ilaria pascucci space telescope science institute department of physics & astronomy, johns...
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ILARIA PASCUCCI
Space Telescope Science InstituteDepartment of Physics & Astronomy, Johns
Hopkins University
Monitoring of the Wavelength Calibration Lamps for the Hubble
Space Telescope
Pascucci, I. , Proffitt, C., Ghavamian, P., Sahnow, D., Oliveira, C., Aloisi, A., Keyes, T., Penton, S. V. – Proc. SPIE, Vol. 7731, 77313B (2010)
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STIS and COS Lamps
STIS : 3 hollow cathode Pt-Cr-Ne lamps
COS : 2 hollow cathode Pt-Ne lamps
~1130-3200Å
~5400-8000Å~3200-
5400Å
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When do we take a lamp spectrum?
STIS : every time we use a new grating or tilt position and generally after ~1 orbit
COS : lamp exposure contemporaneous to science observations
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1. Metals sputtered from the cathode trap Ne atoms➔ reduced gas pressure ➔ need higher turn-on voltage
2. Aging of the barium getter ➔ impurities mainly H ➔ H lines
3. COS: lamp beams become larger with time (not intrinsic fading)
Causes for lamps fading
typical lifetime 15,000 mA h or 1,500 h at 10 mA current
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STIS Lamps
STIS : 3 Pt-Cr-Ne lamps – LINE, HITM1 and HITM2
Different locations and optics: LINE brightest on the detector ➔ FUV echelle modesHITM1 and 2 ➔ optical low-res modes
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STIS – Lamps Fading with Time
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STIS – Lamps Fading in the FUV
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STIS – Lamp flux vs Usage
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STIS – Current Lamp Flux Ratios
PID 12079 : 4 internal orbits
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STIS – Early vs Recent Lamp Exposures
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STIS – The Most Affected Setting
➔ allow for the HITM2 lamp
current exp time with LINE = 46s
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COS and STIS Lamp comparison
when the COS sensitivity degradation is removed
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Aged-lamps Intensities
Nave et al. 2008
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Summary• The STIS LINE lamp, which was the brightest at the beginning of operation in 1997, has faded dramatically at the shortest FUV wavelengths (1150-1200Å) and is now fainter than the other two STIS lamps
• The STIS LINE lamp output remains higher than the HITM1 and HITM2 lamp outputs by factors of ~5-10 at all wavelengths > 1300Å
• The fading of the STIS LINE lamp between 1997 and 2010 in absolute terms is factor of ~15 at the very short FUV wavelengths, much greater than what expected from accelerated aging tests in the laboratory
• We have evidence that all STIS lamps fade even when they are not used indicating that on-orbit factors are impacting the lifetime of the lamps • The 6-month monitoring of the COS P1 lamp shows that the lamp output fades similarly to the STIS lamps as a function of lamp usage
Pascucci, I. , Proffitt, C., Ghavamian, P., Sahnow, D., Oliveira, C., Aloisi, A., Keyes, T., Penton, S. V. – Proc. SPIE, Vol. 7731, 77313B (2010)