Examples of Sources Near an Edge


 

Bright source at the edge of a CCD with a bad position:

[000393-M2] [000393-M2] [000393-M2]
 EPIC M2 image (netscape)  EPIC M2 image (ds9)  EPIC M2 image with sources overlaid (ds9): The fat green circle has the source comment 'Position offset' and the flags #6 ('Near edge') and #5 ('Position suspect') are set.
 
M1 for comparison:
[000393-M1] [000393-M1]
 EPIC M1 image (ds9)  EPIC M1 image with sources overlaid (ds9): The fat green circle has the source comment 'Near edge of field' and the flag #6 is set ('Near edge').
 

 

Sources at inside corner of CCD edge detected normally:

[000364-M1] [000364-M1] [000364-M1]
 EPIC M1 image (netscape)  EPIC M1 image (ds9)  EPIC M1 image with sources overlaid (ds9): The fat green circles have the source comment 'Near edge of CCD' and the flag #6 is set ('Near edge'). The positions are fine (see M2 image below).
 
M2 for comparison:
[000364-M2] [000364-M2]
 EPIC M2 image (ds9)  EPIC M2 image with sources overlaid (ds9): The fat green circles coincide with the sources in M1 (above). They lie inside the CCD and field of view and have no flags set.
 

 

Medium bright source with light spilled outside the field of view:

[001083-PN] [001083-PN] [001083-PN]
 EPIC PN image (netscape)  EPIC PN image (ds9)  EPIC PN image with sources overlaid (ds9): The fat green circle has the source comment 'Near edge of field' and the flags #6 ('Near edge') and #5 ('Position suspect') are set (cf. the small blue circle as the M1 detection). Since the PSF is affected by the location of the source at the edge of the field of view the total count rate is possibly not correct either.
 
M1 for comparison:
[001083-M1] [001083-M1]
 EPIC M1 image (ds9)  EPIC M1 image with sources overlaid (ds9): The fat green circle has about the same position as the source in PN above (small blue circles in this image indicate PN detections). It lies inside the CCD and field of view and has no flags set. However, the source indicated by the fat circle at the corner of the two CCDs has the flag #6 set ('Near edge') with the source comment 'Near edge of CCD'. The position is more acceptable here. It might be helpful to the user if the faint source to the left at the edge of the field of view were also flagged but since the field of view is often indistinguishable and the effect of the edge not obvious such flagging is not always necessary and/or possible.


Screening Notes Example: Version 29.05.2003