Bryce Croll

Stellar activity of planetary host star HD 189733

Aims. Extra-solar planet search programs require high-precision velocity measurements. They need to determine how to differentiate between radial-velocity variations due to Doppler motion and the noise induced by stellar activity. Methods. We monitored the active K2V star HD 189733 and its transiting planetary companion, which has a 2.2-day orbital period. We used the high-resolution spectograph SOPHIE mounted on the 1.93-m telescope at the Observatoire de Haute-Provence to obtain 55 spectra of HD 189733 over nearly two months. We refined the HD 189733b orbit parameters and placed limits on both the eccentricity and long-term velocity gradient. After subtracting the orbital motion of the planet, we compared the variability in spectroscopic activity indices with the evolution in the radial-velocity residuals and the shape of spectral lines. Results. The radial velocity, the spectral-line profile, and the acti vity indices measured in He I (5875.62 A), Hα (6562.81 A), and both of the Ca II H&K lines (3968.47 A and 3933.66 A, respectively) exhibit a periodicity close to the stellar-rotation pe riod and the correlations between them are consistent with a spotted stellar surface in rotation. We used these correlations to corr ect for the radialvelocity jitter due to stellar activity. This results in ach ieving high precision in measuring the orbital parameters, with a semi-amplitude ◦ .

Near-infrared Thermal Emission from WASP-12b: Detections of the Secondary Eclipse in Ks, H, and J

We present Ks, H, & J-band photometry of the very highly irradiated hot Jupiter WASP-12b using the Wide-field Infrared Camera on the Canada-France-Hawaii telescope. Our photometry brackets the secondary eclipse of WASP-12b in the Ks and H bands, and in J band starts in mid-eclipse and continues until well after the end of the eclipse. We detect its thermal emission in all three near-infrared bands. Our secondary eclipse depths are 0.309+0.013 ?0.012% in Ks band (24?), 0.176+0.016 ?0.021% in H band (9?), and 0.131+0.027 ?0.029% in J band (4?). All three secondary eclipses are best fit with a consistent phase, , that is compatible with a circular orbit: = 0.4998+0.0008 ?0.0007. The limits on the eccentricity, e, and argument of periastron, ?, of this planet from our photometry alone are thus |ecos ?| < 0.0040. By combining our secondary eclipse times with others published in the literature, as well as the radial-velocity and transit-timing data for this system, we show that there is no evidence that WASP-12b is precessing at a detectable rate and that its orbital eccentricity is likely zero. Our thermal-emission measurements also allow us to constrain the characteristics of the planets atmosphere; our Ks-band eclipse depth argues strongly in favor of inefficient day to nightside redistribution of heat and a low Bond albedo for this very highly irradiated hot Jupiter. The J- and H-band brightness temperatures are slightly cooler than the Ks-band brightness temperature, and thus hint at the possibility of a modest temperature inversion deep in the atmosphere of WASP-12b; the high-pressure, deep atmospheric layers probed by our J- and H-band observations are likely more homogenized than the higher altitude layer probed by our Ks-band observations. Lastly, our best-fit Ks-band eclipse has a marginally longer duration than would otherwise be expected; this may be tentative evidence for material being tidally stripped from the planet?as was predicted for this system by Li and collaborators, and for which observational confirmation was recently arguably provided by Fossati and collaborators.

Near-Infrared Thermal Emission from TrES-3b: A Ks-band detection and an H-band upper limit on the depth of the secondary eclipse

We present H- and Ks-band photometry bracketing the secondary eclipse of the hot Jupiter TrES-3b using the Wide-field Infrared Camera on the Canada-France-Hawaii Telescope. We detect the secondary eclipse of TrES-3b with a depth of 0.133+0.018 ?0.016% in the Ks band (8?)?a result that is in sharp contrast to the eclipse depth reported by de Mooij & Snellen. We do not detect its thermal emission in the H band, but place a 3? limit of 0.051% on the depth of the secondary eclipse in this band. A secondary eclipse of this depth in Ks requires very efficient day-to-nightside redistribution of heat and nearly isotropic reradiation, a conclusion that is in agreement with longer wavelength, mid-infrared Spitzer observations. Our 3? upper limit on the depth of our H-band secondary eclipse also argues for very efficient redistribution of heat and suggests that the atmospheric layer probed by these observations may be well homogenized. However, our H-band upper limit is so constraining that it suggests the possibility of a temperature inversion at depth, or an absorbing molecule, such as methane, that further depresses the emitted flux at this wavelength. The combination of our near-infrared measurements and those obtained with Spitzer suggests that TrES-3b displays a near-isothermal dayside atmospheric temperature structure, whose spectrum is well approximated by a blackbody. We emphasize that our strict H-band limit is in stark disagreement with the best-fit atmospheric model that results from longer wavelength observations only, thus highlighting the importance of near-infrared observations at multiple wavelengths, in addition to those returned by Spitzer in the mid-infrared, to facilitate a comprehensive understanding of the energy budgets of transiting exoplanets.

The Differential Rotation of κ1 Ceti as Observed by MOST

We first reported evidence for differential rotation of ?1 Ceti in Paper I. In this paper we demonstrate that the differential rotation pattern closely matches that for the Sun. This result is based on additional MOST observations in 2004 and 2005, as well as those from 2003. Using StarSpotz, a program developed specifically to analyze MOST photometry, we have solved for k, the differential rotation coefficient, and Peq, the equatorial rotation period using the light curves from all three years. The absolute range in spot latitudes is 10?-75? and k = 0.090, less than the solar value but consistent with the younger age of the star; k is also well constrained by the independent spectroscopic estimate of v sin i. We demonstrate independently that the pattern of differential rotation with latitude is indeed solar. Details are given of the parallel tempering formalism used in finding the most robust solution, which gives Peq = 8.77 days, smaller than that usually adopted, implying an age <750 My. Our values of Peq and k can explain the range of rotation periods others have found by spots or activity at a variety of latitudes. Historically, Ca II activity seems to occur consistently between latitudes 50? and 60?, which might indicate a permanent magnetic feature. Knowledge of k and Peq is key to understanding the dynamo mechanism and rotation structure in the convective zone, as well assessing age for solar-type stars. We recently published values of k and Peq for Eri based on MOST photometry and expect to analyze MOST light curves for several more spotted, solar-type stars.

MOST* Space-based Photometry of the Transiting Exoplanet System HD 189733: Precise Timing Measurements for Transits across an Active Star

We have measured transit times for HD 189733b passing in front of its bright (V = 7.67), chromospherically active, and spotted parent star. Nearly continuous broadband optical photometry of this system was obtained with the Microvariability and Oscillations of Stars (MOST) space telescope during 21 days in 2006 August, monitoring 10 consecutive transits. We have used these data to search for deviations from a constant orbital period which can indicate the presence of additional planets in the system that are as yet undetected by Doppler searches. There are no transit timing variations above the level of ±45 s, ruling out super-Earths (of masses 1-4 M⊕) in the 1:2 and 2:3 inner resonances, and planets of 20 M⊕ in the 2:1 outer resonance of the known planet. We also discuss complications in measuring transit times for a planet that transits an active star with large starspots, and how the transits can help constrain and test spot models. This has implications for the large number of such systems expected to be discovered by the COROT and Kepler missions.

Looking for giant earths in the HD 209458 system : A search for transits in most space-based photometry

We have made a comprehensive transit search for exoplanets down to 1.5-2 Earth radii in the HD 189733 system, based on 21 days of nearly uninterrupted broadband optical photometry obtained with the MOST (Microvariability and Oscillations of STars) satellite in 2006. We have searched these data for realistic limb-darkened transits from exoplanets other than the known hot Jupiter, HD 189733b, with periods ranging from about 0.4 days to 1 week. Monte Carlo statistical tests of the data with synthetic transits inserted into the data set allow us to rule out additional close-in exoplanets with sizes ranging from about 0.15-0.31 RJ (Jupiter radii), or 1.7-3.5 -->R? (Earth radii), on orbits whose planes are near that of HD 189733b. These null results constrain theories that invoke lower mass hot super-Earth and hot Neptune planets in orbits similar to HD 189733b, due to the inward migration of this hot Jupiter. This work also illustrates the feasibility of discovering smaller transiting planets around chromospherically active stars.

Markov Chain Monte Carlo Methods Applied to Photometric Spot Modeling

ABSTRACT I demonstrate that Markov chain Monte Carlo methods can be used very effectively to determine best‐fit values, uncertainties, and possible correlations or degeneracies in the fitted parameters of photometric spot modeling. Details of the Markov chain Monte Carlo methods applied here are briefly described, including the Metropolis‐Hastings algorithm and the tests that are used to ensure proper convergence and mixing. This Markov chain Monte Carlo functionality is applied to recent observations of ϵ Eridani by the Microvariablity and Oscillations of Stars (MOST) satellite, and the two‐spot solution showing differential rotation, as discussed in B. Croll et al. Conclusions in the latter are largely confirmed, but a strong correlation between the inclination and other fitted parameters is noted. The Markov chain Monte Carlo functionality has been included in StarSpotz, a freely available program for photometric spot modeling.

RADIAL VELOCITY STUDIES OF CLOSE BINARY STARS. XIV

Radial velocity (RV) measurements and sine curve fits to the orbital RV variations are presented for 10 close binary systems: TZ Boo, VW Boo, EL Boo, VZ CVn, GK Cep, RW Com, V2610 Oph, V1387 Ori, AU Ser, and FT UMa. Our spectroscopy revealed two quadruple systems, TZ Boo and V2610 Oph, while three stars showing small photometric amplitudes, EL Boo, V1387 Ori, and FT UMa, were found to be triple systems. GK Cep is a close binary with a faint third component. While most of the studied eclipsing systems are contact binaries, VZ CVn and GK Cep are detached or semidetached double-lined binaries, and EL Boo, V1387 Ori, and FT UMa are close binaries of uncertain binary type. The large fraction of triple and quadruple systems found in this sample supports the hypothesis of formation of close binaries in multiple stellar systems; it also demonstrates that low photometric amplitude binaries are a fertile ground for further discoveries of multiple systems.

First Assessment of Mountains on Northwestern Ellesmere Island, Nunavut, as Potential Astronomical Observing Sites

Ellesmere Island, at the most northerly tip of Canada, possesses the highest mountain peaks within 10 degrees of the pole. The highest is 2616 m, with many summits over 1000 m, high enough to place them above a stable low-elevation thermal inversion that persists through winter darkness. Our group has studied four mountains along the northwestern coast which have the additional benefit of smooth onshore airflow from the ice-locked Arctic Ocean. We deployed small robotic site testing stations at three sites, the highest of which is over 1600 m and within 8 degrees of the pole. Basic weather and sky clarity data for over three years beginning in 2006 are presented here, and compared with available nearby sea-level data and one manned mid-elevation site. Our results point to coastal mountain sites experiencing good weather: low median wind speed, high clear-sky fraction and the expectation of excellent seeing. Some practical aspects of access to these remote locations and operation and maintenance of equipment there are also discussed.

High-precision photometry with WIRCam at the CFHT

We present a new observing mode using WirCam on the Canada-France-Hawaii Telescope (CFHT). The staring mode with WIRCam can observe a target for several hours on the same pixels of the array. This allows for characterization of the photometric variations of the target to less than 0.02%, or to a signal-to-Noise Ratio ≥ 5000. The technical challenges encountered to implement this mode are described as well as a simple model to estimate the idealized performance of this observing mode. Early results are also presented and compared to the models.