[AZ-Observing] Re: The Spectroscopy-Photometry Meeting in Dewey
- From: Jeff Hopkins <phxjeff@xxxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Sun, 7 Sep 2008 16:44:33 -0700
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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