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Register a new userFollow-Up Observations of PTFO 8-8695: A 3 MYr Old T-Tauri Star Hosting a Jupiter-mass Planetary Candidate
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We present Spitzer 4.5micron light curve observations, Keck NIRSPEC radial velocity observations, and LCOGT optical light curve observations of PTFO~8-8695, which may host a Jupiter-sized planet in a very short orbital period (0.45 days). Previous work by citet{vaneyken12} and citet{barnes13} predicts that the stellar rotation axis and the planetary orbital plane should precess with a period of $300 - 600$ days. As a consequence, the observed transits should change shape and depth, disappear, and reappear with the precession. Our observations indicate the long-term presence of the transit events ($>3$ years), and that the transits indeed do change depth, disappear and reappear. The Spitzer observations and the NIRSPEC radial velocity observations (with contemporaneous LCOGT optical light curve data) are consistent with the predicted transit times and depths for the $M_star = 0.34 M_odot$ precession model and demonstrate the disappearance of the transits. An LCOGT optical light curve shows that the transits do reappear approximately 1 year later. The observed transits occur at the times predicted by a straight-forward propagation of the transit ephemeris. The precession model correctly predicts the depth and time of the Spitzer transit and the lack of a transit at the time of the NIRSPEC radial velocity observations. However, the precession model predicts the return of the transits approximately 1 month later than observed by LCOGT. Overall, the data are suggestive that the planetary interpretation of the observed transit events may indeed be correct, but the precession model and data are currently insufficient to confirm firmly the planetary status of PTFO~8-8695b.
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Hot Jupiters are giant Jupiter-like exoplanets that orbit 100x closer to their host stars than Jupiter does to the Sun. These planets presumably form in the outer part of the primordial disc from which both the central star and surrounding planets are born, then migrate inwards and yet avoid falling into their host star. It is however unclear whether this occurs early in the lives of hot Jupiters, when still embedded within protoplanetary discs, or later, once multiple planets are formed and interact. Although numerous hot Jupiters were detected around mature Sun-like stars, their existence has not yet been firmly demonstrated for young stars, whose magnetic activity is so intense that it overshadows the radial velocity signal that close-in giant planets can induce. Here we show that hot Jupiters around young stars can be revealed from extended sets of high-resolution spectra. Once filtered-out from the activity, radial velocities of V830 Tau derived from new data collected in late 2015 exhibit a sine wave of period 4.93 d and semi-amplitude 75 m/ s, detected with a false alarm probability <0.03%. We find that this signal is fully unrelated to the 2.741-d rotation period of V830 Tau and we attribute it to the presence of a 0.77 Jupiter mass planet orbiting at a distance of 0.057 au from the host star. Our result demonstrates that hot Jupiters can migrate inwards in <2 Myr, most likely as a result of planet-disc interactions, and thus yields strong support to the theory of giant planet migration in gaseous protoplanetary discs.
We search for signatures of a distant planet around the two-million-year-old classical T-Tauri star CI Tau hosting a hot Jupiter candidate (M_{p} sin{i} ~ 8.1 M_{Jupiter}) in an eccentric orbit (e ~0.3). To probe the existence of an outer perturber, we reanalyzed 1.3 mm dust continuum observations of the protoplanetary disk around CI Tau obtained by the Atacama Large Millimeter/submillimeter Array. We found a gap structure at ~0.8 in CI Taus disk. Our visibility fitting assuming an axisymmetric surface brightness profile suggested that the gap is located at a deprojected radius of 104.5+/-1.6 au and has a width of 36.9+/-2.9 au. The brightness temperature around the gap was calculated to be ~2.3 K lower than that of the ambient disk. Gap-opening mechanisms such as secular gravitational instability and dust trapping can explain the gap morphology in the CI Tau disk. The scenario that an unseen planet created the observed gap structure cannot be ruled out, although the coexistence of an eccentric hot Jupiter and a distant planet around the young CI Tau would be challenging for gravitational scattering scenarios. The mass of the planet was estimated to be between ~0.25 M_{Jupiter} and ~0.8 M_{Jupiter} from the gap width and depth (0.41 +0.04/-0.06) in the modeled surface brightness image, which is lower than the current detection limits of high-contrast direct imaging. The young classical T-Tauri CI Tau may be a unique system to explore the existence of a potential distant planet as well as the origin of an eccentric hot Jupiter.
PTFO 8-8695 (CVSO 30) is a star in the 7-10 million year old Orion-OB1a cluster that shows brightness dips that resemble planetary transits. Although strong evidence against the planet hypothesis has been presented, the possibility remains debated in the literature. To obtain further clues, we inspected data from the NASA Transiting Exoplanet Survey Satellite (TESS) and the ESA Gaia mission. The Gaia data suggest that PTFO 8-8695 is a binary: the photometric data show it to be overluminous with respect to members of its kinematic group, and the astrometric data are inconsistent with a single star. The TESS light curve shows two different photometric periods. The variability is dominated by a sinusoidal signal with a period of 11.98 hr, presumably caused by stellar rotation. Also present is a 10.76 hr signal consisting of a not-quite sinusoid interrupted by hour-long dips, the type of signal previously interpreted as planetary transits. The phase of the dips is nearly 180$^circ$ away from the phase of the originally reported dips. As noted previously, this makes them difficult to explain as planetary transits. Instead, we believe that PTFO 8-8695 is a pair of young and rapidly rotating M dwarfs, one of which shows the same transient-dipper behavior that has been seen in at least 5 other cases. The origin of these transient dips is still unknown but likely involves circumstellar material.
We present emph{Herschel} PACS observations of 8 Classical T Tauri Stars in the $sim 7-10$ Myr old OB1a and the $sim 4-5$ Myr old OB1b Orion sub-asscociations. Detailed modeling of the broadband spectral energy distributions, particularly the strong silicate emission at 10 $mu$m, shows that these objects are (pre)transitional disks with some amount of small optically thin dust inside their cavities, ranging from $sim 4$ AU to $sim 90$ AU in size. We analyzed emph{Spitzer} IRS spectra for two objects in the sample: CVSO-107 and CVSO-109. The IRS spectrum of CVSO-107 indicates the presence of crystalline material inside its gap while the silicate feature of CVSO-109 is characterized by a pristine profile produced by amorphous silicates; the mechanisms creating the optically thin dust seem to depend on disk local conditions. Using millimeter photometry we estimated dust disk masses for CVSO-107 and CVSO-109 lower than the minimum mass of solids needed to form the planets in our Solar System, which suggests that giant planet formation should be over in these disks. We speculate that the presence and maintenance of optically thick material in the inner regions of these pre-transitional disks might point to low-mass planet formation.
We report the spectroscopic confirmation of the Kepler object of interest KOI-183.01 (Kepler-423b), a half-Jupiter mass planet transiting an old solar-like star every 2.7 days. Our analysis is the first to combine the full Kepler photometry (quarters 1-17) with high-precision radial velocity measurements taken with the FIES spectrograph at the Nordic Optical Telescope. We simultaneously modelled the photometric and spectroscopic data-sets using Bayesian approach coupled with Markov chain Monte Carlo sampling. We found that the Kepler pre-search data conditioned (PDC) light curve of KOI-183 exhibits quarter-to-quarter systematic variations of the transit depth, with a peak-to-peak amplitude of about 4.3 % and seasonal trends reoccurring every four quarters. We attributed these systematics to an incorrect assessment of the quarterly variation of the crowding metric. The host star KOI-183 is a G4 dwarf with $M_star=0.85pm0.04$ M$_rm{Sun}$, $R_star=0.95pm0.04$ R$_rm{Sun}$, $T_mathrm{eff}=5560pm80$ K, $[M/H]=-0.10pm0.05$ dex, and with an age of $11pm2$ Gyr. The planet KOI-183b has a mass of $M_mathrm{p}=0.595pm0.081$ M$_mathrm{Jup}$ and a radius of $R_mathrm{p}=1.192pm0.052$ R$_mathrm{Jup}$, yielding a planetary bulk density of $rho_mathrm{p}=0.459pm0.083$ g/cm$^{3}$. The radius of KOI-183b is consistent with both theoretical models for irradiated coreless giant planets and expectations based on empirical laws. The inclination of the stellar spin axis suggests that the system is aligned along the line of sight. We detected a tentative secondary eclipse of the planet at a 2-$sigma$ confidence level ($Delta F_{mathrm{ec}}=14.2pm6.6$ ppm) and found that the orbit might have a small non-zero eccentricity of $e=0.019^{+0.028}_{-0.014}$. With a Bond albedo of $A_mathrm{B}=0.037pm0.019$, KOI-183b is one of the gas-giant planets with the lowest albedo known so far.
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