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Astronomy Department
This report covers the period October 1, 1995-September 30, 1996. It does not cover activities in the Physics Department that are of an astrophysical nature
Bob Bless' introductory text book entitled "Discovering the Cosmos" was published by University Science Books. Karen and Jon Bjorkman left the Department in August for positions at the University of Toledo. Karen is an Assistant Professor and Jon is a Senior Scientist in that Department. Cassinelli organized a special topics session at the Madison AAS meeting on "Disks and Bipolar outflows from Hot Stars." Cassinelli presented a review on disk formation during this session. Jon Bjorkman summarized Wind Compresssed Disk theory and Churchwell presented a review of "Bipolar Outflows from Massive Star Formation Regions." Churchwell organized a special session on "Radio Astronomy Yesterday, Today, and Tomorrow" at the June 1996 AAS Meeting. Churchwell continued to serve on the NRAO Visitors Committee. Code became the WIYN Observatory Scientist and is spending 1996-97 at NOAO in Tucson, AZ. Gallagher served as Chair for the 1995 National Astronomy and Ionosphere Center Visiting Committee, as a member of the U. S. and International Gemini 8-m Telescopes Project science advisory committees, and as a member of the Space Science Advisory Committee for NASA. Hoessel was on sabbatical leave for the 1995-96 academic year. Mathis retired on June 30 and was awarded Emeritus status. He continues to work at Washburn Observatory. Mathieu was promoted to full professor. He serves on the Kitt Peak National Observatory Users Committee, the Task Group for Space Astronomy and Astrophysics (National Research Council), and the WIYN Board and Scientific Advisory Committee. Percival was appointed to the review board of the IAU Working Group on Astronomical Standard's initiative called SOFA: "Standards of Fundamental Astronomy." Ronald J. Reynolds joined the Astronomy faculty as a full professor from the UW Physics Department. Savage continued as a Councilor of the American Astronomical Society and to serve as President of the WIYN Board of Directors. Savage served on the Star Formation and Interstellar Medium Panel of the Task Group for Space Astronomy and Astrophysics. This panel prepared an updated science strategy which will be used by NASA to assess new space mission concepts for the latter part of this decade. Savage became a member of NASA's Origins Subcommittee. This commitee advises NASA on science programs to be pursued as part of their Origins Program. Sparke gave an invited review on "Polar Ring Galaxies" at the June 1996 AAS meeting. Ted von Hippel has continued in his position as the McKinney Assistant Scientist stationed in Tucson at the NOAO headquarters where he supports Wisconsin observers at the WIYN Telescope. Emeritus Professor Albert E. Whitford of Lick Observatory moved to Madison and became a Visiting Professor in June 1996. Eric Wilcots was promoted to Assistant Professor as of 1 July 1996. Kenneth Wood obtained a NASA Long Term Space Astrophysics grant to extend his Monte Carlo radiation transfer code to include the effects of metal line blanketing in the UV and develop 2D and 3D radiative equilibrium codes. The entire Department was saddened by the sudden death of Jason Cardelli who was a post doc and scientist in the Department for 9 years before going to Villanova in 1995.
The following graduate students received doctorates during the year:
Andrew Afflerbach "Galactic Abundances from Ultracompact HII Regions," now a senior scientist with Columbia Telecommunications Co. in Columbia MD.
Brian W. Casey "The Pre-Main Sequence Binary TY CrA," has since established a software company called Imagiware.
David Cohen "High Energy Emission from B Stars and its Relation to Stellar Winds," now Postdoctoral fellow in the departments of Astronomy and Nuclear Engineering at University of Wisconsin-Madison.
Andrea Cox "Neutral Hydrogen and Radio Continuum Emission in Polar Ring Galaxies," now a Visiting Assistant Professor at the Univ. of Iowa.
Richard Ignace "Theoretical and Observational Consequences of Stellar Rotation and Magnetic Fields in Stellar Winds," now a post doctoral fellow at Glasgow Univ.
Eric Jensen "Observations of Disks Around Pre-Main Sequence Binary Stars," now a lecturer at Ariz. State Univ.
Andrea Schweitzer "The Absolute Proper Motions, Membership and Kinematics of Dwarf Spheroidal Galaxies," now at Honeywell in Colorado.
Deborah Shepherd "Bipolar Molecular Outflows in Massive Star Formation Regions," now a post doctoral fellow at Caltech.
Anderson is the high resolution spectroscopy lead in the UW effort to study comet Hale-Bopp with the WIYN and other UW instruments. The initial effort will use the most compact HYDRA fiber assignment possible on WIYN to sample a large number of points in the coma. The echelle grating of the MOS will be used to observe a region near 6300 A which contains lines of H20+, NH2 and [O I ].
Fox has investigated the albedos of Venus, Mars, and Jupiter and the polarization of Mars and Io from data collected by WUPPE. Fox has also investigated the visual polarimetric variability of Mars from data collected at PBO.
Anderson continues to monitor the symbiotic star AG Draconis with the EUVE satellite and PBO in the visual. Polarized emission has so far eluded detection at EUV wavelengths. The ground based observations of AG Dra, which are spectropolarimetric, show a double loop in the QU plane well phased with the reported 554 day period. Also detected in polarization are the ultraviolet lines of OVI, Raman scattered (and polarized) into the red by neutral hydrogen.
Fox has investiagated the polarimetric variability of HD108 from observations taken at McDonald observatory.
Von Hippel is continuing his work with C. Jones (IoA, Cambridge), M. Storrie-Lombardi (IoA, Cambridge), M. Irwin (RGO, Cambridge), and N. Houk (U. Michigan) to automate visual stellar classification. They are using Artificial Neural Network techniques as the basis for automated classification. To date 100 of Houk's plates, covering 10% of the southern sky, have been analyzed. Deeper CCD data for nearly 20 square degrees is currently being analyzed.
Wood has been applying his Monte Carlo transfer code to a variety of problems. Wood, Stassun, and Kenyon (CfA) have been investigating the photopolarimetric variability of T Tauri stars. Wood, Nordsieck, Cole have been modeling the scattered light images of the LMC obtained by WISP and Wood, Karen and Jon Bjorkman have been diagnosing the circumstellar structure of Herbig Ae/Be stars. Wood, Ogle (Caltech), and Goodrich (IfA, Hawaii) are investigating the polarization properties of QSOs.
Ignace, Cassinelli, and Bjorkman (1996) completed a paper describing equatorial compression effects for stellar winds across the H-R Diagram that result from stellar rotation. This study is based on the Wind Compressed Disk model of Bjorkman and Cassinelli (1993), but focuses on the regime of stellar rotation where significant equatorial density enhancements occur, but a shock-bounded disk is not produced. Such a model is called a Wind Compressed Zone (WCZ) model. They find that velocity distributions that increase gradually to terminal speed, significant equatorial wind compressions can be achieved at stellar rotations of about 20% break-up. The WCZ model may have general relevance for understanding the occurrence of many axisymmetric stellar winds observed among single stars, including LBV stars, B[e] stars, Novae, and even AGB stars if they are spun-up by tidal effects of a companion.
Ignace is pursuing research on the Hanle effect as a diagnostic of stellar magnetic fields. It is expected that the Far Ultraviolet Spectro-Polarimeter, a rocket payload of Nordsieck's, will provide the first opportunity to observe the Hanle effect in a star other than the Sun in 1998.
Cassinelli and Ignace obtained infrared spectra using the Infrared Satellite Observatory (ISO) for the Wolf Rayet star WR134. The initial analysis of the data suggests that WR134 has a velocity law that would make the star susceptible to equatorial compressions at relatively slow stellar rotation speeds. This inference is consistent with the observed polarization of WR134.
Cassinelli presented a review entitled "Wind Compression Effects in WR Winds, and the Hanle Effect as a Magnetic Field Diagnostic" at a conference on Wolf Rayet stars held in Liege in July. For weak field strengths, the magnetic field follows the mass flux, which is enhanced at the equator owing to stellar rotation. The equatorial field strength can increase by an order of magnitude relative to the non-rotating case at a stellar rotation of only 20% break-up. Such field enhancements may have interesting effects for particle acceleration in hot star winds and possibly for shaping wind bubbles.
Kenneth Wood, along with Jon Bjorkman, Karen Bjorkman, and Mary Putman continued to investigate the circumstellar structure of Be stars. By modeling UV through optical spectropolarimetry as well as IRAS fluxes using detailed 3D Monte Carlo radiation transfer codes, they were able to constrain the circumstellar geometry of several Be stars to be very thin equatorial disks consistent with Bjorkman's dynamical models of rotating stellar winds.
Anderson has been using WIYN/HYDRA/MOS to monitor the strength of the Ca II H & K-line emission toward more than 50 stars in the range 11 < V < 14 and B-V > 0.5 in the young cluster NGC226. Several stars show variations on a one year timescale. If the instrument proves to be sufficiently stable to track variations on short (flare), intermediate (rotational modulation) and long (spot cycle) time scales, the program may be extended to other clusters and fields.
Cole, Gallagher, W. Freedman (Carnegie Obs) and R. Phelps (Carnegie Obs) are observing the hot stellar components of intermediate-age star clusters in the Large Magellanic Cloud through UV imaging with WFPC2. The first results for the 1 Gyr old cluster NGC 1783 show an unexpected population of moderate luminosity, UV-bright stars. Analysis of these results and similar observations for other clusters are in progress.
Dolan and Mathieu began a program to produce high-precision stellar radial velocities with the WIYN telescope and Multi-Object Spectrograph. As part of the WIYN Open Cluster Study (WOCS), they have obtained high-resolution spectra of over 150 stars in NGC 188. Precisions better than 1 km/sec appear to be achievable.
Walter (Stony Brook) and Mathieu began WIYN/MOS observations of ROSAT X-ray sources in the Orion association. Specifically they are searching for strong lithium absorption lines, which in conjunction with high-precision radial velocities will establish youth and membership. Additional fibers are being placed on other stars in the fields having appropriate colors for pre-main-sequence stars. Initial observations revealed a surprisingly large number of lithium-strong stars.
von Hippel, with collaborators G. Gilmore, N. Tanvir, D. Robinson (IoA, Cambridge University), and D.H.P. Jones (RGO) published their study of the low mass luminosity functions in two old open clusters. They demonstrated remarkable similarities between these two stellar populations, despite their large differences in ages and abundances.
von Hippel published a study of the use of gravitational redshifts to measure the radii of open cluster stars. von Hippel, in collaboration with G. Gilmore and D.H.P. Jones continued a search for white dwarfs in open clusters, to intercompare white dwarf cooling ages with main sequence stellar evolutionary ages.
von Hippel and A. Sarajedini (NOAO) continue to obtain photometry for selected open clusters using the KPNO and CTIO Schmidt telescopes, the KPNO 0.9m, and WIYN in support of the WIYN Open Cluster Survey. They are currently analyzing data for NGC 188, one of the oldest known open clusters.
Stassun, Mathieu, Mazeh (Tel Aviv) and Vrba (USNO) continued work on a survey for photometric variability of stars within a roughly 1 x 2 degree region centered on the Trapezium. Light curves of about 5000 stars are nearing completion. These light curves will be used to search for eclipsing binaries, laying the foundation for mass determinations of pre-main-sequence stars and their rotation periods.
Shepherd and Churchwell continued their study of molecular outflows associated with massive star formation regions. They have shown that outflows are a common feature of massive star formation regions and that usually several outflows are found in each region. Further, they have shown that the masses and kinetic energies of massive outflows scale with the luminosity of the central star as do those from low-mass stars. Outflow masses can be several tens of solar masses. Churchwell has shown that such masses cannot be provided by a stellar wind or entrained interstellar material in bipolar jets. He has argued instead for deflection of accreting material into bipolar jets and estimates that 14% or less of the material that takes part in in-fall actually reaches the star, most is ejected into bipolar outflows.
Acord, Walmsley (Arcetri), and Churchwell have submitted a detailed study of the massive outflow associated with the UC HII region G5.89 in multiple transitions of SiO. The physical properties of the outflow are derived and the fraction of Si tied up in SiO in outflows is estimated.
J. Hoffman, K. Nordsieck, and G. Fox have analyzed WUPPE and PBO spectropolarimetry of the interacting binary star b Lyrae. They find that the intrinsic polarization show a sharp 90 degree "flip" in postion angle at the Balmer Jump, indicating the presence of a bipolar flow perpendicular to the accretion disk. They also find that the hydrogen and helium emission lines of b Lyrae possess complex intensity and polarization profiles, which vary with phase and differ substantially from that of the surrounding continuum.
Jensen, Koerner (Cal Tech) and Mathieu published their millimeter-wave interferometric study of the pre-main-sequence quadruple UZ Tau. They showed that the 50-AU binary had substantially less millimeter emission than the spectroscopic binary, indicative of greater disk disruption by a stellar companion at separations comparable to the disk size. Unresolved emission from the binary was detected, indicating the continued presence of a massive circumstellar disk. The circumbinary disk around the spectroscopic binary was resolved. It shows a Keplerian-like velocity gradient, much like disks found around single stars.
Mathieu, Lattanzi (Torino), Zinnecker (Wurzburg) and Dolan continued an HST FGS program to obtain an astrometric orbit of the pre-main-sequence single-lined spectroscopic binary 045251+3016. This program will provide absolute orbits of both stars, thus providing both the orbital inclination and the mass ratio. When combined with the existing spectroscopic orbital elements, precise masses of the stars and the distance to the binary will be obtained. The first observations successfully resolved this 7-yr period binary.
Carr (NRL), Mathieu and Najita (CfA) continued a program of high-resolution near-infrared spectroscopy (CO fundamental and overtone transitions) to explore the circumstellar gas in several young binaries. The program has been expanded to investigate stars showing evidence for cleared inner regions of their disks, perhaps indicative of planet formation.
Casey, Mathieu, Vaz (Brazil), Andersen (Copenhagen) and Suntzeff (CTIO) completed analysis of their uvby light curves of TY CrA. The 3.2 Mo. primary is very near the main sequence, while the 1.6 Mo. secondary is at the base of its Hayashi track. Pre-main-sequence evolutionary tracks have been tested against the stellar parameters derived from observations.
Martin (Instituto de Astrofisica de Canarias), Mathieu and Maguzzu (Catania) have obtained preliminary orbital elements for the classical T Tauri spectroscopic binary UZ Tau E. With the discovery that UZ Tau E is a binary with a period of 19.1 days, the UZ Tau system becomes a quadruple. Intriguingly, prior to its discovery as a spectroscopic binary every property of UZ Tau E was ÒtypicalÓ of a classical T Tauri star surrounded by an actively accreting circumstellar disk. As with DQ Tau, how all of the diagnostics for such an accretion disk can survive in the presence of companions within 0.1 AU is a challenge to understand.
Jensen and Mathieu have studied the spectral energy distributions of short-period pre-main-sequence spectroscopic binaries. Several show structure indicative of cleared gaps or holes in disks on size scales of the binaries; some show power-law-like SEDs with little indication of disk clearing.
Mathieu, Stassun, Basri (Berkeley), Jensen, Johns-Krull (Texas), Valenti (Colorado) and Hartmann (CfA) completed their radial-velocity and photometric study of the classical T Tauri spectroscopic binary DQ Tau. The most significant result is photometric modulation with a period identical to the binary orbital period, 15.8 days. The star brightens by as much as a factor 2 in V at most periastron passages.
Anderson has continued to lead the study of interstellar polarization using data from both Astro-1 and Astro-2, combined with visual data from the Pine Bluff and WIYN Observatories. Initial results will appear in the 1996 December AJ. Weitenbeck and Anderson continued their study of the distribution of interstellar material toward the cluster NGC 1502 based on polarimetry from PBO and WIYN.
Mathis worked on models of interstellar grains (see 1996, ApJ, Dec. 1) that incorporate the recently discovered amount of carbon in the gas phase of the ISM: C/H(gas) = (140 +/- 20) ppM (parts per million) (Cardelli et al. ApJ 467, 334, 1996). His models also take into account the strong possibility that the ISM contains only about 0.7 of the total heavy element abundance of the Sun. The models consist of composite grains containing amorphous carbon and silicates, along with 25% - 50% vacuum. Some models contain oxides as well. The vacuum increases the extinction per gram. He is considering the problem of explaining the strength of the 9.7 and 18 micron silicate absorption features if the heavy element abundances are reduced. If grains are oblate, there is enough silicon even with models of 70% solar composition.
Wood and Mathis have considered the transfer of radiation through simple plane-parallel dusty slabs, including scattering by dust, using a Monte Carlo technique. They find a simple expression that approximates the emergent intensities. Their work will predict the intensity of galaxies as functions of inclination and dust properties.
In order to explain the interstellar extinction law and the observed depletions of the most depleted elements in the gas phase of the ISM (e.g., Al, Ca, and Ti), J. E. O'Donnell (UNAM) and Mathis considered grain-grain and grain-gas collisions, with circulation between the diffuse gas and clouds. They find that additional and rapid circulation between very dense regions and the diffuse ISM is needed.
Afflerbach and Churchwell in collaboration with Acord (UW), Hofner (Univ. Cologne), Kurtz (UNAM), and DePree (NRAO) completed a study of the electron temperatures in ultracompact HII regions as a function of galactocentric position. Multiple radio recombination lines were measured with the VLA and analyzed using a nonLTE code to derive average electron temperatures. They found that temperatures systematically increase with galactocentric radius with a slope of 320(64)K/kpc and show that this is most easily explained by a decrease in the abundance of the primary coolants of HII regions. In a related study, Afflerbach, Churchwell, and Werner measured fine structure lines of O, S, and N at FIR wavelengths toward about 35 UC HII regions using the KAO. They found that all three elements increase in abundance toward the galactic center at about the same rate. The abundance gradients of these elements with galactocentric radius are entirely consistent with the electron temperature gradient in UC HII regions.
Hofner and Churchwell have completed a high resolution study of water masers associated with UC HII regions using the VLA. Several morphological patterns are identified.
Churchwell, Winnberg (Chalmers), Cardelli (Villanova), Cooper (Fermi Lab), and Suntzeff (CTIO) have completed a study of CS and CN emission toward the western rim of the Vela Shell. Physical properties of the gas are derived and it is shown that the transition from ionized to molecular gas occurs very abruptly along a projected boundary of more than 3 pc.
Weitenbeck is also analyzing WUPPE observations made during HUT and UIT pointings that might be of use to the WUPPE interstellar medium program.
Gibson continued an investigation of the neutral gas structure and kinematics, light scattering geometry, and dust scattering properties in the Pleiades extended reflection nebula for his Ph.D. thesis under Nordsieck's direction.
Reynolds, Tufte, Haffner, and Hausen (undergraduate) used the recently completed Wisconsin H-Alpha Mapper (WHAM) facility located temporarily at the Pine Bluff Observatory to obtain the first detections of extremely faint diagnostic emission lines from the diffuse interstellar medium (ISM), including the He I 5876 recombination line, the [O I] 6300 line, and the [N II] 5755 line. They found the He I line to be fainter relative to H-alpha in the diffuse background than in the brighter, traditional O star H II regions. This challenges standard O star ionization models of the warm ionized medium (WIM). The [O I] detections have provided a measure of the ionization fraction of hydrogen in the WIM, and the intensity of the [N II] 5755 line, relative to that of the much brighter [N II] red line, provides a direct measurement of the electron temperature.
Tufte, Haffner, and Reynolds also carried out WHAM observations toward the high velocity cloud complex M and obtained the first detections of H-alpha and [S II] 6716 emission from this - 112 km/s H I structure located 1.4-4.4 kpc above the Galactic disk.
Haffner, Reynolds, and Tufte obtained the first detection of diffuse [O III] 5007 emission at high Galactic latitudes, which has provided new information about the hotter (100,000 K) temperature phase of the ISM.
Savage, Sembach (JHU), and Lu (CIT) are completing their study of the highly ionized gas in the Galactic halo. They have obtained GHRS 15 km/sec resolution observations of absorption in the lines of N V 1238, 1242 and C IV 1548, 1550 towards bright extragalactic objects including 3C 273, H 1821+643, Fairall 9, Mrk 509, PKS 2155-304, and NGC 5548. These observations are being combined with earlier IUE and GHRS measurements along extragalactic and galactic sight lines to study the distribution and kinematics of highly ionized gas in the Galactic disk and halo. They find that the scale height of C IV is larger than for N V, a result consistent with the large observed increase in N(C IV)/ N(O VI) between the disk and halo (Spitzer 1996, ApJ L, 458,29). Evidently the mix of gas types is changing as a function of distance away from the Galactic plane.
Sembach (JHU), Savage and Tripp have used the GHRS to study the properties of the highly ionized gas, as traced by N V, C IV, and Si IV, in the direction of galactic radio loops I and IV. The high ion column densities for sight lines through these loops are enhanced by factors of three compared to typical lines of sight through Galactic disk and halo gas. The ionic ratios are also substantially modified. The inhomogeneous nature of the high ion absorption in the Galaxy is produced in part by an enhancement in the number density of the high ions in Galactic radio loops. In the case of radio loop IV, it appears that a hybrid model consisting of roughly equal contributions to the highly ionized gas from turbulent mixing layers and conductive interfaces/SNR bubbles is required to explain the observations.
Sembach (JHU), Savage, Lu (CIT) and Murphy (JHU) are studying a new type of Galactic high velocity cloud, the C IV-HVCs. The first C IV-HVC was seen in HST GHRS ultraviolet absorption line data toward the bright Seyfert galaxy Mrk 509 (l = 36, b = -30). The cloud exhibits strong C IV absorption from -170 to -340 km/sec with no associated Si II or N V absorption. Collisional ionization in a hot gas with T> 10^5K can not be ruled out as the origin of the ionization. However, a more likely possibility is that the cloud is the ionized boundary of a H I-HVC with the source of ionization being the extragalactic EUV background. Further work on this and two other such clouds are underway. The C IV-HVCs may provide important insights on the origin of the very common highly ionized QSO absorption line systems which are most often detected in the C IV doublet lines.
The late Jason Cardelli (Villanova), Meyer (Northwestern), Jura (UCLA), and Savage have used the GHRS to determine the abundance of carbon in the diffuse neutral interstellar gas toward six stars in the Galactic disk using the very weak [C II] intersystem line at 2325 Å. They observed a gas phase abundance of C/ H = (140+/-20) x 10-6 Adopting a cosmic abundance C/H = (240+/- 50) x 10-6, the gas phase abundance implies a dust phase carbon abundance of 50 < (C/H)x10-6 < 150. This amount of carbon in the dust could explain the 2175 Å extinction bump but does not provide much carbon to explain the continuous ultraviolet and optical extinction.
Gallagher participated in a study of the optical structure of the Crab Nebula which is led by J. Jeff Hester (Arizona State University). The primary result from this project is a set of time series observations with WFPC2 that show a variety of systematic dynamic processes within the inner regions of the Crab Nebula.
Han and Hoessel continued their participation on the HST Extragalactic Distance Scale team. Work is nearing completion on 14 Cepheids discovered in NGC 7331, in collaboration with Dr. Shaun Hughes (RGO) and the rest of the Key Project Team. They find a corrected distance modulus of 30.85 for this galaxy.
Han, Hoessel and Gallagher continued their work in support of the HST Wide Field/ Planetary Camera 2 (WFPC2) Investigation Team. Deep observations were made in an inner and outer field of NGC 147 in V and I to produce color-magnitude diagrams for 80,000 resolved stars. A new multi-isochrone fitting technique has been developed which can recover the distance and extinction to a galaxy while simultaneously determining the distribution of stars in age-abundance space for such a composite population.
Han is using WIYN to study the morphology of clusters of galaxies and dwarf galaxies in clusters (with Gallagher). He is also working on the HST Key Project on the extragalatic distance scale (with Hoessel and others) and investigating kinematics and photometric properties of galaxies and globular clusters.
Gallagher, Han, and R. Wyse (Johns Hopkins) are using the WIYN Telescope to study the structures of dwarf galaxies in dense clusters. A deep set of CCD images for a few Virgo dwarf galaxies obtained at San Pedro Martir Observatory S. Levine and L. Aguilar (National Observatory) provided a comparison sample, which was analyzed by P. M. Carey (Toronto) under Gallagher's direction for his senior thesis. Work on more distant clusters (e.g., Perseus and Coma) is now in progress with high quality surface photometry being obtained from the WIYN CCD images.
Hoessel and Saha (STScI) continued their study of the Cepheid variables in a sample of 15 nearby dwarf irregular galaxies in the distance range 1 - 3 Mpc. The observational program has been transferred from the KPNO 2.1 meter to the WIYN telescope. New Cepheid distance modulii were obtained to IC 10 (24.59) and NGC 2366 (27.68).
Nordsieck and Harris, using the Wide Field Imaging Survey Polarimeter (WISP) sounding rocket payload, observed the polarization of the UV diffuse light in the Large Magellanic Cloud (LMC). The UV diffuse light is polarized at a low level and is distributed similarly to the IRAS thermal light. This implies that direct UV light supplies the majority of the energy to heat the diffuse dust in the LMC.
Gallagher led an initial effort to recover the star formation history of the Large Magellanic Cloud from the analysis of a color magnitude diagram obtained in V and I with WFPC2 on the HST. He is also participating in follow-on investigations with J. Holtzman (New Mexico State U.) as part of the WFPC2 Team program, and in a related series of WFPC2 observations of Local Group dwarf irregular galaxies.
Gallagher continued his work with SUNY Stony Brook graduate student L. Matthews on her Ph.D. thesis exploration of the structure and evolution of extreme late-type galaxies. An initial anaylsis of photometric properties based on CTIO CCD images in combination with HI pencil beam measurements have been used to study the Tully-Fisher relationship for this sample, which seems to contain larger than normal amounts of dark matter. HI surveys for this thesis are continuing at Green Bank and with the Nancay Radio Telescope in collaboration with W. van Driel (Meudon).
In a related project Gallagher, Matthews, J. Krist, and C. Burrows (STScI) have used the WFPC2 Planetary Camera to observe the structures of nuclei in extreme late-type galaxies. The nucleus in NGC 4395 provides an example of an ultra-low luminosity Sy1, which we have found contains the usual bipolar cone structures of an active nucleus which are absent in comparison observations of inactive nuclei.
Gallagher continues his studies of star burst galaxy nuclei in collaboration with A. Watson (New Mexico State). This WFPC2 program is yielding new insights into the structures of starbursts, the role of dust in these systems, and the properties of the super star clusters which they spawn.
As an external advisor on Annette Ferguson's Ph.D. thesis, which is under the direction of R. Wyse at Johns Hopkins, Gallagher has been involved in studies of faint emission line regions in nearby galaxies. Initial measurements of diffuse ionized gas in Sculptor Group late-type galaxies are now complete and work on outer HII regions in giant spiral galaxies is in progress.
Sparke and Andrea Cox have used CCD photometry and VLA HI mapping of the edge-on late-type disk galaxy NGC 7170 to show that the very thin stellar disk has a strong and slightly asymmetrical warp. The neutral hydrogen layer follows approximately the same warped plane, as expected if the warp is gravitational in origin. The ratio of HI mass to dynamical mass is normal for a late-type spiral, but the mass-to-light ratio is high, about 25 in solar units, indicating that most of the mass is in a dark halo. The galaxy is a 'superthin' system, and further optical observations are planned with WIYN to measure the vertical structure.
Andrea Cox's Ph.D. thesis, under Linda Sparke's direction, presents VLA imaging of the HI gas in polar rings and radio continuum emission from the central galaxies: these systems have rings of gas, dust and stars circling over the pole of the central S0 or elliptical system. High-resolution HI images of 5 polar rings are presented. They are using the velocity fields to measure the gravitational potential, and are searching for diffuse HI which may link the rings to neighboring galaxies. Radio continuum data show that most of the galaxies have no more emission than E or S0 galaxies lacking polar rings, which suggests that the ring gas is stable, and is not falling into the central galaxy.
Sparke and Wesley Colley (a Princeton graduate student) have used a tilted-ring formalism to study the way tilted gas disks in a galaxy may settle to the symmetry planes of the potential. They find that disks in triaxial galaxy potentials settle somewhat more rapidly than in axisymmetric systems, since they are being twisted about two axes simultaneously. Unfortunately some of the results from hydrodynamic simulations of settling gas disks seem not to be general, but appear to reflect the particular form of viscous dissipation present in the codes.
Sparke, Watson (New Mexico State U.), and Cox are using multicolor optical and H-band images to constrain the ages of stars in polar rings. Sparke is also involved in a single-dish survey of polar ring galaxies using the Nancay radio telescope, which will yield average HI masses and line widths, and provide further candidates for high-resolution mapping. With Magda Arnaboldi and Ken Freeman (Mt Stromlo), Sparke is collaborating on optical and near-IR imaging of Southern polar ring galaxies.
von Hippel, H. Ferguson (Space Telescope Science Institute), and N. Tanvir (IoA, Cambridge) are using HST photometry to detect intergalactic stars in the Virgo Cluster of galaxies. Intergalactic stars are expected from the cluster formation process, which should have involved numerous galaxy collisions and disruptions. So far no intergalactic stars have been detected.
Erwin and Sparke are conducting an imaging program with WIYN to search the centers of nearby barred galaxies for small nuclear bars or asymmetries. About 20 galaxies have been observed, most in three colors. Copious evidence for small and previously undetected structures on scales of a few arc seconds have been found. Its good image quality makes WIYN particularly suited to this kind of imaging survey.
Maciejewski and Sparke are investigating stellar orbits and gas flow in galaxies having small central bars within larger kiloparsec-scale bars. Because dynamical times are shorter in the centers of galaxies, it is likely that the figure of the small bar is rotating faster than that of the large bar, so that the gravitational potential is not constant in any rotating frame. It has previously been thought that orbits in such a time-varying potential were likely to be highly chaotic, and that smooth gas flow would not be possible. They have shown that the potentials allow a set of closed loops, which return to themselves after the two bars have made half a rotation relative to each other; gas in these loops can orbit without crossing any other gas streams, so that a stable flow is possible.
Savage is a member of the team of scientists undertaking a spectroscopic survey of bright quasars with the HST in order to study the quasar absorption line phenomena at low redshift. This project is one of the three "Key Projects" being pursued with the HST. The reduction of FOS spectra of approximately 60 quasars is now complete. Savage and Lu (CIT) are using these spectra to study the Milky Way absorption by Mg II and Fe II toward the QSOs to determine the sky covering factor of Galactic high velocity Mg II and Fe II. The metal line high velocity cloud covering factor will be compared to the covering factor found from H I 21 cm emission line studies.
Tripp, Lu (Caltech), and Savage have completed a high resolution high signal-to-noise study of QSO absorption line systems in the spectra of two luminous high z QSOs, HS 1946+7658 and HS 1700+6416. Two damped Lyman alpha absorbers are detected in the spectrum of HS 1946+7658, and the measured abundance's in these damped absorbers indicate that these are young objects detected in very early stages of chemical enrichment (Lu et al.1995). In contrast, the "associated" absorption system of HS 1946+7658 has attained abundance's comparable to or greater than solar despite its high redshift, z = 3.05 (Tripp et al. 1996). The associated absorber in the spectrum of HS 1700+6416 shows similar solar or supersolar abundance's (Tripp et al. 1997). Tripp et al. (1997) also present abundance measurements in Lyman limit absorbers in the direction of HS 1700+6416. The spectrum of HS 1700+6416 also contains a complex cluster of C IV doublets in which two pairs of C IV doublets are apparently line locked. This is surprising because the complex is displaced by 24000 km/s from the QSO systemic redshift, so radiation pressure from the QSO, which provides a natural explanation of line locking, would be negligible if the velocity displacement is due to the Hubble flow.
Tripp, Lu, and Savage have been conducting a study of the relationship between galaxies and intergalactic Lyman alpha (H I) clouds at low redshifts using the WIYN telescope with the MOS/HYDRA and the GHRS on the Hubble Space Telescope. For this program, the HST GHRS provides a high signal-to-noise spectrum of a low z QSO which is used to measure the redshifts and properties of the intergalactic clouds including weak clouds with equivalent widths as low as 50 mA. The WIYN HYDRA is used to carry out a survey of redshifts of all galaxies brighter than B = 19.5 in the one degree fields centered on the QSO. They find (1) Lyman alpha clouds are clustered at low redshifts, (2) O VI is clearly detected at z = 0.2249.
Wilcots, Hunter (Lowell), Gallagher, and H. van Woerden (Leiden) continued work on a VLA mosaic of the extended HI disk surrounding NGC 4449, a nearby Magellanic Irregular. They have discovered a spectacularly complex distribution of gas around NGC 4449, including an arc spanning nearly 80 kpc. NGC 4449 has either recently accreted a small companion, or is still in the process of accumulating primordial gas.
Wilcots, Miller (Dept. of Terrestrial Magnetism) and Hodge (U. Washington) continued work on the distribution and kinematics of HI gas in the Local Group dwarf irregular IC 10. IC 10 is in the process of accreting a small HI cloud, which may be fueling its current starburst. The ISM in IC 10 is highly disturbed.
Wilcots is also carrying out more VLA HI mosaics on two other Local Group dwarf irregulars - IC 1613 (with K. Olsen and P. Hodge [U Washington]) and Sextans A (with D. Hunter [Lowell]). They are acquiring WIYN images for each galaxy to look for any stellar population that may be associated with the extended gas, to study the star formation rates and H II region populations, and to understand the recent star formation histories in these galaxies.
B. Miller (DTM) and Wilcots initiated a Near-IR study of a sample of barred Magellanic spirals (SBm). The IR images indicate that the bars in these galaxies are old and stable. Wilcots continues optical studies of the morphology and star formation characteristics of SBm galaxies with the WIYN telescope. Wilcots, D.J. Pisano (U. Wisconsin), Bruce Elmegreen (IBM), and Gallagher are using VLA HI and WIYN optical observations to determine the corotation radius and pattern speeds in these galaxies.
Wilcots and Turnbull (undergrad) are studying the distribution and kinematics of far flung HI gas around Seyfert galaxies to see if such gas could be triggering the nuclear activity.
Gallagher and Wilcots acquired CO observations of several fields in the outer disk of M101. Their data suggests that the CO emission is strongest in those fields with the smallest (but more numerous) HII regions. There is little CO in the fields with the giant HII regions.
Mathieu and Dolan completed development of computer-based laboratory exercises for use in the introductory astronomy course. The course was taught with the laboratory component for the first time in Spring 1996. StudentsÕ perceptions were highly favorable; an assessment of success is underway in collaboration with Gina Brissenden of the School of Education .
The WIYN Observatory consortium is composed of the University of Wisconsin, Indiana University, Yale University and the National Optical Astronomy Observatory (NOAO). The WIYN advanced technology optical observatory is located on the western ridge at the Kitt Peak National Observatory. The University of Wisconsin has a 26% share in the observing time. WIYN began full scientific operations in July 1995. WIYN is producing optical images of excellent quality. The statistics for image quality show a median RMS FWHM for the R band based on exposures with integration times of more than 10 seconds of 0.8" for the period through 1996 September. Approximately 10% of the time the R band images have been 0.6" or better and 25% of the time 0.7'" or better. The best images obtained so far have FWHM of approximately 0.4".
The "general use" instruments for WIYN, which are available to all WIYN institutions and to the general astronomical community, include the multi-object spectrograph (MOS) and fiber positioner (HYDRA) and an imaging camera system. Both instruments are fully operational and producing excellent data. MOS/HYDRA with its fiber postioner and bench mounted spectrograph allows the simultaneous acquisition of 100 optical spectra with low to moderate spectral resolution over the full one degree field of WIYN. The imaging camera contains a 2048x2048 CCD providing a field of 6.7'x6.7' and 0.2"/pixel sampling.
The HPOL spectropolarimeter was mounted on the WIYN telescope for the first time in Feb.-Apr. 1996. Clayton, Bjorkman, Nordsieck, Zellner, and Schulte-Ladbeck obtained observations of R Cor Bor during its recent obscuration event; comet Hyuakutake was observed by Nordsieck, Harris, Wood, and Fox; and, several pre-main sequence stars were observed by Bjorkman.
Percival continued his work on Progressive Image Transmission, which enables very large images to be sent over very slow network connections. This is a central feature of the WIYN Remote Observing System which allows WIYN images to be received and examined in less than 1% of the expected transmission time. Percival also continued his work on the WIYN Remote Engineering Data System, which allows remote users to monitor every aspect (tracking, servos, voltages, temperatures) of an observing session.
von Hippel and R. Seaman (NOAO) are developing an Archive and Data Distribution System for WIYN based on CD recordable media. The goal of this effort is to ease the data distribution process and begin the creation of a long-term WIYN data archive.
Members of the WIYN consortium institutions have begun the WIYN Open Cluster Study (WOCS). The WIYN telescope, with its wide field and multi-object spectrograph, is optimal for extensive studies of open clusters. One goal of WOCS is to select a set of key clusters which will be intensively studied and characterized, thereby increasing the number of fundamental clusters and the sampling of clusters in age, metallicity, etc. Initial efforts are focusing on NGC 188.
The Halfwave Spectropolarimeter (HPOL)
HPOL, constructed at SAL (PI Nordsieck), split time between WIYN and PBO this past year. HPOL was at WIYN for 3 months and obtained 12 nights of observations in which 36 targets were observed. While mounted on the PBO 36" telescope, 153 observations of 80 different targets were obtained. To disseminate the increasingly vast amount of polarimetric data now being compiled by the HPOL instrument a www site has been established to report simulated broadband (UBVRI) polarimetric values for all archived HPOL data (1989-94). This site (http://www.sal.wisc.edu/HPOL) will continue to be updated as more data continues to be archived.
The Wisconsin H-Alpha Mapper (WHAM)
The new WHAM Fabry-Perot facility (Reynolds, PI) was assembled at the Pine Bluff Observatory near Madison in November 1995. It saw first light in January 1996, and is scheduled to begin the H-alpha sky survey at Kitt Peak in early 1997. The WHAM spectrometer, built by the Department's Space Astronomy Laboratory with funding from the NSF, is 100 times more efficient than the Fabry-Perot system that it replaces.
Telescope Control System (TCS)
Percival finished the Telescope Control System software for the Wisconsin H-Alpha Mapper. The WHAM TCS is a workstation-based soft-real-time system modeled on the WIYN 3.5m Telescope Control System software, also designed and built by Percival. Like the WIYN system, the WHAM system is portable, distributed, and network transparent.
The Spatial Heterodyne Spectrometer (SHS)
Development continued on the SHS sounding rocket payload. SHS is a NASA supported collaboration between the Department of Physics (F. Roesler, PI, and W. Sanders), the Space Astronomy Laboratory (Reynolds), and St. Cloud State University, MN (J. Harlander) to build a new type of extremely high throughput Fourier transform spectrometer for investigations of faint ultraviolet line emission from the "coronal'' (100,000 K) component of the ISM. A suborbital flight is tentatively scheduled for 1997 to obtain the first radial velocity resolved map of C IV 1550 emission from the Cygnus Loop.
Goddard High Resolution Spectrometer (GHRS)
Savage and Wakker are continuing their scientific interpretation of high and medium resolution UV spectroscopic data obtained by the GHRS. These efforts are being supported by students Howk and Tripp. The GHRS will be removed from HST during the Space Shuttle servicing mission in February 1997. The replacement UV spectrograph will be the Space Telescope Imaging Spectrograph (STIS).
Far Ultraviolet Spectrometer Explorer (FUSE)
Savage is a Co-Investigator for the FUSE satellite which is being prepared for a late 1998 launch. FUSE will be a dedicated spectroscopy mission operating in the 912 to 1200 A wavelength region at a resolution of 30,000 or 10 km s-1. Savage's observational program with FUSE will involve measurements of O VI absorption produced by the hot interstellar medium of the Milky Way disk and halo. The goal will be to study the distribution and kinematics O VI to gain insights about the origin(s) of the hot gas in the interstellar medium.
Wisconsin Ultraviolet Photopolarimeter Experiment (WUPPE)
Data from the two WUPPE missions on theSpace Shuttle continue to be analyzed and published by the WUPPE team and others.
Other
Reynolds is collaborating with A. Kutyrev and C. Bennett (PI) at Goddard Space Flight Center and F. Roesler (UW Physics) in the development of a high throughput (WHAM-like) infrared Fabry-Perot spectrometer for high spectral resolution studies of the 4 micron Br-alpha line from optically obscured diffuse HII regions.
Automatic stellar classification is under development by von Hipple and colleagues using Artificial Neural Network techniques.
The department continues to be actively involved in a variety of public outreach programs. Students and faculty routinely speak to elementary, middle, and high school students; more than 25 such engagements in the past year. The department continues to support Space Place, a family-oriented interactive astronomy museum, with frequent public lectures and presentations. Public observing sessions at the Washburn Observatory are held every other week during the academic year. The department initiated its "Universe in the Park" program this summer, funded by a NASA IDEA grant. This program provides public sky-viewing sessions and lectures at Wisconsin's state parks. Faculty members often make radio and TV appearances to discuss astronomical events in the news. Through these activities, the department is working to heighten public awareness of science and astronomy within the local community and the state.
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Heath-Jones, D., et al. (including Gallagher and Hoessel), "Visible and Far Ultraviolet WFPC2 Imaging of the Nucleus of the Galaxy NGC 205," 1996, Ap. J., 466, 742.
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Hester, J.J., Stone, J.M., Scowen, P.A., Jun, B., Gallagher, J.S. & WFPC2 IDT "WFPC2 Studies of the Crab Nebula III Magnetic Rayleigh-Taylor Instabilities and the Origin of the Filaments." 1996, ApJ, 456, 225.
Holtzman, J.A., Watson, A.M., Mould, J.R., Gallagher, J.S., & WFPC2 IDT "Star Clusters in Interacting and Cooling Flow Galaxies." 1996, AJ, 112, 416.
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Jensen, E.L.N., Mathieu, R. D., Fuller, G. A. "The Connection between Submillimeter Continuum Flux and Binary Separation in Young Binaries: Evidence of Interaction between Stars and Disks" 1996, ApJ, 458, 312.
Jones, C.A.L., Irwin, M., & von Hippel, T. "The Application of Artificial Neural Networks to Stellar Classification," 1996, in Astronomical Data Analysis Software and Systems V, ed. G.H. Jacoby & J. Barnes, (San Fransisco: ASP), 21.
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Kelson, D., et al. (including Hoessel)," The Extragalactic Distance Scale Key Project III. The Discovery of Cepheids and a New Distance to M101 Using the Hubble Space Telescope," 1996, Ap, J.,463, 26.
Korista, K. and others including L.S.Sparke "Steps towards determination of the size and structure of the broad-line reguion in active galactic nuclei 8: An intensive HST, IUE and ground-based study of NGC 5548," 1995, ApJ Supp 97, 285.
Lamers, H.J.G.L.M. and Cassinelli, J. ``Mass Loss from Stars," invited review 1996, "From Stars to Galaxies: The Impact of Stellar Physics on Galactic Evolution," (ed by C. Leitherer, U. Fritze-v. Alvensleben, and J. Huchra (ASP:San Francisco)), p.162.
Linsky, J.L., Diplas, A., Wood, B.E., Brown, A., Ayres, T.R., and Savage, B.D. "Deuterium and the Local Interstellar Medium for the Procyon and Capella Lines of Sight," 1995, ApJ, 451,335.
Lu, L., Savage, B.D., Tripp, T. M. and Meyer, D.M. "Metal Abundances and Physical Conditions in Two Damped Lyman Alpha Systems Toward HS1946+76," 1995, ApJ, 447, 597.
MacFarlane J. J., Cohen, D. H., & Cassinelli, J.P. "Ionization in the Winds of Early-B stars: Constraints Imposed by EUVE" 1996, Astrophysics in the Extreme Ultraviolet, (ed. by S. Bowyer and R.F. Malina)(Kluwer:Dordrecht). p375.
Maciejewski, W., Mathis, J. S., & Edgar, R. J. "Effects of Conduction Fronts on Derived Compositions of H II Regions," 1996, ApJ, 462, 347.
Maciejewski, W., Murphy, E., Lockman, F.J. and Savage, B.D. "The Aquila Supershell: a Remnant of Multiple Supenovae," 1996, ApJ, 469, 238.
Mathieu, R. D., "Binary Frequencies among Pre-Main Sequence Stars" in "The Origins, Evolution, and Destinies of Binary Stars in Clusters" eds. E. Milone and J.-C. Mermilliod (Kluwer, Dordrecht), 1996, ASP Conf. Series, San Francisco), 90, 278.
Mathieu, R. D. "Observations of Disks Around Pre-Main-Sequence Binaries," NATO Advanced Study Institute on "Evolutionary Processes in Binary Stars," edited by Wijers, R.A.M.J., Davies, M.B. and Tout, C.A. (Kluwer, Dordrecht), 1996, p.11.
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Metcalfe, T.S., Mathieu, R.D., Latham, D.W. and Torres, G. "The Low-Mass Double-Lined Eclipsing Binary CM Draconis: A Test of the Primordial Helium Abundance and the Mass-Radius Relation near the Bottom of the Main Sequence" 1996,Ap J., 456, 356.
Mould, J.R., Watson, A.M., Gallagher, J.S. & WFPC2 IDT "Far-Ultraviolet Imaging of the Globular Cluster NGC 7099 with the Second Wide-Field and Planetary Camera." 1996, ApJ, 461, 762.
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Murphy, E., Lockman, F.J. and Savage, B.D. " A Sensitive Search for High Velocity Clouds," 1995, ApJ, 447, 642.
Najarro, F., Kudritzki,R., Cassinelli, J.P., Stahl, O. & Hillier D. J. "Stellar Winds and the EUV Continuum Excess of Early B-Giants,"1996, AA 306, 892.
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