W. Van Hamme

New limb-darkening coefficients for modeling binary star light curves

We present monochromatic, passband-specific, and bolometric limb-darkening coefficients for a linear as well as nonlinear logarithmic and square root limb-darkening laws. These coefficients, including the bolometric ones, are needed when modeling binary star light curves with the latest version of the Wilson-Devinney light curve progam. We base our calculations on the most recent ATLAS stellar atmosphere models for solar chemical composition stars with a wide range of effective temperatures and surface gravitites. We examine how well various limb-darkening approximations represent the variation of the emerging specific intensity across a stellar surface as computed according to the model. For binary star light curve modeling purposes, we propose the use of a logarithmic or a square root law. We design our tables in such a manner that the relative quality of either law with respect to another can be easily compared. Since the computation of bolometric limb-darkening coefficients first requires monochromatic coefficients, we also offer tables of these coefficients (at 1221 wavelength values between 9.09 nm and 160 micrometer) and tables of passband-specific coefficients for commonly used photometric filters.

Third-Body Parameters from Whole Light and Velocity Curves

Eclipsing binaries can improve multiple system statistics via the light-time effect and radial velocity shifts. Here an algorithm operates on data of mixed type to exploit these opportunities. Main reasons for enhanced reliability are that (1) combined light and velocity curves give better timewise coverage than either type alone, (2) properly weighted solutions impersonally balance light and velocity information, and (3) the entire theory is within the computer model, so observations are used directly without corrections. A brief history of mixed whole-curve solutions is given and the relative importance of light-time and radial velocity input for third-body parameters is discussed and quantified. Period sifting by power spectral analysis is essentially indispensable in preliminary work. Applications are to the Algol-type system DM Persei and the detached system VV Orionis. An assumption of coplanarity for DM Pers inner and outer orbits is tested and quantified by dynamical experiments. Derived third-body parameters for DM Per are mainly reasonable and self-consistent. For comparison with whole-curve results, we also investigated DM Pers ephemeris in terms of eclipse timings and found whole-curve solutions to give smaller standard errors in reference epoch (T0), binary orbit period (P), and dP/dt, over a similar baseline in time. An astonishing outcome is lack of evidence that can pass reasonable validity tests for VV Oris well-accepted third star with P ≈ 120 days. Estimates of third light do indicate a third star, but the correct period cannot now be established, so the star cannot be identified as the one heretofore recognized from radial velocity evidence. The much cited 120 day period appears to be an artifact of the window function for VV Oris historical velocity observations.

CN Andromedae: A Broken-Contact Binary?

We solve new UBV light curves of the eclipsing binary CN Andromedae simultaneously with radial velocities by the method of differential corrections. We find it semidetached with the more massive star filling its limiting lobe and the less massive star very close to lobe-filling. Our solutions of earlier light curves have the same configuration. Within the uncertainties, the system may be in a broken or a marginal contact stage as it undergoes thermal relaxation oscillations. The light curves are strongly affected by a large dark spot at high latitude on the more massive star and by a bright substellar spot on the companion. Spot locations and temperatures do not differ significantly from epoch to epoch. Based on single star evolutionary models, the primarys mass (1.299 ± 0.045 M⊙) and radius (1.425 ± 0.016 R⊙) are consistent with those of a star of age 2.9 × 109 yr that will leave the main sequence in another 2.0 × 109 yr. The orbital period has decreased during the past 50 yr according to traditional eclipse timings and also according to our generalized light and velocity solutions that include a reference epoch T0 and a rate of period change dP/dt. We find dP/dt = -0.01951 ± 0.00054 s yr-1, which is consistent with mass transfer from the more to the less massive star of 1.4 × 10-7 M⊙ yr-1, assuming no mass is lost from the system. Reliable absolute dimensions are determined.

Rotation statistics of Algol-type binaries and results on RY Geminorum, RW Monocerotis, and RW Tauri

Rotation rates and other parameters are estimated from light curves of three Algol-type binaries, and rotation statistics based on both spectral line broadening and light curves are collected for 36 Algol systems. The statistics suggest that a subset of Algols have primary stars which rotate at the centrifugal limit and that many Algols have sufficient continual mass transfer to maintain nonsynchronous rotation. A formal procedure for estimating the critical rotation rate (centrifugal limit) is described. It is found that RY Gem rotates about 14 times faster than synchronously, but not close to its centrifugal limit of about 24 times. For RW Mon, the rotation is about five times synchronous. For RW Tau it was not possible to estimate the rotation from the light curves, but consistency with a published result from line broadening is found. 97 refs.

RZ Scuti as a double contact binary

Etude de la morphologie de cette binaire a contact et de la rotation de la composante primaire dans un tel cas

Distances to Four Solar Neighborhood Eclipsing Binaries from Absolute Fluxes

Eclipsing binary (EB)-based distances are estimated for four solar neighborhood EBs by means of the Direct Distance Estimation (DDE) algorithm. Results are part of a project to map the solar neighborhood EBs in three dimensions, independently of parallaxes, and provide statistical comparisons between EB and parallax distances. Apart from judgments on adopted temperature and interstellar extinction, DDEs simultaneous light-velocity solutions are essentially objective and work as well for semidetached (SD) and overcontact binaries as for detached systems. Here, we analyze two detached and two SD binaries, all double lined. RS Chamaeleontis is a pre-main-sequence (MS), detached EB with weak ? Scuti variations. WW Aurigae is detached and uncomplicated, except for having high metallicity. RZ Cassiopeiae is SD and has very clear ? Scuti variations and several peculiarities. R Canis Majoris (R CMa) is an apparently simple but historically problematic SD system, also with weak ? Scuti variations. Discussions include solution rules and strategies, weighting, convergence, and third light problems. So far there is no indication of systematic band dependence among the derived distances, so the adopted band-calibration ratios seem consistent. Agreement of EB-based and parallax distances is typically within the overlapped uncertainties, with minor exceptions. We also suggest an explanation for the long-standing undermassiveness problem of R CMas hotter component, in terms of a fortuitous combination of low metallicity and evolution slightly beyond the MS.

Synthetic light-curve analysis of the very short period binaries TY Bootis, AD Cancri, and V523 Cassiopeiae

New photometric observations of TY Boo, AD Cnc, and V523 Cas are subjected to synthetic light-curve analyses using the Wilson-Devinney code. Solutions for each of the systems, and the several competing theories of contact binary structure are discussed in light of the results. Both AD Cnc and V523 Cas are modeled with subluminous regions, and the resulting starspot parameters are reported. A simultaneous solution of the B, V light curves and the radial-velocity curves of V523 Cas is presented. Spectroscopic and photometric mass ratios were found to be discordant for both TY Boo and V523 Cas. However, recent spectroscopic work by Groissman seems to remove the discordancy for TY Boo. Absolute parameters are derived for V523 Cas. 43 refs.

The V471 Tauri System: A Multi-Data-Type Probe

V471 Tauri, a white dwarf--red dwarf eclipsing binary in the Hyades, is well known for stimulating development of common envelope theory, whereby novae and other cataclysmic variables form from much wider binaries by catastrophic orbit shrinkage. Our evaluation of a recent imaging search that reported negative results for a much postulated third body shows that the object could have escaped detection or may have actually been seen. The balance of evidence continues to favor a brown dwarf companion about 12 AU from the eclipsing binary. A recently developed algorithm finds unified solutions from three datatypes. New radial velocities (RVs) of the red dwarf and BV RCIC light curves are solved simultaneously along with white dwarf and red dwarf RVs from the literature, uvby data, the MOST mission light curve, and 40 years of eclipse timings. Precision-based weighting is the key to proper information balance among the various datasets. Timewise variation of modeled starspots allows unified solution of multiple data eras. Light curve amplitudes strongly suggest decreasing spottedness from 1976 to about 1980, followed by approximately constant spot coverage from 1981 to 2005. An explanation is proposed for lack of noticeable variation in 1981 light curves, in terms of competition between spot and tidal variations. Photometric spectroscopic distance is estimated. The red dwarf mass comes out larger than normal for a K2V star, and even larger than adopted in several structure and evolution papers. An identified cause for this result is that much improved red dwarf RVs curves now exist.

UBVRc Ic Analysis of the Recently Discovered Totally Eclipsing Extreme Mass Ratio Binary V1853 Orionis, and a Statistical Look at 25 Other Extreme Mass Ratio Solar-type Contact Binaries

We present precision CCD light curves, a period study, photometrically derived standard magnitudes, and a five-color simultaneous Wilson code solution of the totally eclipsing, yet shallow amplitude (Av ~ 0.4 mag) eclipsing, binary V1853 Orionis. It is determined to be an extreme mass ratio, q = 0.20, W-type W UMa overcontact binary. From our standard star observations, we find that the variable is a late-type F spectral-type dwarf, with a secondary component of about 0.24 solar masses (stellar type M5V). Its long eclipse duration (41 minutes) as compared to its period, 0.383 days, attests to the small relative size of the secondary. Furthermore, it has reached a Roche lobe fill-out of ~50% of its outer critical lobe as it approaches its final stages of binary star evolution, that of a fast spinning single star. Finally, a summary of about 25 extreme mass ratio solar-type binaries is given.

Accuracy of close binary mass determinations from parallaxes

Absolute masses for W Ursae Majoris and Algol-type close binaries can be determined from their parallax, if observed, and the relative sizes of the stars and their mass ratio, obtained from a light curve solution. An error propagation study compares the typical order of magnitude of the various terms involved, and shows how accurate parallaxes have to be in order to make the procedure work, i.e., making the parallax term not larger than the combined non-parallax terms, and producing reasonably low mass errors. Some comments are made on the possibilities with respect to the HIPPARCOS program.