Paving the Road to the Habitable Worlds Observatory with High-Resolution Imaging I: New and Archival Speckle Observations of Potential HWO Target Stars

One of the key goals of the Habitable Worlds Observatory (HWO) is to directly image about 25 potentially habitable exoplanets and determine their properties. This challenge will require a large survey of nearby, bright stars –∼100 according to the Astro2020 Decadel Survey. To ensure the success of the mission and to help guide design decisions, the stellar multiplicity of the target stars must be well-understood. To this end, we present optical speckle imaging of stars in the NASA Exoplanet Exploration Program (ExEP) provisional HWO star list, which is currently the Tier 1 target list for the HWO Target Stars and Systems Sub-Working Group. We obtained new observations using ‘Alopeke and Zorro at Gemini Observatory and queried the Exoplanet Follow-up Observing Program Archive for archival observations, resulting in speckle imaging data for 80 of the 164 stars. We confirmed one candidate companion detected previously by Gaia (HD 90089) and obtained an ambiguous detection of a known companion (HD 212330). To examine our sensitivity to companions, we simulated stellar companions down to∼ 0.1M⊙ for each target and found that 75%-85% would be detected in our speckle images; the remaining simulated companions are either too faint or too close-in, and will require follow-up using other methods such as long-term spectroscopic measurements and space-based techniques. This work represents a first step towards surveying potential HWO targets for close-in stellar companions and helping to inform the target selection process for the HWO direct-imaging survey, bringing us closer towards the discovery of potential habitable worlds.

宜居世界天文台（Habitable Worlds Observatory, HWO）的核心目标之一，是直接成像约25颗潜在宜居系外行星并测定其属性。要完成这一任务，需要对附近明亮恒星开展大规模巡天——根据《天文2020十年巡天》（Astro2020 Decadel Survey），该巡天的目标恒星数量约为100颗。为保障任务成功并辅助指导设计决策，必须充分了解目标恒星的恒星多重性特征。为此，我们针对美国国家航空航天局系外行星探索计划（NASA Exoplanet Exploration Program, ExEP）的暂定HWO恒星列表开展了光学散斑成像观测；该列表目前为HWO目标恒星与系统子工作组的一级目标列表。我们使用双子座天文台（Gemini Observatory）的阿洛佩克（‘Alopeke）与佐罗（Zorro）设备获取了新观测数据，并检索了系外行星后续观测计划档案库以获取归档观测结果，最终为164颗恒星中的80颗获得了散斑成像数据。我们验证了盖亚（Gaia）此前探测到的一颗候选伴星（HD 90089），并对已知伴星HD 212330得到了模棱两可的探测结果。为评估我们对伴星的探测灵敏度，我们为每颗目标恒星模拟了质量低至0.1倍太阳质量的恒星伴星，并发现75%至85%的模拟伴星可在我们的散斑成像中被探测到；剩余的模拟伴星要么亮度不足，要么轨道距离过近，需要采用长期光谱测量、天基技术等其他方法开展后续观测。本研究为针对HWO潜在目标开展近距离恒星伴星巡天迈出了第一步，有助于为HWO直接成像巡天的目标选择流程提供参考，进一步拉近了我们发现潜在宜居行星的距离。