CHAPTER 5. NEXT STEPS
to simulate a cold night). Take a large number of im-
ages, and create a set of master darks from them just
once.
5.2.3 Exposure time
We suggest you always use the same exposure time
for your observations (typically 5 minutes - 300 sec-
onds - for faint objects). Of course, the total exposure
time will depend on the object magnitude, but you
can adapt the total exposure time by changing the
number of exposure. They are several avantages to
proceeding this way:
– You can always use the same dark frames,
– Data reduction is very fast (no parameter is changed),
– No risk of error during acquisition (you never
change the time).
There are some limits with this process, for instance
for bright or extremely faint objects, but in general it
will make your life easier.
5.2.4 Prepare for your observation
Amateur astronomers often wait for the last minute
to decide what to observe. We recommend to prepare
for your observation well in advance. If you properly
organize your observing session, you will optimize the
target order, their position in the sky (higher is bet-
ter), and so on. You can even define the exposure time
for each object, depending on their brightness.
If you are looking for target and observing pro-
grams, you can look at the Shelyak Instruments web-
site
2
: we’ve listed many ideas, ranging from from easy
to ambitious.
5.2.5 One directory per observing session
This is a basic advice, but doing spectroscopy will
quickly produce a high volume of files. To be sure that
you will be able to proceed with a reliable data re-
duction, it is important to not mix files from different
observing sessions. We recommend that you to create
a new empty directory at the beginning of each ob-
serving session (an observing session is generally an
observing night). Put your log file (see section 5.1.7)
in this directory.
5.2.6 Reduce your data quickly
It is very common that astronomers use the time
during the night to observe and wait until the day af-
ter to reduce the data. Be careful: if you wait too long,
you’ll probably never reduce your data. And having
just raw data on your hard disk is the same as if you
did nothing. We strongly encourage you to reduce
your data immediately after acquisition. This way it
is all fresh in your mind, and there is much less risk
of mistakes during the data reduction.
5.3 Share your results
Our experience shows that the best way to improve
your data is to compare your results with others. When
you compare your spectra with the results from ex-
perienced people - with comparable instruments, of
course - you can get an idea of the potential for im-
provement you have in front of you. We encourage
you, for instance, to observe Be stars, and look at the
BeSS database
3
for comparable observations. You can
even send your spectra to the database - they will be
checked by administrators who give feedback on po-
tential improvements.
In addition, spectroscopy is certainly still at a pio-
neering stage. All the data you collect are of the high-
est interest for the scientific community: don’t keep
them to yourself.
5.4 Get pro-like quality spectra
Very often, amateur astronomers think they are not
able to provide high quality data, comparable to those
produced by professionals. Of course, amateurs usu-
ally don’t have professional quality instruments - but
the quality of the data is more a question of method-
ology than instrumentation and you will quickly see
that you can reach professional quality, with just as
much rigour. You can even contribute to research in
several Pro-Amateur collaborations. In a few words,
to get good quality data, you need to pay attention
to:
– Accurate auto-guiding
– Repeatable configuration and processing
– Correct data reduction: SNR, Wavelength calibra-
tion, Instrumental response curve correction.
– Standard file format (see for instance BeSS file
format)
– Archiving and backing up the raw data
Never forget that when you’re observing the
spectra of an object, you’re probably the only
one doing it at this time on earth - this is incred-
ibly valuable data... and you must absolutely
archive it very carefully (raw images as well as
processed data).
2. www.shelyak.com - menu spectroscopy / educationnal &
projects
3. http://basebe.obspm.fr/basebe/Accueil.php?flag_lang=en
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