COE Observatory Report 1993-1994

Bull. A. A. S., Vol. 27, 622, 1995

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

This report covers the interval October 1, 1993, through September 30, 1994. The astrophysics program in the Center of Excellence at TSU continues to concentrate on understanding magnetic activity in cool stars, managing robotic telescopes, and applying automation to astronomy. Astronomy staff in 1993-94 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, with Fekel taking up residence in the Center in July 1994. The following worked in the Center as astrophysics student assistants: Coretta L. Bell, Terria Lee, Mark Newsom, Deena Rembert, and Felicia Shaw.

Tennessee State served as a sponsor for the symposium ``Robotic Telescopes" held at the 106th Annual Meeting of the Astronomical Society of the Pacific in Flagstaff, Arizona in June 1994. Henry presented papers on ``The Development of High-Precision Robotic Photometry" and ``The TSU/Fairborn Robotic Telescope Operations Model" and Eaton one on ``The Rationale for an Automatic Spectroscopic Telescope". Henry is serving as the editor of a proceedings volume for the meeting.


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 four APT's, the Fairborn 10-inch in collaboration with S. Baliunas, the SAO 30-inch in collaboration with Baliunas, the Vanderbilt/Tennessee State 16-inch in collaboration with D.S. Hall, and the new TSU 32-inch. All four telescopes are now housed at Mt. Hopkins in Arizona and maintained by Louis J. Boyd of Fairborn Observatory.

The Fairborn 10-inch collected 7179 group observations on 249 nights of approximately 40 semiregular variable stars in the VRI bands during the past year (3Q93-2Q94). During the 1994 summer shutdown, Boyd rebuilt the drive of this telescope and converted it to full ATIS control. The Vanderbilt/Tennessee State 16-inch collected 14,626 group observations of approximately 130 chromospherically active stars on 243 nights during the past year. This was the seventh year of operation for this telescope, which continues to produce data at its photon and scintillation noise limits. The SAO 30-inch collected 7889 observations of 61 quartet groups containing lower-main-sequence stars on 257 nights during the past year. This was the first full year that it reached its full potential to make high precision observations of solar-like stars.

The new TSU 32-inch telescope, originally on Mt. Wilson, was scheduled to begin high precision photometric observations of solar duplicate stars by 1993. However, because AutoScope Corporation had failed to deliver a working system a full 1.5 years past the contractually agreed date, the Center of Excellence cancelled its contract with AutoScope and moved the unfinished 32-inch APT to Mt. Hopkins in March 1994. A contract was made with Fairborn Observatory to bring the telescope into operation on Mt. Hopkins alongside our other APT's, and it is now expected to begin observing in Fall 1994. The Fairborn contract includes a completely redesigned two-channel precision photometer, which will make simultaneous measurements of stars in two colors. This device will allow a doubling of the integration times without any sacrifice in the number of stars observed. Since scintillation will be the largest source of noise in the data, this longer integration time will provide a welcome further improvement in the precision achieved. Experience with the SAO 30-inch suggests that this telescope should routinely achieve 0.001 mag precision on photometric nights. Henry will use it to measure luminosity changes of true solar duplicate stars, which have the smallest anticipated variation of any of the stars observed at TSU.


Henry began a collaboration with the Artificial Intelligence (AI) Research Branch at NASA Ames Research Center to develop an automated scheduling and management system for robotic telescopes. This system, called the Associate Principal Astronomer (APA) package, will combine sophisticated AI-based scheduling of observations designed to maximize the precision and scientific usefulness of robotic telescope observations with automated quality control, data reduction, and telescope management features that will greatly simplify the operation of these telescopes. The APA system will run on a single workstation or high-end personal computer and will be capable of simultaneously managing the operation of several multi-user robotic telescopes in real time over the Internet. The implications for this kind of automated management of automatic telescopes might be substantial considering the enormous cost of managing current large ground-based telescopes and especially space telescopes.

Henry, Eaton, and Fekel have continued collaborating with Hall on interpretations of highly spotted chromospherically active stars, observed photometrically mostly with the VU/TSU telescope. Henry, Hall, and others have analyzed over 20 years of photometry of the chromospherically active binary V350 Lac. It was puzzling that this K2 IV-III star, which should have a strong dynamo and actually does show strong chromospheric emission, was not known previously to have the large starspots characteristic of other such stars. The photometric analysis yielded an ellipsoidal variation of 0.08 mag peak-to-peak in V. After removal of this ellipticity effect, the light curve showed measurable starspot variability in 15 of 16 data groups. Ten starspots were identified and their rotation periods determined, confirming synchronous rotation and revealing differential rotation. A slow variation in mean brightness of almost 0.1 mag was detected, implying a cycle at least two decades in length. A paper on this star has been submitted to Astronomical Journal.

Henry and Fekel have begun searching for light variation in photometric data for 64 potential variable stars obtained by the 16-inch APT over the past several years. These stars were placed on the menu as a result of H-alpha, Ca II H & K, and X-ray surveys that identified them as chromospherically active. A large percentage of these objects are being identified as new variable stars with the APT data. Henry and Fekel are determining the rotational periods and light amplitudes. They will combine the photometric results with existing spectroscopic results to identify the single and binary stars in the sample and, where possible, to check for synchronous, pseudosynchronous, or asynchronous rotation of the binary stars.

Eaton and Henry have collected photometry from the 16-inch APT, high-dispersion spectra from NSO, and ultraviolet spectra from IUE for the chromospherically active close binary SZ Psc. This star is difficult to observe at a single site because of its 3.96-day period. Nevertheless, a nearly complete light curve collected in the 1993/94 season shows depression of the star's light by spots at practically all phases.

Collaborating with Baliunas, Henry has begun an extensive analysis of the first year of high-precision data from the SAO 30-inch APT. This analysis has confirmed that the 30-inch has reached the photon- and scintillation-noise limits for the internal precision of its observations, but it has also revealed subtle degradations of the external precision of some group observations due to insufficient measurements of the sky background on nights when the moon was bright. Henry has reprogrammed the telescope during the 1994 summer shutdown to make the additional sky background measurements to reduce or eliminate this problem. As part of this program, he has begun a period analysis of the 30-inch data to determine which stars show rotational modulation of brightness due to individual active regions. Preliminary results suggest rotational modulation on at least several stars. While the 30-inch has so far returned only one year of data for lower-main-sequence stars, which cannot yet detect long-term brightness variations, Henry has initiated a collaboration with Wes Lockwood of Lowell Observatory to combine their data for those Olin Wilson HK stars that they are jointly observing. This should result in a paper detailing the 10-year brightness variations of these 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 IUE observations of 31 Cyg away from atmospheric eclipses and of AL Vel in an abnormally strong atmospheric eclipse. He has spent most of this time analyzing very extensive new observations of 31 Cyg during its eclipse of 1992/93 and archival ultraviolet spectra of delta Sge and 22 Vul.

Eaton and Bell finished collecting and analyzing IUE spectra of 31 Cyg (K4 Ib + B3-4) for 32 epochs of its eclipse of 1992/93, 31 of them during the atmospheric eclipse. In addition, they obtained violet data from NSO at a few critical phases to measure strengths of Balmer lines and a few metallic lines. These spectra constitute the most extensive, probably the best, data set yet obtained for a zeta Aur binary, and they allow mass column densities through the wind and chromosphere to be measured accurately from the strength of Ly-alpha absorption. The detailed analysis of these extensive data has improved our understanding of cool supergiant stars' chromospheres substantially and changed it dramatically in some ways. In a paper scheduled for the December, 1994, Astronomical Journal, Eaton and Bell find the following about 31 Cyg's chromosphere and wind: Most of the motion along a line of sight through the chromosphere comes not from 15-25 km/s microturbulence, as previously thought, but from differential expansion of the atmosphere. The allowed microturbulence may be up to 15 km/s at depth, but it is no more than 10 km/s higher up in the wind. Excitation temperatures measured for the singly ionized metals are similar to excitation temperatures found in other zeta Aur binaries and to the kinetic temperatures required in semiempirical chromospheric models of single stars. Measured electron densities deep in the chromosphere are like those deduced for single stars from C II] multiplet ratios. Hydrogen Ly-alpha has departure coefficients, measured from strengths of violet Balmer lines, that fall rapidly with height, as in semiempirical chromospheric models, but which are somewhat larger at depth than expected from such models. Ly-alpha thermalizes in the deeper layers of the chromosphere. The wind and chromosphere are likely to be separate structures, and the wind flow seems to be continuous but with sporadic bursts superimposed on it.

Eaton has collaborated with W.I. Hartkopf, H.A. McAlister, and B.D. Mason of Georgia State University to analyze the zeta Aur binary delta Sge (M2 Ib-II + B9.5 V). A combination of speckle interferometry with a radial-velocity solution by Batten gives a 40-degree inclination for this system and a luminosity and mass placing the M giant on the asymptotic giant branch. Shell lines of singly ionized metals give a wind from the M star with terminal velocity of 16-18 km/s and a mass-loss rate of 1.1 +/- 0.4 x 10-8 solar masses/yr. Highly variable lines of more highly ionized species (Si IV, Al III, and C IV), as well as Mg II and C II, show motions both toward and away from the B dwarf at speeds up to several hundred km/s. These features are taken as evidence for variable accretion onto the B star, accompanied by a variable wind from the interior of an accretion disc. The accretion luminosity liberated in this system, as well as in eclipsing zeta Aur systems, should be sufficient to ionize the M star's wind further by the Auger effect and thus give the narrow C IV and Si IV lines seen during total eclipse of such binaries.

Eaton and Shaw have analyzed the archival IUE observations of 22 Vul, finding properties for the chromospheric gas similar to those found in other zeta Aur systems, although the intrinsically stronger lines are obviously broadened by the differential expansion of the wind along the line of sight.

Eaton has observed for the past year the H-alpha variations of zeta Aur binaries and single K supergiants with the McMath-Pierce solar telescope at the National Solar Observatory. Chromospheres of these stars are so optically thick that their cores form in the region where the wind is beginning to expand. Intensifications of the wind, such as one Eaton and Bell detected in IUE spectra of 31 Cyg, would thus produce extra absorption in blue wing of H-alpha, and this is actually seen occasionally for both zeta Aur binaries and single K supergiants.

Fekel, in collaboration with C. Scarfe (Univ. of Victoria) and others, is continuing spectroscopic observation of about 20 close multiple systems and a half dozen speckle binaries to obtain fundamental parameters. For most of the systems speckle observations have been obtained by the CHARA group (Georgia State Univ.) Analysis of the following systems is nearly completed. Fekel and W. Hartkopf, B. Mason, and H. McAlister of the CHARA group are working on combined visual and spectroscopic orbital solutions of two F or G dwarf binary systems, HR 6697 and 31 Ari. Fekel, Scarfe, and Barlow (Univ. of Victoria) now have a complete 13-year cycle of spectroscopic observations for HR 2130 and are updating the short- and long-period orbits of this late-B type triple system. Fekel and R. Griffin (Cambridge University) are analyzing data of HR 1455. This star is a triple system consisting of an F star and an unseen companion in a short period orbit. These stars orbit a K III with a period of 1.3 years. This separation is too small to be resolved by current speckle interferometry.

Fekel continued work on chromospherically active stars with a variety of collaborators. He has finished a spectroscopic orbit of the chromospherically active binary HD 8357 = AR Psc. This system is one of only a half dozen in which H-alpha is always in emission. Despite such strong chromospheric activity and a 14.3-day orbital period, it is a BY Draconis system rather than an RS CVn binary. That this pair of K dwarfs is relatively young is indicated by the orbit's modest eccentricity of 0.18 and the primary star's lithium feature. Two other papers on K dwarf binaries, HD 30957 with V. Dadonas (Vilnius Univ.) and HD 163621 with R. Griffin, are in press. V. Dadonas and Fekel have finished a paper on the single-lined chromospherically active binary HD 28591.

Fekel, in collaboration with C. Ambruster (Villanova Univ.) and A. Brown (Univ. of Colorado), continues to provide near simultaneous ground based spectroscopic observations at KPNO for a half dozen ZAMS K dwarfs that are being observed with the IUE and EUVE satellites. Photometric observations of these stars are also being obtained with the Vanderbilt/Tennessee State 16-inch telescope. These observations will be used to study the rotation-activity relation from the corona to the chromosphere in stars in which hydrogen ignition has just occurred.

Fekel and S. Balachandran (Ohio State Univ.) are continuing their analysis of lithium in additional chromospherically active stars both binary and single. They have also obtained spectra with the IUE satellite of chromospherically active pop. II binaries. Preliminary UV results support ground based findings that binaries with periods of 10 days or less have active chromospheres. Additional observations will be obtained during the final year of IUE's operations.


Dempsey, R.C., Bopp, B.W., Henry, G.W., & Hall, D.S. 1994, ``The Spot Cycle of IM Peg," in Cool Stars, Stellar Systems, and the Sun, Eighth Cambridge Workshop, ed. J.-P. Callault ASP Conf. Ser. Vol. 64, p. 393

Eaton, J.A. 1993, ``31 Cygni: The B Star and Wind," AJ, 106, 2081

Eaton, J.A. 1994, ``A Deep Atmospheric Eclipse of AL Velorum," AJ, 107, 729

Eaton, J.A., & Chapman, R.D. 1993, ``The 1992/93 Atmospheric Eclipse of 31 Cygni," unpublished presentation at Cosmic Winds and the Heliosphere, Tucson, AZ.

Eaton, J.A., Henry, G.W., & Seeds, M.A. 1994, ``Geometry of the Binary System 22 Vul=QS Vul," in Cool Stars, Stellar Systems, and the Sun, Eighth Cambridge Workshop, ed. J.-P. Callault, ASP Conf. Ser. Vol. 64, p. 696

Fekel, F.C., & Bopp, B.W. 1993, ``Optical Spectroscopy of the Dusty K5 V Star HD 98800," ApJ, 419, L89

Fekel, F.C., Henry, G.W., Busby, M.R., & Eitter, J.J. 1993, ``Chromospherically Active Stars. XI. Giants with Compact Hot Companions and the Barium Star Scenario," AJ, 106, 2370

Fekel, F.C., Henry, G.W., Hampton, M.L., Fried, R., & Morton, M.D. 1994, ``Chromospherically Active Stars. XII. ADS 11060C: A Double Lined K Dwarf Binary in a Quintuple System," AJ, 108, 694

Hall, D.S., & Henry, G.W. 1994, ``The Law of Starspot Lifetimes," IAPPP Comm., 55, 51

Hall, D.S., & Henry, G.W. 1993, ``An Intimate Relation with Two Automatic Telescopes for Almost Nine Years," in Stellar Photometry--Current Techniques and Future Develpoments, eds. C.J. Butler and I. Elliott (Cambridge: Univ. Press), p. 205

Henry, G.W., & Hall, D.S. 1994, ``The Quest for Precision Robotic Photometry," IAPPP Comm., 55, 36

Henry, G.W., & Hall, D.S. 1994, ``Optical Variability in the Unusual K5 V Infrared-Excess Star HD 98800," ApJ, 425, L25

Kondo, Y., McCluskey, G.E., Silvas, J.M.S., Polidan, R. S., McCluskey, C.P.S., & Eaton, J.A. 1994, ``Ultra- violet Light Variations of beta Lyrae: Comparison of OAO-A2, IUE, and Voyager Observations," ApJ, 421, 787

Luttermoser, D.G., Johnson, H.R., & Eaton, J.A. 1994, ``Chromospheric Structure of the Cool Giant Star g Herculis," ApJ, 422, 351

Strassmeier, K.G., Hall, D.S., & Henry, G.W. 1994, ``Time-series photometric spot modeling II. Fifteen years of photometry of the bright RS CVn binary HR 7275," A\&A, 282, 535

Van Hamme, W.V., Hall, D.S., Hargrove, A.W., Henry, G.W., Wasson, R., Barksdale, W.S., Chang, S., Fried, R.E., Green, C.L., Lines, H.C., Lines, R.D., Nielsen, P., Powell, H.D., Reisenweber, R.C., Rogers, C.W., Shervais, S., & Tatum, R. 1994, AJ, 107, 1521

Zola, S., Hall, D.S., & Henry, G.W. 1994, ``Rediscussion of photometric data and an accretion disk model for the 96-day binary UU Cancri," A&A, 285, 531