COS Training Series COS Update: pre-SMOV / Cycle Tony Keyes March 2009

COS 2009 Training Schedule  Session 1: COS Update: pre-SMOV and Cycle 17 – COS Introduction and Overview – new front-end capabilities – new pipeline capabilities – COS associations – target acquisition recap – COS Data Handbook  Session 2: COS “Roundtable” – SMOV and C17 cal plans – Future calcos updates: (improved wavecals; spectrum extraction) – In-depth questions and answers on any topic

COS Introduction and Overview

Cosmic Origins Spectrograph   COS is a highly-optimized ultraviolet spectrograph for HST to be installed during SM4   COS Project, IDT, and Science Team are led by COS PI: Dr. James Green, University of Colorado   SI selected in open competition in 1997 – – STScI participation in project commenced in spring 1998   Instrument built at Ball Aerospace, Boulder, CO – – FUV detector provided by UC Berkeley – – NUV detector is STIS flight spare

COS Science Design Requirements  Moderate Resolution (R~20,000) point-source UV spectroscopy; 0.1 arcsec pointing; 15 km/sec absolute (5 km/sec relative) radial velocity accuracy  Highest Possible Throughput  Maximize wavelength coverage per exposure

COS Design  Science Design Requirements met using a combination of HST capabilities – large collecting area – UV coatings – excellent pointing stability – superb image quality (after aberration correction); and  FUV: – single reflection system; fully corrected along dispersion, astigmatism perpendicular to dispersion – large format, windowless, solar-blind cross delay line (XDL) detector – high-efficiency 1st-order holographic gratings  NUV: – FUV concept not available (no large format detectors) – STIS flight spare MAMA, fully aberration-corrected system, enhance wavelength coverage through use of three camera optics

COS Design at a Glance

COS Mechanisms   External Shutter (STIS heritage)   Aperture mechanism (translational motion in x and y perpendicular to beam)   Optic Select Mechanisms 1 and 2   FUV Detector Door

COS Apertures  Apertures – Primary Science Aperture (PSA): 2.5 arcsec circular field stop – Bright Object Aperture (BOA): 2.5 arcsec + ND2 (~150x attenuation) circular field stop – Wavelength Calibration Aperture (WCA) – Flat Field Aperture (FFA)

COS Detectors  FUV: Cross Delay Line (XDL) detector – windowless, CsI photocathode, MCPs feed XDL anode; photon counting; pulse heights available; high gain (~10 7 ) – two 85 mm (dispersion-direction) x 10 mm segments (~9 mm gap between segments) – 2 x 16,384 x 1024 pixels; 6  m x 24  m pixel size (0.023 x arcsec) – 6 pixels per resolution element (resel) along dispersion; 10 pixels per resel perpendicular to dispersion; (0.136 x 0.92 arcsec per resel) – Electronic “stim pulses” to characterize stretching and shifting in both coordinates (more robust than FUSE)  NUV: MAMA (STIS flight spare) – sealed CsTe photocathode; photon counting; no pulse-heights – 25 mm x 25 mm detector format (constrains optical design) – 1024 x 1024 pixels; 25  m x 25  m pixel size (0.024 x arcsec) ; no subarrays – 3 x 3 pixels per resel (0.072 x arcsec per resel) – opto-isolator problem fixed

170 mm COS Detectors FUV XDL

FUV Detector Format   Remember: FUV detector has two segments (A and B)

COS Detectors – NUV MAMA in the enclosure

COS Physical Characteristics Summary ** MAMA dark limits quoted are one-fourth of STIS values; actual dark rates TBD on-orbit **

COS Optical Elements  Optical Elements (Gratings, Mirrors) – FUV: G130M, G160M, G140L – NUV: G185M, G225M, G285M, G230L, TA1 mirror (as MIRRORA and MIRRORB)

COS Spectral Resolution (PSA*) and Bandpass Summary For BOA, wedge in ND filter degrades resolution by factor of ~2.5 for FUV modes and ~4 for NUV modes. Spectral Element Range (Å) Coverage (Å per exp) Resolving Power  Dispersion (Å / pixel) G130M1150– ,000–24,000~ G160M1405– ,000–24,000~ G140L1230–2050> –3000~ G185M1700–21003 x 3516,000–20,000~ G225M2100–25003 x 3520,000–24,000~ G285M2500–32003 x 4120,000–24,000~ G230L1700–3200(1 or 2) x –3200~0.3887

FUV Central Wavelengths and Wavelength Ranges per Segment Optic Central (Å) Observed Wavelengths (Å) G130M , , , , , G160M , , , , , G140L1105** 1230 < (not usable – zero-order), < , Yellow text indicates default setting ** always used with SEGMENT A only

NUV Central Wavelengths Spectral Central (Å) G185M1786, 1817, 1835, 1850, , 1890, 1900, 1913, , 1953, 1971, 1986, 2010 G225M2186, 2217, 2233, 2250, 2268, 2283, 2306, 2325, 2339, 2357, 2373, 2390, 2410 G285M2617, 2637, 2657, 2676, , 2719, 2739, 2850, , 2996, 3018, 3035, , 3094 G230L2635, 2950, 3000, 3360 Yellow text indicates default setting

COS Imaging Summary Optical Element Range (Å) Plate ScaleField-of- View (arcsec 2 ) FOV (Number of Pixels) TA11650– arcsec/pixel arcsec/resel 12.5 full diameter 4.9 un- vignetted 166 full diameter 100 un- vignetted

COS Optical Layout OSM1 positions 1 of 4 optics 2 degrees of freedom (rotation, focus) OSM2 positions 1 of 5 optics 1 degree of freedom (rotation) Aperture Mechanism positions 1 of 2 science and 2 calibration Apertures 2 degrees of freedom (x & y translation) FUV Detector Head (DVA) NCM2 (Collimating mirror) NCM3a, 3b, 3c (Focusing mirrors) Calibration Fold Mirror External Shutter (not shown) NUV Detector (MAMA) Calibration Platform 4 lamps, 3 beam splitters

COS Optical Layout

Optics Select Mechanisms (OSM)  Full 360 Degree Rotation; 101 arcsecond step size, with selectable step rate; gratings move with OSM  NO separate grating rotation  User can specify minimum one-step movement via FP-POS command OSM1 OSM2

FP-POS  COS provides optional parameter FP- POS to perform dispersion-direction or wavelength dithers – One FP-POS step corresponds to the minimum movement (one step) of the OSM carrying the spectral element being used – For an exposure with any grating and c, the observer may specify FP-POS = 1, 2, 3, 4, or AUTO (all) [default is FP-POS=3] > AUTO corresponds to an automatic sequence of four separate exposures - that is, one at each FP- POS in the order FP-POS=1,2,3,4; APT exp time is TOTAL for all four positions in this case – The central wavelength for any grating corresponds to FP-POS=3 (default) for that grating; the table gives the offset from c in OSM steps for each allowed FP-POS FP-POS Offset from c (OSM-steps) NOTE: For the FUV gratings, the c are always separated by four OSM1 steps, so there is a continuous increment between FP-POS of adjacent central wavelength settings. This is not the case for the NUV gratings.

FP-POS / c Illustration for FUV 14 c =1309 | c =1300 |

FUV Default Wavelength Ranges (FP-POS=3) YELLOW: Segment B RED: Segment A G130M } } G160M G140L }  Note: G140L segment A records signal in “FUSE band” ( < l 100 Å )

FUV Bridging the “Gap”   G130M and G160M: an 8 OSM1-step offset is required to bridge the segment A/B detector gap (any two non-adjacent c settings at same FP-POS) – – G130M: gap is ~17 Å; one FP-POS step ~2.3 Å; step between successive c (e.g., 1309 to 1318) is ~9 Å – – G160M: gap is ~21 Å; one FP-POS step ~2.9 Å; step between successive c (e.g., 1600 to 1611) is ~11.6 Å YELLOW: Segment B RED: Segment A 1300 FP= FP= FP= FP= FP= FP= FP= FP= FP=

NUV Default Wavelength Ranges (FP-POS=3) G185M G225M G285M G230L A B C (this labeling for M modes only)

FUV MCP (1 of 2 segments) External Science Internal PtNe Wavecal COS FUV Spectral Layout for Simultaneous Internal Wavecals and Science Spectra

COS NUV Spectral Layout for Simultaneous Internal Wavecals and Science Spectra ExternalTarget PtNeWavecal

Single grating tilt yields 3 stripes G285M R ~ 20,000 Sample NUV PtNe Wavecal Spectra

Important Modes/Parameters  TIME-TAG: position and time of each valid event are saved – 32 msec time-stamps; pulse heights are recorded for FUV, but not NUV. Doppler correction is performed in the pipeline – Default and highly recommended; CS will enforce – requires BUFFER-TIME (time to fill one-half buffer or 2.3 million counts – think of it as defining the count-rate) [use ETC to estimate]; > select 2/3 * ETC value; – BUFFER-TIME always LESS THAN exposure time – use for all targets less than 21,000 cts/sec [BUFFER-TIME > 110 sec]; – OK up to 30,000 cts/sec with some continuity breaks (flux cal OK) [BUFFER-TIME: sec];  Important optional parameters: – FP-POS=1,2,3,4 or AUTO – FLASH=YES (TIME-TAG and PSA only; so-called TAGFLASH) – FLASH=YES may now be used with COS imaging!

Important Modes/Parameters  ACCUM: each event increments memory location for recording pixel; only final accumulated image is saved. – 16384x128 (or 1024x1024) x 16 bits; for all count-rates > 30,000; must justify for any other target – Pixel locations shifted on-board for orbital doppler correction  Important optional parameters: – FP-POS=1,2,3,4 or AUTO – FLASH=NO required (no TAGFLASH)

Internal Calibrations  Wavelength Calibration Lamps – Pt-Ne hollow cathode lamps used with WCA – Routinely used with TAGFLASH and AUTO wavecal exposures. – Always done as TIME-TAG  Flat Fields – D 2 hollow cathode lamps used with FCA > Calibration Programs only > Always done as TIME-TAG > May be difficult to get required S/N in FUV – Also done with external targets

Spectral Drift G160M # G285M # G140L # Drift exceeds 1 resolution element Steep Rise Plateau Drift exceeds 1 resolution element  Optic Select Mechanism residual settling (“drift”) – Non-repeatable post-rotation motion measured in TV and ambient testing

Spectral Drift Correction (TAGFLASH)   Correction needed to meet design requirements – – Spectral resolution (and perhaps more importantly, line shape) – – Wavelength zero point   TAGFLASH (FLASH=YES) will embed wavecals in science time – – TIME-TAG mode ONLY; no correction for ACCUM – – No overhead for wavecals at all – – CALCOS corrects for drifts

Spectrum Drift Correction (TAGFLASH)  Analysis of thermal vac data shows image motion can be corrected to <0.25 resel/hr  FLASH=YES (TAGFLASH) now implemented as default observing mode for COS  Lamp is flashed at beginning and at intervals during every TIME-TAG exposure (based on time since last mechanism motion)  GO does not specify flash intervals or durations  Projected lamp usage sufficient to support COS over projected lifetime

Flash Characteristics and Monitoring   Flash Frequency (after major OSM move) – – Always flash at start of exposure and at automatic intervals – – First orbit following OSM move (4 flashes) > > Flash at beginning exposure as reference > > Intermediate flash early (after 600 sec) to follow fast drift > > Intermediate flash after another ~1800 sec to follow change in drift slope > > Flash every 2400 sec thereafter If CVZ, then flash again after another 2400 sec, etc   Flash durations typically 5-10 seconds   SMOV and early Cycle 17 tests and monitoring planned – – Determine drift character on-orbit for suite of OSM motions – – Method allows changes for on-orbit understanding of drift – – Early pattern is conservative (more flashes)

COS FUV/NUV switching  Nominally both COS Detectors are on at all times – No SPECIFIC overhead is required to switch observation between detectors  Must use different optical element on OSM1 for FUV and NUV – an OSM1 rotation is required when switching between detectors ( sec depending on element) – OSM2 may also have to rotate (executed in sequence after OSM1 rotation is completed) depending upon last optical element used for NUV observation ( sec depending on element, typically ~2 min)

COS Overheads (1 of 2)

COS Overheads (2 of 2)

COS and the SAA  COS will not dump data within the SAA  COS FUV will not take science data within the SAA  COS NUV will not take science data within the SAA  COS FUV may observe in SAA-impacted orbits  COS NUV may observe in SAA-impacted orbits  COS FUV contour is Model 31  COS NUV contour is Model 32  Initially, both Model 31 and Model 32 are exact copies of STIS MAMA operational contour Model 25.

Detector Lifetime  FUV Lifetime requirement: ≤ 1% loss in QE after 10 9 events mm –2. Estimates of COS usage show that the total number of events detected in the FUV channel over a seven- year mission would be a few times this value.  A cumulative signal image of the FUV & NUV detectors will be maintained to monitor the extracted charge.  Spectrum can be moved in the cross dispersion direction onto a previously-unused portion of the detector by offsetting the aperture mechanism. This can be done up to four times.

Bright Object Mitigation Strategies  Use MIRRORB – Attenuates by a factor of ~15 (~3 magnitudes) – Forms double image

Bright Object Issues - Summary  Both COS MCP detectors are subject to damage if subject to overlight conditions  Use COS ETC to evaluate target safety  All science targets and field objects must be checked for safety  The BOA (for all observing modes) and MIRRORB (for NUV imaging only) can be used to attenuate light  Bright Object Tool in APT has many useful features – GALEX data can accurately clear objects (or not!) – ORIENT specification can be used to avoid bright field objects (but use this sparingly)

New pipeline capabilities  New user coordinate system – Defined with x-coordinate along dispersion; y-coordinate increasing in direction of +V2,+V3 – Coincident with pos_targ frame – Pos_targ frame has same orientation (and APT-specification) for both detectors  Association definition improved – Aperture changes and pointing changes now force new association – x1dsum and fltsum are products of spectroscopic and imaging associations, respectively  Data quality handling improved  Photometric calibration of imaging mode and ACQ/IMAGE exposures

TIME-TAG data files  For each exposure: – Raw event lists: rawtag_a, rawtag_b, or rawtag – Corrected event lists: corrtag_a, corrtag_b, or corrtag – 2-d flat-fielded image: flt_a, flt_b, flt – 1-d extracted spectrum: x1d

ACCUM data files  For each exposure: – Raw data: rawaccum_a rawaccum_b, or rawaccum – Pseudo-corrected event lists: corrtag_a, corrtag_b, or corrtag – 2-d flat-fielded image: flt_a, flt_b, flt – 1-d extracted spectrum: x1d

Association product data files  For associations of one or more exposures (may include both TIME-TAG and ACCUM exposures): – Imaging mode: > fltsum: final association product combining all exposures in association – Spectroscopy: > x1dsum(#), where #=1,2,3, or 4 corresponding to FP-POS settings with >1 exposure > x1dsum: final association product combining all exposures in association

COS Associations  Only associations required for data processing will be constructed by TRANS  COS associations consist of all consecutive exposures for which the grating/mirror, central wavelength, pointing, and aperture are the same (note: FP-POS may change)  The association table, which contains information about each associated dataset, controls CALCOS processing  Observations will complete Generic Conversion as individual exposures, be held by a Data Collector until all member exposures are present, and the product will be created by CALCOS.  Each individual exposure member of an association is fully processed to produce _x1d (spectroscopy) or _flt (imaging)

COS Associations (continued)  There will be 1 product, and only 1 product, for each association. – For spectroscopic associations with one or more exposure members, the members are combined; the product will always be an _x1dsum file – For imaging associations with one or more exposure members, the members are combined; the product will always be an _fltsum file  COS associations will consist of – All associated science exposures (one or more FP-POS exposures) – Wavecal exposures as obtained > TAGFLASH wavecals produce _lampflash tables > ACCUM and TIME-TAG FLASH=NO produce separate AUTO wavecal exposures which are executed after each grating, central wavelength, mirror, pointing, or aperture change; with at least one each orbit. > Wavecals can NOT be shared between associations

Data File Type for each Exposure Type Exposure type raw tag rawaccum rawacq corrtag pha counts flt fltsum x1d X1dsum X1dsum asn trl spt TIME-TAG FUV NUVXXXXXXXXXXXXXXXXXX ACCUM FUV NUVXXXXXXXXXXXXXXXXX IMAGE TIME-TAG XXXXXXXX IMAGE ACCUM XXXXXXX ACQ/IMAGEXXXXXX ACQ/SEARCH and PEAKUPs XXX WAVECALXXXXXXXX FLAT and DARK XXXXXX

Target Acquisition Recap

Target Acquisition Modes  ACQ/IMAGE – preferred option, “faint” targets; precise centering  ACQ/SEARCH – spiral-search; “bright” targets or poorer initial coordinates; moderate centering  ACQ/PEAKXD – cross-dispersion peakup  ACQ/PEAKD – along-dispersion peakup (must follow ACQ/PEAKXD)

COS Target Acquisition Types  ACQ/IMAGE ( arcsec accuracy) – Use MIRRORA or B, NUV with either PSA or BOA; obtain image of field; centroid brightest object in field; obtain confirmation image  ACQ/SEARCH (~ arcsec accuracy) – Imaging: use MIRROR A or B, NUV with either PSA or BOA; search square grid (N=2-5) in spiral pattern; various centering algorithms – Dispersed Light: use FUV or NUV grating with either PSA or BOA; search square grid (N=2-5) in spiral pattern; various centering algorithms;  ACQ/PEAKXD (~ arcsec accuracy) – Dispersed Light: use FUV or NUV grating with either PSA or BOA; obtain centroid of cross-dispersion signal distribution  ACQ/PEAKD (~0.1 arcsec accuracy) – Dispersed Light: use FUV or NUV grating with either PSA or BOA; search along dispersion (N=3,5,7, or 9) in linear pattern; various centering algorithms

The spiral search  Default (and recommended) STEP-SIZE = arcsec  Initial point offset by half step if SCAN-SIZE = 2 or 4.

Target Acquisition Overheads  ACQ/IMAGE – 3 min + 2 x exposure time  ACQ/SEARCH – N (typically 4 or 9) x [20 sec + exposure per dwell]  ACQ/PEAKXD – FUV: 80 sec + exp time; NUV 70 sec + exp time  ACQ/PEAKD – N (typically 5) x [20 sec + exposure per dwell] Acq Type T exp =10 secT exp =20 secT exp =30 secT exp =1 minT exp =5 min ACQ/IMAGE 3 min 20 sec3 min 40 sec4 min5 min13 min ACQ/SEARCH 2x2 2 min2 min 40 sec3 min 20 sec5 min 20 sec21 min 20 sec ACQ/SEARCH 3x3 4 min 30 sec6 min7 min 30 sec12 min48 min ACQ/PEAKXD 1 min 30 sec1 min 40 sec1 min 50 sec2 min 20 sec6 min 20 sec ACQ/PEAKD5 2 min 30 sec3 min 20 sec4 min 10 sec6 min 40 sec26 min 40 sec

Initial pointing and sky searches COS has a very small aperture (2.5 arcsec), although the image plane “sees” slightly more of the sky than that. How much sky should be searched (ACQ/SEARCH) to ensure a good acquisition every time without unduly wasting telescope time? The quality of dead-reckoning pointings after SM4 is not yet known, but with the advent of the GSC2 coordinate system and with regular aperture location determinations, initial pointings with errors < 1 arcsec are anticipated. Our Cycle 17 recommendation is that observers use a 2x2 spiral at the start of their acquisition sequence to guarantee acquiring the target. This may be eliminated in Cycle 18.

Acquisition Scenarios

COS Data Handbook

 COS Instrument Overview  COS Data Files  COS Calibration  COS Error Sources  COS Data Analysis  Clear treatment of COS data-processing, association descriptions, and data file description

COS Typical File Sizes 1. Values pertain to x1d_a or x1d_b files only. These files are temporary output products from calcos processing 2. Values are in addition to amounts given for each segment

COS Typical Data Volume MB

STIS or COS?  COS is 10-30x faster than STIS in FUV at R=20,000 for point sources; even greater advantage at faint end due to low noise and pulse-height discrimination capability  COS has quite degraded resolution for extended objects (see table below); for FUV, portions of objects closer than 1 arcsec apart will overlap; for NUV, spectrum stripes will partially overlap for objects more than 1 arcsec in spatial extent R R R source size G140L G130M G230L point " diameter " diameter " diameter " diameter " diameter

COS or STIS?  In NUV, COS M mode observing is inefficient for cases requiring large spectral coverage  In NUV, COS background rate is expected to be 4x lower than STIS, but is TBD  COS has no resolution higher than 20,000 and is a UV- only instrument  COS FUV TIME-TAG mode includes the pulse-height for superior noise rejection  STIS TIME-TAG has higher time-resolution and may be used on brighter targets  The answer depends upon your application: refer to the IHBs and use the ETCs to evaluate your targets

 Limiting Flux to achieve S/N=10 in 3600 sec exposures with uniform binning corresponding to R~20,000 (0.08 Å). COS PSA aperture used; STIS slit losses included.

 Limiting Flux to achieve S/N=10 in 3600 sec exposures with uniform binning corresponding to R~20,000 (0.12 Å). COS PSA aperture used; STIS slit losses included.

SMOV Plan and C17 Cal Plan

COS SMOV4 NUV Sequence COS-01 Recovery from SAFE COS Onboard Memory Check COS Science Data Buffer Check COS NUV Initial HV Turn-on/Ramp-up COS v5 NUV Fold Test COS NUV Internal Functionality & Operation COS NUV Dark Measure COS OTA to FGS Alignment (NUV) COS NUV Optical Alignment /Focus visit 1-3 COS Internal NUV Wavelength Verify COS NUV Optical Alignment vis 4-5 COS Internal NUV Wavelength Meas & Grating Eff. Vis 1, 3 – lamp 2 COS NUV Imaging Acq Verify COS NUV High S/N Verification COS NUV Imaging Performance COS NUV Int/External Wavelength Scales COS NUV Structural & Thermal Stability COS NUV Dispersed Acq Verify Do NOT Require Wavelength Scale Update External Observations May require wait FUV SMOV sequence HST release MAMA LV on Internal pressure <20 micro-Torr BEA Complete Alignment OK Alignment Not OK COS Internal NUV Wavelength Meas Wavelength Ranges Not OK Wavelength Ranges OK Enable Wavecal- dependent NUV Calibration and Science COS v2-n NUV Spectr. Sensitivity COS NUV Ext. Spectr. Perf. Part 1 COS NUV Ext. Spectr. Perf. Part 2 COS NUV Flat Fields Internal pressure <10 micro-Torr Require Wavelength Scale Update 5 September 2008 Uplink 24-hour data turnaround required COS v1 NUV Spectr. Sensitivity Quick ERO REF SCI IHB SIAF update available REF 24h data Uplink SIAF update start Uplink 24h data 24h data 24h data 24h data 24h data Uplink 24h data REF 15 Jul 1 Jul 15 Jun 15 Jul – 30 Aug 1 Jun

COS SMOV4 FUV Sequence COS-01 COS COS COS-22 FUV Detector Door Open COS FUV Initial HV Turn-on/Ramp-up COS FUV Internal Functionality & Operation COS FUV Dark Measure COS NUV Optical Alignment /Focus COS FUV Optical Alignment /Focus visit 1-3 COS Internal NUV Wavelength Verify COS Internal FUV Wavelength Meas Vis 2 – lamp 2 COS FUV Dispersed Acq Verify COS FUV Structural & Thermal Stability COS FUV Int/External Wavelength Scales COS v2-4 FUV Spectr. Sensitivity External Observations May require wait Internal Pressure <100 micro- Torr BEA Complete Alignment OK COS Internal FUV Wavelength Meas – Vis 1 Uplink Wavelength Ranges Not OK Wavelength Ranges OK Enable Wavecal- dependent FUV Calibration and Science COS FUV Flat Fields COS FUV Ext. Spectr. Perf. Part 1 COS FUV Ext. Spectr. Perf. Part 2 COS FUV High S/N Verification Internal Pressure <10 micro- Torr Require Wavelength Scale Update Does NOT Require Wavelength Scale Update HST release NUV SMOV sequence 5 September 2008 XDL at OPER SIAF update start Pressure Gauge OFF Rapid data turnaround required Outgassing Concern? COS v1 FUV Spectr. Sensitivity - Quick COS NUV Optical Alignment /Focus uplink Enable FUV ERO No wavecal; use offset ERO SCI REF IHB SIAF update available REF 24h data Rapid data turnaround required Required to enable ERO Required to enable science Analysis produces reference file Results reported in IHB REF 24h data 24h data 24h data 24h data 24h data COS FUV Optical Alignment /Focus Verif. - visit 4-5 Uplink 24h data 24h data 15 Jul 15 Jul – 30 Aug 28Jun 5 Jul 15Jun

White Balance