AI 中文总结
本研究提出Gaia发射线星等（GEM）图工具，利用Gaia XP光谱构建Hα伪等值宽度与消光校正绝对星等的关系图，可有效从主序带下方背景恒星中筛选激变变星候选体，为全天巡天的CV统计选择提供更可靠框架。
AI 中文摘要
Gaia DR3为全天巡天中的银河系恒星种群普查，尤其是激变变星（CVs）的证认，打开了新窗口。虽然绝大多数CVs分布在Gaia赫罗图的主序带下方，但在占主导的背景恒星种群中识别它们仍是一项重大挑战。在此，我们提出Gaia发射线星等（GEM）图——一种用于从主序带下方的背景恒星中分离CV候选体的工具。利用Gaia测光数据和低分辨率BP/RP（XP）光谱，我们通过绘制消光校正后的绝对星等（$M_{G0}$）与H$α$线的伪等值宽度（$pgEW_{Hα}$）的关系构建GEM图，其中$pgEW_{Hα}$通过高斯线轮廓近似计算得出。我们发现，已知的CVs和主要的恒星背景种群（包括白矮星、热亚矮星以及白矮星-主序双星）在GEM图上占据不同的区域，这既反映了它们的物理性质，也体现了Gaia XP光谱的低分辨率特性。我们在GEM图上定义了一条经验选择线，用于将真正发射H$α$的CVs与背景污染物区分开。作为概念验证，我们将GEM图应用于距离250 pc以内（$G<17.5$ mag）、分布在主序带下方的Gaia体积限定样本，成功找回了已知的CVs。此外，我们还证认出3个新的CV候选体，其吸积本质得到了存档X射线数据和光学变异性的支持。与传统的基于光学颜色的选择技术相比，GEM图利用Gaia的低分辨率光谱在全天巡天中进行初始目标识别。这为在地面光谱后续观测之前统计性地选择CV候选体提供了更可靠的框架，并且可以扩展到未来的Gaia数据发布，以绘制银河系发射线恒星种群的分布图。
英文摘要
Gaia DR3 opens a new window for the census of Galactic stellar populations in all-sky surveys, specifically for identifying cataclysmic variables (CVs). While the majority of CVs are distributed below the main sequence on the Gaia HR diagram, identifying them among dominant background stellar populations remains a significant challenge. Here, we present the Gaia Emission-line Magnitude (GEM) diagram - a tool designed to isolate CV candidates from background stars located below the main sequence. Using Gaia photometric data and low-resolution BP/RP (XP) spectra, we construct the GEM diagram by plotting the extinction-corrected absolute magnitude ($M_{G0}$) against the pseudo-equivalent width of the H$α$ line ($pgEW_{Hα}$), which is computed via a Gaussian line-profile approximation. We find that known CVs and major stellar background populations, including white dwarfs, hot subdwarfs, and white dwarf-main sequence binaries, occupy distinct regions on the GEM diagram, reflecting both their physical properties and the low-resolution nature of the Gaia XP spectra. We define an empirical selection line on the GEM diagram to separate true H$α$-emitting CVs from background contaminants. As a proof of concept, we apply the GEM diagram to a Gaia volume-limited sample within 250 pc ($G<17.5$ mag) distributed below the main sequence, recovering known CVs. Additionally, we identify three new CV candidates whose accreting nature is supported by archival X-ray data and optical variability. Compared to traditional optical color-based selection techniques, the GEM diagram uses Gaia's low-resolution spectra for initial target identification in all-sky surveys. This provides a more reliable framework for the statistical selection of CV candidates prior to ground-based spectroscopic follow-up and can be scaled to future Gaia data releases to map Galactic emission-line star populations.
Comments17 pages, 10 figures, 1 table. Submitted to OJAp
