NEWSLETTER OF CHEMICALLY PECULIAR RED GIANT STARS Number 12 - June 1992 Edited by Sandy Yorka Denison University Yorka@Denison I. PRG Working Group News The IAU Working Group on Peculiar Red Giants has not had any formal activities since the distribution of the previous issue of this Newsletter (December 1991). Several members of the WG were, however, responsible for organizing a topical session on red giant stars at the recent meeting of the American Astronomical Society and/or participated in it as invited speakers, as described below. A. REPORT ON THE SPECIAL TOPICAL SESSION ON "SPECTROSCOPY AND ABUNDANCES IN RED GIANT STARS" AT THE 180th MEETING OF THE AAS IN COLUMBUS, OHIO At the recently-concluded 180th meeting of the Americal Astronomical Society in Columbus, Ohio, a half-day Topical Session on "Spectroscopy and Abundances in Red Giant Stars" was held on the morning of June 10, 1992. The program, which was organized by Hollis Johnson (Indiana) with assistance from David Lambert (Texas), George Wallerstein (Washington), and Robert Wing (Ohio State), consisted of five 20-min invited talks and three 10-min contributed papers, as follows: Robert F. Wing (Ohio State): "Two-Dimensional Spectral Classification for K,M Supergiants in the LMC" Marc H. Pinsonneault (Yale): "Rotation and Mixing in Giants" Catherine A. Pilachowski (Kitt Peak): "Lithium in Low-Mass Red Giants" Glenn M. Wahlgren (CSC/GHRS): "Spectroscopic Analyses of RV Tauri Variables" R. Earle Luck (Case Western Reserve U.) and Howard E. Bond (STScI): "Chemical Abundance Patterns in Metal-Poor Stars" Verne V. Smith (Texas): "Abundances and Nucleosynthesis in the S and Carbon Stars" George Wallerstein (Washington): "Recent Abundance Analyses of Red Giants in Globular Clusters" Robert F. Garrison (Toronto): "New Spectral Types for the Hyades Giants" The program concluded with a panel discussion moderated by Johnson, with the invited speakers (Wing, Pinsonneault, Pilachowski, Smith, and Waller- stein) serving as the panelists. Attendance was already substantial at the session's 8:30 a.m. start (much to the surprise of the first speaker) and increased throughout the morning; from this we judge the session to have been a success. The Columbus meeting was the first trial by the AAS of its plan to devote two days of its summer meetings to topical sessions proposed and organized by Society members. We hope that the high standards set by the session on Red Giant Stars and the interest shown by those attending have demonstrated the usefulness and potential of this meeting format. Abstracts of most of the papers listed above have been published in the Bulletin of the AAS (v. 24, no. 2, 1992). There is no general plan to publish the texts of the papers. We have, however, prevailed upon Verne Smith to provide a write-up of his talk for this issue of the Newsletter (see below). - - - submitted by Robert F. Wing WG Chairman B. NEXT ISSUE We plan to distribute the next issue of the Newsletter in December 1992. Please send your contributions (e.g. brief accounts of your re- search activity, notices of future meetings, ...) to the Editor, Sandy Yorka, preferably by e-mail to yorka@denison by October 15. Preprints and other paper communications should be mailed to: Dr. Sandy Yorka Dept. of Physics and Astronomy Denison University Granville, Ohio 43023 USA II. Review NUCLEOSYNTHESIS IN THE S AND C STARS Verne V. Smith University of Texas, Austin The focus here is on three aspects of nucleosynthesis in stars evolving along the asymptotic giant branch (AGB): the production of the heavy-element s-process nuclei which result from neutron captures, the appearance of lithium in a certain fraction of AGB stars, and the possible synthesis of fluorine during 4He-burning thermal pulses. One of the long-standing questions concerning the operation of the s-process in AGB stars has been the identity of the neutron source: the two candidates under consideration have been 22Ne(alpha,n)25Mg and 13C(alpha,n)16O. The recent thesis work of Andrew Vanture at the University of Washington (Vanture 1992, AJ, submitted) on the s-process abundances in metal-poor CH giants has provided powerful evidence that the 13C-source is the driving force of the s-process. Recall that one of the difficulties with the 13C neutron source is the lack of any 13C in the 4He-burning shells of AGB stars: one has been forced to invoke the mixing of protons into the regions near the He shell in order to produce 13C via 12C(p,gamma)13N(beta+,neutrino)13C. Hollowell and Iben (1988, ApJL, 333, L25) have worked hard on the nature of this mixing and it now seems that from the point of view of theory, it is quite possible to produce a "pocket" of 13C which is engulfed by the convective shell created by the 4He-burning thermal pulse, and neutrons are then produced to drive the s-process. Vanture has concentrated on the most metal-poor of the CH stars ([Fe/H] approx. -1.8 to -0.5) and finds that the abundance distribution of the s-process elements is very different in these metal-poor, heavy-element-enriched red giants when compared to more metal-rich CH or Barium stars; he finds that the ratio of "heavy" s-process elements (e.g. Ba, La, Nd, or Gd) to "light" s-process species (e.g. Sr, Y, Zr, or Mo) increases dramatically towards lower metallicities. This trend suggests a neutron source with a strength which increases with decreasing metallicity. This is in qualitative agreement with the suggestion by Clayton (1988, MNRAS, 234, 1) that the strength of the 13C neutron-source should increase with decreasing metallicity. Clayton shows that if a neutron source is independent of metallicity, while the number of neutron absorbers is dependent upon metallicity, then a larger neutron irradiance of the heavy s-process elements can be produced in stars of lower metallicity. The 13C source fulfills the requirement of being independent of metallicity, as the 13C is produced by proton captures onto 12C (which is the product of 4He burning) at the site of the s-process; the 22Ne source, on the other hand, is produced from two alpha captures onto 14N, which results from CNO burning, and is thus proportional to the intial C+N+O abundance in the star. Vanture's results provide strong hints of the 13C neutron-source being responsible for the s-process. Smith, Lubowich, and Lambert (1992, in preparation) have now surveyed approximately 150 red giants in the Magellanic Clouds for the presence, or absence, of the Li I 6707A resonance doublet. The most recent results strengthen the earlier conclusions from Smith and Lambert (1989, ApJL, 345, L75; 1990, ApJL, 361, L69) that the most luminous AGB stars in the Clouds tend to have rather strong Li I lines: the Li appears in all of the MS and S stars with luminosities above about Mbol -6. In the lower-luminosity MS, S and C stars, virtually none of these AGB stars show a detectable Li I line (one S and one C star out of 38 surveyed between Mbol -4 and -6 show the Li I line). For the luminous C stars, four Li-strong stars are found that are more luminous than approx. Mbol = -6. The Li is believed to result from "hot-bottom burning" at the base of a deep convective envelope. Recently Sackmann and Boothroyd (1992, ApJL, 392, L71) have explored the production of 7Li in their higher-mass (4-6 Msun) AGB models. Sackmann and Bothroyd's models produce large abundances of Li (Log eps(Li) approx. 3-5.5), and their abundances agree with what is observed in the Clouds (Smith and Lambert 1989) and in Galactic Li-rich S and C stars (Abia, Boffin, Isern, and Rebolo 1991, A&A, 245, L1). Whether these massive AGB stars dominate the source of 7Li that is required to raise the Li abundance from the Big Bang value of Log eps(Li) = 2.1 to the currently observed Disk value of 3.3 remains to be seen: the critical parameter will be how many of these rather masssive AGB stars can survive to these high luminosities before mass loss removes the star's outer envelope. Another interesting aspect of AGB evolution that has recently come to light is the possibility that Fluorine may be synthesized during thermal pulses along the AGB. Jorissen, Smith, and Lambert (1992, A&A, in press) and Forestini, Goriely, Jorissen, and Arnould (1992, A&A, in press) find 19F overabundances in the S and C stars, with [F/O] proportional to the 12C/16O ratio, indicating that 19F is being produced in He-burning environments. It is suggested that 14N(alpha,gamma)18F(beta+,neutrino)18O(p,alpha)15N (alpha,gamma)19F is responsible for the 19F production, with the protons provided by 14N(n,p)14C and the neutrons coming from 13C(alpha,gamma)16O. The efficiency of 19F synthesis through this chain is limited by the number of available protons, which is itself limited by the 13C supply. It is found that, for most of the S and C stars, the 13C supply provided by the CNO ashes of the H-burning shell can account for the observed [F/O] abundances; however, for the most F-rich S and C stars, a larger primary abundance of 13C is required and must involve the mixing of protons into the 4He-rich and 12C-rich layers. The observed 19F abundances will provide constraints on the physical conditions in the thermal pulses and seem certain to lead to a greater understanding of the details of evolution along the AGB through the thermally pulsing phase. III. Research News A. Dupree (Harvard), D. Sasselov (Toronto), and J. Lester (Toronto) (Ap. J. Letters, 387, L85, 1992) report the discovery of a fast wind from a field population II giant star. The He I 10830 A absorption in the metal-deficient field giant star HD 6833 extends to -90 km/sec, a value that is comparable to or exceeds the escape velocity from the photosphere of the star. This spectrum provides strong observational evidence for mass loss. Because this field giant is a surrogate for red giants in globular clusters, and a velocity of 90 km/sec is larger than the central escape velocity from most globular clusters, this observa- tion suggests that material lost from globular cluster stars may easily escape from the cluster, thus resolving the dilemma of the missing interstellar medium in globular clusters. On Dec. 2, 1991, after a half-year interval, using the Baldone Schmidt telescope, A. Alksnis (Riga) and colleagues resumed monitoring of DY Per, a carbon star with unusual light variations similar in some ways to those of long-period variables and in some ways to RCB-variables. The star was found to be in a deep minimum: B=17.0, V=15.7, R(0.63)=14.7. During the next four months the light of the star recovered by 0.3 mag in B, 1.1 mag in V, and 1.5 mag in red light. The brightening of the star during the current minimum is much slower, 0.013 mag/d compared to 0.036 mag/d in the previous minimum. It is not yet clear if the current fading is similar to that of RCB-variables or to that of long-period variables. Observations of the star obtained at other observatories during May - Nov. 1991 when DY Per faded might help to solve the question. The reddening of the star during the light rise, however, is not typical for either case. Jorgensen (Copenhagen) and Johnson (Indiana) have computed photospheric carbon star models and merged them with empirical chromospheric models, in order to study the synthetic spectra of such combined models. The computations show that the upper part of the atmosphere must be inhomogeneous to prevent (as is required by observations) the lines of CO from going into emission. The filling factor for the hot material is estimated to be no more than 0.1. Jorgensen (Copenhagen), Carlsson (Oslo) and Johnson (Indiana) have cal- culated (in NLTE) the equivalent width of the Ca infrared triplet lines for a broad range of gravity, effective temperature, and metallicity. Formulas for use in models of the integrated spectra of galaxies are given. Comparison with observations indicate that Ca/Fe is an increasing function of metallicity. Jorgensen (Copenhagen) has reviewed the available molecular data for opacity and synthetic spectrum calculations of cool stars. A description of the sampling methods in use is also given (Revista Mexicana de Astronomia y Astrofisica 1992, in press). H. Alsbury, Jr. and B. Bopp (Univ. of Toledo) are continuing to monitor HD 35155 and several other known S-star binaries for profile variations in H-alpha, the Ca II infrared triplet, and the Na D-lines. MacConnell (STScI), Wing (Ohio State), and Costa (U. de Chile) have completed the first of a series of papers on "Red Supergiants in the Southern Milky Way". This paper, which is scheduled to appear in the August 1992 issue of the A.J., discusses the techniques the authors are using to find, classify, and determine the distance to faint red stars which have great potential for clarifying the spiral-arm structure of the Galaxy. Supergiant candidates are identified on deep near-infrared objective-prism plates, and eight- color narrow-band photometry is used to classify the stars in two dimensions and to determine their reddening and distance. CCD spectroscopy is used to weed out peculiar stars and to provide an independent estimate of luminosity. All observations are made in the near infrared, where late-type supergiants are brightest and the interstellar medium is relatively transparent. The paper gives photometric standard stars for the eight-color system and the vari- ous calibrations needed for distance determinations. The project has already confirmed more than 200 new late-type supergiants at distances up to five times the limits of previous surveys. IV. Comments Received SPECTROSCOPIC DATA ARCHIVES: AN INDISPENSIBLE TOOL FOR ASTROPHYSICS Elizabeth Griffin (Cambridge, England) Virtually all studies of any type of celestial object suffer from a shortage of adequate data. Even with the relative richness of today's harvest of spectroscopic data there is not enough accumulated evidence in most cases to separate with complete confidence the exception from the norm. If only the data that are available could be suitably coordinated it would be possible to conduct complementary studies of individual objects in different spectral domains or at different epochs. The characteristics pertaining to a star that is labelled "chemically peculiar" may, for instance, prove to be associated with allied peculiarities in other types of stars, and thus provoke an astrophysical justification for a newly recognized group. Alternatively, statistical studies of whole classes or types of object will engender a deeper understanding of the processes of evolution. In order to realise the full potential of what is already to hand, an efficient and widespread form of archiving and distributing the data has to be established. The concept of creating archives of spectroscopic data is not new; there are many vaults of photographic spectra in existence which date back to the early part of this century if not before, with catalogues that record detailed information about each plate. Unfortunately, as astronomical instrumentation has become more diversified and projects which were once the interest of a whole observatory or institution have given way to individual programs, the need still to keep abreast of archiving spectra has no longer been adequately addressed. The situation today is addition- ally complicated by the sheer volume of spectroscopic data coming from many instruments, in particular those in space, and is exacerbated by the fact that digital data can easily be erased. It is not hard to imagine, however, that the automatic storage on-line of all "raw" data everywhere would soon cause mounting problems that would detract from the usefulness that spectroscopic archives ought to provide. On the other hand, data from which the instrumental signatures have already been removed and the spectra extracted ("reduced" data) are not only considerably less bulky but are also in a digital format that is readily comprehensible by people who are not normally accustomed to that particular type of observation. With a view to getting to grips with this problem before it gets too large to control, an IAU Working Group on Spectroscopic Data Archives has recently been established. The following extract from a Statement which it has drawn up sets out the basic philosophy behind its endeavours:- "Astronomical observations are the building blocks of astrophysics. The accumulation of observational data throughout the presently access- ible electromagnetic spectrum has enabled the development of an apparently consistent theory of stellar evolution within the framework of fundamental physics. This has encouraged the formulation of cosmo- logical theories, not only to interpret cosmological observations but also to connect general astrophysics with high-energy physics. These cosmological and theoretical considerations point to the existence of an interval of some 15 billion years, between the present state of the Uni- verse and its beginnings, which has to be spanned by theory; at the foundation of this theoretical bridge lies the concept that the Universe is relatively static, and that variations take place in only two modes: secular ones, on time-scales comparable with those of stellar evolution itself, or strictly periodic ones. "The combination of modern observations with the very limited avail- able archival records has now demonstrated that the power spectrum of variability in astrophysics contains much more energy in the higher frequencies -- time-scales of the order of weeks to decades -- than was previously suspected. This implies that the foundations of the theoreti- cal bridge that connects the current epoch with the early stages of the Universe may contain serious errors. The size of its span could be re- duced empirically by one to two orders of magnitude, if access to past observations through well-defined archiving procedures were an everyday practicality." In more practical terms the WG aims to stimulate efforts to maintain well-catalogued and easily accessible archives of spectroscopic data, initially in both raw and reduced form, to promote their use by astronomers worldwide, and to evolve a long-term solution for the continued preservation and use of photographic spectrograms. In setting out to achieve these ends the WG members will individually and collectively consult with astronomical observatories, with the worldwide astronomical community, with agencies and with astronomical data centres. The members of the WG are themselves astronomers who perceive archiving as a low-key but essential habit that stands to increase greatly the cost-effectiveness of astronomical research. * * * * * * * * PRELIMINARY ANNOUNCEMENT OF MK50 C. J. Corbally (Vatican Observatory, Tucson) The 50th Anniversary of the MKK Atlas is coming up in 1993. A celebration is being planned in the form of a workshop from 20-24 September, 1993, in Tucson, Arizona. It will be sponsored by the Vatican Observatory, whose research group is located in Tucson. A preliminary title is "The MK Process at 50 Years: A Powerful Tool for Astrophysical Insight." This expresses the desire of the organizing committee (to date, C.J. Corbally, R.F. Garrison, R.O. Gray, D.M. Mihalas, E.H. Olsen) to celebrate the science currently done through spectral classification, while laying foundations for future applications of the MK Process that will take advantage of digital tech- nology. Further information can be obtained from Chris Corbally at: corbally@as.arizona.edu V. Meetings September 14-16, 1992 Astronomy from Large Databases II Hagenau, France Contact: Andre Heck Observatoire Astronomique 11, rue de l'Universite F-67000 Strasbourg France heck@frccsc21 (Bitnet) heck@ccsmvs.u-strasbg.fr (Internet) September 16-18, 1992 Sky Surveys: Protostars to Protogalaxies Pasadena, California Contact: T. Soifer or E. Becklin Caltech 320-47 Dept. of Astronomy, UCLA Pasadena, CA 91125 Los Angeles, CA 90024 bts@mop.caltech.edu becklin@bonnie.astro.ucla.edu May 24-29, 1993 Molecular Opacities in the Stellar Environment Copenhagen, Denmark Contact: Uffe Graae Jorgensen Niels Bohr Institute Blegdamsvej 17 DK-2100 Copenhagen, Denmark uffegj@nbivax.nbi.dk June 3-6, 1993 Technical Conferences on Optical Spectroscopic Instrumentation and Techniques Albuquerque, New Mexico Contact: SPIE September 20-24, 1993 50th Anniversary of the MKK Atlas Tucson, Arizona Contact: Chris Corbally corbally@as.arizona.edu VI. The WG Organizing Committee Hollis R. Johnson Uffe Grae Jorgensen Antonio Mario Magalhaes Astronomy Dept. Niels Bohr Institute Instituto Astronomico e Indiana University Blegdamsvej 17 Geofisico Swain West 319 DK-2100 Copenhagen Universidade de Sao Paulo Bloomington, IN 47405 Denmark Caixa Postal 30627 USA 01051 Sao Paulo johnsonh@iubacs.bitnet uffegj@nbivax.nbi.dk Brazil Monique Querci Verne V. Smith Robert E. Stencel Observatoire du Pic-du- Dept. of Astronomy Center for Astrophysics & Midi et de Toulouse University of Texas Space Astronomy (CASA) 14 Avenue Edouard Belin Austin, TX 78712 University of Colorado F-31400 Toulouse USA Campus Box 391 France Boulder, CO 80309 USA verne@astro.as.utexas.edu stencel%galaxy@vaxf. colorado.edu Takashi Tsuji Robert F. Wing (chairman) Sandra Yorka Tokyo Astronomical Astronomy Dept. Dept. of Physics and Observatory Ohio State University Astronomy Mitaka 174 West 18th Avenue Denison University Tokyo 181 Columbus, OH 43210 Granville, OH 43023 Japan USA USA ttsuji@c1.mtk.nao.ac.jp ts4718@ohstmvsa.acs. yorka@denison.bitnet ohio-state.edu