Spacewatch 0.9-meter Telescope

0.9-m telescope
The Spacewatch 0.9-m telescope (left) on beautiful Kitt Peak during the winter.
(Photograph by Jim Scotti)

A little history:
     Spacewatch personnel run the Steward Observatory 0.9-meter telescope, the oldest on Kitt Peak. It was installed in 1921 on the University of Arizona campus and houses the first large telescope mirror successfully cast in the United States. The telescope was then moved to Kitt Peak in 1962. In 1969 it was used to discover the first optical pulsar. By the year 1982 the telescope had fallen into disuse, so the Director of the Steward Observatory granted the Spacewatch Project exclusive access to the telescope on the condition that Spacewatch take on all the tasks of refurbishing the telescope and performing all maintenance. Spacewatch rose to this challenge, developed an electronic imaging detector system, and made the first trial scans with a small CCD in May 1983.
     On this telescope, Spacewatch developed the technique of scanning the sky with a charge-coupled device (CCD), and has been using it to survey for asteroids and comets since 1984. In October of 2002 the conversion to a mosaic of CCDs was completed and a new primary mirror was installed. See the Photo Gallery of the conversion.

                      (Photograph circa 1994 by Jim Scotti)                                                                        (Photograph October 2002 by Robert McMillan)
                        1983 May - 2002 April                                                          2002 October - Present

Observatory information:
Latitude:         31o 57' 43" N
Longitude:    111o 35' 58" W (7h 26m 24s West of prime meridian)
Elevation:     2091 m (6860 ft)
IAU Observatory Code:  691

Optical configuration Old System Mosaic of CCDs
Optics Newtonian, f/5.34, coma corrected and field flattened Corrected prime focus, f/3
Filter Schott OG 515 * Schott OG-515
Primary mirror diameter 0.946 m (37.25 inches) 0.946 m (37.25 inches)
Masked mirror diameter 0.882 m (34.7 inches) Clear aperture - 36.75 inches
Image scale (at corrected focus) 43.8 arcsec/mm 74.0 arcsec/mm
CCD Tektronix TK2048EB1-1 (2048x2048 pixels), thinned, backside illuminated Four  E2V Technologies Model: CCD42-90-I-941, 4608 x 2048 pixels each, thinned, and backside illuminated
Pixel size 24 microns 13.5 microns
Image scale 1.05 arcsec/pixel 1.00 arcsec/pixel
Effective field of view 37' x 33' (RA x Dec) 2.9 square degrees
Exposure time 2m23s at 0o Dec;  2m38s at +/-25o Dec (drift scanning) 120 seconds (stare mode)
Limiting magnitude V = 21.5 V = 21.7

(Drawing by Joe Montani)

Optical layout of 0.9-meter -- past system and present upgrades.

(Drawing by Joe Montani)

Full scale focal plane compared with projected effective size of 2k x 2k CCD used previously.

Successful recovery of potentially hazardous asteroid 2002 TD66 (a=1.86 AU, e=0.54, i=4.93) taken by the 0.9 meter Spacewatch Mosaic on Oct 23, 2002 between 03:50:50 and 04:04:55 UT. Observation was taken at Right Ascension 22:50:54 and Declination +08:49:14 in of date coordinates. The asteroid was V=19.5, or more than a quarter of a million times fainter than the faintest star visible with the unaided eye. The asteroid moved 30 arcseconds in 15 minutes -- an motion equivalent to a person walking from the front bumper to the tail bumper of a car 13 miles away.

The first "long" (120 second) exposure of the Spacewatch Mosaic Camera on the sky (RA 20:31:34, DEC +31:57:48), taken 2002 October 23 at 02:01:41 UT during engineering trials in bright moonlight. This "printer-friendly" version is like a photographic negative in which brighter sources are blacker and the dark sky shows white. Three CCDs are aligned east/west and the fourth one is aligned north/south to fill a round field of view as efficiently as possible. Each CCD covers 0.6 x 1.3 degrees on the sky, so the total area covered by the system is 15 times greater than that usually covered by the Earth's moon. It is also 9 times larger than that covered by the usable area of the detector we had previously on this telescope.

The gaps between the CCDs are much smaller in reality than the spacing between these images. This is a "raw" (unprocessed) image that shows various effects that are easy to correct in post-processing. The variations of the background level are due to the nonuniformity of sensitivity across the CCDs. The image also shows slight differences between electronic bias levels between the two halves of the CCDs, due to the fact that the image areas are read out in two directions through two different amplifiers. Black (in reality bright) lines are due to signal bleeding away from overly saturated images of bright stars. Whitish (dark) lines are either dead columns or crosstalk from bright lines located elsewhere on the CCD. Such crosstalk is an unavoidable but removable characteristic of data collected from mosaics of CCDs.

The image validates several aspects of our engineering. The uniformity of focus and quality of the star images over the whole area shows that the CCDs were mounted in the same plane and that the optical system is collimated and works as designed. Furthermore there is no "ghost pupil", or "donut" image of the optical entrance pupil, another validation of the fine optical system. The roundness of the star images also shows that the charge transfer efficiency of the CCDs is good.

Discovery and Followup of Amor Asteroid 2003 EN16; First NEO Discovered with Spacewatch CCD Mosaic. In MPEC 2003-E38.

MPECs from observations with Spacewatch CCD Mosaic

MPEC Object Type H Obs. Type Vmag Comments
2003-E38 2003 EN16 Amor 18.7 Discovery 20.4 First discovery
2003-E41 2003 EZ16 Amor 22.7 Discovery 20.4 Not planet crossing
2003-F57 2003 FQ6 Amor 21.1 Discovery 21.0 Low e, i
2003-F58 2003 FR6 Amor 19.9 Discovery 19.4 High e, i
2003-G38 2003 GJ21 Amor 23.1 Discovery 20.2 High e
2003-G44 2003 GS22 Amor 23.0 Discovery 21.6 High a, e
2003-H36 2003 HB6 Amor 17.8 Precovery 19.8 High a, e
2003-J05 2003 HU42 Amor 18.6 Discovery 21.5 N/A
2003-J21 2003 JG4 Amor 23.1 Discovery 21.4 High e
2003-J35 2003 JC11 MC 18.6 Discovery 21.0 High a, e, i
2003-J41 2003 JC13 Apollo 20.6 Discovery 19.8 PHA; low a
2003-J45 2003 JF13 MC 21.0 Discovery 21.6 High e
2003-J52 2003 JV14 Apollo 21.1 Discovery 19.4 High e
2003-K14 C/2002 U2 Comet N/A Incidental 20.0T Comet LINEAR
2003-K26 2003 KU2 Apollo 17.9 Discovery 20.7 PHA; High e
2003-K34 P/2003 H4 Comet N/A Incidental 17.8T Comet LINEAR
2003-K37 C/2003 K1 Comet N/A Discovery 20.2N Comet Spacewatch
2003-K54 2003 KN18 Apollo 19.1 Discovery 20.8 PHA; High e
2003-L11 2003 KK20 Hungaria 17.9 Discovery 22.0 a=3.02, e=0.24, i=42
2003-L30 0053P Comet N/A IA Obs. 14.7T N/A
2003-L33 C/2003 L1 Comet N/A Discovery 19.7T Comet Scotti
2003-M42 2003 MT Amor 19.1 Discovery 18.7 High a,e
2003-M43 2003 MU Amor 20.5 Precovery 20.4 PHA; high e

Asteroid Detections by Spacewatch 0.9m telescope


Last Update: 2005 Feb 22

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