View Full Version here: : Photometry
18-05-2009, 09:25 PM
Just to start a new thread based on Bernard's comments on UBVRI filters etc.
I found "Astronomical Photometry" by Henden and Kaitchuck to be very usefull, although it shows it's age ( published in 1982) it's a wealth of knowledge on the subject! Just replace the references to the standard IP21 photmultiplier with current CCD technology.
The other, that was recommended to me was "The Photoelectric Photometry Handbook" by Genet, Genet and Genet ( yes the whole family was involved!) published in 1987. I found this totally useless for me! Didn't address any of the problems and issues I was concerned with.
Henden&Kaitchuck is probably all you need.
19-05-2009, 01:00 AM
Henden's book, as you say, is pretty dated ... which is why I never us it these days, except for the basic theory.
I do suggest Brian D. Warner's "Lightcurve Photometry and Analysis" ... the 2006 Springer edition which is much better than his 2003 self published edition which was a bit of a mess. Berry & Burnell's HAIP is pretty good.
19-05-2009, 12:44 PM
On another tack, I had done some thinking about using spectroscopy results for B-Vmag estimates. UVBRI filters seem hard to get hold of.
As each filter has a bandwidth, would it be possible to use the area-under-curve method and a standard "candle" eg Vega to calculate colour magnitudes and thus distance?
19-05-2009, 03:46 PM
Got both editions of Brians book. I actually found the 2003 edition better - gave me a better understanding of All Sky photometry but the 2006 edition is more concise and compact.
Hendens book is good but most of it is really is aimed at Photoelectric photometry.
HAIP is a good book as well.
The one thing that amazes me is how many amateurs baulk at doing photometry. For most of us, precision all sky photometry is pie in the sky since we (well at least me) don't get that many photometric skies and Differential Photometry is quite simple and very straight forward.
19-05-2009, 05:19 PM
I agree 100% re Differential Photometry.
The current databases avialable in CdC, TheSky etc together the with Photometry sub-programs in software like AstroArt4 make it a no brainer!
Hmmmm - you may have something there... need to think about it; filters are a lot easier to use for this type of work!
19-05-2009, 06:36 PM
I think you mean Jeff, Bern... er, Ken.;)
Yeah, I know... from where you're sitting we both look the same!:whistle::lol:
19-05-2009, 08:01 PM
Sorry mate! Just another Senior moment!!:(
I can never remember their names in the morning - "Yes...Honey!";)
19-05-2009, 09:43 PM
While I would agree that theoretically it should be possible to generate synthetic BVRI filter output I doubt the exercise is worth the effort ... a lot of calibration and adjustments vs photometric star and filter standards would be needed. Leaving cost aside (a set of 1.25" BVRI filters isn't that expensive) doing photometry is a lot easier than spectroscopy (at least when compared to the slit type). I strongly believe the small filter investment is well worth it and your data will be a lot more acceptable (level of confidence in the results) if/when submitted to, say, the AAVSO.
19-05-2009, 09:48 PM
I thought there must be a reason.
Just wondered if anybody had tried it.
20-05-2009, 09:39 AM
I agree that photometry is not difficult and more should do it.
What made me delay starting was the difficulty getting filters. They don't seem to be sold at all in Oz and the Schuller BVRI ones I bought from OS arn't available anymore. Shame really.
20-05-2009, 06:11 PM
Terry, Good point!
I'm aware of AstroDon and their Sloan photometric filters
... are there any others???
20-05-2009, 11:17 PM
The sloan filters may become a standard but are difficult to transform to the older data at present.
The new UBVRI filters here (http://www.astrodon.com/products/filters/astrodon_photometrics_-_uvbric/) are dear at US$150 each for 11/4" filters.
I paid $300 for all 4 of the older ones and the Aussie dollar was worth much more then.:shrug:
21-05-2009, 07:24 AM
I wasn't aware the 'Schuler' filters were discontinued ... must be fairly recent. I guess it was understandable that Don (owner of Astrodon) decided to change the design as the Schuler filters (he purchased the original Chuck Schuler business a couple of years back) were prone to all sorts of hygroscopic deterioration. I'm on my second set, and some of them are starting to degrade after a few years :(
The Custom Scientific BVRI filters sold by SBIG have a very good reputation, but were always more expensive (US$175 ea) than the original Schulers. Andover Corpalso sell photometric filters, but I don't know anyone using them (http://www.andovercorp.com/Web_store/UBVRI/UBVRI.php)
In the amateur community the choice was always Schuler for cheapness or Custom Scientific for quality.
21-05-2009, 06:15 PM
AstroArt 4 has a module for photometry ( diaphragm size, location, back ground sky compensation etc), but what then?
Is there any graphic program to assist in the analysis of the light curves etc; or do we just use Excel????? many more a variable star question than pure photometry!???
21-05-2009, 08:40 PM
There a a few programs that do it. I measure my magnitudes using AIP4WIN. It is nice and easy to use and the magnitude measuring tool is under constant development to make it even better.
The other program I use that has graph analysis tools is MPO Canopus (http://www.minorplanetobserver.com/MPOSoftware/MPOCanopus.htm). It is much more complex than AIP4WIN and can be used to perform all sky photometry as well as light curve analysis.
Both of these programs are relatively inexpensive. AIP4WIN comes with Richard Berry's great book "The Handbook of Astronomical Imaging (http://www.willbell.com/aip/index.htm)"
22-05-2009, 08:48 AM
I've used MaxIm, AIP4WIN, Canopus and Peranso. Canopus wins hands down and when it comes to analysis is far, far, far more advanced than any of the other packages (though some of the features are very advanced - ie Professional level - dual period analysis, shape modelling etc). However, it is very, very easy to use once you get the hang of it. ie I can reduce and period resolve a target from 90 images inside 5 minutes usign it's differential photometry engine. All Sky takes longer of course.
23-05-2009, 05:59 PM
I have been trying Wratten #25 for Photometry with resulting error of 0.3 magnitude. All brighter stars are saturated when I use this filter but it shows some interesting objects (carbon stars for one) very nicely. Recently I have read article Wratten Filter Photometry by J.E Hoot. http://adsabs.harvard.edu/abs/2002SASS...21...29H (http://adsabs.harvard.edu/abs/2002SASS...21...29H)
It seems that you can use Wratten #23 and #58 for Photometry and get better then 0.1 magnitude results when those filters are combined with IR blocking filter. I will try it when the clouds clear. Proper Photometry filters are financially beyond my reach.
Another interesting webside is Photometry for dummies http://brucegary.net/dummies/x.htm (http://brucegary.net/dummies/x.htm)
23-05-2009, 08:20 PM
please post your results when you get around to testing..this is very interesting and a much more affordable option now that the price of even the V filter has gone up so much
28-05-2009, 12:43 PM
Just back from the RASNZ Wellington conference, and workshops, where Eric Rumbo (he wasn't present) had a display board presentation of his 'Nerik Photometry' and 'Nerik Period' software package ... plus a bunch of free DVDs, which went fast! I've only had a brief play with them using the included sample data and my initial impressions are that they are good. One of the nice photometry features is that the aperture measuring annulus can me divided into 16 (18?) segments which can be individually deselected if any contain unwanted star(s). The whole process, including deriving the magnitudes of up to 999 stars in every image for multiple images, is all automated and reminds me of the Canopus program.
The package also includes a separate 'Nerik Period' program which produces the period of any regular variable object, using FFT, and it work well.
I've not found any website for the Nerik software but if you are interested in getting hold of a copy (which I assume are free) you can contact Eric at erumbo AT bigpond DOT net DOT au.
28-05-2009, 05:12 PM
I've just ordered the canopus software from Dr Brian Warner... should be here next week.
30-05-2009, 12:57 PM
Dr Brian Warner..... Hmmmm I don't think Brian has a doctorate (yet).
There are some features in Canopus people probably aren't aware of like StarBGone. This actually subtracts unwanted stars from all images and is very reliable (down to 0.02mag precision dependant on the relative brightness of the subtracted star to the object being measured). I beleive he is also workign on varible shaper apertures to cater for trailed images (or trailed targets/comps depending on your method of image acquisition)
30-05-2009, 03:35 PM
Hmmm.. I must have had another Senior moment!!
No Dr. Warner:doh:
Just Brian D. Warner, at Palmer Divide Observatory.
31-05-2009, 12:34 AM
There is a Professor (Dr) Brian Warner, from South Africa and author of "Cataclysmic Variable Stars", the bible on the subject, and "High Speed Photometry" ... a world renowned and highly respected astronomer at the University of Cape Town ... but not the author of Canopus (by the american Brian D(ale) Warner of minor planet fame and author of "Lightcurve Photometry and Analysis").
The 'Canopus' Brian D. Warner, in his preface to the book just mentioned, states "I'm the other Brian Warner. The real Brian Warner is the famous and distinguished one...", which is why he uses the 'D' to differentiate himself.
01-06-2009, 01:47 AM
That's probably where the Freudian slip came from. I spent 10 years is South Africa and was an active member of the ASSA.
24-07-2009, 06:58 PM
To day I have received Wratten #21, #58 and #47 filters to try for photometry as my previous post. To my dismay they donít fit in my Apogee Filter Wheel although they appear to have standard tread and fit in all camera adapters I got.
I had everything prepared to motorise this Filter Wheel, jut to drill mounting holes for the motor. What a bummer. Anyone knows how many different treads there are for 1 ľ ď filters?
24-07-2009, 07:28 PM
As far as I know the standard 1.25" filter thread, if you can call it that is a 28.5mm thread.
Over the years I've found many problems (like you at the moment!) where filters will just not fit!!
All I can say is the Celestron, Meade, Schuler, Baader and many of the "filter extensions" and the x0.5 GSO reducer all seem to fit my TV plossls.
The problem is somewhere between the eyepiece manufacturer and the accuracy of the filter thread.
For filter wheels, all my filters fit the AtiK USB wheel but I did have problems earlier on with a manual filter wheel from the states, where very few, if any of my normal filters would fit.
BTW the thickness of the filters can also vary ( especially the Baader) and some filter wheels don't have enough internal clearance to allow them to operate.
Just my 2c
24-07-2009, 07:58 PM
Well, yes short of spending $300 on some other Filter Wheel I will have to take camera out and screw new filter in the adapter. Not ideal solution as you never can put camera back at same position angle as before. If I can find very thin nuts with same tread as standard filters I would drill/machine offending tread out and fix the Wratten filters to the wheel. Never mind the original interference filters, I use them seldom. I donít think it is possible to recut original tread, as the metal is only about 2mm thick. Well this is Astronomy Ė when you figure out what you want to do. things donít fit.
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