ASTRONOMICAL SPECTRA by HPOL
ASTRONOMICAL SPECTRA by HPOL (v2.1)
Anthony J Weitenbeck
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
Some of these stars were observed as part of HPOL
polarimetric projects, some were observed solely as spectrum
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
[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
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:
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
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
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,
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