CADC

Solar System Object Search Documentation
This pages provides documentation for the Solar System Object Search (SSOS) page. The page itself can be found here. Unlike regular astronomical image search pages, which allow you to search at a fixed RA and Dec, SSOS allows you to search image archives for a moving object. There are currently four search methods: All of these methods will return a list of images that contain the object. Documentation for the search return page can be found below.

Currently, SSOS will search images from MegaCam and CFH12K on CFHT , SuprimeCam on Subaru, GMOS on Gemini, WFPC2, ACS, and WFC3 on HST, WFI, VIMOS, VIRCAM, SUSI/SUSI2, FORS1/2, EMMI, EFOSC, HAWKI,and NAOS/CONICA on various ESO telescopes, and WFI on AAT, and the SDSS. There are a total of 6.5 million images in the database. Other archives will be added in the future.

Search by arc
This search allows you to enter an series of observations. SSOS then fits an orbit to these observations and produces an ephemeris and then searches that ephemeris for images. There are two orbit fitting routines:
  • The New Object Ephemerides generator from the Minor Planet Center. This fits a Väiäslä orbit to the data. It should be used for main belt asteroids. If this option is selected, the observations are submitted to the MPC which does the orbit fitting and returns an ephemeris.
  • The "fit_radec" package, of Bernstein and Kushalani which is optimized for KBOs, but not main-belt asteroids. In this case the fitting is done on CADC computers.
If you have any doubts on the accuracy of either of these fitting programs (neither of which are maintained by the CADC), you should generate your ephemeris and submit it to the Search by ephemeris option.

Search by object name
This search allows you to enter the name of an object and search for observations. There are three ephemeris generators: In the first two cases, the Solar System Object Search takes the name you supply and queries the selected service; the service then returns an ephemeris. In general, these services have a limit to the number of times that can be queried, so this can take a while. Alternatively, if the CADC option is selected the orbital elements are looked up in a local database (which is regularly updated copy of the MPC orbital element database. These orbital elements are passed on to orbfit which generates an ephemeris. The ephemeris is then matched with the image database. Object names must be entered in a way that these services can understand. The MPC, for example can be case-sensitive.

Again, if you have any doubts on the accuracy of either of ephemeris generator or their abilities to parse the object name, you should generate your ephemeris and submit it to the Search by ephemeris option.

Search by orbital elements
This search allows you to enter the orbital elements. These orbital elements are used as input to orbfit which generates an ephemeris.

Search by ephemeris
While this search method is less convenient than the other methods, it has the advantage that it does not rely on third party software. You provide a series of time, RA and Dec and SSOS searches the database for matching observations. Each line should have three columns separated by one or more blank spaces. The columns should be time,RA,Dec.

Time can be specified in any of the following formats: 

YYYYMMDDHHMMSS
YYYY-MM-DD HH:MM:SS
YYYY/MM/DD HH:MM:SS
YYYY-MM-DDTHH:MM:SS
YYYY/MM/DDTHH:MM:SS
Thus the following examples are acceptable (and equivalent): 
19680117053522
1968-01-17 05:35:22
1968/01/17 05:35:22
1968-01-17T05:35:22
1968/01/17T05:35:22
Alternatively, you can use Julian Dates or Modified Julian Dates 
2439872.7328935185
39872.2328935185
For RA and Dec, use any of the following formats 
HH:MM:SS.SS     DD:MM:SS.SS
HHhMMmSS.SSs    DDdMMm.SS.SSs
DDD.DDDDDDDDD   DD.DDDDDDDDD
but not 
HH MM SS.SS DD MM SS.SS
(no spaces are allowed inside a coordinate) The following examples are acceptable. 
12:34:56
12:34:56.7
12:34:56.78
12:34:56.789
12h34m56.789
188.7366209
Note that if an RA is given sexigesimal format, it is assumed to be in hours, but if given in decimal format, it is assumed to be in degrees.

No checking is done on the ephemeris. It is up to the user to ensure that the values are reasonable and that the observations are in chronological order.

Other parameters
There are a number of parameters common to all the search functions.
Date Range:
You can specify a range of dates to search. The dates can be specified in the same formats as in the "Search by ephemeris" section above (ie, . The date range will be rounded to the nearest integer day. If the date range is smaller, the search will take less time If you leave the boxes empty, they will default to earliest and latest available observations. The date range for the "Search by ephemeris" function are the first and last dates in the ephemeris

Positional uncertainty:
If this is left blank or set to zero, only images which actually contain the predicted RA, Dec of the object will be returned. If this is set to a non-zero value, images which lie near the predicted position of the object (but do not actually overlap the position) will also be returned. The positional uncertainty is handled as a box with centred on the true position with sides twice the size specified.

Obviously, real positional uncertainties are better represented by ellipses, and real positional uncertainties vary with time. Some of the ephemeris generators behind the search functions described above produce good error ellipses. Others do not. Having box-shaped positional uncertainties represents a compromise. Note also, while the coverage of the images is known in some cases to very high precision (for example the MegaCam images which have been processed with MegaPipe) others are known to fairly low accuracy (such most of the CFH12K archive).

Resolve to extension:
By default, the search returns only a link to the full image. Downloading all of a MegaCam image (300Mb, compressed) can take a while. Setting "Resolve to extension" to "Yes" means that when an image is found a second search is done to determine which chip the object lies in. A link to that single extension is then returned. If the positional uncertainty is large, it is possible that many extensions will lie within the area. In this case all matching extensions are returned. It is also possible, if positional uncertainty is small, that object may lie in the gap between CCDs. In this case only the link to the whole image is returned. Doing this second search slows the query down. SuprimeCam images are never resolved to the extension level.

Resolve to X,Y:
If this is enabled, the predicted location of the object in an image are given in pixel values. SuprimeCam images are never resolved to the X,Y level. This secondary search also slows the query down. Setting "Resolve to X,Y" to "yes" also sets "Resolve to extension".

Search return page
There are three stages to each query:

The first step is to generate an ephemeris. This is done by a variety of methods as discussed above. Except for the "Search by ephemeris" function, the ephemeris is generated at 24 hour intervals.

The second step is to retrieve a the list of possible images, currently there are about 130 000 images. This list is clipped down the requested date range. It is also clipped by position: If the object never leaves the ecliptic, there is no point looking at an observation at Dec=73. Similarly, the RA range may be small either because the date range is short or because it is a slow moving, outer solar system object.

The third step is to match the ephemeris to the list of observations. For each observation the position is estimated at the midpoint of the exposure time. This is done by linearly interpolating the ephemeris. The linear interpolation is key to keeping the queries reasonably fast. Doing a full orbital prediction for each of the images is not feasible. This is sufficiently accurate for the majority of queries, where the object either moves slowly or in a fairly straight line. For faster moving, nearby objects, it may be necessary to supply a sample the ephemeris at higher resolution.

The search return page first returns some diagnostic information about the ephemeris generation and database querying. This can either be nearly instantaneous or take up to a minute. The cross-matching part typically takes less than 10 seconds unless further "Resolve to ..." flags are set. Each of the flags typically adds 1 second per found observation.

The links in the table are either direct links to the data (if the image is hosted at the CADC) or a link another query page which should return only the relevant image extensions (if the image is hosted at SMOKA). The direct links use CADC's getData utility.

In addition to the data links, there are two other buttons. Clicking on the first button returns a "regions" file which can be used to with the image display program ds9. This will give you a line showing the (linearly) interpolated orbit and circles indicating the positions of the object on matching images. The second button gives you a plot showing the orbit of the object with as a line with red circles indicating the location of matching images.

 
Please send comments or questions to Stephen.Gwyn@nrc.ca