[Aavso-photometry] Aavso-photometry Digest, Vol 65, Issue 14

[Russ Garrett]

Tom,
The real reason for the switch to the Sloan filters is Arne gets a 10% kick
back on Sloan filters sold through Astrodon!


On Tue, Jun 23, 2009 at 11:00 AM, <aavso-photometry-request at aavso.org>wrote:

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> Today's Topics:
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>   1. BVRI vs. griz (Tom Krajci)
>   2. Re: BVRI vs. griz (arne)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 23 Jun 2009 08:13:34 -0600
> From: Tom Krajci <tom_krajci at tularosa.net>
> Subject: [Aavso-photometry] BVRI vs. griz
> To: aavso-photometry at aavso.org
> Message-ID: <4A40E30E.509 at tularosa.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Why did the pro's make the switch from BVRI to griz?
>
> Is there an astrophysics advantage?  (Better, more accurate
> classification/ID of stars because the bandpasses don't overlap?)
>
> Is it a better match for typical CCD response?
>
> Other?
>
> Thanks in advance.
>
> --
> -------------------------------------------
> Tom Krajci
> Cloudcroft, New Mexico
> http://picasaweb.google.com/tom.krajci
>
> Center for Backyard Astrophysics (CBA)
> http://cbastro.org/ CBA New Mexico
>
> American Association of Variable Star
> Observers (AAVSO): KTC http://www.aavso.org/
> -------------------------------------------
>
>
>
>
> ------------------------------
>
> Message: 2
> Date: Tue, 23 Jun 2009 11:04:44 -0400
> From: arne <arne at aavso.org>
> Subject: Re: [Aavso-photometry] BVRI vs. griz
> To: Tom Krajci <tom_krajci at tularosa.net>
> Cc: aavso-photometry at aavso.org
> Message-ID: <4A40EF0C.2020905 at aavso.org>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Tom Krajci wrote:
> > Why did the pro's make the switch from BVRI to griz?
> >
> > Is there an astrophysics advantage?  (Better, more accurate
> > classification/ID of stars because the bandpasses don't overlap?)
> >
> > Is it a better match for typical CCD response?
> >
> > Other?
> >
> The pros switched because SDSS happened. :-)
> Seriously, SDSS used these specific filters for discrimination
> between stars and galaxies, since it was a large-scale structure
> project and needed to place its spectroscopic fibers efficiently
> on galaxies.  In addition, Jim Gunn was the primary architect
> for SDSS, and he designed these filters many years earlier;
> people tend to use what they know.
>
> Since SDSS measured some 230 million sources, it is the "king"
> as far as photometric surveys are concerned.  For stellar work,
> you just need broad-band magnitudes of some sort in order to
> classify objects, so SDSS works essentially as well as Johnson/Cousins.
> Since much of the big telescope time is used for galaxies,
> they have Sloan filters at those observatories, and it is
> more convenient to stick with that filter set than to change
> them out every time someone wants to do stellar work.
>
> There is still a lot of professional Johnson/Cousins imaging
> taking place, so it is by no means a complete changeover in
> the professional world.  The trend is certainly towards
> Sloan, however, especially now that inexpensive filters
> are available.  APASS will measure stars in both Johnson
> and Sloan filters as a transition survey (though only for about
> 50 million objects).
> Arne
>
>
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> End of Aavso-photometry Digest, Vol 65, Issue 14
> ************************************************
>