THE AsTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 32:651-680, 1976 December © 1976. The American Astronomical Society. All rights reserved. Printed in U.S.A. 1976ApJS...32..651K METALLICISM AND PULSATION: AN ANALYSIS OF THE DELTA DELPHINI STARS DONALD W. KURTZ* University of Texas at Austin, and McDonald Observatory Received 1976 February 23; revised 1976 April 12 ABSTRACT Fine abundance analyses of eight o Delphini stars and one o Scuti star relative to four com­ pariso~ s~ndard stars are presented. Five of the o Delphini stars are shown to have abundances most s1nnlar to the evolved Am stars. It is argued that these abundances are different from the main-sequence Am star and Ap star abundances, and that similarities to the Ba II star abundances are coincidental. We suggest that the anomalous-abundance oDelphini stars are evolved metallic­ ~?e stars on the basis _of t~eir at;>u~dances, position in the (ft, Mv) plane, inferred rotation veloc­ ities, and perhaps th~ir bmary mc1~e?ce. Some of the o Delphini stars are o Scuti pulsators. We argue that pulsation and metallic1sm are mutually exclusive among the classical Am stars but may ~oexist in other stars related to the classical Am stars. A preference for the diffusion­ hyp~thes1s model for the metallic-line stars is stated and supported, and the implications of the coexistence of pulsation and diffusion are discussed. Subject headings: stars: abundances - stars: o Scuti - stars: metallic-line - stars: pulsation I. INTRODUCTION th~ Ca II H and K lines are weak for the MKA type. The o Delphini stars were defined as a class by It 1s also noted that all of the o Scuti variables that Bidelman (1965), who designated 15 of 82 metallic­ they classify have a luminosity class brighter than line stars as 8 Delphini from an objective-prism sur­ class V. Malaroda (1973, 1975) uses the MKA cri­ vey. The only clarification of the classification was teria for 8 Scuti variables with peculiar spectra to that the 8 Delphini stars are metallic-line stars "in classify some stars as o Delphini. We agree that the which the difference between the metallic-line type MKA peculiar 8 Scuti stars are, for classification pur­ and the K-line type is rather small." The class was poses, o Delphini stars, but we believe that there is a used by Cowley and Cowley (1964), who classified a possible confusion between the 8 Delphini and 8 star as having a spectrum "like 8 Del." They (Cowley Scuti classes which should be clarified. and Cowley 1965) reexamined Bidelman's Am and We use the 8 Scuti classification to refer to photo­ 8 D~lphi~ stars using slit spectra, and changed the metrically variable stars within 3 magnitudes of the class1ficat10n of some stars but did not elaborate on main sequence, with periods between 0.5 and 5 hours, the o Delphini classification. and with amplitudes generally less than a few hun­ Cowley (1968) states that "the metallic line spectrum ~redths of a magnitude (Baglin et al. 1973). They are [of a 8 Delphini star] resembles that of an F2 IV star mterpreted as pulsational variables lying in the exten­ but the hydrogen and ionized calcium lines are very sion of the Cepheid instability strip where it crosses narrow." This description is expanded in the Bright A the main sequence between spectral types A2 and FO. Star Catalog (Cowley et al. 1969) in the description of We use the o Delphini classification to refer to stars o Del itself: "The spectrum of 8 Del shows rather with spectra similar to that of 8 Del itself-that is, narrow but equal H and K lines. Hydrogen lines are late A and early F subgiants and giants with dispar­ narrow; metallic line spectrum is rich and similar to ate K-line and metal-line spectral types. Delta Scuti that of a late A metallic line star." It is further ex­ is a photometric classification and 8 Delphini a plained (Cowley and Crawford 1971) that ,\,\ 4173- spectroscopic classification; the two, as will be shown, 4178 (Fe r, Y II, Fe II) and ,\ 4150 (Zr II) are especially cannot be used interchangeably. enhanced, whereas ,\ 4417 (Ti II) is weak, as are the Following the initial calculations of Michaud (1970), other metals (Cowley 1973). Watson (1970, 1971) and Smith (1971) suggested that I~ the defining paper for the MKA system for element diffusion could account for the anomalous F giants, Morgan and Abt (1972) classify 14 of the abundance patterns seen in the metallic line stars. 16 8 Scuti variables listed by Danziger and Dickens Smith (1971, 1973a) used his extensive observational (1967). Four of these stars, including o Del itself data to build a qualitative model for the Am stars in (PO IVp), are noted to have peculiar spectra in which which it was suggested that element diffusion occurs in the radiative zone between the H 1, He 1, and the . * Visiting Student, Kitt Peak National Observatory, which is operated by the Association of Universities for Research in He II ionization zones. This model explains the ob­ Astronomy, Inc., under contract with the National Science served abundance anomalies, their temperature depen­ Foundation. dence, the low-temperature cutoff of the Am domain, 651 © American Astronomical Society • Provided by the NASA Astrophysics Data System 652 KURTZ Vol. 32 . and the correlation between metallicism and rotation. used to help determine whether the members of the The major drawback of the model is that the dif­ class are astrophysically related. In discussing these fusion velocities are predicted to be on the order of stars we find it convenient to break them up into two 10- 5 cm s-1 , whereas there is little theoretical evi­ subgroups based on their apparent visual magnitudes 1976ApJS...32..651K dence indicating whether stability against turbulent and the source of their spectral-type classifications. or convective mixing on that velocity scale is plausible The first group we will refer to as the bright S Del­ or not. Latour et al. (1975) suggest that convective phini stars. They are stars classified o Delphini or Fp overshoot from the He II ionization zone may disrupt from slit spectra by Cowley et al. (1969), Cowley and the above radiative zone sufficiently that element Crawford (1971), Morgan and Abt (1972), and Mala­ diffusion may not be able to occur there. roda (1975) and which have mv < 6.7 mag. The Breger (1970) showed that, in general, Am stars second group we will refer to as the faint 8 Delphini do not pulsate, and he hypothesized (Breger 1972) stars. They are stars originally classified as o Delphini that, within the diffusion model for A stars, either by Bidelman (1965) from objective-prism plates and (i) pulsation disrupts the extreme stability necessary later reclassified by Cowley and Cowley (1965) using for diffusion to occur to produce an Am star, or slit spectra. They have mv > 6.4 mag. There is some (ii) in a star in which diffusion does occur the helium overlap in apparent visual magnitude between the sinks out of the He II ionization zone, thus damping two subgroups, so we reiterate that the subdivision is the driving mechanism for pulsation in 8 Scuti stars. for convenience of discussion only, with no a priori Baglin (1972) and Vauclair et al. (1974) calculate implication about the physical nature of the members that, in a star in which diffusion occurs, helium sinks of each group. rapidly from the He II ionization zone. Several stars Table 1 lists the photometric indices of the uvbyf3 have been labeled pulsating Am stars, but Kurtz et al. system from Lindemann and Hauck (1973) for the (1976) have shown that other explanations are more bright 8 Delphini stars. Table 2 lists the indices ob­ plausible in each of these cases. There is at present no tained by the author for the faint 8 Delphini stars known exception to the exclusion between the classical along with the classification of those stars by Bidel­ Am stars and the 8 Scuti pulsators. man (1965) and by Cowley and Cowley (1965). Some of the 8 Delphini stars, however, appear to be related to both the Am stars and the 8 Scuti stars. a) uvbyf3 Photometry of the As these 8 Delphini stars are subgiants and giants Faint Delta Delphini stars with Am-like spectra, one might a priori postulate that they may have evolved from Am stars. Some of Observations were obtained on 1974 September 6 the 8 Delphini stars are also large-amplitude 8 Scuti and September 8 and on 1975 February 15 with the pulsators. This leads us to ask, Is there a region of University of Texas Volksphotometer attached to the H-R diagram where pulsation and metallicism the McDonald Observatory 76 cm telescope. Each can coexist? If so, what effect does this have on the plausibility of the diffusion hypothesis as applied to TABLE 1 the Am stars and to the o Scuti variables? What is the physical nature of the 8 Delphini stars? In this BRIGHT DELTA DELPHINI STARS paper we will begin to answer these questions. HR v b-y m1 C1 /3 Reference* In § II we analyze uvbyf3 photometry of the 8 Del­ phini stars and compare it with uvbyf3 photometry of 421. ... 5.68 0.208 0.151 0.674 2.726 4, 6 the metallic-line stars. In § III the relationships among 1706 .... 5.06 0.130 0.180 0.998 2.799 1 rotation, pulsation, and metallicism and their implica­ 1974 .... 6.44 0.160 0.175 0.764 2.746 1 2094 ...