疏散星团Pismis 19的盖亚视差差异及δ Scuti星与造父变星的分离
The Gaia parallax discrepancy for the cluster Pismis 19, and separating $δ$ Scutis from Cepheids
AI总结：
针对疏散星团Pismis 19的盖亚视差与先前距离的分歧，本研究用2MASS红团簇法确定其距离为2.90±0.15千秒差距以验证盖亚零点校正需求，并结合维森海特-莱维特定律的周期断点提出区分δ Scuti星与造父变星的判据。
摘要：
盖亚卫星之前测定的疏散星团Pismis 19的距离与盖亚视差结果存在分歧。因此，我们基于2MASS的JK_s红团簇方法建立了Pismis 19的距离（2.90±0.15千秒差距），这再次证实盖亚视差需要零点校正（如Lindegren等人2021年的研究）。基于DR3自行数据及2MASS+VVV色-星等图中位于拐点附近的位置，OGLE GD-CEP-1864被确认为Pismis 19的成员星。这颗周期为0.3天的变星更可能是δ Scuti星而非经典造父变星。该案例揭示了结合维森海特-莱维特定律中的周期断点（约0.5天）来区分这两类变星的相关判据：断点之前是δ Scuti星，而断点之后主要是首次穿越不稳定带的一阶泛音经典造父变星。
英文摘要：
Pre-Gaia distances for the open cluster Pismis 19 disagree with Gaia parallaxes. A 2MASS $JK_s$ red clump distance was therefore established for Pismis 19 ($2.90\pm0.15$ kpc), which reaffirms that zero-point corrections for Gaia are required (e.g., Lindegren et al.~2021). OGLE GD-CEP-1864 is confirmed as a member of Pismis 19 on the basis of DR3 proper motions, and its 2MASS+VVV color-magnitude position near the tip of the turnoff. That $0^{\rm d}.3$ variable star is likely a $δ$ Scuti rather than a classical Cepheid. The case revealed a pertinent criterion to segregate those two populations in tandem with the break in the Wesenheit Leavitt Law ($\simeq 0^{\rm d}.5$). Just shortward of that period discontinuity are $δ$ Scutis, whereas beyond the break lie first overtone classical Cepheids mostly observed beyond the first crossing of the instability strip.
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