Results for "L. Fossati"

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Polarimetric StandardizationOct 09 2006The use of polarimetric techniques is nowadays widespread among solar and stellar astronomers. However, notwithstanding the recommandations that have often been made about the publication of polarimetric results in the astronomical literature, we are ... More
Accuracy of atmospheric parameters of FGK dwarfs determined by spectrum fittingNov 19 2015We performed extensive tests of the accuracy of atmospheric parameter determination for FGK stars based on the spectrum fitting procedure Spectroscopy Made Easy (SME). Our stellar sample consists of 13 objects, including the Sun, in the temperature range ... More
Spectral Energy Distributions of Gamma-ray BlazarsDec 09 1996Average Spectral Energy Distributions (SED) for different subgroups of blazars are derived from available homogeneous (but small) data sets, including the gamma-ray band. Comparing Flat Spectrum Radio Quasars (FSRQ) with BL Lacs extracted from radio (RBL) ... More
Understanding Exoplanet Atmospheres with UV Observations I: NUV and Blue/OpticalMar 21 2019Much of the focus of exoplanet atmosphere analysis in the coming decade will be atinfrared wavelengths, with the planned launches of the James Webb Space Telescope (JWST) and the Wide-Field Infrared Survey Telescope (WFIRST). However, without being placed ... More
Spectral Energy Distributions of 3C 279 revisited: BeppoSAX observations and variability modelsNov 27 2001We present the BeppoSAX observations of 3C 279 performed in 1997 January 13-23 simultaneously with gamma-ray pointings with EGRET on board CGRO and optical observations at the Torino Observatory (1997 January 11-18). ISO data close to this epoch are also ... More
Elemental abundances of HD 87240, member of the young open cluster NGC 3114Oct 10 2018We have determined the abundances of several chemical elements in the atmosphere of HD 87240, a member of the young open cluster NGC 3114. We have used the code ATLAS9 to compute a model atmosphere for HD 87240 for the effective temperature and surface ... More
Elemental Abundance Analysis of the Early Type Members of the Open Cluster M6: Preliminary ResultsJan 20 2014Differences in chemical composition among main sequence stars within a given cluster are probably due to differences in their masses and other effects such as radiative diffusion, magnetic field, rotation, mixing mechanisms, mass loss, accretion and multiplicity. ... More
On the consistency of magnetic field measurements of Ap stars: lessons learned from the FORS1 archiveNov 20 2014CONTEXT. The ESO archive of FORS1 spectropolarimetric observations may be used to create a homogeneous database of magnetic field measurements. However, no systematic comparison of FORS field measurements to those obtained with other instruments has been ... More
A bimodal correlation between host star chromospheric emission and the surface gravity of hot JupitersOct 15 2015The chromospheric activity index logR'HK of stars hosting transiting hot Jupiters appears to be correlated with the planets' surface gravity. One of the possible explanations is based on the presence of condensations of planetary evaporated material located ... More
Improved fundamental parameters and LTE abundances of the CoRoT solar-type pulsator HD49933May 19 2009The knowledge of accurate stellar parameters is a key stone in several fields of stellar astrophysics, such as asteroseismology and stellar evolution. Although the parameters can be derived both via spectroscopy and multicolor photometry, the obtained ... More
On the ultraviolet anomalies of the WASP-12 and HD 189733 systems: Trojan satellites as a plasma sourceMay 09 2016May 30 2016We suggest an additional possible plasma source to explain part of the phenomena observed for the transiting hot Jupiters WASP-12b and HD 189733b in their ultraviolet (UV) light curves. In the proposed scenario, material outgasses from the molten surface ... More
Progress in understanding Blazars from BeppoSAX observationsFeb 03 1999Results obtained with BeppoSAX observations of blazars within various collaborative programs are presented. The spectral similarity "paradigm", whereby the spectral energy distributions of blazars follow a sequence, leading to a unified view of the whole ... More
A new unifying model for X--ray and radio--selected BL LacsDec 09 1996We discuss alternative interpretations of the differences in the Spectral Energy Distributions (SEDs) of BL Lacs found in complete Radio or X--ray surveys. In order to explain the different properties of radio and X-ray selected within the assumption ... More
A theoretical unifying scheme for gamma-ray bright blazarsJul 30 1998The phenomenology of gamma-ray bright blazars can be accounted for by a sequence in the source power and intensity of the diffuse radiation field surrounding the relativistic jet. Correspondingly, the equilibrium particle distribution peaks at different ... More
Abundance analysis of seven delta Scuti StarsApr 15 2008The current knowledge of the abundance pattern in delta Scuti stars is based on the analysis of just a few field stars. We aim to determine the general chemical properties of the atmospheres of delta Scuti stars based on a statistically relevant sample ... More
Stellar magnetism through the polarized eyes of the FORS1 instrumentSep 23 2011During the last decade, the FORS1 instrument of the ESO Very Large Telescope has been used to obtain low resolution circular polarized spectra for about 500 stars, with the aim of measuring their mean longitudinal magnetic fields. Magnetic field estimates ... More
Stellar physics with high-resolution UV spectropolarimetryMar 15 2019Current burning issues in stellar physics, for both hot and cool stars, concern their magnetism. In hot stars, stable magnetic fields of fossil origin impact their stellar structure and circumstellar environment, with a likely major role in stellar evolution. ... More
Collective Evidence for Inverse Compton Emission from External Photons in High-Power BlazarsMar 22 2012May 03 2012We present the first collective evidence that Fermi-detected jets of high kinetic power (L_kin) are dominated by inverse Compton emission from upscattered external photons. Using a sample with a broad range in orientation angle, including radio galaxies ... More
Gamma-ray Clues to the Relativistic Jet DichotomyNov 28 2011Jan 26 2012In examining a select sample of over 200 blazars of known jet kinetic power (L_kin) and well-characterized SEDs, we found (Meyer et al., 2011) that Intermediate synchrotron-peaking (ISP) blazars may have lower gamma-ray output than high synchrotron-peaking ... More
Blue supergiants as descendants of magnetic main sequence starsSep 18 2015About 10$\%$ of the massive main sequence stars have recently been found to host a strong, large scale magnetic field. Both, the origin and the evolutionary consequences of these fields are largely unknown. We argue that these fields may be sufficiently ... More
Magnetic field measurements and their uncertainties: the FORS1 legacyDec 16 2011During the last decade, the FORS1 instrument of the ESO VLT has been extensively used to study stellar magnetism. A number of interesting discoveries of magnetic fields in several classes of stars have been announced, many of which obtained at a ~3 sigma ... More
Explaining the Praesepe blue straggler HD 73666Nov 10 2009The blue straggler phenomenon is not yet well explained by current theory; however, evolutionary models of star clusters call for a good knowledge of it. Here we try to understand the possible formation scenario of HD 73666, a blue straggler member of ... More
Average Spectral Energy Distributions of Blazars from Radio to Gamma-RaysJun 18 1997The average Spectral Energy Distributions (SED) of different classes of blazars from the radio to the gamma-ray band are studied adopting a "complete-sample" approach. The SED are globally similar, despite systematic differences in specific frequency ... More
ROSAT Observations of Blazars from a Polarized Radio Selected SampleDec 01 1994We have observed with ROSAT six blazars from the sample of 31 polarized objects constructed by Impey and Tapia (1988). Results of the spectral analysis in the ROSAT band of three objects, PKS 0301-243, PKS 1055+018 and PG 1424+240 are presented here and ... More
Breaking the Blazar Sequence: A New View of Radio Loud AGN UnificationMay 03 2012In recent work, we have identified two sub-populations of radio-loud AGN which appear to be distinguished by jet structure, where low-efficiency accreting systems produce `weak' jets which decelerate more rapidly than the `strong' jets of black holes ... More
Toward a New Paradigm for the Unification of Radio Loud AGN and its Connection to AccretionNov 21 2011We recently argued (Meyer 2011) that the collective properties of radio loud active galactic nuclei point to the existence of two families of sources, one of powerful sources with single velocity jets and one of weaker jets with significant velocity gradients ... More
The spectroscopic Hertzsprung-Russell diagram of hot massive stars in the SMCOct 10 2018We present a comprehensive stellar atmosphere analysis of 329 O- and B-type stars in the Small Magellanic Cloud (SMC) from the RIOTS4 survey. Using spectroscopically derived effective temperature (Teff) and surface gravities, we find that classical Be ... More
The FORS1 catalogue of stellar magnetic field measurementsAug 16 2015The FORS1 instrument on the ESO Very Large Telescope was used to obtain low-resolution circular polarised spectra of nearly a thousand different stars, with the aim of measuring their mean longitudinal magnetic fields. A catalogue of FORS1 magnetic measurements ... More
A comprehensive and critical re-analysis of FORS spectropolarimetric observations: the case of HD92207Feb 03 2015Stellar spectropolarimetry has become extremely popular during the last decade, and has led to major advances in our understanding of stellar magnetic fields and of their impact on stellar structure and evolution. Many important discoveries have been ... More
A Unifying View of the Spectral Energy Distributions of BlazarsApr 09 1998We collect data from the radio to the gamma-ray range for three complete samples of blazars: the Slew Survey and the 1Jy samples of BL Lacs and the 2Jy sample of Flat Spectrum Radio-Loud Quasars (FSRQs). The fraction of objects detected in gamma-rays ... More
From the Blazar Sequence to the Blazar Envelope: Revisiting the Relativistic Jet Dichotomy in Radio-loud AGNJul 26 2011We revisit the concept of a blazar sequence that relates the synchrotron peak frequency ({\nu}peak) in blazars with synchrotron peak luminosity (Lpeak, in {\nu}L{\nu}) using a large sample of radio-loud AGN. We present observational evidence that the ... More
Standard stars for linear polarizationOct 22 2006We present the analysis of the observations of standard stars for linear polarization obtained from 1999 to 2005 within the context of the calibration plan of the FORS1 instrument of the ESO VLT. We have considered observations carried out both in imaging ... More
Chemical abundance studies of CP stars in open clustersNov 22 2013In stellar astrophysics, the study of the atmospheres of early-type stars plays a very special role. The atmospheres of these stars display a variety of different phenomena, such as the presence of large magnetic fields, strong surface convection, pulsation, ... More
Detection of magnetic field in the B2 star $ρ$ Oph A with ESO FORS2Dec 03 2017Circumstantial evidence suggests that magnetism and enhanced X-ray emission are likely correlated in early B-type stars: similar fractions of them ($\sim$ 10 %) are strong and hard X-ray sources and possess strong magnetic fields. It is also known that ... More
Absorbing gas around the WASP-12 planetary systemMar 14 2013Near-UV observations of the planet host star WASP-12 uncovered the apparent absence of the normally conspicuous core emission of the Mg2 h&k resonance lines. This anomaly could be due either to (1) a lack of stellar activity, which would be unprecedented ... More
Correlation between the TeV and X-ray emission in high--energy peaked BL Lac objectsDec 16 2004We discuss the correlation between the evolution of the TeV emission and X-ray radiation observed in high-energy peaked BL Lac objects. We describe such a correlation by a simple power law. In the first part of this work we present correlations obtained ... More
Stellar wind induced soft X-ray emission from close-in exoplanetsMar 24 2015In this paper, we estimate the X-ray emission from close-in exoplanets. We show that the Solar/Stellar Wind Charge Exchange Mechanism (SWCX) which produces soft X-ray emission is very effective for hot Jupiters. In this mechanism, X-ray photons are emitted ... More
Regular frequency patterns in the young delta Scuti star HD 261711 observed by the CoRoT and MOST satellitesFeb 14 2013We concentrate on an asteroseismological study of HD 261711, a rather hot delta Scuti type pulsating member of the young open cluster NGC 2264 located at the blue border of the instability region. HD 261711 was discovered to be a pre-main sequence delta ... More
The influence of stellar flare on dynamical state of the atmosphere of exoplanet HD 209458bJul 06 2018Sep 04 2018By applying an one-dimensional aeronomic model of the upper atmosphere of the close-in giant planet HD 209458b, we study the reaction of the planetary atmosphere to an additional heating caused by the influence of a stellar flare. It is shown that the ... More
Looking for a connection between the Am phenomenon and hybrid delta Sct - gamma Dor pulsation: a determination of the fundamental parameters and abundances of HD 114839 and BD +18 4914Sep 13 2011Delta Sct - gamma Dor hybrids pulsate simultaneously in p- and g-modes, which carry information on the structure of the envelope as well as to the core. Hence they are key objects for investigating A and F type stars with asteroseismic techniques. An ... More
A spectroscopic study of the open cluster NGC 6250Dec 17 2016We present the chemical abundance analysis of 19 upper main-sequence stars of the young open cluster NGC 6250 (log t ~ 7.42 yr). This work is part of a project aimed at setting observational constraints on the theory of atomic diffusion in stellar photospheres, ... More
A measurement of the z = 0 UV background from H$α$ fluorescenceFeb 15 2017Mar 04 2017We report the detection of extended Halpha emission from the tip of the HI disk of the nearby edge-on galaxy UGC 7321, observed with the Multi Unit Spectroscopic Explorer (MUSE) instrument at the Very Large Telescope. The Halpha surface brightness fades ... More
XUV Radiation from A-stars: Implications for Ultra-hot JupitersNov 13 2018Extremely irradiated, close-in planets to early-type stars might be prone to strong atmospheric escape. We review the literature showing that X-ray-to-optical measurements indicate that for intermediate-mass stars (IMS) cooler than $\approx$8250 K, the ... More
A Spectroscopic Study of DD UMa: Ursa Major Group Member and Candidate for BRITEJul 25 2011The Ursa Major group is a nearby stellar supercluster which, while not gravitationally bound, is defined by co-moving members. DD UMa is a $\delta$ Scuti star whose membership in the Ursa Major group is unclear. The objective of this study is to confirm ... More
Bright low mass eclipsing binary candidates observed by STEREOSep 10 2012Observations from the Heliospheric Imagers (HI-1) on both the STEREO spacecraft have been analysed to search for bright low mass eclipsing binaries (EBs) and potential brown dwarf transits and to determine the radii of the companions. A total of 9 EB ... More
The effect of rotation on the abundances of the chemical elements of the A-type stars in the Praesepe clusterMar 25 2008We study how chemical abundances of late B-, A- and early F-type stars evolve with time, and we search for correlations between the abundance of chemical elements and other stellar parameters, such as effective temperature and Vsini. We have observed ... More
The spectroscopic Hertzsprung-Russell diagram of Galactic massive starsOct 13 2014The distribution of stars in the Hertzsprung-Russell diagram narrates their evolutionary history and directly assesses their properties. Placing stars in this diagram however requires the knowledge of their distances and interstellar extinctions, which ... More
BeppoSAX Observations of the TeV Blazar Mkn 421Apr 09 1998The blazar Mkn 421 has been observed, as part of the AO1 Core Program, five times from 2 to 7 May 1997. In the LECS+MECS energy band the spectrum shows convex curvature, well represented by a broken power--law. Flux variability (more than a factor 2) ... More
3D Gas Dynamic Simulation of the Interaction Between the Exoplanet WASP-12b and Its Host StarDec 12 2012Dec 13 2012HST transit observations in the near-UV performed in 2009 made WASP-12b one of the most "mysterious" exoplanets; the system presents an early-ingress, which can be explained by the presence of optically thick matter located ahead of the planet at a distance ... More
Halpha Imaging of the Herschel Reference Survey. The star formation properties of a volume-limited, K-band-selected sample of nearby late-type galaxiesApr 08 2015We present new Halpha+[NII] imaging data of late-type galaxies in the Herschel Reference Survey aimed at studying the star formation properties of a K-band-selected, volume-limited sample of nearby galaxies. The Halpha+[NII] data are corrected for [NII] ... More
Searching for links between magnetic fields and stellar evolution. II. The evolution of magnetic fields as revealed by observations of Ap stars in open clusters and associationsJun 03 2007The evolution of magnetic fields in Ap stars during the main sequence phase is presently mostly unconstrained by observation because of the difficulty of assigning accurate ages to known field Ap stars. We are carrying out a large survey of magnetic fields ... More
Confronting uncertainties in stellar physics II. exploring differences in main-sequence stellar evolution tracksJan 12 2016We assess the systematic uncertainties in stellar evolutionary calculations for low- to intermediate-mass, main-sequence stars. We compare published stellar tracks from several different evolution codes with our own tracks computed using the stellar codes ... More
A photometric study of chemically peculiar stars with the STEREO satellites. II. Non-magnetic chemically peculiar starsNov 07 2012We have analysed the photometric data obtained with the STEREO spacecraft for 558 non-magnetic chemically peculiar (CP) stars to search for rotational and pulsational variability. Applying the Lomb-Scargle and the phase dispersion minimisation methods, ... More
The chemical abundance analysis of normal early A- and late B-type starsJun 29 2009Modern spectroscopy of early-type stars often aims at studying complex physical phenomena. Comparatively less attention is paid to identifying and studying the "normal" A- and B-type stars and testing how the basic atomic parameters and standard spectral ... More
The nature of p-modes and granulation in HD 49933 observed by CoRoTNov 28 2008Dec 15 2009Context: Recent observations of HD49933 by the space-photometric mission CoRoT provide photometric evidence of solar type oscillations in a star other than our Sun. The first published reduction, analysis, and interpretation of the CoRoT data yielded ... More
On the incidence of weak magnetic fields in DA white dwarfsAug 17 2012Context: About 10% of white dwarfs have magnetic fields with strength in the range between about 10^5 and 3x10^8 G. It is not known whether the remaining white dwarfs are not magnetic, or if they have a magnetic field too weak to be detected with the ... More
Far-UV spectroscopy of the planet-hosting star WASP-13: high-energy irradiance, distance, age, planetary mass-loss rate, and circumstellar environmentDec 02 2015Several transiting hot Jupiters orbit relatively inactive main-sequence stars. For some of those, the logR'HK activity parameter lies below the basal level (-5.1). Two explanations have been proposed so far: (i) the planet affects the stellar dynamo, ... More
A probable pre-main sequence chemically peculiar star in the open cluster Stock 16Jun 20 2014We used the Ultraviolet and Visual Echelle Spectrograph of the ESO-Very Large Telescope to obtain a high resolution and high signal-to-noise ratio spectrum of Stock 16-12, an early-type star which previous Delta-a photometric observations suggest being ... More
Investigating the possible connection between lambda Bootis stars and intermediate Population II type starsJun 16 2014Jun 24 2014The lambda Bootis (LB) stars are located at the upper main sequence of the H-R diagram and exhibit a peculiar abundance pattern. The light elements (C, N, O, and S) present solar abundances whereas all other elements are moderately to strongly underabundant. ... More
The shocking transit of WASP-12b: Modelling the observed early ingress in the near ultravioletJun 15 2011Near ultraviolet observations of WASP-12b have revealed an early ingress compared to the optical transit lightcurve. This has been interpreted as due to the presence of a magnetospheric bow shock which forms when the relative velocity of the planetary ... More
A new method of measuring center-of-mass velocities of radially pulsating stars from high-resolution spectroscopyNov 15 2017We present a radial velocity analysis of 20 solar neighborhood RR Lyrae and 3 Population II Cepheids variables. We obtained high-resolution, moderate-to-high signal-to-noise ratio spectra for most stars and obtained spectra were covering different pulsation ... More
BONNSAI: correlated stellar observables in Bayesian methodsOct 25 2016In an era of large spectroscopic surveys of stars and big data, sophisticated statistical methods become more and more important in order to infer fundamental stellar parameters such as mass and age. Bayesian techniques are powerful methods because they ... More
Swift UVOT near-UV transit observations of WASP-121 bJan 29 2019Close-in gas planets are subject to continuous photoevaporation that can erode their volatile envelopes. Today, ongoing mass loss has been confirmed in a few individual systems via transit observations in the ultraviolet spectral range. We demonstrate ... More
A photometric long-term study of CP stars in open clustersDec 01 2010Photometric variability of chemically peculiar (CP) stars of the upper main sequence is closely connected to their local stellar magnetic field and their rotational period. Long term investigations, as presented here, help us to identify possible stellar ... More
SMARTS optical and infrared monitoring of 12 gamma-ray bright blazarsJan 20 2012We present multiwavelength data for twelve blazars observed from 2008-2010 as part of an ongoing optical-infrared photometric monitoring project. Sources were selected to be bright, southern (dec < 20 deg) blazars observed by the Fermi Gamma-Ray Space ... More
Young planets under extreme UV irradiation. I. Upper atmosphere modelling of the young exoplanet K2-33bDec 21 2017The K2-33 planetary system hosts one transiting ~5 R_E planet orbiting the young M-type host star. The planet's mass is still unknown, with an estimated upper limit of 5.4 M_J. The extreme youth of the system (<20 Myr) gives the unprecedented opportunity ... More
SALT observations of the Chromospheric Activity of Transiting Planet Hosts: Mass Loss and Star Planet InteractionsDec 06 2016We measured the chromospheric activity of the four hot Jupiter hosts WASP-43, WASP-51/HAT-P-30, WASP-72 & WASP-103 to search for anomalous values caused by the close-in companions. The Mount Wilson Ca II H&K S-index was calculated for each star using ... More
Scientific Report on Low Energy Absorption Features Detected by BeppoSAX LECS in Bright Blazar TargetsApr 27 1998Apr 28 1998The apparency of low energy absorption features in Blazar LECS spectra has been reported during the early phase of the BeppoSAX mission (e.g. by Grandi et al. 1997 for 3C~273 SVP data; Giommi et al. 1997 for PKS 2155--304 SVP data), with data reduction ... More
The Riemann Problem for Hyperbolic Equations under a Nonconvex Flux with Two Inflection PointsFeb 24 2014This report addresses the solution of Riemann problems for hyperbolic equations when the nonlinear characteristic fields loose their genuine nonlinearity. In this context, exact solvers for nonconvex 1D Riemann problems are developed. First a scalar conservation ... More
An In-Depth Spectroscopic Analysis of RR Lyr Variations over the Pulsation CycleOct 16 2014The stellar parameters of RR Lyrae stars vary considerably over a pulsation cycle, and their determination is crucial for stellar modelling. We present a detailed spectroscopic analysis of the pulsating star RR Lyr, the prototype of its class, over a ... More
Suppressed Far-UV Stellar Activity and Low Planetary Mass Loss in the WASP-18 SystemFeb 03 2018WASP-18 hosts a massive, very close-in Jupiter-like planet. Despite its young age ($<$1 Gyr), the star presents an anomalously low stellar activity level: the measured logR'$_{\rm HK}$ activity parameter lies slightly below the basal level; there is no ... More
Supermassive Hot Jupiters Provide More Favourable Conditions for the Generation of Radio Emission via the Cyclotron Maser Instability - A Case Study Based on Tau Bootis bJul 31 2018We investigate under which conditions supermassive hot Jupiters can sustain source regions for radio emission, and whether this emission could propagate to an observer outside the system. We study Tau Bootis b-like planets (a supermassive hot Jupiter ... More
The quenching of the star formation activity in cluster galaxiesSep 02 2016We study the star formation quenching mechanism in cluster galaxies by fitting the SED of the Herschel Reference Survey, a complete volume-limited K-band-selected sample of nearby galaxies including objects in different density regions, from the core ... More
Magnetic Field and Atmospheric Chemical Abundances of the Magnetic Ap Star HD 318107Oct 13 2011New spectra have been obtained with the ESPaDOnS spectropolarimeter supplemented with unpolarised spectra from the ESO UVES, UVES-FLAMES, and HARPS spectrographs of the very peculiar large-field magnetic Ap star HD 318107, a member of the open cluster ... More
A photometric study of chemically peculiar stars with the STEREO satellites. I. Magnetic chemically peculiar starsOct 28 2011About 10% of upper main sequence stars are characterised by the presence of chemical peculiarities, often found together with a structured magnetic field. The atmospheres of most of those chemically peculiar stars present surface spots, leading to photometric ... More
Late stages of the evolution of A-type stars on the main sequence: comparison between observed chemical abundances and diffusion models for 8 Am stars of the Praesepe clusterOct 02 2007Aims. We aim to provide observational constraints on diffusion models that predict peculiar chemical abundances in the atmospheres of Am stars. We also intend to check if chemical peculiarities and slow rotation can be explained by the presence of a weak ... More
The accuracy of stellar atmospheric parameter determinations: a case study with HD 32115 and HD 37594Jun 22 2011We present detailed parameter determinations of two chemically normal late A-type stars, HD 32115 and HD 37594, to uncover the reasons behind large discrepancies between two previous analyses of these stars performed with a semi-automatic procedure and ... More
A detailed spectroscopic analysis of the open cluster NGC 5460Dec 14 2010Within the context of a large project aimed at studying early F-, A- and late B-type stars we present the abundance analysis of the photospheres of 21 members of the open cluster NGC 5460, an intermediate age cluster (logt ~ 8.2) previously unstudied ... More
Similarity of the Optical-IR and Gamma-Ray Time Variability of Fermi BlazarsJan 20 2011Mar 07 2012We present the time variability properties of a sample of six blazars, AO 0235+164, 3C 273, 3C 279, PKS 1510-089, PKS 2155-304, and 3C 454.3, at optical-IR as well as gamma-ray energies. These observations were carried out as a part of the Yale/SMARTS ... More
gamma Doradus pulsation in two pre-main sequence stars discovered by CoRoTJan 06 2013Pulsations in pre-main sequence stars have been discovered several times within the last years. But nearly all of these pulsators are of delta Scuti-type. gamma Doradus-type pulsation in young stars has been predicted by theory, but lack observational ... More
Detection of a magnetic field in three old and inactive solar-like planet-hosting starsFeb 04 2013Our understanding of magnetic fields in late-type stars is strongly driven by what we know of the solar magnetic field. For this reason, it is crucial to understand how typical the solar dynamo is. To do this we need to compare the solar magnetic field ... More
The Role of N2 as a Geo-Biosignature for the Detection and Characterization of Earth-like HabitatsApr 26 2019Since the Archean, N2 has been a major atmospheric constituent in Earth's atmosphere. Nitrogen is an essential element in the building blocks of life, therefore the geobiological nitrogen cycle is a fundamental factor in the long term evolution of both ... More
CUTE Data Simulator and Reduction PipelineJul 20 2018The Colorado Ultraviolet Transit Experiment (CUTE) is a 6U NASA CubeSat carrying a low-resolution (R ~3000), near-ultraviolet (255 - 330nm) spectrograph fed by a rectangular primary Cassegrain. CUTE, is planned for launch in spring 2020 and it will monitor ... More
Understanding Exoplanet Atmospheres with UV Observations II: The Far UV and Atmospheric EscapeMar 26 2019Much of the focus of exoplanet atmosphere analysis in the coming decade will be at infrared wavelengths, with the planned launches of the James Webb Space Telescope (JWST) and the Wide-Field Infrared Survey Telescope (WFIRST). However, without being placed ... More
A detailed spectropolarimetric analysis of the planet hosting star WASP-12Jul 19 2010The knowledge of accurate stellar parameters is paramount in several fields of stellar astrophysics, particularly in the study of extrasolar planets, where often the star is the only visible component and therefore used to infer the planet's fundamental ... More
New Extreme Synchrotron BL Lac ObjectsJan 24 2000Feb 01 2000We report on the BeppoSAX observations of four "extreme" BL Lacs, selected to have high synchrotron peak frequencies. All have been detected also in the PDS band. For 1ES 0120+340, PKS 0548-322 and H 2356-309 the spectrum is well fitted by a convex broken ... More
X-ray Rapid Variability of MKN 421Jul 29 1999We present a detailed Cross Correlation analysis of the light curves of the X-ray bright BL Lac object Mkn 421 observed with $Beppo$SAX period 1997-1998. Monte Carlo simulations are performed in order to estimate the uncertainties. We found that in one ... More
Extreme synchrotron BL Lac objectsMar 21 2001Mar 30 2001We performed an observational program with the X-ray satellite BeppoSAX to study objects with extreme synchrotron peak frequencies (nu_peak > 1 keV). Of the seven sources observed, four showed peak frequencies in the range 1-5 keV, while one (1ES 1426+428) ... More
Spectral Evolution of PKS 2155-304 observed with BeppoSAX during an Active Gamma-ray PhaseMar 22 1999We present the results of BeppoSAX observations of PKS 2155-304 during an intense gamma-ray flare. The source was in a high X-ray state. A temporal analysis of the data reveals a tendency of the amplitude of variations to increase with energy, and the ... More
Relationship between low and high frequencies in Delta Scuti stars: Photometric Kepler and spectroscopic analyses of the rapid rotator KIC 8054146Sep 21 2012Two years of Kepler data of KIC 8054146 (delta Sct/gamma Dor hybrid) revealed 349 statistically significant frequencies between 0.54 and 191.36 c/d (6.3 microHz to 2.21 mHz). The 117 low frequencies cluster in specific frequency bands, but do not show ... More
X-ray Emission of Mkn 421: New Clues From Its Spectral Evolution. II. Spectral Analysis and Physical ConstraintsMay 03 2000Mkn 421 was repeatedly observed with BeppoSAX in 1997-1998. The source showed a very rich phenomenology, with remarkable spectral variability. This is the second of two papers presenting the results of a thorough temporal and spectral analysis of all ... More
Looking for High Energy Peaked BlazarsJul 03 2000Blazars can be classified on the basis of their overall Spectral Energy Distribution (SED). BL Lac objects are usually divided in LBL or HBL (Low or High energy peaked BL Lacs), according to the peak frequency of the synchrotron emission, if in the optical ... More
B fields in OB stars (BOB): FORS2 spectropolarimetric follow-up of the two rare rigidly rotating magnetosphere stars HD23478 and HD345439May 10 2015Massive B-type stars with strong magnetic fields and fast rotation are very rare and provide a mystery for theories of both star formation and magnetic field evolution. Only two such stars, called sigma Ori E analogs, were previously known. Recently, ... More
Spectral Energy Distributions of Flat Spectrum Radio Quasars observed with BeppoSAXJul 08 2002We report the BeppoSAX observations of 6 Flat Spectrum Radio Quasars. Three of them have a clear detection up to 100 keV with the PDS instrument. For 4 objects the X-ray spectrum is satisfactorily fitted by a power-law continuum with Galactic absorption. ... More
Four Years Monitoring of Blazar PKS 2155-304 with BeppoSAX: Probing the Dynamics of the JetFeb 20 2002PKS 2155--304 is one of the brightest blazars in the X-ray band. It was repeatedly monitored with BeppoSax during three long campaigns of about 2 days each in November of 1996, 1997 and 1999. The source underwent different states of intensity and was ... More
X-ray Emission of Mkn 421: New Clues From Its Spectral Evolution. I. Temporal AnalysisMay 03 2000Mkn 421 was repeatedly observed with BeppoSAX in 1997-1998. This is the first of two papers where we present the results of a thorough temporal and spectral analysis of all the data available to us, focusing in particular on the flare of April 1998, which ... More
BeppoSAX Observations of PKS 2155-304 during an active Gamma-ray StateAug 18 1998PKS 2155-304 was observed with BeppoSAX in November 1997 for 64 ksec (total elapsed time 33.5 hours) and, for the first time, simultaneously in gamma-rays with EGRET on board the Compton Gamma Ray Observatory and with the ground based TeV telescope CANGAROO, ... More
Far-Ultraviolet Activity Levels of F, G, K, and M dwarf Exoplanet Host StarsSep 19 2018We present a survey of far-ultraviolet (FUV; 1150 - 1450 Ang) emission line spectra from 71 planet-hosting and 33 non-planet-hosting F, G, K, and M dwarfs with the goals of characterizing their range of FUV activity levels, calibrating the FUV activity ... More
Effect of stellar wind induced magnetic fields on planetary obstacles of non-magnetized hot JupitersAug 04 2017We investigate the interaction between the magnetized stellar wind plasma and the partially ionized hydrodynamic hydrogen outflow from the escaping upper atmosphere of non- or weakly magnetized hot Jupiters. We use the well-studied hot Jupiter HD 209458b ... More
The role of bars in quenching star formation from z = 3 to the present epoch. Halpha3: an Halpha imaging survey of HI selected galaxies from ALFALFA, VIMay 28 2015Jun 05 2015A growing body of evidence indicates that the star formation rate per unit stellar mass (sSFR) decreases with increasing mass in normal "main-sequence" star forming galaxies. Many processes have been advocated as responsible for such a trend (also known ... More