Photospheric solar activity index: VIRGO/SPM Sph and GOLF Svel (D4.2)

The photospheric solar activity index, Sph (Mathur, Salabert et al. 2014), is calculated from the photometric observations collected by the Variability of Solar Irradiance and Gravity Oscillations (VIRGO, Fröhlich et al. 1995) instrument onboard the Solar and Heliospheric Observatory (SoHO) spacecraft launched on December 2, 1995 (Domingo et al. 1995). A similar activity index, Svel, can be obtained  from the radial velocity observations collected by the Global Oscillations at Low Frequency instrument (GOLF, Gabriel et al. 1995) onboard SoHO.

The VIRGO instrument is composed of three Sun photometers (SPM) at 402nm (blue channel), 500nm (green channel), and 862nm (red channel). The VIRGO/SPM photometric observations were calibrated as described in Jiménez et al. (2002) but using a high-pass filter with a cut-off at 60 days and then processed using the KADACS Kepler pipeline as described in Garcia et al. (2011).
The response functions of the photometric VIRGO observations are shown to peak between ±10km of the base of the photosphere (Fligge et al. 1998). Values for Sph are provided for each SPM individually, ie, the blue, green, and red channels, and for the composite observations as well between the green and red channels which have the closest bandwidth to Kepler observations (Basri et al., 2010).

The GOLF instrument measures the Doppler wavelength shift in the D1 and D2 Fraunhofer sodium lines at 589.6 and 589.0 nm respectively. The GOLF Doppler velocity time series have been obtained following the procedure explained in García et al. 2005 but using a high-pass filter with a cut-off at 70 days.

The VIRGO/SPMs and GOLF observations were divided into sub series of 5xProt = 125 days (for a solar rotation of 25 days) with an overlap of factor 8, i.e. of 15.625 days.

The available ASCII files contain 7 columns as following:

  • Column 1: Number of the analyzed 125-day sub series (non-independent sub series were analyzed as an overlap of a factor 8 was used, i.e. 15.6250 days)
  • Column 2: Day of the first data point
  • Column 3: Month of the first data point
  • Column 4: Year of the first data points
  • Column 5: VIRGO photometric index (Sph in ppm) or GOLF radial velocity index (Svel in m/s)
  • Column 6: Error on Sph (or Svel) index
  • Column 7: Duty cycle in % of each sub-series

And 2 additional columns for GOLF only:

  • Column 8: flag indicating if the analyzed sub series contains observations from the red-wing period (1 no / 2 yes)
  • Column 9: percentage (%) of measurements from the red-wing period in the analyzed sub series

Available data sets:


  • Basri, G., Walkowicz, L. M., Batalha, N., et al. 2010, Astrophys. J. Lett., 713, L155
  • Fligge, M., Solanki, S. K., Unruh, Y. C., Froehlich, C., & Wehrli, C. 1998, A&A, 335, 709
  • Fröhlich, C., Romero, J., Roth, H., et al. 1995, Solar Phys., 162, 101
  • García, R. A., Hekker, S., Stello, D., et al. 2011, Mon. Not. Roy. Astron. Soc., 414, L6
  • Jiménez, A., Roca Cortés, T., & Jiménez-Reyes, S. J. 2002, Solar Phys., 209, 247
  • Mathur, S., Salabert, D., García, R. A., & Ceillier, T. 2014, Journal of Space Weather and Space Climate, 4, A15
  • Domingo, V., Fleck, B. and Poland, A.I., 1995, Solar Phys., 162, 1
  • Gabriel, A.~H., Grec, G., Charra, J. et al., 1995, Solar Phys., 162, 61
  • García, R.~A., Turck-Chièze, S., Boumier, P., et al. 2005, A&A, 442, 385

(The data available on this page is the Deliverable D4.2 within the SpaceInn project.)

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