UVIS Calibration Update Greg Holsclaw, Bill McClintock June 8, 2009

Outline Recent calibration observations Increase in starburn depth More Spica variability Stellar flux comparisons with SOSLTICE

Recent UVIS Calibrations FUV2009_108_19_52_14_UVIS_109IC_ALPVIR001_PRIME Data from first ~1/3 of slew along the slit was lost FUV2009_121_01_12_45_UVIS_109IC_ALPVIR002_PRIME

Total signal vs position Total FUV signal from Spica vs position of the star within the slit for all obsevations in the last four years Each curve is normalized to the value at row 20 Significant increase in starburn depth is seen time

Starburn in both channels EUV FUV This recent increase in depth of the FUV starburn is also seen in the EUV

Sharp change in response within the starburned rows This plot shows the total signal from Spica as a function of time for when the stellar image is centered at row 20 and row 31 A slow decline in overall sensitivity is evident in row 20

Depth of Starburn vs time This shows the ratio of the signal when the star is centered at row 31 to that of when the star is centered at row 20 This is measure of the increasing depth of the starburn area Were there a lot of occultation measurements in late 2008 / early 2009 where a star was located in the starburned area?

Spectral ratio of row 31 to row 20 This shows the ratio of the spectrum in row 31 to that in row 20 This looks like the inverted signal from a star (Spica?) 8

Spectral ratio of row 31 to row 20 This shows the ratio of the spectrum in row 31 to that in row 20 This looks like the inverted signal from a star (Spica?) With Flat-field 9

Spica variability

Background on Alpha Vir (Spica) Spica is a non-eclipsing double-lined spectroscopic binary system Though not spatially resolvable, each component is detectable through measurements of out-of-phase Doppler shifts in the constituent spectral lines Non-eclipsing due to large apparent orbital inclination of ~70 degrees Both stars are of a similar spectral class: Primary: B1V Secondary: B4V Spica is the brightest rotating ellipsoidal variable star The stars have a distorted ellipsoidal shape due to mutual gravitation effects As the components revolve, the visible area (and thus the observed flux) changes with orbital phase Since this is a geometric effect, it should be roughly wavelength-independent Orbital period is 4.01454 days Amplitude of flux variation in V-filter ~3% The primary of Spica is a Cepheid variable Periodic variation in the pulsating primary star is much shorter than the system’s orbital period and about a factor of 2 less in magnitude Period is 4.17 hours Amplitude of flux variation in V-filter ~1.5% This short-term variation, identified in 1968, became undetectable in the early 1970’s (but may return again due to precession of the primary’s rotation axis relative to the orbital plane, which has a period of 200 years [Balona, 1986]) http://observatory.sfasu.edu

Ellipsoidal variation model Variation in flux is given by [Shobbrook, 1969; Sterken et al, 1986]: dE = A M2/M1 (R/D)3 (1+e cos(TA+Φ))3 (1-3cos2(TA+TA0+Φ) sin2i ) Where: A=0.822 (wavelength dependent “photometric distortion”) M2/M1 = 1/1.59 (ratio of masses) R = 7.6 Rsun = 5.2858e6 km (polar radius of primary) D = 1.92916e7 km (mean separation between stars) e = 0.14 (orbital eccentricity) TA (true anomaly) T0 = 4.01454 days (orbital period) TA0 = 150 degrees (apparent angle to line of apsides in year 2005, has precession period of 128 years) i = 65.9 degrees (orbital inclination) Φ = empirical phase shift, a free parameter to match with data One period of the expected variation in flux from Spica

Normalized signal vs time New data The left plot shows the total FUV signal vs time (normalized to the mean), with a line fit The right plot shows the same data with this linear trend removed, along with a theoretical model of the Spica ellipsoidal variation that has been fit to the curve (optimizing only the magnitude and phase offset parameters)

Data vs model The Spica model continues to be consistent with the observed variability

Stellar flux comparisons At the last meeting, an effort was made to compare the stellar spectra from UVIS with that derived from the SORCE-SOLSTICE instrument In order to include as many stars as possible, it was necessary to use spectra from when the star was located in the star-burned rows of the detector The next few slides summarize those results

Ratio of UVIS to SOLSTICE This plot shows the ratio of UVIS spectra (1.1nm bins) to SOLSTICE over 130-180 nm Here, UVIS spectra were reduced using the flat-field While the magnitude varies, a consistent shape in the ratio is apparent WITH flat-field

Ratio of UVIS to SOLSTICE Normalized to a mean value of one

Ratio of UVIS to SOLSTICE This plot shows the average ratio of UVIS to SOLSTICE for all stars observed (except Alp PsA) No normalization has been done here 18

Ratio of UVIS to SOLSTICE This plot shows the average ratio of UVIS to SOLSTICE for all stars observed (except Alp PsA) No normalization has been done here 19

Comparison of UVIS to SOLSTICE away from the starburn Only two stars have along-slit slew scans and are sufficiently comparable: Alp Vir (Spica) and Eta Uma The left plot shows the absolute spectra from UVIS and SOLSTICE The right plot shows the ratio of UVIS to SOLSTICE Most of the shape in the ratio appears consistent with the previous results with the stars located in the starburn

Ratio of UVIS to SOLSTICE This shows the ratio of spectra where the star is located away from the starburn The dashed lines are from where the star was located in the starburn (row 31)

Ratio of UVIS to SOLSTICE with flat-field applied This shows the ratio of spectra where the star is located away from the starburn The dashed lines are from where the star was located in the starburn (row 31) 22

Lots more to do Quantify sensitivity decrease at and around Lyman alpha, include in calibration routine Develop sensitivity correction based on comparisons to SORCE-SOLSTICE Compare with Don’s sensitivity curve Develop a flat-field corrector based on the hypothesis of spatially variant PSF

Summary Significant increase in the depth of the starburn in the last 6 months Both in FUV and EUV More stellar occultations recently? Spica variability model continues to match the observations Comparisons of UVIS spectra with SOLSTICE suggest that a shape correction in the FUV is required UVIS Calibration paper Work continues, but not quite ready to distribute a draft

Ratio of UVIS to SOLSTICE This plot shows the average ratio of UVIS to SOLSTICE for all stars observed (except Alp PsA) Average of all stars

Ratio of UVIS to SOLSTICE This plot shows the average ratio of UVIS to SOLSTICE for all stars observed (except Alp PsA) Expanded vertical scale