The CARMENES search for exoplanets around M dwarfs

Abstract

Context. The main goal of the CARMENES survey is to find Earth-mass planets around nearby M-dwarf stars. Seven M dwarfs included in the CARMENES sample had been observed before with HIRES and HARPS and either were reported to have one short period planetary companion (GJ 15 A, GJ 176, GJ 436, GJ 536 and GJ 1148) or are multiple planetary systems (GJ 581 and GJ 876). Aims. We aim to report new precise optical radial velocity measurements for these planet hosts and test the overall capabilities of CARMENES. Methods. We combined our CARMENES precise Doppler measurements with those available from HIRES and HARPS and derived new orbital parameters for the systems. Bona-fide single planet systems were fitted with a Keplerian model. The multiple planet systems were analyzed using a self-consistent dynamical model and their best fit orbits were tested for long-term stability. Results. We confirm or provide supportive arguments for planets around all the investigated stars except for GJ 15 A, for which we find that the post-discovery HIRES data and our CARMENES data do not show a signal at 11.4 days. Although we cannot confirm the super-Earth planet GJ 15 Ab, we show evidence for a possible long-period (Pc = 7030-630+970 d) Saturn-mass (mcsini = 51.8-5.8+5.5M⊕) planet around GJ 15 A. In addition, based on our CARMENES and HIRES data we discover a second planet around GJ 1148, for which we estimate a period Pc = 532.6-2.5+4.1 days, eccentricity ec = 0.342-0.062+0.050 and minimum mass mcsini = 68.1-2.2+4.9M⊕. Conclusions. The CARMENES optical radial velocities have similar precision and overall scatter when compared to the Doppler measurements conducted with HARPS and HIRES. We conclude that CARMENES is an instrument that is up to the challenge of discovering rocky planets around low-mass stars.

3D magneto-hydrodynamical simulations of stellar convective noise for improved exoplanet detection

“…These methods assume that the observations (or their residuals in the case where some periodicities have been removed) contain only noise and that this noise is further uncorrelated with unknown variance. The noise statistics are estimated from the observations (see e.g., Jenkins et al 2013, Hobson, M. J. et al 2018, Trifonov et al 2018, Ment et al 2018). The FAP is evaluated by estimating the distribution of the test statistic using fake data, typically obtained by shuffling the data.…”

The CARMENES search for exoplanets around M dwarfs

“…The most likely stellar rotation frequency is shown with red dashed line, while the red shaded area denotes its uncertainties, as given by Díez Alonso et al (2019). extended HIRES data time series yields an additional RV signal with a period of ∼ 530 d, likely due to a second massive planet in the system. In Trifonov et al (2018b), we added 52 CARMENES RVs and performed a combined Doppler analysis, which revealed the two-planet configuration of the GJ 1148 system. We found the following orbital configuration for GJ 1148 b: m b sin i = 0.304 M Jup , P b = 41.380 d, e b = 0.379, a b = 0.166 au, and for GJ 1148 c: m c sin i = 0.214 M Jup , P c = 532.6 d, e c = 0.341, a c = 0.913 au.…”

“…In our first paper on GJ 1148 (Trifonov et al 2018b), we performed dynamical modeling of the GJ 1148 RV data and we studied the long-term stability of the best fit to the system, but at that time we did not perform a detailed long-term dynamical analysis of the GJ 1148 system. In this second paper, we aim to analyze the possible orbital configurations and planetary mass regimes based on an extensive long-term dynamical analysis that includes additional CARMENES Doppler data from recent observations.…”

“…In this paper, we provide the first detailed analysis of the dynamics of the rare GJ 1148 system, which was reported to host two Saturn-mass planets orbiting around the M dwarf on moderately eccentric orbits (Trifonov et al 2018b). We provide new precise Doppler measurements from the CARMENES 2 instrument (Quirrenbach et al 2016;Reiners et al 2018b) and focus on the long-term dynamical properties of the system, which could provide important information on the primordial protoplanetary conditions needed to form two Saturn-mass planets around a low-mass star.…”

The CARMENES search for exoplanets around M dwarfs

“…The main goal of CARMENES is to discover and characterize Earth-like planets around an initial sample of about 300 M dwarfs (Reiners et al 2018b). To date, the program has already confirmed eight planet candidates from large-scale photometric and spectroscopic surveys (e.g., Trifonov et al 2018;Sarkis et al 2018) and detected more than ten new planets (e.g., Reiners et al 2018a;Kaminski et al 2018;Luque et al 2018Luque et al , 2019Ribas et al 2018;Nagel et al 2019;Perger et al 2019;Zechmeister et al 2019;Morales et al 2019).…”