old open clusters and globular clusters for better understanding of population type range, age range, mass range etc. for the whole Delta Scuti complex. We are obliged to Dr. P.N. Kholopov, to Dr. Yu.N. Efremov and to Dr. M. Breger for useful comments and discussion. M.S. FROLOV B.N. IRKAEV Astronomical Council of the Dushanbe Astrophysical Institute of USSR Academy of Sciences Tadjik Academy of Sciences USSR USSR References: Becker W, and Fenkart R., 1971, Astron. Astrophys. Suppl. 4, 241 [BIBCODE 1971A&AS....4..241B ] Eggen O.J., 1979, Astrophys. J. Suppl. 41, 413 [BIBCODE 1979ApJS...41..413E ] Jorgensen H.E., 1982, Astron. Astrophys 108, 99 [BIBCODE 1982A&A...108...99J ] Kholopov P.N., 1980, Russian Astron. J., 57, 12 [BIBCODE 1980AZh....57...12K ] Lindoff U., 1968, Ark. Astr. 5, No. 1, 1 [BIBCODE 1968ArA.....5....1L ] Peterson D.M., Baron R.L., Dunham E. and Mink D., 1981, Astron. J., 86, 1090 [BIBCODE 1981AJ.....86.1090P ] Rufener F., 1981, Astron. Astrophys. Suppl. 45, 207 [BIBCODE 1981A&AS...45..207R ]