2025ApJ...983...37S

We have observed the ¹³CH₃OH 5₁-4₁ A⁺, ¹³CH₃OH 14₁-13₂ A^–, and CH₂DOH 8_2,6-8_1,7e₀ lines toward 24 high-mass star-forming regions by using Atacama Large Millimeter/submillimeter Array with an angular resolution of about 0$\mathop{.}\limits^{\unicode{x02033}}$3. This resolution corresponds to a linear scale of 400-1600 au, allowing us to resolve individual cores properly. We detected the ¹³CH₃OH and CH₂DOH emission near the continuum peaks in many of these regions. From the two ¹³CH₃OH lines, we calculated the temperature toward the ¹³CH₃OH peaks, and confirm that the emission traces hot (>100 K) regions. The N(CH₂DOH)/N(¹²CH₃OH) ratio in the observed high-mass star-forming regions is found to be lower than that in low-mass star-forming regions. We have found no correlation between the N(CH₂DOH)/N(¹³CH₃OH) or N(CH₂DOH)/N(¹²CH₃OH) ratios and either temperatures or distance to the sources, and have also found a source-to-source variation in these ratios. Our model calculations predict that the N(CH₂DOH)/N(¹²CH₃OH) ratio in hot cores depends on the duration of the cold phase; the shorter the cold phase, the lower the deuterium fractionation in the hot cores. We have suggested that the lower N(CH₂DOH)/N(¹²CH₃OH) ratio in high-mass star-forming regions compared to that in low-mass star-forming regions is due to the shorter duration of the cold phase and that the diversity in the N(CH₂DOH)/N(¹²CH₃OH) ratio in high-mass star-forming regions is due to the diversity in the length of the cold prestellar phase, and not the time that the objects have been in the hot core phase.