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Maciejewski G.,Nicolaus Copernicus University | Dimitrov D.,Bulgarian Academy of Science | Seeliger M.,Astrophysikalisches Institute und Universitats Sternwarte | Raetz S.,Astrophysikalisches Institute und Universitats Sternwarte | And 42 more authors.
Astronomy and Astrophysics | Year: 2013

Aims. The transiting planet WASP-12 b was identified as a potential target for transit-timing studies because a departure from a linear ephemeris has been reported in the literature. Such deviations could be caused by an additional planet in the system. We attempt to confirm the claimed variations in transit timing and interpret their origin. Methods. We organised a multi-site campaign to observe transits by WASP-12 b in three observing seasons, using 0.5-2.6-metre telescopes. Results. We obtained 61 transit light curves, many of them with sub-millimagnitude precision. The simultaneous analysis of the best-quality datasets allowed us to obtain refined system parameters, which agree with values reported in previous studies. The residuals versus a linear ephemeris reveal a possible periodic signal that may be approximated by a sinusoid with an amplitude of 0.00068 ± 0.00013 d and period of 500 ± 20 orbital periods of WASP-12 b. The joint analysis of timing data and published radial velocity measurements results in a two-planet model that explains observations better than do single-planet scenarios. We hypothesise that WASP-12 b might not be the only planet in the system, and there might be the additional 0.1 M Jup body on a 3.6-d eccentric orbit. A dynamical analysis indicates that the proposed two-planet system is stable on long timescales. © 2013 ESO.

MacIejewski G.,Nicolaus Copernicus University | Dimitrov D.,Bulgarian Academy of Science | Fernandez M.,Institute Astrofisica Of Andalucia Iaa Csic | Sota A.,Institute Astrofisica Of Andalucia Iaa Csic | And 15 more authors.
Astronomy and Astrophysics | Year: 2016

Aims. Most hot Jupiters are expected to spiral in toward their host stars because the angular momentum of the orbital motion is transferred to the stellar spin. Their orbits can also precess as a result of planet-star interactions. Calculations show that both effects might be detected for the very-hot exoplanet WASP-12 b using the method of precise transit-timing over a time span of about 10 yr. Methods. We acquired new precise light curves for 29 transits of WASP-12 b, spannning four observing seasons from November 2012 to February 2016. New mid-transit times, together with those from the literature, were used to refine the transit ephemeris and analyze the timing residuals. Results. We find that the transit times of WASP-12 b do not follow a linear ephemeris with a 5σ confidence level. They may be approximated with a quadratic ephemeris that gives a change rate in the orbital period of (-2.56 ± 0.40) × 10-2 s yr-1. The tidal quality parameter of the host star was found to be equal to 2.5 × 105, which is similar to theoretical predictions for Sun-like stars. We also considered a model in which the observed timing residuals are interpreted as a result of the apsidal precession. We find, however, that this model is statistically less probable than the orbital decay. © 2016 ESO.

Maciejewski G.,Nicolaus Copernicus University | Fernandez M.,Institute Astrofisica Of Andalucia Iaa Csic | Aceituno F.J.,Institute Astrofisica Of Andalucia Iaa Csic | Ohlert J.,Michael Adrian Observatorium | And 13 more authors.
Astronomy and Astrophysics | Year: 2015

Aims. The transiting hot-Jupiter planet Qatar-1 b exhibits variations in transit times that could be perturbative. A hot Jupiter with a planetary companion on a nearby orbit would constitute an unprecedented planetary configuration, which is important for theories of the formation and evolution of planetary systems. We performed a photometric follow-up campaign to confirm or refute transit timing variations. Methods. We extend the baseline of transit observations by acquiring 18 new transit light curves acquired with 0.6-2.0 m telescopes. These photometric time series, together with data available in the literature, were analyzed in a homogenous way to derive reliable transit parameters and their uncertainties. Results. We show that the dataset of transit times is consistent with a linear ephemeris leaving no hint of any periodic variations with a range of 1 min. We find no compelling evidence of a close-in planetary companion to Qatar-1 b. This finding is in line with a paradigm that hot Jupiters are not components of compact multiplanetary systems. Based on dynamical simulations, we place tighter constraints on the mass of any fictitious nearby planet in the system. Furthermore, new transit light curves allowed us to redetermine system parameters with better precision than reported in previous studies. Our values generally agree with previous determinations. © ESO 2015.

Maciejewski G.,Nicolaus Copernicus University | Niedzielski A.,Nicolaus Copernicus University | Wolszczan A.,Pennsylvania State University | Nowak G.,Nicolaus Copernicus University | And 31 more authors.
Astronomical Journal | Year: 2013

There have been previous hints that the transiting planet WASP-3b is accompanied by a second planet in a nearby orbit, based on small deviations from strict periodicity of the observed transits. Here we present 17 precise radial velocity (RV) measurements and 32 transit light curves that were acquired between 2009 and 2011. These data were used to refine the parameters of the host star and transiting planet. This has resulted in reduced uncertainties for the radii and masses of the star and planet. The RV data and the transit times show no evidence for an additional planet in the system. Therefore, we have determined the upper limit on the mass of any hypothetical second planet, as a function of its orbital period. © 2013. The American Astronomical Society. All rights reserved.

Maciejewski G.,Nicolaus Copernicus University | Ohlert J.,Michael Adrian Observatorium | Ohlert J.,Mittelhessen University of Applied Sciences | Dimitrov D.,Bulgarian Academy of Science | And 9 more authors.
Acta Astronomica | Year: 2014

We present thirteen new transit light curves for the WASP-1b exoplanet. Observations were acquired with 0.5 m-1.2 m telescopes between 2007 and 2013. Our homogeneous analysis, which also includes the literature data, results in determining precise system parameters. New values are in agreement with those reported in previous studies. Transit times follow a linear ephemeris with no sign of any transit time variations. This finding is in line with the paradigm that Jupiter-like planets on tight orbits are devoid of close planetary companions.

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