From: Terrence Redding <tredding@mac.com>

Date: July 24, 2009 7:20:34 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Photometry on an asteroid 790 Pretoria

Very interesting.  I just spent an enjoyable hour on your website and reading about the cooler on your camera.  I have Mag 2 skies here in West Palm Beach most clear nights.  I check by walking out my front door and looking at Polaris.

I checked a few minutes ago and there was a band of clouds across its location - but blue below that - so I am hoping it will clear. I just checked and Vega and Deneb can be seen but not Polaris.  But the night is very young here and I suspect it will get much better.

You raise a few very good points.  I may never be able to do exoplanet work from here because of the city lights.  Though I was hoping with filters to do some work that is independent of city lights - we shall see.  

Thanks for the help.  I plan to make it an early night and then get up at 4 AM for my first effort with Jupiter.  I am anxious to give it a go.

Cheers,

Terry - W6LMJ

Terrence R. Redding, Ph.D. RTN

http://olt.net/learningstyle/Site_2/Learning_Style_Research.html

How do amateur astronomers learn?

On Jul 24, 2009, at 7:05 PM, Milton Aupperle wrote:

Hi Terrence;

On 24-Jul-09, at 4:26 PM, Terrence Redding wrote:

It appears I can skip the DSLR color camera and simply use Astro-IIDC to gather a periodic set of frames of the asteroid for the highly sensitive photometric work.  I am currently bumping up against a .2 mag change limit with my occultation setup.  How sensitive might I get with the DMK 21?

The sensitivity is somewhat camera dependent (high inherent gains like your occultation setup make it very poor for accurate photometry) , but it's also sky dependent (turbulence and transparency) and how careful you are with tracking, darks and flats - which I mentioned in the Astro IIDC starting at  on page 52, starting with the line "To do reasonably accurate (< 0.1 magnitude variance)....". I also have a set of url links to organizations like AAVSO which discuss it in more detail too.

Eventually i have to be able to achive the .02 range for exoplanet work.  Might I do that with Astro-IIDC?

Yes, but I doubt if your going to get that low with an 8 bit uncooled camera. I gave mention of what I can achieve using a C8 and a Grasshopper 16 bit cooled camera an example as far as accuracy goes. At the dark site, I wasn't even doing Flat frames and was getting +/- 0.01 to 0.03 error magnitude accuracy just using a IR Cut filter, instead of one of the UVBI required filters.  If your skies are really dark and transparent, you can probably go to 0.02 or lower, which is what I was getting last summer in my initial tests. The worse your light pollution and lower your transparency, the bigger your error factor is.

Since my last move, my skies have improved a lot (generally Mag 4 or lower), but there is barely 2 hours of real darkness during my summer (will be 14+ hours come this winter) so doing qualitative measurements is tough right now.

HTH..

Milton J. Aupperle