Spectroscopic standards should be chosen to have featureless spectra and, preferably, to have known photometric magnitudes. Often it is necessary to use a star close to the object in airmass and position on the sky in order to accurately cancel atmospheric absorption features. A large list of spectroscopic standard stars is then useful. Such a list is reproduced in Table 24. These stars are taken from a variety of sources (MSSSO photometric standards, IRPS/FIGS G dwarfs spectroscopic standards, UKIRT spectroscopic standards, NASA Infrared Catalog, Bright Star Catalog) and have correspondingly uncertain photometric magnitudes. The IRPS/FIGS G dwarf spectroscopic standards are to be preferred, but these and F dwarfs have hydrogen (Paschen and Brackett) absorption that should be allowed for during data reduction. One approach is to measure a later type star to determine the hydrogen line strength in the standard, and then remove this feature before dividing object spectra by the corrected standard star spectrum.
Photometric magnitudes come from the following refereences: M = McGregor (1994,
PASP, 106, 508), C = Carter (1990, MNRAS, 242, 1), B = Bouchet, Manfroid, &
Schmider (1991, A&A Suppl., 91, 409), A = Allen & Cragg (1983, MNRAS, 203,
777). Stars with magnitudes listed but lacking a reference annotation in
Table 24 are taken from the NASA Catalog, and their
photometry should be consider uncertain at the 
0.05 mag level. Other
stars lacking measured photometric magnitudes should be used only as flat
spectrum stars to remove terrestrial absorption features; flux calibration
should be obtained separately.
As a last resort, bright stars from the Ephemeris can be used, but generally these have unknown infrared magnitudes.
The file MAIA::[PETER.OBSERVE]STAND.COORD also contains coordinates for the these stars.
Table 24: Composite List Of Bright Spectroscopic Standards
