CARMENES - RV search for terrestrial planets around M dwarfs

CARMENES. I. A radial-velocity survey for terrestrial planets in the habitable zones of M dwarfs. A historical overview
http://arxiv.org/abs/1210.5465

Uses two spectrographs in the wavelength range 550 ­– 1700 nm, expected to start mid 2014.

Interesting the two spectrographs-approach - observing in different wavelengths could allow to filter jitter and stellar activity noise in RV measurements

http://carmenes.caha.es/ext/publications/CARMENES_Quirrenbachetal2010_SanDiego.pdf

Quote :

The concept of a dual-channel spectrograph will permit the determination of radial velocity variations at different wavelengths simultaneously. Activity-induced velocity variations are expected to be wavelength dependent, which is strictly not the case for orbital variations. Thus, it will be possible to differentiate an orbital period from activity, and the wavelength dependence will provide valuable information on the spot temperature and distribution.

That's useful, I recall a couple of planets have been retracted for this reason. TW Hydrae springs to mind...

The abstract for the upcoming presentation by Trifon Trifonov at the AG meeting 2017 Exoplanets splinter group may be of interest. A couple of new planets, plus a non-detection of a previously-reported one.

Reiners et al. "The CARMENES search for exoplanets around M dwarfs: High-resolution optical and near-infrared spectroscopy of 324 survey stars"
https://arxiv.org/abs/1711.06576

Some interesting points about the optimal wavelength range for M-dwarf surveys.

Quote :

Our results answer the question at which wavelength the best RV precision can be reached in observations of M dwarfs with a stabilized spectrograph: the optimal range for M-dwarf RV spectroscopy is the spectral range 700–900 nm. Calculating the spectroscopic quality factor Q and the S/N for three example stars, we showed that our conclusions about the RV uncertainties are consistent with the spectroscopic information we find in the spectra. At wavelengths shorter than 700 nm, the lack of photons limits the RV precision; at wavelengths longer than 900 nm, the amount of spectroscopic information is so much lower than at shorter wavelengths that the advantage in S/N cannot compensate for the loss in RV precision. Only in the latest spectral types (M8 and M9) did we find the RV precision at near-infrared wavelengths to match the amount of information at shorter wavelengths.

New brown dwarf companions at GJ 912 and GJ 3626 and a possible long-period planetary one at LP 427-016

The CARMENES search for exoplanets around M dwarfs: Spectroscopic orbits of nine M-dwarf multiple systems, including two triples, two brown dwarf candidates, and one close M-dwarf-white dwarf binary

Quote :

M dwarfs are ideal targets for the search of Earth-size planets in the habitable zone using the radial velocity method, attracting the attention of many ongoing surveys. As a by-product of these surveys, new multiple stellar systems are also found. This is the case also for the CARMENES survey, from which nine new SB2 systems have already been announced. Throughout the five years of the survey, the accumulation of new observations has resulted in the detection of several new multiple stellar systems with long periods and low radial-velocity amplitudes. Here, we newly characterise the spectroscopic orbits and constrain the masses of eight systems and update the properties of a system that we reported earlier. We derive the radial velocities of the stars using two-dimensional cross correlation techniques and template matching. The measurements are modelled to determine the orbital parameters of the systems. We combine CARMENES spectroscopic observations with archival high-resolution spectra from other instruments to increase the time-span of the observations and improve our analysis. When available, we also added archival photometric, astrometric, and adaptive optics imaging data to constrain the rotation periods and absolute masses of the components. We determine the spectroscopic orbits of nine multiple systems, eight of which are presented for the first time. The sample is composed of five SB1s, two SB2s, and two ST3s. The companions of two of the single-line binaries, GJ 3626 and GJ 912, have minimum masses below the stellar boundary and, thus, could be brown dwarfs. We find a new white dwarf in a close binary orbit around the M star GJ 207.1. From a global fit to radial velocities and astrometric measurements, we are able to determine the absolute masses of the components of GJ 282C, which is one of the youngest systems with measured dynamical masses.