University of Hertfordshire

From the same journal

From the same journal

By the same authors

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  • 904798

    Accepted author manuscript, 623 KB, PDF document

  • J Barnes 1

    Final published version, 1.17 MB, PDF document

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Original languageEnglish
Pages (from-to)591-604
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume424
Issue1
Early online date6 Jun 2012
DOIs
Publication statusPublished - 1 Jul 2012

Abstract

We present the first results from our Red Optical Planet Survey (ROPS) to search for low mass planets orbiting late type dwarfs (M5.5V - M9V) in their habitable zones (HZ). Our observations, with the red arm MIKE spectrograph (0.5 - 0.9 micron) at the 6.5 m Magellan Clay telescope at Las Campanas Observatory indicate that >= 92% of the flux lies beyond 0.7 micron. We use a novel approach that is essentially a hybrid of the simultaneous iodine and ThAr methods for determining precision radial velocities. We apply least squares deconvolution to obtain a single high S/N ratio stellar line for each spectrum and cross correlate against the simultaneously observed telluric line profile, which we derive in the same way.
Utilising the 0.62 - 0.90 micron region, we have achieved an r.m.s. precision of 10 m/s for an M5.5V spectral type star with spectral S/N ~160 on 5 minute timescales. By M8V spectral type, a precision of ~30 m/s at S/N = 25 is suggested, although more observations are needed. An assessment of our errors and scatter in the radial velocity points hints at the presence of stellar radial velocity variations. Of our sample of 7 stars, 2 show radial velocity signals at 6$\sigma$ and 10-sigma of the cross correlation uncertainties. We find that chromospheric activity (via Halpha variation) does not have an impact on our measurements and are unable to determine a relationship between the derived photospheric line profile morphology and radial velocity variations without further observations. If the signals are planetary in origin, our findings are consistent with estimates of Neptune mass planets that predict a frequency of 13 - 27% for early M dwarfs.
Our current analysis indicates the we can achieve a sensitivity that is equivalent to the amplitude induced by a 6 M_Earth planet orbiting in the habitable zone. Based on simulations, we estimate that <10 M_Earth habitable zone planets will be detected in a new stellar mass regime, with <=20 epochs of observations. Higher resolution and greater instrument stability indicate that photon limited precisions of 2 m/s are attainable on moderately rotating M dwarfs (with vsin <=5 km/s) using our technique.

Notes

This document is the Accepted Manuscript version of the following article: J. R. Barnes, et al, ‘Red Optical Planet Survey: a new search for habitable earths in the southern sky’, Monthly Notices of the Royal Astronomical Society, Vol. 424 (1): 591-604, first published online 27 March 2012. The version of record is available at doi: 10.1111/j.1365-2966.2012.21236.x © 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

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