标题： HAT-P-57b：通过多普勒断层扫描确认的绕明亮快速旋转A8V恒星运行的短周期巨行星 显示英文标题

标题： HAT-P-57b: A Short-Period Giant Planet Transiting A Bright Rapidly Rotating A8V Star Confirmed Via Doppler Tomography

摘要： 我们报告了HAT-P-57b的发现，这是一颗公转周期为2.4653天的凌星行星，围绕一颗视星等为V = 10.465 ± 0.029，有效温度Teff = 7500 ± 250 K的主序A8V型恒星运行，其投影自转速度为v sin i = 102.1 ± 1.3 km s^-1。 我们测量了该行星半径为R = 1.413 ± 0.054 RJ，基于视向速度观测，我们以95%置信度给出了其质量上限为M < 1.85 MJ。 根据理论恒星演化模型，宿主恒星的质量和半径分别为1.47 ± 0.12 Msun和1.500 ± 0.050 Rsun。 Keck-I/HIRES在部分凌星事件期间进行的光谱观测显示了HAT-P-57b的多普勒阴影在HAT-P-57平均光谱线轮廓上移动，确认该目标为一个行星系统。 我们利用这些观测数据，结合我们推导出的用于分析光谱线变形的解析公式，确定了HAT-P-57自转轴与HAT-P-57b轨道轴之间的投影夹角。 数据允许两种可能的解，在95%置信度下，λ的角度范围为-16.7° < λ < 3.3° 或 27.6° < λ < 57.4°，且两种模式的相对概率分别为26%和74%。 MMT/Clio2的自适应光学成像揭示了距离HAT-P-57 2.7"处的一个由两个相隔0.22"的点源组成的物体。 伴星的H和L波段星等与它们物理关联于HAT-P-57一致，在这种情况下，它们的质量分别为0.61 ± 0.10 Msun和0.53 ± 0.08 Msun。 HAT-P-57是目前已知自转最快的恒星，也是第四颗已知拥有凌星行星的主序A型恒星。 显示英文摘要

摘要： We present the discovery of HAT-P-57b, a P = 2.4653 day transiting planet around a V = 10.465 +- 0.029 mag, Teff = 7500 +- 250 K main sequence A8V star with a projected rotation velocity of v sin i = 102.1 +- 1.3 km s^-1. We measure the radius of the planet to be R = 1.413 +- 0.054 R_J and, based on RV observations, place a 95% confidence upper limit on its mass of M < 1.85 M_J . Based on theoretical stellar evolution models, the host star has a mass and radius of 1.47 +- 0.12 M_sun, and 1.500 +- 0.050 R_sun, respectively. Spectroscopic observations made with Keck-I/HIRES during a partial transit event show the Doppler shadow of HAT-P-57b moving across the average spectral line profile of HAT-P- 57, confirming the object as a planetary system. We use these observations, together with analytic formulae that we derive for the line profile distortions, to determine the projected angle between the spin axis of HAT-P-57 and the orbital axis of HAT-P-57b. The data permit two possible solutions, with -16.7 deg < lambda < 3.3 deg or 27.6 deg < lambda < 57.4 deg at 95% confidence, and with relative probabilities for the two modes of 26% and 74%, respectively. Adaptive optics imaging with MMT/Clio2 reveals an object located 2.7" from HAT-P-57 consisting of two point sources separated in turn from each other by 0.22". The H and L -band magnitudes of the companion stars are consistent with their being physically associated with HAT-P-57, in which case they are stars of mass 0.61 +- 0.10 M_sun and 0.53 +- 0.08 M_sun. HAT-P-57 is the most rapidly rotating star, and only the fourth main sequence A star, known to host a transiting planet.