Asteroid Astrometry

Introduction

Currently, the primary work at Hunters Hill Observatory is to image Minor Planets and NEOs (Near Earth Objects).  This imaging is used to determine the position of the object (Astrometry) and variance of the objects brightness (Lightcurves).  The astrometry component is used to determine the orbital parameters of the object (also known as improving the orbit).  This data allows us to predict the objects location at any time in the future, primarily for collision mitigation ie to determine if the object is likely to collide with the Earth at any time.

Equipment

The 14" LX-200GPS SCT using the Starlight Xpress MX716 with f/3.3 Focal Reducer with extension to provide a focal ratio of f/3.4 is used for all imaging runs.  The observatory has been since upgraded to an SBIG ST-8E at f/4.  This set-up gives me a plate resolution of around 2"/pixel.  Considering that my seeing averages 2-4"/pixel it is the best possible set-up.  The telescope and camera are controlled by a 1GHz Athlon PC with 768mb RAM running Windows 2000 Professional. This PC is located in the observatory and connected to the house LAN 15 metres away via a 100mb/sec HUB.  Inside the residence I can control the observing session from my laptop computer.  

Exposures

Exposures with the 0.36m SCT vary from 15s to 120s, depending on the brightness of the target asteroid and how fast it is moving.  For Very fast and fast movers (my set-up limit is no faster than 30"/min) I take 60 images at 15s.  For main belt object motion as faint as m21.5 I take 15 images at 120s.  Once the images are taken they are "track and stacked' on the target objects motion (the reason my scope can reach down to magnitude 20 on dark, clear nights) 

Software

I started astrometry using Astroart and it's built in modified GSC 1.1 catalogue.  The data produced barely met the minimum requirements of the MPC so I shopped around.  Then came Astrometrica.  It does automatic reduction and it does a wonderful job with a 100% success rate for reducing images and a 90% success rate at discovering moving objects and best of all it only costs 25 Euro.  I now use the UCAC2 or USNO B1 catalogue after having used both the UNSO A2.0 and UNSO SA2.0 catalogues.  This move from USNO A2 to UCAC2 catalogues has improved my plate reduction residuals to better then 0.1" in RA and Dec and more often than not I am achieving 0.05" and that's with 2"/pixel image resolution.

To control the scope and the observation session I use the ACP3 suite.  This comprises ASCOM, ACP3, Pinpoint 4, MaxIm DL/CCD and FocusMax.  You can see more details on my automation page.

General Program Description

My first port of call is the MPC NEOCP page.  This page lists all newly reported discoveries from amateurs, professionals and the Surveys (LINEAR, NEAT, LONEOS etc)  I choose those objects within the reach of my set-up and add them to my observing list.  Next I visit the NEODys Priority site and choose all objects on their list (new discoveries that require further observation) within my reach.  Finally I visit the MPC customise list page to search all objects that have not been observed recently.  I then choose those objects that are listed by the MPC as requiring further observation.  At the end of the schedule I end up with around 30-40 objects for study.  These objects are added to the observing schedule of Astroplanner.

 My LAN is then connected to my Garmin eTrex handheld GPS unit and using NMEATime, set my computers time to GPS time.  (Although the Desktop PC's do maintain good time, the Laptop can often be off by as much as 8 seconds a day).  Now that everything is setup it is time to commence the run.   Using the scope control and HPP (high precision pointing) functionality in Astroplanner I target the first object and start it's imaging run.  After the first image is taken I load it into Astrometrica to determine if the scope is pointed correctly.  If not (very rare) I restart the telescope and realign.  I reduce the images and determine the astrometry in 'real time' - manually.  I then move onto the next target and that's the process for the rest of the night.  Its all manual but it gets the job done.  I am currently limited to around 12 objects a night. 

Data Reduction

I reduce the images and determine the astrometry in 'real time' - manually - using Astrometrica.  The objects is identified by blinking 3 sets of track and stack images.  Anything that moves is reported, the results of the reduction being 3 sets of Date, Time, RA, Dec and magnitude for each object.  I then move onto the next target and that's the process for the rest of the night.  Its all manual but it gets the job done.  I am currently limited to around 12 objects a night

● Email Me: higginsdj at bigpond dot com ●