ILARIA PASCUCCI Space Telescope Science Institute Department of Physics & Astronomy, Johns Hopkins University Monitoring of the Wavelength Calibration.
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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)
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
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
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
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
STIS – Lamps Fading with Time
STIS – Lamps Fading in the FUV
STIS – Lamp flux vs Usage
STIS – Current Lamp Flux Ratios
PID 12079 : 4 internal orbits
STIS – Early vs Recent Lamp Exposures
STIS – The Most Affected Setting
➔ allow for the HITM2 lamp
current exp time with LINE = 46s
COS and STIS Lamp comparison
when the COS sensitivity degradation is removed
Aged-lamps Intensities
Nave et al. 2008
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)
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