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Doc Greiner Research Observatory Minor Planet Astrometry Procedure

By Matt Mills

 

POINTS TO BE COVERED:

  • About the Minor Planet Project
  • Our Mission Statement
  • Main Goals of the Minor Planet Project
  • Software Used by the Minor Planet Project
  • Choosing Targets for Minor Planet Astrometry
  • Filtering Minor Planet Data
    • Extended Minor Planet Command in TheSky
    • Filtering the MPCORB database file using MPCorb
  • Creating Plans for Minor Planet Runs
    • Developing a Night’s Plan using the Select_Asteroid_Planner
    • Developing a night’s plan using a mosaic plan
  • Length of Run and Number of Minor Planets to Image per Plan
  • Time Sync with Dimension4
  • Minor Planet Astrometry
    • Using PinPoint to Find and Measure Minor Planets
    • FITS format, WCS World Coordinate System (WCS) and Astrometry
    • Catalogue Selection
    • Minor Planet Settings in PinPoint
    • Plate Solving
    • Automatic Detections
    • Manual Detections
    • Known Object Overlay in Astrometrica
  • Find Determination
    • Checking your finds with Find_Orb
  • Submitting astrometry to the Minor Planet Center
    • Interpretation of the reply from the Minor Planet Center
    • The best way to follow-up a new discovery
    • If you are unable to follow-up a new discovery
    • Quick reference guide to submissions to the MPC
    • Fast Moving Object (FMO)
    • Track & Stack Technique
    • NEOCP Uncertainty Maps & Variant Orbits
    • Explanation of Uncertainty Map
    • Difficulties using Uncertainty Maps
  • Trouble Shooting Problems
    • Most common Minor Planet Astrometry Problems
  • Big Surveys

 

About the Minor Planet Project (MPP):

The MPP was begun in 2000 by Greg Sellek and Matt Mills under the guidance of Doc Greiner.  The MPP Team used the DocG and DocG2 observatories at the Yanna Research Station of the Madison Astronomical Society to perform minor planet astrometry.  During the first four years measurements were submitted to the Minor Planet Center (MPC) by the Team.  In 2004, Doc Greiner began discussions with a select group of the observers at YRS to build a private observatory.  In 2005, the Greiner Research Observatory (GRO) was built near Middleton, WI.  In 2008, The Doc Greiner Research Observatory was built near Evansville, WI.

 

The mission of the Minor Planet Project is to gather astrometric observations of Small Solar-System Bodies and submit those measurements to the Minor Planet Center.  Our goal is to obtain follow up observations, on One-Opposition Unnumbered Objects, so their orbits can be better defined.

 

Main Goals of the Minor Planet Project:

  1. Confirmation and early follow-up of NEOs

It will involve confirmatory observations and follow-up astrometry of newly discovered bright NEOs with a limiting magnitude of mV =18.7. 

  1. Recoveries of minor planets in the second opposition

Our objective is to improve the orbit of the object.  If the Current Ephemeris Uncertainty (CEU) is larger than the RMS of our standard measurements, we can generally improve the orbit.  But if your RMS is larger than the CEU, we are definitely not helping the orbit.  As a rule, objects with uncertainties < 0.7" never need additional observations.  We generally select > 2.0", and filter for second-opposition objects.

  1. Follow-up astrometry of newly discovered One-Opposition Unnumbered Objects.
  2. Search for new minor planets

Our primary goal is astrometric follow-up of One-Opposition Unnumbered Objects.  If observations are planned effectively, there will be also time for searching new minor planets using the mosaic technique.  All CCD images are processed not only for target objects, but also blinked  for possible new objects.

 

Software Used by the Minor Planet Project:

  • Astronomer’s Control Panel
  • TheSky
  • MaxIm DL
  • Astrometrica
  • MPCorb
  • FocusMax
  • Find_Orb
  • Orbitas
  • PinPoint
  • Select_Asteroid _Planner

 

The following methods and techniques are used routinely by the Minor Planet Project Team to successfully perform minor planet astrometry and photometry for submission to the Minor Planet Center.

 

Choosing Targets for Minor Planet Astrometry:

Every minor planet imaging sessions begins with choosing the night’s targets.  It should be understood that minor planets can be found everywhere in the sky, but they are highly concentrated along the ecliptic plane.  The best choice for new discoveries would be areas of the sky which have not recently been swept for minor planets by the Big Surveys (See: “Notes regarding professional programs”.)   Observations within the Doc Greiner Research Observatory’s Minor Planet Project are done on any (at least partly) clear night throughout each lunation.

 

Selection of targets

We apply two kinds of criteria for selecting minor planet astrometry targets.  Observability of particular objects depends on its brightness, motion and position on the sky (especially its solar elongation).  Then we deliberate the ephemeris uncertainty depending especially on the length of observing arc in the discovery apparition.  A special case is selecting targets for confirmatory observations of newly discovered NEO candidates. They are listed on the NEO Confirmation Page (NEOCP) maintained by the Minor Planet Center.  The NEOCP gives very preliminary ephemerides for newly discovered NEO candidates, uncertainty maps are computed and presented on the NEOCP especially for NEO candidates observed for one night only.  We check this page nightly just after its updates. 

 

The MPC Orbit (MPCORB) database contains the orbital elements of minor planets that have been published in the Minor Planet Electronic Circulars (MPEC).  It gives orbits for all numbered and observable unnumbered minor planets.  MPCORB is available for downloading from the anon-ftp link:

ftp://cfa-ftp.harvard.edu/pub/MPCORB/

 

Presently, there are 351,000 known minor planets out of an estimated 1 million, of which, 938 are known Potentially Hazardous Asteroids (PHA). 

 

Filtering Minor Planet Data:

Extended Minor Planets command (Data menu in TheSky)  
Use this command to select a Minor Planet data file to plot the positions of all known minor planets on the Virtual Sky.  Each time this command is selected, the positions of all minor planets in the selected minor planet file are computed and updated. 

To obtain the minor planet file that contains information about the most recent minor planet discovered go to:

http://cfa-www.harvard.edu/iau/Ephemerides/Unusual/Soft06Unusual.txt

to retrieve the list of unusual minor planets and Import into TheSky. 


Filtering the MPCORB database file using MPCOrb

Using the MPCOrb program and the MPCORBcr.DAT file you can quickly filter for Minor Planets.

 

A useful text file is also created called AstPos.txt:

Posiciones para Lat: +43 07 13  Lon: +089 35 59  Alt: 0350 Día 03/10/2006 a las 0 horas TU.

Asteroide                   A.R.                 Dec.                            Mag.              "/min

------------  -----------  ------------  ----  -----

2006 NM                    20h 27m 38s  +36° 28' 58"              16.2                3.4

2006 QL39                01h 11m 44s  -01° 27' 41"               16.8               0.5

2006 QW57               00h 03m 43s  +13° 56' 39"              17.5                0.6

2006 RZ                     20h 46m 53s  +34° 56' 54"              14.4                17.3

2006 SS134              00h 49m 21s  +16° 17' 47"              16.7                11.4

2005 LC18                03h 06m 18s  +17° 39' 38"              17.8                0.3

                                                                                                                      

NEOs can be easily determined.

 

Creating Plans for Minor Planet Runs:

Developing a night’s plan using the Select_Asteroid_Planner

Obtain Greg Sellek’s visual basic Select_asteroid_planner_ACP2.1vbs for use with ACP in TheSky.

 

This simple script allows for selecting the number of sets, how long the exposure (in seconds) and how many objects you have to image.  A plan is then generated which is used in Astronomer’s Control Panel (ACP).  ACP provides an interface for scripting automatic control of telescope mounts and CCD cameras.

 

First, open TheSky and click on Data, set the Site Information to the run mid-point or use the time skip function to approximate the run mid-point Date and Time.

 

Populate the minor planets from the mpcorb.dat or Unusual Minor Planets databases to choose your target asteroids.

 

Next, open the Select_asteroid_planner_ACP2.1vbs program.  The script is designed to use the information found in TheSky to create the minor planet run.

 

You will be asked three questions in the asteroid planner script:

  1. How Many Sets?  ENTER  4
  2. How long Exposure? ENTER 240
  3. How Many Objects do you have? ENTER the number of targets you wish to image between 5-12 per run

After the three questions have been answered the remaining fields are entered using data from TheSky by clicking on the object and using the Object Information under the General Tab.

 

Asteroid Planner Procedure:

Highlight the minor planet name 2006 AR2 and copy it in the field for Object Name #1

 

Highlight the (only use Epoch 2000 coordinates) and copy it into the field for What are the coordinates for 2006 AR2?

 

Continue entering the fields until the plan is finished. Here is what the finished visual basic output form Select_asteroid_planner_ACP2.1vbs looks like:

#SETS 3

#INTERVAL 180

1994 RM1                     19h 46m 07s     -02º 48' 58"

2000 LS34                     20h 04m 40s     -05º 58' 58"

1999 JO98                     20h 10m 23s     -07º 14' 36"

2001 UO121                  20h 27m 34s     -00º 34' 05"

1991 BE                        20h 26m 51s     +01º 13' 41"

 

Note: Once the plan has been created it will be found the same folder where the Select_asteroid_planner_ACP2.1vbs is located.  The following commands (directives) may be added to your asteroid plan to customize the night’s runs:

 

#DIR D:\images\2006\MPP\01-01-2006   in the mm-dd-yyyy format

(THIS COMMAND IS MANDATORY) Indicate the location of the file which you created on the drive D:\images\ for your nights run.  By convention we name the file for the night/morning run MM-DD-YYYY.

 

#waituntil 1, 25-Nov-2005 06:00:30    ; UTC

If the run does not need to begin until a specific time add this line.  Be sure to use UT. 

 

#CHAIN D:\plans\11-24-2005planB.txt

Runs may be linked together so imaging can be performed over the entire night.  Be sure to use different plan names for each run.

 

#AUTOFOCUS

Use the auto focus command line to add a FocusMax routine at the beginning of your run.

 

#afinterval 30

Use this command line to add a FocusMax routine at a specific time interval, 30 minutes in this instance.

 

Here is an example of a typical DGRO run, note the ‘chain’ to a second run at the end of the plan:

 

#DIR D:\images\2007\MPP\05-19-2007                ;begin 1:20 AM

#SETS 3

#INTERVAL 180

#AUTOFOCUS

1994 PX                        15h 26m 35s     +01º 14' 31"

1998 RE2                      15h 27m 03s     -03º 21' 47"

1999 YF5                      15h 34m 20s     -02º 18' 37"

2002 CN108                  15h 42m 02s     -04º 42' 45"

1998 FY11                    15h 55m 03s     -05º 16' 41"

2002 FF22                     16h 09m 29s     -07º 13' 26"

1997 CR                        16h 14m 27s     -00º 22' 05"

#CHAIN D:\plans\2007FK1plan.txt

Developing a night’s plan using a mosaic plan

While there are many times when you may want to specifically select certain objects for observation, there are other times when you may just want to 'cast the net' and see what you find.  Use TheSky’s Mosaic Tool to cover an imaging area.

 

 

Then use the, Sky6MosaicToPlan.vbs, script to generate a mosaic plan from the Mosaic Tool’s advance “Copy to Clipboard” function.

#DIR D:\images\2008\MPP\2-24-2008

#SETS 3

#INTERVAL 180

#AUTOFOCUS

STACKALIGN 3

Mosaic_0          10.57802392      18.73864312

STACKALIGN 3

Mosaic_1          10.60154277      18.73960883

STACKALIGN 3

Mosaic_2          10.625061         18.73993072

STACKALIGN 3

Mosaic_3          10.64857923      18.73960883

STACKALIGN 3

Mosaic_4          10.67209808      18.73864312

STACKALIGN 3

Mosaic_5          10.57811598      18.40456931

STACKALIGN 3

Mosaic_6          10.6015888       18.40553309

STACKALIGN 3

Mosaic_7          10.625061         18.40585435

STACKALIGN 3

Mosaic_8          10.6485332       18.40553309

STACKALIGN 3

Mosaic_9          10.67200602      18.40456931

STACKALIGN 3

Mosaic_10        10.57820609      18.07050108

STACKALIGN 3

Mosaic_11        10.60163386      18.07146301

STACKALIGN 3

Mosaic_12        10.625061         18.07178365

So the images are stacked and aligned in MaxIM and ACP.

 

Length of run and number of asteroids to image per plan

Our minimum number of asteroid targets in a run is 6.  Three images per set is the minimum, four is better.  The exposure duration can be 180 seconds to reach magnitude 18.7 on an average Wisconsin moonless night. 

 

[Run Time for 6 objects x 180 second exposure + 1 focus and syncing = 1.5 hours]

 

The maximum number of targets per run before a second run would need to be ‘chained’ is 12.  Be sure not to begin such a long run past the meridian in the West or the targets will surely set before the run has completed.

 

Time Sync

This may be one of the most IMPORTANT steps in performing astrometry.  Since the object’s location is constantly moving, time is an equally important an element as location is for measurement.  So syncing the computer’s clock to Atomic Time is essential in providing sub-arcsecond determinations for the MPC.

Dimension4 software is used to time sync the DGRO computer prior to beginning a night’s session. 

Routine procedure:

·        In ACP choose Browse and select AcquireImages.vbs

·        Next choose Main and select the plan you have created and save in D:\images\2007\MPP\

·        Once the plan is opened the run will begin slewing to the first object’s position and continue till all images have been acquired.

Minor Planet Astrometry

The Minor Planet Project uses many different programs in its minor planet search routine.  TheSky, ACP, MaxIM and FocusMax software are used to point the telescope, take images and focus the optics.  PinPoint is used to measure the minor planets position and perform plate solving.  MPCOrb is used to filter the MPCORB.dat database.  Astrometrica is used to overlay known objects in an image.  Orbitas is used to determine the best window of time for peak magnitude and opposition.  Find_Orb is the orbital software which gives us the residual used to determine if our astrometry is acceptable.

Using PinPoint to find and measure minor planets

PinPoint is an astrometric tool than can identify star fields.  This can be used to adjust telescope pointing and re-sync a telescope mount with the sky.  PinPoint uses the ASCOM Platform.  PinPoint is an image analysis program which pattern matches reference stars, plate solves the image, and saves WCS World Coordinate System (WCS) information to the FITS header.  PinPoint also analyzes sets of three images and finds moving objects, providing astrometric and photometric information on each, and formatting a report for submission to the MPC.

 

FITS format, WCS World Coordinate System (WCS) and Astrometry

Astrometry is the precise measurement of the position of celestial objects, such as stars, minor planets (asteroids), supernovae, and comets. In the case of new discoveries, this can be extremely important for orbit determination and for planning follow-up observations.  Each image you take and save to a FITS format has additional information imbedded in the image too.  The most important information for astrometry is the WCS information.

 

Once PinPoint  is set up for the star catalog and the general characteristics of your images, the analysis is fully automatic. The program finds all the stars in the image, matches against catalog positions for stars in that vicinity, and then calculates a mapping between the catalog and the image.  This mapping is stored as WCS values in the FITS Header of the image.  The WCS header information is standardized, so it is compatible with many other software applications.

 

Note, since this PinPoint version utilized in MaxIM is using the GSC (a limited catalog) a second plate solve is required with a larger and more accurate catalog to submit to measurements to the MPC.                                                  

 

Catalogue Selection

The most important factor in success of plate solving is the selection of the reference catalog. PinPoint requires a certain number of stars to match, depending on the number of image and catalog stars available.  The absolute minimum is 6 stars. As the number of stars detected in the image increases, and/or the number of catalogue stars in the field increases, that minimum number is dynamically adjusted upward to 50. If there are many catalog stars in the area, yet few image stars, the chances of a false match are increased.  Thus, you need to expose down to the faintest stars in the catalog, usually a 30 second exposure will do.

 

Catalogs

The USNO-B catalog is the successor of the USNO-A2.0 and presents positions, proper motions and magnitudes for more than a billion objects.  Due to the enormous size (80 Gigabytes), this catalog is not distributed by the USNO, but it is available online through the Internet.

The full USNO-A2.0 catalog contains entries for more than 526 million stars.

The Tycho 2 catalog contains 2.5 million entries over the whole sky.

The ACT Reference Catalog contains entries for 988758 stars over the entire sky.

The UCAC 2 (second U.S.N.O. CCD Astrograph Catalog) contains positions and proper motions for 48 million stars down to R = 16, covering the sky from the south celestial pole to mid-northern declinations.

The Guide Star Catalog 1.1 (GSC) is the most commonly used catalog, and is suitable for most images.  It contains stars down to about 17th magnitude, so any fainter stars in the image cannot be used for matching and solution.  The GSC is used in our MaxIM/PinPoint LE version to speed up the search process since it is a much smaller catalog. 

It is the recommendation of the Minor Planet Center that observers not submit measurements using the GSC as their reference catalog.  Instead observers should submit using astrometry from the UCAC 2 catalog or USNO-B catalog.

 

Use these minor planet settings in PinPoint

Plate Solving

Plate solving is the process matching stars in the image to known stars in a reference catalog and writing transformation info to the FITS Header. This transformation info the World Coordinate System (WCS) data allows a FITS image to be used for direct astrometric measurements since the image scale, projection geometry, and center-point coordinates are accurately known.  This also allows use of the image for astrometric purposes at later times without re-matching to a catalog and re-solving the plate.

Find Asteroids

PinPoint can handle multiple sets of two or more images for blinking.  If you have three or more images in a set, you can also use PinPoint's automatic detection capability. If you use more than three images in a set, the minor planet must be detected on all plates.  While using four images in a set will reduce false detections.

Use these solve settings in PinPoint

 

Find Asteroid Sequence

  1. In the Find Asteroids tab of Visual PinPoint, use the Add Files button or drag-and-drop to put a few sets of your images into the list window.  They will automatically organize themselves into sets in a tree display.  You can also use the Get Solved button to automatically transfer any images listed in the Solve Plates list into the Find Asteroids list.
  2. Select Blink All Image Sets.
  3. Click Find Asteroids.  All sets containing three or more images will be scanned for minor planets, and those that are found automatically will be entered into a database.
  4. After a while a blink display will appear.  If there are automatically detected asteroids, they will be indicated by crosshairs.  The yellow/green marked one is the one you are verifying.  If you think it's real, click Accept, otherwise click Reject. 
  5. Eventually the blink display will switch to manual mode.  You can tell this by the appearance of the Report button in place of the Accept button. You will see all of the automatic detections and previously reported manual detections marked by blue cross hairs.
  6. If you see an unmarked asteroid, click anywhere once to stop the blinking.  Use the mouse or F6-F7 keys to step between the frames and mark the asteroid.  Click Report to add it to the MPC report (Find.txt).
  7. Repeat for each manual detection.  When you have reported everything you found manually, click the “Done” button.
  8. The report contains astrometry on the moving object detections and the MPC report header lines.

 

Automatic Detections in PinPoint (DO NOT RELY ON AUTOMATIC DETECTION TO FIND ALL MINOR PLANETS PRESENT IN YOUR IMAGES.   EXAMINE EACH SET MANUALLY FOR MINOR PLANETS THAT WERE MISSED BY AUTOMATED DETECTION)

autobuttonsIf any objects were detected automatically, the blink window first appears with the three buttons shown on the image to the right and the first automatically detected object is marked in each frame by yellow reticules.  The other (as yet un-reviewed) automatic detections are marked with blue reticules.

 

To accept a detection (and have it included in the MPC report), click Accept.

 

To reject a detection and go on to the next (e.g., it is a false detection), click Reject.  If you want to skip all remaining automatic detections and proceed to manual marking, click Manual.

 

Once all automatic detections have been reviewed and either accepted or rejected, or if the Manual button is clicked, the blink window switches to the manual detection mode (see the next section).  If you want to stop blinking completely, click the [X] box in the upper right corner of the blink window.

 

Manual Detections in PinPoint

manualbuttonsOnce in manual mode, the three buttons change to those shown in the image to the right.  Click on the object to be marked on a frame and a yellow reticule will appear at its astrometric position.  If the reticule appears on a nearby object, the one you tried to mark was not detected by PinPoint.  Adjust your detection sensitivity settings to go deeper (at the possible cost of more false detections).

Mark an object on at least one frame (usually on all frames). Then click Report to add the marked/reported positions for this object to the MPC report.  Once you report a manual detection, the window will again start blinking and the just-reported positions will appear with blue reticules (so you can avoid re-reporting them).  Repeat this cycle for each object that you want to report manually.

When you have finished marking and reporting objects manually, click Done.  The MPC report will appear in Notepad as your Find.txt.

 

Known Object Overlay

Not all Minor Planets can be easily seen in the blinked images in PinPoint.   Astrometrica has a command which will mark the nominal position of all known minor planets and comets on the currently loaded CCD images.  Besides the packed designation of these objects, the predicted magnitude is also displayed.  Note that the nominal position is calculated from the orbital elements in the MPCOrb database, without taking account for planetary perurbations, so this command is useful for identifying of locating a minor planet on the frames, but should not be used to judge the quality of a measurement.  The Known Object Overlay command can also be enabled with the blinking feature on.

 

The following settings are used in Astrometrica:

Find Determination:

Checking your finds with Find Orb

Click here to download the 32-bit version of Find Orb the ‘Find’ checking and orbit determination software.  This program is a useful tool in determining your measurement residuals.  When you attempt to determine an orbit for an object, you will always find some difference between the "observed" positions (measured from a CCD image), and the "computed" positions (computed using the orbit you have determined).  These differences are known variously as "residual errors", or "residuals".  The measurement is in "RMS" = "Root mean square"; it's a modified version of the average of the residuals.  It is the square root of the average value of the square of the residuals.  If you took the squares of all the residuals, averaged them, and took the square root of the result, you would have the RMS error.

 

Your Find.txt from the night’s asteroid run is checked for residual error in the Find Orb program.  Be sure to save your Finds in a separate file and name it.

 

Open Find Orb to check the residual error in your finds. 

 

Click Open in Find Orb.  Highlight the Find.txt file and click Open.

 

Now click on each designation and make sure the RMS error is < 0.7 to accept (our criteria of submission to the MPC).  Delete those designations which have RMS error > 0.7 from your find text before submission unless the CEU can be improved upon.  Most of the residual error we find will be <0.2.  If the residual error is between 0.7 and 0.5 use the Minor Planet Checker to verify the find, as below.  If the MPChecker indicates,” No known minor planets” or offset different from ‘0.0E’ RA and ‘0.0S’ DEC, you may have discovered a new minor planet.