Globular Cluster colors . . .

[nemo129]

Wow, great thread! Looking forward to 1.8.5! 

[RickS]

Juan was kind enough to let me play with an early release of 1.8.5.  Here's a comparison of "classic" ColorCalibration vs PhotometricColorCalibration for a couple of different white references (G2V and "average spiral galaxy").  There are also variants which correct for galactic dust extinction.  The target is the greatest of all globs, Omega Cen.

http://www.astrobin.com/299315/F/?nc=user

Kudos to Juan Conejero for the very ambitious and new-feature-rich 1.8.5 release, and to Vicent Peris for the PCC tool and the model for extinction correction. Thanks, guys!

Cheers,
Rick.

[vicent_peris]

Hi!

I just made some research that can be very informative. I downloaded a catalog of globular clusters in M31:

http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=V%2F143

In this catalog we have the Johnson B and V magnitudes plus the color excess due to dust reddening. Moreover, it has a flag indicating which clusters have been confirmed to be real clusters. So I filtered only the confirmed clusters which have the three magnitudes. Attached to this message is the histogram of the B-V color index distribution. The median B-V color index of this sample is 0.67 magnitudes, which is very close to a G2V star (0.66) and a bit redder than the generic spiral galaxy we have implemented in PCC (0.71). This means that, if we correct for galactic dust reddening, then the overall color of the average globular cluster should be close to white if we calibrate with a G2V star, or slightly bluish if we calibrate with a spiral galaxy.

On the other hand, you can see that there are a lot of globular clusters with very blue colors. Some of them even bluer than Vega!

By the way, in PhotometricColorCalibration you'll be able to correc the dust reddening imposed by the Milky Way for extragalactic objects. This means that we'll be able to look at those object as if we were shooting them outside the Milky Way. :-)


Best regards,
Vicent.

[vicent_peris]

Juan was kind enough to let me play with an early release of 1.8.5.  Here's a comparison of "classic" ColorCalibration vs PhotometricColorCalibration for a couple of different white references (G2V and "average spiral galaxy").  There are also variants which correct for galactic dust extinction.  The target is the greatest of all globs, Omega Cen.

http://www.astrobin.com/299315/F/?nc=user

Kudos to Juan Conejero for the very ambitious and new-feature-rich 1.8.5 release, and to Vicent Peris for the PCC tool and the model for extinction correction. Thanks, guys!

Cheers,
Rick.

Thank you Rick! Looking at your pictures, I see that PCC is running very well. :-) As listed by Simbad, the color index of Omega Cen without dust reddening is 0.64 magnitudes. To me, this value agrees perfectly with the results you're sharing: with G2V it should be white while it the spiral gal calibration should show it slightly bluish. :-) I think the merit of this precision is due to the linear fitting we have implemented in PCC. To me, the APASS catalog is very nice, provided that you're able to remove the possible outliers.

Best regards,
Vicent.