[Aavso-photometry] Tu Cas - some random thoughts

[Tim Crawford]

Some random thoughts RE TU Cas

1) Since the BOSS (Arne) is asking we need to try and
include this target on our viewing lists
. Especially
since this is about the third request in the last
three or four months.

2) The AAVSO E chart lists only three comps
..
however, the separation is so large between all three
of the comps and TU Cas that some pre-planning is
required to minimize the difficulties.

The 10.4 comp star is approximately 7 arcsec from Tu
Cas
The 9.0 comp star is approximately 12 arcsec from Tu
Cas
The 9.2 comp star is approximately 16 arcsec from Tu
Cas

For most of us the reality then is going to be that we
will only be able to get the one 10.4 comp star within
our field of view and still have room for the analysis
“rings.”  

A 12”  f/10 scope with a ST-9E, for example can get
the target and 10.4 star OK
A 12” f/6.3 scope with a ST-9E  MIGHT  manage to get
both the 10.4 and the 9.0 comp star.
A 12” f/10 scope with a ST-7E will not be able to
acquire any comps with the target
A 12” f/6.3 scope with a ST-7E will be able to get the
10.4 star and the target
An 8” f/10 scope with the ST-7E will be able to get
the 10.4 star and the target
An 8” f/6.3 scope with the ST-7E MIGHT manage to get
both the 10.4 and the 9.0 comp star.

This link will bring up a CCD calculator to see the
effects of different scopes and CCD’s:

http://www.starizona.com/ccd/equipbasicsccd.htm


3)  TU Cas is a bright target.  6.88-8.18 according to
the chart.

The other night (26th) at a V of 7.279 my exposure
time with the ST-9E on a 12” f/10 scope was 5 seconds.
 B filter was  30 Seconds, R filter was 3 seconds and
the I filter was 10 seconds.

What I have done the two nights that I sampled this
target was to use the focus capture, at full size,
with CCDOPS, which shows the maximum pixel value
 I
experimented with each filter until I could get
reasonable ADU counts with out getting to close to
saturation then when I was satisfied to go ahead and
save that image rather than doing a grab which might
have different values.

As this target gets close to maximum I may have to use
my aperture mask so that longer integrations can be
accomplished.

I use one of the commercial Hartmann focusing masks
that are for sale with two or three 3-inch openings
for my 12” scope; however, I have enlarged one of the
holes to four inches.  As I was not actually able to
enlarge the hole smoothly to four inches (metal Mask) 
I enlarged it slightly larger then I overlaid a clean
and smooth cut piece of thin cardboard with a
four-inch opening.  This was then taped to the Mask
and the area sprayed with black paint (the other two
holes have their own covers).  Works great and I have
used this on stars in the 5.5 range with reasonable
effectiveness.

Here is a link for making a Hartmann Focusing mask:

http://www.cloudynights.com/item.php?item_id=518

Here is a link for purchasing commercial Metal masks
(they usually come with covers for each of the holes),

www.buytelescopes.com/search.asp?q=Kwik+Focus&x=15&y=10&s=

4) Somebody posted a question about Time Series.  The
original post that came out RE observing this target,
some time back, stated the following:

“Observers should use BVRI filters and try to get one
image per night.  When time permits, time series runs
with multifilter observations sets separated by 30
minutes would be useful."
________________

The other night My CCD failed just as I was starting
another BVRI run on this target.  SBIG has been very
gracious and offered to replace my boards as the
problem has been intermittent.  Therefore I will,
again, be out of service for one to two weeks,
although I may try and see if it will work tonight
before sending it off.

CS


Tim Crawford CTX
Arch Cape Observatory

http://homepage.mac.com/windwalker1/ACObserv.htm