[Aavso-photometry] how many stars can I measure

[Radu Corlan]

On Fri, 29 Oct 2004, David Craft wrote:

> Hi Everyone,
> 
> As you will see, I'm completely inexperienced, not even a newbee yet.  
> I'm attempting to develop an observatory program and I've discovered an 
> important area of my ignorance.
> 
> Would a few knowledgeable folks please tell me how many say, magnitude 
> 17 stars it is reasonable to measure in one 10 hour evening?
> 
> What I would like to know is:  assuming clear skies, flawless automated 
> hardware, intelligent slewing, blah blah blah, 600 minutes might give 
> 200 images. I imagine that  the post-processing of these images to 
> develop say, 0.01 mag photometric solutions will take more than 10 
> hours.  

If you want 0.01 noise on mag17 stars, you need to integrate about 1000 
seconds with a 12'' scope, 500 sec with a 18'' scope, assuming you have a 
relatively dark sky, so it doesn't contribute significant noise. You won't 
get a great number of frames at this level. To truly achieve 0.01 error at 
mag 17 is not easy. 

I run an automated system, and it will slew to a new star, get a short 
exposure to check the field, and correct the pointing in about 20 seconds 
if the slew is not very far from the previous object. With 20-sec 
exposures i usually get a new object every minute. the noise is 0.01 
around mag 12.5-13 or so.

> Problem is, I only have my guess, I have no knowledge regarding 
> the degree of automation that may be possible or the degree of operator 
> involvement required to say, match dark frames to the nightly variations 
> in camera temperature 

This really depends on how the particular camera behaves. Some need more 
frequent darks or bias frames, some less frequent.

> and to correctly position the apertures on the images.

This task is fit for automation. IRAF can be made to do this (calculate 
the frame's world coordinates and place the apertures according to the 
catalog positions of stars). If you are satisfied with fixed-aperture 
photometry, my gcx program (linux only) can do the same, and it's easier 
to learn than IRAF. All the frames i take are reduced automatically.

Unless you take just a few frames a night, i'm sure that you will want to 
build a reduction pipeline of sorts that requires little manual 
intervention.

Radu


> Please inform me about what a reasonable expectation would be for an 
> experienced operator using AIP4WIN, Canopus or MIRA (anything except 
> IRAF) unless someone would like to offer a compelling benefit of IRAF.  
> I wish to scale my observing program properly, and I am completely 
> ignorant in this area..
> 
> Thanks in advance.
> 
> Dave Craft
> 
> 
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-- 

-------------
Radu Corlan       Snail Mail: Bucuresti sect. 1, 
rcorlan at pcnet.ro  str. Argentina nr. 28, Romania

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