标题： 原行星状星云中的变化性：IX. 十年间演化的证据 显示英文标题

标题： Variability in Protoplanetary Nebulae: IX. Evidence for Evolution in a Decade

摘要： 我们对12个原行星 nebulae（处于恒星演化从AGB到PN阶段的短暂过渡期的天体）进行了新的测光V,Rc研究。这些天体之前曾被研究过，使用的是1994年至2007年的数据，发现这12个天体都具有周期性变化，脉动周期范围约为38至150天。它们都是富碳星，光谱类型为F-G型。我们将我们的新数据（2008-2018年）与公开可用的ASAS-SN数据相结合，并确定了它们变异性新的周期。较旧和较新的周期值被比较以调查周期变化的证据，理论支持在某些情况下这种变化可能在十年左右的时间内被检测到。由于光变曲线复杂，包含多个周期、振幅变化以及冲击证据，这种检测具有挑战性。然而，我们发现了其中一个，甚至可能是两个这样的案例，这些案例与样本中较高温度的恒星（7250和8000K）相关联。这些结果最符合质量范围下限处碳星的演化，约1.5-2太阳质量。有几个恒星显示出长期亮度增加（六例）或减少（一例）的趋势，我们认为这很可能是因为周围尘埃消光的变化。除了较短的脉动外，还有一个可能的~1.8年周期的情况。这被解释为可能存在的伴星轨道证据。 显示英文摘要

摘要： We have carried out a new photometric V,Rc study of 12 protoplanetary nebulae, objects in the short-lived transition between the AGB and PN phases of stellar evolution. These had been the subjects of an earlier study, using data from 1994-2007, that found that all 12 varied periodically, with pulsation periods in the range of ~38 to ~150 days. They are all carbon-rich, with F-G spectral types. We combined our new (2008-2018) data with publicly-available ASAS-SN data and determined new periods for their variability. The older and newer period values were compared to investigate evidence of period change, for which there is theoretical support that it might be detectable in a decade or two in some cases. Such a detection is challenging since the light curves are complicated, with multiple periods, changing amplitudes, and evidence of shocks. Nevertheless, we found one, and possibly two, such cases, which are associated with the higher temperature stars in the sample (7250 and 8000 K). These results are most consistent with the evolution of stars at the lower end of the mass range of carbon stars, ~1.5-2 M(sun). Several of the stars show longer-term trends of increasing (six cases) or decreasing (one case) brightness, which we think most likely due to changes in the circumstellar dust opacity. There is one case of a possible ~1.8 yr period in addition to the shorter pulsation. This is interpreted as possible evidence of an orbiting companion.