Ten days of photometric data were obtained during the commissioning phase of the Kepler mission, including data for the previously known giant transiting exoplanet HAT-P-7b. The data for HAT-P-7b ...show a smooth rise and fall of light from the planet as it orbits its star, punctuated by a drop of 130 ± 11 parts per million in flux when the planet passes behind its star. We interpret this as the phase variation of the dayside thermal emission plus reflected light from the planet as it orbits its star and is occulted. The depth of the occultation is similar in photometric precision to the detection of a transiting Earth-size planet for which the mission was designed.
We present results from spectroscopic follow-up observations of stars identified in the Kepler field and carried out by teams of the Kepler Follow-up Observation Program. Two samples of stars were ...observed over 6 yr (2009-2015): 614 standard stars (divided into "platinum" and "gold" categories) selected based on their asteroseismic detections and 2667 host stars of Kepler Objects of Interest (KOIs), most of them planet candidates. Four data analysis pipelines were used to derive stellar parameters for the observed stars. We compare the Teff, log(g), and Fe/H values derived for the same stars by different pipelines; from the average of the standard deviations of the differences in these parameter values, we derive error floors of ∼100 K, 0.2 dex, and 0.1 dex for Teff, log(g), and Fe/H, respectively. Noticeable disagreements are seen mostly at the largest and smallest parameter values (e.g., in the giant star regime). Most of the log(g) values derived from spectra for the platinum stars agree on average within 0.025 dex (but with a spread of 0.1-0.2 dex) with the asteroseismic log(g) values. Compared to the Kepler Input Catalog (KIC), the spectroscopically derived stellar parameters agree within the uncertainties of the KIC but are more precise and thus an important contribution toward deriving more reliable planetary radii.
ABSTRACT
We report on precise Doppler measurements of L231-32 (TOI-270), a nearby M dwarf (d = 22 pc, M⋆ = 0.39 M⊙, R⋆ = 0.38 R⊙), which hosts three transiting planets that were recently discovered ...using data from the Transiting Exoplanet Survey Satellite (TESS). The three planets are 1.2, 2.4, and 2.1 times the size of Earth and have orbital periods of 3.4, 5.7, and 11.4 d. We obtained 29 high-resolution optical spectra with the newly commissioned Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) and 58 spectra using the High Accuracy Radial velocity Planet Searcher (HARPS). From these observations, we find the masses of the planets to be 1.58 ± 0.26, 6.15 ± 0.37, and 4.78 ± 0.43 M⊕, respectively. The combination of radius and mass measurements suggests that the innermost planet has a rocky composition similar to that of Earth, while the outer two planets have lower densities. Thus, the inner planet and the outer planets are on opposite sides of the ‘radius valley’ – a region in the radius-period diagram with relatively few members – which has been interpreted as a consequence of atmospheric photoevaporation. We place these findings into the context of other small close-in planets orbiting M dwarf stars, and use support vector machines to determine the location and slope of the M dwarf (Teff < 4000 K) radius valley as a function of orbital period. We compare the location of the M dwarf radius valley to the radius valley observed for FGK stars, and find that its location is a good match to photoevaporation and core-powered mass-loss models. Finally, we show that planets below the M dwarf radius valley have compositions consistent with stripped rocky cores, whereas most planets above have a lower density consistent with the presence of a H-He atmosphere.
Non‐technical summary A single bout of resistance exercise stimulates the synthesis of new muscle proteins. Chronic performance of resistance exercise (i.e. weight training) is what makes your ...muscles grow bigger; a process known as hypertrophy. However, it is unknown if increasing the time that muscle is under tension will lead to greater increases in muscle protein synthesis. We report that leg extension exercise at 30% of the best effort (which is a load that is comparatively light), with a slow lifting movement (6 s up and 6 s down) performed to fatigue produces greater increases in rates of muscle protein synthesis than the same movement performed rapidly (1 s up and 1 s down). These results suggest that the time the muscle is under tension during exercise may be important in optimizing muscle growth; this understanding enables us to better prescribe exercise to those wishing to build bigger muscles and/or to prevent muscle loss that occurs with ageing or disease.
We aimed to determine if the time that muscle is under loaded tension during low intensity resistance exercise affects the synthesis of specific muscle protein fractions or phosphorylation of anabolic signalling proteins. Eight men (24 ± 1 years (sem), BMI = 26.5 ± 1.0 kg m−2) performed three sets of unilateral knee extension exercise at 30% of one‐repetition maximum strength involving concentric and eccentric actions that were 6 s in duration to failure (SLOW) or a work‐matched bout that consisted of concentric and eccentric actions that were 1 s in duration (CTL). Participants ingested 20 g of whey protein immediately after exercise and again at 24 h recovery. Needle biopsies (vastus lateralis) were obtained while fasted at rest and after 6, 24 and 30 h post‐exercise in the fed‐state following a primed, constant infusion of l‐ring‐13C6phenylalanine. Myofibrillar protein synthetic rate was higher in the SLOW condition versus CTL after 24–30 h recovery (P < 0.001) and correlated to p70S6K phosphorylation (r = 0.42, P = 0.02). Exercise‐induced rates of mitochondrial and sarcoplasmic protein synthesis were elevated by 114% and 77%, respectively, above rest at 0–6 h post‐exercise only in the SLOW condition (both P < 0.05). Mitochondrial protein synthesis rates were elevated above rest during 24–30 h recovery in the SLOW (175%) and CTL (126%) conditions (both P < 0.05). Lastly, muscle PGC‐1α expression was increased at 6 h post‐exercise compared to rest with no difference between conditions (main effect for time, P < 0.001). These data show that greater muscle time under tension increased the acute amplitude of mitochondrial and sarcoplasmic protein synthesis and also resulted in a robust, but delayed stimulation of myofibrillar protein synthesis 24–30 h after resistance exercise.
Most of our knowledge of extrasolar planets rests on precise radial-velocity measurements, either for direct detection or for confirmation of the planetary origin of photometric transit signals. This ...has limited our exploration of the parameter space of exoplanet hosts to solar- and later-type, sharp-lined stars. Here we extend the realm of stars with known planetary companions to include hot, fast-rotating stars. Planet-like transits have previously been reported in the light curve obtained by the SuperWASP survey of the A5 star HD 15082 (WASP–33; V= 8.3, v sin i= 86 km s−1). Here we report further photometry and time-series spectroscopy through three separate transits, which we use to confirm the existence of a gas-giant planet with an orbital period of 1.22 d in orbit around HD 15082. From the photometry and the properties of the planet signal travelling through the spectral line profiles during the transit, we directly derive the size of the planet, the inclination and obliquity of its orbital plane and its retrograde orbital motion relative to the spin of the star. This kind of analysis opens the way to studying the formation of planets around a whole new class of young, early-type stars, hence under different physical conditions and generally in an earlier stage of formation than in sharp-lined late-type stars. The reflex orbital motion of the star caused by the transiting planet is small, yielding an upper mass limit of 4.1 MJupiter on the planet. We also find evidence of a third body of substellar mass in the system, which may explain the unusual orbit of the transiting planet. In HD 15082, the stellar line profiles also show evidence of non-radial pulsations, clearly distinct from the planetary transit signal. This raises the intriguing possibility that tides raised by the close-in planet may excite or amplify the pulsations in such stars.
ABSTRACT
We present a detailed analysis of HARPS-N radial velocity observations of K2-100, a young and active star in the Praesepe cluster, which hosts a transiting planet with a period of 1.7 d. We ...model the activity-induced radial velocity variations of the host star with a multidimensional Gaussian Process framework and detect a planetary signal of 10.6 ± 3.0 ${\rm m\, s^{-1}}$, which matches the transit ephemeris, and translates to a planet mass of 21.8 ± 6.2 M⊕. We perform a suite of validation tests to confirm that our detected signal is genuine. This is the first mass measurement for a transiting planet in a young open cluster. The relatively low density of the planet, $2.04 _{ - 0.61 } ^ { + 0.66 }$ ${\rm g\, cm^{-3}}$, implies that K2-100b retains a significant volatile envelope. We estimate that the planet is losing its atmosphere at a rate of $10^{11}\!-\!10^{12}\, {\rm g\, s^{-1}}$ due to the high level of radiation it receives from its host star.
ABSTRACT
We analysed 68 candidate planetary systems first identified during Campaigns 5 and 6 (C5 and C6) of the NASA K2 mission. We set out to validate these systems by using a suite of follow-up ...observations, including adaptive optics, speckle imaging, and reconnaissance spectroscopy. The overlap between C5 with C16 and C18, and C6 with C17, yields light curves with long baselines that allow us to measure the transit ephemeris very precisely, revisit single transit candidates identified in earlier campaigns, and search for additional transiting planets with longer periods not detectable in previous works. Using vespa, we compute false positive probabilities of less than 1 per cent for 37 candidates orbiting 29 unique host stars and hence statistically validate them as planets. These planets have a typical size of 2.2 R⊕ and orbital periods between 1.99 and 52.71 d. We highlight interesting systems including a sub-Neptune with the longest period detected by K2, sub-Saturns around F stars, several multiplanetary systems in a variety of architectures. These results show that a wealth of planetary systems still remains in the K2 data, some of which can be validated using minimal follow-up observations and taking advantage of analyses presented in previous catalogues.
Context. The Sun shows abundance anomalies relative to most solar twins. If the abundance peculiarities are due to the formation of inner rocky planets, that would mean that only a small fraction of ...solar type stars may host terrestrial planets. Aims. In this work we study HIP 56948, the best solar twin known to date, to determine with an unparalleled precision how similar it is to the Sun in its physical properties, chemical composition and planet architecture. We explore whether the abundances anomalies may be due to pollution from stellar ejecta or to terrestrial planet formation. Methods. We perform a differential abundance analysis (both in LTE and NLTE) using high resolution (R ~ 100 000) high S/N (600–650) Keck HIRES spectra of the Sun (as reflected from the asteroid Ceres) and HIP 56948. We use precise radial velocity data from the McDonald and Keck observatories to search for planets around this star. Results. We achieve a precision of σ ≲ 0.003 dex for several elements. Including errors in stellar parameters the total uncertainty is as low as σ ≃ 0.005 dex (1%), which is unprecedented in elemental abundance studies. The similarities between HIP 56948 and the Sun are astonishing. HIP 56948 is only 17 ± 7 K hotter than the Sun, and log g, Fe/H and microturbulence velocity are only + 0.02 ± 0.02 dex, +0.02 ± 0.01 dex and +0.01 ± 0.01 km s-1 higher than solar, respectively. Our precise stellar parameters and a differential isochrone analysis shows that HIP 56948 has a mass of 1.02 ± 0.02 M⊙ and that it is ~1 Gyr younger than the Sun, as constrained by isochrones, chromospheric activity, Li and rotation. Both stars show a chemical abundance pattern that differs from most solar twins, but the refractory elements (those with condensation temperature Tcond ≳ 1000 K) are slightly (~0.01 dex) more depleted in the Sun than in HIP 56948. The trend with Tcond in differential abundances (twins − HIP 56948) can be reproduced very well by adding ~3 M⊕ of a mix of Earth and meteoritic material, to the convection zone of HIP 56948. The element-to-element scatter of the Earth/meteoritic mix for the case of hypothetical rocky planets around HIP 56948 is only 0.0047 dex. From our radial velocity monitoring we find no indications of giant planets interior to or within the habitable zone of HIP 56948. Conclusions. We conclude that HIP 56948 is an excellent candidate to host a planetary system like our own, including the possible presence of inner terrestrial planets. Its striking similarity to the Sun and its mature age makes HIP 56948 a prime target in the quest for other Earths and SETI endeavors.
Most extrasolar planet discoveries using radial velocity measurements have been for solar-like G-stars. In order to understand better the role stellar mass for the formation of planets we must learn ...more about the frequency of planetary companions around both high- and low-mass stars. Radial velocity searches for planets around high mass main-sequence stars are difficult due to the paucity of lines and often rapid rotation of these early-type stars. On the other hand, evolved stars that have moved off the main sequence offer us the possibility of searching for planets around higher mass stars by means of precise radial velocity measurements. Here we present radial velocity measurements for the star HD 13189 using measurements taken at the Thüringer Landessternwarte Tautenburg, the Harlan J. Smith Telescope at McDonald Observatory, and the Hobby-Eberly Telescope. We classify the spectral type of this star as K2 with luminosity class II. The radial velocity measurements show long-period variations with a period of 472 days and an amplitude of 173 m s-1. The Ca II S-index is consistent with an inactive star and this shows no variations with the radial velocity period. We also investigated possible changes in the line shapes by measuring spectral line bisectors. These show no variations with the radial velocity period. We interpret the 472-day period as being caused by a sub-stellar companion. Based on the estimated absolute magnitude and a comparison to evolutionary tracks we estimate the mass of the progenitor star between 2 and 7 $M_\odot$ which results in a projected mass of the companion of m sin i = 8–20 MJ. HD 13189 may be the most massive star known to possess an extrasolar planet. This suggests that the formation of giant planets can also occur around early-type stars. HD 13189 also shows significant short term radial velocity variability on time scales of days that is most likely due to stellar oscillations. This behavior is typical for K giant stars.
We present an experimental study investigating laser-driven proton acceleration via target normal sheath acceleration (TNSA) over a target thickness range spanning the typical TNSA-dominant regime ...(∼1 m) down to below the onset of relativistic laser-transparency (<40 nm). This is done with a single target material in the form of freely adjustable films of liquid crystals along with high contrast (via plasma mirror) laser interaction (∼2.65 J, 30 fs, I > 1 × 10 21 W cm−2). Thickness dependent maximum proton energies scale well with TNSA models down to the thinnest targets, while those under ∼40 nm indicate the influence of relativistic transparency on TNSA, observed via differences in light transmission, maximum proton energy, and proton beam spatial profile. Oblique laser incidence (45°) allowed the fielding of numerous diagnostics to determine the interaction quality and details: ion energy and spatial distribution was measured along the laser axis and both front and rear target normal directions; these along with reflected and transmitted light measurements on-shot verify TNSA as dominant during high contrast interaction, even for ultra-thin targets. Additionally, 3D particle-in-cell simulations qualitatively support the experimental observations of target-normal-directed proton acceleration from ultra-thin films.
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