George P. McCook

A Catalog of Spectroscopically Identified White Dwarfs

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 authors 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.

A NEW LOOK AT THE LOCAL WHITE DWARF POPULATION

We have conducted a detailed new survey of the local population of white dwarfs lying within 20 pc of the Sun. A new revised catalog of local white dwarfs containing 122 entries (126 individual degenerate stars) is presented. This list contains 27 white dwarfs not included in a previous list from 2002, as well as new and recently published trigonometric parallaxes. In several cases new members of the local white dwarf population have come to light through accurate photometric distance estimates. In addition, a suspected new double degenerate system (WD 0423+120) has been identified. The 20 pc sample is currently estimated to be 80% complete. Using a variety of recent spectroscopic, photometric, and trigonometric distance determinations, we re-compute a space density of 4.8 ± 0.5 × 10–3 pc–3 corresponding to a mass density of 3.2 ± 0.3 × 10–3 M ☉ pc–3 from the complete portion of the sample within 13 pc. We find an overall mean mass for the local white dwarfs of 0.665 M ☉, a value larger than most other non-volume-limited estimates. Although the sample is small, we find no evidence of a correlation between mass and temperature in which white dwarfs below 13,000 K are systematically more massive than those above this temperature. Within 20 pc 25% of the white dwarfs are in binary systems (including double degenerate systems). Approximately 6% are double degenerates and 6.5% are Sirius-like systems. The fraction of magnetic white dwarfs in the local population is found to be 13%.

Interpreting Epsilon Aurigae

Photoelectric observations of the eclipsing binary e Aurigae, consisting of an F0 supergiant and cool, mysterious eclipsing companion with an orbital period of 27.1 yr, are presented. The bright star undergoes semiregular light variations both inside and outside of eclipse, with a caracteristic time scale of a few months which are found to be correlate extremely well with changes in color index. It appears that these light and color variations arise from pulsations of the supergiant. A computer code is developed to model the eclipse with these constraints, and possible configurations of the disk are explored.

Eclipsing Binaries as Astrophysical Laboratories: Internal Structure, Core Convection, and Evolution of the B-Star Components of V380 Cygni

New photometric solutions have been carried out on the important eccentric eclipsing system V380 Cygni (B1.5 II-III + B2 V) from UBV differential photoelectric photometry obtained by us. The photometric elements obtained from the analysis of the light curves have been combined with the spectroscopic solution recently published by Popper & Guinan and have led to the physical properties of the system components. The effective temperature of the stars has been determined by fitting IUE UV spectrophotometry to Kurucz model atmospheres and compared with other determinations from broadband and intermediate-band standard photometry. The values of mass, absolute radius, and effective temperature for the primary and secondary stars are 11.1 ± 0.5 M☉, 14.7 ± 0.2 R☉, 21,350 ± 400 K, and 6.95 ± 0.25 M☉, 3.74 ± 0.07 R☉, 20,500 ± 500 K, respectively. In addition, a redetermination of the systems apsidal motion rate has been done from the analysis of 12 eclipse timings obtained from 1923 to 1995. The apsidal motion study yields the internal mass distribution of the more luminous component. Using stellar structure and evolutionary models with modern input physics, tests on the extent of convection in the core of the more massive B1.5 II-III star of the system have been carried out. Both the analysis of the log g- log Teff diagram and the apsidal motion study indicate a star with a larger convective core, and thus more centrally condensed, than currently assumed. This has been quantified in form of an overshooting parameter with a value of αov ≈ 0.6 ± 0.1. Finally, the tidal evolution of the system (synchronization and circularization times) has also been studied.

9 Aurigae: strong evidence for non-radial pulsations

We present further photometric observations of the unusual F0 V star 9 Aurigae and present evidence that this star’s radial velocity, spectroscopic line widths and line depths are also variable with the same frequencies as the photometric data (f1 � 0.795 and f2 � 0.345 d 1 ). The phases of these sinusoids are stable over time scales of longer than one year, though the amplitudes can vary, making the prediction of photometric behavior impossible. Given that a variety of other explanations have already been discounted (e.g. interactions with a close companion, the existence of a lumpy, orbiting ring of dust, or star spots) and that these variations occur on time scales an order of magnitude slower than the fundamental radial pulsation period, we have very strong evidence that 9 Aurigae exhibits non-radial g-mode pulsations. Since the power spectrum of the radial velocity data shows frequency f2 but does not clearly show f1, the present data suggest that f2 is associated with a low degree spherical harmonic (l = 1 or 2), while f1 is associated with a higher degree harmonic. 9 Aurigae, along with such stars as γ Doradus, HD 224638, HD 224945, and HD 164615, appear to constitute a new class of pulsating variables. These stars are to be found at or beyond the cool edge of the Cepheid instability strip in the HR Diagram. Prior to this, only much hotter stars have been shown to exhibit non-radial g-modes.

Light curve variations and H-alpha flaring of FK Comae

Multiband photoelectric observations reveal that the rapidly rotating giant FK Coms light curve is rapidly changing with respect to amplitude, shape, and light minimum phase. Analysis of the light curves indicates that these variations are due to rotational modulation by two large, subluminous regions on the stars surface, which appear to be about 800 + or - 150 K cooler than the stars photosphere. Flaring activity in the H-alpha emission is also noted, but there is no modulation of this emission with the 2.4-day photometric period or with any other period. This behavior is contrasted with the mechanisms suggested in the Walter and Basri (1982) model for the light variations.

H ALF PHOTOMETRY OF UX ARI DURING 1979-80.

The 6.438 d RS CVn-type binary UX Ari was photoelectrically observed on 17 nights from October 1979 to February 1980. Using narrow- and intermediate-band interference filters centered near tne Balmer H-alpha line, the alpha index was formed from data yielding the net H-alpha line strength. The light curve formed from 6585 wavelength intermediate-band data was observed with an amplitude of 0.04 m, and minimum light occurring near the 0.87 phase. The value of the alpha index indicates H-alpha emission at all orbital phases and a study of all available photometry of the system reveals significant changes in the light amplitude, mean light level, and the phase at which minimum light occurs. It is concluded that small light amplitudes are due to star spots located at high stellar latitudes or spread evenly over the stellar surface, and large amplitudes are the result of spots located closer to the equator.

ξTauri: a unique laboratory to study the dynamic interaction in a compact hierarchical quadruple system

Context. Compact hierarchical systems are important because the effects caused by the dynamical interaction among its members occur ona human timescale. These interactions play a role in the formation of close binaries through Kozai cycles with tides. One such system is ξ Tauri: it has three hierarchical orbits: 7.14 d (eclipsing components Aa, Ab), 145 d (components Aa+Ab, B), and 51 yr (components Aa+Ab+B, C). Aims. We aim to obtain physical properties of the system and to study the dynamical interaction between its components. Methods. Our analysis is based on a large series of spectroscopic photometric (including space-borne) observations and long-baseline optical and infrared spectro-interferometric observations. We used two approaches to infer the system properties: a set of observation-specific models, where all components have elliptical trajectories, and an N -body model, which computes the trajectory of each component by integrating Newton’s equations of motion. Results. The triple subsystem exhibits clear signs of dynamical interaction. The most pronounced are the advance of the apsidal line and eclipse-timing variations. We determined the geometry of all three orbits using both observation-specific and N -body models. The latter correctly accounted for observed effects of the dynamical interaction, predicted cyclic variations of orbital inclinations, and determined the sense of motion of all orbits. Using perturbation theory, we demonstrate that prominent secular and periodic dynamical effects are explainable with a quadrupole interaction. We constrained the basic properties of all components, especially of members of the inner triple subsystem and detected rapid low-amplitude light variations that we attribute to co-rotating surface structures of component B. We also estimated the radius of component B. Properties of component C remain uncertain because of its low relative luminosity. We provide an independent estimate of the distance to the system. Conclusions. The accuracy and consistency of our results make ξ Tau an excellent test bed for models of formation and evolution of hierarchical systems.

Revised physical elements of the astrophysically important O9.5+O9.5V eclipsing binary system Y Cygni ,,

Context. Rapid advancements in light-curve and radial-velocity curve modelling, as well as improvements in the accuracy of observations, allow more stringent tests of the theory of stellar evolution. Binaries with rapid apsidal advance are particularly useful in this respect since the internal structure of the stars can also be tested. Aims. Thanks to its long and rich observational history and rapid apsidal motion, the massive eclipsing binary Y Cyg represents one of the cornerstones of critical tests of stellar evolutionary theory for massive stars. Nevertheless, the determination of the basic physical properties is less accurate than it could be given the existing number of spectral and photometric observations. Our goal is to analyse all these data simultaneously with the new dedicated series of our own spectral and photometric observations from observatories widely separated in longitude. Methods. We obtained new series of UBV observations at three observatories separated in local time to obtain complete light curves of Y Cyg for its orbital period close to 3 days. This new photometry was reduced and carefully transformed to the standard UBV system using the HEC22 program. We also obtained new series of red spectra secured at two observatories and re-analysed earlier obtained blue electronic spectra. Reduction of the new spectra was carried out in the IRAF and SPEFO programs. Orbital elements were derived independently with the FOTEL and PHOEBE programs and via disentangling with the program KOREL. The final combined solution was obtained with the program PHOEBE. Results. Our analyses provide the most accurate value of the apsidal period of (47.805 ± 0.030) yr published so far and the following physical elements: M1 = 17.72 ± 0.35 M� , M2 = 17.73 ± 0.30 M� , R1 = 5.785 ± 0.091 R� ,a ndR2 = 5.816 ± 0.063 R� . The disentangling thus resulted in the masses, which are somewhat higher than all previous determinations and virtually the same for both stars, while the light curve implies a slighly higher radius and luminosity for star 2. The above empirical values imply the logarithm of the internal structure constant log k2 = −1.937. A comparison with Claret’s stellar interior models implies an age close to 2 × 10 6 yr for both stars. Conclusions. The claimed accuracy of modern element determination of 1–2 per cent still seems a bit too optimistic and obtaining new high-dispersion and high-resolution spectra is desirable.

Multiband Photometry of the Chromospherically Active & Spotted Binary System IM Peg—the Guide Star for the Gravity Probe B Mission

We report on the starspot properties of IM Pegasi—the guide star of the Gravity Probe B (GP-B) satellite. GP-Bs mission is to measure two predicted consequences of general relativity—the frame-dragging and geodetic effects—via its extremely precise onboard gyroscopes. However, IM Peg is a chomospherically active binary system with a luminous K2 III primary star showing rotationally modulated (Prot ≈ 24.5 days) light variations from starspots. The starspots can potentially cause problems as GP-B can erroneously interpret a change in starspot coverage (and corresponding shifts in the light center) as the stars movement. This apparent shift can also be exacerbated by possible changes in the light center (photocenter) of the binary system arising from changes in the light balance with the fainter ~1 M⊙ (main-sequence early G-type star) component. Since 2000, we have carried out multiband high-precision photoelectric photometry of IM Peg to determine its activity and starspot coverage. Our photometry uses Stromgren uvby intermediate-band filters, VRI filters, and TiO (720/750 nm) narrowband filter sets. Measurements were made relative to nearby comparison and check stars using 0.8 m and 0.25 m telescopes. Analysis of TiO and multiband continuum photometry constrains the starspot areas, temperatures, and surface distributions. The photometry has been modeled using the maximum entropy and Tikhonov regularizations to determine the properties of starspots and to evaluate the effects of changing starspot areas and distributions on the light center of the binary. Our results indicate that IM Pegs activity should not affect the GP-B mission. We also present a study of IM Pegs long-term starspot cycle, which shows evidence of being 20 yr long. Lastly, we have determined the intrinsic (unspotted) brightness of the star to be V mag = 5.62 ± 0.03.