The URAT project Norbert Zacharias Greg Bredthauer Mike DiVittorio Charlie Finch Ralph Gaume Fred Harris Ted Rafferty Al Rhodes Mike Schultheis John Subasavage Trudy Tilleman Gary Wieder nz@usno.navy.mil 1
layout of talk introduction, goals of the program URAT history instrument begin of survey observing first results 2
URAT USNO Robotic Astrometric Telescope 3
URAT concept and goals new all-sky ground-based astrometric survey follow-up to UCAC, more accurate, deeper access also to bright stars (to about 3 rd mag) multiple overlaps / year, solve for position, proper motion and parallaxes (subset) improve optical reference frame and our knowledge of galactic structure and kinematics before a Gaia catalog becomes available 4
URAT history 2000 : plans for follow-up of UCAC: new tel. 2005 : design of 0.9 m astrometric telescope completed, order primary mirror 2007 : single 10k detector successful (STA 1600) 2008 : funding of 4-shooter camera provided, decide to go with astrograph red-lens again 2010 : most of camera complete, dewar behind 2011 : first light in Washington, DC 2012 : begin of survey at NOFS 5
single 10k camera dewar 6
astrograph with single10k camera, 2008 7
URAT observing survey began 2012 April 24 at NOFS observe 2 to 3 years then move to CTIO 28 sq.deg single exposure, 0.9 /pixel 4 CCDs: each 10,560 x 10,560 pixels + 3 guide CCDs single bandpass (window = filter) 680-750 nm gain 2 mag dyn.range: clocked anti-blooming (CAB) 60s, 240s expos. each field regular survey 20s expos. survey with 4.5 mag grating total dynamic range: R = 3 18 mag 20 mas precision / exposure, 10 x overlap/yr 8
STA1600B 2x2 Mosaic Camera Head Concept Front View Cryostat window 320mm diameter, 300mm clear aperture, 25 mm thick 9
rebuilding astrograph in 24in dome, 2008 10
astrograph May 2009 at USNO 11
STA 1600 CCD packaging 12
2010, June 29: successful image backside, thinned 10k detector in lab at STA, 16 outputs 13
14
URAT setup standard container = control room tube assembly, all mechanics: USNO instrument shop fiberglass dome + a lot of lightning protection 1 computer (Linux RHEL) controls all Bonn University shutter (Klaus Reif) 3 guide / focus CCDs (2k by 10k, 8 microns) need for movable counterweight (LN2 weight change) camera electronics + telescope interface from Greg Bredthauer (STA) 15
16
17
URAT dynamic range 240 sec exposure: limiting mag almost 18 traditional saturation at 11 mag clocked-anti-blooming: gain 2 mags 9 60 sec exposure: shift by about 1.5 mag use of grating (bright star survey): 4.5 mag 20 and 10 sec exposures : gain about 1.5 mag 18
over-exposed star in CAB mode 19
20
21
22
23
summary URAT: new all-sky astrometric survey use re-furbished astrograph, 4-18 mag, 5-30 mas 28 sq. deg / exposure, survey begun 2012 April 10-fold overlap / year for about 3 years per hemisphere solve for position, proper motion, parallax (subset) Gaia will be better for most aspects, not all, but we don't yet have a Gaia star catalog: continue ground-based efforts for now 24