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Any triple doubles?

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29 replies to this topic

#26 ssmith

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Posted Today, 08:10 AM

Hi tdfwds!

I going to have to read your comments over several times...way to much technical stuff for this retired brain!! grin.gif I refer to myself as a dumb photographer.

 

As far as the formula goes...it came to me by way of a someone with whom I collaborate to get revised photometrics for double stars with suspicious component magnitudes. This is a spreadsheet with the formula embedded into it. I have attached a screen image of the spreadsheet. I just substitute the pertinent J-band and K-band values and it churns out an estimated Vmag. That is as much as I know.

 

Cheers, Chris.   

 

Chris - I believe it was me who steered you to this formula.  It comes from Bruce Gary's Website.  He details numerous methods  for converting or measuring magnitudes and explains their various limitations.


Edited by ssmith, Today, 08:33 AM.


#27 c2m2t

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Posted Today, 11:24 AM

Hi Steve!

You may be very well correct! It has been a few years and a few thousand checked magnitudes later. It has been a great tool! Thanks!

 

Cheers, Chris.

 

P.S. I had a chuckle when I open Bruce Gary's website just now...."Photometry for Dummies"....Right On!! waytogo.gif



#28 tdfwds

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Posted Today, 12:38 PM

btw, you do know in aladin you can do photometry on whatever image you're looking at from a menu drop down option.  Of course the "passband" is whatever the image was taken at, which is just glass plate emulsion for DSS.  So not necessarily V.  NB, rhetorical, a just in case thing.



#29 c2m2t

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Posted Today, 03:49 PM

Hi tdfwds!

Oh really!! Can I indulge you in some quick instruction? There are others who might find this useful!!

 

Cheers, Chris.



#30 tdfwds

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Posted Today, 06:21 PM

Hi tdfwds!

Oh really!! Can I indulge you in some quick instruction? There are others who might find this useful!!

 

Cheers, Chris.

I'm afraid I only ever played with it, and for various reasons most of the time I only use Aladin 7 (it's a standalone 32bit .exe that launches quick, though is flakey at times and doesn't always do what it is supposed to).  I do at other times use the aladin10 jar, but to me like all software, the more bells and whistles they add, the more stuff ends up less usable.

 

So, again, I played with it a bit once, it seems to match images with circles around them, no doubt a fixed aperture thing, but relative to the star size if I remember rightly (must be three years since I last played with it, I like to play with catalogued photometry, not measure it) and then does some simple psf (point source function, the sort of thing that takes a cross section and you get a guassian, or 'bell curve' as they like to say in usaland, and do maths on that to derive the magnitude.  I assume the code gets all the other info it needs from the fits header of the image, but I don't really know how it works, I'm not into kit, it takes too long to learn and I need to keep up on my physics and TRY (somewhat unsuccessfully most of the time) to extend my maths skills.

 

There seems to be an option under the IMAGE menu drop down, "greyed" out when there is no image loaded.  It used to be a SEXTRACTOR option, so I don't know how much it has changed.  I'm still on Aladin 10 as I can't update my java any further on this particular box.  I think it's aladin 11 at least now.  I know it keeps nagging me to tell me a newer version is available, no matter how hard I try to turn that off!  I think you just used to be able to hover the pointer over a star and the mag appeared in the dialogue  bit below, where the vizier text info etc tends to crop up.

 

Aladin is still the best fits (image) viewer I've seen, topcat the best fits (table) viewer.  Zooming and the pixel histogram get a lot of use.  However, now 10 does RGB, or colour in general images, the pixel histogram has separate RGB graphs that have to be fiddled with individually, but not also a monochrome one or alternatively a way to lock the three against each other, so you can shift them all at once to the exact same spot.

 

Ball's back in your court : þ  Aladin's made to be part way intuitive, be brave.

 

The manual

 

https://aladin.u-str...ladinManual.pdf

 

If you're running aladin thro' a browser, download the desktop, browsers too easily have memory issues, and javascript is slow compared to direct code or even java.  Just search for aladin cds




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