Doc Greiner Research Observatory Minor Planet Astrometry Procedure
By
Matt Mills
POINTS TO BE COVERED:
- About
the Minor Planet Project
- Our
- 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
- Interpretation
of the reply from the
- 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
The mission of the Minor Planet Project is to gather astrometric observations of Small Solar-System Bodies and
submit those measurements to the
Main Goals of the Minor Planet Project:
- 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.
- 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.
- Follow-up astrometry of newly discovered
One-Opposition Unnumbered Objects.
- 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
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
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:
- How
Many Sets? ENTER
4
- How
long Exposure? ENTER 240
- 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,
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
#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
[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.
·
In
ACP choose Browse and select AcquireImages.vbs
·
Next
choose
·
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
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
- 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.
- Select Blink All Image Sets.
- 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.
- 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.
- 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.
- 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).
- Repeat for each manual detection. When you have reported everything you
found manually, click the “Done” button.
- 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)
If 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
Once 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.
