tokens: 1,20−19 (252,789.82 MHz), U253020, U267402, U268464, U268485, and U268833. 5. Comparison to single-dish results. Eight light curves were studied in detail in our single-dish work (He et al. 2017 ), but only six of them can be compared to the ACA results, because the other two lines (of C 4 H) suffer from the interferometric baseline problems in the ACA data, showing negative artifacts, as mentioned earlier. Two of the six line features (SiS 14−13 at 254,103 MHz and the blended lines of C 3 N+HCN+C 4 H at 267,120 MHz) follow the NIR light curve well in both the single-dish and ACA data. However, for the four line features that were anticorrelated with the NIR light in the single-dish results, none of them shows the anticorrelation in the ACA data: two of them (HCN, v 2 = 1, 3−2, l = 1 f at 267,199 MHz and the blended lines of 29 SiS+HCN, v 2 =2 0 at 267,243 MHz) show strong variations in phase with the NIR light and continuum; 30 SiO,6−5 at 254,216 MHz varies similarly but with a smaller amplitude; and the blended line feature of Na 37 Cl+CH 2 NH+HC 3 N at 254,700 MHz shows modest variation. Why are the anticorrelation cases in the single-dish data missing in the ACA results, while the correlated cases remain unchanged? The ALMA monitoring started about 7 yr (∼four stellar pulsation cycles) later than our single-dish work, and thus secular changes of stellar pulsations could have occurred. However, the different phase behaviors of the different lines cannot be explained solely by this; some unknown mechanisms operating in the circumstellar envelope (CSE) are necessary to create differences among them. The mechanisms are possibly related to the missing flux in the ACA data, as discussed earlier, and the different telescope beam sizes involved in the two works, 29′′ for the single-dish versus 4′′ × 8′′ (or 6′′) for ACA. However, a radial phase delay due to radiation transportation is unlikely, because the difference in beam radii only corresponds to ∼1552 au at a source distance of 135 pc, which can produce a phase lag of only ∼9 days with the speed of light. This is insufficient to explain the observed change from anticorrelations to correlations with the NIR or millimeter continuum light. The only known candidate mechanism is that proposed by Cernicharo et al. ( 2014 ) from their simulations in which the evacuation of molecular populations in low- J energy levels by IR excitation is different for different molecular lines at different radii of the CSE. We will analyze the time series of ALMA ACA maps and do simulations to further explore this idea in coming papers. 6. Remarks on special species. A special case is Na 37 Cl. Its J = 20−19 (254,663.465 MHz) and 21−20 (267,365.833 MHz) transitions have similarly strong broad line profiles, with peak fluxes of about 1.5 Jy beam –1 . However, while the former shows little difference between its maximum- and minimum-phase line profiles in Figure 4 , the latter has its line profile definitely varying
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