The SPM instrument

Please improve the description of the instrument! TWavelengths and Bandwidths The choices of the SPM wavelengths are made partly of scientific, partly of technical reasons and partly out of prejudice. The scientific background is to get an observational handle on the spectral redistribution and variation of global oscillations and solar variability. The Si detectors are effectively limited to observe at the required accuracy between 320 and 900 nm. The original proposal had the shortest wavelength at 335 nm, but this was discarded because of the extreme sensitivity to contamination at this wavelength, this was shown with the IPHIR experiment. The 402nm wavelength was chosen as a short wavelength compromise and because it permits the use of more stable filter glasses and lies just above the Ca II H&K lines; going into the H or K lines would give a small advantage only with a high spectral resolution. The visible and near-infrared channel wavelengths are mainly due to the history of previous experiments.
 
 

Wavelengths: 402 nm

 500 nm

 862 nm

 Bandwidths: 5 nm

 5 nm

 5 nm

 Effective bandpass The spectral profiles can be found on the ftp server:ftp.estec.esa.nl/pub/loitenerife/PurpleBook.

 They are ascii files called virgospmblu.dat, virgospmgrn.dat, virgospmred.dat with 2 columns (wavelength, transmission).

Effective opacity /optical depth: To be derived from the bandpasses
 
 

3.1.2 Detectors

The detectors are silicon photodiode S1337 from Hamamatsu, Japan mounted in a common housing with the interference filters.

 Power on detectors 402 nm: 23 uW

 500 nm: 28 uW

 862 nm: 30 uW

 Lifetime sensitivity variation: 402 nm: 95% (IPHIR and SOVA2, 335 nm)

 500 nm: 49% (IPHIR and SOVA2)

 862 nm: 17% (IPHIR and SOVA2)

 Detector stability

 Temperature sensitivity (effect of the filter included)

 402 nm: -710 ppm/K

 500 nm: -1040 ppm/K

 862 nm: -270 ppm/K

 Aging

 402 nm: TBD

 500 nm: TBD

 862 nm: TBD
 
 

3.1.3 Filters

Filter degradation

 Temperature sensitivity: See above

 Particle sensitivity:

 Transmission drop: 402 nm: 52%

 500 nm: 7%

 862 nm: 1%

 UV sensitivity: No UV data available (yet!)

 Surface contamination: Unknown

 Angular sensitivity: Unknown
 
 

3.1.4 Noise Levels

Amplifier and resistors: included in total instrumental noise

 V/F converters: included in total instrumental noise
 
 

Total Instrumental Noise

 Short Term (above 1 mHz) 402 nm: See Fig SPM-I

 500 nm: better than at 402 nm

 862 nm: better than at 402 nm
 
 

Long Term (below 1mHz) 402 nm: See Fig SPM-I

 500 nm: better than at 402 nm

 865 nm: better than at 402 nm
 
 

 Figure SPM-I: Power spectral density of the dark-current noise of the SPM blue channel, and an LOI pixel calculated from time series of 68 h and 45 h respectively. In the 5-minute range the noise of the SPM is about 5 x 10⁵ times smaller than the noise between the p modes of IPHIR (= 0.5 ppm² uHz^-1). For the LOI pixel it is about 1.2 x 10⁶ times smaller than the noise expected for a 12th of the solar disk (12 time the noise power of the full disk)
 
 

3.1.5 Observing sequence

Please refer to the VIRGO operation manual.

 Last updated by Thierry Appourchaux on February 14, 2002