A search for transit timing variations and orbital decay in WASP-46b
Authors:
Petrucci et al
Abstract:
We present 12 new transit observations of the exoplanet WASP-46b obtained with the 1.54-m telescope at Estación Astrofísica de Bosque Alegre (EABA, Argentina) and the 0.40-m Horacio Ghielmetti and 2.15-m Jorge Sahade telescopes at Complejo Astronómico El Leoncito (CASLEO, Argentina). We analyse them together with 37 light curves from the literature to re-determine the physical parameters and search for additional planets via transit timing variations (TTVs). We consider the 31 transits with uncertainties in their mid-transit times (eT0 eT0) less than 1 minute, to perform the first homogeneous study of TTVs for the system, finding a dispersion of σ = 1.66 minutes over a 6 year baseline. Since no periodic variations are found, our interpretation for this relatively high value of σ is that the stellar activity could be affecting the measured mid-transit times. This value of dispersion allows us to rule out the presence of additional bodies with masses larger than 2.3, 4.6, 7, and 9.3 M⊕ M⊕ at the first-order mean-motion resonances 2:1, 3:2, 4:3, and 5:4 with the transiting planet, respectively. Despite the 6 year baseline and a typical light curve precision of 2 × 10−3, we find that we cannot significantly demonstrate a slow decrease of the orbital period of WASP-46b. We place a lower limit of Q⋆ greater than 7 × 103 on the tidal quality factor and determine that an additional 6 year baseline is required to rule out Q⋆ less than 105.
Star-planet interactions. IV. Possibility of detecting the orbit-shrinking of a planet around a red giant
Authors:
Meynet et al
Abstract:
The surface rotations of some red giants are so fast that they must have been spun up by tidal interaction with a close companion, either another star, a brown dwarf, or a planet. We focus here on the case of red giants that are spun up by tidal interaction with a planet. When the distance between the planet and the star decreases, the spin period of the star decreases, the orbital period of the planet decreases, and the reflex motion of the star increases. We study the change rate of these three quantities when the circular orbit of a planet of 15 MJ that initially orbits a 2 M⊙ star at 1 au shrinks under the action of tidal forces during the red giant phase. We use stellar evolution models coupled with computations of the orbital evolution of the planet, which allows us to follow the exchanges of angular momentum between the star and the orbit in a consistent way. We obtain that the reflex motion of the red giant star increases by more than 1 m s−1 per year in the last ∼40 years before the planet engulfment. During this phase, the reflex motion of the star is between 660 and 710 m s−1. The spin period of the star increases by more than about 10 minutes per year in the last 3000 y before engulfment. During this period, the spin period of the star is shorter than 0.7 year. During this same period, the variation in orbital period, which is shorter than 0.18 year, is on the same order of magnitude. Changes in reflex-motion and spin velocities are very small and thus most likely out of reach of being observed. The most promising way of detecting this effect is through observations of transiting planets, that is, through{\it } changes of the beginning or end of the transit. A space mission like PLATO might be of great interest for detecting planets that are on the verge of being engulfed by red giants.
The Apparently Decaying Orbit of WASP-12b
Authors:
Patra et al
Abstract:
We present new transit and occultation times for the hot Jupiter WASP-12b. The data are compatible with a constant period derivative: $\dot{P}=-29\pm 3$ ms yr−1 and $P/\dot{P}=3.2\,\mathrm{Myr}$. However, it is difficult to tell whether we have observed orbital decay or a portion of a 14-year apsidal precession cycle. If interpreted as decay, the star's tidal quality parameter ${Q}_{\star }$ is about $2\times {10}^{5}$. If interpreted as precession, the planet's Love number is 0.44 ± 0.10. Orbital decay appears to be the more parsimonious model: it is favored by ${\rm{\Delta }}{\chi }^{2}=5.5$ despite having two fewer free parameters than the precession model. The decay model implies that WASP-12 was discovered within the final ~0.2% of its existence, which is an unlikely coincidence but harmonizes with independent evidence that the planet is nearing disruption. Precession does not invoke any temporal coincidence, but it does require some mechanism to maintain an eccentricity of $\approx 0.002$ in the face of rapid tidal circularization. To distinguish unequivocally between decay and precession will probably require a few more years of monitoring. Particularly helpful will be occultation timing in 2019 and thereafter.
Ruling out the orbital decay of the WASP-43b
Authors:
Hoyer et al
Abstract:
We present 15 new transit observations of the exoplanet WASP-43b in the i′,g′, and R filters with the 1.0-m telescopes of Las Cumbres Observatory Global Telescope (LCOGT) Network and the IAC80 telescope. We combine our 15 new light curves with 52 others from literature, to analyze homogeneously all the available transit light curves of this exoplanet. By extending the time span of the monitoring of the transits to more than 5 yr, and by analyzing the individual mid-times of 72 transits, we study the proposed shortening of the orbital period of WASP-43b. We estimate that the times of transit are well-matched by our updated ephemeris equation, using a constant orbital period. We estimate an orbital period change rate no larger than P˙=−0.02±6.6 ms yr−1, which is fully consistent with a constant period. Based on the timing analysis, we discard stellar tidal dissipation factors Q∗ less than 105. In addition, with the modelling of the transits we update the system parameters: a/Rs=4.867(23), i=82.11(10)∘ and Rp/Rs=0.15942(41), noticing a difference in the relative size of the planet between optical and NIR bands.
Departure from the constant-period ephemeris for the transiting exoplanet WASP-12 b
Authors:
Maciejewski et al
Abstract:
Most hot Jupiters are expected to spiral in towards their host stars due to transfering of the angular momentum of the orbital motion to the stellar spin. Their orbits can also precess due to planet-star interactions. Calculations show that both effects could be detected for the very-hot exoplanet WASP-12 b using the method of precise transit timing over a timespan of the order of 10 yr. We acquired new precise light curves for 29 transits of WASP-12 b, spannning 4 observing seasons from November 2012 to February 2016. New mid-transit times, together with literature ones, were used to refine the transit ephemeris and analyse the timing residuals. We find that the transit times of WASP-12 b do not follow a linear ephemeris with a 5 sigma confidence level. They may be approximated with a quadratic ephemeris that gives a rate of change in the orbital period of -2.56 +/- 0.40 x 10^{-2} s/yr. The tidal quality parameter of the host star was found to be equal to 2.5 x 10^5 that is comparable to theoretical predictions for Sun-like stars. We also consider 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.
The Possible Orbital Decay and Transit Timing Variations of the Planet WASP-43b
Authors:
Jiang et al
Abstract:
Motivated by the previously reported high orbital decay rate of the planet WASP-43b, eight newly transit light curves are obtained and presented. Together with other data in literature, we perform a self-consistent timing analysis with data covering a timescale of 1849 epochs. The results give an orbital decay rate dP/dt = -0.02890795\pm 0.00772547 sec/year, which is one order smaller than previous values. This slow decay rate corresponds to a normally assumed theoretical value of stellar tidal dissipation factor. In addition, through the frequency analysis, the transit timing variations presented here are unlikely to be periodic, but could be signals of a slow orbital decay.
