Publications of the Astronomical Society of the Pacific 90:201-203, April 1978 SPECTRAL TYPES in the PLEIADES HELMUT A. ABT

Publications of the Astronomical Society of the Pacific 90:201-203, April 1978

SPECTRAL TYPES IN THE PLEIADES

HELMUT A. ABT AND HUGO LEVATO* Kitt Peak National Observatory,f Tucson Received 1977 October 4, revised 1978 January 23

New spectral classification of 49 of the brightest stars in the Pleiades shows the following peculiarities: (1) three Ap(Si) stars, of which one is a member of a 2^46111 double-lined binary with an Am secondary, (2) an Ap(Hg,Mn) star that may be a member of the cluster, (3) four Am stars, of which two are only marginally abnormal, and (4) three shell spectra that include the pronounced case of Pleione and two mild shell spectra called "sn". The Ap + Am system should be checked for eclipses. Key words: open clusters—peculiar stars—spectral classification

The Pleiades is an open cluster at 128 pc (Crawford terisks in Table I were observed with only the lower and Perry 1976) in which the brightest stars are rapid- ly-rotating late Β stars, most of the A's have nearly TABLE I normal rotational velocities, and the main sequence ex- Spectral Classification and Absolute Magnitudes tends to the M dwarfs (Johnson and Mitchell 1958). Hz HD Spectral Type Mv This last conclusion indicates that the duration of star 43 23194 Am (K/H/M=A5/A7V/A7) + 2^2 8 88 23247 F3 V + 3. 24 formation was extended (Pesch 1961) from about 2.2 92 23246 A8 V +2 . 60 8 7 117 23288 Β 7 V -0.28 X 10 to 6 χ 10 yr ago (Herbig 1962). Photometry 126 23302 B6 III -1.84 on the UBV system has been published by Mitchell 145* 23326 F 4 V + 3.40 and Johnson (1957) and Johnson and Mitchell (1958), 146* 23325 Am (K/H/M=A4/F1V/F2) + 2.72 150 23324 B8 V (standard) + 0.01 and on the Strömgren four-color system by Crawford 156 23338 B6 IV (standard) -1.31 and Perry (1976). Mendoza (1956) has classified the 187 23361 A3 V + 2.22 brighter cluster stars. The cluster has one known pro- 206 23375 A9 V + 2.83 216 23387 Al Vp(Cr,Si) + 1.01 nounced shell star (Mendoza 1956), namely Pleione = 242 23408 B7 Illsn -1.83 251 23409 A3 V + 2 .13 HD 23862, and several marginal Am stars (Mendoza 255 23432 B8 V + 0.05 1956; Abt 1958; Conti 1967). The apparent lack of Ap 265 23441 B9 Vn + 0.73 and pronounced Am stars in the Pleiades has lead sev- 313 23479 AS V +2.31 323 23480 B6 V -1.58 eral authors (Eggen 1965; Abt et al. 1965; van den 341 23489 A2 V + 1.68 23512 A2 V + 1.66 Heuvel 1967) to suppose that such stars can occur only 371 388* 23511 F5 V + 3.59 in older clusters, such as the Hyades, Coma, Praesepe, 436 23568 B9 Vn +1.00 and Ursa Major stream. There are other interesting as- 44 7 23567 F0 V + 2.41 457 23585 F0 V + 2.72 pects and observations about the cluster, but they do 484* 23608 F5 : V + 3.02 not seem to be related to the present search for abnor- 501 23607 F0 V + 2.49 508 23629 AO V +0.64 mal spectra in this cluster. 510 23632 Al V +1.30 We classified 49 of the brightest cluster members. 513 23628 A4 V +1.93 520 23631 Am (K/H/M=A0/A2V/A2.5) +1.38 These include all but three (HD 23156, HD 23410, 534 23643 A3. 5 V +2.16 HD 23924) of the stars listed by Mendoza and brighter 540 23642 AO Vp(Si) + Am +0.96 542 23630 Β7 III (standard) -2.74 than Β = 8% plus 12 fainter stars. The stars are listed 693 23733 A9 V + 2.59 in Table I with their Hertzsprung (1923) and Henry 722 23753 B8 Vn -0.19 Draper numbers. We obtained wide (1.2 mm) spectra 742 23763 A2 V +1.45 -1 757* 23778 F7 V + 3.34 of 128 Â mm reciprocal dispersion with the 90-cm 792 23791 F0 V + 2.65 -1 870 23850 B8 III (standard) -2.00 Cassegrain spectrograph and of 39 Â mm with the 878 23862 B8 Vn + shell (Hl^e II,Ca II) -0.58 2.1-m Cassegrain spectrograph. Star numbers with as- 885 23863 A8 V + 2.51 891 23872 A2.5 Vn +1.89 910 23873 B9.5 IVsn + 0.97 ö 924 23886 A4 V +2.30 Now a member of the Carrera del Investigador Cientifico del 977 23923 B8.5 Vn + 0.52 Consejo Nacional de Investigaciones Científicas y Técnicas de la Re- 996 23948 A2 V +1.93 publica Argentina. 1003 23964 B9.5 Vp(Si,Sr,Cr)s +0.82 •¡•Operated by the Association of Universities for Research in As- 1069 24013 A3 Vn +1.87 tronomy, Inc. under contract No. AST 74-04129 with the National 1129 24076 A2 V + 0.98 Science Foundation. HR 1185 23950 B9 IVp(Hg,Mn,Si)sn 201

Spectral Type Fig. 1—An H-R diagram for the Pleiades derived from new spectral types and absolute magnitudes based mostly on the photometry of Craw- ford and Perry (1976). The zero-age main sequence (ZAMS) is taken from Johnson (1963). Stars with luminosity classes other than V and ones with abnormal spectral characteristics (Ap, Am, shell) are marked; normal-luminosity class V stars are indicated with filled dots.

dispersion. The spectra were classified on a Boiler and ally strong Si h λλ4128-30 lines. The combination of Chivens spectra-comparator against standards by Mor- Ap -f Am has been found before, e.g. a Piscium, but gan and Keenan (1973) or in a forthcoming atlas by not in so closely spaced a binary. This makes a search Morgan, Abt, and Tapscott (1978). The types are listed for eclipses even more important because an eclipsing in Table I along with absolute magnitudes, Mv, based Ap star would tell us much about star spots. mostly on corrected visual magnitudes by Crawford Bidelman (see Abt and Morgan 1969) pointed out and Perry (1976), and a distance modulus of 5^54; a that HR 1185 = HD 23950, an Ap(Hg,Mn) star, may few M^'s came from the Mitchell-Johnson photometry be a member of the cluster. Although it is nearly 2° and corrections for reddening derived from the present south of Atlas (HD 23850), it has almost identically the types. Figure 1 shows the H-R diagram with the Ap, same proper motions and a similar radial velocity. Our Am, shell, and non-V stars marked. classification for this star is B9 ÍVp(Hg,Mn,Si)sn, which Our spectral types agree very well for the normal agrees approximately with that by Cowley et al. stars with those by Mendoza; ours average 0.04 ± 0.08 (1969). If it were a cluster member, it would fit {Mv = spectral classes later and we agree by 0 ± 0.3 in lumi- -(-0^4, B9) very close to the other three Ap stars in nosity classes. However, we found more abnormal Figure 1. The presence of an Hg,Mn star in a cluster spectra in the cluster, mostly through the use of the as old as the Pleiades is no longer surprising in view of higher dispersion spectra. Let us discuss these peculiar the results of other recent cluster classification studies. stars. In addition to being an Ap star, HR 1185 has a weak 1. Ap stars. There are three silicon stars in the clus- shell spectrum (see §3). ter. HD 23387 has strong lines of Cr ι and Si n. 2. Am stars. We found four Am stars in the cluster. HD 23964 has very sharp lines with unusually strong Two are moderately pronounced examples: the one Sin λλ4128-30, Sni λλ4077 and 4215, Cn λλ4354 (HD 23325) mentioned by Mendoza and the companion and 4360, and perhaps Mg π λ4481 and Fe π lines. But to HD 23642 (see above). The remainder (HD 23194, the most interesting Ap star is the double-lined binary HD 23631) are marginal Am stars with ranges of only HD 23642, which has a period of 2Í46111 (Pearce 0.2-0.3 classes between the Ca π Κ and metallic-line 1957; Abt 1958). The secondary is known to be an Am types. We agree in this with Conti (1967), who found star because its strongest Fe ι lines are stronger than its HD 23631 and two other outlying stars (HD 22615, Ca h Κ line. Now we note that the primary has unusu- HD 24368) to have Am spectra.

3. Shell stats. Pleione (HD 23862) has a pronounced shall refrain from a further analysis until the whole set shell spectrum at present showing sharp absorption of clusters can be discussed. cores in the Balmer lines and shell lines due to Fe n, Ca π H and K, and others; all these are superimposed REFERENCES on a broad-lined B8 V spectrum. In addition the cluster Abt, H. A. 1958, Ap. J. 128, 139; errata Ap. J. 129, 524. has several stars like those in the Orion association Abt, H. A, and Levato, H. 1977, Pub. A.S.P. 89, 797. Abt, Η. Α., and Morgan, W. W. 1969, AJ. 74, 813. (Abt and Levato 1977) that have both sharp and broad Abt, Η. Α., Barnes, R. C., Biggs, E. S., and Osmer, P. S. 1965, Ap. lines. The sharp lines are generally due to Ca n, Si π, J. 142, 1604. Fe π, and C ii; the broad lines are mostly due to He i. Conti, P. S. 1967, in The Magnetic and Related Stars, R. C. Cam- These stars show mild examples of the effects exhibited eron, ed. (Baltimore: Mono Book Corp.), p. 321. by extreme shell stars such as Pleione and 48 Librae. Cowley, Α., Cowley, C., Jaschek, M., and Jaschek, C. 1969, A./. 74, 375. We labeled these stars "sn", a combination of the stan- Crawford, D. L., and Perry, C. L. 1976, AJ. 81, 419. dard symbols for sharp and broad (nebulous) lines. In Eggen, O. J. 1965, in Galactic Structure, A. Blaauw and M. this cluster there are two such stars (HD 23408, Schmidt, eds. (Chicago: University of Chicago Press), p. 111. HD 23873) plus the possible member HR 1185. Huang Herbig, G. H. 1962, Αρ. J. 135, 736. and Struve (1956) suggested that the peculiarities in Hertzsprung, Ε. 1923, Effective Wavelengths of Stars in the Pleiades (Mem. Acad. r. Sei. Lettres de Denmark, Copenhague). HD 23408 = Maia are due to a pole-on aspect. Huang, S.-S., and Struve, O. 1956, Ap. J. 123, 231. Johnson, H. L. 1963, in Basic Astronomical Data, K. Aa. Strand, ed. 4. Luminous stars. Note that most of the stars more (Chicago: University of Chicago Press), p. 204. than lm above the ZAMS in Figure 1 are recognized Johnson, H. L., and Mitchell, R. I. 1958, Ap. J. 128, 31. giants or subgiants or a shell star (Pleione) or an SB2 Mendoza V, Ε. Ε. 1956, Αρ. J. 123, 54. Mitchell, R. I., and Johnson, H. L. 1957, Αρ. J. 125, 414. (HD 23642). The reverse is not true: HD 23873 seems Morgan, W. W., Abt, H. Α., and Tapscott, J. W. 1978 (in prepara- to have a subgiant spectrum (and a weak "sn^ shell) tion). but is close to the ZAMS. Morgan, W. W., and Keenan, P. C. 1973, Ann. Rev. of Astr. and This is the 12th of about 16 clusters and associations Αρ. 11, 29. to be searched for abnormal spectra. Since the number Pearce, J. Α. 1957, Pub. Dominion Astrophys. Obs. 10, 435. Pesch, P. 1961, Ap. J. 133, 1085. of such spectra is statistically small per cluster, we van den Heuvel, E. P. J. 1967, Bull. Astr. Inst. Netherlands 19, 11.