Some Bright Stars with Smooth Continua for Calibrating the Response of High Resolution Spectrographs

TL;DR

This paper identifies and compiles a list of bright, hot stars with smooth continua suitable for calibrating high resolution spectrographs, addressing the challenge of finding featureless sources for precise instrument response characterization.

Contribution

The authors provide an empirically derived list of hot stars with smooth continua, useful for spectrograph calibration, based on observational criteria rather than theoretical parameters.

Findings

Compiled a list of suitable calibration stars visible from the Northern Hemisphere.

Identified criteria for selecting stars with minimal spectral features.

Provided a resource for improving spectrograph response calibration.

Abstract

When characterizing a high resolution echelle spectrograph, for instance for precise Doppler work, it is useful to observe featureless sources such as quartz lamps or hot stars to determine the response of the instrument. Such sources provide a way to determine the blaze function of the orders, pixel-to-pixel variations in the detector, fringing in the system, and other important characteristics. In practice, however, many B or early A stars do not provide a smooth continuum, whether because they are not rotating rapidly enough or for some other reason. In fact, we have found that published rotational velocities and temperatures are not a specific and sensitive guide to whether a star's continuum will be smooth. A useful resource for observers, therefore, is a list of "good" hot stars: bright, blue stars known empirically to have no lines or other spectral features beyond the Balmer series with minima below 95% of the continuum. We have compiled a list of such stars visible from Northern Hemisphere telescopes. This list includes all stars listed in the Yale Bright Star Catalog (Hoffleit & Jaschek 1991) as being single with V < 5.5, v sin i > 175 km/s, and declination > -30, and many other hot stars that we have found useful for calibration purposes. The list here of "bad" stars may also be of interest in studies of hot, slowly rotating stars.