GAIA binary star simulations: Tests of sampling windows and observation strategies Staffan Söderhjelm Lund Observatory Sampling window-size Window allocation

Increase sampling window from 6x8 to 12x8 pixels Standard strategy for binaries: But: To see consequences, full simulation of observations + reductions needed

First experiments Statistical scanning- law Single idealized PSF One window-size in all scans 1-dim PSF-fit y-cutoff assumed only dependent on y Std LS, started close to (known) true parameters For simulation of obsFor reduction-part

Typical runs Doubles with primary G=12.5,15,17.5,20 Secondary dm=0.0,(0.75),1.5,(2.5), doubles per type, sep= mas Actual and formal errors for 12 parameters

Systematic effect in separation depending mainly on window-size. (independent of magnitude) 6x8 12x8 12x10 12x12

Excess mean errors for secondary parallax/p.m. again mostly dependent on window-size and not on magnitude.) 6x8 12x8 12x10 12x12

Conclusions (I): across-scanWindow-effects (dsep, sigpi...) start at separation depending on the across-scan window-size. Effects independent of magnitude, obvious for bright doubles, drowned in photon noise at fainter magnitudes ‘Double’-window should not be 12x8, but rather 12x10 or 12x12

Work in progress: Tests of window allocation algorithms Most of the old programming used (scan- law, PSF, LS-solutions) One or several sampling windows in each scan Observing strategy (incl pointing)

I. Single window/modified pointing Replace std ‘pointing at photocentre’ with ‘pointing at geometrical centre’ Much better for secondary, not that much worse for primary

II. Two or three large windows (E. Høg, CUO-100) Added windows ‘too large’ (much empty sky gives programming problems) Clearly increased errors in middle range (around 0.5 arcsec)

III. Best so far... For along-scan sep < 8 (pxl) and across-scan sep < 8, single 12x12 window with geometrical centre pointing For larger separations, individual 6x8 windows

More questions... Color-dependent PSF => much more complicated reductions, other optima? Bright stars (obs at diffraction spikes) Faint stars (no ASM duplicity detection) ‘other field’ spurious components (GAIA 2)...