Astronomical Spectroscopy

TL;DR

This paper provides a comprehensive overview of astronomical spectroscopy, covering instrument types, observational techniques, data reduction practices, and practical examples for both point and extended sources.

Contribution

It offers a detailed synthesis of spectroscopic methods, emphasizing best practices and trade-offs, with practical insights from real observational experiences.

Findings

Standard flat-fielding practices can sometimes degrade data quality.

Multi-object spectroscopy enhances observational efficiency.

Real-life examples illustrate practical instrument use and data analysis.

Abstract

Spectroscopy is one of the most important tools that an astronomer has for studying the universe. This chapter begins by discussing the basics, including the different types of optical spectrographs, with extension to the ultraviolet and the near-infrared. Emphasis is given to the fundamentals of how spectrographs are used, and the trade-offs involved in designing an observational experiment. It then covers observing and reduction techniques, noting that some of the standard practices of flat-fielding often actually degrade the quality of the data rather than improve it. Although the focus is on point sources, spatially resolved spectroscopy of extended sources is also briefly discussed. Discussion of differential extinction, the impact of crowding, multi-object techniques, optimal extractions, flat-fielding considerations, and determining radial velocities and velocity dispersions provide the spectroscopist with the fundamentals needed to obtain the best data. Finally the chapter combines the previous material by providing some examples of real-life observing experiences with several typical instruments.