Dirk Terrell

Planet Hunters: A Transiting Circumbinary Planet in a Quadruple Star System

We report the discovery and confirmation of a transiting circumbinary planet (PH1b) around KIC 4862625, an eclipsing binary in the Kepler field. The planet was discovered by volunteers searching the first six Quarters of publicly available Kepler data as part of the Planet Hunters citizen science project. Transits of the planet across the larger and brighter of the eclipsing stars are detectable by visual inspection every ~137 days, with seven transits identified in Quarters 1-11. The physical and orbital parameters of both the host stars and planet were obtained via a photometric-dynamical model, simultaneously fitting both the measured radial velocities and the Kepler light curve of KIC 4862625. The 6.18 ± 0.17 R_⊕ planet orbits outside the 20 day orbit of an eclipsing binary consisting of an F dwarf (1.734 ± 0.044 R_☉, 1.528 ± 0.087 M_☉) and M dwarf (0.378 ± 0.023 R_☉, 0.408 ± 0.024 M_☉). For the planet, we find an upper mass limit of 169 M_⊕ (0.531 Jupiter masses) at the 99.7% confidence level. With a radius and mass less than that of Jupiter, PH1b is well within the planetary regime. Outside the planets orbit, at ~1000 AU, a previously unknown visual binary has been identified that is likely bound to the planetary system, making this the first known case of a quadruple star system with a transiting planet.

KOI-142, The King of Transit Variations, is a Pair of Planets near the 2:1 Resonance

The transit timing variations (TTVs) can be used as a diagnostic of gravitational interactions between planets in a multi-planet system. Many Kepler Objects of Interest (KOIs) exhibit significant TTVs, but KOI-142.01 stands out among them with an unrivaled ≅12 hr TTV amplitude. Here we report a thorough analysis of KOI-142.01s transits. We discover periodic transit duration variations (TDVs) of KOI-142.01 that are nearly in phase with the observed TTVs. We show that KOI-142.01s TTVs and TDVs uniquely detect a non-transiting companion with a mass ≅0.63 that of Jupiter (KOI-142c). KOI-142.01s mass inferred from the transit variations is consistent with the measured transit depth, suggesting a Neptune-class planet (KOI-142b). The orbital period ratio P{sub c} /P{sub b} = 2.03 indicates that the two planets are just wide of the 2:1 resonance. The present dynamics of this system, characterized here in detail, can be used to test various formation theories that have been proposed to explain the near-resonant pairs of exoplanets.

RECENT IMPROVEMENTS TO A VERSION OF THE WILSON-DEVINNEY PROGRAM

We summarize recent improvements to a version of the Wilson-Devinney program that is widely used for the analysis of eclipsing binary data, and we describe the new WD95 program. WD95 contains the University of Calgary version of the Wilson-Devinney code, which supports the use of the Kurucz atmo- sphere models; it provides options to use multiple epoch data and multiwavelength synoptic passbands. The WD95 program contains an improved input/output interface, simplex algorithms for initial searches and tests, and versions of Wilson-Devinney DC and LC programs and options to switch to automatic di†erential corrections or a damped least-squares solver using normal equations that are modi-ed as per the Levenberg-Marquardt scheme. This paper describes some tests of the damped least-squares solver with simulated data. Subject headings: binaries: eclipsing E methods: numerical

Analysis of the rotation period of asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger - search for the YORP effect

Context. The spin state of small asteroids can change on a long timescale by the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect, the net torque that arises from anisotropically scattered sunlight and proper thermal radiation from an irregularly-shaped asteroid. The secular change in the rotation period caused by the YORP effect can be detected by analysis of asteroid photometric lightcurves. Aims. We analyzed photometric lightcurves of near-Earth asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger with the aim to detect possible deviations from the constant rotation caused by the YORP effect. Methods. We carried out new photometric observations of the three asteroids, combined the new lightcurves with archived data, and used the lightcurve inversion method to model the asteroid shape, pole direction, and rotation rate. The YORP effect was modeled as a linear change in the rotation rate in time dω/dt .V alues of dω/dt derived from observations were compared with the values predicted by theory. Results. We derived physical models for all three asteroids. We had to model Eger as a nonconvex body because the convex model failed to fit the lightcurves observed at high phase angles. We probably detected the acceleration of the rotation rate of Eger dω/dt = (1.4 ± 0.6) × 10 −8 rad d −2 (3σ error), which corresponds to a decrease in the rotation period by 4. 2m s yr −1 . The photometry of Cerberus and Ra-Shalom was consistent with a constant-period model, and no secular change in the spin rate was detected. We could only constrain maximum values of |dω/dt| < 8 × 10 −9 rad d −2 for Cerberus, and |dω/dt| < 3 × 10 −8 rad d −2 for Ra-Shalom.

A BVRCIC Survey of W Ursae Majoris Binaries

We report on a BVRcIc survey of field W Ursae Majoris binary stars and present accurate colors for 606 systems that have been observed on at least three photometric nights from a robotic observatory in southern Arizona. Comparison with earlier photometry for a subset of the systems shows good agreement. We investigate two independent methods of determining the interstellar reddening, although both have limitations that can render them less effective than desired. A subset of 101 systems shows good agreement between the two reddening methods.

Photo-dynamical Analysis of Three Kepler Objects of Interest with Significant Transit Timing Variations

KOI-227, KOI-319 and KOI-884 are identified here as (at least) two planet systems. For KOI-319 and KOI-884, the observed Transit Timing Variations (TTVs) of the inner transiting planet are used to detect an outer non-transiting planet. The outer planet in KOI-884 is ≅2.6 Jupiter masses and has the orbital period just narrow of the 3:1 resonance with the inner planet (orbital period ratio 2.93). The distribution of parameters inferred from KOI-319.01s TTVs is bimodal with either a ≅1.6 Neptune-mass (M{sub N}) planet wide of the 5:3 resonance (period 80.1 days) or a ≅1 Saturn-mass planet wide of the 7:3 resonance (period 109.2 days). The radial velocity measurements can be used in this case to determine which of these parameter modes is correct. KOI-227.01s TTVs with large ≅10 hr amplitude can be obtained for planetary-mass companions in various major resonances. Based on the Bayesian evidence, the current TTV data favor the outer 2:1 resonance with a companion mass ≅1.5 M{sub N}, but this solution implies a very large density of KOI-227.01. The inner and outer 3:2 resonance solutions with sub-Neptune-mass companions are physically more plausible, but will need to be verified.

Photometric investigation of a very short period W UMa-type binary: does CE Leonis have a large superluminous area?

A complete photometric analysis of BVRI Johnson-Cousins photometry of the high northern latitude galactic variable, CE Leo is presented. These observations were taken at Kitt Peak National Observatory on May 31, 1989-June 7, 1989. Three new precise epochs of minimum light were determined and a linear and a quadratic ephemeris were computed from these and previous data covering 28 years of observation. The light curves reveal that the system undergoes a brief 20 min totality in the primary eclipse, indicating that CE Leo is a W UMa W-type binary. A systemic velocity of about -40 km/s was determined. Standard magnitudes were found and a simultaneous solution of the B, V, R, I light curves was computed using the new Wilson-Devinney synthetic light curve code which has the capability of automatically adjusting star spots. The solution indicates that the system consists of two early K-type dwarfs in marginal contact with a fill-out factor less than 3 percent. Evidence for the presence of a large (45 deg radius) superluminous area on the cooler component is given.

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.

New Light Curves and Orbital Solution for AM Leonis

New UBVRI photometry has been obtained for the W UMa eclipsing system AM Leonis. The data have been used to derive nine times of minimum and to construct light curves. The minimum timings show that the system recently had a significant period increase. Modeling of the light curves shows AM Leo to be an overcontact system with a mass ratio of 2.51. Both Rucinski & Duerbecks absolute magnitude calibration for W UMa stars applied to our photometry and the radial velocity curve combined with our derived parameters indicate a distance near 125 pc, larger than the 77 pc from the Hipparcos parallax.

Observational studies of early-type binary stars: VV Orionis

ABSTRACT New and previously published observations of the bright eclipsing binary VV Ori-onis areanalyzed.We presentnew radial velocitiesand interstellarreddening measure-ments from high-resolution spectra of this detached, short-period (P=1.48 d) binary.We discuss the validity of prior claims for the existence of a third body and show thatour new velocities and light curve solution cast doubt on them. The components ofVV Ori are shown to be a B1 V primary with a mass M 1 = 10.9±0.1M⊙ and a radiusR 1 = 4.98± 0.02R⊙ and a B4.5 V secondary with a mass M 2 = 4.09±0.05M⊙ anda radius R 2 = 2.41±0.01R⊙.Key words: binaries: eclipsing – binaries: spectroscopic 1 INTRODUCTIONVV Orionis (HD 36695) is a bright (V =5.4), double-linedeclipsing binary consisting of main sequence B-type starsin a detached configuration. The inclination is high enoughto produce complete eclipses, enabling the very accuratedetermination of fundamental parameters of the system.Since the discovery of its photometric variability over acentury ago, the system has been the subject of sev-eral spectroscopic and photometric studies as discussed bySarma & Vivekananda Rao (1995). Unfortunately, the de-rived absolute parameters in these previous studies varyconsiderably and this led us to obtain additional spectro-scopic and photometric data on the system as part of ourprogram on early-type binaries (viz. Terrell, et al. (2003),Terrell, et al. (2005)).Dating back to the first comprehensive spectroscopicstudy by Daniel (1915), spectroscopic investigators, includ-ing Struve & Luyten (1949), Beltrami & Galeotti (1969),Duerbeck (1975) and Popper (1993), have concluded that athird star orbits the eclipsing pair. The evidence for claims ofthis third body rests solely on higher than expected resid-uals in fits to the radial velocities of the primary as thethird body’s lines are not seen in the system’s spectrum.Daniel (1915) offered the third body hypothesis ”with greatreserve” and Struve & Luyten (1949) pointed out that the