0000000000053397
AUTHOR
Rafael Rebolo
The HADES RV Programme with HARPS-N@TNG. III. Flux-flux and activity-rotation relationships of early-M dwarfs
(Abridged) Understanding stellar activity in M dwarfs is crucial for the physics of stellar atmospheres as well as for ongoing radial velocity exoplanet programmes. Despite the increasing interest in M dwarfs, our knowledge of the chromospheres of these stars is far from being complete. We aim to test whether the relations between activity, rotation, and stellar parameters and flux-flux relationships also hold for early-M dwarfs on the main-sequence. We analyse in an homogeneous and coherent way a well defined sample of 71 late-K/early-M dwarfs that are currently being observed in the framework of the HArps-n red Dwarf Exoplanet Survey (HADES). Rotational velocities are derived using the cr…
The Baryon Oscillation Spectroscopic Survey of SDSS-III
The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large-scale structure. BOSS uses 1.5 million luminous galaxies as faint as i = 19.9 over 10,000 deg(2) to measure BAO to redshifts z < 0.7. Observations of neutral hydrogen in the Ly alpha forest in more than 150,000 quasar spectra (g < 22) will constrain BAO over the redshift range 2.15 < z < 3.5. Early results from BOSS include the first detection of the large-scale three-dimensional clustering of the Ly alpha forest and a strong detection from the Data R…
HADES RV Programme with HARPS-N at TNG. IV. Time resolved analysis of the Ca II H&K and Hα chromospheric emission of low-activity early-type M dwarfs
Context. M dwarfs are prime targets for current and future planet search programs, particularly those focused on the detection and characterization of rocky planets in the habitable zone. In this context, understanding their magnetic activity is important for two main reasons: it affects our ability to detect small planets and it plays a key role in the characterization of the stellar environment. Aims: We analyze observations of the Ca II H&K and Hα lines as diagnostics of chromospheric activity for low-activity early-type M dwarfs. Methods: We analyze the time series of spectra of 71 early-type M dwarfs collected in the framework of the HADES project for planet search purposes. The HARPS-…
Radio emission in ultracool dwarfs: the nearby substellar triple system VHS 1256$-$1257
Aims. With the purpose of investigating the radio emission of new ultracool objects, we carried out a targeted search in the recently discovered system VHS J125601.92-125723.9 (hereafter VHS 1256-1257); this system is composed by an equal-mass M7.5 binary and a L7 low-mass substellar object located at only 15.8 pc. Methods. We observed in phase-reference mode the system VHS 1256-1257 with the Karl G. Jansky Very Large Array at X band and L band and with the European VLBI Network at L band in several epochs during 2015 and 2016. Results. We discovered radio emission at X band spatially coincident with the equal-mass M7.5 binary with a flux density of 60 μJy. We determined a spectral index α …
A giant exoplanet orbiting a very-low-mass star challenges planet formation models
Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. Dynamical models show that the high eccentricity is most likely due to planet-planet interactions. We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories, and that it puts con…
ESPRESSO highlights the binary nature of the ultra-metal-poor giant HE 0107-5240
Context. The vast majority of the known stars of ultra low metallicity ([Fe=H] >-4:5) are known to be enhanced in carbon, and belong to the 'low-carbon band' (A(C) = log(C=H) + 12 7:6). It is generally, although not universally, accepted that this peculiar chemical composition reflects the chemical composition of the gas cloud out of which these stars were formed. The first ultra-metalpoor star discovered, HE 0107-5240, is also enhanced in carbon and belongs to the 'low-carbon band'. It has recently been claimed to be a long-period binary, based on radial velocity measurements. It has also been claimed that this binarity may explain its peculiar composition as being due to mass transfer fro…
HADES RV programme with HARPS-N at TNG: XII. The abundance signature of M dwarf stars with planets
[Context] Most of our current knowledge on planet formation is still based on the analysis of main sequence, solar-type stars. Conversely, detailed chemical studies of large samples of M dwarfs hosting planets are still missing.
Prompt and Follow-up Multi-wavelength Observations of the GRB 161017A
This paper presents data on the simultaneous and complementary observations of the gamma-ray burst (GRB) GRB 161017A for optical, X-ray, and gamma wavelengths obtained by the Russian multi-messenger Lomonosov space observatory and supplemented by additional data from the Swift satellite as well as the ground-based MASTER Global Robotic Net and the 10 m Gran Telescopio Canarias. Multifrequency spectra of this very powerful explosion indicate that it originated at a distance of 10 billion light years from Earth. Here, we present the results of the prompt, early, and afterglow optical observations. The light curves and spectra suggest that the prompt optical and high-energy emissions occur in …
The HADES RV Programme with HARPS-N@TNG VIII. Gl15A: A multiple wide planetary system sculpted by binary interaction
We present 20 years of radial velocity (RV) measurements of the M1 dwarf Gl15A, combining 5 years of intensive RV monitoring with the HARPS-N spectrograph with 15 years of archival HIRES/Keck RV data. We carry out an MCMC-based analysis of the RV time series, inclusive of Gaussian Process (GP) approach to the description of stellar activity induced RV variations. Our analysis confirms the Keplerian nature and refines the orbital solution for the 11.44-day period super Earth, Gl15A\,b, reducing its amplitude to $1.68^{+0.17}_{-0.18}$ m s$^{-1}$ ($M \sin i = 3.03^{+0.46}_{-0.44}$ M$_\oplus$), and successfully models a long-term trend in the combined RV dataset in terms of a Keplerian orbit wi…