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tokens: a few megahertz, and this is the reason why some of the unidentified lines seen in the 80–116 GHz range were not properly assigned to CHD 2 CCH and CH 2 DCCD by Agúndez et al. (2019) . In fact, the identification of these two molecules drastically reduces the number of lines pending identification in the λ 3 mm line survey of L483 (see Table A.2 of Agúndez et al. 2019 ). The parameters derived for the lines assigned to the two doubly deuterated isotopologues of methyl acetylene are given in Table 1 and the observed line profiles are shown in Fig. 1 for CHD 2 CCH and in Fig. 2 for CH 2 DCCD. We note that the line at 91971.307 MHz, assigned to the 6 1,6 –5 1,5 transition ofCHD 2 CCH, was incorrectly assigned to the transition 5 3 –4 3 F = 6–5 of CH 3 CN by Agúndez et al. (2019) . The astronomical frequencies observed in the 72–116 GHz range (see Table 1 ) and the laboratory frequencies measured inthe 29–47 GHz range ( Thomas et al. 1955 ) were used to derive more accurate spectroscopic parameters for CHD 2 CCH and CH 2 DCCD (see Table 2 ). These constants are a considerable improvement on those reported by Thomas et al. (1955) and enable us to predict the rotational spectrum of the two molecules with an accuracy better than 0.1 MHz up to 200 GHz. Since the lines of doubly deuterated CH 3 CCH are relatively bright in L483, it would not be surprising to detect the triply deuterated species CHD 2 CCD, which should be three times more abundant than CD 3 CCH. However, the rotational spectrum has only been measured in the 28–43 GHz range with modest accuracy ( Thomas et al. 1955 ), which may translate to frequency errors of a few megahertz for lines lying above 72 GHz. It would therefore be interesting to measure the rotational spectrum of triply deuterated CH 3 CCH at millimeter wavelengths. Table 1 Observed line parameters of CHD 2 CCH and CH 2 DCCD in L483. Notes. Numbers in parentheses are 1 σ uncertainties in units of the last digits. Line parameters were derived from a Gaussian fit to the line profile. Observed frequencies are obtained adopting V LSR = 5.30 km s −1 ( Agúndez et al. 2019 ) and have an uncertainty of 20 kHz for all the lines. The full width at half maximum is Δ v . 3.2 Observed column densities We derived beam-averaged column densities for methyl acetylene and its singly and doubly deuterated isotopologues in L483 assuming local thermodynamic equilibrium. Values for CH 3 CCH and the two singly deuterated forms were already reported by Agúndez et al. (2019) . Here we have revised some of these values including new lines observed in the 72–80 GHz range and using new values for the electric dipole moments. The dipole moment of CH 3 CCH was experimentally measured by Burrell et al. (1980) to be 0.7839 D. For CH 3 CCD, the dipole moment was measured by Muenter Laurie (1966) . Here, we adopt the value measured by these latter authors corrected by using a more accurate value of the dipole moment of OCS, which is used as reference (see