A catalog of 2249 white dwarfs which have been identified spectroscopically is presented complete through 1996 April. This compilation is the fourth edition of the Villanova Catalog of Spectroscopically Identified White Dwarfs. For each degenerate star, the following data entries with references are provided: (1) a catalog coordinate designation or WD number, in order of right ascension; (2) the right ascension and declination for epoch 1950.0; (3) the spectral type based upon the new system; (4) a catalog symbol denoting binary membership; (5) a list of most names known to exist for a given star; (6) proper motion and position angle; (7) broadband UBV photometry, V, B-V, U-B; (8) multichannel spectrophotometry, v(MC), g-r; (9) Stromgren narrowband photometry, y, b-y, u-b; (10) an absolute visual magnitude based upon the best available color-magnitude calibration or trigonometric parallax; (11) the observed radial velocity uncorrected for gravitational redshift or solar motion; and (12) the trigonometric parallax with mean error when available. Notes for unusual or peculiar stars and a coded Reference Key alphabetized by the first author's last name are presented, as well as an expanded table cross-referencing all names to the catalog WD number. An introduction and full descriptions of the entries are provided in the text.

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A Catalog of Spectroscopically Identified White Dwarfs

▪ Abstract Broad emission lines hold fundamental clues about the kinematics and structure of the central regions in AGN. In this article we review the most robust line profile properties and correlations emerging from the best data available. We identify fundamental differences between the profiles of radio-quiet and radio-loud sources as well as differences between the high- and low-ionization lines, especially in the radio-quiet majority of AGN. An Eigenvector 1 correlation space involving FWHM Hβ, W(FeIIopt)/W(Hβ), and the soft X-ray spectral index provides optimal discrimination between all principal AGN types (from narrow-line Seyfert 1 to radio galaxies). Both optical and radio continuum luminosities appear to be uncorrelated with the E1 parameters. We identify two populations of radio-quiet AGN: Population A sources (with FWHM(Hβ) 4000 km s−1, generally strong FeII emission and a soft X-ray excess) show almost no parameter space overlap with radio-loud sources. Population B shows optical properties...

Phenomenology of Broad Emission Lines in Active Galactic Nuclei

Aims. We have calculated variability Doppler boosting factors, Lorentz factors, and viewing angles for a large sample of sources by using total flux density observations at 22 and 37 GHz and VLBI data. Methods. We decomposed the flux curves into exponential flares and determined the variability brightness temperatures of the fastest flares. By assuming the same intrinsic brightness temperature for each source, we calculated the Doppler boosting factors for 87 sources. In addition we used new apparent jet speed data to calculate the Lorentz factors and viewing angles for 67 sources. Results. We find that all quasars in our sample are Doppler-boosted and that the Doppler boosting factors of BL Lacertae objects are lower than of quasars. The new Lorentz factors are about twice as high as in earlier studies, which is mainly due to higher apparent speeds in our analyses. The jets of BL Lacertae objects are slower than of quasars. There are some extreme sources with very high derived Lorentz factors of the order of a hundred. These high Lorentz factors could be real. It is also possible that the sources exhibit such rapid flares that the fast variations have remained undetected in monitoring programmes, or else the sources have a complicated jet structure that is not amenable to our simple analysis. Almost all the sources are seen in a small viewing angle of less than 20 degrees. Our results follow the predictions of basic unification schemes for AGN.

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Doppler factors, Lorentz factors and viewing angles for quasars, BL Lacertae objects and radio galaxies

White dwarf stars, compact objects with extremely high interior densities, are the most common end product in the evolution of stars. The authors review the history of their discovery, and of the realisation that their structure is determined by the physics of the degenerate electron gas. Spectral types and surface chemical composition show a complicated pattern dominated by diffusion processes and their interaction with accretion, convection and mass loss. While this interaction is not completely understood in all its detail at present, the study may ultimately lead to important constraints on the theory of stellar evolution in general. Variability, caused by nonradial oscillations of the star, is a common phenomenon and is shown to be a powerful probe of the structure of deeper layers that are not directly accessible to observation. Very strong magnetic fields detected in a small fraction of white dwarfs offer a unique opportunity to study the behaviour of atoms under conditions that cannot be simulated in terrestrial laboratories.

https://iopscience.iop.org/article/10.1088/0034-4885/53/7/001/pdf

Physics of white dwarf stars

Since the discovery of the first isolated magnetic white dwarf (MWD) Grw +70°8047 nearly 60 years ago, the number of stars belonging to this class has grown steadily. There are now some 65 isolated white dwarfs classified as magnetic, and a roughly equal number of MWDs are found in the close interacting binaries known as the magnetic cataclysmic variables (MCVs). The isolated MWDs comprise ~5% of all WDs, while the MCVs comprise ~25% of all CVs. The magnetic fields range from ~ 3 × 104–109 G in the former group with a distribution peaking at 1.6 × 107 G, and ~ 107–3 × 108 G in the latter group. The space density of isolated magnetic white dwarfs with fields in the range ~3 × 104–109 G is estimated to be ~1.5 × 10–4 pc–3. The MCVs have a space density that is about a hundred times smaller.About 80% of the isolated MWDs have almost pure H atmospheres and show only hydrogen lines in their spectra (the magnetic DAs), while the remainder show He i lines (the magnetic DBs) or molecular bands of C2 and CH (magnetic DQs) and have helium as the dominant atmospheric constituent, mirroring the situation in the nonmagnetic white dwarfs. The incidence of stars of mixed composition (H and He) appears to be higher among the MWDs.There is growing evidence based on trigonometric parallaxes, space motions, and spectroscopic analyses that the isolated MWDs tend as a class to have a higher mass than the nonmagnetic white dwarfs. The mean mass for 16 MWDs with well-constrained masses is 0.95 M⊙. Magnetic fields may therefore play a significant role in angular momentum and mass loss in the post-main-sequence phases of single star evolution affecting the initial-final mass relationship, a view supported by recent work on cluster MWDs. The progenitors of the vast majority of the isolated MWDs are likely to be the magnetic Ap and Bp stars. However, the discovery of two MWDs with masses within a few percent of the Chandrasekhar limit, one of which is also rapidly rotating (Pspin = 12 minutes), has led to the proposal that these may be the result of double-degenerate (DD) mergers. An intriguing possibility is that magnetism, through its effect on the initial-final mass relationship, may also favor the formation of more massive double degenerates in close binary evolution. The magnetic DDs may therefore be more likely progenitors of Type Ia supernovae.A subclass of the isolated MWDs appear to rotate slowly with no evidence of spectral or polarimetric variability over periods of tens of years, while others exhibit rapid rotation with coherent periods in the range of tens of minutes to hours or days. There is a strong suggestion of a bimodal period distribution. The "rapidly" rotating isolated MWDs may include as a subclass stars which have been spun up during a DD merger or a previous phase of mass transfer from a companion star.Zeeman spectroscopy and polarimetry, and cyclotron spectroscopy, have variously been used to estimate magnetic fields of the isolated MWDs and the MWDs in MCVs and to place strong constraints on the field structure. The surface field distributions tend in general to be strongly nondipolar and to a first approximation can be modeled by dipoles that are offset from the center by ~10%-30% of the stellar radius along the dipole axis. Other stars show extreme spectral variations with rotational phase which cannot be modeled by off-centered dipoles. More exotic field structures with spot-type field enhancements appear to be necessary. These field structures are even more intriguing and suggest that some of the basic assumptions inherent in most calculations of field evolution, such as force-free fields and free ohmic decay, may be oversimplistic.

https://www.jstor.org/stable/10.1086/316593

Magnetism in Isolated and Binary White Dwarfs

The optical polarization properties of "normal" quasars.

An optical linear-polarization survey testing the relationships between polarization and other properties of QSOs is presented. Polarimetric observations of 239 QSOs have been made. Data from the literature are used to analyze the relationships between polarization and radio, optical, and X-ray properties. The highly polarized QSOs are generally compact radio sources, are associated with radio properties such as low-frequency variability and superluminal motion, exhibit large-amplitude rapid photometric variability, have steep nonthermal optical continua, and may show excess X-ray emission. No relationship is seen between polarization and redshift, optical luminosity, or the equivalent width of emission lines. The results are discussed in the context of both isotropic and anisotropic (beaming) models. While the associations between the optical and radio properties of highly polarized QSOs provide strong motivation for the anisotropic model, the lack of associations with redshift, optical luminosity, and emission-line strength is inconsistent with this model. It is concluded that the highly polarized QSOs are probably fundamentally different in their physical properties from low-polarization QSOs.

A comparison of the properties of highly polarized QSOs versus low-polarization QSOs.

Observations at radio, optical, and X-ray wavelengths of six sources from the Bonn-NRAO 5 GHz survey are reported. The sources were selected on the basis of their flux densities and spectral indices at 5 GHz. All have been shown to contain compact radio cores and to emit strongly at X-ray wavelengths; five are strongly polarized at optical wavelengths. The measured flux densities suggest that the sources are of comparable luminosity (per fractional bandwidth) in the X-ray and optical regions. The interpretation of these results in terms of a synchrotron-self-Compton mechanism is briefly discussed.

Observations of six flat spectrum sources from the 5 GHz survey

Comparaison du spectre de cette naine blanche magnetique avec un haut rapport signal-bruit, avec le spectre de l'hydrogene jusqu'a 10 9 G

The optical spectrum of hydrogen at 160-350 million gauss in the white dwarf GRW +70 deg 8247

Time-resolved HST UV eclipse spectrophotometry is presented for the magnetic CVs V1309 Ori, MN Hya, V2301 Oph, and V1432 Aql. Separation of the light curves into wavebands allows the multiple emission components to be distinguished. Photospheric hot spots are detected in V1309 Ori and V2301 Oph. The emission- line spectra of V1309 Ori and MN Hya are unusual, with the strength of N V 1240 and N IV 1718 suggesting an overabundance of nitrogen. Three epochs of observation of the asynchronous V1432 Aql cover ~1/3 of a 50-day lap cycle between the white dwarf spin and binary orbit. The light curves vary from epoch to epoch and as a function of waveband. The dereddened UV spectrum is extremely bright and the spectral energy distribution coupled with the duration of eclipse ingress indicate that the dominant source of energy is a hot (T~35,000K) white dwarf. Undiminished line emission through eclipse indicates that the eclipse is caused by the accretion stream, not the secondary star. The hot white dwarf, combined with its current asynchronous nature and rapid timescale for relocking, suggests that V1432 Aql underwent a nova eruption in the past 75-150 yr. The reversed sense of asynchronism, with the primary star currently spinning up toward synchronism, is not necessarily at odds with this scenario, if the rotation of the magnetic white dwarf can couple to the ejecta during the wind phase of the eruption.

H. S. Stockman

Papers

The optical polarization properties of "normal" quasars.

A comparison of the properties of highly polarized QSOs versus low-polarization QSOs.

Observations of six flat spectrum sources from the 5 GHz survey

The optical spectrum of hydrogen at 160-350 million gauss in the white dwarf GRW +70 deg 8247

Time-Resolved HST Spectroscopy of Four Eclipsing Magnetic Cataclysmic Variables