Optical-infrared interferometry can provide direct geometrical measurements of the radii of Cepheids and/or reveal unknown binary companions of these stars. Such information is of great importance for a proper calibration of Period-Luminosity relations and for determining binary fraction among Cepheids. We observed the Cepheid X Sgr with VLTI/AMBER in order to confirm or disprove the presence of the hypothesized binary companion and to directly measure the mean stellar radius, possibly detecting its variation along the pulsation cycle. From AMBER observations in MR mode we performed a binary model fitting on the closure phase and a limb-darkened model fitting on the visibility. Our analysis indicates the presence of a point-like companion at a separation of 10.7 mas and 5.6 magK fainter than the primary, whose flux and position are sharply constrained by the data. The radius pulsation is not detected, whereas the average limb-darkened diameter results to be 1.48+/-0.08 mas, corresponding to 53+/-3 R_sun at a distance of 333.3 pc.
Cepheids with giant companions. I. Revealing a numerous population of double-lined binary Cepheids
经典造父变星的质量为3至11 M $\odot$的理论预测，但那些测量，在3.6和5 M $\odot$之间的集群。因此，它们的质量-光度关系受到很差的约束，阻碍了我们对基本恒星物理和莱维特定律的理解。所有造父变星的质量都来自对11个双星系统的分析，其中只有5个是双线的，非常适合精确的动力学质量测定。我们提出了一个项目来分析一个新的，众多的造父变星在双线二进制（SB 2）系统提供质量测定在一个很宽的质量区间，并研究它们的演变。我们分析了一个样本的41个候选二进制LMC造父变星沿P-L关系，这可能是伴随着发光的红巨星，并提出间接和直接的指标，他们的二进制。在光谱研究的子样本的18个最明亮的候选人，为16个我们检测到线的两个组成部分的光谱，已经翻两番的造父变星的数量在SB 2系统。因此，对整个样本的观测可能会使目前所有的造父变星质量估计值增加四倍。对于我们的大多数候选人，不稳定的固有周期变化占主导地位的光旅行时间的影响，由于二进制。然而，后者可以解释四颗造父变星的周期性相位调制。我们的项目为LMC，银河系和其他星系中造父变星的未来精确动力学质量测定铺平了道路，这将有可能增加已知造父变星质量的数量，甚至是10倍，极大地提高了我们对这些重要恒星的了解。
The VELOCE modulation zoo III. Detecting additional pulsation modes in optical spectra of classical Cepheids using semi-partial distance correlation periodograms
Discovery of an Extremely Luminous Type II Cepheid in the Andromeda Giant Stellar Stream: Evidence for a Hierarchical Triple with an Inner Binary Merger
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Astronomy and Space Science, University of the Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；South-Western Institute for Astronomy Research, Yunnan University（云南大学西南天文研究所）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿天文与天体物理研究所）；School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）
A solution to the paradox of youth in the Galactic centre
Universidade de Coimbra（科英布拉大学）；Universidade do Porto（波尔图大学）；Universidade de Lisboa（里斯本大学）；Observatoire de Paris, Université PSL, Sorbonne Université（巴黎天文台，巴黎文理研究大学，索邦大学）；University of Amsterdam（阿姆斯特丹大学）
