Eclipsing Binary Science via the Merging of Transit and Doppler Exoplanet Survey Data—A Case Study with the MARVELS Pilot Project and SuperWASP

Exoplanet transit and Doppler surveys discover many binary stars during their operation that can be used to conduct a variety of ancillary science. Specifically, eclipsing binary stars can be used to study the stellar mass-radius relationship and to test predictions of theoretical stellar evolution models. By cross-referencing 24 binary stars found in the MARVELS Pilot Project with SuperWASP photometry, we find two new eclipsing binaries, TYC 0272-00458-1 and TYC 1422-01328-1, which we use as case studies to develop a general approach to eclipsing binaries in survey data. TYC 0272-00458-1 is a single-lined spectroscopic binary for which we calculate a mass of the secondary and radii for both components using reasonable constraints on the primary mass through several different techniques. For a primary mass of M 1 = 0.92 ± 0.1 M sun, we find M 2 = 0.610 ± 0.036 M sun, R 1 = 0.932 ± 0.076 R sun, and R 2 = 0.559 ± 0.102 R sun, and find that both stars have masses and radii consistent with model predictions. TYC 1422-01328-1 is a triple-component system for which we can directly measure the masses and radii of the eclipsing pair. We find that the eclipsing pair consists of an evolved primary star (M 1 = 1.163 ± 0.034 M sun, R 1 = 2.063 ± 0.058 R sun) and a G-type dwarf secondary (M 2 = 0.905 ± 0.067 M sun, R 2 = 0.887 ± 0.037 R sun). We provide the framework necessary to apply this analysis to much larger data sets.

SuperWASP observations of pulsating Am stars

We have studied over 1600 Am stars at a photometric precision of 1 mmag with SuperWASP photometric data. Contrary to previous belief, we find that around 200 Am stars are pulsating d Sct and ? Dor stars, with low amplitudes that have been missed in previous, less extensive studies. While the amplitudes are generally low, the presence of pulsation in Am stars places a strong constraint on atmospheric convection, and may require the pulsation to be laminar. While some pulsating Am stars have been previously found to be d Sct stars, the vast majority of Am stars known to pulsate are presented in this paper. They will form the basis of future statistical studies of pulsation in the presence of atomic diffusion. An extended version of Table 1 containing all the detected frequencies and amplitudes is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/535/A3

Novae in the SuperWASP data base

We present the results of trawling through the SuperWASP data base for classical and recurrent novae. We report light curves for a nova in eruption, and for classical novae and a recurrent nova in quiescence. For five objects in quiescence, we report periodicity, arising in most cases from orbital modulation of the light from the cool secondary star. The stability of the SuperWASP system means that these data have huge potential for the study not only of novae in eruption, but also of the long-term modulations of light during quiescence.

WASP-54b, WASP-56b and WASP-57b: Three new sub-Jupiter mass planets from SuperWASP

We present three newly discovered sub-Jupiter mass planets from the SuperWASP survey: WASP-54b is a heavily bloated planet of mass 0.636$^{+0.025}_{-0.024}$ \mj and radius 1.653$^{+0.090}_{-0.083}$ \rj. It orbits a F9 star, evolving off the main sequence, every 3.69 days. Our MCMC fit of the system yields a slightly eccentric orbit ($e=0.067^{+0.033}_{-0.025}$) for WASP-54b. We investigated further the veracity of our detection of the eccentric orbit for WASP-54b, and we find that it could be real. However, given the brightness of WASP-54 V=10.42 magnitudes, we encourage observations of a secondary eclipse to draw robust conclusions on both the orbital eccentricity and the thermal structure of the planet. WASP-56b and WASP-57b have masses of 0.571$^{+0.034}_{-0.035}$ \mj and $0.672^{+0.049}_{-0.046}$ \mj, respectively; and radii of $1.092^{+0.035}_{-0.033}$ \rj for WASP-56b and $0.916^{+0.017}_{-0.014}$ \rj for WASP-57b. They orbit main sequence stars of spectral type G6 every 4.67 and 2.84 days, respectively. WASP-56b and WASP-57b show no radius anomaly and a high density possibly implying a large core of heavy elements; possibly as high as $\sim$50 M$_{\oplus}$ in the case of WASP-57b. However, the composition of the deep interior of exoplanets remain still undetermined. Thus, more exoplanet discoveries such as the ones presented in this paper, are needed to understand and constrain giant planets' physical properties.

New exoplanets from the SuperWASP-North survey

We present the current status of the WASP search for transiting exoplanets, focusing on recent planet discoveries from SuperWASP-North and the joint equatorial region (-20≤Dec≤+20) observed by both WASP telescopes. We report the results of monitoring of WASP planets, and discuss how these contribute to our understanding of planet properties and their diversity.

New transiting exoplanets from the SuperWASP-North survey

The Wide Angle Search for Planet (WASP) project is one of the leading projects in the discovery of transiting exoplanets. We present 1) the current status of the WASP-North survey, 2) our recent exoplanet discoveries, and 3) we exemplify how these results fit into our understanding of transiting exoplanet properties and how they can help to understand exoplanet diversity.

The WASP project in the era of robotic telescope networks

We present the current status of the WASP project, a pair of wide angle photometric telescopes, individually called SuperWASP. SuperWASP-I is located in La Palma, and SuperWASP-II at Sutherland in South Africa. SW-I began operations in April 2004. SW-II is expected to be operational in early 2006. Each SuperWASP instrument consists of up to 8 individual cameras using ultra-wide field lenses backed by high-quality passively cooled CCDs. Each camera covers 7.8 x 7.8 sq degrees of sky, for nearly 500 sq degrees of total sky coverage. One of the current aims of the WASP project is the search for extra-solar planet transits with a focus on brighter stars in the magnitude range similar to 8 to 13. Additionally, WASP will search for, optical transients, track Near-Earth Objects, and study many types of variable stars and extragalactic objects. The collaboration has developed a custom-built reduction pipeline that achieves better than I percent photometric precision. We discuss future goals, which include: nightly on-mountain reductions that could be used to automatically drive alerts via a small robotic telescope network, and possible roles of the WASP telescopes as providers in such a network. Additional technical details of the telescopes, data reduction, and consortium members and institutions can be found on the web site at: http://www.superwasp.org/. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A fast hybrid algorithm for exoplanetary transit searches

We present a fast and efficient hybrid algorithm for selecting exoplanetary candidates from wide-field transit surveys. Our method is based on the widely used SysRem and Box Least-Squares (BLS) algorithms. Patterns of systematic error that are common to all stars on the frame are mapped and eliminated using the SysRem algorithm. The remaining systematic errors caused by spatially localized flat-fielding and other errors are quantified using a boxcar-smoothing method. We show that the dimensions of the search-parameter space can be reduced greatly by carrying out an initial BLS search on a coarse grid of reduced dimensions, followed by Newton-Raphson refinement of the transit parameters in the vicinity of the most significant solutions. We illustrate the method's operation by applying it to data from one field of the SuperWASP survey, comprising 2300 observations of 7840 stars brighter than V = 13.0. We identify 11 likely transit candidates. We reject stars that exhibit significant ellipsoidal variations caused indicative of a stellar-mass companion. We use colours and proper motions from the Two Micron All Sky Survey and USNO-B1.0 surveys to estimate the stellar parameters and the companion radius. We find that two stars showing unambiguous transit signals pass all these tests, and so qualify for detailed high-resolution spectroscopic follow-up.

WASP-4b: A 12th magnitude transiting hot Jupiter in the southern hemisphere

We report the discovery of WASP-4b, a large transiting gas-giant planet with an orbital period of 1.34 days. This is the first planet to be discovered by the SuperWASP-South observatory and CORALIE collaboration and the first planet orbiting a star brighter than 16th magnitude to be discovered in the southern hemisphere. A simultaneous fit to high-quality light curves and precision radial velocity measurements leads to a planetary mass of 1.22(-0.08)(+0.09) M-Jup and a planetary radius of 1.42(-0.04)(+0.07) R-Jup. The host star is USNO-B1.0 0479-0948995, a G7 V star of visual magnitude 12.5. As a result of the short orbital period, the predicted surface temperature of the planet is 1761 K, making it an ideal candidate for detections of the secondary eclipse at infrared wavelengths.

The main-sequence rotation-colour relation in the Coma Berenices open cluster

We present the results of a photometric survey of rotation rates in the Coma Berenices (Melotte 111) open cluster, using data obtained as part of the SuperWASP exoplanetary transit-search programme. The goal of the Coma survey was to measure precise rotation periods for main-sequence F, G and K dwarfs in this intermediate-age (~600 Myr) cluster, and to determine the extent to which magnetic braking has caused the stellar spin periods to converge. We find a tight, almost linear relationship between rotation period and J - K colour with an rms scatter of only 2 per cent. The relation is similar to that seen among F, G and K stars in the Hyades. Such strong convergence can only be explained if angular momentum is not at present being transferred from a reservoir in the deep stellar interiors to the surface layers. We conclude that the coupling time-scale for angular momentum transport from a rapidly spinning radiative core to the outer convective zone must be substantially shorter than the cluster age, and that from the age of Coma onwards stars rotate effectively as solid bodies. The existence of a tight relationship between stellar mass and rotation period at a given age supports the use of stellar rotation period as an age indicator in F, G and K stars of Hyades age and older. We demonstrate that individual stellar ages can be determined within the Coma population with an internal precision of the order of 9 per cent (rms), using a standard magnetic braking law in which rotation period increases with the square root of stellar age. We find that a slight modification to the magnetic-braking power law, P ~ t0.56, yields rotational and asteroseismological ages in good agreement for the Sun and other stars of solar age for which p-mode studies and photometric rotation periods have been published.

Line-profile tomography of exoplanet transits - II. A gas-giant planet transiting a rapidly rotating A5 star

Most of our knowledge of extrasolar planets rests on precise radial-velocity measurements, either for direct detection or for confirmation of the planetary origin of photometric transit signals. This has limited our exploration of the parameter space of exoplanet hosts to solar- and later-type, sharp-lined stars. Here we extend the realm of stars with known planetary companions to include hot, fast-rotating stars. Planet-like transits have previously been reported in the light curve obtained by the SuperWASP survey of the A5 star HD15082 (WASP-33 V = 8.3, v sini = 86 km s-1). Here we report further photometry and time-series spectroscopy through three separate transits, which we use to confirm the existence of a gas-giant planet with an orbital period of 1.22d in orbit around HD15082. From the photometry and the properties of the planet signal travelling through the spectral line profiles during the transit, we directly derive the size of the planet, the inclination and obliquity of its orbital plane and its retrograde orbital motion relative to the spin of the star. This kind of analysis opens the way to studying the formation of planets around a whole new class of young, early-type stars, hence under different physical conditions and generally in an earlier stage of formation than in sharp-lined late-type stars. The reflex orbital motion of the star caused by the transiting planet is small, yielding an upper mass limit of 4.1MJupiter on the planet. We also find evidence of a third body of substellar mass in the system, which may explain the unusual orbit of the transiting planet. In HD 15082, the stellar line profiles also show evidence of non-radial pulsations, clearly distinct from the planetary transit signal. This raises the intriguing possibility that tides raised by the close-in planet may excite or amplify the pulsations in such stars.

WASP-21b: a hot-Saturn exoplanet transiting a thick disc star

We report the discovery of WASP-21b, a new transiting exoplanet discovered by the Wide Angle Search for Planets (WASP) Consortium and established and characterized with the FIES, SOPHIE, CORALIE and HARPS fiber-fed echelle spectrographs. A 4.3-d period, 1.1% transit depth and 3.4-h duration are derived for WASP-21b using SuperWASP-North and high precision photometric observations at the Liverpool Telescope. Simultaneous fitting to the photometric and radial velocity data with a Markov Chain Monte Carlo procedure leads to a planet in the mass regime of Saturn. With a radius of 1.07 RJup and mass of 0.30 MJup, WASP-21b has a density close to 0.24 ?Jup corresponding to the distribution peak at low density of transiting gaseous giant planets. With a host star metallicity [Fe/H] of -0.46, WASP-21b strengthens the correlation between planetary density and host star metallicity for the five known Saturn-like transiting planets. Furthermore there are clear indications that WASP-21b is the first transiting planet belonging to the thick disc.

WASP-38b: a transiting exoplanet in an eccentric, 6.87d period orbit

Aims: We report the discovery of WASP-38b, a long period transiting planet in an eccentric 6.871815 day orbit. The transit epoch is 2 455 335.92050 ± 0.00074 (HJD) and the transit duration is 4.663 h. Methods: WASP-38b's discovery was enabled due to an upgrade to the SuperWASP-North cameras. We performed a spectral analysis of the host star HD 146389/BD+10 2980 that yielded Teff = 6150 ± 80 K, log g = 4.3 ± 0.1, v sin i = 8.6 ± 0.4 km s-1, M_* = 1.16 ± 0.04 M? and R_* = 1.33 ± 0.03 R?, consistent with a dwarf of spectral type F8. Assuming a main-sequence mass-radius relation for the star, we fitted simultaneously the radial velocity variations and the transit light curves to estimate the orbital and planetary parameters. Results: The planet has a mass of 2.69 ± 0.06 MJup and a radius of 1.09 ± 0.03 RJup giving a density, ?p = 2.1 ± 0.1 ?J. The high precision of the eccentricity e = 0.0314 ± 0.0044 is due to the relative transit timing from the light curves and the RV shape. The planet equilibrium temperature is estimated at 1292 ± 33 K. WASP-38b is the longest period planet found by SuperWASP-North and with a bright host star (V = 9.4 mag), is a good candidate for followup atmospheric studies. Photometry and RV data are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/525/A54

Independent Discovery of the Transiting Exoplanet HAT-P-14b

We present SuperWASP observations of HAT-P-14b, a hot Jupiter discovered by Torres et al. The planet was found independently by the SuperWASP team and named WASP-27b after follow-up observations had secured the discovery, but prior to the publication by Torres et al. Our analysis of HAT-P-14/WASP-27 is in good agreement with the values found by Torres et al. and we provide additional evidence against astronomical false positives. Due to the brightness of the host star, V-mag = 10, HAT-P-14b is an attractive candidate for further characterization observations. The planet has a high impact parameter and the primary transit is close to grazing. This could readily reveal small deviations in the orbital parameters indicating the presence of a third body in the system, which may be causing the small but significant orbital eccentricity. Our results suggest that the planet may undergo a grazing secondary eclipse. However, even a non-detection would tightly constrain the system parameters.