Common Envelope (CE) systems are the result of Roche lobe overflow in interacting binaries. The subsequent evolution of the CE, its ejection and the formation of dust in its ejecta while the primary is on the Red Giant Branch (RGB), gives rise to a recently identified evolutionary class -- dusty post-RGB stars. Their spectral energy distributions (SEDs) suggest that their mass-ejecta are similar to dusty post-Asymptotic Giant Branch (post-AGB) stars. We have modeled the SEDs of a select sample of post-RGB and post-AGB stars in the Large Magellanic Cloud (LMC), quantified the total dust mass (and gas mass assuming gas-to-dust ratio) in the disks and shells and set constraints on the dust grain compositions and sizes. We find that the shell masses in the post-RGBs are generally less than those in post-AGBs, with the caveat that substantial amount of mass in both types of objects may lie in cold, extended shells. Our models suggest that circumstellar disks, when present, are geometrically thick structures with a substantial opening angle, consistent with numerical simulations of CE evolution (CEE). Comparison of our model dust masses with the predictions of dust production during CEE on the RGB suggest that CEE occurred near or at the tip of the RGB for our post-RGB sources. A surprising result is that some post-RGB stars harbor carbon-rich dust, believed to form when C/O $>$ 1, e.g. following triple-alpha nucleosynthesis and third dredge-up events in AGB stars. This anomaly strengthens the hypothesis that dusty post-RGBs are born in binary systems.
On the formation of subdwarf B stars via engulfment of substellar companions I. Conditions for and occurrence of envelope ejection events
Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège（列日大学空间科学、技术与天体物理研究研究所）；Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles (ULB)（布鲁塞尔自由大学天文与天体物理研究所）
The evolutionary nature of RV Tauri stars in the SMC and LMC
根据它们的恒星参数和由于星周尘埃而存在的中红外过量，金牛座RV星被归类为后AGB星。然而，我们最近的研究揭示了金牛座RV恒星之间的不同SED，这表明它们可能也占据了其他进化通道。本文的目的是提出不同的SED RV金牛星的特点，并调查其演化性质作为其SED的功能。我们在SMC和LMC中对金牛座RV星进行了系统的研究，因为它们的距离和光度是已知的。他们的SED分为三类：灰尘（盘型），非灰尘（非IR）和不确定。周期光度颜色（PLC）的关系进行了校准。PLC的光度与使用SED发现的光度进行了补充，恒星被放置在HR图上。本研究的四个主要结果是：1）金牛座RV星具有明显的IR过剩，具有盘型SED，这表明尘埃被捕获在稳定的盘中。鉴于星系中圆盘型SED和双星之间的紧密联系，我们假设它们也是双星。这些涵盖了一系列的光度，我们认为，更明亮的是后AGB星，而较低的光度可能是后红巨星分支（后RGB）星。2)其中两个天体的平均亮度变化周期分别为916天和850天，这是由轨道运动期间的可变消光造成的。3)没有尘埃的金牛座RV星和具有不确定SED的天体的演化使得星周尘埃已经分散。如果它们是单星，它们是低初始质量的后AGB天体（$<$ 1.25 M $_\odot$），而如果它们是双星，样本中的低光度部分可能是后RGB恒星。4)我们发现带有尘埃的金牛座RV恒星平均比样本的其余部分更明亮。
Two hot pre-white dwarfs inside the red-giant-branch planetary nebula Pa 13 -- Double core evolution or common envelope-induced rejuvenation?
Zentrum für Astronomie der Universität Heidelberg, Landessternwarte（海德堡大学天文中心，兰德斯施特恩瓦尔特）；Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Departamento de Astrofísica, Universidad de La Laguna（拉帕尔马大学天体物理学系）；Department of Physics and Astronomy, Valparaiso University（瓦尔帕莱索大学物理与天文学系）；Instituto de Astrofísica de La Plata, UNLP-CONICET（拉普拉塔天体物理研究所，UNLP-CONICET）；Institut für Physik und Astronomie, Universität Potsdam（波茨坦大学物理与天文学研究所）；Department of Astronomy, University of Geneva（日内瓦大学天文学系）
