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Newbie question about BVRI data

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#1 ASTERON

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Posted 04 September 2012 - 11:17 AM

Pardon me if I am asking a question with an obvious answer.

What is the advantage of collecting BVR ( or BVRI) photometric data Vs. collecting only V data ?
I think I understand that both types of data serve to obtain some kind of stadardized measurement so different results from different sources can be compared.
Why would I want BVR Data ? I guess it has something to do with some variables having maximum output in different spectral bands, but I am not sure thats the only reason why one would want a full BVR data set as opposed to a single data set using a Johnson V filter.
Can anyone point to me for which kind of work one can do only V type measurements and what kind of work would benefit more from a BVR data set?

Thanks

Lihu

#2 brianb11213

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Posted 04 September 2012 - 12:57 PM

Well ... BVRI is a sort of shorthand spectrum, changes in the colur index point out changes in temperature (at different heights in the atmosphere of the star depending on which colour index is chosen) and therefore points at the mechanism by which the star is varying.

V measures alone are far better than nothing & match in pretty well with the huge back catalogue of visual estimates which have been made over the last hundred years or more.

Suggestion, start off making V measures & stick at it until you're getting good consistency. Then think about adding other wavelengths.

#3 gavinm

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Posted 04 September 2012 - 05:51 PM

I use BVR (actually g'r'i') to measure the colours of stars in my FOV simply to choose comparison stars. By using comparison stars of the same colour and magnitude, I can minimise effects such as extinction. Then I only take time-series photometry with one filter, usually r' or broad band.

#4 ASTERON

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Posted 05 September 2012 - 02:04 AM

Brian and Gavin,
Thank you both for the great comments and advice. This is really helping me to make a decision. I will now do some more reading and make a final enquiry with SBIG and then make a decision and buy.
Keep these great comments coming
Thanks
Lihu

#5 ASTERON

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Posted 22 October 2012 - 02:59 PM

Update,
Ordered and received the BVIC Filterwheel for the ST 402-ME a few days ago. Upon arrival I found out that two of the glued filters were cleanly detached from the filter wheel and lying on their on in the box. Luckily, as there was some soft paper packing in the box, the detached filters did not get scratched or damaged.
I contacted Astronomics and they immediately offered to replace the defective wheel by sending me a new one.
I am shipping them the defective unit tomorrow.
I hope the new one would have better glue ( or better gluing technique, anyway) than the one I received.

Kudos to astronomics for the great customer service :bow: :bow:

#6 Ed Wiley

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Posted 22 October 2012 - 03:38 PM

Make sure to test your BVIC wheel to make sure it is seating properly and rotating correctly. My first one was not. I sent it to SBIG and they fixed it for no charge. Now it works perfectly. I don't think this is very common, but do check.

Ed

#7 ASTERON

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Posted 22 October 2012 - 05:04 PM

Ed ,
Thanks for the tip, I will make sure to check this.
Anyway I w'ont be getting the new filter wheel before middle of November. A friend is bringing it from the USA for me.

I was actually amazed by how flimsy the wheel looked to be -I hope it works better than it looks, OTOH, it does not have to be very sturdy since it is very small and lightweight.






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