Search for radial velocity variations in eight M-dwarfs with NIRSPEC/Keck II

TL;DR

This study used near-infrared spectra from NIRSPEC/Keck II to search for radial velocity variations in eight late M-dwarfs, finding no evidence of companions and highlighting instrumental effects on RV measurements.

Contribution

First application of NIRSPEC at Keck II to search for short-period companions around late M-dwarfs in the J-band, demonstrating RV precision and instrumental effects.

Findings

No RV variations detected in the sample.

RV precision achieved was 180-300 m/s.

Instrumental profile asymmetries affected previous RV measurements.

Abstract

Context. Radial velocity (RV) measurements from near-infrared spectra have become a potentially powerful tool to search for planets around cool stars and sub-stellar objects. As part of a large survey to characterize M-dwarfs using NIRSPEC at Keck II, we obtained spectra of eight late M-dwarfs (spectral types M5.0-M8.0) during two or more observing epochs per target. These spectra were taken with intermediate spectral resolving powers (R \sim 20,000) in the J-band. Aims. We search for relative radial velocity variability in these late M-dwarfs and test the NIRSPEC capability of detecting short period brown dwarf and massive planetary companions around low-mass stars in the J-band (\approx 1.25 micron). Additionally, we reanalyzed the data of the M8-type star vB10 (one of our targets) presented in Zapatero Osorio et al. (2009), which were obtained with the same instrumentation as our data. Methods. [...] Results. For the entire M-dwarf sample, we do not find any evidence of relative RV variations induced by a short period brown dwarf or massive planetary companion. The typical RV precision of the measurements is between 180 and 300 m/s, which is sufficient to detect hot Neptunes around M-dwarfs. Also, we find that the spurious RV shift in Zapatero et al. (2009) of the star VB10 was caused by asymmetries in the instrumental profile between different observing epochs, which were not taken into account in their analysis.