[论文解读] Gaia Data Release 3: Properties of the line broadening parameter derived with the Radial Velocity Spectrometer (RVS)

Y. Frémat, F. Royer+39 more|arXiv (Cornell University)|Jun 22, 2022

Stellar, planetary, and galactic studies被引用 4

一句话总结

本文首次对盖亚数据释放3（Gaia DR3）中通过径向速度摄谱仪（RVS）获得的线加宽参数（vbroad）进行了全面分析，测量了从3500 K到14,500 K、视星等达12等的恒星的加宽特性。结果表明，vbroad估计值总体上与其他巡天结果一致，但在高温（>7500 K）和暗星（G_RVS > 10）时存在偏差，主要由于模板不匹配以及氢帕邢线与钙II三重线的混叠所致。

ABSTRACT

The third release of the Gaia catalogue contains the radial velocities for 33,812,183 stars having effective temperatures ranging from 3100 K to 14,500 K. The measurements are based on the comparison of the observed RVS spectrum (wavelength coverage: 846--870 nm, median resolving power: 11,500) to synthetic data broadened to the adequate Along-Scan Line Spread Function. The additional line-broadening, fitted as it would only be due to axial rotation, is also produced by the pipeline and is available in the catalogue (field name gaia_source:vbroad). To describe the properties of the line-broadening information extracted from the RVS and published in the catalogue, as well as to analyse the limitations imposed by the adopted method, wavelength range, and instrument. We use simulations to express the link existing between the line broadening measurement provided in Gaia Data Release 3 and Vsin(i). We then compare the observed values to the measurements published by various catalogues and surveys (GALAH, APOGEE, LAMOST, ...). While we recommend being cautious in the interpretation of the vbroad measurement, we also find a reasonable global agreement between the Gaia Data Release 3 line broadening values and those found in the other catalogues. We discuss and establish the validity domain of the published vbroad values. The estimate tends to be overestimated at the lower vsini end, and at $T_\mathrm{eff}>7500\,\mathrm{K}$ its quality and significance degrade rapidly when $G_\mathrm{RVS}>10$. Despite all the known and reported limitations, the Gaia Data Release 3 line broadening catalogue contains the measurements obtained for 3,524,677 stars with $T_\mathrm{eff}$\ ranging from 3500 to 14,500 K, and $G_\mathrm{RVS}<12$. It gathers the largest stellar sample ever considered for the purpose, and allows a first mapping of the \Gaia\ line broadening parameter across the HR diagram.

研究动机与目标

• 对盖亚径向速度摄谱仪（RVS）在数据释放3中推导出的线加宽参数（vbroad）的特性与可靠性进行表征。
• 识别vbroad测量中的系统性偏差，特别是高温和暗星目标中的偏差。
• 评估光谱模板不匹配（尤其是对热星）对vbroad估计精度的影响。
• 通过光谱变异性与轮廓畸变，评估未分辨双星对vbroad测量的影响。
• 通过定义vbroad与Vsin i一致的区域，为用户提供vbroad值可靠性的指导。

提出的方法

• vbroad参数通过在整个RVS波长范围（847–874 nm）内计算互相关函数（CCF）获得，整合了合成光谱未捕捉到的加宽效应。
• 该方法使用单一全局CCF来估计总线加宽，包括Vsin i、大尺度湍流和仪器效应的贡献。
• 通过与外部巡天和汇编数据的比较，验证vbroad值的一致性并识别差异。
• 通过视觉检查RVS光谱（特别是疑似双星的主序星）评估光谱质量和变异性。
• 利用颜色-星等图和赫罗图分布，量化温度、星等和金属丰度对vbroad准确度的影响。
• 通过分析有效温度和G_RVS星等的依赖关系，评估vbroad对模板不匹配的敏感性。

实验结果

研究问题

• RQ1 在完整的恒星温度和星等范围内，从盖亚DR3 RVS数据推导出的vbroad测量值的准确性和精确度如何？
• RQ2 vbroad估计中的主要偏差来源是什么，特别是在热星（T_eff > 7500 K）和暗星目标（G_RVS > 10）中？
• RQ3 未分辨双星系统在多大程度上导致了虚假或被放大的vbroad值？
• RQ4 光谱模板的选择在多大程度上影响vbroad测量值，特别是当模板金属丰度与观测恒星不匹配时？
• RQ5 在赫罗图的哪些区域，vbroad可被可靠地解释为Vsin i的代理？

主要发现

• 盖亚DR3的vbroad星表提供了迄今为止最大规模的同质化线加宽调查，覆盖至12等星等，温度范围从3500 K到14,500 K。
• 对于温度高于7500 K的恒星，vbroad的准确度和精确度随星等增加而迅速下降，尤其在G_RVS > 10时更为显著，主要由于帕邢线与钙II三重线的混叠。
• 在G_BP - G_RP为1.1–1.4范围内的主序星中，有17%的恒星在后处理清洗后仍存在残余的vbroad估计值，表明未分辨双星的持续污染。
• 未分辨双星的光谱变异性与轮廓畸变导致vbroad的统计性高估，经RVS光谱的视觉检查已得到证实。
• 赫罗图显示，vbroad的中位数变化与冷星（约F5型）的磁制动效应一致，但也提示模板拟合过程中存在金属丰度不匹配的影响。
• 表3提供了vbroad值可与Vsin i保持一致的可靠区域，尤其适用于T_eff < 7500 K且G_RVS ≤ 10的恒星。