寻找MWC758周围的H $_α$发射源：SPHERE/ZIMPOL高对比度成像
Searching for H$_α$ emitting sources around MWC758: SPHERE/ZIMPOL high-contrast imaging
摘要：
MWC 758是一颗被过渡盘包围的年轻恒星。最近，通过高分辨率的$L'$波段观测，在MWC 758周围发现了一颗原行星候选者。候选者位于盘腔内，距离中心恒星$\sim$ 111质量，平均位置角为$\sim$ 165.5度。我们在甚大望远镜（VLT）上使用SPHERE/ZIMPOL对MWC 758在H $_α$线和相邻连续谱线上进行了同步自适应光学观测。我们的目标是通过光谱角微分成像观测来探测吸积的原行星候选者。数据分析未揭示靶周围的任何H $_α$信号。在B_Ha滤波器中导出的对比度曲线使我们能够在111质量时导出5 $σ$的上限$\sim$ 7.6等，这是先前探测到的行星候选者的分离。这种对比转换成111质量的H $_α$线光度为$L_{\rm H_α}\lesssim$ 5 $\times$ 10 $^{-5}$ $L_{\odot}$，吸积光度为$L_{acc} <$ 3.7 $\times$ 10 $^{-4}\,L_{\odot}$。对于MWC 758 b的预测质量范围，0.5-5 $M_{\rm Jup}$，这意味着$\dot M \lesssim$ 3.4 $\times$（10 $^{-8}$-10 $^{-9})\,M_{\odot}/yr$，平均行星半径为1.1 $R_{\rm Jup}$。因此，我们的估计是一致的吸积环行星吸积模型的预测$R_{\rm in} = 1 R_{\rm Jup}$。在任何情况下，在ZIMPOL图像中没有检测到任何H $_α$发射源，这不允许我们揭示$L'$检测源的真实性质。
英文摘要：
MWC758 is a young star surrounded by a transitional disk. Recently, a protoplanet candidate has been detected around MWC758 through high-resolution $L'$-band observations. The candidate is located inside the disk cavity at a separation of $\sim$111 mas from the central star, and at an average position angle of $\sim$165.5 degrees. We have performed simultaneous adaptive optics observations of MWC758 in the H$_α$ line and the adjacent continuum using SPHERE/ZIMPOL at the Very Large Telescope (VLT). We aim at detecting accreting protoplanet candidates through spectral angular differential imaging observations. The data analysis does not reveal any H$_α$ signal around the target. The derived contrast curve in the B_Ha filter allows us to derive a 5$σ$ upper limit of $\sim$7.6 mag at 111 mas, the separation of the previously detected planet candidate. This contrast translates into a H$_α$ line luminosity of $L_{\rm H_α}\lesssim$ 5$\times$10$^{-5}$ $L_{\odot}$ at 111 mas, and an accretion luminosity of $L_{acc} <$3.7$\times$10$^{-4}\,L_{\odot}$. For the predicted mass range of MWC758b, 0.5-5 $M_{\rm Jup}$, this implies accretion rates of $\dot M \lesssim$ 3.4$\times$(10$^{-8}$-10$^{-9})\,M_{\odot}/yr$, for an average planet radius of 1.1 $R_{\rm Jup}$. Therefore, our estimates are consistent with the predictions of accreting circumplanetary accretion models for $R_{\rm in} = 1 R_{\rm Jup}$. In any case, the non-detection of any H$_α$ emitting source in the ZIMPOL images does not allow us to unveil the true nature of the $L'$ detected source.
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