We present a statistical analysis of 482 6.7 GHz methanol maser sources from the available literature, on their maser emission and the characteristics of their associated infrared sources. On the color-color diagram, ...We present a statistical analysis of 482 6.7 GHz methanol maser sources from the available literature, on their maser emission and the characteristics of their associated infrared sources. On the color-color diagram, more than 70% of the objects fall within a very small region (0.57 ≤ [25-12] ≤ 1.30 and 1.30 ≤ [60-12] ≤ 2.50). This suggests that 6.7 GHz methanol maser emission occurs only within a very short evolutionary phase during the earliest stage of star formation. The velocity ranges of the masers belong to two main groups: one from 1 to 10 km s<SUP>?1</SUP>, and one from about 11 to 20 km s<SUP>?1</SUP>. These velocity ranges indicate that the masers are probably associated with both disks and outflows. The correlations between the maser and infrared flux densities, and between the maser and infrared luminosities, suggest that far-infrared radiation is a possible pumping mechanism for the masers which most probably originate from some outer molecular envelopes or disks.展开更多
We present multi-frequency, high resolution, radio structures of NRAO 150 with VLBA and EVN array respectively, both of which show a very collimated one-sided jet structure beyond an angular distance of 80 mas. Model ...We present multi-frequency, high resolution, radio structures of NRAO 150 with VLBA and EVN array respectively, both of which show a very collimated one-sided jet structure beyond an angular distance of 80 mas. Model fitting is performed for observations at 2.3 GHz and 8.4 GHz which reveal the source to be consisting of several components at position angle -30°. According to the light curves at 4.8 GHz, 8.0 GHz and 14.5 GHz an outburst is currently occurring in its rising stage, which suggests that a new component is probably in the course of forming. Spectral analysis reveals that the new component probably has a higher spectral index. The maximum proper motion of -0.46 mas yr-1 is expected if we suppose that the new component is moving away from core at the beginning of the flaring.展开更多
基金Supported by the National Natural Science Foundation of China.
文摘We present a statistical analysis of 482 6.7 GHz methanol maser sources from the available literature, on their maser emission and the characteristics of their associated infrared sources. On the color-color diagram, more than 70% of the objects fall within a very small region (0.57 ≤ [25-12] ≤ 1.30 and 1.30 ≤ [60-12] ≤ 2.50). This suggests that 6.7 GHz methanol maser emission occurs only within a very short evolutionary phase during the earliest stage of star formation. The velocity ranges of the masers belong to two main groups: one from 1 to 10 km s<SUP>?1</SUP>, and one from about 11 to 20 km s<SUP>?1</SUP>. These velocity ranges indicate that the masers are probably associated with both disks and outflows. The correlations between the maser and infrared flux densities, and between the maser and infrared luminosities, suggest that far-infrared radiation is a possible pumping mechanism for the masers which most probably originate from some outer molecular envelopes or disks.
基金which is supported by the National Natuxal Science Foundation the by funds of University of MichiganThe work is suppo
文摘We present multi-frequency, high resolution, radio structures of NRAO 150 with VLBA and EVN array respectively, both of which show a very collimated one-sided jet structure beyond an angular distance of 80 mas. Model fitting is performed for observations at 2.3 GHz and 8.4 GHz which reveal the source to be consisting of several components at position angle -30°. According to the light curves at 4.8 GHz, 8.0 GHz and 14.5 GHz an outburst is currently occurring in its rising stage, which suggests that a new component is probably in the course of forming. Spectral analysis reveals that the new component probably has a higher spectral index. The maximum proper motion of -0.46 mas yr-1 is expected if we suppose that the new component is moving away from core at the beginning of the flaring.
