[AZ-Observing] Re: The Spectroscopy-Photometry Meeting in Dewey

Yesterday I gave a paper at the meeting in Dewey, AZ on methods to do 
wavelength calibration of a hydrogen alpha spectrum profile.  One may 
wonder why the interest in hydrogen alpha.

When hydrogen gas is excited it will emit a bright red spectral line. 
This line is known as the hydrogen alpha line. There are other lines 
emitted also, but this is most prominent. In this case the line would 
be an emission line. When there is a continuous spectrum, e.g., from 
an incandescent light or interior of a star, and a surrounding gas 
shell of hydrogen (e.g., a star's atmosphere) the hydrogen atoms in 
the gas shell will absorb the hydrogen alpha line and the continuous 
spectrum will have a hole or dark line (an absorption line) at the 
wavelength of the hydrogen alpha photons. In the case of Be stars and 
others, it is even more interesting as there may be emission line 
horns on each side of the absorption line, one at a longer wavelength 
and one at a shorted wavelength. Lots of good information there.

Why is this of interest in astronomy? Since most stars are mainly 
hydrogen and there is lots of hydrogen gas around, this line provides 
some very interesting information about a star. The profiles of the 
line can tell a great deal and the  shift in wavelength due to a 
Doppler shift can tell even more. Hydrogen alpha is one of them most 
interesting lines in stellar spectrums.

The following is the paper abstract.

Hydrogen Alpha Wavelength Calibration

************************************
Jeff Hopkins
Hopkins Phoenix Observatory
6 September 2008

Abstract

To provide useful spectral wavelength information, a stellar spectrum 
must be wavelength calibrated. This paper will discuss ways to use 
VSpec software to wavelength calibrate a high resolution (2,400 
lines/mm) stellar hydrogen alpha spectrum. The paper will discuss 
using neon spectral lines to provide a linear calibration. The use of 
atmospheric water absorption lines to create a non-linear calibration 
will also be discussed. Finally the use of a heliocentric calibration 
will be discussed. The resulting wavelength calibrated spectrum can 
be used to determine radial velocities to a high degree of accuracy.

************************************

A pdf (~ 2MB) of the paper can  be downloaded at

http://www.hposoft.com/HaCalibration.pdf


Clear skies.

Jeff

-- 
Jeff Hopkins
HPO SOFT
Counting Photons
http://www.hposoft.com/Astro/astro.html
Hopkins Phoenix Observatory
7812 West Clayton Drive
Phoenix, Arizona 85033-2439 U.S.A.
(623)849-5889
(623) 247-1190 (Fax)
www.hposoft.com
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