Bujarrabal V, Castro-Carrizo A, Van Winckel H, Alcolea J, Sánchez Contreras C, Santander-García M, Hillen M
Observatorio Astronómico Nacional (OAN-IGN), Apartado 112, E-28803 Alcalá de Henares, Spain.
Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406, Saint Martin d'Hères, France.
Astron Astrophys. 2017 Jun 1;614. doi: 10.1051/0004-6361/201732422.
In order to study the effects of rotating disks in the post-asymptotic giant branch (post-AGB) evolution, we observe a class of binary post-AGB stars that seem to be systematically surrounded by equatorial disks and slow outflows. Although the rotating dynamics had only been well identified in three cases, the study of such structures is thought to be fundamental to the understanding of the formation of disks in various phases of the late evolution of binary stars and the ejection of planetary nebulae from evolved stars.
We present ALMA maps of CO and CO =3-2 lines in the source IRAS 08544-4431, which belongs to the above mentioned class of objects. We analyzed the data by means of nebula models, which account for the expectedly composite source and can reproduce the data. From our modeling, we estimated the main nebula parameters, including the structure and dynamics and the density and temperature distributions. We discuss the uncertainties of the derived values and, in particular, their dependence on the distance.
Our observations reveal the presence of an equatorial disk in rotation; a low-velocity outflow is also found, probably formed of gas expelled from the disk. The main characteristics of our observations and modeling of IRAS 08544-4431 are similar to those of better studied objects, confirming our interpretation. The disk rotation indicates a total central mass of about 1.8 , for a distance of 1100 pc. The disk is found to be relatively extended and has a typical diameter of ~ 4 10 cm. The total nebular mass is ~ 2 10, of which ~ 90% corresponds to the disk. Assuming that the outflow is due to mass loss from the disk, we derive a disk lifetime of ~ 10000 yr. The disk angular momentum is found to be comparable to that of the binary system at present. Assuming that the disk angular momentum was transferred from the binary system, as expected, the high values of the disk angular momentum in this and other similar disks suggest that the size of the stellar orbits has significantly decreased as a consequence of disk formation.
为了研究旋转盘在渐近巨星分支后（后渐近巨星分支，post-AGB）演化中的作用，我们观测了一类似乎被赤道盘和缓慢外流系统环绕的双星后渐近巨星分支恒星。尽管旋转动力学仅在三个案例中得到明确识别，但对这类结构的研究被认为是理解双星后期演化各阶段盘的形成以及演化恒星抛出行星状星云的基础。
我们展示了源IRAS 08544 - 4431中CO和CO =3 - 2线的阿塔卡马大型毫米/亚毫米波阵列（ALMA）地图，该源属于上述类别。我们通过星云模型分析数据，该模型考虑了预期的复合源并能重现数据。通过我们的建模，我们估计了主要星云参数，包括结构和动力学以及密度和温度分布。我们讨论了导出值的不确定性，特别是它们对距离的依赖性。
我们的观测揭示了一个旋转的赤道盘的存在；还发现了一个低速外流，可能由从盘中喷出的气体形成。我们对IRAS 08544 - 4431的观测和建模的主要特征与研究更充分的天体相似，证实了我们的解释。对于1100秒差距的距离，盘的旋转表明总中心质量约为1.8 。发现盘相对延伸，典型直径约为4×10厘米。星云总质量约为2×10，其中约90%对应于盘。假设外流是由于盘的质量损失造成的，我们得出盘的寿命约为10000年。发现盘的角动量目前与双星系统的角动量相当。假设盘的角动量如预期那样从双星系统转移而来，该盘和其他类似盘中盘角动量的高值表明由于盘的形成恒星轨道大小显著减小。
