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)