Search

We report an investigation of X-ray induced desorption of neutrals, cations and anions from CO ice. The desorption of neutral CO, by far the most abundant, is quantified and discussed within the context of its application to astrochemistry. The desorption of many different cations, including large cations up to the mass limit of the spectrometer, are observed. In contrast, the only desorbing anions detected are O$^-$ and C$^-$. The desorption mechanisms of all these species are discussed with the aid of their photodesorption spectrum. The evolution of the X-ray absorption spectrum shows significant chemical modifications of the ice upon irradiation, which along with the desorption of large cations gives a new insight into X-ray induced photochemistry in CO ice., Comment: Accepted in PCCP

Electronic excitations near the surface of water ice lead to the desorption of adsorbed molecules, through a so far debated mechanism. A systematic study of photon-induced indirect desorption, revealed by the spectral dependence of the desorption (7 to 13 eV), is conducted for Ar, Kr, N2, and CO adsorbed on H2O or D2O amorphous ices. The mass and isotopic dependence and the increase of intrinsic desorption efficiency with photon energy all point to a mechanism of desorption induced by collisions between adsorbates and energetic H or D atoms, produced by photodissociation of water. This constitutes a direct and unambiguous experimental demonstration of the mechanism of indirect desorption of weakly adsorbed species on water ice, and sheds new light on the possibility of this mechanism in other systems. It also has implications for the description of photon-induced desorption in astrochemical models., Comment: Supplemental Material available freely at https://journals.aps.org/prl/supplemental/10.1103/PhysRevLett.126.156001

Vacuum-UV (VUV) photodesorption from water-rich ice mantles coating interstellar grains is known to play an important role in the gas-to-ice ratio in star- and planet-forming regions. Quantitative photodesorption yields from water ice are crucial for astrochemical models. We aim to provide the first quantitative photon-energy dependent photodesorption yields from water ice in the VUV. This information is important to understand the photodesorption mechanisms and to account for the variation of the yields under interstellar irradiation conditions. Experiments have been performed on the DESIRS beamline at the SOLEIL synchrotron, delivering tunable VUV light, using the SPICES (Surface Processes and ICES) set-up. Compact amorphous solid water ice (H$_2$O and D$_2$O) has been irradiated from 7 to 13.5 eV. Quantitative yields have been obtained by detection in the gas phase with mass-spectrometry for sample temperatures ranging from 15 K to 100 K. Photodesorption spectra of H$_2$O (D$_2$O), OH (OD), H$_2$ (D$_2$) and O$_2$ peak around 9-10 eV and decrease at higher energies. Average photodesorption yields of intact water at 15 K are 5 $\times$ 10$^{-4}$ molecule/photon for H$_2$O and 5 $\times$ 10$^{-5}$ molecule/photon for D$_2$O over the 7-13.5 eV range. The strong isotopic effect can be explained by a differential chemical recombination between OH (OD) and H (D) photofragments originating from lower kinetic energy available for the OH photofragments upon direct water photodissociation and/or possibly by an electronic relaxation process. It is expected to contribute to water fractionation during the building-up of the ice grain mantles in molecular clouds and to favor OH-poor chemical environment in comet-formation regions of protoplanetary disks. The yields of all the detected species except OH (OD) are enhanced above (70 $\pm$10) K, suggesting an ice restructuration at this temperature., Comment: Submitted to A&A. In revision

Electron-stimulated desorption (ESD) of cryosorbed molecules on surfaces is a process of relevance to fields as varied as vacuum dynamics in accelerators and astrochemistry. While desorption from such molecular systems induced by keV electrons and fast ions has been extensively studied, the sub-keV electron regime is comparatively little known. We measured and quantified electron-stimulated desorption from molecular ice systems (layers of N$_2$, CO, CO$_2$, Ar and H$_2$O/D$_2$O condensed at cryogenic temperatures) in the 150-2000 eV electron energy range. In this regime stopping power is no longer sufficient to explain the electron energy dependence of ESD yields. We introduce the notion of desorption-relevant depth, which characterizes the transition between two energy deposition regimes near the surface. We then apply this notion to the different systems, showing how ESD in the sub-keV regime can for example reveal the differences in species diffusion in crystalline and porous amorphous CO$_2$ ices., Comment: The following article has been accepted by the Journal of Applied Physics. After it is published, it will be found at https://publishing.aip.org/resources/librarians/products/journals/

The understanding of complex and/or large vacuum systems operating at cryogenic temperatures requires a specific knowledge of the vacuum science at such temperatures. At room temperature, molecules with a low binding energy to a surface are not pumped. However, at cryogenic temperatures, their sojourn time is significantly increased, thanks to the temperature reduction, which allow a "cryopumping". This lecture gives an introduction to the field of cryogenic vacuum, discussing surface desorption, sticking probability, thermal transpiration, adsorption isotherms, vapour pressure of usual gases, industrial surfaces and roughness factors. These aspects are illustrated with the case of the Large Hardon Collider explaining its beam screen and its cryosorber, leaks and beam vacuum system modelling in a cryogenic environment. Finally, operation of cryogenic beam vacuum systems is discussed for LHC and other cryogenic machines., Comment: 34 pages, contribution to the CAS - CERN Accelerator School: Vacuum for Particle Accelerators, 6-16 June 2017, Glumsl\"ov, Sweden

Core-excitation of water ice releases many different molecules and ions in the gas phase. Studying these desorbed species and the underlying mechanisms can provide useful information on the effects of X-ray irradiation in ice. We report a detailed study of the X-ray induced desorption of a number of neutral, cationic and anionic species from amorphous solid water. We discuss the desorption mechanisms, and the relative contributions of Auger and secondary electrons (X-ray induced Electron Stimulated Desorption) and initial excitation (\rev{direct desorption}) as well as the role of photochemistry. Anions are shown to desorb not just through processes linked with secondary electrons but also through direct dissociation of the core-excited molecule. The desorption spectra of oxygen ions (O$^+$, OH$^+$, H$_2$O$^+$, O$^-$, OH$^-$) give a new perspective on their previously reported very low desorption yields for most types of irradiation of water, showing that they mostly originate from the dissociation of photoproducts such as H$_2$O$_2$., Comment: Accepted in Journal of Chemical Physics

Photon-stimulated desorption (PSD) is a process of interest for the two seemingly unrelated topics of accelerator vacuum dynamics and astrochemistry. Here we present an approach to studying PSD of interstellar ice analogs, i.e. condensed films of molecules of astrophysical interest at cryogenic temperatures, using synchrotron radiation. We present results obtained in the VUV range on various pure and layered ices, focusing on elucidating the desorption mechanisms, and results in the X-ray range for H$_2$O., Comment: Proceedings of the ECLOUD'18 6th workshop on electron-cloud effects (3-7 June 2018 La Biodola (Isola d'Elba) Italy). To be published as a CERN yellow report

Water is the main constituent of interstellar ices, and it plays a key role in the evolution of many regions of the interstellar medium, from molecular clouds to planet-forming disks. In cold regions of the ISM, water is expected to be completely frozen out onto the dust grains. Nonetheless, observations indicate the presence of cold water vapor, implying that non-thermal desorption mechanisms are at play. Photodesorption by UV photons has been proposed to explain these observations, with the support of extensive experimental and theoretical work on ice analogues. In contrast, photodesorption by X-rays, another viable mechanism, has been little studied. The potential of this process to desorb key molecules, such as water, intact rather than fragmented or ionised, remains unexplored. We experimentally investigated X-ray photodesorption from water ice, monitoring all desorbing species. We find that desorption of neutral water is efficient, while ion desorption is minor. We derive for the first time yields that can be implemented in astrochemical models. These results open up the possibility of taking into account the X-ray photodesorption process in the modelling of protoplanetary disks or X-ray dominated regions.

The study and quantification of UV photon-induced desorption of frozen molecules furthers our understanding of the chemical evolution of cold interstellar regions. Nitric oxide (NO) is an important intermediate species in both gas-phase and solid-phase chemical networks. In this work, we present quantitative measurements of the photodesorption of a pure NO ice.We used the tunable monochromatic synchrotron light of the DESIRS beamline of the SOLEIL facility near Paris to irradiate NO ices in the 6 - 13.6 eV range and measured desorption by quadrupole mass spectrometry.We find that NO photodesorption is very efficient, its yield being around 1e-2 molecule per incident photon for UV fields relevant to the diffuse and dense interstellar medium. We discuss the extrapolation of our results to an astrophysical context and we compare photodesorption of NO to previously studied molecules., Comment: A&A, Accepted

Chapter 12 in High-Luminosity Large Hadron Collider (HL-LHC) : Preliminary Design Report. The Large Hadron Collider (LHC) is one of the largest scientific instruments ever built. Since opening up a new energy frontier for exploration in 2010, it has gathered a global user community of about 7,000 scientists working in fundamental particle physics and the physics of hadronic matter at extreme temperature and density. To sustain and extend its discovery potential, the LHC will need a major upgrade in the 2020s. This will increase its luminosity (rate of collisions) by a factor of five beyond the original design value and the integrated luminosity (total collisions created) by a factor ten. The LHC is already a highly complex and exquisitely optimised machine so this upgrade must be carefully conceived and will require about ten years to implement. The new configuration, known as High Luminosity LHC (HL-LHC), will rely on a number of key innovations that push accelerator technology beyond its present limits. Among these are cutting-edge 11-12 tesla superconducting magnets, compact superconducting cavities for beam rotation with ultra-precise phase control, new technology and physical processes for beam collimation and 300 metre-long high-power superconducting links with negligible energy dissipation. The present document describes the technologies and components that will be used to realise the project and is intended to serve as the basis for the detailed engineering design of HL-LHC., Comment: 11 pages, chapter 12 in High-Luminosity Large Hadron Collider (HL-LHC) : Preliminary Design Report

With the advent of the space missions CoRoT and Kepler, it has become feasible to determine precise asteroseismic masses and ages for large samples of red-giant stars. In this paper, we present the CoRoGEE dataset -- obtained from CoRoT lightcurves for 606 red giant stars in two fields of the Galactic disc which have been co-observed for an ancillary project of APOGEE. We have used the Bayesian parameter estimation code PARAM to calculate distances, extinctions, masses, and ages for these stars in a homogeneous analysis, resulting in relative statistical uncertainties of $\sim2\%$ in distance, $\sim4\%$ in radius, $\sim9\%$ in mass and $\sim25\%$ in age. We also assess systematic age uncertainties due to different input physics and mass loss. We discuss the correlation between ages and chemical abundance patterns of field stars over a large radial range of the Milky Way's disc (5 kpc $

Among the known groups of pulsating stars, $\delta$ Sct stars are one of the least understood. Theoretical models do not predict the oscillation frequencies that observations reveal. Complete asteroseismic studies are necessary to improve these models and better understand the internal structure of these targets. We study the $\delta$ Sct star HD 41641 with the ultimate goal of understanding its oscillation pattern. The target was simultaneously observed by the CoRoT space telescope and the HARPS high-resolution spectrograph. The photometric data set was analyzed with the software package PERIOD04, while FAMIAS was used to analyze the line profile variations. The method of spectrum synthesis was used for spectroscopically determining the fundamental atmospheric parameters and individual chemical abundances. A total of 90 different frequencies was identified and analyzed. An unambiguous identification of the azimuthal order of the surface geometry could only be provided for the dominant p-mode, which was found to be a nonradial prograde mode with m = +1. Using $T_\mathrm{eff}$ and $\log g$, we estimated the mass, radius, and evolutionary stage of HD 41641. We find HD 41641 to be a moderately rotating, slightly evolved $\delta$ Sct star with subsolar overall atmospheric metal content and unexpected chemical peculiarities. HD 41641 is a pure $\delta$ Sct pulsator with p-mode frequencies in the range from 10 d$^{-1}$ to 20 d$^{-1}$. This pulsating star presents chemical signatures of an Ap star and rotational modulation due to surface inhomogeneities, which we consider indirect evidence of the presence of a magnetic field., Comment: 11 pages, 11 figures, accepted for publication in A&A

We study the distribution of the photometric rotation period (Prot), which is a direct measurement of the surface rotation at active latitudes, for three subsamples of Sun-like stars: one from CoRoT data and two from Kepler data. We identify the main populations of these samples and interpret their main biases specifically for a comparison with the solar Prot. Prot and variability amplitude (A) measurements were obtained from public CoRoT and Kepler catalogs combined with physical parameters. Because these samples are subject to selection effects, we computed synthetic samples with simulated biases to compare with observations, particularly around the location of the Sun in the HR diagram. Theoretical grids and empirical relations were used to combine physical parameters with Prot and A. Biases were simulated by performing cutoffs on the physical and rotational parameters in the same way as in each observed sample. A crucial cutoff is related with the detectability of the rotational modulation, which strongly depends on A. The synthetic samples explain the observed Prot distributions of Sun-like stars as having two main populations: one of young objects (group I, with ages younger than ~1 Gyr) and another of MS and evolved stars (group II, with ages older than ~1 Gyr). The proportions of groups I and II in relation to the total number of stars range within 64-84% and 16-36%, respectively. Hence, young objects abound in the distributions, producing the effect of observing a high number of short periods around the location of the Sun in the HR diagram. Differences in the Prot distributions between the CoRoT and Kepler Sun-like samples may be associated with different Galactic populations. Overall, the synthetic distribution around the solar period agrees with observations, which suggests that the solar rotation is normal with respect to Sun-like stars within the accuracy of current data., Comment: 13 pages, 8 figures, A&A accepted

A few Galactic classical Cepheids were observed in the programmes of space missions as Coriolis, MOST and Kepler. An appealing opportunity was to detect additional nonradial modes, thus opening the possibility to perform asteroseismic studies and making the pulsational content of Galactic Cepheids more similar to that of Magellanic Clouds ones. However, only hints of cycle-to-cycle variations were found, without any strict periodicity. In this context the potential of the CoRoT exoplanetary data base was not fully exploited despite the wide area covered on the Galactic plane. Therefore, we investigated all the candidate Cepheids pointed out by the automatic classification of the CoRoT curves. At the end we could identify seven bona-fide Cepheids. The light curves were investigated to remove some instrumental effects. The frequency analysis was particularly delicate since these small effects can be enhanced by the large amplitude, resulting in the presence of significant, but spurious, peaks in the power spectrum. Indeed, the careful evaluation of a very attracting peak in the spectra of CoRoT 0102618121, allowed us to certify its spurious origin. Once that the instrumental effects were properly removed, no additional mode was detected. On the other hand, cycle-to-cycle variations of the Fourier parameters were observed, but very small and always within 3 sigma. Among the seven Cepheids, there are two Pop. I first-overtone pulsators, four Pop. I fundamental mode pulsators, and one Pop. II star. The CoRoT colours allowed us to measure that times of maximum brightness occur a little earlier (about 0.01 period) at short wavelengths than at long ones., Comment: Accepted for publication in MNRAS. 14 pages, 12 figures, 4 tables. Light-curve solutions reported in Appendix A

We report the detection of a rare transiting brown dwarf with a mass of 59 M_Jup and radius of 1.1 R_Jup around the metal-rich, [Fe/H] = +0.44, G9V star CoRoT-33. The orbit is eccentric (e = 0.07) with a period of 5.82 d. The companion, CoRoT-33b, is thus a new member in the so-called brown dwarf desert. The orbital period is within 3% to a 3:2 resonance with the rotational period of the star. CoRoT-33b may be an important test case for tidal evolution studies. The true frequency of brown dwarfs close to their host stars (P < 10 d) is estimated to be approximately 0.2% which is about six times smaller than the frequency of hot Jupiters in the same period range. We suspect that the frequency of brown dwarfs declines faster with decreasing period than that of giant planets., Comment: 13 pages, 8 figures, accepted for publication in A&A

For 6 years the Convection, Rotation, and Planetary Transits (CoRoT) space mission has acquired photometric data from more than one hundred thousand point sources towards and directly opposite from the inner and outer regions of the Galaxy. The high temporal resolution of the CoRoT data combined with the wide time span of the observations has enabled the study of short and long time variations in unprecedented detail. From the initial sample of 2534 stars classified as M-giants in the CoRoT databasis, we selected 1428 targets that exhibit well defined variability, using visual inspection. The variability period and amplitude of C1 stars (stars having Teff < 4200 K) were computed using Lomb-Scargle and harmonic fit methods. The trends found in the V-I vs J-K color-color diagram are in agreement with standard empirical calibrations for M-giants. The sources located towards the inner regions of the Galaxy are distributed throughout the diagram while the majority of the stars towards the outer regions of the Galaxy are spread between the calibrations of M-giants and the predicted position for Carbon stars. The stars classified as supergiants follow a different sequence from the one found for giant stars. We also performed a KS test of the period and amplitude of stars towards the inner and outer regions of the Galaxy. We obtained a low probability that the two samples come from the same parent distribution. The observed behavior of the period-amplitude and period-Teff diagrams are, in general, in agreement with those found for Kepler sources and ground based photometry, with pulsation being the dominant cause responsible for the observed modulation. We also conclude that short-time variations on M-Giant stars do not exist orare very rare and the few cases we found are possibly related to biases or background stars., Comment: 11 pages, 6 figures

Context. The availability of asteroseismic constraints for a large sample of red giant stars from the CoRoT and Kepler missions paves the way for various statistical studies of the seismic properties of stellar populations. Aims. We use the first detailed spectroscopic study of 19 CoRoT red-giant stars (Morel et al 2014) to compare theoretical stellar evolution models to observations of the open cluster NGC 6633 and field stars. Methods. In order to explore the effects of rotation-induced mixing and thermohaline instability, we compare surface abundances of carbon isotopic ratio and lithium with stellar evolution predictions. These chemicals are sensitive to extra-mixing on the red-giant branch. Results. We estimate mass, radius, and distance for each star using the seismic constraints. We note that the Hipparcos and seismic distances are different. However, the uncertainties are such that this may not be significant. Although the seismic distances for the cluster members are self consistent they are somewhat larger than the Hipparcos distance. This is an issue that should be considered elsewhere. Models including thermohaline instability and rotation-induced mixing, together with the seismically determined masses can explain the chemical properties of red-giants targets. However, with this sample of stars we cannot perform stringent tests of the current stellar models. Tighter constraints on the physics of the models would require the measurement of the core and surface rotation rates, and of the period spacing of gravity-dominated mixed modes. A larger number of stars with longer times series, as provided by Kepler or expected with Plato, would help for ensemble asteroseismology., Comment: Accepted 03/05/2015

Context. We present the discovery of two transiting extrasolar planets by the satellite CoRoT. Aims. We aim at a characterization of the planetary bulk parameters, which allow us to further investigate the formation and evolution of the planetary systems and the main properties of the host stars. Methods. We used the transit light curve to characterize the planetary parameters relative to the stellar parameters. The analysis of HARPS spectra established the planetary nature of the detections, providing their masses. Further photometric and spectroscopic ground-based observations provided stellar parameters (log g,Teff,v sin i) to characterize the host stars. Our model takes the geometry of the transit to constrain the stellar density into account, which when linked to stellar evolutionary models, determines the bulk parameters of the star. Because of the asymmetric shape of the light curve of one of the planets, we had to include the possibility in our model that the stellar surface was not strictly spherical. Results. We present the planetary parameters of CoRoT-28b, a Jupiter-sized planet (mass 0.484+/-0.087MJup; radius 0.955+/-0.066RJup) orbiting an evolved star with an orbital period of 5.208 51 +/- 0.000 38 days, and CoRoT-29b, another Jupiter-sized planet (mass 0.85 +/- 0.20MJup; radius 0.90 +/- 0.16RJup) orbiting an oblate star with an orbital period of 2.850 570 +/- 0.000 006 days. The reason behind the asymmetry of the transit shape is not understood at this point. Conclusions. These two new planetary systems have very interesting properties and deserve further study, particularly in the case of the star CoRoT-29., Comment: 19 pages, 21 figures. Revised version to update affiliations and title, according to published version

The study of RR Lyrae stars has recently been invigorated thanks to the long, uninterrupted, ultra-precise time series data provided by the Kepler and CoRoT space telescopes. We give a brief overview of the new observational findings concentrating on the connection between period doubling and the Blazhko modulation, and the omnipresence of additional periodicities in all RR Lyrae subtypes, except for non-modulated RRab stars. Recent theoretical results demonstrate that if more than two modes are present in a nonlinear dynamical system such as a high-amplitude RR Lyrae star, the outcome is often an extremely intricate dynamical state. Thus, based on these discoveries, an underlying picture of complex dynamical interactions between modes is emerging which sheds new light on the century-old Blazhko-phenomenon, as well. New directions of theoretical efforts, like multi-dimensional hydrodynamical simulations, future space photometric missions and detailed spectroscopic investigations will pave the way towards a more complete understanding of the atmospheric and pulsation dynamics of these enigmatic touchstone objects., Comment: Proceedings of the CoRoT Symposium 3 / Kepler KASC-7 joint meeting, Toulouse, July 2014. To be published by EPJ Web of Conferences

The exploitation of the CoRoT treasure of stars observed in the exoplanetary field allowed the detection of a unusual triple-mode Cepheid in the Milky Way, CoRoT 0223989566. The two modes with the largest amplitudes and period ratio of 0.80 are identified with the first (P1=1.29 d) and second (P2=1.03 d) radial overtones. The third period, which has the smallest amplitude but able to produce combination terms with the other two, is the longest one (P3=1.89 d). The ratio of 0.68 between the first-overtone period and the third period is the unusual feature. Its identification with the fundamental radial or a nonradial mode is discussed with respect to similar cases in the Magellanic Clouds. In both cases the period triplet and the respective ratios make the star unique in our Galaxy. The distance derived from the period-luminosity relation and the galactic coordinates put CoRoT~0223989566 in the metal-rich environment of the "outer arm" of the Milky Way., Comment: Published as ApJ Letter