Equations are not being displayed properly on some articles. We hope to have this fixed soon. Our apologies.

Nicholson, M. (2010). Asteroid Astrometry using the Lowell Observatory Hierarchical Observation Protocol (HOP). PHILICA.COM Article number 181.

ISSN 1751-3030  
Log in  
Register  
  1249 Articles and Observations available | Content last updated 22 November, 19:47  
Philica entries accessed 3 439 822 times  


NEWS: The SOAP Project, in collaboration with CERN, are conducting a survey on open-access publishing. Please take a moment to give them your views

Submit an Article or Observation

We aim to suit all browsers, but recommend Firefox particularly:

Asteroid Astrometry using the Lowell Observatory Hierarchical Observation Protocol (HOP)

Martin Nicholsonconfirmed user (Independent Researcher)

Published in astro.philica.com

Abstract
The Sierra Stars Observatory Network (SSON) offers the amateur astronomer the opportunity to image asteroids as faint as magnitude 20+ using only a 90-second. exposure. There are literally tens of thousand of targets within range and this paper explains how the on-line Lowell Observatory Hierarchical Observation Protocol software (http://asteroid.lowell.edu/cgi-bin/hop) enables the creation of a prioritised list of asteroids requiring observation based on the capabilities of the equipment to be used.

Article body


  Asteroid Astrometry using the Lowell Observatory Hierarchical Observation Protocol (HOP)

The Sierra Stars Observatory Network (SSON) offers the amateur astronomer the opportunity to image asteroids as faint as magnitude 20+ using only a 90-second. exposure. There are literally tens of thousand of targets within range and this paper explains how the on-line Lowell Observatory Hierarchical Observation Protocol software (http://asteroid.lowell.edu/cgi-bin/hop) enables the creation of a prioritised list of asteroids requiring observation based on the capabilities of the equipment to be used.

HOP has many user-selectable parameters that filter the asteroids returned from the database.  Figures 1 and 2 show the parameters most commonly used during this project.



Figure 1


Figure 2  

Field

Significance

Observatory and Code

Observatory codes are allocated by staff at the Minor Planet Center. The code for the Sierra Stars Observatory is G68.

Limiting Magnitude (Mag)

Even a small change in the selected value makes a large change in the total number of possible targets identified by the software. Few, if any, suitable targets were brighter than magnitude 19 but by selecting a limiting magnitude of 20, well within the range of the telescope and CCD facilities available to the observer, many candidates were identified.

Maximum Zenith Angle (Deg)

The zenith is the point directly overhead. As the  maximum zenith angle increases so does the atmospheric absorption and the exposure required to image faint objects. 

Minimum Solar Elongation (Deg)

Light pollution makes it impossible to image very faint (magnitude 19+) objects close to the sun.

Minimum Lunar Elongation (Deg)

Light pollution makes it impossible to image very faint (magnitude 19+) objects close to the moon. The most appropriate value to use depends on the phase of the moon and can be much smaller when the moon is a thin crescent rather than full.

Galactic Latitude (Deg)

Galactic Latitude - The angular distance of a body above or below the galactic equator.

Probability of Imaging (%)

Reducing the probability of imaging increases the number of target asteroids but decreases the chances that the chosen asteroid will be in the field of view of the telescope.

Field of View (deg)

The chosen value is based on the quoted value for the current telescope and CCD (http://www.sierrastars.com/gp/SSO/SSO-CA.aspx)

Asteroid Types and

Other Selection Criteria

Main Belt Objects (MBO) are by far the largest sub-group of asteroids and in this study were given the highest selection weighting of 9. The maximum number of targets is generated by selecting "Maximise orbit improvement". It is also not certain that all the Other Selection Criteria listed as options have been fully implemented in the software.

Output Format

Choices made here are not of astronomical significance. They reflect the personal preferences of the individual observer

Table 1 - Details of the user-selectable fields in the HOP software

Figure 3 shows the tabular results returned by HOP using the input-parameters shown in figure and figure 2.

Figure 3

 

Field

Significance

Asteroid Name

Asteroid names are allocated by the Minor Planet Center and must be used when reporting observations.

Schedule for Observation

This field is included for administrative convenience.

Arc (days)

The number of days between the first and the last observation of the asteroid. In most cases the longer the arc the more reliable the published data about the asteroid.

RA

The right ascension of the asteroid when the table of results was generated.

Decl

The declination of the asteroid when the table of results was generated. The further north the object then the higher in the sky it would be when culminating. This means less atmospheric extinction and hence an asteroid  that would be easier to image

RA Motion s/day

How fast the asteroid is moving in right ascension. (east/west). Fast moving objects necessitate shorter exposures if the image is not to be elongated but shorter exposures restrict the imaging of very faint objects.

Decl Motion "/day

How fast the asteroid in moving in declination (north/south). Fast moving objects necessitate shorter exposures if the image is not to be elongated but shorter exposures restrict the imaging of very faint objects.

V mag

The predicted magnitude of the asteroid in the V band. The larger the number the fainter the object.

Uncertainty (1-sig) arcsec

The uncertainty value, in arcsec, gives an idea of likely positional accuracy in the quoted position of the asteroid. A value of 26.71 (as for 2000 RB37) means there is a 68% chance of the object being within 26.71 arcsec of the quoted position.

Selection scores

This field is included for administrative convenience and is a reminder of the input setting previously selected by the observer.

Relative Score

This field is included for administrative convenience.

Table 2 - Details of the output fields in the HOP software

Once a potential target has been identified it can be inserted into the ephemeris generator available at the Minor Planet Center web site (figures 4 and 5).

 http://www.cfa.harvard.edu/iau/MPEph/MPEph.html

Figure 4

Figure 5

2000 RB37, with an uncertainty of 26.71 arcsec, has a relatively well established orbit. Any further measurements taken during 2009/2010 would further refine the quoted figures and the uncertainties are such that the asteroid is almost certain to be on any image centred on the quoted ephemeris position. Looking at the residuals (figure 6)  gives the observer a good idea of the observing history of the object as does the published summary data (41 observations at 2 oppositions, 2000-2007)

Figure 6

As the probability of successfully imaging the target is reduced the software will identify asteroids with ever larger uncertainty in their position. For example 2005 ER126 has a 68% chance of being within about 51 arc minutes of the published position.

2005 ER126 - Uncertainty 3057.98 arcsec. 21 observations, 34 day arc

Figure 7

An even more extreme example would be 2005 GA1. It has a 68% chance of being within about 700 arc minutes of the published position. Realistically the asteroid can be regarded as lost. It would also be extremely difficult to link any observations made in 2010 with astrometry from April 2005.

2005 GA1 - Uncertainty 42042.46 arcsec. 14 observations 4 day arc

Figure 8

The significance of the relationship between the time span between the first and last observations of an asteroid and the positional accuracy some years later should not be under-estimated!

Case Studies

1997 JY10 - Discovered in 1997 with a 20 day arc.

1997 JY10 was recovered, probably by accident, four years later. The only observations during the 2009 opposition were by me working via observatory G68. There were no observations reported during the 2007 and 2008 oppositions. Note the long period (11.7 years) of this Trojan asteroid.

Figure 9

2005 QR69 - Discovered in 2005 with a 2 ½ month arc.

The only observations made after the discovery series were those made during the 2009 opposition were by me (G68) and there were no observations during the 2006, 2007 and 2008 oppositions. 

Figure 10

2003 HK52 - Discovered in 2003 with a 35 day arc.

There is a 3½  year gap between the observations made during the 2005 opposition and those made in 2009 at three different observatories (691, 703 and G68).

Figure 11

Recovering Asteroids Discovered at G68

There is going to be a gap of several years between discovering an asteroid in 2009 and the next time there is a realistic opportunity to image it.

For example:

#138 - 2009 SP18. The next time the asteroid will be brighter than magnitude 20 will be in July 2013 but declination will then be -51 degrees.

#148 - 2009 SA168. The next time the asteroid will be brighter than magnitude 20 will be in October 2015.

#154 - 2009 UP128. The asteroid will not be brighter than magnitude 20 at any time during the period to 2017.

#157 - 2009 UG129. The next time the asteroid will be brighter than magnitude 20 will be in August 2014.

If all the other factors such as the sampling density and accuracy of the astrometric measurements are constant then the shorter the arc used to calculate the orbit the less accurate the calculated orbit will be.

Without an accurate orbit the best, or perhaps only, chance of recovering the asteroid will be via the activities of the various wide-ranging surveys. In other words recovery  will be serendipitous.

Searching specifically for any one asteroid, perhaps one you discovered, will be very taxing if the positional errors are greater than the field of view of the scope being used.

If the asteroid orbit is based on a very short arc it might not be possible to link any subsequent observations to those taken in 2009. It all comes down to the age-old dilemma of quantity v quality of observations. If you want to be able to image your own discoveries then my advice it that you should concentrate on obtaining at least a 30 day orbital arc.

Appendix

This was the original project submission with a couple of subsequent additions added.

Title of the proposed project.

Asteroid Astrometry using the Lowell Observatory Hierarchical Observation Protocol

Project premise and objective.

The Lowell Observatory Hierarchical Observation Protocol allows for the creation of a prioritised list of asteroids requiring observation based on the capabilities of the equipment to be used. 

It is proposed to concentrate on the sub-group of asteroids where new observations would maximise the improvement in the calculated orbit. At the time of writing there are over 80 asteroids brighter than magnitude 19.5 in this group - although of course not all are currently visible . In all cases the Minor Planet Center rates the need for further observations of asteroids in this group as at least "Desirable".

Carrying out these observations would be of significant benefit to both the professional and amateur the astronomical community.

Detailed description of the methods, tools, and presentation of the project.

Each object on the target list would require four observations (on each night and on two separate nights) . This is to follow the advice on the Minor Planet Website that states, "Observers are reminded of the efficiency of making and reporting observations of specific objects on pairs of nearby nights, as the accuracy of an isolated single-night observation can be difficult to judge."

For objects down to magnitude 19.5 unfiltered images of 120 seconds duration have proved adequate for astrometrical analysis using Astrometrica. Hence the "basic unit of observation" for these objects is 8 minutes (4 x 120 seconds) per target. (In fact 4 x 90 seconds was adequate in most cases). Results would be submitted to the Minor Planet Center and this would constitute peer reviewed publication - "From time to time, the question arises as to whether inclusion of observations in the MPC's can be construed as publication in the `refereed' astronomical literature. The Minor Planet Center stresses most emphatically that astrometric observations of comets and minor planets submitted for publication in the MPCs are indeed subjected to close, critical study, and that erroneous observations are returned to their authors for amendment"

Acknowledgements
This project was carried out under the auspices of the Sierra Stars Observatory Grant Program. Many thanks are due to all those colleagues who invested their time and money in this project.

Information about this Article
This Article has not yet been peer-reviewed
This Article was published on 23rd February, 2010 at 09:47:56 and has been viewed 6036 times.

Creative Commons License
This work is licensed under a Creative Commons Attribution 2.5 License.
The full citation for this Article is:
Nicholson, M. (2010). Asteroid Astrometry using the Lowell Observatory Hierarchical Observation Protocol (HOP). PHILICA.COM Article number 181.


<< Go back Review this ArticlePrinter-friendlyReport this Article



Website copyright © 2006-07 Philica; authors retain the rights to their work under this Creative Commons License and reviews are copyleft under the GNU free documentation license.
Using this site indicates acceptance of our Terms and Conditions.

This page was generated in 0.3327 seconds.