Bull. A. A. S., Vol. 26, 647, 1994

Tennessee State University
Center of Excellence in Information Systems
Nashville, Tennessee 37203-3401

This report covers the interval October 1, 1992, through September 30, 1993. Since it is our first, we begin by describing the development of the astrophysical research program at TSU. The Center of Excellence is a multidisciplinary research laboratory founded in 1986 as part of a program to increase the amount of research being done at Tennessee's state universities. The staff now consists of nine researchers, two support staff, and various students working part-time. Besides astronomy, the Center has programs in advanced control systems, expert systems, and management information systems. The astrophysics program began in 1988 with a NASA grant to M.R. Busby to manage robotic telescopes and define the properties of spots in chromospherically active stars, and robotic telescopes continue to be a prime interest of the staff. The Center's astronomical research is concentrated on understanding magnetic activity in cool stars, with ancillary interests in binary stars and pulsating variables. Astronomy staff in 1992-93 were Michael R. Busby, Joel A. Eaton, and Gregory W. Henry. Sallie L. Baliunas (CfA), Francis C. Fekel (NASA/Marshall SFC), and Douglas S. Hall (Vanderbilt University), acted as consultants and adjunct staff. The following students worked in the Center as astrophysics student assistants: Coretta L. Bell, Melissa Hampton, Mark Newsom, Deena Rembert, and Felicia Shaw.

I. OBSERVING FACILITIES

The initial research of the Center of Excellence has been in managing robotic telescopes, which to date have been used for photoelectric photometry. The center now manages three APT's, the Fairborn 10-inch in collaboration with S. Baliunas, the SAO 30-inch in collaboration with Baliunas, and the Vanderbilt/Tennessee State 16-inch in collaboration with D. S. Hall. All three telescopes are housed at Mt. Hopkins in Arizona and maintained by Louis J. Boyd of Fairborn Observatory. Over the past five years Henry has greatly refined the operation of these three telescopes, making them much more reliable. He has developed procedures and computer programs that automatically reduce the photometric data and monitor the quality of the observations on a daily basis. In the past two years Henry has begun using statistical process control to detect mechanical problems with a telescope and to formulate hypotheses for correcting them. He has developed a procedure of scanning an aperture (a photometer diaphragm) over a star in both right ascension and declination at the beginning of each night that has proved especially useful in detecting mechanical problems. Examples of problems actually detected are incorrect centering, poor focus, optical misalignment, vignetting caused by slipping filter wheels, and intermittent problems with stepper motors. Observations of standard stars for determining nightly transformation and extinction coefficients have been especially useful for determining changes in the photometric system and quality of the night. Over the past four years, probable errors in the photometry of the VU/TSU telescope have improved from roughly 0.010 mag to 0.004 mag, and this photometry has become at least as good as manual photometry.

The Fairborn 10-inch telescope is being used to monitor a group of about 40 stars, mostly semiregular variable M giants. Systems now being observed regularly are EG And, V450 Aql, RZ Ari, psi1 Aur, X Cnc, BC CMi, TU CVn, rho Cas, mu Cep, FS Com, W Cyg, RS Cyg, CH Cyg, V1070 Cyg, P Cyg, EU Del, eta Gem, V642 Her, alpha1 Her, 30 g Her, 89 Her, RX Lep, Y Lyn, UX Lyn, UW Lyn, R Lyr, beta Lyr, V523 Mon, V614 Mon, omega Ori, 4 omicron1 Ori, psi1 Ori, Z Psc, TV Psc, ST UMa, VY UMa, and SW Vir. Data sets for them now cover typically seven years. Observations are collected in the VRI bands with a precision of 0.01-0.02 mag. These data have shown all the semiregular variables analyzed to be multiply periodic. While about seven of the semiregular variables have been analyzed by Henry and Baliunas, there remains considerable opportunity for using these data. Proposals for collaboration should be addressed to S. Baliunas.

The Vanderbilt/Tennessee State 16-inch is being used to monitor the brightness in B and V of about 120 chromospherically active stars, mostly known or potential RS CVn binaries. The telescope can now be programmed on a daily basis through a computer-to-computer connection to monitor a particular variable star throughout a specified part of a night, and this capability has been used to obtain complete light curves of RS CVn in 1991 and 1992 (Henry and Eaton), a complete light curve of V819 Her (by Henry and Hall), and part of a primary eclipse in TT Hya (Henry and Eaton). This instrument is now achieving external errors near 0.004 mag in differential photometry.

The SAO 30-inch telescope is being used by Henry to perfect techniques of observing needed to achieve the 0.001-mag precision required to measure rotational and long-term changes in brightness of slowly rotating Sun-like dwarf stars. TSU replaced the original photometer on this telescope with a new photometer capable of achieving this precision in 1992. Henry has used his techniques for diagnosing problems with APT's to isolate and correct mechanical and electrical problems with this instrument, and it is now achieving precision as good as 0.0010 mag on truly photometric nights, thus routinely achieving its capabilities by making measurements limited only by photon or scintillation noise.

II. RESEARCH

Henry and Eaton have continued collaborating with Hall and Fekel on interpretations of highly spotted chromospherically active stars, observed photometrically mostly with the VU/TSU telescope.

Henry, Eaton, Hall, and two students have finished an analysis of four well observed RS CVn binaries with a simplified spot model. The systems considered were observed extensively with robotic telescopes as well as manually, and all four have data based on photometry spanning close to 20 years. The analyses gave 15 spots for V711 Tau, 12 spots for II Peg, 16 spots for sigma Gem, and 11 spots for lambda And. There were hints of cyclic changes in color and mean brightness in these systems, but the apparent changes were not in the same sense in all of them. The evidence of these stars argues that more spots exist than the one or two generally postulated.

Hall, Henry, Eaton, et al. have found that the orbit of BM Cam has a slightly longer period (80.9 vs. 80.17 days) and is markedly less eccentric (e ~ 0.05 vs. 0.35) than found previously by Abt, Dukes, and Weaver. This eliminates the question of why the spotted star's rotation is synchronized with mean orbital motion instead of with the much faster motion near periastron. With a low eccentricity, the spotted star is essentially rotating synchronously. This investigation detected the ellipticity effect at a level of 0.049 mag peak-to-peak, using it to constrain the masses and radii of the two stars somewhat, found nine dark starspots in photometry covering 13 years, and measured differential rotation of these spots at a level one-third as great as differential rotation in the Sun.

Strassmeier, Hall, and Henry have analyzed 15 years of photometry of HR 7275, finding 20 different spots that lived 2.2 years on the average. There was no conclusive evidence of long-term magnetic cycles in these data.

Hampton, Henry, Eaton, R. Nolthenius, and Hall have analyzed photometry of the spotted variable HD 12545 obtained with the 16-inch APT and by Nolthenius observing manually. This photometry caught the star with the greatest amplitude of light variation yet detected for modulation by spots. Hampton et al. obtained spot solutions for various assumed inclinations in which they tried to measure the temperatures and stellar latitudes of the spots. Moderately well defined temperatures were derived, but the latitudes were indeterminate in spite of the large amplitude.

Fekel, Henry, and Busby along with J. J. Eitter (Iowa St. Univ.) have analyzed ground based and ultraviolet spectroscopic observations of three chromospherically active binaries that have white dwarf or B subdwarf companions, which were detected with the IUE satellite. Orbital elements have been determined to see if these systems are consistent with the Ba-star scenario. 29 Dra has a period of 915 days, which is similar to many barium stars. From a limited comparison with the spectra of normal giants, it does not appear to have s-process abundance anomalies but a extensive abundance analysis would be extremely useful. The mild barium star HD 165141 has a period of roughly 5200 days, quite consistent with the periods of other such systems. This long period indicates that no Roche lobe overflow was possible and lends support for mass transfer via an enhanced stellar wind. The third star, HD 185510, is an eclipsing binary with a period of 20.7 days. Such a short period indicates that it did not evolve to the s-process creation stage before mass transfer from the sdB star began.

Fekel and Balachandran (Univ. of North Carolina) have finished their initial study of the lithium abundances of a number of evolved chromospherically active (CA) stars, both single and binary. Many of these stars have lithium abundances equal to or greater than the predictions of standard evolutionary theory. The single stars appear to be first ascent giants that have acquired rapid rotation from their rapidly rotating cores. This has apparently caused an increased amount of lithium to come to the visible surface. Whether all stars go through such a stage and how long such a stage may last remains to be determined. Several dozen additional single and binary CA stars are being analyzed to provide a larger sample.

Fekel in collaboration with C. Scarfe (Univ. of Victoria) and others is continuing spectroscopic observations of about 20 close multiple systems and a half dozen speckle binaries to obtain fundamental parameters. For most of these systems, speckle observations have been obtained by the CHARA group at Georgia State Univ. Fekel and the CHARA group are analyzing two F or G dwarf systems, HR 6697 and 31 Ari.

Fekel and B. W. Bopp (Univ. of Toledo) have analyzed high-dispersion spectroscopic observations of HD 98800, a K5 V triple system that has a Vega-like disk. The system is a close visual binary, one component of which is a single-lined spectroscopic binary. It has significant emission flux at H-alpha and a very strong lithium line. Although such multiplicity significantly complicates the analysis, several lines of argument indicate that the system is only 10 million years old and is certainly a pre-main sequence star. Henry and Hall added HD 98800 to the menu of the VU/TSU 16-inch APT and quickly discovered optical variability with an amplitude of about 0.07 mag in V and a period of 14.4 days, presumably due to starspot activity.

Fekel is obtaining high-dispersion spectra of CA binary candidates listed in the second Catalog of Chromospherically Active Binary Stars. A number of systems have been confirmed as binaries while some of the chromospherically active stars have turned out to be single. One single star, 1E1751+7046, has been analyzed with C. W. Ambruster and E. F. Guinan (Villanova Univ.). The fundamental properties of this rapidly rotating giant have been significantly revised and two scenarios appear to be possible for its previous evolution. It may be a coalesced short-period binary, or perhaps have received its rapid rotation from angular momentum transferred from its core. A proper motion is needed to help decide whether it is a young pop I or old disk system.

Fekel and Henry are obtaining spectroscopic and photometric data for a number of newly discovered chromospherically active stars. Henry and Newsom are analyzing the first few months of photometry for these stars obtained with the 16-inch APT and have found approximately 30 new variable stars.

Henry and Newsom surveyed four years of archival UBV photometry of 69 chromospherically active stars obtained with the Phoenix-10 automatic telescope in search of the signatures of optical flares on these stars. While a small number of previously unrecognized events were found on the extremely active stars II Peg, UX Ari, and AR Psc, the survey demonstrated clearly that observable optical flares are a rare occurrence on these extremely active stars.

Eaton has continued his analyses of zeta Aurigae binaries as probes of stellar chromospheres and winds. During the period of this report, he published analyses of archival IUE plus optical observations of zeta Aur and 32 Cyg. He has spent most of this time analyzing ultraviolet spectra of 31 Cyg away from atmospheric eclipses and of AL Vel in an atmospheric eclipse and obtaining new observations of 31 Cyg during the eclipse of 1992/93.

Eaton finished collecting and analyzing IUE spectra of 31 Cyg (K4 Ib + B3-4) for the three years before its atmospheric eclipse of 1992/93. In a paper scheduled for the November, 1993, AJ, he finds the following about the 31 Cyg system: The wind is highly ionized around the B star, the tracers O I and N I arguing that even hydrogen is mostly ionized in this region. Ionization drops in the parts of the wind shielded by the body and chromosphere of the K supergiant, as well as in the unshielded gas at moderately large distances from the binary. The Doppler width of gas in the wind is ~ 13 km/s, and this likely represents acceleration of the wind at great distance from the binary. Lines of the B star recorded at short wavelength give an incomplete velocity curve of the B star, which changes the mass ratio only slightly from values found from ground based spectra.

Eaton has also finished and submitted to AJ an analysis of IUE spectra of AL Vel (K0 II + B8) obtained in April-May 1992. These spectra detected a very pronounced atmospheric eclipse, implying a more massive chromosphere than expected for the star's size and mass. Blueshifted wind lines similarly required a more massive wind with a mass loss rate near 10^-8 solar masses/yr. In fact, the chromospheric densities and mass loss rate in this star seem to vary by two orders of magnitude on timescales of months.

Eaton and R.D. Chapman began observing the 1992/93 atmospheric eclipse of 31 Cyg in October, 1992 and have continued throughout this year. These observations, which include 7 epochs of ingress and at least 21 epochs of egress, will be the most extensive ever made in the ultraviolet for a zeta Aur binary. Eaton has also arranged to get complementary Balmer-line observations of 31 Cyg at the National Solar Observatory. Reductions to date show the atmospheric eclipse detected in Ly-alpha throughout the orbital-phase range 0.9649--0.0332 with mass column densities too slowly varying with height for absorption in a hydrostatic chromosphere. Rather, the density variation with height implies extinction in a wind, which has a mass loss rate of the order of 10^-8 solar masses/yr.

Eaton and Rembert have identified the emission lines in a set of deeply exposed IUE spectra 32 Cygni. Almost all the lines identified with any certainty appear in the eclipse spectrum of zeta Aur, and the stronger ones are also seen in 31 Cyg. About 75% of the emission lines are Fe II.

Eaton has observed the Algol binary TT Hya in a total eclipse (2 December 1992) with IUE at high dispersion to determine kinematically the source of emission lines in the system. The spectra obtained are noisy but show mostly highly broadened emission lines of an accretion disc, not the narrower lines expected of a strong stellar wind that might originate in the disc.

Eaton, Henry, and M. Seeds (Franklin and Marshall College) have used photometry from two robotic telescopes to measure the ellipsoidal light variation of 22 Vul = QS Vul, a 250-day zeta Aur binary. Light varies by 0.015 mag peak to peak at V. They have also used red spectra to determine a rotational velocity, vsini = 17 +/- 2 km/s, which implies a radius near 76 solar radii for the G supergiant component. This G supergiant is rotating synchronously with its orbit, and velocity shifts from the rotation have been detected in radial velocities of shell lines in archival IUE spectra. With synchronous rotation, the chromospheric shell lines should appear at the radial velocity of the B star, which gives another way to measure the orbital velocity of the B star and thus the mass ratio. Shaw and Eaton have started analyzing the archival IUE spectra of 22 Vul.

Eaton has obtained H-alpha spectra of 250 G-M giants with the McMath-Pierce solar telescope and used them to define changes with spectral type in chromospheric absorption of the cool giant stars. These extend previous H-alpha spectra significantly into the M spectral types. All of these cool giants earlier than middle M have strong H-alpha absorption. The central depths (residual intensity ~ 0.2 in almost all stars observed) require the chromospheric absorption to be roughly uniformly spread over the faces of all the cool giants. Theoretical calculations for chromospheres representative of alpha Tau have been calculated to constrain conditions producing the sort of H-alpha absorption measured.

Henry, former summer student J. Armour, and Busby have analyzed seven semiregular variables in collaboration with S. Baliunas. They find that all of these systems studied are multiply periodic, with periods ranging from tens to hundreds of days. Eaton, collaborating with H. R. Johnson and R. Cadmus, has monitored semiregular variables in chromospheric emission lines with IUE and has begun a program with the McMath-Pierce solar telescope at NSO to detect changes of these stars in chromospheric H-alpha. Two more years' worth of IUE data for about six semiregular variables shows the tendency of chromospheric emission strength to be correlated with the photospheric brightness, as found by Eaton, Johnson, and Cadmus (1990, ApJ, 364, 259).

III. NEW INSTRUMENTATION

The Center has recently placed a 32-inch robotic telescope atop Mt Wilson to be used to monitor Sun-like stars in conjunction with the 30-inch SAO telescope. The goal of this program is to define on weekly to yearly timescales the brightness variations of slowly rotating, chromospherically inactive stars like the Sun. Roughly 100 of these stars are being monitored in Ca II by the Mt Wilson HK project, managed by S. Baliunas. In collaboration with her, Henry is measuring brightness variations of these same stars to find statistically how luminosity changes as chromospheric emission changes. This has the potential to determine in roughly a decade of observing the range of instantaneous solar luminosity heating the Earth and as yet not considered adequately in climatic models. The advantage of having two telescopes observing is that both are needed to make an adequate number of observations of all the stars, and having telescopes at two sites with complementary weather patterns lets the program stars be observed throughout the year.

The 32-inch telescope is a state of the art photometric telescope designed by Autoscope Corp. It was installed at Mt Wilson in July, 1993, and will be put into operation during fall, 1993, and managed by Henry. Henry has refined the procedures required for obtaining the necessary precision on the 30-inch SAO telescope. He will run the same program on the two telescopes for the first six months of 32-inch operation so as to determine how reliably data from more than one APT may be combined.

Henry served during this year on a committee to revise ATIS (Automatic Telescope Instruction Set), the language used to communicate with robotic telescopes. The new version maintains all the flexibility for running photometric programs but includes new commands for running CCD's, retrieving environmental data, and communicating in real time with remote automatic schedulers using the latest techniques of artificial intelligence to further improve the performance of automatic telescopes.

IV. PUBLICATIONS

Barlow, D. J., Fekel, F. C., and Scarfe, C. D. 1993, ``A Three-Dimensional Solution for the Orbit of Capella," PASP, 105, 476

Boyd, L. J., Epand, D., Bresina, J, Drummond, M., Swanson, K., Crawford, D. L., Genet, D.R., Genet, R. M., Henry, G. W., McCook, G. P., Neely, W., Schmidtke, P., Smith, D.P., and Trueblood, M. 1993, ``Automatic Telescope Instruction Set 1993," Comm. I.A.P.P.P., No. 52, p. 23

Dempsey, R. C., Bopp, B. W., Henry, G. W., and Hall, D.S. 1993, ``Observations of the Ca II Infrared Triplet in Chromospherically Active Single and Binary Stars," ApJS, 86, 293

Donati, J.-F., Brown, S. F., Semel, M., Rees, D. E., Dempsey, R. C., Mathews, J. M., Henry, G. W., and Hall, D. S. 1992, ``Photospheric Imaging of the RS CVn System HR 1099," A&A, 265, 682

Eaton, J. A. 1992, ``The intrinsic lines of zeta Aurigae binaries," MNRAS, 258, 473

Eaton, J. A. 1993, ``On the Chromospheric Structure of Zeta Aurigae," ApJ, 404, 305

Eaton, J. A. 1993, ``On the Chromosphere of 32 Cygni," AJ, 105, 1525

Eaton, J.A., Henry, G.W., Bell, C., and Okorogu, A. 1993, ``Spots on RS CVn from Spectroscopy and Photometry," AJ, 106, 1181

Fekel, F. C., and Balachandran, S., 1993, ``Lithium and Rapid Rotation in Chromospherically Active Single Giants," ApJ, 403, 1993

Fekel, F.C., Browning, J., Henry, G.W., Morton, M.D., and Hall, D.S. 1993, ``Chromospherically Active Stars. X. Spectroscopy and Photometry of HD 212280," AJ, 105, 2265

Hall, D. S. and Henry, G. W., 1992, ``Two New Spotted Variables--HD 191262 and HD 191011," AJ, 104, 1936

Henry, G. W., and Hall, D. S. 1993, ``ATIS and the Evolution of Automatic Telescopes," Comm. I.A.P.P.P., No. 52, p. 82.