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USNO Robotic Astrometric Telescope (URAT)

Recent News

  • 2016 Jan: A poster was presented at the AAS meeting regarding URAT parallaxes
  • 2015 Oct: The telescope is up and running at CTIO, for a new 1-year observing program for bright stars (all up to Sirius) plus shallow general survey to R=17 and Dec <+25 (see here)
  • 2015 Jun: The 3-year observing program at NOFS was finished, and the instrument disassembled.
  • 2015 May: Publication of the bright star astrometry program in RevMex (ADeLA)
  • 2015 Mar: The URAT1 star catalog was published, 228 million stars, based on first 2 years of observing at NOFS (see here)
  • 2014 Nov: The URAT1 catalogwas  constructed of 220 million stars (mainly northern hemisphere) based on first 2 years of URAT observing at NOFS, supplemented by APASS, 2MASS, and proper motion data. This catalog is currently under USNO internal review.
  • 2014 Apr: A poster paper outlining the progress of URAT was presented at the DDA meeting in Philadelphia.
  • 2012 Aug: A number of UCAC- and URAT-related talks were presented in the Commission 8 (Astrometry) science sessions at the International Astronomical Union (IAU) General Assembly. These may be downloaded from the link here.


  • new observational program, successor of UCAC
  • astrometric survey including 1 bandpass photometry, multiple epochs
  • uses "redlens" of USNO 20cm astrograph (same as for UCAC)
  • this time utilizes the large field-of-view the lens is designed for, covering 28 sq.deg per exposure
  • will begin all-sky survey at NOFS (Arizona), continue from CTIO (Chile)
  • will cover magnitude range R = 9 to 17.5 mag, using single 670-750 nm bandpass


Astrograph (photo gallery)

  • uses existing B&C mount and "redlens", with
  • completely new electronics / control system and
  • completely new tube assembly (built in USNO Instrument Shop)
  • uses shutter from Bonn University group


Detector (photo gallery)

  • new camera is based on the "10k" ST1600B CCD from Semiconductor Technology Associates (STA)
  • backside detector, thinning is underway at Univ.of Arizona (M. Lesser)
  • 10,560 by 10,560 pixels (111 Mpx) of 9 by 9 micons
  • 16 outputs
  • read at 1 Mpx/sec
  • option for clocked anti-blooming to extend dynamic range at bright end for astrometry
  • A milestone was passed on 29 June 2010 with successful testing of a fully functional back-side illuminated 10K detector at Semiconductors Technology Associates (STA).


Camera (photo gallery)

  • the 4-shooter camera contains 4 STA1600B detectors for imaging
  • mounted on the sides are 3 guide / focus chips (2k by 5k, 8 microns)
  • camera window (25mm thick) serves also as fixed filter
  • camera shutter has 280 x 280 mm clear aperture, over 1 meter long
  • camera electronics is custom design (Aura system) by G. Bredthauer (STA)
  • dewar weighs about 140 kg, with 30 liter LN2, built by G. Luppino (Hawaii)
  • camera, telescope and dome controlled by a single Linux computer


First Light (Washington)  (photo gallery)


URAT had successful first light on Aug 23 2011. The 4-shooter camera arrived on Thu, Aug 18 and was lifted into the dome at USNO Washington DC the following day. By Tue, Aug 23 all was installed at the astrograph and the dewar filled with LN2. First light was the same night, with more test observing performed on Wed night. All 4 10k detectors and all 3 guide CCDs are working. A single raw frame is 1 GB. A first look revealed stellar images of about 2.5 pixel FWHM at 0.9 arcsec/pixel are seen all over the focal plane with some degradation at one corner due to tilt of the array, which can be adjusted easily. Noise properties are as expected and the dewar is nicely holding vacuum and operating temperature at -80 C.

First Light (Flagstaff)  (photo gallery)


URAT was shipped to Flagstaff and achieved first light there on Sept 26, 2011.



The Project

  • exposure times per field about 3 to 4 min
  • 5 to 10 fold sky overlap per year, 0.90 arcsec/pixel
  • observe 2 to 3 years per site (north, then south)
  • derive positions, proper motions, and parallaxes
  • goal: 10-15 mas per single exposure per coordinate for high S/N stars
  • direct link to optical counterparts of ICRF quasars
  • direct link to faint end of Hipparcos Catalog
  • observe selected bright stars through neutral density spot on filter




research and development of 10k detector
funding for 4-shooter camera becomes available
successful production of 10k chips
construction of new telescope tube
delivery of Bonn shutter
2010 Feb
completion of camera electronics
2010 Apr
computer control of mount
2010 Jun
successful testing of 10K x 10K back-side illuminated CCD at STA
2010 Jul
2nd thinned 10k chip characterized: excellent quality, remaining 2 chips in queue for thinning
2010 Sep
successful operation of mount under computer control
2010 Nov
set of 3 guider chips completed
2011 May
camera head assembly completed at STA
2011 Jun
dewar completed, no leaks, hold time about 60 hours with no load
2011 Jul
completed 4-shooter camera tested at STA
2011 Aug 23
first light at USNO
2011 Sep 26
first light at NOFS
2011 Nov 4
dewar taken off and shipped to STA for upgrades and improvements
2012 Mar 25
dewar back on telescope, commissioning effort continues
2012 Apr 24
URAT survey begins