[Aavso-photometry] Tu Cas - some random thoughts

Tue Sep 27 16:42:55 EDT 2005

Thanks, Tim, very helpful.

I was using 25 second exposures last night in V. Haven't reduced the  
data yet. I can get all three comp stars in the field. I had (yet  
another) equipment problem so my run is only about 2.5 hours long. I  
suspect with a period this long runs like mine may not have that much  
value. I will be interested in seeing if there is microvariability.  
Even if there is not, it might be fun to get very dense coverage and  
get a high-quality light curve of the entire cycle a couple of times.  
I'll wait for more learned minds to tell me if this is a waste of  
time or not. Because of my small (~6") scope I thought I'd adopt this  
star for the winter and see how it goes.

Michael

On Sep 27, 2005, at 3:16 PM, Tim Crawford wrote:

> 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
>
>
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