Summary (Updated - AF 11/01/2012)

MOPS has reported some peculiar magnitudes in y-band MD data offsets and larger scatter compared to predictions of asteroid y-band magnitudes while the same comparison to 3PI photometry looks reasonable (both cases are photometry from the respective diffims). Also, have found photometry from Warp-Stack (WS) difference images for two sequential MD exposures unrealistically different by >0.5 mag.

Plot of average value for (observed - predicted) magnitudes per night for 3pi and MD detections in y-band. An offset in the MD data making objects ~0.4 mag brighter is seen.

Plot of average value for (observed - predicted) magnitudes per night for 3pi and MD detections in z-band. No offset is seen.

Example: MD10 sequential exposure pair, asteroid (12891) (Peter Vereš)

o6157g0218o
o6157g0219o

ra: 353.142622 
ra: 353.142215

dec:-0.086658
dec: -0.086867

Chip/camera photometry from the SMF catalogs below agree to that expected -- yes, but can't be more exact because asteroid (12891) previously unstudied.

o6157g0218o: 17.06 o6157g0219o: 17.048

Example: MD09, TNO145452 (Alan Fitzsimmons)

TNO 145452

• a bit faint but its' the best one I've found so far, as it stays in the field for a long long time.
• in MD09 where we can predict the y magnitude should be within 0.1 mag of ~19.3 for the below observations
• a bunch of y-band exposures and positions on two separate dates:

  o6107g0064o  334.194813  +0.274227  
  o6107g0065o  334.199167  +0.283357  
  o6107g0066o  334.194763  +0.292497  
  o6107g0067o  334.184892  +0.294695  
  o6107g0068o  334.176975  +0.288368  
  o6201g0056o  334.176975  +0.288387
  o6201g0057o  334.176992  +0.278257
  o6201g0058o  334.184921  +0.271952
  

This is the best example in the database because of the density of measurements and the known small amplitude of any lightcurve. In warp-warp diffs the slow motion will mean that 3PI and OSS measurements would be incorrect due to self-subtraction of the flux. But this should not only occur in MD fields as MOPS is being fed warp-stack measurements, and it would make the object fainter not brighter as seen. The variation in z-band and in other filters in 2012 is also puzzling.

Plot of observed magnitudes converted to V (top), and residual of magnitude (observed - predicted), in 2011 and 2012: (Key: g=green, r=red,i=orange,z=purple,y=cyan)

Example: MD01, MBA 131130 (Alan Fitzsimmons)

This is a nice example of the offset plus large scatter in y-band for a Main Belt Asteroid seen this year.

o6169g0184o 36.353429    -4.350323    
o6169g0185o 36.353441    -4.350616    
o6170g0586o 36.360948    -4.446235    
o6170g0588o 36.360938    -4.446831    
o6170g0590o 36.360927    -4.447427    
o6170g0591o 36.360922    -4.447725    
o6170g0593o 36.360911    -4.448320    
o6171g0613o 36.362699    -4.549196    
o6171g0614o 36.362676    -4.549499    
o6171g0616o 36.362631    -4.550103    
o6171g0617o 36.362608    -4.550406    
o6171g0619o 36.362562    -4.551012    
o6172g0677o 36.358383    -4.654112    
o6172g0682o 36.358181    -4.655647    
o6172g0683o 36.358141    -4.655956    
o6172g0684o 36.358101    -4.656264    

Plot of observed magnitudes converted to V (top), and residual of magnitude (observed - predicted) in 2012. The large gap in the data was caused by telescope shutdown due to rotator problems. (Key: g=green, r=red,i=orange,z=purple,y=cyan)