Adolfo S. Carvalho, Lynne A. Hillenbrand, Kevin France and Gregory J. Herczeg
{"title":"A Far-ultraviolet-detected Accretion Shock at the Star–Disk Boundary of FU Ori","authors":"Adolfo S. Carvalho, Lynne A. Hillenbrand, Kevin France and Gregory J. Herczeg","doi":"10.3847/2041-8213/ad74eb","DOIUrl":null,"url":null,"abstract":"FU Ori objects are the most extreme eruptive young stars known. Their 4–5 mag photometric outbursts last for decades and are attributed to a factor of up to 10,000 increase in the stellar accretion rate. The nature of the accretion disk-to-star interface in FU Ori objects has remained a mystery for decades. To date, attempts to directly observe a shock or boundary layer have been thwarted by the apparent lack of emission in excess of the accretion disk photosphere down to λ = 2300 Å. We present a new near-ultraviolet and the first high-sensitivity far-ultraviolet (FUV) spectrum of FU Ori. The FUV continuum is detected for the first time and, at λ = 1400 Å, is more than 104 times brighter than predicted by a viscous accretion disk. We interpret the excess as arising from a shock at the boundary between the disk and the stellar surface. We model the shock emission as a blackbody and find that the temperature of the shocked material is TFUV ≈ 16,000 ± 2000 K. The shock temperature corresponds to an accretion flow along the surface of the disk that reaches a velocity of 40 km s−1 at the boundary, consistent with predictions from simulations.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"2024-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"The Astrophysical Journal Letters","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.3847/2041-8213/ad74eb","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
FU Ori objects are the most extreme eruptive young stars known. Their 4–5 mag photometric outbursts last for decades and are attributed to a factor of up to 10,000 increase in the stellar accretion rate. The nature of the accretion disk-to-star interface in FU Ori objects has remained a mystery for decades. To date, attempts to directly observe a shock or boundary layer have been thwarted by the apparent lack of emission in excess of the accretion disk photosphere down to λ = 2300 Å. We present a new near-ultraviolet and the first high-sensitivity far-ultraviolet (FUV) spectrum of FU Ori. The FUV continuum is detected for the first time and, at λ = 1400 Å, is more than 104 times brighter than predicted by a viscous accretion disk. We interpret the excess as arising from a shock at the boundary between the disk and the stellar surface. We model the shock emission as a blackbody and find that the temperature of the shocked material is TFUV ≈ 16,000 ± 2000 K. The shock temperature corresponds to an accretion flow along the surface of the disk that reaches a velocity of 40 km s−1 at the boundary, consistent with predictions from simulations.
FU Ori天体是已知爆发最剧烈的年轻恒星。它们4-5马格的光度爆发持续数十年之久,其原因是恒星吸积速率增加了高达10,000倍。FU Ori天体的吸积盘-恒星界面的性质几十年来一直是个谜。迄今为止,直接观测冲击层或边界层的尝试都因吸积盘光球以下至 λ = 2300 Å 范围内明显缺乏发射而受挫。我们展示了 FU Ori 的新近紫外光谱和首个高灵敏度远紫外(FUV)光谱。我们首次探测到了 FUV 连续波,在 λ = 1400 Å 处,其亮度比粘性吸积盘的预测亮度高 104 倍以上。我们将这一过量解释为来自星盘和恒星表面边界的冲击。我们将冲击发射建模为黑体,发现冲击物质的温度为 TFUV ≈ 16,000 ± 2000 K。冲击温度对应于沿圆盘表面的吸积流,在边界处的速度达到 40 km s-1,与模拟预测一致。