Gravitational microlensing, when finite size source effects are relevant, provides an unique tool for the study of source star stellar atmospheres through an enhancement of a characteristic polarization signal. This is due to the differential magnification induced during the crossing of the source star. In this paper we consider a specific set of reported highly magnified, both single and binary exoplanetary systems, microlensing events towards the Galactic bulge and evaluate the expected polarization signal. To this purpose, we consider several polarization models which apply to different types of source stars: hot, late type main sequence and cool giants. As a result we compute the polarization signal P,which goes up to P=0.04% for late type stars and up to a few percent for cool giants, depending on the underlying physical polarization processes and atmosphere model parameters. Given a I band magnitude at maximum magnification of about 12, and a typical duration of the polarization signal up to 1 day, we conclude that the currently available technology, in particular the polarimeter in FORS2 on the VLT, potentially may allow the detection of such signals. This observational programme may take advantage of the currently available surveys plus follow up strategy already routinely used for microlensing monitoring towards the Galactic bulge (aimed at the detection of exoplanets). In particular, this allows one to predict in advance for which events and at which exact time the observing resources may be focused to make intensive polarization measurements.
The Microlensing Event Rate and Optical Depth Toward the Galactic Bulge from MOA-II
We present measurements of the microlensing optical depth and event rate toward the Galactic Bulge based on two years of the MOA-II survey. This sample contains ~1000 microlensing events, with an Einstein Radius crossing time of t_E < 200 days between -5 <l< 10 degree and -7 <b< -1 degree. Our event rate and optical depth analysis uses 474 events with well defined microlensing parameters. In the central fields with |l| < 5 degree, we find an event rates of Γ= [2.39+/-1.1]e^{[0.60 \pm 0.05](3- |b| )}x 10^{-5}/star/yr and an optical depth of τ_{200} = [2.35+/-0.18]e^{[0.51+/-0.07](3- |b| )}x 10^…
Revealing Short-period Exoplanets and Brown Dwarfs in the Galactic Bulge using the Microlensing Xallarap Effect with the \textit{Nancy Grace Roman Space Telescope}
\textit{Nancy Grace Roman Space Telescope}（\textit{ Roman}）将提供大量的微透镜光变曲线，其测光精度比正在进行的地面观测高得多。这样的光变曲线将使我们能够观察到以前难以检测的高阶微透镜效应。在本文中，我们研究了\textit{Roman}利用源星的轨道运动，即所谓的xallarap效应，探测和表征源系统中短周期行星和棕矮星（BD）的潜力。我们分析估计xallarap参数的测量不确定度使用Fisher矩阵分析。我们表明，\textit{Roman}银河系外行星巡天（RGES）可以检测到温暖的彗星质量下降到0.5 $M_{\rm Jup}$和轨道周期为30天，通过xallarap效应。假设由\citet{Cumming+2008}得到的行星频率函数，我们发现在微透镜巡天中，\textit{Roman}将探测到$\sim10$热、暖彗星和$\sim30$近距离黑洞。这些探测很可能伴随着对伴星质量和轨道要素的测量，这将有助于研究银河系凸起中近距离行星和BD种群的物理特性。
An Updated SynthPop Model for Microlensing Simulations I: Model Description & Evaluation
University of California Berkeley（加州大学伯克利分校）；The Ohio State University（俄亥俄州立大学）；Louisiana State University（路易斯安那州立大学）；NASA Jet Propulsion Laboratory（美国宇航局喷气推进实验室）；Space Science Institute（空间科学研究所）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；Institute of Astronomy, University of Cambridge（剑桥大学天文学研究所）
Historic microlensing events in the euclid Galactic Bulge Survey
Università di Salerno（萨莱诺大学）；Istituto Nazionale di Fisica Nucleare, Sezione di Napoli（意大利国家核物理研究所那不勒斯分部）；Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Capodimonte（意大利国家天体物理研究所卡波迪蒙特天文台）；Università degli studi di Napoli Federico II（那不勒斯费德里科二世大学）；Université Marie et Louis Pasteur, CNRS, Institut UTINAM UMR 6213（玛丽与路易·巴斯德大学，法国国家科学研究中心，UTINAM联合研究实验室）；Greenhill Observatory & School of Natural Sciences, University of Tasmania（塔斯马尼亚大学格林山天文台与自然科学学院）；Sorbonne Université, CNRS UMR 7095, Institut d’Astrophysique de Paris（索邦大学，法国国家科学研究中心，巴黎天体物理学研究所）；Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM（巴黎萨克雷大学，巴黎西岱大学，法国原子能和替代能源委员会，法国国家科学研究中心，天体物理信息与测量联合研究实验室）
HAT Discovery of 76 Bright Periodic Variables Toward the Galactic Bulge
本文报道了银河系核球附近147个亮（8<I<13）周期变星的I波段测光观测结果，其中包括76个新发现。2005年，我们使用HATnet望远镜中的一架，在88个夜晚获得了151次曝光，视场为8.4 x 8.4 deg^2，中心约为（l，b）=（1.73，-4.68）。作为微透镜可行性研究的一部分，我们在2005年观察了银河系的隆起（Nataf et al. 2009），在这里我们讨论了我们在数据中发现的周期变量。在我们的发现中，我们计算了52个新的食双星和24个其他周期变量。
Comparing Observed Stellar Kinematics and Surface Densities in a Low Latitude Bulge Field to Galactic Population Synthesis Models
我们提出了一个分析银河核球恒星从哈勃太空望远镜（HST）宽视场相机3（WFC 3）观测的Stanek窗口（l，b=[0.25，-2.15]），从两个时代大约相隔两年。该数据集邻近临时宽视场红外巡天望远镜（WFIRST）微透镜场。在I $\approx$ 21处测量了大约115，000颗V波段低至28等和I波段低至25等的恒星的自行，精度为0.5 mas yr $^{-1}$（20 km s $^{-1}$）。对纵向自行$μ_l$的切割使我们能够分离星盘和球丘星群，并产生只包含球丘的恒星计数，这些恒星计数是根据自行切割的光度完整性和效率进行校正的。在外地的运动分散和表面密度进行比较，附近的SWEEPS视线，发现一个略大于预期的恒星密度梯度。所观察到的球星计数和运动学的贝桑松，银河系和GalMod银河系人口合成模型进行了进一步比较。我们发现，大多数模型低估低质量的隆起星的$\sim$ 33%以下的主序列关闭，并在更红的J和H波段的$\sim$ 70%以上。在考虑银河系模型中的不准确性的同时，我们给出了WFIRST微透镜任务对系外行星产量的影响。
