Torsion-rotational transitions in methanol as a probe of fundamental physical constants–electron and proton masses

We report on the using of torsion-rotational transitions in the CH$_3$OH and $^{13}$CH$_3$OH molecules to evaluate possible variations of the electron-to-proton mass ratio $\mu = m_e/m_\rho$ from spectral observations of emission lines detected in the microwave range towards the dense molecular cloud Orion-KL. An estimate of the upper limit on the relative changes in $\mu$ is obtained by two independent ways with 13CH3OH lines and with the combination of $^{13}$CH$_3$OH and CH$_3$OH lines. The calculated upper limit $\Delta\mu/\mu<1.1\times10^{-8}(1\sigma)$ is in line with the most stringent constraints on the variability of fundamental physical constants established by other astrophysical methods.