We present the discoveries of three faint companions to young stars in the Scorpius-Centaurus region, imaged with the NICI instrument on Gemini South. We have confirmed all three companions through common proper motion tests. Follow-up spectroscopy has confirmed two of them, HIP 65423 B and HIP 65517 B, to be brown dwarfs, while the third, HIP 72099 B, is more likely a very low-mass star just above the hydrogen burning limit. The detection of wide companions in the mass range of ~40--100 Mjup complements previous work in the same region, reporting detections of similarly wide companions with lower masses, in the range of ~10--30 Mjup. Such low masses near the deuterium burning limit have raised the question of whether those objects formed like planets or stars. The existence of intermediate objects as reported here could represent a bridge between lower-mass companions and stellar companions, but in any case demonstrate that mass alone may not provide a clear-cut distinction for the formation of low-mass companions to stars.
New members of the TW Hydrae Association and two accreting M-dwarfs in Scorpius-Centaurus
我们报告了在寻找30-40万年前的Octans协会新成员时发现的几颗年轻的中M星的偶然发现。只有一颗恒星可能被认为是Octans（近）成员。然而，这两颗恒星的自行、运动学距离、径向速度、测光和Li I 6708 AA的测量结果与800万至1000万年前的长蛇座TW星协成员一致。另一个可能是长蛇座TW的外围成员，但其速度与Octans成员的预测相似。我们还确定了邻近的天蝎座-半人马座OB协会（Sco-Cen）的两个新的富锂成员。两者都表现出大的12和22微米的过剩和强大的，可变的H-α发射，我们归因于吸积从拱盘。这样的恒星被认为在Sco-Cen的1600万年中位年龄是非常罕见的，它们只加入了上天蝎座之外的一个其他确认的M型和三个更高质量的吸积物。偶然发现的两颗吸积恒星承载着大量的星周物质，可能表明斯科-岑的年龄分布相当大，或者进一步证明在低质量恒星周围，圆盘分散和行星形成的时间尺度更长。为了帮助未来的研究Sco-Cen，我们还提供了一个新编制的目录305早期型依巴谷成员的光谱径向速度来源于文献。
The nearest region of massive star formation - the Scorpius-Centaurus OB2 association (Sco-Cen) - is a local laboratory ideally suited to the study of a wide range of astrophysical phenomena. Precision astrometry from the Gaia mission has expanded the census of this region by an order of magnitude. However, Sco-Cen's vastness and complex substructure make kinematic analysis of its traditional three regions, Upper Scorpius, Upper Centaurus-Lupus and Lower Centaurus-Crux, challenging. Here we use Chronostar, a Bayesian tool for kinematic age determination, to carry out a new kinematic decomposit…
A Search for L/T Transition Dwarfs With Pan-STARRS1 and WISE. III. Young L Dwarf Discoveries and Proper Motion Catalogs in Taurus and Scorpius-Centaurus
我们提出了在金牛座恒星形成区和天蝎座-半人马座OB协会中发现的八颗年轻的M7-L2矮星，这是在使用Pan-STARRS 1（光学）和WISE（中红外）测光进行L/T过渡矮星的宽视场搜索期间偶然发现的。我们将PSO J060.3200+25.9644（近红外光谱类型L1）和PSO J077.1033+24.3809（L2）确定为金牛座的新成员，这是基于它们的VL-G重力分类，它们的测光和自行与先前已知的金牛座天体的一致性，以及被场天体污染的可能性很低。PSO J077.1033+24.3809是迄今为止发现的最冷的金牛座亚恒星成员。这两个金牛座天体都是有史以来发现的质量最低的自由漂浮天体之一，估计质量为$\approx$ 6 M $_{\rm Jup}$，并提供了进一步的证据，证明孤立的行星质量天体可以作为正常恒星形成过程的一部分形成。PSO J060.3200+25.9644（又名DANCe J040116.80+255752.2）之前被认为是昴星团的成员（年龄$\approx125$ Myr），但它的VL-G重力分类和近红外测光意味着一个更年轻的年龄，因此指向金牛座成员。我们还在天蝎座-半人马座的外围区域发现了6颗M7-L1矮星，其测光、自行和低重力光谱特征与成员资格一致。这些物体的估计质量为$\approx$ 15-36 M $_{\rm Jup}$。M7矮星PSO J237.…
Pulsating B stars in the Scorpius-Centaurus Association with TESS
Indian Institute of Technology Roorkee（印度理工学院鲁尔基分校）；Sydney Institute for Astronomy, School of Physics, University of Sydney（悉尼大学物理学院天文研究所）；Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University（奥胡斯大学物理与天文学系恒星天体物理学中心）；Astronomical Institute, Graduate School of Science, Tohoku University（东北大学理学研究科天文学研究所）
The Kinematics of the Scorpius-Centaurus OB Association from Gaia DR1
我们提出了一个运动学研究的天蝎座，半人马座（Sco Cen）OB协会（Sco OB 2）使用盖亚DR 1松弛和自行。我们的目标是测试的经典理论，OB协会是密集和紧凑的星团被破坏的过程，如残余气体排出的扩展残余。该协会433名成员中有258名成员可以使用盖亚天体测量法，其余成员使用经修订的依巴谷天体测量法。我们使用这些数据来证实，这三个小组的Sco-Cen的引力不受约束，并具有非各向同性的速度色散，这表明他们还没有时间动态放松。我们还探讨了内部的运动学的子群，以寻找证据的扩张。我们测试Blaauw的经典线性膨胀模型，搜索沿银河系轴的速度趋势，比较膨胀和非膨胀收敛点，进行回溯分析，假设两个线性轨迹，并使用epicentric近似，并评估证据膨胀在适当的运动校正虚拟膨胀/收缩。这些方法都没有提供一致的证据，扩大的亚组，没有证据表明，亚组有一个更紧凑的配置在过去。我们发现的证据，支持的观点，他们不是由个别星团的中断形成的亚组内的运动学结构。我们的结论是，天蝎座-Cen可能出生高度亚结构，多个小规模的恒星形成事件有助于整体OB协会，而不是单一的，整体的集群恒星形成的爆发。
Young stellar associations represent a key site for the study of star formation, but to accurately compare observations to models of stellar evolution, the age of an association must be determined. The Upper Scorpius region is the youngest section of the Scorpius-Centaurus OB association, which is the largest collection of nearby, young, low-mass stars. The true age of Upper Scorpius is not clear, and an observed mass-dependent age gradient in Upper Scorpius, as well as in other star-forming regions, complicates age measurements. The age gradient may indicate a genuine astrophysical feature or…
The Scorpius-Centaurus (Sco-Cen) young and nearby massive star-forming region is particularly well suited for extrasolar planet searches with both direct imaging and radial velocity (RV) techniques. The RV search, however, is challenging, as the stars are faster rotators on average than their older stellar counterparts of similar spectral types. Moreover, the RV time series show strong signatures of stellar variability (spots and faculae) and/or stellar pulsations. Our aim is to search for giant planets (GPs) and brown dwarfs at short orbital distances around star members of the Sco-Cen associ…
Discovering wide companions of stellar systems allows us to constrain the dynamical environment and age of the latter. We studied four probable wide companions of four different stellar systems. The central stars are V4046 Sgr, HIP 74865, HIP 65426, and HIP 73145, and their probable wide companions are 2MASS J18152222-3249329, 2MASS J15174874-3028484, 2MASS J13242119-5129503, and 2MASS J14571503-3543505 respectively. V4046 Sgr is a member of $β$-Pictoris Moving Group while the rest of the stellar systems are acknowledged as members of the Scorpius-Centaurus association. The selected stellar sy…
K2 Discovery of Young Eclipsing Binaries in Upper Scorpius: Direct Mass and Radius Determinations for the Lowest Mass Stars and Initial Characterization of an Eclipsing Brown Dwarf Binary
Stellar associations can be discerned as overdensities of sources not only in the physical space but also in the velocity space. The common motion of their members, gradually eroded by the galactic tidal field, is partially reminiscent of the initial kinematic structure. Using recent data from Gaia EDR3, combined with radial velocities from GALAH and APOGEE, we traced back the present positions of stars belonging to Upper Scorpius, a subgroup of Scorpius-Centaurus, the nearest OB association. About one half of the subgroup (the "clustered" population) appears composed of many smaller entities,…
We aim at identifying very low-mass isolated planetary-mass member candidates in the nearest OB association to the Sun, Upper Scorpius (145 pc; 5-10 Myr), to constrain the form and shape of the luminosity function and mass spectrum in this regime. We conducted a deep multi-band ($Y$=21.2, $J$=20.5, $Z$=22.0 mag) photometric survey of six square degrees in the central region of Upper Scorpius. We extend the current sequence of astrometric and spectroscopic members by about two magnitudes in $Y$ and one magnitude in $J$, reaching potentially T-type free-floating members in the association with p…
A Thermal Infrared Imaging Study of Very Low-Mass, Wide Separation Brown Dwarf Companions to Upper Scorpius Stars: Constraining Circumstellar Environments
A large moving group within the Lower Centaurus Crux association
天蝎座-半人马座是最近的OB协会，它的数百名成员被分为子组，包括下半人马座Crux。在这里，我们研究的动力学下半人马座Crux区恒星的内容。我们报告的启示，一个大型的移动组包含超过1800中间和低质量的年轻恒星的对象和褐矮星，逃脱识别，直到盖亚DR 2允许执行运动学和光度选择。我们调查的恒星和亚恒星的内容，这个移动组使用盖亚DR 2天体测量和光度测量。成员的平均距离为114.5秒差距，80%的成员距离太阳102至135秒差距。我们的新成员涵盖了5 M $_\odot$到0.02 M $_\odot$的质量范围，加起来总质量约为700 M $_\odot$。现今的质量函数遵循对数正态律，其中m $_c$ = 0.22 M $_\odot$且$σ$ = 0.64。我们在样本中发现了200多颗褐矮星。恒星形成速率在约900万年前达到最大值$8\times10^{-5}\rm M_\odot yr^{-1}$。我们将新成员分成四个密度较大的亚群，它们的年龄从700万年增加到1000万年，周围是混合年龄的“自由浮动”年轻恒星。我们的等时线年龄，现在基于精确的岩石圈，与该地区的几个早期研究是兼容的。整个建筑群目前正在扩张，扩张开始于800万至1000万年前。二百名成员显示红外线过剩兼容的拱盘从完整的碎片盘。这一发现为磁盘和系外行星研究提供了附近年轻恒星和亚恒星物体的大量样本。
Context: A rich population of low-mass brown dwarfs and isolated planetary mass objects has been reported recently in the Upper Scorpius and Ophiuchus star forming complex. Aims: We investigate the membership, nature and properties of 17 of these isolated planetary mass candidates using low-resolution near-infrared spectra. Methods: We investigate the membership by looking for evidences of youth using four diagnostics: the slope of the continuum between the J and Ks band, the Hcont and TLI-g gravity sensitive indices, and by comparing the spectra to young and field (old) M and L-dwarf standard…
Carina is a nearby young stellar association. So far, only a small number of stars have been clearly identified as members of this association. In this paper we reanalyse the membership of the association in light of Gaia DR2 data, in particular finding that HD 95086 is a potential member (probability of 71%). This star is noteworthy as one of the few stars that hosts both a detected debris disc and a directly imaged planet. It has previously only been considered as a potential member of the Lower Centaurus Crux (LCC) - part of the Scorpius-Centaurus association. We also reanalyse the age of t…
We present the largest sample of brown dwarf (BD) protoplanetary disk spectral energy distributions modeled to date. We compile 49 objects with ALMA observations from four star-forming regions: $ρ$ Ophiuchus, Taurus, Lupus, and Upper Scorpius. Studying multiple regions with various ages enables us to probe disk evolution over time. Specifically, from our models we obtain values for dust grain sizes, dust settling, and disk mass; we compare how each of these parameters vary between the regions. We find that disk mass decreases with age. We also find evidence of disk evolution (i.e., grain growt…
