%R 1994PASP..106..425L %J-435 %T Comets Disguised as Asteroids %A JANE LUU %B Comets and asteroids were previously thought to be two completely distinct groups of solar system objects, with marked contrast in both physical and dynamical characteristics. A comet is operationally defined by the presence of a coma, while an asteroid has no coma. However, recent observations have shown that comets can sometimes take on asteroidal appearances and even asteroidal photometric behavior. Thus the observational distinction between comets and asteroids is not as clear cut as it once seemed. The possible presence of comets hidden among known asteroids forces us to reconsider the criterion by which we distinguish comets from asteroids and possibly our inventory of both comet and asteroid populations. %R 1994PASP..106..436C %J-443 %T A Revised Effective Temperature Calibration for the DDO Photometric System %A JUAN J. CLARIA, ANDRES E. PIATTI and EMILIO LAPASSET %B A revised effective temperature calibration for the DDO photometric system is presented. Recently published photometric and spectroscopic observations of field and open cluster G and K stars allow a better definition of the solar-abundance fiducial relation in the DDO C_0(45-48) vs C_0(42-45) diagram. The ability of the DDO system to predict MK spectral types of G and K giants is demonstrated. The new DDO effective temperature calibration reproduces satisfactorily the infrared temperature scale of Bell and Gustafsson (1989). It is shown that Osborn's (1979) calibration underestimates the effective temperatures of K giants by ~170 K and those of late-type dwarfs by ~150 K. %R 1994PASP..106..444T %J-451 %T Analyses of Archival Data for Cool Dwarfs. I. The Solar B - V Problem Reconsidered %A BENJAMIN J. TAYLOR %B In a previous paper, Taylor has found that the solar value of (R-I)_c is 0.337 +/- 0.0024 mag. This result can be converted to a value of (B-V) by combining it with blanketing corrections and a Hyades color-color relation. The latter are derived and discussed in this paper. The resulting value of (B-V) turns out to be 0.633 +/- 0.009 mag. Annoyingly, this datum differs from the mean a number of previous results at better than 99.5% confidence. A survey of the problem reveals a wavelength boundary: H-beta and H-alpha yield the result quoted above, while spectroscopy at wavelengths shortward of H-beta yields (B-V) = 0.665 +/- 0.003 mag. The Balmer-line derivations are largely blanketing-insensitive, so for the present, it seems defensible to assume that the Balmer-line result is correct and that its short-wavelength counterparts are affected by some unknown property of the solar blanketing. %R 1994PASP..106..452T %J-461 %T Analyses of Archival Data for Cool Dwarfs. II. A Catalog of Temperatures %A BENJAMIN J. TAYLOR %B A calibration presented in a previous paper is used in this paper to derive temperatures for FGK stars near the main sequence. The calibration is checked against published counterparts, and it is found that previous calibrations have not established K-dwarf temperatures in particular beyond reasonable doubt. The data base assembled to derive the temperatures is described, and the problems posed by close binaries are evaluated. The newly derived temperatures are used to check a line-depth ratio proposed as a thermometer by Gray and Johanson (1991), and it is found that the ratio is metallicity-sensitive. Temperatures are given for a total of 417 stars. %R 1994PASP..106..462R %J-471 %T M_V = M_V(Log P, Log T_e) Calibrations for W UMa Systems %A S. M. RUCINSKI %B We use the basic expression for luminosities of contact systems, L proportional to area * T_e^4, to derive calibrations of their absolute magnitudes M_V in terms of the orbital period and color indices B-V and V-I_C. These calibrations can serve as a consistency check on membership of W UMa systems in stellar clusters and will permit the use of W UMa binaries as distance indicators for stellar systems consisting of solar-type stars. \par The calibrating sample at this time is based on 3 systems with trigonometric parallaxes, 11 systems in high galactic latitude open clusters and 3 systems with main-sequence visual companions. The ranges in period and color are quite narrow and the results must be considered as preliminary, especially for the V-I_C calibration. \par One of the possible applications of the calibrations, as a sieve to remove the foreground interlopers, is illustrated. The result is that the cluster and field frequencies of optically detected W UMa systems seem to be equal at about one per about 280 surveyed stars (uncorrected for the inclination bias of about two times), which is about 3-4 times higher in the field than estimated before. %R 1994PASP..106..472M %J-480 %T A Photometric Study of XX Virginis and V716 Ophiuchi %A D. H. MCNAMARA and M. D. PYNE %B We present Stromgren photometry of the two Population II variables XX Vir and V716 Oph. Our analysis of the photometry yields the following physical parameters of the variables: for XX Vir = 6410 K, [Fe/H] = 2.0, and = 1.95; for V716 Oph = 6450 K, [Fe/H]=2.1, and = 1.67. The values of these two metal-poor variables are considerably smaller than the metal-strong variable BL Herculis (=2.37). The big surprise in this investigation is that the surface gravity of V716 Oph (P=1.12), the shorter-period variable, is smaller than the surface gravity of XX Vir (P=1.35), the longer period variable. With the aid of P square root of rho = Q relation we derive a semi-theoretical P-L relation for the Type II Cepheids of the form M_V=-1.88 log P+0.13. This expression is in rough agreement (within the uncertainties of many quantities used in deriving the expression) with the observational data. The relatively gentle slope of the P-L relation (compared with the slope of the P-L relations of other pulsating stars) is probably a consequence of the fact that the masses of the Type II Cepheids are constant or nearly constant, independent of period, and a large variations of the M/R values with period. %R 1994PASP..106..481J %J-485 %T Spectroscopy and Photometry of the Dwarf Nova BZ UMa and the CV Line-Width/K, Mass-Ratio Relation %A J. S. JURCEVIC, R. K. HONEYCUTT, E. M. SCHLEGEL, and R. F. WEBBINK %B Time resolved spectroscopy of the dwarf nova BZ UMa revelas periodic velocity variations in the hydrogen emission lines with P = 97.9 +/- 0.1 minutes and K = 73 +/- 6 km s^-1. CCD photometry over a 16-month interval shows three outbursts of about 4 mag with a mean separation of 181 days. The mean FWHM for the H-beta emission is large, prompting a re-calibration of the FWHM/K vs. mass ratio relation, giving a mass ratio (M_RD/M_WD) of 0.20 for BZ UMa. The short period, long outburst interval, and small mass ratio supports the suggestion of BZ UMa being in the SU UMa subclass of dwarf novae. %R 1994PASP..106..486A %J-499 %T vbyH-beta CCD Photometry of Melotte 66: A Disk Analog of omega Centauri %A BARBARA J. ANTHONY-TWAROG, BRUCE A. TWAROG, and MARIAN SHEERAN %B A CCD study of the peculiar open cluster, Melotte 66, on the vbyH-beta system is presented. The V, (b-y) color-magnitude diagram of this metal-deficient, old disk cluster confirms the anomalous features found in photographic BV studies and extends the main sequence to V = 20. The main sequence exhibits a (b-y) color rang significantly larger than expected from photometric errors alone; the (b-y) colors are correlated with H-beta implying that the dispersion is real and not the result of variable reddening across the cluster. The m_1 indices for the turnoff stars imply a spread in [Fe/H] too small to explain the color range. Though the subgiant region is poorly defined, the region above the turnoff in the Hertzsprung gap is richly populated by a group of yellow stragglers whose membership is confirmed by radial star counts and radial velocities. The giant branch is richly populated but shows a smaller spread in color at a given V than one would expect from the turnoff region. More important, the giants exhibit a large scatter in m_1, in contradiction with the turnoff observations. Various explanations for these observations are discussed, including CN variations among the gaints triggered by either binary evolution or rapid rotation among the main sequence stars. %R 1994PASP..106..500G %J-507 %T On the Expansion Velocities of Planetary Nebulae and the Circumstellar Envelopes of AGB Stars %A G. T. GUSSIE and A. R. TAYLOR %B The distribution of expansion velocities of the gas of planetary nebulae are compared to the distribution of the circumstellar envelopes of AGB stars. We have examined the relationship between ionized and neutral expansion velocities for the nebulae with detected circumnebular neutral shells. It is found that compact planetary nebulae with ionized radii less than about 0.05 pc show a distribution of expansion velocities that is similar to AGB envelopes, while large planetary nebulae with ionized radii greater than about 0.30 pc show a significantly different expansion velocity distribution than AGB envelopes. Among the large planetary nebula subset, only those nebulae of Greig's class C have an expansion velocity distribution significantly different than AGB stars, while large Grieg's class B nebulae have the same expansion velocity distribution as AGB stars. The average velocity difference between AGB stars and large Grieg's class C nebulae is well predicted by the interacting stellar winds model of planetary nebula evolution. However, the acceleration of ionized gas predicted by the interaction of stellar winds is not evident in the observed expansion velocity distribution of large Grieg's class B nebulae. %R 1994PASP..106..508M %J-514 %T The MSSSO Near-Infrared Photometric System %A PETER J. MCGREGOR %B The JHKL photometric system curently used at MSSSO is described via an extensive list of standard star values and filter transmission curves. At JHK this system is identifcal to the MSO system defined by Jones \& Hyland (1982), except for small zero point differences which we impose here. Transformations are given between the MSSSO system and several near-infrared photometric systems in use in other observatories and the homogenised JHKL system proposed by Bessell \& Brett (1988). %R 1994PASP..106..515Z %J-522 %T The La Palma Data Archive %A E. J. ZUIDERWIJK, R. MARTIN, E. RAIMOND, and G. N. J. VAN DIEPEN %B The operation of the La Palma Data Archive is described in detail. The archive contains data taken since early 1986 with the Isaac Newton Group; 74% of the 260,000 entries were of astronomical sources. Several hundreds of queries are made on the catalogue each year, resulting in approximately one request per week for data. The rate at which data are retrieved makes the archive (now) roughly the equivalent of 1/3 of a telescope. We discuss the archiving process from the logistics of data taking to maintenance of astronomically relevant information in the catalogue and give an indication of the potential of the archive as data resource. A brief discussion of the benefits of an archive is presented in the closing sections. %R 1994PASP..106..523C %J-531 %T On-Chip Image Processing Algorithm for Real-Time CCD-Based Star Trackers and Wavefront Sensors %A MAREK CHMIELOWSKI %B In this paper, we describe on-chip and off-chip image procesing algorithms utilizing the internal architect of recently developed CCD sensors to provide high speed readout of selected portions of the imager or accelerated scanning of an entire CCD frame. Image processing time comparable tothe star tracker sensor exposure time and to the characteristic time of the atmospheric fluctuations (10 ms) has been achieved. On-chip image processing is particularly suitable for space or ground-based real-time applications (position determination, tip-tilt correctors, wavefront sensing for adaptive optics systems) where the speed or acquisition and processing data from the "regions of interest" is critical. An example of a star trackers (based on the Texas Instruments TC217 CCD image sensor) for space applications capable of providing real-time multiple position updates with high angular resolution is given and achieved performance is discussed. %R 1994PASP..106..532R %J-541 %T Detection and Classification of CCD Defects with an Artificial Neural Network %A R. D. ROGERS and A. G. RIESS %B We have developed an artificial neural network (ANN) system which locates and classifies defects in CCDs. This system, based on a feedforward neural network, was trained with a conjugate gradient training algorithm using observational data from an astronomical telescope. The network was tested with data from four large CCDs (2048x2048 pixels each) and found defects with a higher efficiency and in a much shorter time than human inspectors. This method of detecting and classifying objects in images is quite general and we discuss other applications in astronomy. In an appendix we provide a recipe for neural computing to make this technique more accessible to the astronomical community. %R 1994PASP..106..542H %J-547 %T The Effect of Double Stars on the Guiding System of the Hubble Space Telescope %A JOHN L. HERSHEY and PIERRE Y. BELY %B The interferometric system used for guidance of HST is sensitive to close binaries. Before the launch of HST it was believed that up to 25% of all guide star pairs would lead to guidance failure due to duplicity. After more than 3 years of operation the actual failure rate ascribable to duplicity is estimated to be just below 1%. A computer simulator has been developed to understand the causes of the discrepancy. The simulation indicates a failure rate of under 2% per guide-star pair, in much closer agreement with the observed performance of the guiding system. The failure criterion originally used, was based on the manufacturer's expectations, and was too conservative. The proportion of binary guide stars in the critical separation range had also been somewhat overestimated. %R 1994PASP..106..548B %J-548 %T Time Variability of Broad-Absorption-Line QSOs %A THOMAS A. BARLOW %B We present the results of a three year project to monitor broad absorption-line QSOs (BALQSOs) with both broadband imaging (for continuum flux changes) and spectrophotometry (for broad absorption-line variations). About 10% of all optically selected QSOs show broad absorption-lines blueward of the high ionization resonance emission lines, indicating that gas is flowing outward from the QSO continuum source at velocities as high as 0.2c. Of 54 BALQSOs monitored with broadband imaging, ~33% showed significant time variability with deviations of 0.1 to 0.3 magnitudes. The time scale for variability was at least three months to a year in the QSO rest frame. \par Spectroscopic monitoring of 23 BALQSOs resulted in the detection of broad absorption-line time variations in 15 BALQSOs. Six of these cases showed small (marginally significant) changes, while four objects showed large BAL changes (+-0.2 - 0.4 in normalized intensity). All of the BAL time variations appear to be changes in the residual intensity, or normalized flux, within the line, rather than variations in the velocity structure of the outflowing BAL gas. Our primary hypothesis is that a variable photoionizing continuum causes a change in the ionization levels, and thus a redistribution of the fractional abundances of the ions, resulting in the strengthening or weakening of the absorption lines. \par The BAL changes will appear nearly simultaneous with the continuum variations if the BAL variation mechanism travels in step with the continuum photons, and the mechanism induces rapid changes in the ionization levels of the gas. Therefore, unlike studies of broad emission-line variability in active galactic nuclei, BAL variability does not (for the simplest models) yield direct information about the size of the region. Our studies of BAL time variability have suggested that the velocity of the BAL gas varies monotonically with distance from the continuum source. With this assumption, BAL time variability provides the opportunity for detailed study of the ionization properties, column density, and elemental abundance of the BAL gas. \par In our data, we have found cases of BAL variability that appear to be correlated with a change in continuum flux. However, we have also discovered a few cases where the BALs varied, but no change was detected (to a limit of ~0.06 magnitudes) in the broadband flux. These results suggest that the ionizing flux (lambda ~100 - 400A) varies with greater amplitude and possibly in a non-synchronous manner with the observed continuum flux ({lambda} ~ 2000{AA}). \par For one object, we observed a large continuum level change (factor of 2) without a corresponding BAL change. However, this same QSO later exhibited BAL changes apparently synchronous with small continuum level changes. Despite this apparent conflict, ionizing flux variability of the continuum source is still the best explanation for the BAL changes. The simultaneous changes over a range of outflow velocities observed in several BALQSOs suggest that the mechanism inducing the BAL changes must propagate through the BAL region at (or close to) the speed of light. Also, there is a correlation between those QSOs which show continuum level changes and those which show BAL variations. \par From the changes observed in various ions (e.g. C IV lambda-1549, N V lambda-1240, Si IV lambda-1397, and Al III lambda-1857) in a few BALQSOs, we deduce that the ionization parameter (the ratio of the densities of ionizing photons and electrons) must be relatively high (U>0.05). We have also estimated a lower limit on the electron density of 10^4 cm^-3 from limits on the response time scale of the BAL changes. From these limits, we deduce that the absorbing gas cannot be further than a few hundred parsecs from the ionizing source. \par In the few variable QSOs where the continuum slope (alpha, where L(nu) proportional to nu^alpha) was measured, our data indicate that the slope increases as the continuum level increases. Our data also show that the intensities of the permitted broad emission lines often do not appear to follow changes in the observed continuum. This suggests that either this emission arises in a region larger than about one light year, or that the emitting clouds are not ionized by the continuum source seen along our line of sight to the QSO. %R 1994PASP..106..549H %J-549 %T A Multi-Wavelength Exploration of the Nearby Starburst Galaxy Maffei 2 %A ROBERT L. HURT %B This dissertation is an investigation of the basic morphology and dynamics of the galaxy Maffei 2, undertaken at a variety of wavelengths ranging from the near infrared (1.3 micron) to the radio (21 cm). Although it is relatively nearby (~5 Mpc) and large in extent (~10'), Maffei 2 was only discovered and identified about 20 years ago because of visual extinction from intervening dust in the Galactic plane. Observations at longer wavelengths have shown it to exhibit the characteristics of a starburst galaxy. Strong emission in the far infrared and radio continuum together with large quantities of molecular gas all point to vigorous massive star formation in its nucleus. \par We have observed Maffei 2 at a number of key wavelengths in an attempt to build up a consistent model for the dynamical processes driving the starburst. High resolution ^13CO (1-0) observations from Owens Valley Millimeter Interferometer allow us to trace the density distribution of molecular gas in the nuclear starburst region with high fidelity. Single dish ^12CO(3-2) observations of the nucleus made with the Caltech Submillimeter Observatory probe the physical conditions in the warmer molecular regions in the starburst. Near infrared observations obtained with NOAO's SQIID allow us to penetrate the obscuring dust in the plane of the Milky Way to see the overall morphology of the galaxy. HI mapping of the galaxy with the NRAO VLA reveals the kinematics of the extended disk, allowing us to see the mechanisms of large-scale gas flow. \par Our studies have led to the conclusion that Maffei 2 is a strongly barred galaxy with nuclear star formation most likely triggered by a recent interaction. From near infrared images we make the first determination of this obscured galaxy's Hubble type: SBb(s) pec. The stellar bar and spiral arms, which can be traced at several wavelengths, display striking asymmetries reminiscent of tidally interacting galaxies. The large-scale velocity field has a strong non-circular component that is typical of barred galaxies. The nuclear gas lies along a narrow ridge that is generally aligned with the bar and is apparently the product of a density wave extending to within tens of parsecs of the dynamical center. Nuclear conditions are consistent with warm gas (~50 K) at surface column densities of 10^23 cm^-3 across 150 pc scales. One feature, extending from the northern bar end, resembles a leading spiral arm and is most likely a tidal feature (possibly connected to a small, gas-free satellite galaxy). The picture of a dynamically recent tidal interaction driving a nuclear gas inflow and starburst is consistent with current simulation studies of such phenomena. %R 1994PASP..106..550W %J-550 %T Studies of Large-Amplitude Delta Scuti Variables. I. A Case Study of EH Librae %A W. J. F. WILSON, E. F. MILONE, and D. J. I. FRY %B Erratum of Publ. Astron. Soc. Pac., 105, 809 (1993) %R 1994PASP..106..550N %J-550 %T A General Bayesian Image-Reconstruction Algorithm with Entropy Prior. Preliminary Application to HST Data %A JORGE NUNEZ and JORGE LLACER %B Erratum of Publ. Astron. Soc. Pac., 105, 1192 (1993)