Good day.
I am between choosing filters for photometry of stars and I don’t quite understand. As I understand, Sloan filters are now being praised and local astronomy enthusiasts say that they should be taken. But I don’t understand how to enter photometry data into the database later? Will there be problems? Since I see that Johnson filters are still often used.
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Greetings,
Both Sloan and standard Johnson-Cousins filters are supported by the AAVSO extended format. So data submission should be easy enough.
https://www.aavso.org/aavso-extended-file-format
Which filters should you acquire and use, that is the question:… – Shakespeare
U B V Rc and Ic filters have been used for many decades so there is a long period of data taken using these filters. In the early days these filter bandpasses were optimized for photomultiplier tubes and later filters were designed for the different response of CCDs.
If you want to be on the front edge of the astronomy wave then Sloan filters may be appropriate for you. Your Sloan photometry may then be comparable to the current filters being used by many professionals. I do not have any Sloan filters in my wheels… that could change tho! Baader has a basic write up on their filters.
Perhaps HQ or a “real astronomer” may comment on if there are any significant differences between the two filter systems for elucidating the physics of variable stars.
Jim (DEY)
I’m not a ‘real astronomer’ (no formal training as such), but I have done a lot of photometry. With regard to the original post, for starting out I would not bother with anything except B and V.
One of the problems with the Sloan system is that there are no high-accuracy standards, and each implementation of the system has differed (SDSS, Pan-STARRS, SkyMapper etc). One can adopt the ATLAS ‘refcat2’ g,r,i in any field, but the data are somewhat soft (a few percent).
The Cousins R,I and Sloan r,i passbands are similar enough that, from the standpoint of stellar astrophysics, they are interchangeable. My opinion is that Sloan g is poorly placed as regards stellar spectra, and V is better (or B and V). There is also the historical legacy of the V/visual set-up — but remember that the future is longer than the past, so the visual connection could go away a long time from now.
Upcoming is a complete change to the system defined by the GAIA (or future space-based) spectrophotometry. At the moment the extremely broad GAIA passbands mean the data are unable to deal with reddening or metal-abundances issues etc as regards stars (mainly from no violet filter). This means you can get amazingly high precision, but it requires knowing your specific system passbands quite accurately (atmosphere+telescope+filter+detector). So things are, um, in flux for now on this point.
\Brian
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