Characterising stellar and circumstellar properties of embedded young stellar objects (YSOs) is mandatory for understanding the early stages of the stellar evolution. This task requires the combination of both spectroscopy and photometry, covering the widest possible wavelength range, to disentangle the various protostellar components and activities. As part of the POISSON project, we present a multi-wavelength spectroscopic and photometric investigation of embedded YSOs in L1641, aimed to derive the stellar parameters and evolutionary stages and to infer their accretion properties. Our database includes low-resolution optical-IR spectra from the NTT and Spitzer (0.6-40 um) and photometric data covering a spectral range from 0.4 to 1100 um, which allow us to construct the YSOs spectral energy distributions (SEDs) and to infer the main stellar parameters. The SED analysis allows us to group our 27 YSOs into nine Class I, eleven Flat, and seven Class II objects. However, on the basis of the derived stellar properties, only six Class I YSOs have an age of ~10^5 yr, while the others are older 5x10^5-10^6 yr), and, among the Flat sources, three out of eleven are more evolved objects (5x10^6-10^7 yr), indicating that geometrical effects can significantly modify the SED shapes. Inferred mass accretion rates (Macc) show a wide range of values (3.6x10^-9 to 1.2x10^-5 M_sun yr^-1), which reflects the age spread observed in our sample. Average values of mass accretion rates, extinction, and spectral indices decrease with the YSO class. The youngest YSOs have the highest Macc, whereas the oldest YSOs do not show any detectable jet activity in either images and spectra. We also observe a clear correlation among the YSO Macc, M*, and age, consistent with mass accretion evolution in viscous disc models.
First Science Observations with SOFIA/FORCAST: Properties of Intermediate-Luminosity Protostars and Circumstellar Disks in OMC-2
我们检查八个年轻的恒星对象在OMC-2恒星形成区域的基础上，从SOFIA/FORCAST早期科学阶段，斯皮策太空望远镜，赫歇尔空间天文台，2MASS，APEX，和其他文献中的结果的观测。我们展示了这些物体从近红外到毫米波长的光谱能量分布，并将SED与原恒星和星周盘的片坍缩模型的SED进行了比较。其中四个天体可以被模拟为具有下落包层的原恒星，两个是被圆盘包围的年轻恒星，剩下的两个天体具有双峰SED。我们的双峰源作为二进制包含一个年轻的恒星与磁盘和原恒星模型。在0.15 x 0.25 pc区域内的密集组中发现了六个最明亮的光源;这些光源的亮度范围从300 L_sun到20 L_sun。嵌入最深的源（OMC-2 FIR 4）可以用0级原恒星模型拟合，该模型的光度约为50 L太阳，质量下降速率约为每年10 ^-4太阳质量。
The evidence of a relation between the mass accretion rate and the disk mass is established for young, Class II pre-main sequence stars. This observational result opened an avenue to test theoretical models and constrain the initial conditions of the disk formation, fundamental in the understanding of the emergence of planetary systems. However, it is becoming clear that the planet formation starts even before the Class II stage, in disks around Class 0 and I protostars. We show for the first time evidence for a correlation between the mass accretion rate and the disk mass for a large sample o…
W33A is a well-known example of a high-mass young stellar object showing evidence of a circumstellar disc. We revisited the $K$-band NIFS/Gemini North observations of the W33A protostar using principal components analysis tomography and additional post-processing routines. Our results indicate the presence of a compact rotating disc based on the kinematics of the CO absorption features. The position-velocity diagram shows that the disc exhibits a rotation curve with velocities that rapidly decrease for radii larger than 0\farcs1 ($\sim$250 AU) from the central source, suggesting a structure ab…
Observed changes in protostellar brightness can be complicated to interpret. In our JCMT~Transient monitoring survey, we discovered that a young binary protostar, HOPS 373, is undergoing a modest $30\%$ brightness increase at 850 $μ$m, caused by a factor of 1.8$-$3.3 enhancement in the accretion rate. The initial burst occurred over a few months, with a sharp rise and then shallower decay. A second rise occurred soon after the decay, and the source is still bright one year later. The mid-IR emission, the small-scale CO outflow mapped with ALMA, and the location of variable maser emission indic…
The protostar FU Orionis may not be bursting: dramatic accretion suppression in embedded young eccentric binaries
Heidelberg Institute for Theoretical Studies（海德堡理论研究所）；Research School of Astronomy & Astrophysics, Australian National University（澳大利亚国立大学天体物理与天文研究学院）
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…
Estimating the Luminosities of Protostars with Limited Infrared Photometry
Middlebury College（米德尔伯里学院）；Universidad Nacional Autónoma de México, Instituto de Radioastronomía y Astrofísica（墨西哥国立自治大学，射电天文与天体物理研究所）；Centro de Astrobiología (CAB), CSIC-INTA（天体生物学中心（CAB），西班牙国家科学技术研究委员会-国家航空航天技术研究所）；Universität Innsbruck（因斯布鲁克大学）；University of Vienna（维也纳大学）；State University of New York at Fredonia（纽约州立大学弗雷多尼亚分校）
The formation and early evolution of low mass young stellar objects (YSOs) are investigated using three-dimensional non-ideal magneto-hydrodynamics simulations. We investigate the evolution of YSOs up to ~ 10^4 yr after protostar formation, at which protostellar mass reaches ~ 0.1 M_\odot . We particularly focus on the impact of the dust model on the evolution. We found that a circumstellar disk is formed in all simulations regardless of the dust model. Disk size is approximately 10 AU at the protostar formation epoch, and it increases to several tens of AU at ~ 10^4 yr after protostar formati…
Wind-driven outflows are observed around a broad range of accreting objects throughout the Universe, ranging from forming low-mass stars to super-massive black holes. We study the interaction between a central isotropic wind and an infalling, rotating, envelope, determining the steady-state cavity shape formed at their interface under the assumption of weak mixing. The shape of the resulting wind-blown cavity is elongated and self-similar, with a physical size determined by the ratio between wind ram pressure and envelope thermal pressure. We compute the growth of a warm turbulent mixing-layer…
The past photometric history of the FU Ori-type young eruptive star 2MASS J06593158-0405277 = V960 Mon
已知的FU Ori-type年轻爆发恒星非常罕见（大约有十几个确认的物体），2 MASS J 06593158 -0405277在2014年爆发，可能是该家族的最新成员。所有成员国在其有记录的历史中只出现过一次这样的喷发，这一事件持续了几十年。为了测试2 MASS J 06593158 -0405277的FU Ori性质，我们通过测量其在1899-1989年时间间隔的哈佛感光板上的亮度来重建其光度历史。以前没有发现类似于2014年开始的大幅度喷发，就像真正的FU Ori-type物体一样。2 MASS J 06593158 -0405277在静止期的亮度中值为B=15.5，在1935-1950年的时间间隔内，其特征是变化很大（约1等振幅），这与后来时期的光度稳定性形成了鲜明对比。在1935-1950年期间的变化可以归因于2 MASS J 06593158 -0405277本身的一些T Tau活动，或者归因于同样年轻和较暗的恒星2 MASS J 06593168 -0405224，它位于北面5角秒，在哈佛照相底片的天体测量尺度上形成了一对未解析的恒星。
Stars collect most of their mass during the protostellar stage, yet the accretion luminosity and stellar parameters, which are needed to compute the mass accretion rate, are poorly constrained for the youngest sources. The aim of this work is to fill this gap, computing the stellar properties and the accretion rates for a large sample of Class I protostars located in nearby (< 500 pc) star-forming regions and analysing their interplay. We used a self-consistent method to provide accretion and stellar parameters using SED modeling and veiling information from near-IR observations, when possible…
