[Aavso-photometry] Starting up CCD Obs of Variable Stars

[Arne Henden]

On 5/22/07, Greg Crawford <gc at nelsonbay.com> wrote:
> After taking forever and a day to get ready for variable star obs, I think I am
> ready to begin. I thought I might start with the CCD observing program for faint
> CVs and LPVs. I chose a CV because I am reading about them in the book by ("the
> other") Brian Warner. I like to have some intellectual input to complement any
> obs I make so I have an understanding of the physics behind it.
>
> Given my southerly latitude (-32), I thought I'd start with UU Aql. (I had given
> some thought to RX Cen, but the comment about sequence needing extension put me
> off for a first timer).
>
> A few questions:
>
> 1) UU Aql seems to be entered into the following table twice. I'm not sure if
> that is an error or conveys significant information. See here:
> http://www.aavso.org/observing/programs/ccd/ccdlpv.shtml#table
>
Hi Greg,
Obviously an error.  Use the 2nd line, which gives a comment.  I'll get
this table updated when I get back to Boston next week (your email came in
while I was on the road).  UU Aql is a good star to start with, as it has a good
BV sequence (from Henden).  It is about V=16.5 in quiescence, pretty easy
to measure by most CCD observers, with outbursts to V=11 about every
50 days or so.

> 2) How often should observations be made? I am used to tracking an asteroid
> throughout the night with continuous observations from 30 degrees altitude in
> the east to 30 degrees altitude in the west. Are obs of a CV handled in the same
> way?
>
The CCD program for faint CVs is a little dated and needs some revision.
In general, it was designed for obtaining the magnitudes of a selected set
of CVs when they were at quiescence, as anyone can observe these things
when they are in bright outburst.  Therefore, one datapoint per night
is sufficient.
This program is a specific subset of all of the AAVSO activity regarding CVs.
Usually, we highlight those stars that are undergoing rare outbursts (such
as RS Oph last year and GW Lib this year) with Special Notices and Alert
Notices.  If a researcher asks us to set up a campaign on a specific set
of stars, we do so with the same Notices so that things are well documented,
and then often set up a special web page for the campaign so that you can
monitor the progress.  Unlike CBA, we request our observers to use a filter
whenever possible, as researchers utilizing our data may have quite different
needs than the analysis done by CBA.

So bottom line is once per night unless something unusual is happening; then
time series.

> 3) The program appears to only want obs through a V filter. After struggling
> with T/Cs, FOEs and ZPs for limited all-sky photometry for asteroids, I've
> discovered how easy variable star observers get it when they have a (secondary)
> standard field in the field of view. :-) (In MPO Canopus software, after
> measuring the images, a few clicks gives you standardized measures using the
> QuickMags method.) If I also have observations in B and R, should they be
> uploaded to WebObs as well?
>
Sure!  We accept all filtered observations and encourage observers to use more
than one filter if possible for a given "observation set".  Most CV
outbursts are
colorless, so single-filter observations are ok, but in quiescence you can get
quite different colors for CVs, you certainly have different colors
for the comp stars,
and for all other pulsating stars, their color changes during their
cycle so color
information is very useful.  So for fields like UU Aql, where good B and V data
are available for the comp stars, submitting B and V measures is great.  The
problem is when trying to submit Rc and Ic measures, since you have no standard
magnitudes for these comp stars yet.  We're working on that addition, but many
fields *do* have BVRcIc calibration - you just have to look around.

> 4) How do I get an observer code? Do I have to qualify in some way in the same
> way that minor planet observers must submit obs to the MPC?
>
If you go to the Blue and Gold section of the website, and register,
one of the options
is to request an observer code.  There are no requirements.  As a human handles
the request, it may take a day or two so be patient.

There will be a number of changes for CCD observers starting this summer, in
order to improve the quality of the data being submitted and to standardize the
process.
Arne