Title:              High precision Doppler measurements via echelle
                     spectroscopy
 Authors:            BROWN, TIMOTHY M.
 Affiliation:        AA(High Altitude Observatory, Boulder, CO)
 Journal:            IN: CCDs in astronomy; Proceedings of the Conference,
                     Tucson, AZ, Sept. 6-8, 1989 (A91-45976 19-33). San
                     Francisco, CA, Astronomical Society of the Pacific,
                     1990, p. 335-344.
 Publication Date:   00/1990
 Category:           Astronomy
 Origin:             STI
 NASA/STI Keywords:  ASTRONOMICAL SPECTROSCOPY, CHARGE COUPLED DEVICES,
                     DOPPLER EFFECT, FIBER OPTICS, STELLAR OSCILLATIONS,
                     DATA ACQUISITION, NOISE REDUCTION, PHOTONS
 Bibliographic Code: 1990ccda.proc..335B

                                  Abstract

With modern echelle spectrographs and CCD detectors, photon noise permits
one to measure the radial velocity of bright stars with precision as good as
1 m/s in 60 s of observing time. In order to achieve this precision in
practice, measures must be taken to control several sources of instrumental
noise. Two distinct methods have evolved to do this: (1) use of a molecular
absorption cell to impress lines of constant wavelength on the incoming
starlight, or (2) use of a fiber-optic feed for the starlight, in
conjunction with a second fiber carrying light from a stable wavelength
source. At the current state of development, the first method yields better
long-term stability (useful, e.g., for planetary detection), while the
second method provides better S/N per unit time in circumstances where
low-frequency stability is not required (such as observation of stellar
oscillations). For both methods, details of instrument setup, data
acquisition, and data analysis are important for getting the best results.