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Register a new userFurther Evidence for Tidal Spin-Up of Hot Jupiter Host Stars
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Added by
Roberto Tejada Arevalo
Publication date
2021
fields
Physics
and research's language is
English
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For most hot Jupiters around main-sequence Sun-like stars, tidal torques are expected to transfer angular momentum from the planets orbit to the stars rotation. The timescale for this process is difficult to calculate, leading to uncertainties in the history of orbital evolution of hot Jupiters. We present evidence for tidal spin-up by taking advantage of recent advances in planet detection and host-star characterization. We compared the projected rotation velocities and rotation periods of Sun-like stars with hot Jupiters and spectroscopically similar stars with (i) wider-orbiting giant planets, and (ii) less massive planets. The hot Jupiter hosts tend to spin faster than the stars in either of the control samples. Reinforcing earlier studies, the results imply that hot Jupiters alter the spins of their host stars while they are on the main sequence, and that the ages of hot-Jupiter hosts cannot be reliably determined using gyrochronology.
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We provide evidence that the obliquities of stars with close-in giant planets were initially nearly random, and that the low obliquities that are often observed are a consequence of star-planet tidal interactions. The evidence is based on 14 new measurements of the Rossiter-McLaughlin effect (for the systems HAT-P-6, HAT-P-7, HAT-P-16, HAT-P-24, HAT-P-32, HAT-P-34, WASP-12, WASP-16, WASP-18, WASP-19, WASP-26, WASP-31, Gl 436, and Kepler-8), as well as a critical review of previous observations. The low-obliquity (well-aligned) systems are those for which the expected tidal timescale is short, and likewise the high-obliquity (misaligned and retrograde) systems are those for which the expected timescale is long. At face value, this finding indicates that the origin of hot Jupiters involves dynamical interactions like planet-planet interactions or the Kozai effect that tilt their orbits, rather than inspiraling due to interaction with a protoplanetary disk. We discuss the status of this hypothesis and the observations that are needed for a more definitive conclusion.
Ultra-hot Jupiters are the most highly irradiated gas giant planets, with equilibrium temperatures from 2000 to over 4000 K. Ultra-hot Jupiters are amenable to characterization due to their high temperatures, inflated radii, and short periods, but their atmospheres are atypical for planets in that the photosphere possesses large concentrations of atoms and ions relative to molecules. Here we evaluate how the atmospheres of these planets respond to irradiation by stars of different spectral type. We find that ultra-hot Jupiters exhibit temperature
We present the low-resolution transmission spectra of the puffy hot Jupiter HAT-P-65b (0.53 M$_mathrm{Jup}$, 1.89 R$_mathrm{Jup}$, $T_mathrm{eq}=1930$ K), based on two transits observed using the OSIRIS spectrograph on the 10.4 m Gran Telescopio CANARIAS (GTC). The transmission spectra of the two nights are consistent, covering the wavelength range 517--938 nm and consisting of mostly 5 nm spectral bins. We perform equilibrium-chemistry spectral retrieval analyses on the jointly fitted transmission spectrum and obtain an equilibrium temperature of $1645^{+255}_{-244}$ K and a cloud coverage of $36^{+23}_{-17}$%, revealing a relatively clear planetary atmosphere. Based on free-chemistry retrieval, we report strong evidence for TiO. Additional individual analyses in each night reveal weak-to-moderate evidence for TiO in both nights, but moderate evidence for Na or VO only in one of the nights. Future high-resolution Doppler spectroscopy as well as emission observations will help confirm the presence of TiO and constrain its role in shaping the vertical thermal structure of HAT-P-65bs atmosphere.
We announce the discovery of KELT-16b, a highly irradiated, ultra-short period hot Jupiter transiting the relatively bright ($V = 11.7$) star TYC 2688-1839-1. A global analysis of the system shows KELT-16 to be an F7V star with $T_textrm{eff} = 6236pm54$ K, $log{g_star} = 4.253_{-0.036}^{+0.031}$, [Fe/H] = -0.002$_{-0.085}^{+0.086}$, $M_star = 1.211_{-0.046}^{+0.043} M_odot$, and $R_star = 1.360_{-0.053}^{+0.064} R_odot$. The planet is a relatively high mass inflated gas giant with $M_textrm{P} = 2.75_{-0.15}^{+0.16} M_textrm{J}$, $R_textrm{P} = 1.415_{-0.067}^{+0.084} R_textrm{J}$, density $rho_textrm{P} = 1.20pm0.18$ g cm$^{-3}$, surface gravity $log{g_textrm{P}} = 3.530_{-0.049}^{+0.042}$, and $T_textrm{eq} = 2453_{-47}^{+55}$ K. The best-fitting linear ephemeris is $T_textrm{C} = 2457247.24791pm0.00019$ BJD$_{tdb}$ and $P = 0.9689951 pm 0.0000024$ d. KELT-16b joins WASP-18b, -19b, -43b, -103b, and HATS-18b as the only giant transiting planets with $P < 1$ day. Its ultra-short period and high irradiation make it a benchmark target for atmospheric studies by HST, Spitzer, and eventually JWST. For example, as a hotter, higher mass analog of WASP-43b, KELT-16b may feature an atmospheric temperature-pressure inversion and day-to-night temperature swing extreme enough for TiO to rain out at the terminator. KELT-16b could also join WASP-43b in extending tests of the observed mass-metallicity relation of the Solar System gas giants to higher masses. KELT-16b currently orbits at a mere $sim$ 1.7 Roche radii from its host star, and could be tidally disrupted in as little as a few $times 10^{5}$ years (for a stellar tidal quality factor of $Q_* = 10^5$). Finally, the likely existence of a widely separated bound stellar companion in the KELT-16 system makes it possible that Kozai-Lidov oscillations played a role in driving KELT-16b inward to its current precarious orbit.
We report the discovery of WTS-2 b, an unusually close-in 1.02-day hot Jupiter (Mp=1.12MJ, Rp=1.363RJ) orbiting a K2V star, which has a possible gravitationally-bound M-dwarf companion at 0.6 arcsec separation contributing ~20 percent of the total flux in the observed J-band light curve. The planet is only 1.5 times the separation from its host star at which it would be destroyed by Roche lobe overflow, and has a predicted remaining lifetime of just ~40 Myr, assuming a tidal dissipation quality factor of Q*=10^6. Q* is a key factor in determining how frictional processes within a host star affect the orbital evolution of its companion giant planets, but it is currently poorly constrained by observations. We calculate that the orbital decay of WTS-2 b would correspond to a shift in its transit arrival time of T_shift~17 seconds after 15 years assuming Q*=10^6. A shift less than this would place a direct observational constraint on the lower limit of Q* in this system. We also report a correction to the previously published expected T_shift for WASP-18 b, finding that T_shift=356 seconds after 10 years for Q*=10^6, which is much larger than the estimated 28 seconds quoted in WASP-18 b discovery paper. We attempted to constrain Q* via a study of the entire population of known transiting hot Jupiters, but our results were inconclusive, requiring a more detailed treatment of transit survey sensitivities at long periods. We conclude that the most informative and straight-forward constraints on Q* will be obtained by direct observational measurements of the shift in transit arrival times in individual hot Jupiter systems. We show that this is achievable across the mass spectrum of exoplanet host stars within a decade, and will directly probe the effects of stellar interior structure on tidal dissipation.
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