filename: naming_conventions Date: 12 may 98 originat: deh tlm: 27 May 98 Subject: Naming conventions for RRA 1.0 General 2.0 Initial Recommendation 3.0 Merging Detections 4.0 Best Position Determination 1.0 General The IAU recommended convention for naming sources calls for an observatory prefix plus enough digits of the source position to uniquely define the source. At the time of the initial release of the HRI RRA (1998 June) the only positions available are those generated by the standard processing (SASS) for source detections. At a future time, the RRA consortium plans to merge multiple detections and define the best position from all the data. Therefore, the naming convention follows the IAU recommendations, but the initial names refer to detections rather than to 'sources'. For internal purposes, we have also generated a unique label for each detection made up of the sequence number plus the source number. Note that each of these schemes is subject to occasional errors for those sequences which were processed more than once. We continue to make every effort to purge multiple SASS runs from the RRA catalog, but it must be kept in mind that from time to time, reprocessing of some data sets is required, so that in rare instances, a detection may be changed, replaced, or deleted (without warning). 2.0 Initial Recommendation 2.1 Prefix The prefixes that were approved by the IAU committee for the initial PSPC catalogs are: 1RXS for the ROSAT Sky Survey 1RXP for the preliminary PSPC source catalog generated by MPE (1996). The RRA consortium has chosen the additional prefixes: 1RXH for the 1998Jun release of the HRI/RRA detection database. 2RXH reserved for a furture release which will deal with the merging problem 2RXP for the RRA PSPC catalog; the release to follow that of the HRI. 2.2 Detection Name The body of the name is based on the SASS (J2000) position: JHHMMSS.S+DDMMSS where the '+' is northern declinations, '-' for the south. Examples (fictitious) Detection_name 1RXH J182217.5+332111 1RXH J030201.0-000002 The corresponding sequence_detection_names might be: rh801065n00.3 rh300011a01.18 3.0 Merging Detections There are several problems associated with the merging of separate detections into a unique name. Many of these have been dealt with in similar efforts in the past; some are unique to the ROSAT HRI SASS processing. A partial list is included here. 3.1 Aspect Errors Unlike most previous projects, in the case of the ROSAT HRI, we have well documented evidence that aspect errors can be as large as 2 to 3 times the FWHM of the PRF. Therefore, the simple requirement that joins two detections which have a celestial coordinate separation of less than some fixed quantity, will not suffice. 3.2 Extended Sources This is a well known problem that often requires visual inspection to determine correct association. 3.3 Variability For stellar associations in particular, it is often the case that some sources 'turn-off' whilst a very nearby star flares (for the case of multiple observations). 3.4 Multiple detection cell sizes. For each SASS processing, the source detection algorithm (the classical 'sliding box') is run for detect cell sizes of 12", 24", 48", 72", and 128". For strong isolated sources merging of these multiple detections should present no problems, but it is often found that a single large cell corresponds to two or more 12" detections. 3.5 Anamalous positions associated with detections near the field edge. Strong sources near the field edge are found with bad positions since the usual centroiding techniques misses the part of the source which is off the edge. 3.6 Degradation of the PRF off axis. The algorithm will need to successfully join on-axis with off-axis detections. 4.0 Best Position Determination Since the source name requires an accurate position, we need to determine the best position from a set of detections which have been joined by the merging process. In view of the disparity in the quality of the detections, a simple test of s/n (to decide which is best) will not suffice.