Asteroids as radial velocity and resolving power standards for medium and high resolution spectroscopy

Abstract

Echelle spectra of 10 bright asteroids are presented and compared against an observed twilight spectrum and a computed Solar spectrum. Spectra covering a 2130 A spectral range centered on 5785 A are of high resolving power and high signal to noise ratio. So we focus on a comparison of detailed properties of spectral lines and not on albedo variations. It is shown that the normalized Solar and asteroid spectra are identical except for radial velocity (RV) shifts which can be predicted at the accuracy level of 1 m/s. So asteroids are proposed as new and extremely accurate radial velocity standards. Predicted and measured RVs of observed asteroids indeed match within limits of accuracy of the instrument. There are numerous absorption lines in the reflected Solar spectrum. This allows a direct mapping of the resolving power of a spectrograph between and along echelle spectral orders. So asteroid spectra can be used to test wavelength calibration and resolving power of spectrographs on the ground as well as in space, including the Gaia mission of ESA. All spectra are also given in an electronic form.