HADES RV program with HARPS-N at the TNG

Abstract

Aims. The HArps-n red Dwarf Exoplanet Survey (HADES) is providing a major contribution to the widening of the current statistics of low-mass planets, through the in-depth analysis of precise radial-velocity (RV) measurements in a narrow range of spectral sub-types. Using the HARPS-N spectrograph we reach the precision needed to detect small planets with a few earth masses. Our survey is mainly focused on the M-dwarf population of the northern hemisphere. Methods. As part of that program, we obtained RV measurements of Gl 686, an M1 dwarf at d = 8.2 pc. These measurements show a dispersion much in excess of their internal errors. The analysis of data obtained within an intensive observing campaign demonstrates that the excess dispersion is due to a coherent signal with a period of 15.53 d. Almost simultaneous photometric observations were carried out within the APACHE and EXORAP programs to characterize the stellar activity and to distinguish periodic variations related to activity from signals due to the presence of planetary companions, complemented also with ASAS photometric data. We used a Bayesian framework to estimate the orbital parameters and the planet minimum mass, and to properly treat the activity noise. We took advantage of the available RV measurements for this target from other observing campaigns. The analysis of the RV composite time series from the HIRES, HARPS, and HARPS-N spectrographs, consisting of 198 measurements taken over 20 yr, enabled us to address the nature of periodic signals and also to characterize stellar physical parameters (mass, temperature, and rotation). Results. We report the discovery of a super-Earth orbiting at a distance of 0.092 AU from the host star Gl 686. The planet has a minimum mass of 7.1 ± 0.9 M⊕ and an orbital period of 15.532 ± 0.002 d. The analysis of the activity indexes, of the correlated noise through a Gaussian process framework, and of the photometry provides an estimate of the stellar rotation period at 37 d, and highlights the variability of the spot configuration during the long timespan covering 20 yr. The observed periodicities around 2000 d likely point to the existence of an activity cycle.

The CARMENES search for exoplanets around M dwarfs

“…The orbital period of 15.5314 d and a semimajor axis of 0.092 au are very similar. Contrary to the best-fit model in Affer et al (2019), our model suggests a non-zero eccentricity, obtaining a value of 0.077.…”

“…In this study, we analyze 72 and 57 RV measurements of the M3.0 V star LSPM J2116+0234 taken with the VIS and NIR channels of the high-resolution CARMENES échelle spectrograph, respectively. We also confirm and refine the orbital parameters of the super-Earth around the M1.0 V star GJ 686 reported in Affer et al (2019) with the addition of 100 new RV CARMENES measurements.…”

“…To obtain better constraints on the properties of GJ 686 b derived in Affer et al (2019), who used the available RVs from HIRES, HARPS and HARPS-N, we combine these data with the CARMENES-VIS RVs. We derive a slightly smaller and more precise RV semi-amplitude of 3.02 m s −1 , resulting in a lower minimum mass of the planet, of 6.64 M ⊕ .…”

“…In this paper, we analyze the RV data of LSPM J2116+0234 and GJ 686, monitored as part of the CARMENES Guaranteed Time Observations (GTO) M dwarf survey. The data reveal the presence of a mini-Neptune around LSPM J2116+0234 with a period of 14.4 d. Furthermore, we used CARMENES data to refine the orbital parameters of GJ 686b reported by Affer et al (2019; hereafter Aff19), a super-Earth with a period of 15.5 d. In Sect. 2, we introduce the basic properties of the host stars, and we describe the spectroscopic and photometric data in Sect.…”

The CARMENES search for exoplanets around M dwarfs

“…Despite the significant number of discoveries of planetary systems with M dwarf primaries (e.g., Anglada-Escudé et al 2012;Bonfils et al 2013;Astudillo-Defru et al 2015;Suárez Mascareño et al 2017;Affer et al 2019), the properties and the statistics of planets hosted by low-mass stars remain poorly constrained. We are far from understanding such fundamental ques-Article number, page 1 of 44 arXiv:2003.13052v1 [astro-ph.EP] 29 Mar 2020 tions as how planetary systems form and how their architecture changes with the mass of the central star.…”