Context . Ultra-hot Jupiters present a unique opportunity to understand the physics and chemistry of planets, their atmospheres, and interiors at extreme conditions. WASP-12 b stands out as an ...archetype of this class of exoplanets, with a close-in orbit around its star that results in intense stellar irradiation and tidal effects. Aims . The goals are to measure the planet’s tidal deformation, atmospheric properties, and also to refine its orbital decay rate. Methods . We performed comprehensive analyses of the transits, occultations, and phase curves of WASP-12b by combining new CHEOPS observations with previous TESS and Spitzer data. The planet was modeled as a triaxial ellipsoid parameterized by the second-order fluid Love number of the planet, h 2 , which quantifies its radial deformation and provides insight into the interior structure. Results . We measured the tidal deformation of WASP-12b and estimated a Love number of h 2 = 1.55 −0.49 +0.45 (at 3.2σ) from its phase curve. We measured occultation depths of 333 ± 24 ppm and 493 ± 29 ppm in the CHEOPS and TESS bands, respectively, while the nightside fluxes are consistent with zero, and also marginal eastward phase offsets. Our modeling of the dayside emission spectrum indicates that CHEOPS and TESS probe similar pressure levels in the atmosphere at a temperature of ~2900 K. We also estimated low geometric albedos of A g = 0.086 ± 0.017 and A g = 0.01 ± 0.023 in the CHEOPS and TESS passbands, respectively, suggesting the absence of reflective clouds in the high-temperature dayside of the planet. The CHEOPS occultations do not show strong evidence for variability in the dayside atmosphere of the planet at the median occultation depth precision of 120 ppm attained. Finally, combining the new CHEOPS timings with previous measurements refines the precision of the orbital decay rate by 12% to a value of −30.23 ± 0.82 ms yr −1 , resulting in a modified stellar tidal quality factor of Q ′ ★ = 1.70 ± 0.14 × 10 5 . Conclusions . WASP-12 b becomes the second exoplanet, after WASP-103b, for which the Love number has been measured from the effect of tidal deformation in the light curve. However, constraining the core mass fraction of the planet requires measuring h 2 with a higher precision. This can be achieved with high signal-to-noise observations with JWST since the phase curve amplitude, and consequently the induced tidal deformation effect, is higher in the infrared.
Context. HD 179949 is an F8V star, orbited by a close-in giant planet with a period of ~3 days. Previous studies suggested that the planet enhances the magnetic activity of the parent star, producing ...a chromospheric hot spot which rotates in phase with the planet orbit. However, this phenomenon is intermittent since it was observed in several but not all seasons. Aims. A long-term monitoring of the magnetic activity of HD 179949 is required to study the amplitude and time scales of star-planet interactions. Methods. In 2009 we performed a simultaneous optical and X-ray spectroscopic campaign to monitor the magnetic activity of HD 179949 during ~5 orbital periods and ~2 stellar rotations. We analyzed the Ca ii H&K lines as a proxy for chromospheric activity, and we studied the X-ray emission in search of flux modulations and to determine basic properties of the coronal plasma. Results. A detailed analysis of the flux in the cores of the Ca ii H&K lines and a similar study of the X-ray photometry shows evidence of source variability, including one flare. The analysis of the time series of chromospheric data indicates a modulation with a ~11 days period, compatible with the stellar rotation period at high latitudes. Instead, the X-ray light curve suggests a signal with a period of ~4 days, consistent with the presence of two active regions on opposite hemispheres. Conclusions. The observed variability can be explained, most likely, as due to rotational modulation and to intrinsic evolution of chromospheric and coronal activity. There is no clear signature related to the orbital motion of the planet, but the possibility that just a fraction of the chromospheric and coronal variability is modulated with the orbital period of the planet, or the stellar-planet beat period, cannot be excluded. We conclude that any effect due to the presence of the planet is difficult to disentangle.
ABSTRACT
EBLM J0113+31 is a moderately bright (V = 10.1), metal-poor (Fe/H ≈−0.3) G0V star with a much fainter M dwarf companion on a wide, eccentric orbit (= 14.3 d). We have used near-infrared ...spectroscopy obtained with the SPIRou spectrograph to measure the semi-amplitude of the M dwarf’s spectroscopic orbit, and high-precision photometry of the eclipse and transit from the CHEOPS and TESS space missions to measure the geometry of this binary system. From the combined analysis of these data together with previously published observations, we obtain the following model-independent masses and radii: M1 = 1.029 ± 0.025 M⊙, M2 = 0.197 ± 0.003 M⊙, R1 = 1.417 ± 0.014 R⊙, R2 = 0.215 ± 0.002 R⊙. Using R1 and the parallax from Gaia EDR3 we find that this star’s angular diameter is θ = 0.0745 ± 0.0007 mas. The apparent bolometric flux of the G0V star corrected for both extinction and the contribution from the M dwarf (<0.2 per cent) is ${\mathcal {F}}_{\oplus ,0} = (2.62\pm 0.05)\times 10^{-9}$ erg cm−2 s−1. Hence, this G0V star has an effective temperature $T_{\rm eff,1} = 6124{\rm \, K} \pm 40{\rm \, K\, (rnd.)} \pm 10 {\rm \, K\, (sys.)}$. EBLM J0113+31 is an ideal benchmark star that can be used for ‘end-to-end’ tests of the stellar parameters measured by large-scale spectroscopic surveys, or stellar parameters derived from asteroseismology with PLATO. The techniques developed here can be applied to many other eclipsing binaries in order to create a network of such benchmark stars.
Context: The space experiment CoRoT has recently detected transits by a hot Jupiter across the disc of an active G7V star (CoRoT-Exo-2a) that can be considered as a good proxy for the Sun at an age ...of approximately 0.5 Gyr. Aims: We present a spot modelling of the optical variability of the star during 142 days of uninterrupted observations performed by CoRoT with unprecedented photometric precision. Methods: We apply spot modelling approaches previously tested in the case of the Sun by modelling total solar irradiance variations, a good proxy for the optical flux variations of the Sun as a star. The best results in terms of mapping of the surface brightness inhomogeneities are obtained by means of maximum entropy regularized models. To model the light curve of CoRoT-Exo-2a, we take into account the photometric effects of both cool spots and solar-like faculae, adopting solar analogy. Results: Two active longitudes initially on opposite hemispheres are found on the photosphere of CoRoT-Exo-2a with a rotation period of 4.522 ± 0.024 days. Their separation changes by 80° during the time span of the observations. From this variation, a relative amplitude of the surface differential rotation lower than ~1 percent is estimated. Individual spots form within the active longitudes and show an angular velocity ~1 percent lower than that of the longitude pattern. The total spotted area shows a cyclic oscillation with a period of 28.9 ± 4.3 days, which is close to 10 times the synodic period of the planet as seen by the rotating active longitudes. We discuss the effects of solar-like faculae on our models, finding indications of a facular contribution to the optical flux variations of CoRoT-Exo-2a being significantly smaller than in the present Sun. Conclusions: The implications of such results for the internal rotation of CoRoT-Exo-2a are discussed, based on solar analogy. A possible magnetic star-planet interaction is suggested by the cyclic variation of the spotted area. Alternatively, the 28.9-d cycle may be related to Rossby-type waves propagating in the subphotospheric layers of the star.
Gaia Data Release 2 Lanzafame, A. C.; Distefano, E.; Messina, S. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
Recenzirano
Odprti dostop
Context. Amongst the ≈5 × 105 sources identified as variable stars in Gaia Data Release 2 (DR2), 26% are rotational modulation variable candidates of the BY Dra class. Gaia DR2 provides their ...multi-band (G, GBP, and GRP) photometric time series collected by the European Space Agency spacecraft Gaia during the first 22 months of operations as well as the essential parameters related to their flux modulation induced by surface inhomogeneities and rotation. Aims. We developed methods to identify the BY Dra variable candidates and to infer their variability parameters. Methods. BY Dra candidates were pre-selected from their position in the Hertzsprung–Russel diagram, built from Gaia parallaxes, G magnitudes, and (GBP − GRP) colours. Since the time evolution of the stellar active region can disrupt the coherence of the signal, segments not much longer than their expected evolution timescale were extracted from the entire photometric time series, and period search algorithms were applied to each segment. For the Gaia DR2, we selected sources with similar periods in at least two segments as candidate BY Dra variables. Results were further filtered considering the time-series phase coverage and the expected approximate light-curve shape. Results. Gaia DR2 includes rotational periods and modulation amplitudes of 147 535 BY Dra candidates. The data unveil the existence of two populations with distinctive period and amplitude distributions. The sample covers 38% of the whole sky when divided into bins (HEALPix) of ≈0.84 square degrees, and we estimate that this represents 0.7–5% of all BY Dra stars potentially detectable with Gaia. Conclusions. The preliminary data contained in Gaia DR2 illustrate the vast and unique information that the mission is going to provide on stellar rotation and magnetic activity. This information, complemented by the exquisite Gaia parallaxes, proper motions, and astrophysical parameters, is opening new and unique perspectives for our understanding of the evolution of stellar angular momentum and dynamo action.
HD 179949 is an F8V star, orbited by a giant planet at ∼8 R
★ every 3.092 514 d. The system was reported to undergo episodes of stellar activity enhancement modulated by the orbital period, ...interpreted as caused by star-planet interactions (SPIs). One possible cause of SPIs is the large-scale magnetic field of the host star in which the close-in giant planet orbits.
In this paper we present spectropolarimetric observations of HD 179949 during two observing campaigns (2009 September and 2007 June). We detect a weak large-scale magnetic field of a few gauss at the surface of the star. The field configuration is mainly poloidal at both observing epochs. The star is found to rotate differentially, with a surface rotation shear of dΩ= 0.216 ± 0.061 rad d−1, corresponding to equatorial and polar rotation periods of 7.62 ± 0.07 and 10.3 ± 0.8 d, respectively. The coronal field estimated by extrapolating the surface maps resembles a dipole tilted at ∼70°. We also find that the chromospheric activity of HD 179949 is mainly modulated by the rotation of the star, with two clear maxima per rotation period as expected from a highly tilted magnetosphere. In 2009 September, we find that the activity of HD 179949 shows hints of low-amplitude fluctuations with a period close to the beat period of the system.
ABSTRACT The large number of close-in Jupiter-size exoplanets prompts the question whether star-planet interaction (SPI) effects can be detected. We focused our attention on the system HD 17156, ...having a Jupiter-mass planet in a very eccentric orbit. Here we present results of the XMM-Newton observations and of a five month coordinated optical campaign with the HARPS-N spectrograph.10 We observed HD 17156 with XMM-Newton when the planet was approaching the apoastron and then at the following periastron passage, quasi-simultaneously with HARPS-N. We obtained a clear ( ) X-ray detection only at the periastron visit, accompanied by a significant increase of the chromospheric index. We discuss two possible scenarios for the activity enhancement: magnetic reconnection and flaring or accretion onto the star of material tidally stripped from the planet. In any case, this is possibly the first evidence of a magnetic SPI effect caught in action.
ABSTRACT
We report the discovery of a third planet transiting the star TOI-1260, previously known to host two transiting sub-Neptune planets with orbital periods of 3.127 and 7.493 d, respectively. ...The nature of the third transiting planet with a 16.6-d orbit is supported by ground-based follow-up observations, including time-series photometry, high-angular resolution images, spectroscopy, and archival imagery. Precise photometric monitoring with CHEOPS allows to improve the constraints on the parameters of the system, improving our knowledge on their composition. The improved radii of TOI-1260b and TOI-1260c are $2.36 \pm 0.06 \rm R_{\oplus }$, $2.82 \pm 0.08 \rm R_{\oplus }$, respectively while the newly discovered third planet has a radius of $3.09 \pm 0.09 \rm R_{\oplus }$. The radius uncertainties are in the range of 3 per cent, allowing a precise interpretation of the interior structure of the three planets. Our planet interior composition model suggests that all three planets in the TOI-1260 system contains some fraction of gas. The innermost planet TOI-1260b has most likely lost all of its primordial hydrogen-dominated envelope. Planets c and d were also likely to have experienced significant loss of atmospheric through escape, but to a lesser extent compared to planet b.
Over 72days, 33 lambs were fed: concentrates in stall (S), grass at pasture for 8hours (8h), or grass at pasture for 4hours in the afternoon (4h-PM). The 4h-PM treatment did not affect the carcass ...yield compared to the 8h treatment. Meat colour development after blooming was unaffected by the treatments. The 4h-PM treatment increased the proportion of polyunsaturated fatty acids (PUFA; P<0.0005) and of the highly peroxidizable fatty acids (HP-PUFA; P<0.001) in meat compared to the 8h treatment. The S treatment increased lipid oxidation (higher TBARS values) and impaired colour stability (higher H* values) of meat over storage compared to the 8h and 4h-PM treatments (P<0.0005 and P=0.003, respectively). No difference in meat oxidative stability was found between the 8h and the 4h-PM treatments. In conclusion, growing lambs can tolerate a restriction of grazing duration without detrimental effects on performances and meat oxidative stability.
► Reducing the grazing duration from 8 to 4h did not impair lamb carcass yield. ► Reducing the grazing duration from 8 to 4h did not affect lamb meat colour. ► Reducing the grazing duration increased the proportion of PUFA in meat. ► Reducing the grazing duration from 8 to 4h did not affect meat oxidative stability.
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