Okayama Prefectural Mizushima Technical High School

Abstract With the aim of examining how much information of solar rotation can be obtained purely spectroscopically by observing the Sun-as-a-star during the 2012 May 21 eclipse at Okayama Astrophysical Observatory, we studied the variation of radial velocities (Vr), which were derived by using the iodine-cell technique based on a set of 184 high-dispersion spectra consecutively obtained over a time span of ∼ 4 hr. The resulting Vr(t) was confirmed to show the characteristic variation (Rossiter–McLaughlin effect) caused by time-varying visibility of the solar disk. By comparing the observed Vr(t) curve with the theoretical ones [which were simulated with the latitude (ψ) dependent solar rotation law ωsidereal(ψ) = A + B sin 2ψ (degree d−1)] we found that the relation B ≃ −5.5A + 77 gives the best fit, though separate determinations of A and B were not possible. Since this relationship is consistent with the real values known for the Sun (A ≃ 14.5, B ≃ −2.8), we may state that our analysis yielded satisfactory results. This consequence may provide the prospect of getting useful information on stellar rotation of eclipsing binaries from radial-velocity studies during eclipse, if many spectra of sufficiently high time-resolution are available.