UVES radial velocity accuracy from asteroid observations*
I. Implications for fine structure constant variability
INAF – Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34143 Trieste, Italy e-mail: email@example.com
2 Department of Theoretical Astrophysics, Ioffe Physico-Technical Institute, Polytekhnicheskaya Str. 26, 194021 St. Petersburg, Russian Federation
3 CIFIST, Marie Curie Excellence Team and GEPI, Observatoire de Paris, CNRS, Université Paris Diderot; Place Jules Janssen, 92190 Meudon; Observatoire de Paris, CNRS, 61 avenue de l'Observatoire, 75014 Paris, France
4 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
5 European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago, Chile
Accepted: 12 December 2007
Context. High resolution observations of the asteroids Iris and Juno have been performed by means of the UV-Visual Echelle Spectrograph (UVES) at the European Southern Observatory (ESO) Very Large Telescope (VLT) to obtain the effective accuracy of the spectrograph's radial velocity. The knowledge of this quantity has important bearings on studies searching for a variability in the fine structure constant carried out with this instrument.
Aims. Asteroids provide a precise radial velocity reference at the level of 1 m s-1, which allows for instrumental calibration and the recognition of small instrumental drifts and calibration systematics. In particular, radial velocity drifts due to nonuniform slit illumination and slit optical misalignment in the two UVES spectrograph arms can be investigated.
Methods. We compare the position of the solar spectrum reflected by the asteroids with the solar wavelength positions and with that of asteroid and twilight observations at other epochs to asses the UVES instrumental accuracy.
Results. We observe radial velocities offsets in the range of ≈10-50 m s-1, likely due to a nonuniform slit illumination. However, no radial velocity patterns with wavelengths are detected and the two UVES arms provide consistent radial velocities. These results suggest that the detected variability by Levshakov et al. (2007) deduced from a drift of -180 ± 85 m s-1 at = 1.84, between two sets of Fe II lines falling in the two UVES arms, may be real or induced by other kinds of systematics than those investigated here. The proposed technique allows us to make a real time quality check of the spectrograph and should be followed for very accurate measurements.
Key words: techniques: radial velocities / instrumentation: spectrographs / standards / minor planets, asteroids / galaxies: quasars: absorption lines / Sun: photosphere
© ESO, 2008