Context. Since low-mass stars have low luminosities, orbits at which liquid water can exist on Earth-sized planets are relatively closein, which produces Doppler signals that are detectable using state-of-the-art Doppler spectroscopy. Aims. GJ 667C is already known to be orbited by two super-Earth candidates. We have recently applied developed data analysis methods to investigate whether the data supports the presence of additional companions. Methods. We obtain new Doppler measurements from HARPS extracted spectra and combined them with those obtained from the PFS and HIRES spectrographs. We used Bayesian and periodogram-based methods to re-assess the number of candidates and evaluated the confidence of each detection. Among other tests, we validated the planet candidates by analyzing correlations of each Doppler signal with measurements of several activity indices and investigated the possible quasi-periodic nature of signals.Results. Doppler measurements of GJ 667C are described better by six (even seven) Keplerian-like signals: the two known candidates (b and c); three additional few-Earth mass candidates with periods of 92, 62, and 39 days (d, e and f); a cold super-Earth in a 260-day orbit (g) and tantalizing evidence of a ∼1 M ⊕ object in a close-in orbit of 17 days (h). We explore whether long-term stable orbits are compatible with the data by integrating 8 × 10 4 solutions derived from the Bayesian samplings. We assess their stability using secular frequency analysis. Conclusions. The system consisting of six planets is compatible with dynamically stable configurations. As for the solar system, the most stable solutions do not contain mean-motion resonances and are described well by analytic Laplace-Lagrange solutions. Preliminary analysis also indicates that masses of the planets cannot be higher than twice the minimum masses obtained from Doppler measurements. The presence of a seventh planet (h) is supported by the fact that it appears squarely centered on the only island of stability left in the six-planet solution. Habitability assessments accounting for the stellar flux, as well as tidal dissipation effects, indicate that three (maybe four) planets are potentially habitable. Doppler and space-based transit surveys indicate that 1) dynamically packed systems of super-Earths are relatively abundant and 2) M-dwarfs have more small planets than earlier-type stars. These two trends together suggest that GJ 667C is one of the first members of an emerging population of M-stars with multiple low-mass planets in their habitable zones.

Aims. We present first quantitative results of the surface magnetic field measurements in selected M-dwarfs based on detailed spectra synthesis conducted simultaneously in atomic and molecular lines of the FeH Wing-Ford F 4 Δ − X 4 Δ transitions. Methods. A modified version of the Molecular Zeeman Library (MZL) was used to compute Landé g-factors for FeH lines in different Hund's cases. Magnetic spectra synthesis was performed with the Synmast code. Results. We show that the implementation of different Hund's case for FeH states depending on their quantum numbers allows us to achieve a good fit to the majority of lines in a sunspot spectrum in an automatic regime. Strong magnetic fields are confirmed via the modelling of atomic and FeH lines for three M-dwarfs YZ CMi, EV Lac, and AD Leo, but their mean intensities are found to be systematically lower than previously reported. A much weaker field (1.7-2 kG against 2.7 kG) is required to fit FeH lines in the spectra of GJ 1224. Conclusions. Our method allows us to measure average magnetic fields in very low-mass stars from polarized radiative transfer. The obtained results indicate that the fields reported in earlier works were probably overestimated by about 15-30%. Higher quality observations are needed for more definite results.

Molecular FeH provides a large number of sharp and isolated absorption lines that can be used to measure radial velocity, rotation, or magnetic field strength with high accuracy. Our aim is to provide an FeH atlas for M-type stars in the spectral region from 986 nm to 1077 nm (Wing-Ford band). To identify these lines in CRIRES spectra of the magnetically inactive, slowly rotating, M5.5 dwarf GJ1002, we calculated model spectra for the selected spectral region with theoretical FeH line data. In general this line list agrees with the observed data, but several individual lines differ significantly in position or in line strength. After identification of as many as possible FeH lines, we corrected the line data for position and line strength to provide an accurate atlas of FeH absorption lines for use in high precision spectroscopy of low mass stars. For all lines, we used a Voigt function to obtain their positions and equivalent widths. Identification with theoretical lines was done by hand. For confirmation of the identified lines, we used statistical methods, cross-correlation techniques, and line intensities. Eventually, we were able to identify FeH lines from the (0, 0), (1, 0), (1, 1), (2, 1), (2, 2), (3, 2), and (4, 3) vibrational bands in the observed spectra and correct the positions of the lines if necessary. The deviations between theoretical and observed positions follow a normal distribution approximately around zero. In order to empirically correct the line strength, we determined T eff , instrumental broadening (rotational broadening) and a van der Waals enhancement factor for the FeH lines in GJ1002. We also give the scaling factors for the Einstein A values to correct the line strengths. With the identified lines, we derived rotational temperatures from the line intensities for GJ1002. We conclude that FeH lines can be used for a wide variety of applications in astrophysics. With the identified lines it will be possible for example to characterize magnetically sensitive or very temperature sensitive lines, which can be used to investigate M-type stars.

Context. The measurement of line broadening in cool stars is in general a difficult task. In order to detect slow rotation or weak magnetic fields, an accuracy of 1 km s −1 is needed. In this regime the broadening from convective motion becomes important. We present an investigation of the velocity fields in early to late M-type star hydrodynamic models, and we simulate their influence on FeH molecular line shapes. The M star model parameters range between log g of 3.0−5.0 and effective temperatures from 2500 K to 4000 K. Aims. Our aim is to characterize the T eff -and log g-dependence of the velocity fields and express them in terms of micro-and macroturbulent velocities in the one dimensional sense. We present a direct comparison between 3D hydrodynamical velocity fields and 1D turbulent velocities. The velocity fields strongly affect the line shapes of FeH, and it is our goal to give a rough estimate of the log g and T eff parameter range in which 3D spectral synthesis is necessary and where 1D synthesis suffices. We want to distinguish between the velocity-broadening from convective motion and the rotational-or Zeeman-broadening in M-type stars we are planning to measure. For the latter, FeH lines are an important indicator. Methods. In order to calculate M-star structure models, we employ the 3D radiative-hydrodynamics (RHD) code CO 5 BOLD. The spectral synthesis in these models is performed with the line synthesis code LINFOR3D. We describe the 3D velocity fields in terms of a Gaussian standard deviations and project them onto the line of sight to include geometrical and limb-darkening effects. The microand macro-turbulent velocities are determined with the "curve of growth" method and convolution with a Gaussian velocity profile, respectively. To characterize the log g and T eff dependence of FeH lines, the equivalent width, line width, and line depth are examined. Results. The velocity fields in M-stars strongly depend on log g and T eff . They become stronger with decreasing log g and increasing T eff . The projected velocities from the 3D models agree within ∼100 m s −1 with the 1D micro-and macro-turbulent velocities. The FeH line quantities systematically depend on log g and T eff . Conclusions. The influence of hydrodynamic velocity fields on line shapes of M-type stars can well be reproduced with 1D broadening methods. FeH lines turn out to provide a means to measure log g and T eff in M-type stars. Since different FeH lines all behave in a similar manner, they provide an ideal measure for rotational and magnetic broadening.

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