USNO Robotic Astrometric Telescope (URAT)

Overview

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

Timeline

2006-2007: research and development of 10k detector
2008: funding for 4-shooter camera becomes available
2009: 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

Sections