A new window for magnetic activity on Ultracool dwarfs: eROSITA & a synergistic multiwavelength approach

超冷矮星磁活动的新窗口：eROSITA

• 批准号: 456967955
• 负责人: Professorin Dr. Beate Stelzer
• 金额: --
• 依托单位: Abteilungen Astronomie und Hochenergieastrophysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/456967955?language=en
• 关键词: new; window; magnetic; activity; Ultracool

Ultracool dwarfs (UCDs) are defined as objects with spectral type M7 and later. This group spans the hydrogen-burning mass limit (at ~ 0.07 solar masses) and it comprises both very low-mass stars and brown dwarfs. The term UCD avoids misnoming as the mass of such objects is unknown in most cases and, therefore, for a given UCD it is unclear if it is able to burn hydrogen and thus whether it is a star or a brown dwarf.As a result of their faintness the study of magnetic activity on UCDs has advanced only duringthe last ~15 yrs. This uncovered a puzzling behavior: the activity of UCDs might be characterized by a transition from stellar-like (X-ray flaring and radio-faint) to planetary-like (radio-bursting and X-ray faint) magnetic processes. The physical origin of these differences has not yet been identified but the magnetic field strength and morphology that is probably ruled by the rotation rate likely plays a major role. Verifying or refuting the previous evidence for the dichotomy of magnetic activity near the substellar boundary and systematically searching for its origin through a comprehensive multi-wavelength study is the aim of this project. The advent of the (nearly) all-sky space missions eROSITA and TESS opens a new window to UCDs, providing for the first time statistical samples of coronal X-ray emission and photospheric optical activity measures and surface rotation periods. eROSITA will increase the number of X-ray detected UCDs by at least a factor of 10 and it will enable a systematic study of flare variability thanks to its multi-epoch data (8 visits over 4 years). TESS provides optical flares and rotation periods that -- according to previous studies -- appear to be crucial for determining the type of activity in UCDs. This will be complemented by an in-depth study of UCDs for which the applicant of this funding request has collected multi-wavelength observations of all critical parameters for activity (X-rays, radio and rotation). Such extremely high sensitivity observations with XMM-Newton and the JVLA for a carefully selected sample of UCDs with TESS rotation periods is crucial for unvealing the origin of the transition in the activity behavior.

超冷矮星（UCDs）被定义为光谱型为M7及以上的天体。这个群体跨越了氢燃烧质量的极限（约0.07太阳质量），它包括非常低质量的恒星和褐矮星。UCD这个术语避免了误命名，因为在大多数情况下，这类天体的质量是未知的，因此，对于一个给定的UCD，我们不清楚它是否能够燃烧氢，因此它是一颗恒星还是一颗褐矮星。由于它们的模糊性，对ucd上磁活动的研究直到最近15年才取得进展。这揭示了一个令人困惑的行为：ucd的活动可能以从类恒星（x射线耀斑和射电微弱）到类行星（射电爆发和x射线微弱）磁过程的转变为特征。这些差异的物理起源尚未确定，但磁场强度和形态可能是由自转速率决定的，可能起着主要作用。通过全面的多波长研究，验证或驳斥以往关于亚恒星边界附近磁活动二分法的证据，系统地寻找其起源是本项目的目的。（几乎）全天空空间任务eROSITA和TESS的出现为ucd打开了一个新的窗口，首次提供了日冕x射线发射和光球光学活性测量和表面旋转周期的统计样本。eROSITA将使x射线探测到的ucd数量增加至少10倍，并且由于其多历元数据（4年8次访问），它将使耀斑变化的系统研究成为可能。根据之前的研究，TESS提供了光学耀斑和旋转周期，这似乎是确定ucd活动类型的关键。这将由对ucd的深入研究补充，为此，本资助申请的申请人收集了活动的所有关键参数（x射线，无线电和旋转）的多波长观测。利用XMM-Newton和JVLA对具有TESS旋转周期的精心挑选的ucd样本进行如此高灵敏度的观测，对于揭示活动行为转变的起源至关重要。