[Aavso-photometry] RE: [TransitSearch] hd 80606 campaign update

Wed Mar 2 18:20:05 EST 2005

Hi Frank - let me jump in here and fine tune what I meant by red vs any bandpass in general vs no bandpass at all... Aaron Price at AAVSO just conferred w/ me and had some SUPER points to caveat my first sentence... While I was a bit idealistic that a bandpass is better than no bandpass, for collecting for a team effort (and Aaron has run MANY multi-observer campaigns) , Red  - in particular - is actually not a good filter at all, "when it comes to combining data
from multiple observers. Not only do various CCDs add weird effects but the emission lines in red stars act very strange and can effect the photometry". As Aaron well put, you gotta know the spectra of your target (to pick an optimal bandpass)AS WELL AS the comparison/Check stars you use - to check line differences... And that's alot of what occupies AAVSO's preps to run such campaigns...

And why I often stick with (spectra considered) Johnson V filters..

Hope that helps - and thanks, Aaron for making sure the point is clear here-
Paul

-----Original Message-----
From: transitsearch-bounces at ucolick.org
[mailto:transitsearch-bounces at ucolick.org]On Behalf Of Shankland, Paul D
CDR U.S. Naval Observatory
Sent: Wednesday, March 02, 2005 18:02
To: FrankJ12 at aol.com; laugh at ucolick.org; transitsearch at ucolick.org;
tcastellano at mail.arc.nasa.gov; aavso-photometry at aavso.org
Cc: pdshankland at comcast.net
Subject: RE: [TransitSearch] hd 80606 campaign update

Hi Frank,
let me first mention that I applaud the use of the red filters - that tightens the bandpass and ups the S/N; many folks eventually find a V filter because it's a standard, but red is a big plus... And I concur, photometry sounds simple in concept (hey, just count photons), but can be subtle and complicated in practice to operate at the millimag level... The idea is to remove systematic potential/actual sources of noise (hence darks/flats, more in a sec on this)... And while we don't know what we don't know, we still know alot, teased from very subtle science... 

Not to digress alot about the character of transit curves, slopes, typical noise, albedo, etc etc... things like keeping on the linear portion of the CCD response curve, regulated cooling (etc (see Tim Castellano's papers for details: http://www.skywokker.com/transit%20observing%20procedure.doc, http://www.skywokker.com/transitsearchobserving3.pdf, http://www.skywokker.com/transitsearchobservingprocedures.htm and some practical advice by Tom Krajci here: http://overton2.tamu.edu/aset/krajci/photometry_files/frame.htm, and AAVSO's Arne Hendon: http://www.aavso.org/meetings/pcpw1.ppt. 

Starizona (http://www.starizona.com/ccd/index.htm) does a good job of explaining why darks and flats are important - you still need them even if you keep the photons on the same pixels (which is theoretical in itself - the best guiders on permanent instruments aren't that good). http://www.starizona.com/ccd/procadvcal.htm gives an idea. The problem is temporal, focuser etc etc, changes in the darks and flats (hence collecting them around the primary images, a la: http://brucegary.net/tutorial_exoplanet/, http://reductionism.net.seanic.net/HD209458/ExoPlanet.html, http://brucegary.net/ILAqr/, http://scholar.uws.edu.au/~10236680/AIM_StudentPapers/hudgins_arp_final_paper.doc, and http://brucegary.net/TrES-1/... 

A thorough explanation is here http://adsabs.harvard.edu//full/seri/JAVSO/0024//0000019.000.html if I recall.. This one is good too, for general stuff: http://www.aavso.org/observing/programs/ccd/manual/, and http://www.aavso.org/observing/programs/ccd/transitsearch.shtml

Another explain that's good:  http://infomagic.net/~ccdir/hipre.html  another is: http://infomagic.net/~ccdir/howto.html

I agree - any additional looking is always helpful in the world of transitsearching, more is better. As for numbers, feel free to email me them directly - unless you prefer to post them...

LSQ => least squares fit, my generic use of fitting a curve to the data (you might find a host of definitiions via google).
See: http://www.physics.csbsju.edu/stats/QF_NROW_form.html, http://www.physics.csbsju.edu/stats/cstats_NROW_form.html, http://www.physics.csbsju.edu/stats/Index.htmlfor useful online crunchers in non-graphical form, or http://www.physics.csbsju.edu/stats/display.distribution.html...http://www3.sympatico.ca/mcomeau/webpublic/javapage/reg/reg.htm Excel will do fits too...

Yes, Excel is one brand of spreadsheet, and many photometry packages can dump one's numerical results to an output that is directly readable by Excel or the like. 

Not to inundate you with links - but there's plenty of good material out there that very desciptively answers the mail!

Hope that helps!
Best,
Paul

-----Original Message-----
From: FrankJ12 at aol.com [mailto:FrankJ12 at aol.com]
Sent: Wednesday, March 02, 2005 14:24
To: Shankland, Paul D CDR U.S. Naval Observatory; laugh at ucolick.org;
transitsearch at ucolick.org; tcastellano at mail.arc.nasa.gov;
aavso-photometry at aavso.org-
Subject: RE: [TransitSearch] hd 80606 campaign update

   Thanks Paul for analyzing my lightcurves.

   As you know, it is quite tough to monitor something we don't know yet. Yes, I'm not sure either if this is a flux, noise or an actual lightcurve of the transit. 

   >>>can you post such numbers?<<< 

    Yes, if you want me, I can send you the numbers which I got the readings from the raw images. 

     >>>Have you done an LSQ<<<

    I'm not sure what LSQ mean? 

    >>>A spreadsheet?<<<

     I think I have a spreadsheet. Is this the same as Microsoft Excel? 

     >>>Did you do any data reduction in the Starlight Express? <<< 

   The Starlight Xpress is already being calculated for the magnitude difference once the ratio of two objects are found. I used 9 pixels square-shaped for photometry aperture. Of course, I have a choice of using more pixels or less for aperture photometry. But, 9 pixels seem appropriated for this purpose without comparison star HD 80607 intefere the readings.

    >>>I would caution that to maintain rigor, darks, flats and filters become very important for all sequences. I know there is a crowd to argue about, in particular, filters, but for a broad spectrum of reasons, the data needs to have all those run before it's publishable.<<<

   I am totally aware of this. I didn't do any darks and flats field. I thought it wouldn't be necessary because the stars were always imaged on the exact same area or pixels in the field. Also, I've used a Wr, #25 red filter for longer exposure to smooth out the atmospheric disturbances and color corrections. So, the 11 second exposure at f/6.3 was just right without saturating the pixels.

   Yes, it is fun especially to look for something that was never seen before. I would like to see how other observers made out. I still believe there is something about HD 80606 lightcurves and we need more observers and perhaps another campaign to follow-up to see if the results can be repeated.

   More later...

   Frank J Melillo
   ALPO Member
   Holtsville, NY 

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