We report high-resolution spectroscopic detection of TiO molecular signature in the day-side spectra of WASP-33 b, the second hottest known hot Jupiter. We used High-Dispersion Spectrograph (HDS; R ∼ 165,000) in the wavelength range of 0.62 -0.88 µm with the Subaru telescope to obtain the day-side spectra of WASP-33 b. We suppress and correct the systematic effects of the instrument, the telluric and stellar lines by using SYSREM algorithm after the selection of good orders based on Barnard star and other M-type stars. We detect a 4.8-σ signal at an orbital velocity of K p = +237.5 −1 , which agree with the derived values from the previous analysis of primary transit. Our detection with the temperature inversion model implies the existence of stratosphere in its atmosphere, however, we were unable to constrain the volume-mixing ratio of the detected TiO. We also measure the stellar radial velocity and use it to obtain a more stringent constraint on the orbital velocity, K p = 239.0Our results demonstrate that high-dispersion spectroscopy is a powerful tool to characterize the atmosphere of an exoplanet, even in the optical wavelength range, and show a promising potential in using and developing similar techniques with high-dispersion spectrograph on current 10m-class and future extremely large telescopes.
The Hubble constant (H 0 ) measures the current expansion rate of the Universe, and plays a fundamental role in cosmology. Tremendous effort has been dedicated over the past decades to measure H 0 1-10 . Notably, Planck cosmic microwave background (CMB) and the local Cepheid-supernovae distance ladder measurements determine H 0 with a precision of ∼ 1% and ∼ 2% respectively 3, 4, 11 . A 3-σ level of discrepancy exists between the two measurements 4, 12 , for reasons that have yet to be understood. Gravitational wave (GW) sources accompanied by electromagnetic (EM) counterparts offer a completely independent standard siren (the GW analogue of an astronomical standard candle) measurement of H 0 13-15 , as demonstrated following the discovery of the neutron star merger, GW170817 16-18 . This measurement does not assume a cosmological model and is independent of a cosmic distance ladder. The first joint analysis of the GW signal from GW170817 and its EM localization led to a measurement of H 0 = 74 +16 −8 km/s/Mpc (median and symmetric 68% credible interval) 15 . In this analysis, the degeneracy in the GW signal between the source distance and the weakly constrained viewing angle dominated the H 0 measurement uncertainty. Recently, Mooley et al. (2018) 19
We present an analysis of the transit timing variations (TTVs) in the multi-transiting planetary system around Kepler-51 (KOI-620). This system consists of two confirmed transiting planets, Kepler-51b (P b = 45.2 days) and Kepler-51c (P c = 85.3 days), and one transiting planet candidate KOI-620.02 (P 02 = 130.2 days), which lie close to a 1 : 2 : 3 resonance chain. Our analysis shows that their TTVs are consistently explained by the three-planet model, and constrains their masses as , and M 02 = 7.6 ± 1.1M ⊕ (KOI-620.02), thus confirming KOI-620.02 as a planet in this system. The masses inferred from the TTVs are rather small compared to the planetary radii based on the stellar density and planet-to-star radius ratios determined from the transit light curves. Combining these estimates, we find that all three planets in this system have densities among the lowest determined, ρ p 0.05 g cm −3 . With this feature, the Kepler-51 system serves as another example of low-density compact multi-transiting planetary systems. We also identify a curious feature in the archived Kepler light curve during the double transit of Kepler-51b and KOI-620.02, which could be explained by their overlapping on the stellar disk (a planet-planet eclipse). If this is really the case, the sky-plane inclination of KOI-620.02's orbit relative to that of Kepler-51b is given by ∆Ω = −25.3 +6.2 −6.8 deg, implying significant misalignment of their orbital planes. This interpretation, however, seems unlikely because such an event that is consistent with all of the observations is found to be exceedingly rare.
Analysis of the transit light curve deformed by the stellar gravity darkening allows us to photometrically measure both components of the spin-orbit angle ψ, its sky projection λ and inclination of the stellar spin axis i ⋆ . In this paper, we apply the method to two transiting hot Jupiter systems monitored with the Kepler spacecraft, Kepler-13A and HAT-P-7. For Kepler-13A, we find i ⋆ = 81 • ±5 • and ψ = 60 • ± 2 • adopting the spectroscopic constraint λ = 58. • 6 ± 2. • 0 by Johnson et al. (2014). In our solution, the discrepancy between the above λ and that previously reported by Barnes et al. (2011) is solved by fitting both of the two parameters in the quadratic limb-darkening law. We also report the temporal variation in the orbital inclination of Kepler-13Ab, d| cos i orb |/dt = (−7.0±0.4)×10 −6 day −1 , providing further evidence for the spin-orbit precession in this system. By fitting the precession model to the time series of i orb , λ, and i ⋆ obtained with the gravity-darkened model, we constrain the stellar quadrupole moment J 2 = (6.1 ± 0.3) × 10 −5 for our new solution, which is several times smaller than J 2 = (1.66 ± 0.08)× 10 −4 obtained for the previous one. We show that the difference can be observable in the future evolution of λ, thus providing a possibility to test our solution with follow-up observations. The second target, HAT-P-7, is the first F-dwarf star analyzed with the gravity-darkening method. Our analysis points to a nearly pole-on configuration with ψ = 101 • ± 2 • or 87 • ± 2 • and the gravity-darkening exponent β consistent with 0.25. Such an observational constraint on β can be useful for testing the theory of gravity darkening.
The Kepler mission revealed a population of compact multiple-planet systems with orbital periods shorter than a year, and occasionally even shorter than a day. By analyzing a sample of 102 Kepler and K2 multi-planet systems, we measure the minimum difference ∆I between the orbital inclinations, as a function of the orbital distance of the innermost planet. This is accomplished by fitting all the planetary signals simultaneously, constrained by an external estimate of the stellar mean density. We find ∆I to be larger when the inner orbit is smaller, a trend that does not appear to be a selection effect. We find that planets with a/R <5 have a dispersion in ∆I of 6.7 ± 0.6 degrees, while planets with 5 < a/R < 12 have a dispersion of 2.0 ± 0.1 degrees. The planetary pairs with higher mutual inclinations also tend to have larger period ratios. These trends suggest that the shortest-period planets have experienced both inclination excitation and orbital shrinkage.
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