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We present the results of 45 transit observations obtained for the transiting exoplanet HAT-P-32b. The transits have been observed using several telescopes mainly throughout the YETI network. In 25 cases, complete transit light curves with a timing precision better than $1.4:$min have been obtained. These light curves have been used to refine the system properties, namely inclination $i$, planet-to-star radius ratio $R_textrm{p}/R_textrm{s}$, and the ratio between the semimajor axis and the stellar radius $a/R_textrm{s}$. First analyses by Hartman et al. (2011) suggest the existence of a second planet in the system, thus we tried to find an additional body using the transit timing variation (TTV) technique. Taking also literature data points into account, we can explain all mid-transit times by refining the linear ephemeris by 21ms. Thus we can exclude TTV amplitudes of more than $sim1.5$min.
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In this Letter we present observations of recent HAT-P-13b transits. The combined analysis of published and newly obtained transit epochs shows evidence for significant transit timing variations since the last publicly available ephemerides. Variation of transit timings result in a sudden switch of transit times. The detected full range of TTV spans ~0.015 days, which is significantly more than the known TTV events exhibited by hot Jupiters. If we have detected a periodic process, its period should be at least ~3 years because there are no signs of variations in the previous observations. This argument makes unlikely that the measured TTV is due to perturbations by HAT-P-13c.
We present seven light curves of the exoplanet system HAT-P-3, taken as part of a transit timing program using the RISE instrument on the Liverpool Telescope. The light curves are analysed using a Markov-Chain Monte-Carlo algorithm to update the parameters of the system. The inclination is found to be i = 86.75^{+0.22}_{-0.21} deg, the planet-star radius ratio to be R_p/R_star = 0.1098^{+0.0010}_{-0.0012}, and the stellar radius to be R_star = 0.834^{+0.018}_{-0.026} R_sun, consistent with previous results but with a significant improvement in the precision. Central transit times and uncertainties for each light curve are also determined, and a residual permutation algorithm used as an independent check on the errors. The transit times are found to be consistent with a linear ephemeris, and a new ephemeris is calculated as T_c(0) = 2454856.70118 +- 0.00018 HJD and P = 2.899738 +- 0.000007 days. Model timing residuals are fitted to the measured timing residuals to place upper mass limits for a hypothetical perturbing planet as a function of the period ratio. These show that we have probed for planets with masses as low as 0.33 M_earth and 1.81 M_earth in the interior and exterior 2:1 resonances, respectively, assuming the planets are initially in circular orbits.
From its discovery, the low density transiting Neptune HAT-P-26b showed a 2.1-sigma detection drift in its spectroscopic data, while photometric data showed a weak curvature in the timing residuals that required further follow-up observations to be confirmed. To investigate this suspected variability, we observed 11 primary transits of HAT-P-26b between March, 2015 and July, 2018. For this, we used the 2.15 meter Jorge Sahade Telescope placed in San Juan, Argentina, and the 1.2 meter STELLA and the 2.5 meter Nordic Optical Telescope, both located in the Canary Islands, Spain. To add upon valuable information on the transmission spectrum of HAT-P-26b, we focused our observations in the R-band only. To contrast the observed timing variability with possible stellar activity, we carried out a photometric follow-up of the host star along three years. We carried out a global fit to the data and determined the individual mid-transit times focusing specifically on the light curves that showed complete transit coverage. Using bibliographic data corresponding to both ground and space-based facilities, plus our new characterized mid-transit times derived from parts-per-thousand precise photometry, we observed indications of transit timing variations in the system, with an amplitude of ~4 minutes and a periodicity of ~270 epochs. The photometric and spectroscopic follow-up observations of this system will be continued in order to rule out any aliasing effects caused by poor sampling and the long-term periodicity.
Considering the importance of investigating the transit timing variations (TTVs) of transiting exoplanets, we present a follow-up study of HAT-P-12b. We include six new light curves observed between 2011 and 2015 from three different observatories, in association with 25 light curves taken from the published literature. The sample of the data used, thus covers a time span of about 10.2 years with a large coverage of epochs (1160) for the transiting events of the exoplanet HAT-P-12b. The light curves are used to determine the orbital parameters and conduct an investigation of possible transit timing variations. The new linear ephemeris shows a large value of reduced chi-square = 7.93, and the sinusoidal fitting using the prominent frequency coming from a periodogram shows a reduced chi-square around 4. Based on these values and the corresponding O-C diagrams, we suspect the presence of a possible non-sinusoidal TTV in this planetary system. Finally, we find that a scenario with an additional non-transiting exoplanet could explain this TTV with an even smaller reduced chi-square value of around 2.
We present eight new light curves of the transiting extra-solar planet HAT-P-25b obtained from 2013 to 2016 with three telescopes at two observatories. We use the new light curves, along with recent literature material, to estimate the physical and orbital parameters of the transiting planet. Specifically, we determine the mid-transit times (T$_{C}$) and update the linear ephemeris, T$_{C[0]}$=2456418.80996$pm$0.00025 [$mathrm{BJD}_mathrm{TDB}$] and P=3.65281572$pm$0.00000095 days. We carry out a search for transit timing variations (TTVs), and find no significant TTV signal at the $Delta T=$80 s-level, placing a limit on the possible strength of planet-planet interactions ($mathrm{TTV_{G}}$). In the course of our analysis, we calculate the upper mass-limits of the potential nearby perturbers. Near the 1:2, 2:1, and 3:1 resonances with HAT-P-25b, perturbers with masses greater than 0.5, 0.3, and 0.5 $mathrm{M_{oplus}}$ respectively, can be excluded. Furthermore, based on the analysis of TTVs caused by light travel time effect (LTTE) we also eliminate the possibility that a long-period perturber exists with $M_{rm p}> 3000 ,mathrm{M_{J}}$ within $a=11.2,{rm AU}$ of the parent star.
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