Astronomical Spectroscopy - Physics - University of Cincinnati

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Similarly the emphasis here will be primarily on stellar (point) sources, but with some
discussion of how to extend these techniques to extended sources.
The subject of astronomical spectroscopy has received a rich treatment in the literature.
The volume on Astronomical Techniques in the original Stars and Stellar Systems series
contains a number of seminal treatments of spectroscopy. In particular, the introduction to
spectrographs by Bowen (1962) remains useful even 50 years later, as the fundamental physics
remains the same even though photographic plates have given way to CCDs as detectors.
The book on diffraction gratings by Loewen & Popov (1997) is also a valuable resource.
Grey (1976) and Schroeder (1974) provide very accessible descriptions of astronomical spectrographs,
while the “how to” guide by Wagner (1992) has also proven to be very useful.
Similarly the monograph by Walker (1987) delves into the field of astronomical spectroscopy
in a more comprehensive manner than is possible in a single chapter, and is recommended.
2. An Introduction to Astronomical Spectrographs
This section will concentrate on the hardware aspect of astronomical spectroscopy. The
basics are discussed first. The following subsections then describe specific types of astronomical
spectrographs, citing examples in current operation.
2.1. The Basics
When the first author was an undergraduate, his astronomical techniques professor,
one Maarten Schmidt, drew a schematic diagram of a spectrograph on the blackboard,
and said that all astronomical spectrographs contained these essential elements: a slit on
to which the light from the telescope would be focused; a collimator, which would take
the diverging light beam and turn it into parallel light; a disperser (usually a reflection
grating); and a camera that would then focus the spectrum onto the detector. In the
subsequent 35 years of doing astronomical spectroscopy for a living, the first author has yet
to encounter a spectrograph that didn’t meet this description, at least in functionality. In a
multi-object fiber spectrometer, such as Hectospec on the MMT (Fabricant et al. 2005), the
slit is replaced with a series of fibers. In the case of an echelle, such as MagE on the Clay
6.5-m telescope (Marshall et al. 2008), prisms are inserted into the beam after the diffraction
grating to provide cross-dispersion. In the case of an objective-prism spectroscopy, the star
itself acts as a slit “and the Universe for a collimator” (Newall 1910; see also Bidelman 1966).
Nevertheless, this heuristic picture provides the reference for such variations, and a version