Red Barn Observatory MPC/IAU H68

Established 2006

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A Practical Guide To Chasing Asteroids

For The Astrometrist

By: Steve E. Farmer Jr. & Marcelo Saavedra

Chapter 5:  How To Obtain An Observatory Code

Obtaining an observatory code should be a goal set by anyone who is interested in building their own permanent observatory or plan to observe from the same location every viewing session. The primary purpose for obtaining an observatory code is to document specific details about your observing site and the types of instruments used within your observatory. This will not only tell the Minor Planet Center where you are at or what equipment you use, it will also “announce” to many astronomical centers and stations worldwide that there is an active observatory at this particular location.

Obtaining an observatory code takes a little experience in astrometry, a telescope capable of tracking objects for short (or long) periods of time with a CCD camera, astronomical software to accurately measure the object, and a lot of patience. I’ll later explain the steps that I took, in as much detail as possible, in hopes to give a general idea of “what can be done” to achieve this.

Part 1: Getting Started

Telescope:

The proper telescope needed to perform astrometry should be capable of guiding for a period of time usually no less than 30 seconds for the average object. The “go-to” telescope works very well for this and if purchasing a new telescope it should be took into consideration. Below is a list of telescope companies.

Meade

Celestron

Orion

CCD:

A lot of technical details can be brought into consideration when discussing CCD imagers, so this explanation will be kept as simple as possible for a newcomer to CCD astrometry. CCD imagers come in a variety of styles with the most common probably being the SBIG (Santa Barbra Instruments Group) CCD cameras and the Apogee CCD cameras. Below is a list of CCD Imagers that may be used for astrometry.

Apogee

SBIG

Starlight Express

Software:

The software used will be according to the person who will be performing the astrometry. Also needed is a synchronizing program to keep the time clock on the computer extremely precise. Here are some links to various software packages for producing astrometry:

Astrometrica

MPO Software

CHARON Project Pluto

FindOrb

Part 2: Minor Planets to Observe

Once you have your telescope, CCD, and Software packages of your choice, you are now ready to prepare for your astrometric imaging session. The Minor Planet Center requires that you observe a number of “low-numbered” minor planets (400 - 40,000) each on pairs of nearby nights and try to observe objects of various brightness. They are not very specific with an exact number of objects to work on but I would recommend at least 3 objects over a period of 2 nights to produce good results. But, the objects should be well within the limits of your equipment. You should also take into consideration the speed of the objects to measure. You wouldn’t want to try astrometry for the first time on a fast moving object.

These objects can be found in nearly any planetarium program capable of loading asteroids and comets. Some planetarium programs are listed below.

Hallo Northern Sky

Cartes du Ciel

The Sky

Other ways to determine object selection can be found here:

http://www.cometary.net/asteroid_hunting_tips1

Some examples of asteroids to image would be:

(817) Annika 15.6 magnitude on 20070226

(478) Tergeste 13.7 magnitude on 20070226

(1145) Robelmonte 16.8 magnitude on 20070226

(529) Preziosa 15.6 magnitude on 20070226

Remember, these objects will vary accordingly to the equipment being used for the measurements.

Part 3: Imaging the objects

To many people, this is the toughest part. The position of the object has to be determined and centered accordingly. It is very irritating to spend time on imaging an area only to find that the object is just outside the FOV. After many nights of doing this one can loose interest and finally give up. But, by spending a little time learning how to operate your telescope, CCD, and software, this can be easily overcome. For example: If you have a go-to scope such as the Meade LX200 GPS, an SBIG CCD imager, and CCDSoft, you can use the CCD to center the scope on an object. The telescope can be slewed to a brighter star very near the object to be imaged, and then center the star in the FOV by using the auto-center function in CCDSoft (right click on the star in the image). Once the star is centered in the FOV, simply sync the telescope on that star. If the drives are “decent” in the scope, you should be able to accurately slew to the exact location of the object and begin the auto-guide sequence (if needed). Focus the telescope, take your images, save them to a predetermined file, and slew to the next object. Also, collect flat fields and dark frames according to your telescope/CCD combination, CCD temperature, and focal length.

Part 4: The Astrometry

This is the fun part. Everyone has their own special techniques that they do to perform astrometry. I guess this could be considered a “customized” area of astrometry. But the main goal is to produce correct, accurate results.

Currently, there are several programs that are available for producing astrometry. They are used to calculate the stars in a field, and “align” your images with these stars. Once the program has determined the reductions on the images, positions and magnitude estimates can be performed on any objects within the FOV. The techniques used to process your images will be determined by the technique you prefer and the quality of equipment and images you collect.

Here’s a quick example on performing astrometry on an object in your images.

1. Load the Astrometry program.

2. Load your images containing the object.

*These may be single exposed, stacked, have the flats and darks removed, etc…

3. Command the Astrometry program to perform a data reduction on the images. Here you will need to know the center position of the FOV in R.A. and Decl.

4. Click on the object in each of the frames to allow the program to “mark” the object with proper position and magnitude. Assign the object a “user defined” name that contains 6 or 7 characters (letters and numbers). (Ex.000001, 0000001, A00001, 100000A) Just remember to assign one unique identification per object to prevent confusion in the calculations.

5. Check your residuals by using a program such as FindOrb.

6. If the residuals are good, and you are satisfied with your measurements, double check all information and report to the MPC. This report can be made via the program you are using or either by e-mail.  REMEMBER!!  Use XXX for the observatory code when submitting your first set of measurements and/or while waiting for approval and official code assignment from the MPC.  This informs the Minor Planet Center's computers that these reports are coming from a new (unregistered) station and a code is being requested.

You should continue sending reports under XXX code but once you reported your first set of positions for the code, you would want to wait until confirmation from the MPC until you report any more observations.  By doing this, you would verify that your measurements were acceptable.  You could still continue to gather the images and collect measurements while waiting for the code.

Upon receiving your measurements, the Minor Planet Center will review your report for errors. If your report and measurements pass, they will assign your observatory code within a few days.

Here are some of the original positions I sent to the MPC for Observatory Code H68.

Tomeileen (2443)

Mercedes (1136)

Krylov (5247)

Guide to Minor Body Astrometry - Minor Planet Center

Chapter 6: How to Image Fast Moving Objects