Searching for Planets Orbiting Fomalhaut with JWST

We report observations with the JWST/NIRCam coronagraph of the Fomalhaut (α PsA) system. This nearby A star hosts a complex debris disk system discovered by the IRAS satellite. Observations in F444W and F356W filters using the round 430R mask achieve a contrast ratio of ∼4 × 10−7 at 1′′ and ∼4 × 10−8 outside of 3′′. These observations reach a sensitivity limit of <1 MJup across most of the disk region. Consistent with the hypothesis that Fomalhaut b is not a massive planet but is a dust cloud from a planetesimal collision, we do not detect it in either F356W or F444W (the latter band where a Jovian-sized planet should be bright). We have reliably detected 10 sources in and around Fomalhaut and its debris disk, all but one of which are coincident with Keck or Hubble Space Telescope sources seen in earlier coronagraphic imaging; we show them to be background objects, including the “Great Dust Cloud” identified in Mid-Infrared Instrument (MIRI) data. However, one of the objects, located at the edge of the inner dust disk seen in the MIRI images, has no obvious counterpart in imaging at earlier epochs and has a relatively red [F356W]–[F444W] > 0.7 mag (Vega) color. Whether this object is a background galaxy, brown dwarf, or a Jovian-mass planet in the Fomalhaut system will be determined by an approved Cycle 2 follow- up program. Finally, we set upper limits to any scattered light from the outer ring, placing a weak limit on the dust albedo at F356W and F444W.

我们报告了利用詹姆斯·韦伯空间望远镜近红外相机（JWST/NIRCam）日冕仪（coronagraph）对北落师门（Fomalhaut，α PsA）系统的观测结果。这颗邻近的A型恒星拥有由红外天文卫星（IRAS）发现的复杂碎片盘（debris disk）系统。使用圆形430R掩模、通过F444W和F356W滤光片进行的观测，在1角秒处达到约4×10⁻⁷的对比度，在3角秒以外则达到约4×10⁻⁸的对比度。这些观测在盘区的大部分区域达到了<1倍木星质量（MJup）的灵敏度极限。与北落师门b并非大质量行星、而是星子碰撞产生的尘埃云这一假设一致，我们在F356W或F444W滤光片中均未探测到它（后者波段下类木星大小的行星本应明亮）。我们在北落师门及其碎片盘内部和周围可靠地探测到10个源，其中除一个外，其余均与凯克望远镜或哈勃空间望远镜早期日冕仪成像中观测到的源重合；我们证实这些源为背景天体，包括中红外仪器（MIRI）数据中识别出的‘大尘埃云’。最后，我们对来自外环的所有散射光设定了上限，从而对F356W和F444W波段下的尘埃反照率施加了一个较弱的限制。