SOHO/CDS CDS Users’ Meeting, Sep 2005 Dr Peter Young, CCLRC/RAL Tips and Tricks for analysing CDS data Dr Peter Young Dr Peter Young SOHO/CDS Project Scientist CCLRC Rutherford Appleton Laboratory

SOHO/CDS CDS Users’ Meeting, Sep 2005 Dr Peter Young, CCLRC/RAL Overview Photon statisticsPhoton statistics Calibration uncertaintyCalibration uncertainty Cosmic raysCosmic rays NIS1-NIS2 alignmentNIS1-NIS2 alignment Burn-in correctionBurn-in correction SOHO rollSOHO roll

SOHO/CDS CDS Users’ Meeting, Sep 2005 Dr Peter Young, CCLRC/RAL Photon statistics vds_calib yields photons/s/pixelvds_calib yields photons/s/pixel use Bill’s expression to yield fractional noise (f N )use Bill’s expression to yield fractional noise (f N ) –√(2N + n)/N proceed with calibration to yield intensity unitsproceed with calibration to yield intensity units apply f N to yield error on intensityapply f N to yield error on intensity

SOHO/CDS CDS Users’ Meeting, Sep 2005 Dr Peter Young, CCLRC/RAL Calibration uncertainties For large counts, calibration uncertainties dominate over photon statistic errorsFor large counts, calibration uncertainties dominate over photon statistic errors Difference between relative and absolute calibration uncertainties (e.g., line ratios vs. DEM)Difference between relative and absolute calibration uncertainties (e.g., line ratios vs. DEM) Relative uncertainty is λ dependent and varies from 12 to 29%Relative uncertainty is λ dependent and varies from 12 to 29% For absolute uncertainty, additional contribution of 13%For absolute uncertainty, additional contribution of 13% See Sect. 3.3 of Lanzafame et al. (2005, A&A, 432, 1063) for more detailsSee Sect. 3.3 of Lanzafame et al. (2005, A&A, 432, 1063) for more details

SOHO/CDS CDS Users’ Meeting, Sep 2005 Dr Peter Young, CCLRC/RAL Cosmic Ray Removal Three routines available in softwareThree routines available in software –cds_new_spike –cds_clean_exp –cds_clean Make sure to set $CDS_EXTERNAL for routines to run quicklyMake sure to set $CDS_EXTERNAL for routines to run quickly

SOHO/CDS CDS Users’ Meeting, Sep 2005 Dr Peter Young, CCLRC/RAL Fill or not to fill? The cosmic ray routines allow two options for dealing with CRsThe cosmic ray routines allow two options for dealing with CRs 1.fill with median value of surrounding pixels 2.flag as missing data The latter is best option for preserving statisticsThe latter is best option for preserving statistics

SOHO/CDS CDS Users’ Meeting, Sep 2005 Dr Peter Young, CCLRC/RAL NIS1-NIS2 alignment NIS1 and NIS2 images are not spatially coincidentNIS1 and NIS2 images are not spatially coincident IDL> gt_nis_alignment, qlds, x, y Pre-loss: X~1”, Y~2”Pre-loss: X~1”, Y~2” Post-loss: X~1”, Y~3-7”Post-loss: X~1”, Y~3-7” Depends on Y-location!Depends on Y-location!

SOHO/CDS CDS Users’ Meeting, Sep 2005 Dr Peter Young, CCLRC/RAL Burn-in Correction Narrow slit burn-in is not fully corrected for in the CDS softwareNarrow slit burn-in is not fully corrected for in the CDS software Affects both line width and intensityAffects both line width and intensity IDL> result=get_width_corr(’22-sep-2005’,629.7) Currently 20% for O V λ629.7Currently 20% for O V λ629.7

SOHO/CDS CDS Users’ Meeting, Sep 2005 Dr Peter Young, CCLRC/RAL SOHO Roll To find out SOHO roll angle on a particular date:To find out SOHO roll angle on a particular date: IDL> angle=get_soho_roll(’22-sep-2005’) To make CDS images appear in the usual format, useTo make CDS images appear in the usual format, use IDL> data=gt_windata(a,0,/invert)

SOHO/CDS CDS Users’ Meeting, Sep 2005 Dr Peter Young, CCLRC/RAL

SOHO/CDS CDS Users’ Meeting, Sep 2005 Dr Peter Young, CCLRC/RAL User Routines Do you have IDL routines for your CDS analysis that you’d like to share?Do you have IDL routines for your CDS analysis that you’d like to share? Are there any new IDL routines that you’d like to see?Are there any new IDL routines that you’d like to see? Routines can be added to CDS branch of SolarsoftRoutines can be added to CDS branch of Solarsoft Requirements:Requirements: –provide header in standard format –check that obvious errors are caught