ASTRONOMICAL SPECTRA by HPOL (v2.0)
Anthony J Weitenbeck ajw@sal.wisc.edu

This directory contains:
A list of standards plots in the blue spectral region.
A list of standards plots in the red spectral region.
A list of blue spectra 'unknowns' plots.
Some stars with peculiarities in their spectra.
All plots are .ps files.

Spectra of stars which have been defined as spectrum standards have been obtained with the UW-Madison spectropolarimeter HPOL.
Some of these stars were observed as part of HPOL polarimetric projects, some were observed solely as spectrum standards.
The original purpose in making the standards observations and plots was to use them to classify certain faint stars for which we have polarimetry to get spectroscopic parallaxes. [This is the recommended procedure for doing spectral classification: take spectra of known standards with your observing equipment so you know how standards look with your instrument, before attempting to classify unknowns.]
We show them here to illustrate the quality of HPOL spectra for bright stars.

It also appears that HPOL spectra might be useful to educators, either as illustrations during lecture, or as part of a lab (necessarily along with photographic spectra).

The original data covers 3200-10500 Angstroms; only 3500-5000 is plotted here for the blue standards since that is the traditional region used for spectral classification (being the range of old blue-sensitive photographic emulsions). [Also this region contains more diagnostic lines, at least for hotter stars, than longer wavelengths do.]
The grid of blue standards is almost complete for O9-G2 main sequence stars, and fairly complete for giants and supergiants; G's are about half complete; only two K & M have been obtained (and, faint as they are, no M dwarfs are apt to be observed). Other spectra may be added to the list when the observations are reduced.
The resolution is not quite up to traditional photographic classification quality, but is close enough that classification works well with late O, B, A, & F, but might not be so good with hotter (weaker lines) or cooler (very many lines) stars.
Classification works best by first comparing the standard spectra plots to photographic atlases to see which small dips in the plots actually are lines (or, where to look in the plots for lines).
Plots of the red-nearIR spectra are also shown for comparison. They can be used for spectral classification, but with greater difficulty than the blue spectra because of fewer star lines but many Earth atmosphere features.
Some stars with 'peculiar' spectra (i.e., not on the OBAFGKM sequence or with unusual spectral features) and 'unknowns' (for possible laboratory exercises) are given.
Stellar flux standards are observed to measure extinction. Variations in extinction during a night can cause poor determination of the overall flux level or the flux at the shortest or longest wavelengths, or mismatch between the red and blue observation flux levels.
More information about individual stars is in the Bright Star Catalog, or the SIMBAD database: simbad.u-strasbg.fr.

Anyone trying to use the spectrum plots would need references containing photgraphic spectra; the most complete would be:

   Revised MK Atlas for Stars earlier than the Sun,
   W W Morgan, Helmut Abt & J W Tapscott
       and
   Atlas of Spectra of Cooler Stars,
   P C Keenan & R McNeil (Ohio State U Press, 1976),
These would make easier the identification of the particular lines which define the spectral classes on the plots.

Introductory astronomy texts & lab manuals contain pictures of astronomical spectra for use as lecture illustrations and student lab exercises. Examples:
Dale Ferguson: Introductory Astronomy Exercises, Exercise 20
Jay T Pasachoff: Astronomy: from the Earth to the Universe, 6th Ed, figs 24-14, 24-15

To use the spectrum plots as a lab (along with some 'unknowns'), it would probably be necessary to mark up the standard plots with line ID's, and it would be necessary to use the verbal definitions in the atlases of which atom or ion line ratios define spectral types and which lines are strong for which spectral types.
Looking at these plots in a lab would probably be too obscure or tedious for students in a one semester introductory course, except maybe as a small part of an extra long lab which included looking at photographic spectra. However, the spectra might be useful for a two semester course (again, in an extra long lab), and certainly would be useful for more advanced astronomy courses.
Anyone planning to publish any of these, either giving a paper or including it in a textbook, should contact SAL regarding permission.