Deeply embedded and at distances of several kiloparsecs, massive young stellar objects (MYSOs) present numerous challenges for observation and study. In this work, we present spatially-resolved observations of one MYSO, AFGL 4176, together with survey and literature data, ranging from interferometric observations with VLTI/MIDI in the mid-infrared, to single-dish Herschel measurements in the far-infrared, and sub-millimeter data from APEX. We consider this spatially-resolved, multi-wavelength data set in terms of both radiative transfer and geometric models. We find that the observations are well described by one-dimensional models overall, but there are also substantial deviations from spherical symmetry at scales of tens to hundreds of astronomical units, which are revealed by the mid-infrared interferometric measurements. We use a multiple-component, geometric modeling approach to explain the mid-infrared emission on scales of tens to hundreds of astronomical units, and find the MIDI measurements are well described by a model consisting of a one-dimensional Gaussian halo and an inclined (θ=60 deg) circumstellar disk extending out to several hundred astronomical units along a position angle of 160 deg. Finally, we compare our results both with previous models of this source, and with those of other MYSOs, and discuss the present situation with mid-infrared interferometric observations of massive stars.
Results from the BV(RI)c photometric observations of the young stellar object V2492 Cyg collected in the period from April 2018 to September 2020 are presented. These observations are a part of our monitoring of the star that began in 2010 and continuing to date. V2492 Cyg is located in the Pelican Nebula, and its variability was explained by both accretion and extinction events. The new photometric data show that the star continues to exhibit rapid irregular variability in all bands. In the period from March 2019 to May 2020, we registered a prolonged decrease event in the light curve of V249…
A Model for (Quasi-)Periodic Multi-wavelength Photometric Variability in Young Stellar Objects
我们提出的辐射传输模型的旋转年轻恒星物体（YSO）的热点在其大气中，内部磁盘扭曲和其他3-D的影响，在附近的拱星环境。我们的模型是基于磁吸积理论所预期的几何形状，即在磁盘中向内移动的物质沿着磁场线流向恒星，并在撞击时产生恒星热点。由于恒星和磁层的旋转，圆盘被反方向照射。我们将我们的模型光变曲线与Spitzer YSOVAR项目的数据（Morales-Calderon et al. 2014，Cody et al. 2014）进行比较，以确定这些过程是否可以解释在年轻恒星中观察到的光学和中红外波长的变化。我们专注于这些变量表现出“北斗”的行为，可能是周期性的，准周期性的，或非周期性的。我们发现，恒星热点的大小和温度影响光学和近红外线曲线，而形状和垂直程度的内部磁盘扭曲影响中红外光曲线的变化。具有非均匀分形密度结构的星盘分布产生更多的随机光变曲线。我们的结论是，磁吸积理论是一致的某些方面的多波长光度变化所表现出的低质量的YSO。更详细的个别来源的建模可以用来更好地确定恒星热点和内部磁盘的几何形状的特定来源。
Determination of stellar age is a crucial task in astrophysics research. Different methods are nowadays used either model dependent or based on calibrated empirical relations. The most reliable results are generally obtained when different methods are used in complementary way. We propose a new method for the age determination of young stellar associations and open clusters (ages < 125 Myr), which can allow to further constrain the age when used together with other methods. We explore the amplitude of the photometric variability in bins of color and rotation period of five young associations a…
Stellar flybys in star clusters may perturb the evolution of young planetary systems in terms of disk truncation, planetary migration and planetary mass accretion. We investigate the feedback of a young planetary system during a single close stellar encounter in a typical open young stellar cluster. We consider 5 masses for the stellar perturbers: 0.5, 0.8, 1, 3 and 8 M$_{Sun}$, in coplanar, prograde and retrograde orbits respect to the planetary disk, varying the pertruber-host star orbital periastron from 100 AU to 500 AU. We have made 3D modelizations with the smooth particle hydrodynamics …
Energetic particles may have been important for the origin of life on Earth by driving the formation of prebiotic molecules. We calculate the intensity of energetic particles, in the form of stellar and Galactic cosmic rays, that reach Earth at the time when life is thought to have begun ($\sim$3.8Gyr ago), using a combined 1.5D stellar wind model and 1D cosmic ray model. We formulate the evolution of a stellar cosmic ray spectrum with stellar age, based on the Hillas criterion. We find that stellar cosmic ray fluxes are larger than Galactic cosmic ray fluxes up to $\sim$4 GeV cosmic ray energ…
Young stellar objects in their pre-main sequence phase are characterized by irregular changes in brightness, generally attributed to an increase of the mass accretion rate due to various kind of instabilities occurring in the circumstellar disk. In the era of large surveys aimed to monitor the sky, we present a pipeline to detect irregular bursts, in particular EXors-like ( EX Lupi type eruptive variables), in the light curves. The procedure follows a heuristic approach and is tested against the light curves already collected for a few objects presently recognized as bona fide or candidate EXo…
Linking Young Stellar Object Morphology to Evolutionary Stages with Self-Organizing Maps
Universität Wien（维也纳大学）；Natural History Museum Vienna（维也纳自然历史博物馆）；Université de Genève（日内瓦大学）；Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Research Network (HUN-REN)（孔科利天文台，匈牙利研究网络（HUN-REN）地球与天文学研究中心）；CSFK, MTA Centre of Excellence（MTA卓越中心天文研究所）；Department of Experimental Physics, Institute of Physics, University of Szeged（塞格德大学物理学院实验物理系）；HITS gGmbH（海德堡理论研究所）
Energetic particles, such as stellar cosmic rays, produced at a heightened rate by active stars (like the young Sun) may have been important for the origin of life on Earth and other exoplanets. Here we compare, as a function of stellar rotation rate ($Ω$), contributions from two distinct populations of energetic particles: stellar cosmic rays accelerated by impulsive flare events and Galactic cosmic rays. We use a 1.5D stellar wind model combined with a spatially 1D cosmic ray transport model. We formulate the evolution of the stellar cosmic ray spectrum as a function of stellar rotation. The…
The Trifid Nebula is a young, nearby star-forming region where star formation is proposed to have been triggered by cloud-cloud collision (CCC), based on observations of molecular clouds. It offers a unique opportunity to test whether the CCC hypothesis is supported by the spatial distribution and star formation chronology of young stars. We present the first study of the optically visible pre-main sequence (PMS) population of the region using riH$α$ imaging and Gaia astrometry. Combined with an analysis of young stellar objects (YSOs) using infrared imaging, we capture the spatial distributio…
