Sky and Telescope - September 2018 - 70

S&T Test Report

well thereafter. A similar issue occurred
when I tried using a different camera,
so make sure you have installed the latest drivers for your own cameras.

Capturing Spectra
The process of recording spectra is
simple. Select the Live Camera tab and
choose your camera from the list that
appears after clicking the Open button.
Exposure and other adjustments are
accessed with a Configure menu. One
unfamiliar control for spectroscopy
newbies is rotate. This slider allows the
image to be rotated to the standard
convention in spectroscopy, placing the
star's image on the left of the screen
and its spectrum to its right. This only
affects the displayed image and is not
saved with a recording. Finally, two
onscreen "bars" are positioned with the
mouse to frame the star and its spectrum. This tells RSpec to concentrate on
the area between the lines.
You may have wondered what the R
in RSpec means: It stands for real-time,
as in real-time spectroscopy. As soon as
the star and its spectrum are properly
placed in the video window, the spectrum's graph appears in the Profile section of the screen. You can analyze the
star in real time without recording or
saving any images. However, I preferred
to concentrate on getting good recordings in the field and analyze the spectra
the next day.
With star and spectrum onscreen,
I clicked Record to capture my first
target, Vega. It's a bright A-type star,
and RSpec's author warns users to begin
with a star of that spectral type. These
stars display strong hydrogen Balmer
lines, which are useful for calibrating
the program. Like any grating, the Star
Analyzer produces two rainbows - two
spectra, one on either side of the star's
image, and one is brighter than the
other. Use the brighter of the two.

Spectrometry
Browsing the RSpec website and asking
Tom Field a question or two had been
sufficient to allow me to capture spectra, but before beginning to analyze my
stars, I thought I'd better read RSpec's
70

S E P TE M B E R 2 018 * SK Y & TELESCOPE

The final step before RSpec
is ready to analyze spectra is
to calibrate the program using an A-type star using the
Calibrate function from the
pull-down menu. Select the
peak in the left side of the
graph as Calibration Point 1,
and select the first dip in the
spectrum, which should represent the first Balmer line,
H-Beta, and insert "4861"
to denote its wavelength in
angstroms.

When calibration is complete, you can open the Elements window in the Profile
section and overlay the
points of known elements.
This screen shows the location of the hydrogen Balmer
lines found in the spectrum
of Vega.

Calibration should be saved
so you can later apply it to
other recorded spectra like
that of Regulus seen at right.

manual, but I was somewhat surprised
to learn that there is none. Well, at least
no written manual. The program's website contains a library of professionalquality instructional videos detailing
every aspect of the software. While I
still wished for written instructions,
they weren't really necessary. The process of calibrating and analyzing spectra
is amazingly simple.
Before doing anything else, RSpec
must be calibrated. First, the x-axis of

the Profile needs to be converted from
pixels to angstroms (used to express
wavelength). Once calibrated, the elements represented by the dips in the
graph (the absorption lines caused by
elements in the star's atmosphere) are
easy to determine.
Calibration requires just a few steps.
Open your video or image file of an
A-type star and its spectrum. If the
Profile is jumping around as the video
plays due to atmospheric seeing, tick the



Table of Contents for the Digital Edition of Sky and Telescope - September 2018

Contents
Sky and Telescope - September 2018 - Cover1
Sky and Telescope - September 2018 - Cover2
Sky and Telescope - September 2018 - 1
Sky and Telescope - September 2018 - Contents
Sky and Telescope - September 2018 - 3
Sky and Telescope - September 2018 - 4
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