Hilmar W. Duerbeck

A Catalog and Atlas of Cataclysmic Variables: The Living Edition

ABSTRACT The Catalog and Atlas of Cataclysmic Variables (Edition 1: Downes & Shara; Edition 2: Downes, Webbink, & Shara) has been a valuable source of information for the cataclysmic variable community. However, the goal of having a central location for all objects is slowly being lost as each new edition is generated. There can also be a long time delay between new information becoming available on an object and its publication in the catalog. To eliminate these concerns, as well as to make the catalog more accessible, we have created a Web site which will contain a “living” edition of the catalog. We have also added orbital period information, as well as finding charts for novae, to the catalog.

Optical Imaging of Nova Shells and the Maximum Magnitude-Rate of Decline Relationship*

An optical imaging study of 30 recent novae has been undertaken using both ground-based and space-based observations. Resolved shells have been detected around nine objects in the ground-based data, while another four objects have shells detected by Hubble Space Telescope observations; for RW UMi, we fail to detect a shell that was observed 5 years earlier. Images in H?, and when appropriate [O III] ?5007, are shown, and finding charts for novae without shells are given if no published chart is available. Expansion parallaxes for all systems with shells are derived, and absolute magnitudes for a total of 28 objects are presented, along with a discussion of the maximum magnitude?rate of decline relation. We find that separate linear fits for fast and slow novae may be a better representation of the data than a single, global fit. At minimum, most novae have similar magnitudes as those of dwarf novae at maximum and nova-like stars.

A Reference Catalogue and Atlas of Galactic Novae

This catalogue and atlas contains information on 277 objects, mainly classical novae and related objects (recurrent novae, X-ray novae, dwarf novae with long cycle lengths, symbiotic stars and suspected new stars). For most objects, brightness ranges, accurate positions, finding charts and selected bibliographies are given.

LIGHT CURVE TYPES, ABSOLUTE MAGNITUDES, AND PHYSICAL PROPERTIES OF GALACTIC NOVAE.

For 31 classical galactic novae and four recurrent novae distances, absolute magnitudes and extinction data are derived by different methods. A new absolute magnitude - t3 time relation is established. Two groups of novae are found: very fast and fast novae with smooth light curves and absolute magnitudes between -8 and -11, and fast, slow, and very slow novae with structured light curves and absolute magnitudes between -6 and -7. Group I exhibits quasi-instantaneous mass loss at a luminosity far above the Eddington limit. Group II exhibits continued radiation at the Eddington limit from a bloated white dwarf. A classification scheme for nova light curves which is useful in the context of the new luminosity calibration is described and applied to 95 novae.

A search for new variable stars in NGC 6231

NGC 6231 is a well-studied young open cluster hosting several variable stars. In the field six β Cephei stars, several eclipsing binaries and one δ Scuti star are known (as well as a foreground δ Scuti star). In an ongoing effort to map and study the variability in NGC 6231, we present new results based on CCD time-series data optimised for the bright β Cephei stars as well as data optimised for much fainter stars. We detect 17 new variable stars in the cluster, including three δ Scuti stars, three γ Doradus candidates, three Slowly Pulsating B star candidates and one, or possibly two, new β Cephei stars.

The Muenster Redshift Project. III. Observational Constraints on the Deceleration Parameter

The redshift-volume test for determining the deceleration parameter q0 is applied to 89,125 galaxies with redshifts z ? 0.2 (redshift errors ?z = 0.031) and magnitudes 14.0 ? rF ? 18.0 mag, obtained within the Muenster Redshift Project (MRSP). With samples of this size, cosmic curvature effects can be measured even at intermediate redshifts. Comparatively small z-values and red photometric magnitudes assure that biased object selection and galaxy evolution do not affect the measurements in uncontrolled ways. In the first step of our analysis, the redshift-volume test assumes a minimum model of passive galaxy evolution. For the cosmological constant ? = 0 and for the evolutionary models of Rocca-Volmerange & Guiderdoni, the total sample yields the deceleration parameter q0 = 0.10 with the 95% confidence limit, q0 < 0.75. In a second step, we evaluate?within the errors of the first step?whether our q0-value is over- or underestimated, using those observed evolutionary trends that appear to be nearly q0 independent. The trends indicate that our result q0 = 0.10 can be regarded as an upper limit. Effects of incompleteness, errors in the (K + E)-corrections due to extreme galaxy mixtures, as well as different models of population synthesis, large-scale clustering, galactic reddening, and gravitational lensing, are discussed. We conclude that the combination of MRSP redshift data, observed evolutionary trends in the galaxy luminosity functions, and passive galaxy aging suggests an open universe.

Radial Velocity Studies of Southern Close Binary Stars. I. Winter Systems

Radial velocity measurements and sine-curve fits to the orbital velocity variations are presented for nine contact binaries: V1464 Aql, V759 Cen, DE Oct, MW Pav, BQ Phe, EL Aqr, SX Crv, VZ Lib, and GR Vir. For the first five of these, our observations are the first available radial velocity data. For the three remaining radial velocity variables, CE Hyi is a known visual binary, while CL Cet and V1084 Sco are suspected to be multiple systems in which the contact binary is spectrally dominated by its companion (which itself is a binary in V1084 Sco). Five additional variable stars, V872 Ara, BD Cap, HIP 69300, BX Ind, and V388 Pav, are of unknown type, but most are pulsating stars; we give their mean radial velocities and V sin i.

Galactic Distribution and Outburst Frequency of Classical Novae

The observed rate and spatial distribution of galactic novae can be explained with the concept of two nova, populations, the disc novae of faster outburst development, and the slower bulge novae. Similar populations seem to exist in nearby galaxies. The space density of galactic novae depends strongly on the recurrence time, which is unknown and may lie between 500 and 20 000 years. If the recurrence time is long, the population of quiescent novae must be identified; the hibernation scenario may or may not be a solution.

Radial Velocity Studies of Southern Close Binary Stars. II. Spring/Summer Systems*

Radial velocity measurements and sine-curve fits to the orbital velocity variations are presented for 14 close binary stars, S Ant, TT Cet, TW Cet, AA Cet, RW Dor, UX Eri, YY Eri, BV Eri, CT Eri, SZ Hor, AD Phe, TY Pup, HI Pup, and TZ Pyx. All are double-lined binaries, and all except the last one are contact binaries. The orbital data must be considered preliminary because of the relatively small number of observations (6-12), a circumstance that is partly compensated by the good definition of the broadening functions used for the radial velocity determinations.

On the orbital period of the cataclysmic variable V 592 Herculis

We present a spectroscopic study of the long-recurrence-time dwarf nova V 592 Herculis based on observations obtained during its August 1998 superoutburst. From the analysis of the radial velocities of the H emission line we fi nd am ost likely orbital period of 85:5 0:4 min, but the 91:2 0:6 min alias cannot be completely discarded. Both periods imply a very small period excess and supports the brown-dwarf like nature of the secondary star.