[Aavso-photometry] Blazars

[Michael Koppelman]

(Hope you don't mind I'm replying to the group as well.)

It's a good idea, to try having different observers all agree on an  
aperture size in arcseconds. I probably have the least resolution and  
am using apertures around 20 arcseconds in radius. The smallest I can  
meaningfully go is about 14 arcseconds. That is still probably a lot  
bigger than you use?

(Another idea I've wanted to try is to have a lot of simultaneous  
observations so we could combine them and beat down the errors. If  
everyone used the same comps, the same apertures and calculated the  
errors the same way, you could in theory get a pretty high quality  
light curve.)

Cheers,
Michael

On Feb 20, 2006, at 4:54 PM, Michael Armstrong wrote:

> Michael,
> HI!  I enjoy observing these objects when I get the chance.  One  
> thing I
> mentioned to Arne and Aaron was that I think these objects need to be
> considered for "standard apertures."  I've found, with the data I have
> on Mrk 421, that I can get quite a variation in mags (larger than
> normal) by varying the aperture size to specifically include or  
> exclude
> the not-so-obvious nebulosity.
>
> By way of example, during my initial observing runs, I was being very
> careful to exclude the nebulosity and I noticed that my mags were a  
> bit
> dimmer than another observer on the same night, in the same band.   
> This
> caused me to ponder why that might be and I started to play.  I found
> that by increasing my aperture by a mere 2-3 arc-secs, my numbers  
> agreed
> with his to within 0.01 on every observation (we were actually on the
> target at teh same time).  I stacked a load of those images to be able
> to see the nebulosity and there was no doubt that by increasing my
> aperture, I was including nebulosity that wasn't readily apparent  
> in any
> single image.  This led me to consider that we should probably all  
> be on
> a common aperture size with these object.  I know that is easier said
> than done, but I think it needs to be considered, unless we aren't
> looking for inter-observer accuracy, but just object variability.
>
> As long as each observer always uses the same apertures on all their
> images of MRK 421, for example, I guess the difference between  
> observers
> could be normalized. At the very least, this issue certainly makes
> reduction of data from multiple observers a challenge for you :) .
>
> What do you think?
>
> Mike Armstrong (AMN)
>
>
>
> On Mon, 2006-02-20 at 13:20 -0600, Michael Koppelman wrote:
>> I'm taking a class on the structure and evolution of galaxies. We are
>> required to do a presentation at the end of the semester and I
>> decided to do mine on blazars. Being an observational astronomer of
>> the amateur variety, I thought it would be fun to include my own data
>> in the presentation. (I find that young undergraduate students in
>> astronomy are rarely observationally focused.) As you may or may not
>> know the AAVSO has a blazar program.
>>
>> See:
>> http://www.aavso.org/observing/programs/hen/blazar.shtml
>>
>> with charts here:
>> http://www.aavso.org/observing/charts/ccd.shtml
>>
>> I see there are some dedicated observers working on these objects and
>> the long term coverage is actually getting quite good.
>>
>> I bring this to your attention because I would appreciate time-series
>> observations of these objects to include with my own in my
>> presentation. My thought was to report on intra-night variations of
>> these objects. As an example, I got some data on Mark 421 and found
>> the standard deviation in the magnitudes was 4 times higher for this
>> object than the surrounding comparison stars. Bruce Gary, on the top
>> AAVSO link above, has a nice report on the capabilities of amateurs
>> to measure intra-night variations.
>>
>> It is unlikely that this will result in anything publishable, but you
>> never know.
>>
>> If you want to participate all I ask is that you submit your
>> observations normally to the AAVSO and email me so I can correlate
>> our data.
>>
>> Thanks!
>> Michael Koppelman
>> http://www.lolife.com/astronomy/
>>
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>