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Perger M.,Institute Of Ciencies Of Lespai Csic Ieec | Garcia-Piquer A.,Institute Of Ciencies Of Lespai Csic Ieec | Ribas I.,Institute Of Ciencies Of Lespai Csic Ieec | Morales J.C.,Institute Of Ciencies Of Lespai Csic Ieec | And 36 more authors.
Astronomy and Astrophysics | Year: 2017

Context. The distribution of exoplanets around low-mass stars is still not well understood. Such stars, however, present an excellent opportunity for reaching down to the rocky and habitable planet domains. The number of current detections used for statistical purposes remains relatively modest and different surveys, using both photometry and precise radial velocities, are searching for planets around M dwarfs. Aims. Our HARPS-N red dwarf exoplanet survey is aimed at the detection of new planets around a sample of 78 selected stars, together with the subsequent characterization of their activity properties. Here we investigate the survey performance and strategy. Methods. From 2700 observed spectra, we compare the radial velocity determinations of the HARPS-N DRS pipeline and the HARPS-TERRA code, calculate the mean activity jitter level, evaluate the planet detection expectations, and address the general question of how to define the strategy of spectroscopic surveys in order to be most efficient in the detection of planets. Results. We find that the HARPS-TERRA radial velocities show less scatter and we calculate a mean activity jitter of 2.3 m s-1 for our sample. For a general radial velocity survey with limited observing time, the number of observations per star is key for the detection efficiency. In the case of an early M-type target sample, we conclude that approximately 50 observations per star with exposure times of 900 s and precisions of approximately 1 ms-1 maximizes the number of planet detections. © ESO, 2017.


Bonomo A.S.,National institute for astrophysics | Sozzetti A.,National institute for astrophysics | Lovis C.,Observatoire de Geneva | Malavolta L.,University of Padua | And 36 more authors.
Astronomy and Astrophysics | Year: 2014

We characterize the planetary system Kepler-101 by performing a combined differential evolution Markov chain Monte Carlo analysis of Kepler data and forty radial velocities obtained with the HARPS-N spectrograph. This system was previously validated and is composed of a hot super-Neptune, Kepler-101b, and an Earth-sized planet, Kepler-101c. These two planets orbit the slightly evolved and metal-rich G-type star in 3.49 and 6.03 days, respectively. With mass Mp = 51.1-4.7 + 5.1 M⊕, radius Rp = 5.77-0.79 + 0.85 R⊕, and density ρp = 1.45-0.48 + 0.83 g cm-3, Kepler-101b is the first fully characterized super-Neptune, and its density suggests that heavy elements make up a significant fraction of its interior; more than 60% of its total mass. Kepler-101c has a radius of 1.25-0.17 + 0.19 R⊕, which implies the absence of any H/He envelope, but its mass could not be determined because of the relative faintness of the parent star for highly precise radial-velocity measurements (Kp = 13.8) and the limited number of radial velocities. The 1σ upper limit, Mp< 3.8 M⊕, excludes a pure iron composition with a probability of 68.3%. The architecture of the planetary system Kepler-101 - containing a close-in giant planet and an outer Earth-sized planet with a period ratio slightly larger than the 3:2 resonance - is certainly of interest for scenarios of planet formation and evolution. This system does not follow thepreviously reported trend that the larger planet has the longer period in the majority of Kepler systems of planet pairs with at least one Neptune-sized or larger planet. © 2014 ESO.


Dressing C.D.,Harvard - Smithsonian Center for Astrophysics | Charbonneau D.,Harvard - Smithsonian Center for Astrophysics | Dumusque X.,Harvard - Smithsonian Center for Astrophysics | Gettel S.,Harvard - Smithsonian Center for Astrophysics | And 36 more authors.
Astrophysical Journal | Year: 2015

Kepler-93b is a 1.478 ± 0.019 R ⊙ planet with a 4.7 day period around a bright (V = 10.2), astroseismically characterized host star with a mass of 0.911 ± 0.033 M ⊙ and a radius of 0.919 ± 0.011 R ⊙. Based on 86 radial velocity observations obtained with the HARPS-N spectrograph on the Telescopio Nazionale Galileo and 32 archival Keck/HIRES observations, we present a precise mass estimate of 4.02 ± 0.68 M ⊙. The corresponding high density of 6.88 ± 1.18 g cm-3 is consistent with a rocky composition of primarily iron and magnesium silicate. We compare Kepler-93b to other dense planets with well-constrained parameters and find that between 1 and 6 M ⊙, all dense planets including the Earth and Venus are well-described by the same fixed ratio of iron to magnesium silicate. There are as of yet no examples of such planets with masses >6 M ⊙. All known planets in this mass regime have lower densities requiring significant fractions of volatiles or H/He gas. We also constrain the mass and period of the outer companion in the Kepler-93 system from the long-term radial velocity trend and archival adaptive optics images. As the sample of dense planets with well-constrained masses and radii continues to grow, we will be able to test whether the fixed compositional model found for the seven dense planets considered in this paper extends to the full population of 1-6 M⊙ planets. © 2015. The American Astronomical Society. All rights reserved.


Vanderburg A.,Harvard - Smithsonian Center for Astrophysics | Montet B.T.,Harvard - Smithsonian Center for Astrophysics | Montet B.T.,California Institute of Technology | Johnson J.A.,Harvard - Smithsonian Center for Astrophysics | And 47 more authors.
Astrophysical Journal | Year: 2015

We report the first planet discovery from the two-wheeled Kepler (K2) mission: HIP 116454 b. The host star HIP 116454 is a bright (V = 10.1, K = 8.0) K1 dwarf with high proper motion and a parallax-based distance of 55.2 ± 5.4 pc. Based on high-resolution optical spectroscopy, we find that the host star is metal-poor with [Fe/H] = -0.16 ± 0.08 and has a radius R∗= 0.716 ± 0.024 R⊙ and mass M∗= 0.775 ± 0.027 M⊙. The star was observed by the Kepler spacecraft during its Two-Wheeled Concept Engineering Test in 2014 February. During the 9 days of observations, K2 observed a single transit event. Using a new K2 photometric analysis technique, we are able to correct small telescope drifts and recover the observed transit at high confidence, corresponding to a planetary radius of Rp = 2.53 ± 0.18 R⊕. Radial velocity observations with the HARPS-N spectrograph reveal a 11.82 ± 1.33 M⊕ planet in a 9.1 day orbit, consistent with the transit depth, duration, and ephemeris. Follow-up photometric measurements from the MOST satellite confirm the transit observed in the K2 photometry and provide a refined ephemeris, making HIP 116454 b amenable for future follow-up observations of this latest addition to the growing population of transiting super-Earths around nearby, bright stars. ©2015. The American Astronomical Society. All rights reserved.


Affer L.,National institute for astrophysics | Micela G.,National institute for astrophysics | Damasso M.,National institute for astrophysics | Perger M.,Institute Of Ciencies Of Lespai Csic Ieec | And 34 more authors.
Astronomy and Astrophysics | Year: 2016

Context. Many efforts are currently made to detect Earth-like planets around low-mass stars in almost every extra-solar planet search. M dwarfs are considered ideal targets for Doppler radial velocity searches because their low masses and luminosities make low-mass planets orbiting in these stars' habitable zones more easily detectable than those around higher mass stars. Nonetheless, the frequency statistics of low-mass planets hosted by low-mass stars remains poorly constrained. Aims. Our M-dwarf radial velocity monitoring with HARPS-N within the collaboration between the Global architectures of Planetary Systems (GAPS) project, the Institut de Ciències de l'Espai/CSIC-IEEC (ICE) and the Instituto de Astrofísica de Canarias (IAC) can provide a major contribution to the widening of the current statistics through the in-depth analysis of accurate radial velocity observations in a narrow range of spectral sub-types (79 stars, between dM0 to dM3). Spectral accuracy will enable us to reach the precision needed to detect small planets with a few Earth masses. Our survey will contribute to the surveys devoted to the search for planets around M-dwarfs, mainly focused on the M-dwarf population of the northern emisphere, for which we will provide an estimate of the planet occurrence. Methods. We present here a long-duration radial velocity monitoring of the M1 dwarf star GJ 3998 with HARPS-N to identify periodic signals in the data. Almost simultaneous photometric observations were carried out within the APACHE and EXORAP programs to characterize the stellar activity and to distinguish those due to activity and to the presence of planetary companions from the periodic signals. We ran a Markov chain Monte Carlo simulation and used a Bayesian model selection to determine the number of planets in this system, to estimate their orbital parameters and minimum mass, and to properly treat the activity noise. Results. The radial velocities have a dispersion in excess of their internal errors due to at least four superimposed signals with periods of 30.7, 13.7, 42.5, and 2.65 days. Our data are well described by a two-planet Keplerian (13.7 d and 2.65 d) and a fit with two sinusoidal functions (stellar activity, 30.7 d and 42.5 d). The analysis of spectral indexes based on Ca II H & K and Hα lines demonstrates that the periods of 30.7 and 42.5 days are due to chromospheric inhomogeneities modulated by stellar rotation and differential rotation. This result is supported by photometry and is consistent with the results on differential rotation of M stars obtained with Kepler. The shorter periods of 13.74 ± 0.02 d and 2.6498 ± 0.0008 d are well explained with the presence of two planets, with masses of at least 6.26-0.76 +0.79 M⊕ and 2.47 ± 0.27 M⊕ and distances of 0.089 AU and 0.029 AU from the host, respectively. © ESO, 2016.


Dumusque X.,Harvard - Smithsonian Center for Astrophysics | Glenday A.,Harvard - Smithsonian Center for Astrophysics | Phillips D.F.,Harvard - Smithsonian Center for Astrophysics | Buchschacher N.,Observatoire de Geneva | And 16 more authors.
Astrophysical Journal Letters | Year: 2015

Radial velocity (RV) perturbations induced by stellar surface inhomogeneities including spots, plages and granules currently limit the detection of Earth-twins using Doppler spectroscopy. Such stellar noise is poorly understood for stars other than the Sun because their surface is unresolved. In particular, the effects of stellar surface inhomogeneities on observed stellar radial velocities are extremely difficult to characterize, and thus developing optimal correction techniques to extract true stellar radial velocities is extremely challenging. In this paper, we present preliminary results of a solar telescope built to feed full-disk sunlight into the HARPS-N spectrograph, which is in turn calibrated with an astro-comb. This setup enables long-term observation of the Sun as a star with state-of-the-art sensitivity to RV changes. Over seven days of observing in 2014, we show an average 50 cm s-1 RV rms over a few hours of observation. After correcting observed radial velocities for spot and plage perturbations using full-disk photometry of the Sun, we lower by a factor of two the weekly RV rms to 60 cm s-1. The solar telescope is now entering routine operation, and will observe the Sun every clear day for several hours. We will use these radial velocities combined with data from solar satellites to improve our understanding of stellar noise and develop optimal correction methods. If successful, these new methods should enable the detection of Venus over the next two to three years, thus demonstrating the possibility of detecting Earth-twins around other solar-like stars using the RV technique. © 2015. The American Astronomical Society. All rights reserved..


Pariani G.,National institute for astrophysics | Briguglio R.,National institute for astrophysics | Xompero M.,National institute for astrophysics | Riccardi A.,National institute for astrophysics | And 11 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

A particular example of meter class flat mirrors is the adaptive M4 Unit of E-ELT, a deformable six petals mirror of 2.4m in diameter. We studied different approaches to the calibration and certification of M4, in a trade-off between stitching and full aperture measurements. Possibilities to test the mirror with a macro-stitching concept, both in normal and grazing incidence have been considered. Approaches reported in the literature, as the Ritchey-Common or the external Fizeau, and different beam expander setups, varying the collimating mirror and the nulling system, both on-axis and off-axis, have been deeply studied to understand performances and sensitivities to fabrication errors, alignment errors and environmental effects. © 2014 SPIE.


Oliva E.,National institute for astrophysics | Origlia L.,National institute for astrophysics | Scuderi S.,National institute for astrophysics | Benatti S.,National institute for astrophysics | And 18 more authors.
Astronomy and Astrophysics | Year: 2015

Aims. Determining the intensity of lines and continuum airglow emission in the H-band is important for the design of faint-object infrared spectrographs. Existing spectra at low or medium resolution cannot disentangle the true sky continuum from instrumental effects (e.g. diffuse light in the wings of strong lines). We aim to obtain, for the first time, a high-resolution infrared spectrum that is deep enough to set significant constraints on the continuum emission between the lines in the H-band. Methods. During the second commissioning run of the GIANO high-resolution infrared spectrograph at La Palma Observatory, we pointed the instrument directly at the sky and obtained a deep spectrum that extends from 0.97 to 2.4 μm. Results. The spectrum shows about 1500 emission lines, a factor of two more than in previous works. Of these, 80% are identified as OH transitions; half of these are from highly excited molecules (hot-OH component) that are not included in the OH airglow emission models normally used for astronomical applications. The other lines are attributable to O2 or unidentified. Several of the faint lines are in spectral regions that were previously believed to be free of line emission. The continuum in the H-band is marginally detected at a level of about 300 photons/m2/s/arcsec2/μm, equivalent to 20.1 AB-mag/arcsec2. The observed spectrum and the list of observed sky lines are published at the CDS. Conclusions. Our measurements indicate that the sky continuum in the H-band could be even darker than previously believed. However, the myriad of airglow emission lines severely limits the spectral ranges where very low background can be effectively achieved with low- or medium-resolution spectrographs. We identify a few spectral bands that could still remain quite dark at the resolving power foreseen for VLT-MOONS (R ≃ 6600). © ESO, 2015.

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