HADES RV program with HARPS-N at the TNG GJ 3998: An early M-dwarf hosting a system of super-Earths

Abstract

Context. Many efforts to detect Earth-like planets around low-mass stars are presently devoted 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 their habitable zones more easily detectable than those around higher mass stars. Nonetheless, the statistics of frequency of low-mass planets hosted by low mass stars remains poorly constrained. Aims. Our M-dwarf radial velocity monitoring with HARPS-N within the GAPS (Global architectures of Planetary Systems) -ICE (Institut de Ciències de l'Espai/CSIC-IEEC) -IAC (Instituto de Astrofísica de Canarias) project ⋆⋆ 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 bring a 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 occurence. 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 from the periodic signals those due to activity and to the presence of planetary companions. We run an MCMC simulation and use Bayesian model selection to determine the number of planets in this system, to estimate their orbital parameters and minimum masses and for a proper treatment of 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 2-planet Keplerian (13.

The HADES RV Programme with HARPS-N at TNG

“…(2)), we used to model the stellar contribution present in the RV variations in the following section, our primary goal is to investigate some properties of the stellar activity and use them to constrain some parameter priors in the analysis of the radial velocities. This represents a reasonable expectation, because neither the activity indicators nor the RVs have been pre-whitened, and the variability patterns in the former could be present with similar properties in the latter, as was noticed by Affer et al (2016) during the analysis of another HADES target. In this sense, results from the analysis of the activity indicators can be used to train the GP regression of the RVs, by keeping unchanged the way the stellar activity contribution is modelled.…”

“…Affer et al 2016). Also, the h hyperparameter, corresponding to the mean amplitude of the stellar signal, is fully compatible with the expected value derived by Suárez Mascareño et al (2018) from the mean activity level of the star, log R HK , that is K exp = 1.9 ± 0.4 m s …”

HADES RV Programme with HARPS-N at TNG

“…While early surveys tried to avoid active M dwarfs, there is ongoing evidence that M dwarfs show radial velocity signals due to the simultaneous presence of lowmass planets and activity-related phenomena (e.g. Affer et al 2016). Furthermore, thanks to new instrumentation at IR wavelengths where lines are less affected by magnetic activity than in the optical (e.g.…”

“…Our stellar sample is composed of 78 late-K/early-M dwarfs monitored within the HArps-N red Dwarf Exoplanet Survey (HADES), Affer et al (2016); Perger et al (2017), a collaborative effort between the Global Architecture of Planetary Systems project (GAPS; Covino et al 2013) 2 , the Institut de Ciències de l'Espai (ICE/CSIC), and the Instituto de Astrofísica de Canarias (IAC). Seventy-one stars have been observed to date covering a range in effective temperature from 3400 to 3900 K, and with spectral types between K7.5 and M3V.…”

Stellar masks and bisector’s shape for M-type stars observed in the GAPS programme with HARPS-N at TNG

“…They are mainly used for exoplanets search and characterization, an ever evolving field that has recently focused on the Mtype stars (e.g. Bonfils et al, 2013;Affer et al, 2016). These cool stars are very interesting targets for exoplanetary studies, due to their long lives, low masses and close-in habitable zone (e.g.…”