Volume 515, June 2010
|Number of page(s)||6|
|Section||Planets and planetary systems|
|Published online||15 June 2010|
Evaluating the stability of atmospheric lines with HARPS*
Geneva Observatory, University of Geneva, 51 Ch. des Maillettes,
1290-Sauverny, Switzerland e-mail: firstname.lastname@example.org
Accepted: 17 February 2010
Context. When searching for extrasolar systems using the radial velocity technique, the need for high-precision measurements implies that a precise wavelength calibration is required. The choice of the calibrator is a particularly important open question in the infra-red domain, where precision and achievements remain inferior to those in the optical.
Aims. We investigate the long-term stability of atmospheric lines as a precise wavelength reference and analyze their sensitivity to different atmospheric and observing conditions.
Methods. We use HARPS archival data for three bright stars, Tau Ceti, μ Arae, and e Eri, which span 6 years and include high-cadence measurements performed over several nights. We cross-correlate this data with an O2 mask and evaluate both radial velocity and bisector variations to a photon noise level of 1 m/s.
Results. We find that the telluric lines in the three data-sets are stable down to 10 m/s (rms) over the 6 years. We also show that the radial velocity variations can be modeled by simple atmospheric models, yielding a final precision of 1–2 m/s.
Conclusions. The long-term stability of atmospheric lines was 10 m/s over six years, in spite of atmospheric phenomena. Atmospheric lines can be used as a wavelength reference for short timescale programs, yielding a precision of 5 m/s without any correction. A higher precision, of 2 m/s, can be reached if the atmospheric phenomena are corrected for using the simple atmospheric model described, making it a very competitive method even on long timescales.
Key words: atmospheric effects / instrumentation: spectrographs / methods: observational / techniques: radial velocities / planetary systems
© ESO, 2010
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