arXiv subjects

F. Borsa

Publications and source records attributed to F. Borsa.

At least 55 records · Page 3Linked to original sources

arXiv2022

Dynamic effect of electron-number parity in metal nanoparticles

Parity is a ubiquitous notion in science and serves as a fundamental principle for describing a physical system. Nanometer-scale metal objects are predicted to show dramatic differences in physical properties depending on the electron-number parity. However, the identification of the electron-number parity effects in real metal nanoparticles has remained elusive because of the variations in various features of nanoparticles. Here we report the nuclear magnetic resonance (NMR) detection of the dynamic effect of the electron-number parity in silver nanoparticles. With theoretical modeling of the NMR relaxation in silver nanoparticles, the measured nuclear spin-lattice relaxation rate is found to be proportional to the electron-number-parity-dependent susceptibility and to the temperature. This observation demonstrates the electron-number-parity-governed spin dynamics in silver nanoparticles.

cond-mat.mes-hall↗

arXiv2022

Detection of barium in the atmospheres of the ultra-hot gas giants WASP-76b and WASP-121b

High-resolution spectroscopy studies of ultra-hot Jupiters have been key in our understanding of exoplanet atmospheres. Observing into the atmospheres of these giant planets allows for direct constraints on their atmospheric compositions and dynamics while laying the groundwork for new research regarding their formation and evolution environments. Two of the most well-studied ultra-hot Jupiters are WASP-76b and WASP-121b, with multiple detected chemical species and strong signatures of their atmospheric dynamics. We take a new look at these two exceptional ultra-hot Jupiters by reanalyzing the transit observations taken with ESPRESSO at the Very Large Telescope and attempt to detect additional species. To extract the planetary spectra of the two targets, we corrected for the telluric absorption and removed the stellar spectrum contributions. We then exploited new synthetic templates that were specifically designed for ultra-hot Jupiters in combination with the cross-correlation technique to unveil species that remained undetected by previous analyses. We add a novel detection of Ba+ to the known atmospheric compositions of WASP-76b and WASP-121b, the heaviest species detected to date in any exoplanetary atmosphere, with additional new detections of Co and Sr+ and a tentative detection of Ti+ for WASP-121b. We also confirm the presence of Ca+, Cr, Fe, H, Li, Mg, Mn, Na, and V on both WASP-76b and WASP-121b, with the addition of Ca, Fe+, and Ni for the latter. Finally, we also confirm the clear asymmetric absorption feature of Ca+ on WASP-121b, with an excess absorption at the bluer wavelengths and an effective planet radius beyond the Roche lobe. This indicates that the signal may arise from the escape of planetary atmosphere.

astro-ph.EP↗

arXiv2022

The GAPS Programme at TNG. XLI. The climate of KELT-9b revealed with a new approach to high spectral resolution phase curves

[Abridged] We present a novel method to study the thermal emission of exoplanets as a function of orbital phase at very high spectral resolution, and apply it to investigate the climate of the ultra-hot Jupiter KELT-9b. We combine 3 nights of HARPS-N and 2 nights of CARMENES optical spectra, covering orbital phases between quadratures (0.25 < phi < 0.75), when the planet shows its day-side hemisphere with different geometries. We co-add the signal of thousands of FeI lines through cross-correlation, which we map to a likelihood function. We investigate the phase-dependence of: (i) the line depths of FeI, and (ii) their Doppler shifts, by introducing a new method that exploits the very high spectral resolution of our observations. We confirm a previous detection of FeI emission and demonstrate a combined precision of 0.5 km s-1 on the orbital properties of KELT-9b. By studying the phase-resolved Doppler shift of FeI lines, we detect an anomaly in the planet's orbital radial velocity well-fitted with a slightly eccentric orbit (e = 0.016$\pm$0.003, w = 150$^{+13\circ}_{-11},~5σ$ preference). However, we argue that such anomaly can be explained by a day-night wind of a few km s-1 blowing neutral iron gas. Additionally, we find that the FeI emission line depths are symmetric around the substellar point within 10 deg ($2σ$). We show that these results are qualitatively compatible with predictions from general circulation models for ultra-hot Jupiter planets. Very high-resolution spectroscopy phase curves have the sensitivity to reveal a phase dependence in both the line depths and their Doppler shifts throughout the orbit. They are highly complementary to space-based phase curves obtained with HST and JWST, and open a new window into the still poorly understood climate and atmospheric structure of the hottest planets known.

astro-ph.EP↗

arXiv2022

A giant planet shaping the disk around the very low-mass star CIDA 1

(Abridged) Exoplanetary research has provided us with exciting discoveries of planets around very low-mass (VLM) stars (e.g., TRAPPIST-1 and Proxima Centauri). However, current theoretical models strive to explain planet formation in these conditions and do not predict the development of giant planets. Recent high-resolution observations from ALMA of the disk around CIDA 1, a VLM star in Taurus, show substructures hinting at the presence of a massive planet. We aim to reproduce the dust ring of CIDA 1, observed in the dust continuum emission in ALMA Band 7 (0.9 mm) and Band 4 (2.1 mm), along with its $^{12}$CO (J=3-2) and $^{13}$CO (J=3-2) channel maps, assuming the structures are shaped by the interaction of the disk with a massive planet. We seek to retrieve the mass and position of the putative planet. We model the protoplanetary disk with a set of hydrodynamical simulations, varying the mass and locations of the embedded planet. We compute the dust and gas emission using radiative transfer simulations, and, finally, we obtain the synthetic observations treating the images as the actual ALMA observations. Our models indicate that a planet with a minimum mass of $\sim1.4\,\text{M}_\text{Jup}$ orbiting at a distance of $\sim 9-10$ au can explain the morphology and location of the observed dust ring at Band 7 and Band 4. We can reproduce the low spectral index ($\sim 2$) observed where the dust ring is detected. Our synthetic images reproduce the morphology of the $^{12}$CO and $^{13}$CO observed channel maps where the cloud absorption allowed a detection. Applying an empirical relation between planet mass and gap width in the dust, we predict a maximum planet mass of $\sim4 - 8\,\text{M}_\text{Jup}$. Our results suggest the presence of a massive planet orbiting CIDA 1, thus challenging our understanding of planet formation around VLM stars.

astro-ph.EP↗

arXiv2022

The GAPS Programme at TNG XXXVIII. Five molecules in the atmosphere of the warm giant planet WASP-69b detected at high spectral resolution

The field of exo-atmospheric characterisation is progressing at an extraordinary pace. Atmospheric observations are now available for tens of exoplanets, mainly hot and warm inflated gas giants, and new molecular species continue to be detected revealing a richer atmospheric composition than previously expected. Thanks to its warm equilibrium temperature (963$\pm$18~K) and low-density (0.219$\pm$0.031~g cm$^{-3}$), the close-in gas giant WASP-69b represents a golden target for atmospheric characterization. With the aim of searching for molecules in the atmosphere of WASP-69b and investigating its properties, we performed high-resolution transmission spectroscopy with the GIANO-B near-infrared spectrograph at the Telescopio Nazionale Galileo. We observed three transit events of WASP-69b. During a transit, the planetary lines are Doppler-shifted due to the large change in the planet's radial velocity, allowing us to separate the planetary signal from the quasi-stationary telluric and stellar spectrum. Considering the three nights together, we report the detection of CH$_4$, NH$_3$, CO, C$_2$H$_2$, and H$_2$O, at more than $3.3σ$ level. We did not identify the presence of HCN and CO$_2$ with confidence level higher than 3$σ$. This is the first time that five molecules are simultaneously detected in the atmosphere of a warm giant planet. These results suggest that the atmosphere of WASP-69b is possibly carbon-rich and characterised by the presence of disequilibrium chemistry.

astro-ph.EP↗

arXiv2022

The GAPS Programme at TNG XL: A puffy and warm Neptune-sized planet and an outer Neptune-mass candidate orbiting the solar-type star TOI-1422

We investigate the exoplanet candidate TOI-1422b, which was discovered by the TESS space telescope around the high proper-motion G2V star TOI-1422 ($V=10.6$ mag), 155pc away, with the primary goal of confirming its planetary nature and characterising its properties. We monitored TOI-1422 with the HARPS-N spectrograph for 1.5 years to precisely quantify its radial velocity variation. The radial velocity measurements are analyzed jointly with TESS photometry and we also check for blended companions through high-spatial resolution images using the AstraLux instrument. We estimate that the parent star has a radius and a mass of $R^*=1.019_{-0.013}^{+0.014} R_{\odot}$, $M^*=0.981_{-0.065}^{+0.062} M_{\odot}$, respectively. Our analysis confirms the planetary nature of TOI-1422b and also suggests the presence of a Neptune-mass planet on a more distant orbit, the candidate TOI-1422c, which is not detected in TESS light curves. The inner planet, TOI-1422b, orbits on a period $P_{\rm b}=12.9972\pm0.0006$ days and has an equilibrium temperature $T_{\rm eq, b}=867\pm17$ K. With a radius of $R_{\rm b}=3.96^{+0.13}_{-0.11} R_{\oplus}$, a mass of $M_{\rm b}=9.0^{+2.3}_{-2.0} M_{\oplus}$ and, consequently, a density of $ρ_{\rm b}=0.795^{+0.290}_{-0.235}$ g cm$^{-3}$, it can be considered a warm Neptune-size planet. Compared to other exoplanets of similar mass range, TOI-1422b is among the most inflated ones and we expect this planet to have an extensive gaseous envelope that surrounds a core with a mass fraction around $10\%-25\%$ of the total mass of the planet. The outer non-transiting planet candidate, TOI-1422c, has an orbital period of $P_{\rm c}=29.29^{+0.21}_{-0.20}$ days, a minimum mass, $M_{\rm c}\sin{i}$, of $11.1^{+2.6}_{-2.3} M_{\oplus}$, an equilibrium temperature of $T_{\rm eq, c}=661\pm13$ K and, therefore, if confirmed, it could be considered as another warm Neptune.

astro-ph.EP↗

arXiv2022

Transmission spectroscopy of MASCARA-1b with ESPRESSO: Challenges of overlapping orbital and Doppler tracks

Atmospheric studies at high spectral resolution have shown the presence of molecules, neutral and ionised metals, and hydrogen in the transmission spectrum of ultra-hot Jupiters, and have started to probe the dynamics of their atmospheres. We analyse the transmission spectrum of MASCARA-1b, one of the densest ultra-hot Jupiters orbiting a bright (V=8.3) star. We focus on the CaII H&K, NaI, LiI, H$α$, and KI D1 spectral lines and on the cross-correlated FeI, FeII, CaI, YI, VI, VII, CaH, and TiO lines. For those species that are not present in the stellar spectrum, no detections are reported, but we measure upper limits with an excellent precision ($\sim10$ ppm for particular species). For those species that are present in the stellar spectrum and whose planet-occulted spectral lines induce spurious features in the planetary transmission spectrum, an accurate modelling of the Rossiter-McLaughlin effect (RM) and centre-to-limb variations (CLV) is necessary to recover possible atmospheric signals. In the case of MASCARA-1b, this is difficult due to the overlap between the radial velocities of the stellar surface regions occulted by MASCARA-1b and the orbital track along which the planet atmospheric signal is expected to be found. To try to disentangle a possible planetary signal, we compare our results with models of the RM and CLV effects, and estimate the uncertainties of our models depending on the different system parameters. Unfortunately, more precise measurements of the spin-orbit angle are necessary to better constrain the planet-occulted track and correct for the transit effects in the transmission spectrum with enough precision to be able to detect or discard possible planetary absorptions. Finally, we discuss the possibility that non-detections are related to the low absorption expected for a high surface gravity planet such as MASCARA-1b.

astro-ph.EP↗

arXiv2022

The GAPS Programme with HARPS-N at TNG. XXXVII. A precise density measurement of the young ultra-short period planet TOI-1807 b

Great strides have been made in recent years in the understanding of the mechanisms involved in the formation and evolution of planetary systems; despite this, many observational facts still do not have an explanation. A great contribution to the study of planetary formation processes comes from the study of young, low-mass planets, with short orbital periods. In the last years, the TESS satellite has identified many planets of this kind, and their characterization is mandatory to understand how they formed and evolved. Within the framework of the GAPS project, we performed the validation and characterization of the ultra-short period planet (USPP) TOI-1807b, orbiting its young host star BD+39 2643 (~300 Myr) in only 13 hours. This is the youngest USPP discovered so far. Thanks to a joint modeling of the stellar activity and planetary signals in the TESS light curve and in HARPS-N radial-velocity measurements, combined with accurate estimation of stellar parameters, we validated the planetary nature of TOI-1807b and measured its orbital and physical parameters. By using astrometric, photometric, and spectroscopic observations we found that BD+39 2643 is a young, active K dwarf star, member of a 300+/-80 Myr old moving group and that it rotates in Prot=8.8+/-0.1 days. This star hosts an USPP with an orbital period of only P_b=0.54937+/-0.00001 d. Thanks to the exquisite photometric and spectroscopic series, and the accurate information on the stellar activity, we measured both the radius and the mass of TOI-1807b with high precision, obtaining R_b=1.37+/-0.09 R_Earth and M_b=2.57+/-0.50 M_Earth. These planet parameters correspond to a rocky planet with an Earth-like density and no extended H/He envelope. From the analysis of the age-R_P distribution for planets with well measured ages, we inferred that TOI-1807b may have already lost a large part of its atmosphere during its 300 Myr life.

astro-ph.EP↗

arXiv2022

The GAPS Programme with HARPS-N at TNG. XXXV. Fundamental properties of transiting exoplanet host stars

Exoplanetary properties depend on stellar properties: to know the planet with accuracy and precision it is necessary to know the star as accurately and precisely as possible. Our immediate aim is to characterize in a homogeneous and accurate way a sample of 27 transiting planet-hosting stars observed within the GAPS program. We determined stellar parameters (effective temperature, surface gravity, rotational velocity) and abundances of 26 elements (Li,C,N,O,Na,Mg,Al,Si,S,Ca,Sc,Ti,V,Cr,Fe,Mn,Co,Ni,Cu,Zn,Y,Zr,Ba,La,Nd,Eu). Our study is based on high-resolution HARPS-N@TNG and FEROS@ESO spectra and uniform techniques. We derived kinematic properties from Gaia data and estimated for the first time in exoplanet host stars ages using elemental ratios as chemical clocks. Teff of our stars is of 4400-6700 K, while [Fe/H] is within -0.3 and 0.4 dex. Lithium is present in 7 stars. [X/H] and [X/Fe] abundances vs [Fe/H] are consistent with the Galactic Chemical Evolution. The dependence of [X/Fe] with the condensation temperature is critically analyzed with respect to stellar and kinematic properties. All targets with measured C and O abundances show C/O<0.8, compatible with Si present in rock-forming minerals. Most of targets show 1.0<Mg/Si<1.5, compatible with Mg distributed between olivine and pyroxene. HAT-P-26, the target hosting the lowest-mass planet, shows the highest Mg/Si ratio. From our chemo-dinamical analysis we find agreement between ages and position within the Galactic disk. We note a tendency for higher density planets to be around metal-rich stars and hints of higher stellar abundances of some volatiles for lower mass planets. We cannot exclude that part of our results could be also related to the location of the stars within the Galactic disk. We trace the planetary migration scenario from the composition of the planets related to the chemical composition of the hosting stars

astro-ph.SR↗

arXiv2022

The GAPS Programme at TNG XXXIII. HARPS-N detects multiple atomic species in emission from the dayside of KELT-20b

The detection of lines in emission in planetary atmospheres provides direct evidence of temperature inversion. We confirm the trend of ultra-hot Jupiters orbiting A-type stars showing temperature inversions on their daysides, by detecting metals emission lines in the dayside of KELT-20b. We first detect the planetary emission by using the G2 stellar mask of the HARPS-N pipeline, which is mainly composed of neutral iron lines, as a template. Using neutral iron templates, we perform a retrieval of the atmospheric temperature-pressure profile of the planet, confirming a thermal inversion. Then we create models of planetary emission of different species using the retrieved inverted temperature-pressure profile. By using the cross-correlation technique, we detect FeI, FeII and CrI at signal-to-noise ratio levels of 7.1, 3.9 and 3.6, respectively. The latter is detected for the first time in emission in the atmosphere of an exoplanet. Contrary to FeI, FeII and CrI are detected only after the occultation and not before, hinting for different atmospheric properties in view on the pre- and post- occultation orbital phases. A further retrieval of the temperature-pressure profile performed independently on the pre- and post- occultation phases, while not highly significant, points to a steeper thermal inversion in the post-occultation.

astro-ph.EP↗

arXiv2022

The polar orbit of the warm Neptune GJ436b seen with VLT/ESPRESSO

GJ436b might be the prototype of warm Neptunes that have undergone late migration induced by an outer companion. Precise determination of the orbital architecture of such systems is critical to constraining their dynamical history and evaluating the role of delayed migration in the exoplanet population. To this purpose we analyzed the Rossiter-McLaughlin (RM) signal of GJ436 b in two transits - recently observed with ESPRESSO - using three different techniques. The high level of precision achieved in radial velocity (RV) measurements allows us to detect the deviation from the Keplerian orbit, despite the slow rotation of the M dwarf host (vsini = 272.0+40.0-34.0 m/s), and to measure the sky-projected obliquity ($λ$ = 102.5+17.2-18.5$^{\circ}$). The Reloaded RM technique, which allows the stellar RV field along the transit chord to be analyzed, yields $λ$ = 107.5+23.6-19.3$^{\circ}$ and vsini = 292.9+41.9-49.9 m/s. The RM Revolutions technique, which allows us to fit the spectral profiles from all planet-occulted regions together, yields $λ$ = 114.1+22.8-17.8$^{\circ}$ and vsini = 300.5+45.9-57.0 m/s. The consistent results between these three techniques, and with published results from HARPS/HARPS-N data, confirm the polar orbit of GJ436b and support the hypothesis that its origin lies in Kozai migration. Results from a joint RM Revolutions analysis of the ESPRESSO, HARPS, and HARPS-N datasets ($λ$ = 113.5+23.3-17.3$^{\circ}$; vsini = 293.5+43.7-52.2 m/s) combined with a revised stellar inclination ($i_\star$ = 35.7+5.9-7.6$^{\circ}$ or 144.2+7.6-5.9$^{\circ}$) lead us to constrain the 3D obliquity $Ψ$ to 103.2+12.8-11.5$^{\circ}$.

astro-ph.EP↗

arXiv2022

CaRM: Exploring the chromatic Rossiter-McLaughlin effect. The cases of HD 189733b and WASP-127b

In this paper we introduce CaRM, a semi-automatic code for the retrieval of broadband transmission spectra of transiting planets through the chromatic Rossiter-McLaughlin method. We applied it to HARPS and ESPRESSO observations of two exoplanets to retrieve the transmission spectrum and we analyze its fitting transmission models. We used the strong radius dependence of the Rossiter-McLaughlin (RM) effect amplitude, caused by planetary companions, to measure the apparent radius change caused by the exoplanet atmosphere. In order to retrieve the transmission spectrum, the radial velocities, which were computed over wavelength bins that encompass several spectral orders, were used to simultaneously fit the Keplerian motion and the RM effect. From this, the radius ratio was computed as a function of the wavelength, which allows one to retrieve the low-resolution broadband transmission spectrum of a given exoplanet. CaRM offers the possibility to use two Rossiter-McLaughlin models taken from ARoME and PyAstronomy, associated with a Keplerian function to fit radial velocities during transit observations automatically. Furthermore it offers the possibility to use some methods that could, in theory, mitigate the effect of perturbation in the radial velocities during transits. The CaRM code allows one to retrieve the transmission spectrum of a given exoplanet using minimal user interaction. We demonstrate that it allows one to compute the low-resolution broadband transmission spectra of exoplanets observed using high-resolution spectrographs such as HARPS and ESPRESSO.

astro-ph.EP↗

arXiv2021

The GAPS Programme at TNG. XXXII. The revealing non-detection of metastable HeI in the atmosphere of the hot Jupiter WASP-80b

The hot Jupiter WASP-80b has been identified as a possible excellent target for detecting and measuring HeI absorption in the upper atmosphere. We observed 4 primary transits of WASP-80b in the optical and near-IR using the HARPS-N and GIANO-B high-resolution spectrographs, focusing on the HeI triplet. We further employed a three-dimensional hydrodynamic aeronomy model to understand the observational results. We did not find any signature of planetary absorption at the position of the HeI triplet with an upper limit of 0.7% (i.e. 1.11 planetary radii; 95% confidence level). We re-estimated the stellar high-energy emission that we combined with a stellar photospheric model to generate the input for the hydrodynamic modelling. We obtained that, assuming a solar He to H abundance ratio, HeI absorption should have been detected. Considering a stellar wind 25 times weaker than solar, we could reproduce the non-detection only assuming a He to H abundance ratio about 16 times smaller than solar. Instead, considering a stellar wind 10 times stronger than solar, we could reproduce the non-detection only with a He to H abundance ratio about 10 times smaller than solar. We attempted to understand this result by collecting all past HeI measurements looking for correlations with stellar high-energy emission and planetary gravity, but without finding any. WASP-80b is not the only planet with a sub-solar estimated He to H abundance ratio, suggesting the presence of efficient physical mechanisms (e.g. phase separation, magnetic fields) capable of significantly modifying the He to H content in the upper atmosphere of hot Jupiters. The planetary macroscopic properties and the shape of the stellar spectral energy distribution are not sufficient for predicting the presence or absence of detectable metastable He in a planetary atmosphere, as also the He abundance appears to play a major role.

astro-ph.EP↗

arXiv2021

The Rossiter-McLaughlin effect Revolutions: An ultra-short period planet and a warm mini-Neptune on perpendicular orbits

Comparisons of the alignment of exoplanets with a common host star can be used to distinguish among concurrent evolution scenarios. However, multi-planet systems usually host mini-Neptunes and super-Earths, whose size make orbital architecture measurements challenging. We introduce the Rossiter-McLaughlin effect Revolutions technique, which can access spin-orbit angles of small planets by exploiting the full information contained in spectral transit time series. We validated the technique on published HARPS-N data of the mini-Neptune HD3167c, refining its high sky-projected spin-orbit angle (-108.9+5.4-5.5 deg), and we applied it to new ESPRESSO observations of the super-Earth HD3167b, revealing an aligned orbit (-6.6+6.6-7.9 deg). Surprisingly different variations in the contrast of the stellar lines occulted by the planets can be reconciled with a latitudinal dependence of the stellar line shape. In this scenario, a joint fit to both datasets constrains the inclination of the star (111.6+3.1-3.3 deg) and the 3D spin-orbit angles of HD3167b (29.5+7.2-9.4 deg) and HD3167c (107.7+5.1-4.9 deg). The projected spin-orbit angles do not depend on the model for the line contrast variations, and so, with a mutual inclination of 102.3+7.4-8.0 deg, we conclude that the two planets are on perpendicular orbits. This could be explained by HD3167b being strongly coupled to the star and retaining its primordial alignment, whereas HD3167c would have been brought to a nearly polar orbit via secular gravitational interactions with an outer companion. Follow-up observations and dynamical evolution simulations are required to search for this companion and explore this scenario. HD3167b is the smallest exoplanet with a confirmed spectroscopic Rossiter-McLaughlin signal. Our new technique opens the way to determining the orbital architectures of the super-Earth and Earth-sized planet populations.

astro-ph.EP↗

arXiv2021

Retrieving the transmission spectrum of HD 209458b using CHOCOLATE: A new chromatic Doppler tomography technique

Multiband photometric transit observations or low-resolution spectroscopy (spectro-photometry) are normally used to retrieve the broadband transmission spectra of transiting exoplanets in order to assess the chemical composition of their atmospheres. In this paper, we present an alternative approach for recovering the broadband transmission spectra using chromatic Doppler tomography based on physical modeling through the SOAP tool: CHOCOLATE (CHrOmatiC line prOfiLe tomogrAphy TEchnique). To validate the method and examine its performance, we use observational data recently obtained with the ESPRESSO instrument to retrieve the transmission spectra of the archetypal hot Jupiter HD 209458b. Our findings indicate that the recovered transmission spectrum is in good agreement with the results presented in previous studies, which used different methodologies to extract the spectrum, achieving similar precision. We explored several atmospheric models and inferred from spectral retrieval that a model containing H2O and NH3 is the preferred scenario. The CHOCOLATE methodology is particularly interesting for future studies of exoplanets around young and active stars or moderate to fast rotating stars, considering SOAP's ability to model stellar active regions and the fact that the rotational broadening of spectral lines favors its application. Furthermore, CHOCOLATE will allow the broad transmission spectrum of a planet to be retrieved using high signal-to-noise ratio, high-resolution spectroscopy with the next generation of Extremely Large Telescopes (ELTs), where low-resolution spectroscopy will not always be accessible.

astro-ph.EP↗

arXiv2021

Into the Storm: Diving into the winds of the ultra hot Jupiter WASP-76 b with HARPS and ESPRESSO

Despite swift progress in the characterisation of exoplanet atmospheres in composition and structure, the study of atmospheric dynamics has not progressed at the same speed. While theoretical models have been developed to describe the lower layers of the atmosphere and, disconnected, the exosphere, little is known about the intermediate layers up to the thermosphere. We aim to provide a clearer picture of atmospheric dynamics for the class of ultra hot Jupiters, highly-irradiated gas giants, on the example of WASP-76~b. We analysed two datasets jointly, obtained with the HARPS and ESPRESSO spectrographs, to interpret the resolved planetary sodium doublet. We then applied an updated version of the MERC code, with added planetary rotation, also provides the possibility to model the latitude dependence of the wind patterns. We retrieve the highest Bayesian evidence for an isothermal atmosphere, interpreted as a mean temperature of $3389\pm227$ K, a uniform day-to-night side wind of $5.5^{+1.4}_{-2.0}\,$ km/s in the lower atmosphere with a vertical wind in the upper atmosphere of $22.7^{+4.9}_{-4.1}\,$ km/s, switching atmospheric wind patterns at $10^{-3}$ bar above the reference surface pressure ($10$ bar). Our results for WASP-76~b are compatible with previous studies of the lower atmospheric dynamics of WASP-76~b and other ultra hot Jupiters. They highlight the need for vertical winds in the intermediate atmosphere above the layers probed by global circulation model studies to explain the line broadening of the sodium doublet in this planet. This work demonstrates the capability of exploiting the resolved spectral line shapes to observationally constrain possible wind patterns in exoplanet atmospheres, an invaluable input to more sophisticated 3D atmospheric models in the future.

astro-ph.EP↗

arXiv2021

The GAPS Programme with HARPS-N at TNG. XXXI. The WASP-33 system revisited with HARPS-N

[abridged] We analyse four transits of WASP-33b observed with the optical high-resolution HARPS-N spectrograph to confirm its nodal precession, study its atmosphere and investigate the presence of star-planet interactions.We extract the mean line profiles of the spectra by using the LSD method, and analyse the Doppler shadow and the RVs. We also derive the transmission spectrum of the planet, correcting it for the stellar contamination due to rotation, CLV and pulsations. We confirm the previously discovered nodal precession of WASP-33b, almost doubling the time coverage of the inclination and projected spin-orbit angle variation. We find that the projected obliquity reached a minimum in 2011 and use this constraint to derive the geometry of the system, in particular its obliquity at that epoch ($ε=113.99^{\circ}\pm 0.22^{\circ}$) and the inclination of the stellar spin axis ($i_{\rm s}=90.11^{\circ}\pm 0.12^{\circ}$), as well as the gravitational quadrupole moment of the star $J_2=(6.73\pm 0.22)\times 10^{-5}$. We present detections of H$α$ and H$β$ absorption in the atmosphere of the planet with a contrast almost twice smaller than previously detected in the literature. We also find evidence for the presence of a pre-transit signal, which repeats in all four analysed transits. The most likely explanation lies in a possible excitation of a stellar pulsation mode by the presence of the planetary companion. Future common analysis of all available datasets in the literature will help shedding light on the possibility that the observed Balmer lines transit depth variations are related to stellar activity and/or pulsation, and to set constraints on the energetics possibly driving atmospheric escape. A complete orbital phase coverage of WASP-33b with high-resolution spectroscopic (spectro-polarimetric) observations could help understanding the nature of the pre-transit signal.

astro-ph.EP↗

arXiv2021

Constraints on the mass and atmospheric composition and evolution of the low-density young planet DS Tuc A b

We performed a radial velocity (RV) monitoring of the 40 Myr old star DS Tuc A with HARPS at the ESO-3.6m to determine the planetary mass of its 8.14-days planet, first revealed by TESS. We also observed two planetary transits with HARPS and ESPRESSO at ESO-VLT, to measure the Rossiter-McLaughlin (RM) effect and characterise the planetary atmosphere. We measured the high-energy emission of the host with XMM observations to investigate models for atmospheric evaporation. We employed Gaussian Processes (GP) regression to model the high level of the stellar activity, which is more than 40 times larger than the expected RV planetary signal. We extracted the transmission spectrum of DS Tuc A b from the ESPRESSO data and searched for atmospheric elements/molecules either by single-line retrieval and by performing cross-correlation with a set of theoretical templates. Through a set of simulations, we evaluated different scenarios for the atmospheric photo-evaporation of the planet induced by the strong XUV stellar irradiation. While the stellar activity prevented us from obtaining a clear detection of the planetary signal from the RVs, we set a robust mass upper limit of 14.4 M_e for DS Tuc A b. We also confirm that the planetary system is almost (but not perfectly) aligned. The strong level of stellar activity hampers the detection of any atmospheric compounds, in line with other studies presented in the literature. The expected evolution of DS Tuc A b from our grid of models indicates that the planetary radius after the photo-evaporation phase will fall within the Fulton gap. The comparison of the available parameters of known young transiting planets with the distribution of their mature counterpart confirms that the former are characterised by a low density, with DS Tuc A b being one of the less dense.

astro-ph.EP↗