Photometry and Spectroscopy

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bobharris
Posts: 3
Joined: Mon Jun 24, 2019 7:07 am

Photometry and Spectroscopy

#1

Post by bobharris »

SharpCap team,
Southern hemisphere user, polar alignment not a problem with PA option, 5 minutes setup and track within 2 seconds, all's well with SharpCap, now to try out the latest release.
I am now planning to advance my astronomical activity with Photometry and Spectroscopy.
I am particularly interested in capturing variable stars and measuring the change in luminosity then, as well, building up my own catalogue of star types using spectroscopy.
I would appreciate any comments on how SharpCap can assist with these activities and/or additional software that might be required plus users adventures in these areas.
Bob
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oopfan
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Joined: Sat Jul 08, 2017 2:37 pm
Location: New York
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Re: Photometry and Spectroscopy

#2

Post by oopfan »

Hi Bob,

I've done quite a bit with Variable Stars and Exoplanets. I recommend starting with a question: Am I in it to have fun, or to be serious? By serious I mean measuring magnitudes with such precision that your data can be combined with other people's data. And by fun I mean that capturing the shape of the light curve is more important than the accuracy of the magnitudes. Of course you can have fun AND be serious. But to be serious, you need to learn how to calibrate your equipment. Join the American Association of Variable Star Observers (AAVSO). They offer two online courses: "CCD Photometry 1" and "CCD Photometry 2". In my case, I learned that my equipment wasn't good enough. If you have a refractor, you need an APO. My scope is terrible at focusing blue light. At a minimum you need two filters, Photometric "V" and "B", not a small investment. The "B" filter is deep blue, so in my case the star's disc is fuzzy and spread over too many pixels which requires a long exposure to capture properly. Also, consider your camera. Most of these guys use 16-bit CCD's with very deep wells, on the order of 100,000 electrons. If your camera's full well depth is only 25,000 electrons, then you will have problems. The thing is that you need to capture the variable star AND several comparison stars in the same frame. Ideally, the stars are similar magnitude, but that is rarely the case. A sensor with 100,000 electrons FWD can capture a wide range of magnitudes without saturating any one of them. The AAVSO welcomes CMOS cameras, but you should really have a high-end one, cooled, 14-bit minimum.

Here are several links to a web app that I wrote for sharing my work with variable stars and exoplanets:

YZ Boo (period 2.5 hours, p-p amplitude 0.4 magnitudes):
https://u235-varstar.vercel.app/phase-plot/yz-boo

Cze V627 (period 2.1 hours, p-p amplitude 0.05 magnitudes):
https://u235-varstar.vercel.app/phase-plot/cze-v627

Exoplanet HAT-P-5 b:
https://u235-varstar.vercel.app/gallery/hat-p-5-b

By the way, it helps to have a large aperture to capture many photons in the shortest time.

Brian
timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

Re: Photometry and Spectroscopy

#3

Post by timh »

Hi Bob,

There was a short thread on the possibility of adding a comparative photometry tool to track variables recently. Robin put it on his take away to think about list..

viewtopic.php?f=17&t=3930
best wishes
Tim
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oopfan
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Location: New York
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Re: Photometry and Spectroscopy

#4

Post by oopfan »

Bob,

The AAVSO has software, but I use AstroImageJ (free). What's neat is that you can set it up to automatically calibrate frames when they arrive from your data capture software (SC), perform photometry and plot the star's light curve.

Brian
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admin
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Re: Photometry and Spectroscopy

#5

Post by admin »

Hi,

there is not a lot to directly support photometry or spectroscopy sadly, even in v4.0. There is support for the ADV (AstroDigitalVideo) file format which puts a lot of data into the output file along with every frame, but that is most useful on the QHY GPS cameras, and also there is only a limited set of processing software available. Otherwise, I suspect that capture to FITS is probably best for importing into various processing tools, but I've never done any photometry/spectroscopy so I can't give firm advice.

cheers,

Robin
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