Sonntag, 26. Mai 2013

Stream finding & stream follow-up with PS1

I might want to get back into the stream analysis business again. Variety of angles: it's part of the SFB 881 project; I would like to see how well proper motion cleaning works for finding stellar halo streams traced by giants; a good test case to combine proper motions between PS1 & SDSS.

Possible starting point: the Pisces stream, recently found by Martin et al (http://arxiv.org/pdf/1302.2155v1.pdf). This stream appears to be traced in giants,
at a goodly distance of 35 kpc. I wonder whether one can do both a photometric metallicity "cleaning" of the stream, using ugr [XX will look at the metallicity diagnostic of old giants in the
ugr plane]; and the contaminant MS stars at g-r=0.6 and r<19.5 should be at ~3 kpc, where their
dispersion should be ~>60 km/s, hence detectable by proper motions...
This might lead me to re-open the questio of optimal filtering a la Koposov et al 2010.

Montag, 13. Mai 2013

PS1 and astrometry:
Bertrand G. took the PS1 pipeline proper motions and did the mean proper motions of known SDSS quasars in 4x4deg fields. The mean proper motion (reflecting the deviation from an inertial frame),
showed a smooth pattern with an amplitude of ~10 mas/yr.

He will take half the QSO sample correct the other half and see what happens.
That seems to imply that the calibration to the QSO's should work well.
That, in turn, bring new motivation to identify all PS1 quasars by a mix of WISE colors
and variability. In particular, we will need to look at the regions of considerable extinction
at low latitude.  So, let's find quasars at |b|<15, to map the Galaxy.