论文标题
437、439、471和474 GHz的亚毫米级水层朝向进化的星星。最高观测和辐射转移建模
Submillimetre water masers at 437, 439, 471, and 474 GHz towards evolved stars. APEX observations and radiative transfer modelling
论文作者
论文摘要
在这里，我们旨在将437、439、471和474 GHz的亚毫米级水层列为进化的恒星样品。 我们使用Atacama Pathfinder实验（APEX）来观察亚毫米级水转变，而CO（4-3）线向11个进化的恒星。样本包括半规则和MIRA变量，以及红色的超级巨星。我们为水层进行了辐射转移模型。我们还使用CO观测来确定恒星的质量损失率。 从11个进化的恒星的样品中，有7个以437、439、471和474 GHz显示了1个或多个MASER。因此，我们发现这些masers在进化的星际信封中很常见。在恒星速度附近检测到maser线的事实表明，它们很可能源自我们目标的内部室内信封。我们暂时将MASER的存在与目标恒星的可变性程度联系起来，也就是说，MASER在MIRA变量中比半规则变量更有可能存在。我们建议这表明强烈冲击在为Masers创造必要条件时的重要性。通常，437 GHz线是此处研究的Maser线最强的线条线。我们无法在辐射转移模型中重现上述发现。通常，我们发现Maser发射对这里研究的线的灰尘温度非常敏感。为了产生强大的maser发射，尘埃温度必须显着低于气体动力学温度。除了运行模型网格以确定这些线路中强质量器的最佳物理条件外，我们还进行了平滑的风模型，我们无法重现观察到的线形。这也表明，masers必须主要源于内部信封。
Here we aim to characterise submillimetre water masers at 437, 439, 471, and 474 GHz towards a sample of evolved stars. We used the Atacama Pathfinder Experiment (APEX) to observe submillimetre water transitions and the CO (4-3) line towards 11 evolved stars. The sample included semi-regular and Mira variables, plus a red supergiant star. We performed radiative transfer modelling for the water masers. We also used the CO observations to determine mass loss rates for the stars. From the sample of 11 evolved stars, 7 display one or more of the masers at 437, 439, 471, and 474 GHz. We therefore find that these masers are common in evolved star circumstellar envelopes. The fact that the maser lines are detected near the stellar velocity indicates that they are likely to originate from the inner circumstellar envelopes of our targets. We tentatively link the presence of masers to the degree of variability of the target star, that is, masers are more likely to be present in Mira variables than in semi-regular variables. We suggest that this indicates the importance of strong shocks in creating the necessary conditions for the masers. Typically, the 437 GHz line is the strongest maser line observed among those studied here. We cannot reproduce the above finding in our radiative transfer models. In general, we find that maser emission is very sensitive to dust temperature in the lines studied here. To produce strong maser emission, the dust temperature must be significantly lower than the gas kinetic temperature. In addition to running grids of models in order to determine the optimum physical conditions for strong masers in these lines, we performed smooth wind modelling for which we cannot reproduce the observed line shapes. This also suggests that the masers must originate predominantly from the inner envelopes.
