2010AJ....139..302C

We have carried out time monitoring observations of the ²⁸SiO v = 0, 1, 2, J = 2 - 1, ²⁸SiO v = 0, 1, 2, J = 3 - 2, and ²⁹SiO v = 0, J = 3 - 2 transitions in Orion KL with the 14 m radio telescope at Taeduk Radio Astronomy Observatory. The pair of J = 2 - 1 and J = 3 - 2 transitions was simultaneously observed from 1999 January to 2001 March. Each transition shows different characteristics. Both the v = 1, J = 2 - 1, and J = 3 - 2 masers show a relatively stable double-peaked profile and little variation in intensity. The ²⁸SiO v = 2, J = 3 - 2 maser presents the most active intensity variations including a disappearance on 2000 February 17 and 2001 February 16. The v = 2, J = 3 - 2 maser may trace the closest region to the central young stellar object and results in the strongest variations of intensity and line profile. The v = 2, J = 2 - 1 maser was not detected in the monitoring. The ²⁸SiO v = 0, J = 3 - 2 lines showed a large variation of peak intensity compared with ²⁸SiO v = 0, J = 2 - 1 that might be due to partial masing. The different observational results of ²⁸SiO v = 0, 1, J = 2 - 1, ²⁸SiO v = 0, 1, 2, J = 3 - 2, and ²⁹SiO v = 0, J = 3 - 2 transitions might reflect that individual transitions trace different portions of gas.