G. Leto

Magnetic activity in the photosphere of CoRoT-Exo-2a - Active longitudes and short-term spot cycle in a young Sun-like star

Context. The space experiment CoRoT has recently detected transits by a hot Jupiter across the disk of an active G7V star (CoRoTExo-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 variatio ns, 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 both the photometric effects of cool spots as well as those of solar-like faculae, ado pting 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 act ive longitudes and show an angular velocity about∼ 1 percent smaller than that of the longitude pattern. The tot al 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 indication 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 o f CoRoT-Exo-2a are discussed on the basis of solar analogy. A possible magnetic star-planet interaction is suggested by the cyclic variation of the spotted area. Alternatively, t he 28.9-d cycle may be related to Rossby-type waves propagating in the subphotospheric layers of the star.

A comparison of ion irradiation and UV photolysis of CH4 and CH3OH

We have studied by infrared absorption spectroscopy the effects induced by fast ions (30 keV) and Lyman-α photons (10.2 eV) on some molecular ices at low temperature (10-20 K). It is well known that in both cases the physical and chemical properties of the ices are modified. However while the energy released by ions depends mainly on their energy and on the target species, the effects induced by photons also depend on the optical properties of the sample. Here we show that the effects of ion irradiation and UV photolysis are comparable on fresh ices (i.e. at low doses) but are increasingly different as processing is continued (i.e. at high doses).

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium is a worldwide consortium which federates atomic and molecular databases through an e-science infrastructure and an organisation to support this activity. About 90% of the inter-connected databases handle data that are used for the interpretation of astronomical spectra and for modelling in many fields of astrophysics. Recently the VAMDC Consortium has connected databases from the radiation damage and the plasma communities, as well as promoting the publication of data from Indian institutes. This paper describes how the VAMDC Consortium is organised for the optimal distribution of atomic and molecular data for scientific research. It is noted that the VAMDC Consortium strongly advocates that authors of research papers using data cite the original experimental and theoretical papers as well as the relevant databases.

The GAPS programme with HARPS-N at TNG - I. Observations of the Rossiter-McLaughlin effect and characterisation of the transiting system Qatar-1

Context. Our understanding of the formation and evolution of planetary systems is still fragmentary because most of the current data provide limited information about the orbital structure and dynamics of these systems. The knowledge of the orbital properties for a variety of systems and at di erent ages yields information on planet migration and on star-planet tidal interaction mechanisms. Aims. In this context, a long-term, multi-purpose, observational programme has started with HARPS-N at TNG and aims to characterise the global architectural properties of exoplanetary systems. The goal of this first paper is to fully characterise the orbital properties of the transiting system Qatar-1 as well as the physical properties of the star and the planet. Methods. We exploit HARPS-N high-precision radial velocity measurements obtained during a transit to measure the Rossiter-McLaughlin e ect in the Qatar-1 system, and out-of-transit measurements to redetermine the spectroscopic orbit. New photometric-transit light-curves were analysed and a spectroscopic characterisation of the host star atmospheric parameters was performed based on various methods (line equivalent width ratios, spectral synthesis, spectral energy distribution). Results. We achieved a significant improvement in the accuracy of the orbital parameters and derived the spin-orbit alignment of the system; this information, combined with the spectroscopic determination of the host star properties (rotation, Te , logg, metallicity), allows us to derive the fundamental physical parameters for star and planet (masses and radii). The orbital solution for the Qatar-1 system is consistent with a circular orbit and the system presents a sky-projected obliquity of = 8:4 7:1 deg. The planet, with a mass of 1:33 0:05 MJ, is found to be significantly more massive than previously reported. The host star is confirmed to be metal-rich ([Fe/H] = 0:20 0:10) and slowly rotating (v sinI = 1:7 0:3 km s 1 ), though moderately active, as indicated by the strong chromospheric emission in the Caii H&K line cores (logR 0 4:60). Conclusions. We find that the system is well aligned and fits well within the general versus Te trend. We can definitely rule out any significant orbital eccentricity. The evolutionary status of the system is inferred based on gyrochronology, and the present orbital configuration and timescale for orbital decay are discussed in terms of star-planet tidal interactions.

Photospheric activity, rotation, and radial velocity variations of the planet-hosting star CoRoT-7

Context. The CoRoT satellite has recently discovered the transits of an Earth-like planet across the disc of a late-type magnetically active star dubbed CoRoT-7, while a second planet was detected after filtering out the radial velocity (hereafter RV) variations due to stellar activity. Aims. We investigate the magnetic activity of CoRoT-7 and use the results for a better understanding of the impact of magnetic activity on stellar RV variations. Methods. We derived the longitudinal distribution of active regions on CoRoT-7 from a maximum entropy spot model of the CoRoT lightcurve. Assuming that each active region consists of dark spots and bright faculae in a fixed proportion, we synthesized the expected RV variations. Results. Active regions are mainly located at three active longitudes that appear to migrate at different rates, probably as a consequence of surface differential rotation, for which a lower limit of ΔΩ/ Ω= 0.058 ± 0.017 is found. The synthesized activity-induced RV variations reproduce the amplitude of the observed RV curve and are used to study the impact of stellar activity on planetary detection. Conclusions. In spite of the non-simultaneous CoRoT and HARPS observations, our study confirms the validity of the method previously adopted to filter out RV variations induced by stellar activity. We find a false-alarm probability <10 −4 that the RV oscillations attributed to CoRoT-7b and CoRoT-7c are spurious effects of noise and activity. Additionally, our model suggests that other periodicities found in the observed RV curve of CoRoT-7 could be explained by active regions whose visibility is modulated by a differential stellar rotation with periods ranging from 23.6 to 27.6 days.

Hydrogen peroxide production by ion irradiation of thin water ice films

In this paper we present the results of new experiments on ion irradiation of water ice performed on thin films to study the synthesis of the hydrogen peroxide molecule and discuss the possibility of detecting it in icy mantles on interstellar grains. The used experimental technique has been in situ infrared spectroscopy. We have irradiated thin films (i.e. the ice thickness was smaller than the penetration depth of the used ion) with three different ions, namely 200 keV of H + and He + and 400 keV of Ar ++ . The experiments were carried out at temperatures of 16 and 77 K. We have found that hydrogen peroxide is produced by all of the different ions at both temperatures. The detection of such a molecule has been possible from the study of its infrared feature centered at about 2850 cm −1 (3.5 µm). The obtained results also show that the produced H2O2/H2O(%) ratio is greater for the heaviest ion (∼6% for the case of Ar ++ )a nd that H + is the ion that produces the smallest quantity (∼1%). These upper limits in the production of hydrogen peroxide constrain the quantity of H2O2 that can be formed after bombardment by cosmic particles on icy mantles of grains in the interstellar medium.

Ion irradiation experiments relevant to the physics of comets

Abstract We present the results of new experiments on some physical-chemical effects induced by fast ion colliding with solids of relevance for the physics of comets. In particular we have studied the transition from crystalline to amorphous water ice induced by keV ion irradiation at temperatures between 10 and 100 K. After ion-induced amorphization occurred, at low T, the samples have been heated and their crystallization at around 150 K has been studied. Our results are compared with those recently reported in the literature (Hudson and Moore, J. Phys. Chem.96, 6500, 1992). The production of molecular solids, polymer-like materials and amorphous carbon by irradiation of simple carbon-containing ices is discussed as well as some preliminary results on the changes in the sublimation rates of irradiated CO-ices. We also report on a set of experimental results obtained irradiating methanol and water-methanol mixtures. As a consequence of bombardment, different species form. Among these, the formation of CO, CH4 and CO2 is evident. The production of formaldehyde questionable is; upper limits are given. The ratios among different molecules have been evaluated as a function of the deposited energy. The results are compared with those obtained by UV irradiation of the same mixtures (Allamandola et al., Icarus76, 225, 1988). The experimental results are finally discussed in the light of their relevance to cometary physics.

Photospheric activity, rotation, and star-planet interaction of the planet-hosting star CoRoT-6

Context. The CoRoT satellite has recently discovered a hot Jupiter that transits across the disc of a F9 main-sequence star called CoRoT-6 with a period of 8.886 days. Aims. We model the photospheric activity of the star and use the maps of the active regions to study stellar differential rotation and the star-planet interaction. Methods. We apply a maximum entropy spot model to fit the optical modulation as observed by CoRoT during a uninterrupted interval of similar to 140 days. Photospheric active regions are assumed to consist of spots and faculae in a fixed proportion with solar-like contrasts. Results. Individual active regions have lifetimes up to 30-40 days. Most of them form and decay within five active longitudes whose different migration rates are attributed to the stellar differential rotation for which a lower limit of Delta Omega/Omega = 0.12 +/- 0.02 is obtained. Several active regions show a maximum of activity at a longitude lagging the subplanetary point by similar to 200 degrees with the probability of a chance occurrence being smaller than 1 percent. Conclusions. Our spot modelling indicates that the photospheric activity of CoRoT-6 could be partially modulated by some kind of star-planet magnetic interaction, while an interaction related to tides is highly unlikely because of the weakness of the tidal force.

Ion irradiation experiments relevant to cometary physics

During their stay in the Oort cloud (4.6 × 109 years), comets are subject to the flux of galactic cosmic rays. Experimental results on the chemical and physical changes induced by ion and electron irradiation of relevant materials have been recently reviewed with a view to their relevance for cometary astrophysics. In particular, the ability of ion irradiation of simple carbon-containing ices to produce complex refractory organic materials has been discussed. Here we discuss further experiments carried out in our laboratory whose results are relevant to cometary physics. Experiments on targets much thicker than the penetration range of irradiating ions give support to the hypothesis that the ion-produced cometary organic crust can “survive” gas ejection from deeper layers and be as old as the comet itself. A study of IR and Raman spectra obtained “in situ” before, during, and after irradiation of frozen benzene has clarified the processes producing, after long enough exposures, a tridimensional network of aromatic molecules linked together by linear chains. We call this material ion-produced hydrogenated amorphous carbon. Other experimental data demonstrate the transition from crystalline to amorphous water ice induced by ion irradiation at temperatures between 10 and 100 K. Thus the observation of amorphous ice cannot be considered, as it has been up to now, a definitive proof of its formation and permanence at low T.

The GAPS programme with HARPS-N at TNG - V. A comprehensive analysis of the XO-2 stellar and planetary systems

Aims. XO-2 is the first confirmed wide stellar binary system where the almost twin components XO-2N and XO-2S have planets, and it is a peculiar laboratory in which to investigate the diversity of planetary systems. This stimulated a detailed characterization study of the stellar and planetary components based on new observations. Methods. We collected high-resolution spectra with the HARPS-N spectrograph and multi-band light curves. Spectral analysis led to an accurate determination of the stellar atmospheric parameters and characterization of the stellar activity, and high-precision radial velocities of XO-2N were measured. We collected 14 transit light curves of XO-2Nb used to improve the transit parameters. Photometry provided accurate magnitude differences between the stars and a measure of their rotation periods. Results. The iron abundance of XO-2N was found to be +0.054 dex greater, within more than 3σ, than that of XO-2S. The existence of a longterm variation in the radial velocities of XO-2N is confirmed, and we detected a turnover with respect to previous measurements. We suggest the presence of a second massive companion in an outer orbit or the stellar activity cycle as possible causes of the observed acceleration. The latter explanation seems more plausible with the present dataset. We obtained an accurate value of the projected spin-orbit angle for the XO-2N system (λ = 7 ◦ ± 11 ◦ ), and estimated the real 3D spin-orbit angle (ψ = 27 +12 −27 degrees). We measured the XO-2 rotation periods, and found a value of P = 41.6 ± 1.1 days in the case of XO-2N, in excellent agreement with the predictions. The period of XO-2S appears shorter, with an ambiguity between 26 and 34.5 days that we cannot solve with the present dataset alone. The analysis of the stellar activity shows that XO-2N appears to be more active than the companion, perhaps because we sampled different phases of their activity cycle, or because of an interaction between XO-2N and its hot Jupiter that we could not confirm.