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Paper: Minimizing Radial-Velocity Errors Caused by Spectral-Type Mismatch in Early-Type Stars
Volume: 185, Precise Stellar Radial Velocities, IAU Colloquium 170
Page: 108
Authors: Verschueren, W.; David, M.; Vrancken, M.
Abstract: We present the first results of a long-term study to increase the internal precision as well as the external accuracy of radial velocities of early-type stars to the 1 km/s level. The small line density and typically high rotational velocity of early-type stars require a number of specific cross-correlation techniques in order to optimize the internal precision well below the 1 km/s level. These include high-frequency Fourier filtering, rotational matching, and dedicated cross-correlation function fitting prescriptions. The external accuracy of (relative and absolute) radial velocities of early-type stars suffers from important systematic errors caused by unavoidable small object-template cross-correlation mismatch. The latter arises mainly because line shapes and strengths, and in particular blends, vary strongly with spectral type. Based on synthetic spectra sampled at about 0.12 Å /pixel, the magnitude of these mismatch errors is shown in different spectral regions for increasing differences in spectral type between object and template (in the spectral type range A to late B), and for different rotational velocities. A line selection scheme is proposed as a function of (small) spectral-type mismatch, of rotational velocity and of signal-to-noise, which optimizes the accuracy in each case.
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