Prepared by Dr. J Sulentic
UA Astronomy Home Page
keel@bildad.astr.ua.edu Last changes: September 1998
AAS Observatory Annual Report (1995-1997)
| I. | Personnel |
|---|---|
| II. | Theoretical Research |
| III. | Observational Research |
| IV. | Other Activities |
| V. | Publications |
Professors
The major research focus of the astronomy group at U. Alabama is on extragalactic theory and observation. We summarize current results and activities by subtopic in these sections.
Byrd has continued studies of the one-armed spiral galaxy, NGC 4378. In earlier simulations, Byrd, T. Freeman (Walker College) and S. Howard (NSF) found that the single arm which extends over the entire disk can be created by tidal effects of a small companion. In contrast to NGC 4622's single arm, the single arm of NGC 4378 trails the disk rotation. To test this prediction, Byrd, Buta and undergraduate Demetrius McCormick (REU, Tuskegee U.) have processed two color images of NGC 4378 obtained by G. Purcell. They found that the disk orientation and rotation require that the single arm does indeed trail.
With undergraduates Derrick Ousley, Chris Dalla Piazza (REU, Lycoming), and graduate student D. Domingue, Byrd has developed an analytic formulation of dissipative formation of resonance rings in galaxies via the perturbation of a bar on gas clouds in the disk. The rings are periodic orbits of gas clouds in which the clouds do not collide violently yet surface density enhancement promotes star formation. Bar pattern speeds and strengths are determined from the rings and the rotation curve. The formulation has been used to duplicate ring morphology of galaxies which have all ring types (NGC 3081),to those without a clear nuclear ring (ESO 507-16), to those which have only outer rings (ESO 509-98) as a result of slow to fast bar pattern speeds. This pattern was found earlier by Byrd and collaborators in computer simulations. The formulation predicts that high dissipation can cause some rings to be misaligned relative to the bar. Finally, use of disk photometry permits determination of disk surface density.
Byrd and undergraduate student John Brecht (REU, Michigan State) developed an individual time step n-body code to simulate the effects of massive cold molecular clouds on the stellar dynamics of dwarf galaxies. Under supervision of Byrd, graduate student R. Mohr is studying the gravitational effects of M31's small companion M32 on M31's disk and vice versa using computer codes developed by B. Smith (NASA Ames) and R. Miller (U. of Chicago).
Hardee's research involves study of the dynamics and emission from the highly collimated jet outflows observed in extragalactic radio sources, quasars, galactic superluminals, and protostellar outflows. The work includes analytical analysis of the magnetohydrodynamic fluid equations, numerical simulation and modeling of the dynamics and the emission from the jets and comparison with observations of individual objects. Relativistic and non-relativistic adiabatic and radiatively cooling magnetized jets have been studied. Objectives of this research are (1) to learn how analytical theory can be applied to these objects, (2) to directly apply three dimensional numerical simulations to understanding the outflow dynamics of these objects, (3) to use the results to learn how outflow morphology is influenced by the external environment, by the presence of dynamically significant magnetic fields, and by radiative cooling, and (4) to model the emission from jets and understand the relationship between observed emission and the underlying flow.
Simulations of fully 3D outflows with resolution sufficient to make a comparison with predictions made by the linearized MHD equations and with observed astrophysical morphologies was performed in collaboration with D. Clarke (St. Mary's U). A primarily poloidally magnetized overdense jet simulation successfully reproduced features like those seen in the high power (FR II) jet in Cygnus A. Jet distortions observed in this 3D numerical simulation were compared to theoretically predicted distortions. For the first time amplitudes of the observed normal modes were obtained through fitting. In 3D numerical simulations helically twisted fluting structures serve to disrupt ordered flow as a result of filamentation, mass entrainment and shock heating. Light jets slow and are disrupted more easily than dense jets by mass entrainment. Mass entrainment is inhibited by toroidal magnetic fields but not so much inhibited by poloidal magnetic fields. Spatial mass entrainment was shown to go through linear, nonlinear and saturation stages corresponding to linear growth of K-H normal modes, filamentation produced by nonlinear growth of large scale elliptical and helical modes, and saturation at some maximum mixing scale length related to the wavelength and amplitude of the large scale modes. Mass entrainment was found to lead to features like those seen in extragalactic jets in low power (FR I) radio sources, i.e., with tail-like morphology. High power jets with density much less than the ambient medium protect themselves through the formation of a cocoon or lobe of lower density than the jet. The fully active magnetic fields in the numerical simulations provided simulated synchrotron intensity and polarization images which revealed features similar to those in extragalactic jets in FR I and FR II type radio sources.
In protostellar jets the cooling time due to optically thin radiation is comparable to or less than the dynamical time. Determination of the growth or damping and structure of the normal modes (typically K-H unstable) on cooling jets requires a self-consistent stability analysis including the effects of radiative cooling. A stability analysis including the effects of axial magnetic fields was performed and compared to numerical simulations in collaboration with J. Stone (U. Md) and graduate student J. Xu (U. Md). Analytic solutions to the dispersion relation were obtained in useful limits, and numerical techniques were used to find complete solutions. The effect of different cooling curves (one appropriate to photoionized gas and jets in active galaxies, and one appropriate to interstellar gas and protostellar jets) and magnetic fields was studied. The K-H modes were found to be significantly different from the adiabatic limit, and the form of the cooling function strongly affects the results. Inclusion of a dynamically important magnetic field does not strongly modify the important differences between adiabatic and cooling jets, provided jets are supermagnetosonic and not magnetic pressure dominated. Typical fluid displacements associated with the normal modes were computed from the theory and compared to simulation structures. Numerical simulations focused on asymmetric modes which give rise to transverse displacements of the jet beam. The growth rate of waves in the linear regime measured from the numerical simulations was in excellent agreement with the predictions of the linear stability analysis. In the nonlinear regime the simulations showed that asymmetric modes of the K-H instability can affect the structure and evolution of cooling jets significantly. In cooling jets internal shocks produce dense knots and filaments of cooling gas within the jet. Ripples in the surface of the jet generated oblique shock spurs driven into the ambient gas. These shock spurs accelerated ambient gas at large distances from the jet to low velocities, representing a new mechanism by which low velocity bipolar outflows may be driven by high velocity jets.
A set of relativistic jet simulations was analyzed in collaboration with P. Hughes (U. Michigan) and C. Duncan (Bowling Green St.) to study the change in jet structure as a function of Lorentz factor and sound speed. This investigation found that ``hot'' relativistic jets unlike their non-relativistic counterparts can be partially -- but not completely -- stabilized by high Lorentz factors. Fluid displacements, velocities and pressures predicted by the theory were compared to the numerical simulations and a maximum amplitude for the observed normal modes was determined. The form of perturbations to a jet and the coupling between these perturbations and a jet's normal modes was found to play a significant role in a jet's dynamical structure and stability properties. Perturbations are damped when they cannot couple to a growing normal mode of the jet.
Resonance ring galaxies - Buta's work has centered mainly on the detection of resonances in normal galaxies and other problems of internal galaxy dynamics. The most recognizable features that we can reliably associate with dynamical orbit resonances are the inner, outer, and nuclear rings seen in many barred galaxies. These features are ubiquitous, and Buta has compiled a catalog of them for the purpose of evaluating which resonance or resonances are connected with each ring type. This Catalog of Southern Ringed Galaxies, or CSRG, was published in 1995 (ApJS, 96, 39). Since that time, Buta has focussed on measuring the photometric and kinematic properties of a large sample of CSRG and related northern galaxies, with the principal purposes of evaluating CSRG statistics and determining bar pattern speeds.
Buta and F. Combes (Meudon) wrote a lengthy review of resonance ring galaxies for Fundamentals of Cosmics Physics. This review summarizes both the observations and the theory of resonance rings, and highlights some of the difficulties resonance ring theory has in explaining the observed types of ring phenomena.
S. Ryder (now at UKIRT), Buta, and other coworkers carried out HI studies of the large normal ringed barred spirals NGC 1433 and 6300. NGC 1433 is a classic ringed galaxy with all three of the main ring types present: inner, outer, and nuclear rings. The HI gas in NGC 1433 follows the optical structure closely, the inner and outer rings being clearly seen. In NGC 6300, the inner ring is also a concentration of HI gas, but the HI extends well beyond the optical disk light. Rotation curves were used to estimate the bar pattern speed in each case.
Buta and graduate student G. Purcell have completed a detailed optical, near-IR, and kinematic study of the classic resonance ring galaxy NGC 3081, a well-known Seyfert 2 system. Using deep CCD images, they have shown that NGC 3081 is an R1R2' galaxy, a type which shows a distinctive outer ring/pseudoring pattern at large radii that can be linked to orbit families at the outer Lindblad resonance (OLR). Together with an exceptionally strong inner ring and a blue nuclear ring, NGC 3081 has all four of the theoretically-predicted types of resonance rings in coexistence. The near-IR imaging has revealed clear old rings connected to the inner ring and the R1 component of the outer ring/pseudoring pattern. Objective comparison of the B and H-band positions of the inner ring indicate no measurable difference in shape, major axis position angle, or major axis radius between the two passbands. Using an H-band image to define the gravitational potential due to the stellar disk in NGC 3081, a rotation curve from H-alpha Fabry-Perot interferometry, and assumptions concerning the OLR nature of the outer rings, Buta and Purcell have estimated the pattern speed in NGC 3081 to be 3.90 km/s/arcsec.
Buta and REU students Melinda Lewis (Muskingum College), Adina Alpert (University of Pennsylvania), and Greg Madsen (University of Toledo) have been carrying out detailed optical and near-IR photometry and Fabry-Perot interferometry of other CSRG galaxies, including NGC 1326, NGC 6782, NGC 6942, IC 1438, IC 1439, IC 4214, IC 4290, ESO 509-98, ESO 566-24, ESO 294-16, ESO 287-56, ESO 153-20, CSRG 1052, IC 5240, NGC 6398, and ESO 239-4. These studies are being used for determining the orientation parameters of the galaxies and for evaluating the CSRG results that inner and outer rings have significant non-circular shapes and preferred alignments with respect to bars. A dynamical model of IC 4214 is being constructed in collaboration with H. Salo and P. Rautiainen (University of Oulu).
Buta, Crocker, and Byrd have obtained HST WFPC2 images of the large nuclear ring in the peculiar spiral galaxy ESO 565-11. Although very ringlike in ground-based images, this feature is more of a spiral in HST images. The luminosity function of the ring clusters and other characteristics of the inner regions are being derived.
Keel and White continued studies of the dust content of spiral galaxies, using overlapping pairs to give an unusually direct probe of the foreground absorption. Two elliptical/spiral pairs have been imaged using HST, allowing mapping of the absorbing material on scales of tens of parsecs and, in one case, revealing narrow dust lanes remarkably far out in the disk. These data bear out the earlier ground-based results that extinction in interarm regions is quite small except in the inner disks. ISO observations of several pairs are under analysis, and may yield estimates of the clumpiness of dust on all spatial scales by comparing the amount of emission and absorption seen. With graduate student D. Domingue, they have used spectroscopy to distinguish the foreground and background contributions from spiral/spiral pairs, extending this kind of analysis to additional galaxies.
P. Eskridge has continued his study of the X-ray source populations in Local Group dwarf galaxies, in collaboration with R. White and D. Davis (now at MIT) Analysis of archival ROSAT PSPC data indicates that the X-ray source in M32 may be due to a small population of low-mass X-ray binaries, or it may be due to a micro-AGN. The latter interpretation is suggested by dynamical evidence for a central dark mass of roughly 3 million Solar masses. ASCA and ROSAT HRI data have been obtained, and these should settle this question.
Archival PSPC data for NGC 6822 indicate that the X-ray point source in the bar of this dI galaxy may be either a stellar-mass black-hole binary source, or a supersoft source. The x-ray source appears to be associated with the optical emission line object Ho 12. Optical spectrophotometry of Ho 12 and several candidate optical counterparts was obtained this past summer at Apache Point Observatory, in collaboration with P. Hodge (U.Washington). These data confirm that Ho 12 is a supernova remnant. The variability of the X-ray emission (fx changed by roughly a dex between the Einstein HRI observation and the ROSAT PSPC observation) argues that the X-rays are unlikely to be direct emission from the SNR.
Eskridge and A. Schweizer (Honeywell Inc.) are collaborating on a study of the internal structure of the Ursa Minor dwarf spheroidal, based on the proper motion selected sample from Schweizer's PhD dissertation. Previous studies have found evidence that the distribution of stars in Ursa Minor cannot be fit by smooth elliptical isopleths. This structure is obvious in the proper-motion selected sample. Eskridge and Schweizer are investigating techniques for characterising the extent and statistical significance of the excesses.
Eskridge and Pogge are continuing their study of star formation and the ISM in S0 galaxies. The two main areas of effort at present are analysis of spectrophotometry of HII regions in the disks of S0s, and a global multiparametric study of tracers of various phases of the ISM (x-ray emission, H-alpha emission, FIR emission, HI line emission).
Under supervision of Byrd, graduate student S. Gessner Stewart is analyzing for her dissertation observations of dwarf galaxies made during her participation in the Space Shuttle Astro 2 mission. She is processing UIT data on Holmberg II, Sextans A and IC 2574 to characterize the star formation process in these intrinsically simple systems. She was supported by an Alabama Space Grant Consortium Fellowship but is currently employed at the US Naval Observatory. Via a grant-in-aid from the National Academy of Sciences, she obtained optical images of Sextans-A from Las Campanas Observatory.
Graduate student Guy B. Purcell is completing his dissertation on the physical properties of galaxies in a ``slice'' through the de Vaucouleurs revised Hubble Sequence at stage Sbc. The objective of his work is to examine what physical properties may underlie the spread in morphologies at a given Hubble type. The spread includes barred, weakly-barred, and nonbarred families, as well as ringed, pseudoringed, and nonringed varieties. Broadband images and H-alpha Fabry-Perot interferometry have been acquired for 27 galaxies covering all families and varieties at stage Sbc. These observations will be used to examine the influence of pattern speed and other characteristics on the morphology of these galaxies.
With F. Owen (NRAO) and M. Ledlow (UNM), Keel has investigated the host galaxy of the FRI/II radio source 0313-192. Remarkably, this cluster member appears to be a spiral generating a radio source of 200 kpc extent and classical morphology. The properties of this host may shed light on why it is that virtually no spirals manage to produce large, classical double sources.
Keel and REU student Sarah Benfer (Ohio Wesleyan Univ.) have analyzed optical imagery for a set of southern galaxies selected for possible jets from the SRC K sky survey. As expected, most turn out to be photographic artifacts or unrelated objects, but about 10 are good candidates for jet emission. They contribute typically a few percent or less of the host galaxy's V-band light, and are in the same optical luminosity range as observed synchrotron jets. However, they must also be radio-quiet to escape being detected in previous radio surveys. The aim was to see whether there is a whole population of jets like those seen in NGC 1097. In a study with A. Wehrle (IPAC) and D. Jones (JPL), Keel found that these jets are still undetectable by the VLA at 327 MHz, making a fading-synchrotron picture untenable. Their optical colors are appropriate for an intermediate-age stellar population, leaving open the possibility that this system of four features is a fortuitous orientation of tidal structure driven by the small elliptical companion galaxy.
Graduate student J. M. Castro-Ceron is analyzing a body of precise photoelectric measurements of Palomar-Green QSOs obtained by Keel and P. Allan (then of the Univ. of Manchester, UK), in a variability study penetrating to lower levels than hitherto possible for large samples. They find the structure function to increase rapidly to levels about 0.1 magnitude, and slowly up to their tie limit of 3 years thereafter. Almost all the QSOs show evidence of variability at the level of a few percent. The level of variation is essentially constant across the whole luminosity range of the PG sample, which may argue for coherent processes rather than the simplest "Christmas-tree" schemes.
Keel, graduate student B. Irby, and G. Miley (Leiden) continued work on active nuclei selected on the basis of IRAS colors. With the completion of spectroscopy and its analysis for objects selected from the Point-Source Catalog, emphasis is now on objects selected from custom processing of the IRAS Additional Observations (AOs), a set of nearly 1000 small fields around the sky observed in a sensitive slow-scan mode. About 150 candidates were found. Redshifts are still incomplete, but several AGN at redshifts z=0.3-0.54 have been found. The identification content has been improved, even in the absence of spectra for some, through use of the FIRST VLA survey; this has also allowed an estimate of the false-alarm rate of unrelated emission-line galaxies in the error ellipses and of the number of unconfirmed IRAS sources that are not real.
Sulentic has completed a comparison of the X-ray and optical line profile properties for a sample of Seyfert 1 galaxies. This work was carried out in collaboration with M. Calvani/P. Marziani (Padova), D. Dultzin-Hacyan (UNAM) and T. Zwitter (U. Ljubljana). Optical spectra for optical Balmer lines were obtained for virtually all Seyfert 1's with an ASCA detected FeK-alpha line. The motivation was to test the hypothesis that FeK-alpha and H-beta might arise simultaneously from an accretion disk. They developed a disk illumination model, with disk inclination as the only free parameter, that is capable of producing both lines. The bulk emission from the two lines would arise at widely different radii (FeK-alpha < 3-100M; Balmer lines near 1000 M). Most of the other disk model predictions do not conform well with the observations. Inclinations derived for the two lines are incompatible and the FeK$\alpha$ emission line data are not consistent with a single emissivity law. They showed that a simple biconical emitting cloud model is able to reproduce the data better than or equal to the disk models.
Sulentic, Calvani and Marziani also applied their illuminated disk models to the variable FeK-alpha profile of MCG-06-30-15. This Seyfert 1 is perhaps the best studied of any AGN with a detected broad line at 6.4keV. The profile of this source changes dramatically in apparent anti-correlation with continuum variations. They found that self-consistent fits to the high, medium and low phases of the line profile are possible if the broad red-shifted component remains reasonably constant while the narrow 6.4 keV component responds to changes in the index of the power-law emissivity (-0.7 to -3.0). They also suggested that the correct interpretation of the FeK-alpha line in MCG (and perhaps all Seyfert 1's) might involve two independent emitting components: 1) a narrow (unresolved by ASCA) line at 6.4 keV and 2) a broad (FWHM=1.6keV) and redshifted (Eb=5.9keV) component. Two pieces of evidence support that suggestion, beyond the apparent lack of correlation in the continuum response of the broad and narrow features. 1) The expected correlation between FeK-alpha peak energy and profile FWHM for disk models is not observed in the Seyfert 1 data (peak energy almost always occurs at 6.4keV) and 2) the broad component of FeK-alpha in MCG is consistent with a symmetric redshifted Gaussian profile. Such a line profile would be more consistent with a cloud model (no known disk model could account for it).
Keel continued a variety of studies of the rich field of the radio galaxy 53W002 at z=2.39, working with R. Windhorst (Arizona State) and S. Pascarelle (ASU/SUNY Stony Brook). Spectroscopy, including Keck data obtained by L. Armus and N. Scoville, confirms most of the Lyman alpha emitters detected from intermediate-band WFPC2 images, showing that this is indeed a significant population of compact star-forming objects at large redshift. Their scale lengths allow them to be progenitors of spiral bulges, although not directly of luminous ellipticals. Continuum and narrow-band Halpha imagery from the IRTF shows that the spectral energy distributions are most like local starbursts, with only a limited role possible for an older population, and that the non-AGN cluster members have rather weak H-alpha compared to the detected levels of Lyman alpha. Perhaps because of low metallicity, these objects are not destroying Lyman alpha photons through resonant trapping as effectively as some nearby galaxies. A wider field around 53W002 (as well as a few other fields observed with the same HST filters) was observed in matching filters using the KPNO 4m prime-focus system. This resulted in the detection of numerous additional candidates for Lyman alpha emission and absorption at z=2.4, of which two were immediately confirmed to be QSOs at z=2.39. This extends the 53002 clustering to a span of at least 3 Mpc. Additional data on other fields, both in the optical and near-IR, is under reduction to provide a comparison to 53W002. As well, a deep mosaic at 6.5 microns from ISO may provide a firmer estimate of when the cluster members underwent their first significant star formation.
For a counterpoint to studies of Lyman alpha at high redshift, Keel has analyzed archival Voyager 2 spectroscopy of M33 in the deep UV. These data, obtained in the early cruise phase of the mission in 1978, show a clear detection of not only the disk of M33, but NGC 604 as a clear continuum source. Of special interest is the significant Lyman alpha emission associated with the disk overall, but not with NGC 604; one interpretation is that Lyman alpha escapes preferentially from the diffuse interstellar medium, rather than from the giant H II regions which account for much of the H-alpha flux.
Keel, F. Owen (NRAO) and G. Morrison (UNM) have examined an unusual guise of the Butcher-Oemler effect in the cluster Abell 2125 at z=0.25. This cluster contains not only an unusual number of blue galaxies for its redshift and richness, but a dramatically high number of radio sources - 20 have been spectroscopically confirmed as members. The radio emission, mostly from star-forming galaxies, has a shorter characteristic lifetime than some of the usual optical postburst indicators, so that we may be seeing a cluster-wide event as it affects the evolution of individual galaxies. Support for this notion comes from the spatially confined distribution of the radio sources, mostly in one quadrant, and both X-ray and galaxy-count evidence that the cluster has recently absorbed a rich group. A WIYN redshift survey of the cluster is in progress, with WFPC2 imagery of three selected fields rich in radio sources scheduled.
Graduate student V. Andersen is completing his dissertation research on the effect of the cluster environment on star formation. A nearly complete H-alpha survey of the Hercules cluster (Abell 2151), done using the KPNO 0.9m telescope, shows that the relative elevation of star formation is greatest for early Hubble types, and that the star-forming properties of later-type spirals are essentially independent of the environment.
Graduate student W. Wu and Keel continued an investigation of the role of merging on galaxy evolution, considering the influence of changes in the merger rate on both galaxy counts and counts of bound pairs (the most important precursors of mergers). Simultaneous matching of the present-epoch luminosity function of ellipticals and counts from deep HST imagery shows that the merging rate, parametrized as (1+z)^alpha, must obey alpha <3 and is most likely in the range 1-2. The calculations are being extended to several near-IR bands to use upcoming NICMOS and ISO data.
?h3> Polar-Ring GalaxiesP. Eskridge and R. Pogge (Ohio State U.) published the results of their spectrophotometric study of HII regions in the polar ring of NGC 2685. The oxygen abundances in the polar ring are all roughly Solar. This puts strong constraints on models for the formation and evolution of the polar ring, and indicates that it is probably old and self-gravitating, despite its complex appearance. The chemical evolution of polar rings is one line of observational evidence that contributes to our understanding of the relative importance of dark matter in stabilizing these systems, and in the halos of disk galaxies in general. Eskridge and REU student J. Balsley (U. Washington) are extending this research to the polar ring galaxy A0136-0801. This galaxy also appears to have high oxygen abundance in its polar ring, thus indicating that this is a general feature of these objects.
Buta and M. L. McCall (York University) have carried out a detailed photometric study of the IC 342/Maffei 1 Group, a group of about 15 nearby galaxies towards galactic longitude 135, galactic latitude 0-16. The group has the distinctions of being the nearest small group to M31 and also having the nearest giant elliptical galaxy (Maffei 1) to the Local Group. The objectives of the study have been to obtain accurate total magnitudes, color indices, and distances of these galaxies, many of which are heavily reddened by foreground dust in the Milky Way. In the process of imaging the group, Buta and McCall discovered several new dwarf members.
C. Rabaca (Brazil) successfully defended a dissertation titled ``Test of Current Ideas about Compact Groups of Galaxies'' under the supervision of Sulentic. Some results from that work include: 1) confirmation of a weaker than expected optical and FIR enhancement in group members, b) no population of compact group merger postcursors were found in a study of the field galaxy luminosity function, c) compact groups were found to fall closer to rich groups and clusters than a control sample of isolated galaxies--although the signal was strongest for groups with n<4 accordant members, d) photometric analysis of KPNO 4m. images of the VV 172 (HCG55) group reveal an extensive diffuse halo with total luminosity >L* e) analysis of HST WFPC1 images for Seyfert's Sextet (HCG79) reveal a possible ``quiet'' merger in component b and f) evidence that the discordant components in both HCG 55 and 79 lie at their redshift indicated distances.
Sulentic, M. Moles (OAN, Madrid) and I. Marquez (Granada) completed a study of new and old optical and radio data for the most famous compact group of galaxies Stephan's Quintet (HCG 92). They conclude that the bulk of the evidence favors the interpretation that the discordant redshift member NCG 7320 is a foreground projection on the accordant quartet. The evidence also suggests that the quartet is a physically dense interacting system. Evidence for this includes tidal tails, diffuse optical light and stripped HI clouds. Independently Sulentic, Trinchieri (Brera), Pietsch (MPE) and Arp (MPfA) presented new ROSAT HRI observations that show an extended X-ray emission feature most easily understood as a shock front. S, M and M conclude that Stephan's Quintet can be interpreted in three parts. 1) Three of the galaxies (NGC7317, 18a, 19) form a stable triplet imbedded in a diffuse optical halo. The luminosity of the diffuse halo suggests that this triplet has existed for several Gyr. 2) Nearby NGC 7320c is probably responsible for the twin tidal tails that are observed. It probably collided with NGC7319 in the recent past resulting in the almost complete loss of its non stellar component. This galaxy is not currently influencing the group although it may be loosely bound. 3) NGC7318b is now entering the triplet for the first time at a velocity of 1000 km/s. The X-ray shock front represents this collision interface. If Stephan's Quintet is typical of compact groups then they are periodically visited by high velocity intruders which can affect the structure/evolution of group members and build a diffuse halo. The lack of evidence for merging in SQ (and other dense groups) suggests that the intruders may be the mechanism that prolongs the lifetimes of these systems.
Sulentic also reconsidered the statistics of discordant redshift members in compact groups. Approximately 43 of the 100 Hickson groups contain at least one such object. He showed that all previous estimates of the expected frequency of discordants were not statistically reliable. Only discordants that fall within the boundaries of a group defined by its accordant members can be analyzed statistically. Groups with external discordants cannot be well enough constrained to be susceptible to a statistical test because they cannot be defined a priori (except in the sense that they must be isolated enough to be included in the catalog). Analysis of the 6 discordants that fall within their accordant member defined groups (N>3 accordant members) still show a slight excess over expectations (e=1.5) based on the assumption of random projection.
J. L. Higdon (Australia Telescope Compact Array), Buta, and Purcell have completed an optical and HI study of the large interacting ringed barred spiral NGC 5850. This galaxy shows a major distortion of its outer regions (in both HI and optical bands), which these authors suggest is due to a high speed encounter with the nearby elliptical galaxy NGC 5846. As is typical of ringed barred galaxies, the inner ring of NGC 5850 is also an enhanced zone of HI surface density.
The workshop Energy Transport in Radio Galaxies and Quasars was held at the University of Alabama in September 1995. The workshop, attended by astronomers from nine different countries, confronted the latest numerical and theoretical developments with the most recent observations of extragalactic radio sources made using the VLA and the new VLBA. The workshop was supported by the astronomy group's NSF/EPSCoR grant. The workshop proceedings edited by Hardee, Bridle and Zensus have been published in the Astronomical Society of the Pacific (ASP) Conference Series as Volume 100.
The astronomy group uses a network of 11 Sun and three Silicon Graphics workstations. Through these machines there is access to several 600 dpi B/W Postscript printers, both high and low density 8mm tape drives, 4mm DAT drives, a 1/2-inch high-density tape drive and a color Postscript printer. The computer network shares a capacity of approximately 13Gbytes of group-accessible disk space as well as another 18 Gbytes of reserved disk space. All the major astronomical software reduction packages are supported and several IDL licenses are available. The new SRC Equatorial Sky Survey and Palomar II survey have been acquired and are gradually moving towards completion. An extensive collection of data has been collected on CDRoms, including the digitized sky survey (north and south).
Sulentic served on the SOC and Keel presented an invited review (Galaxy Interactions at High Redshift) at a meeting on ``Interacting Galaxies in Pairs, Groups and Clusters'' at Sant'Agata, Italy (Sept. 1995).
Research funding support from NSF and NASA is acknowledged. We also acknowledge observing time with HST, ISO, ROSAT, ASCA, GINGA and ground based time at KPNO, CTIO, ESO, Lowell, San Pedro Martir, Calar Alto as well as supercomputing time at PSC. The Astronomy group REU program completed its fifth year grant. Five students are be supported each year by the REU program.
The UA Astronomy Group maintains a World-Wide Web site (http://www.astr.ua.edu/). It includes information on the graduate program, Research Experiences for Undergraduates (REU) program, an extensive collection of deep-sky images obtained by group members, and instructional material including lab exercises. Under Keel's direction, undergraduates Michael Vrazel and Chris Bayhem (of the Computer-Based Honors Program) converted two upper-division lab exercises into WWW form. The web site also hosts the popular 4000 Years of Women in Science online exhibit.
Publications that appeared within the report period are listed below in alphabetical order irrespective of institutional affiliation. Abstracts and popular articles are not included.
Prepared by Dr. J Sulentic
UA Astronomy Home Page
keel@bildad.astr.ua.edu Last changes: September 1998