To promote the understanding of massive star formation processes, we have studied the 6.6 GHz methanol (CH3OH) masers and their environments—the dense cores and the outer regions of the molecular cloud. The physics o...To promote the understanding of massive star formation processes, we have studied the 6.6 GHz methanol (CH3OH) masers and their environments—the dense cores and the outer regions of the molecular cloud. The physics of the CH3OH maser or the thermal emission formation region is studied by fitting the observational data of the 6.6 GHz 51–60A+ and the 107 GHz 31–40A+CH3OH maser emission, using the radiative transfer calculations. The type II characteristics of the 6.6 GHz CH3OH maser are confirmed by the calculation results. A greater intensity of the radiation field leads to an increase in the peak intensity of the maser; however, high densities tend to turn off the maser. The calculation results show that to be a maser the 6.6 GHz CH3OH emission needs a radiation field of 150–300 K and a density not higher than 107cm?3, while the 107 GHz emission requires a radiation field of 210–300 K and a density not higher than 3×106 cm?3. The 6.6 GHz line is maser towards all six studied sources, while the 107 GHz line is maser towards Cep A only. Moreover, the former’s intensity is much stronger than the latter. The radiative transfer calculations also indicate that the 6.6 GHz maser emission is so strong that the requirements of its formation (e.g. the radiation field, the density and the kinetic parameters) can only be satisfied at a certain stage of the processes of the massive star formation. Therefore it is often used as one of the most prominent tracers for the massive star formation regions. The calculation results of the simutaneous observations of (1,1) through (4,4) inversion lines of the ammonia (NH3) indicate that both the temperature and the density in the 6.6 GHz CH3OH maser formation regions are higher than that of the NH3 line formation regions. Furthermore, the common fact of |Visr(CO)| > |Visr(NH3)|>|Visr(CH3OH 6.6GHz maser)| in all six sources implies the ongoing developing trends of those gas flows driven by the masers.展开更多
We present interferometric observations of the W51 region at 2.7 mm and 3.3 mm with the Berkeley-Illinois-Maryland Association Array. The lines of CH3CN (J = 6 – 5, K = 0,1,2,3,4), CH3OH (15-2 ?151 E), HCOOCH3-A (71...We present interferometric observations of the W51 region at 2.7 mm and 3.3 mm with the Berkeley-Illinois-Maryland Association Array. The lines of CH3CN (J = 6 – 5, K = 0,1,2,3,4), CH3OH (15-2 ?151 E), HCOOCH3-A (71,6 – 61,5), HCOOCH3 -E (71,6 – 61,5) and 13CS (2-1) as well as the 2.7 mm continuum toward W51 have been observed. The derived total beam-averaged column densities NT and fractional abundances of CH3CN, CH3OH, HCOOCH3 and 13CS in W51 cores have been obtained.展开更多
基金the National Natural Science Foundation of China(Grant Nos.19973017 and 10133020).
文摘To promote the understanding of massive star formation processes, we have studied the 6.6 GHz methanol (CH3OH) masers and their environments—the dense cores and the outer regions of the molecular cloud. The physics of the CH3OH maser or the thermal emission formation region is studied by fitting the observational data of the 6.6 GHz 51–60A+ and the 107 GHz 31–40A+CH3OH maser emission, using the radiative transfer calculations. The type II characteristics of the 6.6 GHz CH3OH maser are confirmed by the calculation results. A greater intensity of the radiation field leads to an increase in the peak intensity of the maser; however, high densities tend to turn off the maser. The calculation results show that to be a maser the 6.6 GHz CH3OH emission needs a radiation field of 150–300 K and a density not higher than 107cm?3, while the 107 GHz emission requires a radiation field of 210–300 K and a density not higher than 3×106 cm?3. The 6.6 GHz line is maser towards all six studied sources, while the 107 GHz line is maser towards Cep A only. Moreover, the former’s intensity is much stronger than the latter. The radiative transfer calculations also indicate that the 6.6 GHz maser emission is so strong that the requirements of its formation (e.g. the radiation field, the density and the kinetic parameters) can only be satisfied at a certain stage of the processes of the massive star formation. Therefore it is often used as one of the most prominent tracers for the massive star formation regions. The calculation results of the simutaneous observations of (1,1) through (4,4) inversion lines of the ammonia (NH3) indicate that both the temperature and the density in the 6.6 GHz CH3OH maser formation regions are higher than that of the NH3 line formation regions. Furthermore, the common fact of |Visr(CO)| > |Visr(NH3)|>|Visr(CH3OH 6.6GHz maser)| in all six sources implies the ongoing developing trends of those gas flows driven by the masers.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.19973017 and 10373025).
文摘We present interferometric observations of the W51 region at 2.7 mm and 3.3 mm with the Berkeley-Illinois-Maryland Association Array. The lines of CH3CN (J = 6 – 5, K = 0,1,2,3,4), CH3OH (15-2 ?151 E), HCOOCH3-A (71,6 – 61,5), HCOOCH3 -E (71,6 – 61,5) and 13CS (2-1) as well as the 2.7 mm continuum toward W51 have been observed. The derived total beam-averaged column densities NT and fractional abundances of CH3CN, CH3OH, HCOOCH3 and 13CS in W51 cores have been obtained.
