R. E. Wilson

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.

ECLIPSING BINARY SOLUTIONS IN PHYSICAL UNITS AND DIRECT DISTANCE ESTIMATION

Opportunities for extraction of distances and temperatures from eclipsing binary light curves that are in standard flux units, as opposed to traditional arbitrary units, are examined. Benefits include (1) distance becomes an ordinary solution parameter with a standard error, (2) temperatures of both stars may be derivable in favorable circumstances, and (3) semidetached and overcontact binaries suffer no loss of distance accuracy, vis-a-vis well-detached binaries. Flux calibrations enter only for the observations, while theoretical fluxes are naturally in standard units, so confrontation of theory and observation is direct, and semiempirical quantities based on color-temperature relations are not needed. The monolithic process, called direct distance estimation (DDE), also saves time and effort by avoiding separate distance estimation steps and should lead to routine distance measurements for large numbers of eclipsing binaries (EBs). Discussions compare DDE with traditional EB distance estimation, which has been restricted to well detached binaries in most publications. Aspect dependence of spectroscopic or color temperature, as affected by tides and irradiation, is treated rigorously. A temperature-distance theorem that specifies requirements for finding temperatures and distance from EB light and velocity curves is checked by several kinds of simulations. Demonstration solutions are carried out for the overcontact binary AW UMa and the semidetached binary RZ Cnc, with discussions of temperature and distance results. Although AW UMa has many observational and structural oddities, its DDE and Hipparcos distances agree. Six DDE distances for RZ Cnc, done in several ways and for three photometric bands, fall well within the 1 σ range of its Hipparcos distance. Interactions among calibrative errors, parameter values, and fitting discrepancies are discussed, as is proper weighting.

Photometric Solutions for Semidetached Eclipsing Binaries: Selection of Distance Indicators in the Small Magellanic Cloud

Estimation of distances to nearby galaxies by the use of eclipsing binaries as standard candles has recently become feasible because of new large-scale instruments and the discovery of thousands of eclipsing binaries as spin-off from Galactic microlensing surveys. Published measurements of distances to detached eclipsing binaries in the Large Magellanic Cloud combine stellar surface areas (in absolute units) determined from photometric light and radial velocity curves with surface brightnesses from model atmospheres and observed spectra. The method does not require the stars to be normal or undistorted and is not limited in its applicability to the well-detached systems that have traditionally been considered. We discuss the potential usefulness of semidetached vis a vis detached eclipsing binaries for distance determination and examine and quantify criteria for their selection from large catalogs. Following our earlier paper on detached binaries in the Small Magellanic Cloud (SMC), we carry out semidetached light-curve solutions for SMC binaries discovered by the OGLE collaboration, identify candidates for SMC distance estimation that can be targets of future high-quality observations, and tabulate results of OGLE light-curve solutions. We point out that semidetached binaries have important advantages over well-detached systems as standard candles, although this idea runs counter to the usual view that the latter are optimal distance indicators. Potential advantages are that (1) light-curve solutions can be strengthened by exploiting lobe-filling configurations, (2) only single-lined spectra may be needed for radial velocities because the mass ratio can be determined from photometry in the case of complete eclipses, and (3) nearly all semidetached binaries have sensibly circular orbits, which is not true for detached binaries. We carry out simulations with synthetic data to see if semidetached binaries can be reliably identified and to quantify the accuracy of solutions. The simulations were done for detached as well as semidetached binaries so as to constitute a proper controlled study. The simulations demonstrate two additional advantages for semidetached distance determination candidates; (4) the well-known difficulty in distinguishing solutions with interchanged radii (aliasing) is much less severe for semidetached than for detached binaries and (5) the condition of complete eclipse (which removes a near degeneracy between inclination and the ratio of the radii) is identified with improved reliability. In many cases we find that parameters are accurately determined (e.g., relative errors in radii smaller than 10%) and that detached and semidetached systems can be distinguished. We select 36 candidate semidetached systems (although seven of these are doubtful because of large mass ratios or periods) from the OGLE SMC eclipsing binary catalog. We expected that most semidetached candidates would have light curves similar to those of common Algol binaries, but that turned out not to be the case, and we note that fully Algol-like light curves are nearly absent in the OGLE sample. We discuss possible explanations for the near absence of obvious Algols in OGLE, including whether their paucity is real or apparent.

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.

SPOTTED STAR LIGHT CURVES WITH ENHANCED PRECISION

The nearly continuous timewise coverage of recent photometric surveys is free of the large gaps that compromise attempts to follow starspot growth and decay as well as motions, thereby giving incentive to improve computational precision for modeled spots. Due to the wide variety of star systems in the surveys, such improvement should apply to light/velocity curve models that accurately include all the main phenomena of close binaries and rotating single stars. The vector fractional area (VFA) algorithm that is introduced here represents surface elements by small sets of position vectors so as to allow accurate computation of circle-triangle overlap by spherical geometry. When computed by VFA, spots introduce essentially no noticeable scatter in light curves at the level of one part in 10,000. VFA has been put into the Wilson-Devinney light/velocity curve program and all logic and mathematics are given so as to facilitate entry into other such programs. Advantages of precise spot computation include improved statistics of spot motions and aging, reduced computation time (intrinsic precision relaxes needs for grid fineness), noise-free illustration of spot effects in figures, and help in guarding against false positives in exoplanet searches, where spots could approximately mimic transiting planets in unusual circumstances. A simple spot growth and decay template quantifies time profiles, and specifics of its utilization in differential corrections solutions are given. Computational strategies are discussed, the overall process is tested in simulations via solutions of synthetic light curve data, and essential simulation results are described. An efficient time smearing facility by Gaussian quadrature can deal with Kepler mission data that are in 30 minute time bins.

New Perspectives on AX Monocerotis

AX Moncerotis is a 232d, noneclipsing, interacting binary star that consists of a K giant, a Be-like giant, and large amounts of circumstellar material. The K star is almost certainly a synchronous rotator and is probably in contact with its critical lobe. The Be star was believed to be a rapid rotator based on extremely wide absorption lines, but new spectra show that these lines arise from the circumstellar environment. Hydrogen emission, also circumstellar, is many times stronger than the continuum. Near-ultraviolet light curves exhibit a 0.5 mag dip near phase 0.75, but there is no such variability at longer wavelengths. Gas flow trajectories from the cusp of the K star toward the Be star provide a simple explanation for the photometric and spectroscopic behavior. We may have found a decreasing orbital period, but more data are necessary to confirm this result. We present several models for AX Mon based on (1) new and archival visible photometry, (2) archival ultraviolet spectroscopy, (3) new and archival visible spectroscopy, (4) new visible polarimetry, and (5) new radio photometry. Future observations, including optical interferometry, are proposed.

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.

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.

Convergence of eclipsing binary solutions

Attention is called to the fact that convergence to negligible corrections in differential corrections solutions usually can be achieved, provided that one or both of two common causes of poor convergence are recognized and properly dealt with.