The Status of HST/COS and HST/STIS Cristina Oliveira

1. SPACE TELESCOPE SCIENCE INSTITUTE Operated for NASA by AURA The Status of HST/COS and HST/STISCristina Oliveira COS and STIS - 2014 Cal Workshop

2. Overview • COS is operating well ~5 years after installation on HST • FUV sensitivity continues to degrade, correlation with solar cycle • FUV and NUV dark rates continue to increase, nominal trends, increased scatter correlates with solar cycle • Gain sag in FUV detector leads to localized areas of flux loss. Periodic move to pristine areas of the detector (“Lifetime Positions”) needed to maintain scientific quality of data. Move to Lifetime Position 3 (LP3) will occur in Feb 2015[See talk by J. Roman-Duval and poster by Proffit et al.] • New spectral extraction algorithms being developed to calibrate data at LP3 [See poster by Proffitt et al.] • P-flats to correct fixed pattern noise can allow S/N > 30 and are available for M grating data obtained LP2, on request • Blue modes developed after SM4, offer wavelength coverage down to Lyman limit (912 Å) with effective area and resolution similar to FUSE [See talk by S. Penton] • STIS is operating well ~5 years after repair during SM4 • CCD data affected by CTI; stand alone algorithm being developed following Anderson & Bedin (2010) [See poster by Lockwood et al.] • Dark rate trends are nominal; recent increase in read noise of Amp D from 5.7 to 6.2 e- [See poster by Biretta et al.] • New STIS apertures will be offered in Cycle 23, available with echelles, MAMA 1st order modes • New coronographic positions pushing inner working angle to ~0.15” COS and STIS - 2014 Cal Workshop

3. COS FUV Lifetime • COS FUV XDL MCP detector is subject to gain-sag • Ability to convert incoming photons to e- declines with usage • Can be recovered by increasing operating HV • Once operational HV limit is reached, only option is to move spectrum to a new pristine area of the detector (i.e. new lifetime position) • Gain-sag leads to localized flux loss • Usage is higher in detector regions where geocoronalLya airglow falls – gain-sag “holes” • Leads to absorption-like artifacts in data • If not mitigated gain-sag leads to eventual loss of all information over whole detector • Preparations to move to Lifetime Position 3 under way • Move to COS/FUV lifetime position 2 occurred in July 2012 (3 years at LP1) • UV Initiative has led to increase of COS/FUV usage by ~2x (less than 3 years at LP2) • Plan to move to LP3 in Feb 2015 • Resolution expected to be approximately 15% less than that at start of on-orbit operations and ~5-8% less than that at LP2. Otherwise, performance will be nominal • Will work with PIs of Cycle 22 programs to address concerns about having data obtained across lifetime positions See talk by J. Roman-Duval and poster by C. Proffitt for more details COS and STIS - 2014 Cal Workshop

4. COS FUV TDS • Rate of decline of COS FUV Time Dependent Sensitivity (TDS) varies with time, detector, and l • Steeper TDS slopes in periods of increased solar activity – likely due to atomic O at HST’s orbit reacting with CsIphotocatode of open-faced COS FUV detector • Slight increase (~1%) in sensitivity when HV increased – under study Move to LP2 10.7 cm radio flux TDS slope vs. wavelength t > 2013.8 Breakpoints in slope HV Increase • TDS slopes remained ~ shallow during 2013 • New TDS breakpoint around 2013.8, with steeper slopes, up to ~8% per year • Overall decrease since COS installation varies ~ 10 – 30% COS and STIS - 2014 Cal Workshop

5. COS NUV TDS • G185M and G230L gratings are coated with MgF • G225M and G285M are bare Al G225M G285M • Sensitivity of MgF-coated gratings has remained stable, with TDS slopes close to 0 • Sensitivity of bare Al gratings continues to decrease, with stable slopes between 3 – 12%/yr • For bare Al grating G285M sensitivity is now ~50% of initial value during SMOV4 COS and STIS - 2014 Cal Workshop

6. COS FUV Dark Rates Segment A Mean dark rate (cts/sec/pix) Segment B • COS FUV dark rate correlated with solar activity – Segment A more than B • Increased solar activity leads to increase of base level of dark rate in Segment A as well as increased scatter; only increased scatter in Segment B • Not an issue for calibration since dark rate calculated directly from each science exposure, but affects ETC predictions particularly for background limited obs. • Still, each science spectrum sees < 2 cts/sec over the whole spectrum (FUVA) COS and STIS - 2014 Cal Workshop

7. COS NUV Dark Rate • Dark rate of COS NUV MAMA detector continues to increase on the same trend since SMOV4 • Dark rate correlated with temperature, with increased scatter that seems to correlate with increase in solar activity COS and STIS - 2014 Cal Workshop

8. COS/FUV Pixel-to-Pixel Flat G130M/1309 Segment A Spectrum after P-flat applied Flux Original spectrum P-flat Pixel • 1D flat-fields (P-flats) to correct pixel-to-pixel fixed pattern noise developed for LP2 • P-flats are available for standard cenwaves of G130M and G160M • Useful only for high S/N observations, S/N > 30 resel • Not implemented in CalCOS pipeline as its applicability for data obtained at positions slightly offset in cross-dispersion direction is under study • P-flats are available to all users on a “use at own risk” basis and can be requested by sending email to help@stsci.edu COS and STIS - 2014 Cal Workshop

9. New STIS Apertures • Cycle 19 Outsourced Calibration Program 12567 – PI: Ayres • Study of “available-but-unsupported” ND long slits 31x0.05NDA, 31x0.05NDB, 31x0.05NDC • Provide attenuation factors of about 6x, 14x, and 33x • Previously supported ND slits allowed only attenuation factors of 2x (smallest clear slit), 100x, or 1000x • Gap of 50X in supported attenuation factors can make high S/N observations of many bright stars impractical • New slits are especially important for studies of LISM and bright standard stars with the echelle modes • Calibration reference files produced and implemented for these apertures • New slits, available with echelles and MAMA 1st order modes, will be implemented in ETC and APT to support phase I of Cycle 23 COS and STIS - 2014 Cal Workshop

10. HST Spectroscopic Legacy Archive • Following the 2012 workshop on “Extending the Legacy of HST Spectroscopy” a group of STScI and HST scientists convened a working group (led by A. Aloisi) to translate outcome of workshop into a set of recommendations for action • HST Spectroscopic Legacy Data Products working group recently formed at STScI (led by J. Tumlinson), with outside participants, with the charter of implementing the recommendations from the working group • Identify the key science areas and archival data sets that would benefit from the availability of spectroscopic High Level Science Products (HLSPs) • Define one or more high-priority COS or STIS HLSPs that will enable the scientific community to conduct science investigations relying on spectroscopic datasets quicker, easier, or in new ways • Develop and test algorithms necessary to create these spectroscopic HLSPs • Create examples of prototype HLSPs that should be produced and maintained at STScI through the end of the HST mission COS and STIS - 2014 Cal Workshop

11. COS Mini-Workshop Thursday August 14 – Boardroom – 9 am - 12 pm COS and STIS - 2014 Cal Workshop