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Follow-up Astrometry

Follow-up astrometry and recoveries are made with the ANU 40 inch (1.0-m) f/8 reflector at Siding Spring Observatory (IAU code 413). The 2x2K CCD has 24 micron pixels and a 21'x21' field. It is typically used with 2x2 binning giving pixels of 1".2 which is better than the typical seeing. The 1.0-m is slowly being upgraded to allow remote operation. At the moment, the telescope pointing and dome control are computer controlled from the adjoining control room. The telescope can be pointed with an accuracy of about 20 arcsecs.

Data Reduction

All data are reduced on a PC. Flat-fielding is done using MaxIm DL. The astrometry is done with both Bill Gray's CHARON , which although DOS based is extremely fast and Herbert Raab's Astrometrica which has an excellent track and stack option. As Astrometrica also allows the simple identification of all objects in the field, this is currently the software of choice.

Following the release of UCAC2, virtually all of our astrometry is done using this. An astrometric accuracy in the fit of 0".06 RMS in each coordinate is obtained for several hundred stars within the field. On some fields near the equator we have obtained 0".04 RMS. For high S/N targets, the absolute accuracy of the astrometry is of about the same magnitude; the absolute accuracy of UCAC2 being smaller than this.

Previously we used UCAC1 for regions south of ~-15 deg Dec. It had a similar accuracy to UCAC2. North of UCAC1 we used the GSC-ACT and USNO-A2.0 catalogues which give typical RMS for the star fit of 0".2-0".3 and an even poorer absolute accuracy. USNO-B1.0 is a substantial improvement over GSC-ACT and USNO-A2.0, but doesn't reach the internal or absolute accuracy of UCAC1 or 2. North of UCAC1, USNO-B1.0 was the catalogue of choice, but due to the slow internet link, large file sizes, and inconvenience of downloading from the web, we limited its use to some high priority objects like Virtual Impactors (VIs).

Additional Targets

Dr Paul Price of the ANU has identified the optical counterpart of GRB030418 from observations taken during our NEA astrometry run.

GRB030418 optical counterpart

GRB030418 on April 18 and 19
(c) ANU/RSAA 2003

Animated image, please wait for all frames to load.

The GRB optical counterpart appears in the center of the April 18 image. It appears at mag 18R in this coadded image taken in moonlight and bad seeing. The images taken on April 19 (21 hours later) were taken before moonrise and go much deeper but show no object to mag 21R in the position of the GRB optical counterpart.

Discovery of PHA 2003 XB22 
A routine follow-up of 2003 WY153 on 2003 Dec 15 became much more than routine when a faint object with unusual motion vector was found close to the target asteroid. These observations were submitted to the Minor Planet Center and Tim Spahr noted that the object was possibly of interest. The least exotic orbit solution appeared to be of a moderate inclination but highish-eccentricity Main Belt object and he assisted in providing a search ephemeris for our next run that started on Dec 24. The object was recovered only 2 fields ahead of nominal and indeed, it had accelerated and brightened. Additional observations the same night by Jana Ticha and Milos Tichy at Klet confirmed that this is a Apollo asteroid of ~0.5km diameter which can have occasional close approaches to the Earth (see MPEC:2003-Y63 ). The animation of the discovery below is from three stacks each of six 60 second exposures.

Discovery of 2003 XB22 on 2003 Dec 15 with the 1.0-m at SSO
North is to the left and west is up
(c) ANU/RSAA 2003

Animated image, please wait for all frames to load.

Discovery images of 2003 XB22

P/2004 CB (LINEAR) 
During routine astrometry with the 1.0-m to improve the orbit of the Apollo asteroid 2004 CB, the asteroid was found on March 30 to have a short tail! On IAUC 8314 . it was renamed periodic comet P/2004 CB (LINEAR). The animation below is from three consecutive 10 second exposure on March 30. The comet head is basically asteroidal (FWHM ~2".2 in 1".8 seeing) but a narrow tail extends over 60" in PA ~280.

2004 CB with tail!

2004 CB on 2004 Mar 30, imaged with the 1.0-m at SSO
North is to the left and west is up
(c) ANU/RSAA 2004

Animated image, please wait for all frames to load.

Observing Dates

We have been allocated the following time (thru 2005 Jan) on the SSO 1.0-m
Jan 24 - Feb 01

 The full MSSSO Telescope Schedules can be found here. 


The long lost asteroid 1937 UB (Hermes) was rediscovered in 2003 October by LONEOS. The linked orbit allowed searches through archives for images of this elusive NEO. As it happened, some previous searches for Hermes had been conducted, including one with the 1.0-m at SSO. Lutz Schmaedel and Jochim Schubart of the Astronomisches Rechen-Institut Heidelberg had proposed such a limited search and images had been taken in 2001 August for this project. Hermes was not found at the time, but given the new orbit, faint images of Hermes were identified and a stack of the three images taken 2001 Aug 09 is shown below.

Hermes on 2001 Aug 9, imaged with the 1.0-m at SSO
Three images of 60 sec duration are combined
(c) ANU/RSAA 2001

Image of Hermes in 2001

This is the first image of Hermes since its discovery in 1937 and helped to refine the orbit.


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