Solar rotation inferred from radial velocities of the sun-as-a-star during the 2012 May 21 eclipse

TL;DR

This study demonstrates that radial velocity measurements during a solar eclipse can effectively infer the Sun's rotation law, offering a method to analyze stellar rotation in eclipsing binaries spectroscopically.

Contribution

The paper introduces a spectroscopic method to determine solar rotation profiles during an eclipse, which can be applied to stellar binaries for rotation analysis.

Findings

Radial velocity variations match the Rossiter-McLaughlin effect.

The derived rotation law relation is consistent with known solar values.

Potential to study stellar rotation in eclipsing binaries using high-resolution spectra.

Abstract

With an aim to examine 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 (V_r), which were derived by using the iodine-cell technique based on a set of 184 high-dispersion spectra consecutively obtained over the time span of ~4 hours. The resulting V_r(t) was confirmed to show the characteristic variation (Rossiter-McLaughlin effect) caused by time-varying visibility of the solar disk. By comparing the observed V_r(t) curve with the theoretical ones, which were simulated with the latitude (psi) dependent solar rotation law omega(psi) = A + B sin^2(psi) (deg/day), we found that the relation B = -5.5 A + 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 a 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.