Astron. Astrophys. 362, 585-594 (2000)

The planet search program at the ESO Coudé Echelle spectrometer ^*

I. Data modeling technique and radial velocity precision tests

M. Endl ^1,2, M. Kürster ¹ and S. Els <sup>1,3

1</sup> European Southern Observatory, Casilla 19001, Vitacura, Santiago 19, Chile
² Universität Wien, Institut für Astronomie, Türkenschanzstrasse 17, 1180 Wien, Austria
³ Universität Heidelberg, Institut für Theoretische Astrophysik, Tiergartenstrasse 15, 69121 Heidelberg, Germany

Received 27 January 2000 / Accepted 24 July 2000

Abstract

We present the modeling technique we apply to analyse data of the ESO Coudé Echelle Spectrometer (CES) planet search program, in order to obtain high precision stellar radial velocity (RV) measurements. The detection of the Doppler reflex motion of a star due to an orbiting planet has so far been the most successful method to discover planetary companions to solar-type stars. The first extrasolar planet discovered by the CES program is the companion to the young (ZAMS) G0V star  Hor (Kürster et al. 2000). To achieve a high long-term RV measurement stability the CES spectra are self-calibrated by a superimposed iodine vapor (I₂) reference spectrum. In the modeling process a multi-parameter -optimization is employed to generate an accurate description of the observation. We largely follow the general modeling approach for I₂-calibrated data outlined by Butler et al. (1996) and Valenti et al. (1995). The sharp I₂ reference lines allow the reconstruction of the spectrograph instrumental profile (IP) and the precise determination of the Doppler shift of the stellar absorption lines. We show examples of the application of the modeling technique to CES data obtained over a time span of five and a half years at ESO La Silla. The small spectral bandwidth of only 4.85 nm for CES spectra makes this data challenging for high precision radial velocities. We demonstrate for the known RV-constant star  Cet, for two stars with known extrasolar planets, 51 Peg and 70 Vir, and for  Men and GJ 570A, two stars from our survey that the achievable RV precision for CES data is .

Key words: methods: data analysis techniques: radial velocities stars: planetary systems

* Based on observations collected at the European Southern Observatory, La Silla

Send offprint requests to: M. Endl (endl@astro.univie.ac.at)

SIMBAD Objects

Contents

• 1. Introduction
• 2. The CES instrument and the iodine cell
• 3. The data modeling technique
  • 3.1. Step 1: modeling the pure iodine spectrum
  • 3.2. Step 2: deconvolution of the stellar spectrum
  • 3.3. Step 3: full modeling of the combined star and iodine spectrum
• 4. RV precision tests
  • 4.1. Cet
  • 4.2. 51 Peg
  • 4.3. 70 Vir
  • 4.4.  Men
  • 4.5. GJ 570A
• 5. Outlook
• 6. Summary
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: October 24, 2000
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