High precision radial velocity planet searches in the near-infrared

Spinvelocity-vs-mass-BetaPicb-and-solarsystemSystem along with the recently measured spin rate of the planet Beta Pictoris b. Credit: ESO/I. Snellen (Leiden University). Spin rates are a different matter, but even radial velocities (RV) are notoriously hard to measure for the majority of nearby stars, which are M dwarfs, and this extends to brown dwarfs as well. Very new instrumental developments are beginning to allow RV to be measured in the near-infrared, where the spectra of these stars are less crowded with lines, allowing line widths to be measured properly, with RV and spin rates also much easier to determine. A natural extension into the planet-seeking arena follows. A new paper by Jonathan Gagné, Peter Plavchan (who is a pioneer in this field) and many co-authors has been accepted to the Astrophysical Journal and appears on arXiv:

We present the results of a precise near-infrared (NIR) radial velocity (RV) survey of 32 low-mass stars with spectral types K2-M4 using CSHELL at the NASA IRTF in the K-band with an isotopologue methane gas cell to achieve wavelength calibration and a novel iterative RV extraction method. We surveyed 14 members of young ( 25-150 Myr) moving groups, the young field star ε Eridani as well as 18 nearby (< 25 pc) low-mass stars and achieved typical single-measurement precisions of 8-15 m/sec with a long-term stability of 15-50 m/sec. We obtain the best NIR RV constraints to date on 27 targets in our sample, 19 of which were never followed by high-precision RV surveys. Our results indicate that very active stars can display long-term RV variations as low as 25-50 m/sec at 2.3125 μm, thus constraining the effect of jitter at these wavelengths. We provide the first multi-wavelength confirmation of GJ 876 bc and independently retrieve orbital parameters consistent with previous studies. We recovered RV variability for HD 160934 AB and GJ 725 AB that are consistent with their known binary orbits, and nine other targets are candidate RV variables with a statistical significance of 3-5σ. Our method combined with the new iSHELL spectrograph will yield long-term RV precisions of 5 m/sec in the NIR, which will allow the detection of Super-Earths near the habitable zone of mid-M dwarfs.

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