WHATS_NEW.TXT (Last Update: 27 January 1997) ------------------------------------------------------------------------------- (9 May 1996) Updated announcement of availability of highly improved flux calibration method, the AIS method, NOW for pre- and post-COSTAR observations. 27 March 1996 FOS FLUX CALIBRATION UPDATE The new and highly improved FOS flux calibration method, the Average Inverse Sensitivity (AIS) method, is now available to observers wishing to re-calibrate ANY FOS observations. Greatly improved pre-COSTAR fluxes result from usage of the new calibration and certain post-COSTAR fluxes are also significantly improved. Tables 1 and 2 below list post-COSTAR AIS method reference files and tables (available since 21 February 1996) and pre-COSTAR AIS method reference files and tables (available since 7 March 1996) which are available online at STScI. Since incorporation of AIS reference files into the StarView best reference file reporting facility is not yet complete, we include below a complete listing of reference files and tables necessary to flux calibrate ALL FOS data with the new method. Please contact the FOS team through the STScI Helpdesk (help@stsci.edu) to obtain the information and procedures necessary to re-calibrate with the new method. The FOS Homepage Reference File and Table Reference Guides will be updated shortly to include complete AIS references. Pre-COSTAR observations benefit more substantially from AIS re-calibration, however re-calibration of post-COSTAR observations yields improvement particularly for ultraviolet and/or small aperture observations. Although an initial set of pre-COSTAR AIS reference files has been available for some time, the files listed in Table 2 below provides a much improved calibration. Further, the files provided in Tables 1 and 2 below now place (for the first time) all FOS flux calibration on the SAME ABSOLUTE REFERENCE SYSTEM regardless of observation date. Again, please contact the Helpdesk for detailed information. A detailed discussion of the advantages of re-calibration with the AIS method is provided in the second edition of the HST Data Handbook. Simply put, nearly all FOS observations benefit from this re-calibration. ============================================================= TABLE 1 Listing of "AISHFILE" required reference files for POST-Costar AIS Method FOS Flux Calibration Detector grating header file data file FOS/BL G130H (H13) FAC08361Y.R8H FAC08361Y.R8D FOS/BL G190H (H19) FAC08362Y.R8H FAC08362Y.R8D FOS/BL G270H (H27) FAC08363Y.R8H FAC08363Y.R8D FOS/BL G400H (H40) FAC08364Y.R8H FAC08364Y.R8D FOS/BL G570H (H57) FAC08368Y.R8H FAC08368Y.R8D FOS/BL G160L (L15) FAC08366Y.R8H FAC08366Y.R8D FOS/BL PRISM (PRI) FAC08367Y.R8H FAC08367Y.R8D FOS/RD G190H (H19) FAC0835MY.R8H FAC0835MY.R8D FOS/RD G270H (H27) FAC0835NY.R8H FAC0835NY.R8D FOS/RD G400H (H40) FAC0835PY.R8H FAC0835PY.R8D FOS/RD G570H (H57) FAC0835QY.R8H FAC0835QY.R8D FOS/RD G780H (H78) FAC0835RY.R8H FAC0835RY.R8D FOS/RD G160L (L15) FAC0835SY.R8H FAC0835SY.R8D FOS/RD G650L (L65) FAC0835TY.R8H FAC0835TY.R8D FOS/RD PRISM (PRI) FAC08360Y.R8H FAC08360Y.R8D Also required FOR ALL DETECTORS AND GRATINGS are the following four tables (no other versions of the following tables are valid for POST-COSTAR analysis): FAD1554CY.CYA G1512585Y.CYB FAD1554HY.CYC FAD1554KY.CYD ============================================================= TABLE 2 Listing of "AISHFILE" required reference files for PRE-Costar AIS Method FOS Flux Calibration Detector grating header file data file FOS/BL G130H (H13) G2T1439KY.R8H G2T1439KY.R8D FOS/BL G190H (H19) G2T1439LY.R8H G2T1439LY.R8D FOS/BL G270H (H27) G2T1439NY.R8H G2T1439NY.R8D FOS/BL G400H (H40) G2T1439OY.R8H G2T1439OY.R8D FOS/BL G160L (L15) G2T1439PY.R8H G2T1439PY.R8D FOS/BL PRISM (PRI) G2T1439QY.R8H G2T1439QY.R8D FOS/BL G570H (H57) G2T1439RY.R8H G2T1439RY.R8D FOS/RD G190H (H19) G2T14397Y.R8H G2T14397Y.R8D FOS/RD G270H (H27) G2T14399Y.R8H G2T14399Y.R8D FOS/RD G400H (H40) G2T1439BY.R8H G2T1439BY.R8D FOS/RD G570H (H57) G2T1439CY.R8H G2T1439CY.R8D FOS/RD G780H (H78) G2T1439EY.R8H G2T1439EY.R8D FOS/RD G160L (L15) G2T1439GY.R8H G2T1439GY.R8D FOS/RD G650L (L65) G2T1439HY.R8H G2T1439HY.R8D FOS/RD PRISM (PRI) G2T1439JY.R8H G2T1439JY.R8D Also REQUIRED FOR ALL DETECTORS AND GRATINGS are the following four tables (no other versions of the following tables are valid for PRE-COSTAR analysis): G310947PY.CYA G3109480Y.CYB G3109483Y.CYC G3109487Y.CYD ============================================= This is version 03 of this listing and is current as of 27-MAR-1996. ------------------------------------------------------------------------------- 1 September 1995: Revision of FOS polarimetric capability for Cycle 6 The following memorandum describes IMPORTANT FOS polarimetry status changes that affect ALL FOS programs and future proposals. Cycle 6 proposers should review this carefully. This information SUPERSEDES any information in the Cycle 6 FOS Instrument Handbook. This announcement presents a substantial revision of the status of FOS polarimetric capabilities for Cycle 6 and is effective immediately. Any questions concerning the issues in this announcement should be directed to the SSD Helpdesk [e-mail: help@stsci.edu, telephone: (410) 338-1082]. Analysis of Cycle 4 polarimetric calibration observations indicates an absolute uncertainty of only 1-1.5% for FOS/RD linear polarization measures with spectral elements G190H and G270H. We had expected and advertised an accuracy level of 0.7% and a goal of 0.2% for FOS/RD. Since the throughput of FOS/RD is better by about a factor of two than for FOS/BL, the Cycle 6 FOS Instrument Handbook advised use of FOS/RD and we intended only to further calibrate FOS/RD for polarimetry. Calibrations of FOS/BL have shown limiting accuracies of 0.2% for high S/N observations. As a result, FOS spectropolarimetric recommendations are changed as follows: 1. All Cycle 6 proposers are advised to use FOS/BL for spectropolarimetric observations. 2. No further FOS/RD spectropolarimetric calibrations will be performed by STScI. 3. FOS/BL will be calibrated for spectropolarimetry in cycle 5 instead. The following is a more detailed summary intended to replace polarimetry summaries in sections 1.6.1 and 3.3.6 on pages 11 and 51 of the Cycle 6 FOS Instrument Handbook. Please note that the general discussion of polarimetry, including the calculation of expected polarimetry count rates, provided in section 1.6 (page 10) of the Handbook remains valid. a.) FOS/BL will be calibrated in cycle 5 for G190H, G270H, and G400H. The 1.0 aperture will be used for these calibration observations. For bright spectropolarimetric calibration sources, limiting absolute polarization uncertainty is 0.2% based upon cycle 4 measures. This level of accuracy is obtainable only for very high S/N observations. Naturally, for fainter sources the accuracy is limited by photon statistics obtained and by the intrinsic polarization of the target object. b.) The "B" waveplate should be used for FOS/BL G190H and G270H observations. The "A" waveplate should be used for FOS/BL G400H observations. c.) The 1.0 is the recommended aperture. Smaller apertures than 1.0 may be used, but the photometric aperture throughputs of smaller apertures relative to the 1.0 in polarimetry mode will not be measured by STScI. This will affect only the photometric calibration of small aperture polarimetric observations. Smaller aperture observations will take longer than 1.0 aperture observations to reach the same S/N, of course, but the polarimetric calibration is valid for smaller apertures. d.) Usage of the 4.3 aperture is NOT recommended. e.) FOS/BL G130H polarimetric observations longward of 1300 A. are not absolutely precluded, but will not be calibrated by STScI. Linear polarization limiting accuracies are uncertain, but are expected to be no better than 1 part in 5 or 0.4%, whichever is larger. Observers would be responsible for the lengthy calibration procedures - details are available from the Helpdesk. No spectropolarimetric measurements can be made shortward of 1300 A. ------------------------------------------------------------------------------- 20 June 1995: Low-dispersion POST-COSTAR flat fields now available. New flat field reference files derived from post-COSTAR observation for the low dispersion FOS gratings and both detectors have been delivered to CDBS and installed in the PODPS pipeline. LOW-DISPERSION GO data obtained prior to this date have been reduced with flat fields appropriate to the PRE-COSTAR epoch, which were (until now) the best available flat fields. All LOW- DISPERSION (G160L, G650L, or PRISM) GO data obtained prior to this date should be re-processed with CALFOS and the new reference files. Flat field reference files with filenames of form f67*.* comprise this set of data and are available for ftp in the /cdbs/yref sub-directory here on STEIS. For more details please contact either the help@stsci.edu Hotline or the FOS Instrument Scientists. ------------------------------------------------------------------------------- 6 August 1994: Complete listings of recommended reference files. Complete listings of ALL recommended reference files as a function of USEAFTER date (effective date) for BOTH PRE- and POST-COSTAR epochs is given in four documents (1. Flat Fields, 2. Inverse Sensitivity, 3. Dead Diodes, and 4. all other reference files) in sub-directory recommended_reference_files. Both ASCII-text and Postscript versions of the documents are provided. ------------------------------------------------------------------------------- 13 July 1994: POST-COSTAR flat fields now available. New flat field reference files derived from post-COSTAR observation for the high dispersion FOS gratings and both detectors have been delivered to CDBS and installed in the PODPS pipeline. GO data obtained prior to this date have been reduced with flat fields appropriate to the PRE-COSTAR epoch, which were (until now) the best available flat fields. All GO data obtained prior to this date should be re-processed with CALFOS and the new reference files. Please see file post_costar_flat_field_annoncent.txt in both this sub-directory and the flat_field sub-directory for more details and/or contact either the help@stsci.edu Hotline or the FOS Instrument Scientists. ------------------------------------------------------------------------------- 1 July 1994: PRE-COSTAR polarimetry error corrected. A very small number of PRE-COSTAR polarimetry observations have been affected by a subtle error in the CALFOS polarimetry reduction routines, which has now been fixed. Please see the file polarimetry_CALFOS_bug in the polarimetry sub-directory. All affected observers have been notified. ------------------------------------------------------------------------------- 25 March 1994: POST-COSTAR inverse sensitivity calibration available Observationally-derived POST-COSTAR IVS reference files are now installed in the PODPS pipeline. All FOS observations obtained prior to this date should be re-processed with the new reference files. See file post_costar_ivs_announcement.txt found in both this directory and sub-directory absolute_photometry for additional details. All affected observers have been notified by electronic mail on this date.