Palle, P. L.; Jimenez, A.; Perez Hernandez, F.; Regulo, C.; Roca-Cortés, T.; Sanchez, L.
Bibliographical reference
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 441, no. 2, p. 952-959
Advertised on:
3
1995
Journal
Citations
32
Refereed citations
26
Description
Ten years of continuous measurements of the radial velocity of the Sun
have been used to estimate the contribution of various solar surface
phenomena to the observed background solar velocity spectrum (BSVS). The
characteristics of this spectrum are of great importance, as they
represent the ultimate limit on the sensitivity of measurements of solar
oscillations. A precise determination of this spectrum from the ground
is invariably contaminated by the discontiniuity in the observations,
the unavoidable effect of the Earth's atmosphere and, possibly, by the
instrumentation itself. The present analysis uses observations made with
a very stable instrument to allow comparison of several sets of data,
collected along different phases of the solar activity cycle. The
results show a high stability of the BSVS throughout the frequency
ranges of interest for helioseismology and, moreover, its profile cannot
be modeled using a single exponential function, as the exponent changes
with frequency. The roughness of the spectrum is calculated, allowing an
estimate of the required signal-to-noise ratio in order to detect an
oscillation with a given amplitude. Finally, following the modeling of
the expected background spectrum proposed by Harvey, the rms full disk
velocity of the main solar atmospheric phenomena (granulation,
mesogranulation, supergranulation, and active regions) are calculated.
Despite the limitations of the procedure employed in this analysis, the
main conclusion is the overall good agreement with the model, although
mesogranulation seems to have been underestimated. Comparison with the
different phases of the solar activity cycle reveals a different
behavior of the mesogranulation, while granulation appears to be stable.