arXiv subjects

G. Bruno

Publications and source records attributed to G. Bruno.

At least 127 records · Page 7Linked to original sources

arXiv2016

Disentangling planetary and stellar activity features in the CoRoT-2 light curve

[Abridged] Context. Stellar activity is an important source of systematic errors and uncertainties in the characterization of exoplanets. Most of the techniques used to correct for this activity focus on an ad hoc data reduction. Aims. We have developed a software for the combined fit of transits and stellar activity features in high-precision long-duration photometry. Our aim is to take advantage of the modelling to derive correct stellar and planetary parameters, even in the case of strong stellar activity. Methods. We use an analytic approach to model the light curve. The code KSint, modified by adding the evolution of active regions, is implemented into our Bayesian modelling package PASTIS. The code is then applied to the light curve of CoRoT-2. The light curve is divided in segments to reduce the number of free parameters needed by the fit. We perform a Markov chain Monte Carlo analysis in two ways. In the first, we perform a global and independent modelling of each segment of the light curve, transits are not normalized and are fitted together with the activity features, and occulted features are taken into account during the transit fit. In the second, we normalize the transits with a model of the non-occulted activity features, and then we apply a standard transit fit, which does not take the occulted features into account. Results. Our model recovers the activity features coverage of the stellar surface and different rotation periods for different features. We find variations in the transit parameters of different segments and show that they are likely due to the division applied to the light curve. Neglecting stellar activity or even only bright spots while normalizing the transits yields a $\sim 1.2σ$ larger and $2.3σ$ smaller transit depth, respectively. The stellar density also presents up to $2.5σ$ differences depending on the normalization technique...

astro-ph.EP↗

arXiv2016

DARWIN: towards the ultimate dark matter detector

DARk matter WImp search with liquid xenoN (DARWIN) will be an experiment for the direct detection of dark matter using a multi-ton liquid xenon time projection chamber at its core. Its primary goal will be to explore the experimentally accessible parameter space for Weakly Interacting Massive Particles (WIMPs) in a wide mass-range, until neutrino interactions with the target become an irreducible background. The prompt scintillation light and the charge signals induced by particle interactions in the xenon will be observed by VUV sensitive, ultra-low background photosensors. Besides its excellent sensitivity to WIMPs above a mass of 5 GeV/c2, such a detector with its large mass, low-energy threshold and ultra-low background level will also be sensitive to other rare interactions. It will search for solar axions, galactic axion-like particles and the neutrinoless double-beta decay of 136-Xe, as well as measure the low-energy solar neutrino flux with <1% precision, observe coherent neutrino-nucleus interactions, and detect galactic supernovae. We present the concept of the DARWIN detector and discuss its physics reach, the main sources of backgrounds and the ongoing detector design and R&D efforts.

astro-ph.IM↗

arXiv2016

Physics reach of the XENON1T dark matter experiment

The XENON1T experiment is currently in the commissioning phase at the Laboratori Nazionali del Gran Sasso, Italy. In this article we study the experiment's expected sensitivity to the spin-independent WIMP-nucleon interaction cross section, based on Monte Carlo predictions of the electronic and nuclear recoil backgrounds. The total electronic recoil background in $1$ tonne fiducial volume and ($1$, $12$) keV electronic recoil equivalent energy region, before applying any selection to discriminate between electronic and nuclear recoils, is $(1.80 \pm 0.15) \cdot 10^{-4}$ ($\rm{kg} \cdot day \cdot keV)^{-1}$, mainly due to the decay of $^{222}\rm{Rn}$ daughters inside the xenon target. The nuclear recoil background in the corresponding nuclear recoil equivalent energy region ($4$, $50$) keV, is composed of $(0.6 \pm 0.1)$ ($\rm{t} \cdot y)^{-1}$ from radiogenic neutrons, $(1.8 \pm 0.3) \cdot 10^{-2}$ ($\rm{t} \cdot y)^{-1}$ from coherent scattering of neutrinos, and less than $0.01$ ($\rm{t} \cdot y)^{-1}$ from muon-induced neutrons. The sensitivity of XENON1T is calculated with the Profile Likelihood Ratio method, after converting the deposited energy of electronic and nuclear recoils into the scintillation and ionization signals seen in the detector. We take into account the systematic uncertainties on the photon and electron emission model, and on the estimation of the backgrounds, treated as nuisance parameters. The main contribution comes from the relative scintillation efficiency $\mathcal{L}_\mathrm{eff}$, which affects both the signal from WIMPs and the nuclear recoil backgrounds. After a $2$ y measurement in $1$ t fiducial volume, the sensitivity reaches a minimum cross section of $1.6 \cdot 10^{-47}$ cm$^2$ at m$_χ$=$50$ GeV/$c^2$.

physics.ins-det↗

arXiv2015

SOPHIE velocimetry of Kepler transit candidates XVII. The physical properties of giant exoplanets within 400 days of period

While giant extrasolar planets have been studied for more than two decades now, there are still some open questions such as their dominant formation and migration process, as well as their atmospheric evolution in different stellar environments. In this paper, we study a sample of giant transiting exoplanets detected by the Kepler telescope with orbital periods up to 400 days. We first defined a sample of 129 giant-planet candidates that we followed up with the SOPHIE spectrograph (OHP, France) in a 6-year radial velocity campaign. This allow us to unveil the nature of these candidates and to measure a false-positive rate of 54.6 +/- 6.5 % for giant-planet candidates orbiting within 400 days of period. Based on a sample of confirmed or likely planets, we then derive the occurrence rates of giant planets in different ranges of orbital periods. The overall occurrence rate of giant planets within 400 days is 4.6 +/- 0.6 %. We recover, for the first time in the Kepler data, the different populations of giant planets reported by radial velocity surveys. Comparing these rates with other yields, we find that the occurrence rate of giant planets is lower only for hot jupiters but not for the longer period planets. We also derive a first measurement on the occurrence rate of brown dwarfs in the brown-dwarf desert with a value of 0.29 +/- 0.17 %. Finally, we discuss the physical properties of the giant planets in our sample. We confirm that giant planets receiving a moderate irradiation are not inflated but we find that they are in average smaller than predicted by formation and evolution models. In this regime of low-irradiated giant planets, we find a possible correlation between their bulk density and the Iron abundance of the host star, which needs more detections to be confirmed.

astro-ph.EP↗

arXiv2015

Photo-dynamical mass determination of the multi-planetary system K2-19

K2-19 is the second multi-planetary system discovered with K2 observations. The system is composed of two Neptune size planets close to the 3:2 mean-motion resonance. To better characterise the system we obtained two additional transit observations of K2-19b and five additional radial velocity observations. These were combined with K2 data and fitted simultaneously with the system dynamics (photo-dynamical model) which increases the precision of the transit time measurements. The higher transit time precision allows us to detect the chopping signal of the dynamic interaction of the planets that in turn permits to uniquely characterise the system. Although the reflex motion of the star was not detected, dynamic modelling of the system allowed us to derive planetary masses of $M_b= 44 \pm 12\, M_{\oplus}$ and $M_c = 15.9 \pm 7.0\, M_{\oplus}$ for the inner and the outer planets respectively, leading to densities close to Uranus. We also show that our method allows the derivation of mass ratios using only the 80 days of observations during the first campaign of K2.

astro-ph.EP↗

arXiv2015

Absolute masses and radii determination in multiplanetary systems without stellar models

The masses and radii of extrasolar planets are key observables for understanding their interior, formation and evolution. While transit photometry and Doppler spectroscopy are used to measure the radii and masses respectively of planets relative to those of their host star, estimates for the true values of these quantities rely on theoretical models of the host star which are known to suffer from systematic differences with observations. When a system is composed of more than two bodies, extra information is contained in the transit photometry and radial velocity data. Velocity information (finite speed-of-light, Doppler) is needed to break the Newtonian $MR^{-3}$ degeneracy. We performed a photodynamical modelling of the two-planet transiting system Kepler-117 using all photometric and spectroscopic data available. We demonstrate how absolute masses and radii of single-star planetary systems can be obtained without resorting to stellar models. Limited by the precision of available radial velocities (38 $ms^{-1}$), we achieve accuracies of 20 per cent in the radii and 70 per cent in the masses, while simulated 1 $ms^{-1}$ precision radial velocities lower these to 1 per cent for the radii and 2 per cent for the masses. Since transiting multi-planet systems are common, this technique can be used to measure precisely the mass and radius of a large sample of stars and planets. We anticipate these measurements will become common when the TESS and PLATO mission provide high-precision light curves of a large sample of bright stars. These determinations will improve our knowledge about stars and planets, and provide strong constraints on theoretical models.

astro-ph.EP↗

arXiv2015

Search for Event Rate Modulation in XENON100 Electronic Recoil Data

We have searched for periodic variations of the electronic recoil event rate in the (2-6) keV energy range recorded between February 2011 and March 2012 with the XENON100 detector, adding up to 224.6 live days in total. Following a detailed study to establish the stability of the detector and its background contributions during this run, we performed an un-binned profile likelihood analysis to identify any periodicity up to 500 days. We find a global significance of less than 1 sigma for all periods suggesting no statistically significant modulation in the data. While the local significance for an annual modulation is 2.8 sigma, the analysis of a multiple-scatter control sample and the phase of the modulation disfavor a dark matter interpretation. The DAMA/LIBRA annual modulation interpreted as a dark matter signature with axial-vector coupling of WIMPs to electrons is excluded at 4.8 sigma.

astro-ph.CO↗

arXiv2015

Exclusion of Leptophilic Dark Matter Models using XENON100 Electronic Recoil Data

Laboratory experiments searching for galactic dark matter particles scattering off nuclei have so far not been able to establish a discovery. We use data from the XENON100 experiment to search for dark matter interacting with electrons. With no evidence for a signal above the low background of our experiment, we exclude a variety of representative dark matter models that would induce electronic recoils. For axial-vector couplings to electrons, we exclude cross-sections above 6x10^(-35) cm^2 for particle masses of m_chi = 2 GeV/c^2. Independent of the dark matter halo, we exclude leptophilic models as explanation for the long-standing DAMA/LIBRA signal, such as couplings to electrons through axial-vector interactions at a 4.4 sigma confidence level, mirror dark matter at 3.6 sigma, and luminous dark matter at 4.6 sigma.

astro-ph.CO↗

arXiv2015

Implication for the core collapse supernova rate from 21 years of data of the Large Volume Detector

The Large Volume Detector (LVD) has been continuously taking data since 1992 at the INFN Gran Sasso National Laboratory. LVD is sensitive to neutrino bursts from gravitational stellar collapses with full detection probability over the Galaxy. We have searched for neutrino bursts in LVD data taken in 7335 days of operation. No evidence of neutrino signals has been found between June 1992 and December 2013. The 90% C.L. upper limit on the rate of core-collapse and failed supernova explosions out to distances of 25 kpc is found to be 0.114/y.

astro-ph.HE↗

arXiv2015

Graphene-based perfect optical absorbers harnessing guided mode resonances

We numerically and experimentally investigate graphene-based optical absorbers that exploit guided mode resonances (GMRs) achieving perfect absorption over a bandwidth of few nanometers (over the visible and near-infrared ranges) with a 40-fold increase of the monolayer graphene absorption. We analyze the influence of the geometrical parameters on the absorption rate and the angular response for oblique incidence. Finally, we experimentally verify the theoretical predictions in a one-dimensional, dielectric grating and placing it near either a metallic or a dielectric mirror.

physics.optics↗

arXiv2015

Lowering the radioactivity of the photomultiplier tubes for the XENON1T dark matter experiment

The low-background, VUV-sensitive 3-inch diameter photomultiplier tube R11410 has been developed by Hamamatsu for dark matter direct detection experiments using liquid xenon as the target material. We present the results from the joint effort between the XENON collaboration and the Hamamatsu company to produce a highly radio-pure photosensor (version R11410-21) for the XENON1T dark matter experiment. After introducing the photosensor and its components, we show the methods and results of the radioactive contamination measurements of the individual materials employed in the photomultiplier production. We then discuss the adopted strategies to reduce the radioactivity of the various PMT versions. Finally, we detail the results from screening 216 tubes with ultra-low background germanium detectors, as well as their implications for the expected electronic and nuclear recoil background of the XENON1T experiment.

astro-ph.IM↗

arXiv2015

Conceptual design and simulation of a water Cherenkov muon veto for the XENON1T experiment

XENON is a dark matter direct detection project, consisting of a time projection chamber (TPC) filled with liquid xenon as detection medium. The construction of the next generation detector, XENON1T, is presently taking place at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. It aims at a sensitivity to spin-independent cross sections of $2 \cdot 10^{-47} ~ \mathrm{cm}^{\mathrm{2}}$ for WIMP masses around 50 GeV/c$^{2}$, which requires a background reduction by two orders of magnitude compared to XENON100, the current generation detector. An active system that is able to tag muons and muon-induced backgrounds is critical for this goal. A water Cherenkov detector of $\sim$10 m height and diameter has been therefore developed, equipped with 8 inch photomultipliers and cladded by a reflective foil. We present the design and optimization study for this detector, which has been carried out with a series of Monte Carlo simulations. The muon veto will reach very high detection efficiencies for muons ($>99.5%$) and showers of secondary particles from muon interactions in the rock ($>70%$). Similar efficiencies will be obtained for XENONnT, the upgrade of XENON1T, which will later improve the WIMP sensitivity by another order of magnitude. With the Cherenkov water shield studied here, the background from muon-induced neutrons in XENON1T is negligible.

astro-ph.IM↗

arXiv2015

Measurement of cosmic muon charge ratio with the Large Volume Detector

The charge ratio ${k \equiv μ^+/μ^-}$ for atmospheric muons has been measured using Large Volume Detector (LVD) in the INFN Gran Sasso National Laboratory, Italy (minimal depth is 3000 m w.e.). To reach this depth muons should have the energy at the sea level greater than 1.3 TeV. The muon charge ratio was defined using the number of the decays of stopping positive muons in the LVD iron structure and the decays of positive and negative muons in scintillator. We have obtained the value of the muon charge ratio ${k}$ ${= 1.26 \pm 0.04(stat) \pm 0.11(sys)}$.

hep-ex↗

arXiv2015

Improved parameters of seven Kepler giant companions characterized with SOPHIE and HARPS-N

Radial-velocity observations of Kepler candidates obtained with the SOPHIE and HARPS-N spectrographs have permitted unveiling the nature of the five giant planets Kepler-41b, Kepler-43b, Kepler-44b, Kepler-74b, and Kepler-75b, the massive companion Kepler-39b, and the brown dwarf KOI-205b. These companions were previously characterized with long-cadence (LC) Kepler data. Here we aim at refining the parameters of these transiting systems by i) modelling the published radial velocities (RV) and Kepler short-cadence (SC) data that provide a much better sampling of the transits, ii) performing new spectral analyses of the SOPHIE and ESPaDOnS spectra, and iii) improving stellar rotation periods hence stellar age estimates through gyrochronology, when possible. Posterior distributions of the system parameters were derived with a differential evolution Markov chain Monte Carlo approach. Our main results are as follows: a) Kepler-41b is significantly larger and less dense than previously found because a lower orbital inclination is favoured by SC data. This also affects the determination of the geometric albedo that is lower than previously derived: Ag < 0.135; b) Kepler-44b is moderately smaller and denser than reported in the discovery paper; c) good agreement was achieved with published Kepler-43, Kepler-75, and KOI-205 system parameters, although the host stars Kepler-75 and KOI-205 were found to be slightly richer in metals and hotter, respectively; d) the previously reported non-zero eccentricities of Kepler-39b and Kepler-74b might be spurious. If their orbits were circular, the two companions would be smaller and denser than in the eccentric case. The radius of Kepler-39b is still larger than predicted by theoretical isochrones. Its parent star is hotter and richer in metals than previously determined. [ABRIDGED]

astro-ph.EP↗

arXiv2015

SOPHIE velocimetry of Kepler transit candidates XIV. A joint photometric, spectroscopic, and dynamical analysis of the Kepler-117 system

As part of our follow-up campaign of Kepler planets, we observed Kepler-117 with the SOPHIE spectrograph at the Observatoire de Haute-Provence. This F8-type star hosts two transiting planets in non-resonant orbits. The planets, Kepler-117 b and c, have orbital periods $\simeq 18.8$ and $\simeq 50.8$ days, and show transit-timing variations (TTVs) of several minutes. We performed a combined Markov chain Monte Carlo (MCMC) fit on transits, radial velocities, and stellar parameters to constrain the characteristics of the system. We included the fit of the TTVs in the MCMC by modeling them with dynamical simulations. In this way, consistent posterior distributions were drawn for the system parameters. According to our analysis, planets b and c have notably different masses ($0.094 \pm 0.033$ and $1.84 \pm 0.18$ M$_{\rm J}$) and low orbital eccentricities ($0.0493 \pm 0.0062$ and $0.0323 \pm 0.0033$). The uncertainties on the derived parameters are strongly reduced if the fit of the TTVs is included in the combined MCMC. The TTVs allow measuring the mass of planet b, although its radial velocity amplitude is poorly constrained. Finally, we checked that the best solution is dynamically stable.

astro-ph.EP↗

arXiv2015

SOPHIE velocimetry of Kepler transit candidates. XV. KOI-614b, KOI-206b, and KOI-680b: a massive warm Jupiter orbiting a G0 metallic dwarf and two highly inflated planets with a distant companion around evolved F-type stars

We report the validation and characterization of three new transiting exoplanets using SOPHIE radial velocities: KOI-614b, KOI-206b, and KOI-680b. KOI-614b has a mass of $2.86\pm0.35~{\rm M_{Jup}}$ and a radius of $1.13^{+0.26}_{-0.18}~{\rm R_{Jup}}$, and it orbits a G0, metallic ([Fe/H]=$0.35\pm0.15$) dwarf in 12.9 days. Its mass and radius are familiar and compatible with standard planetary evolution models, so it is one of the few known transiting planets in this mass range to have an orbital period over ten days. With an equilibrium temperature of $T_{eq}=1000 \pm 45$ K, this places KOI-614b at the transition between what is usually referred to as "hot" and "warm" Jupiters. KOI-206b has a mass of $2.82\pm 0.52~{\rm M_{Jup}}$ and a radius of $1.45\pm0.16~{\rm R_{Jup}}$, and it orbits a slightly evolved F7-type star in a 5.3-day orbit. It is a massive inflated hot Jupiter that is particularly challenging for planetary models because it requires unusually large amounts of additional dissipated energy in the planet. On the other hand, KOI-680b has a much lower mass of $0.84\pm0.15~{\rm M_{Jup}}$ and requires less extra-dissipation to explain its uncommonly large radius of $1.99\pm0.18~{\rm R_{Jup}}$. It is one of the biggest transiting planets characterized so far, and it orbits a subgiant F9-star well on its way to the red giant stage, with an orbital period of 8.6 days. With host stars of masses of $1.46\pm0.17~M_{\odot}$ and $1.54 \pm 0.09~M_{\odot}$, respectively, KOI-206b, and KOI-680b are interesting objects for theories of formation and survival of short-period planets around stars more massive than the Sun. For those two targets, we also find signs of a possible distant additional companion in the system.

astro-ph.EP↗

arXiv2014

SOPHIE velocimetry of Kepler transit candidates. XIII. KOI-189 B and KOI-686 B: two very low-mass stars in long-period orbits

We present the radial-velocity follow-up of two Kepler planetary transiting candidates (KOI-189 and KOI-686) carried out with the SOPHIE spectrograph at the Observatoire de Haute Provence. These data promptly discard these objects as viable planet candidates and show that the transiting objects are in the regime of very low-mass stars, where a strong discrepancy between observations and models persists for the mass and radius parameters. By combining the SOPHIE spectra with the Kepler light curve and photometric measurements found in the literature, we obtain a full characterization of the transiting companions, their orbits, and their host stars. The two companions are in significantly eccentric orbits with relatively long periods (30 days and 52.5 days), which makes them suitable objects for a comparison with theoretical models, since the effects invoked to understand the discrepancy with observations are weaker for these orbital distances. KOI-189 B has a mass M = 0.0745 +/- 0.0033 Msun and a radius R = 0.1025 +/- 0.0024 Rsun. The density of KOI-189 B is significantly lower than expected from theoretical models for a system of its age. We explore possible explanations for this difference. KOI-189 B is the smallest hydrogen-burning star with such a precise determination of its fundamental parameters. KOI-686 B is larger and more massive (M = 0.0915 +/- 0.0043 Msun; R = 0.1201 +/- 0.0033 Rsun), and its position in the mass-radius diagram agrees well with theoretical expectations.

astro-ph.SR↗

arXiv2014

Characterization of the four new transiting planets KOI-188b, KOI-195b, KOI-192b, and KOI-830b

The characterization of four new transiting extrasolar planets is presented here. KOI-188b and KOI-195b are bloated hot Saturns, with orbital periods of 3.8 and 3.2 days, and masses of 0.25 and 0.34 M_Jup. They are located in the low-mass range of known transiting, giant planets. KOI-192b has a similar mass (0.29 M_Jup) but a longer orbital period of 10.3 days. This places it in a domain where only a few planets are known. KOI-830b, finally, with a mass of 1.27 M_Jup and a period of 3.5 days, is a typical hot Jupiter. The four planets have radii of 0.98, 1.09, 1.2, and 1.08 R_Jup, respectively. We detected no significant eccentricity in any of the systems, while the accuracy of our data does not rule out possible moderate eccentricities. The four objects were first identified by the Kepler Team as promising candidates from the photometry of the Kepler satellite. We establish here their planetary nature thanks to the radial velocity follow-up we secured with the HARPS-N spectrograph at the Telescopio Nazionale Galileo. The combined analyses of the datasets allow us to fully characterize the four planetary systems. These new objects increase the number of well-characterized exoplanets for statistics, and provide new targets for individual follow-up studies. The pre-screening we performed with the SOPHIE spectrograph at the Observatoire de Haute-Provence as part of that study also allowed us to conclude that a fifth candidate, KOI-219.01, is not a planet but is instead a false positive.

astro-ph.EP↗