University of Hertfordshire

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From the same journal

By the same authors

Precision radial velocities of 15 M5-M9 dwarfs

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Original languageEnglish
Pages (from-to)3094-3113
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Volume439
Issue3
Early online date20 Feb 2014
DOIs
Publication statusPublished - 11 Apr 2014

Abstract

We present radial velocity measurements of a sample ofM5V-M9Vstars from our Red-Optical Planet Survey, operating at 0.652-1.025 μm. Radial velocities for 15 stars, with rms precision down to 2.5m-1 over a week-long time-scale, are achieved using thorium-argon reference spectra. We are sensitive to planets with mp sin i ≥ 1.5M (3M at 2σ) in the classical habitable zone, and our observations currently rule out planets with mp sini ≥ 0.5MJ at 0.03 au for all our targets. A total of 9 of the 15 targets exhibit rms<16m-1, which enables us to rule out the presence of planets with mp sini > 10M in 0.03 au orbits. Since the mean rotation velocity is of the order of 8 km-1 for an M6V star and 15 km -1 for M9V, we avoid observing only slow rotators that would introduce a bias towards low axial inclination (i< 90°) systems, which are unfavourable for planet detection. Our targets with the highest v sin i values exhibit radial velocities significantly above the photon-noise-limited precision, even after accounting for v sin i. We have therefore monitored stellar activity via chromospheric emission from the Hα and Ca II infrared triplet lines. A clear trend of log10(L/Lbol) with radial velocity rms is seen, implying that significant starspot activity is responsible for the observed radial velocity precision floor. The implication that most late M dwarfs are significantly spotted, and hence exhibit time varying line distortions, indicates that observations to detect orbiting planets need strategies to reliablymitigate against the effects of activity-induced radial velocity variations.

Notes

J. R. Barnes, 'Precision radial velocities of 15 M5-M9 dwarfs', Monthly Notices of the Royal Astronomical Society, Vol. 439 (3): 3094 - 3113, first published online 20 February 2014. The version of record is available online at doi: 10.1093/mnras/stu172 © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

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