Spirals and streamers are the hallmarks of mass accretion during the early stages of star formation. We present the first observations of a large-scale spiral and a streamer towards a very young brown dwarf candidate in its early formation stages. These observations show, for the first time, the influence of external environment that results in asymmetric mass accretion via feeding filaments onto a candidate proto-brown dwarf in the making. The impact of the streamer has produced emission in warm carbon-chain species close to the candidate proto-brown dwarf. Two contrasting scenarios, a pseudo-disk twisted by core rotation and the collision of dense cores, can both explain these structures. The former argues for the presence of a strong magnetic field in brown dwarf formation while the latter suggests that a minimal magnetic field allows large-scale spirals and clumps to form far from the candidate proto-brown dwarf.
Context. In the past few years, there has been a rise in the detection of streamers, asymmetric flows of material directed toward the protostellar disk with material from outside the star's natal core. It is unclear how they affect the process of mass accretion, in particular beyond the Class 0 phase. Aims. We investigate the gas kinematics around Per-emb-50, a Class I source in the crowded star-forming region NGC 1333. Our goal is to study how the mass infall proceeds from envelope to disk scales in this source. Results. We discover a streamer delivering material toward Per-emb-50 in H$_2$CO …
The majority of stars are part of gravitationally bound stellar systems, such as binaries. Observations of protobinary systems constrain the conditions that lead to stellar multiplicity and subsequent orbital evolution. We report high-angular resolution observations of the circumbinary disk around [BHB2007] 11, a young binary protostar system. The two protostars are embedded in circumstellar disks that have radii of 2 to 3 astronomical units and probably contain a few Jupiter masses. These systems are surrounded by a complex structure of filaments connecting to the larger circumbinary disk. We…
ANTIHEROES-PRODIGE: Quantifying the connection from envelope to disk with the IRAM 30m telescope and NOEMA I. Attack of the streamers: L1448N's fight for order in the chaos
Characterizing the physical and chemical properties of the Class I protostellar system Oph-IRS 44. Binarity, infalling streamers, and accretion shocks
European Southern Observatory（欧洲南方天文台）；Pontificia Universidad Católica de Chile（智利天主教 Pontificia 大学）；Leiden University（莱顿大学）；University of Michigan（密歇根大学）；National Tsing Hua University（国立清华大学）；RIKEN Cluster for Pioneering Research（理化学研究所前沿研究集群）；University of Copenhagen（哥本哈根大学）
Binary formation is an important aspect of star formation. One possible route for close-in binary formation is disk fragmentation$^{[1,2,3]}$. Recent observations show small scale asymmetries (<300 au) around young protostars$^{[2,4]}$, although not always resolving the circumbinary disk, are linked to disk phenomena$^{[5,6]}$. In later stages, resolved circumbinary disk observations$^{[7]}$ (<200 au) show similar asymmetries, suggesting the origin of the asymmetries arises from binary-disk interactions$^{[8,9,10]}$. We observed one of the youngest systems to study the connection between disk …
Recent observations have shown that coronal shocks driven by coronal mass ejections can develop and accelerate particles within several solar radii in large solar energetic particle (SEP) events. Motivated by this, we present an SEP acceleration study including the process that a fast shock propagates through a streamer-like magnetic field with both closed and open field lines in the low corona region. The acceleration of protons is modeled by numerically solving the Parker transport equation with spatial diffusion both along and across the magnetic field. We show that particles can be suffici…
Early Planet Formation in Embedded Disks (eDisk). VII. Keplerian Disk, Disk Substructure, and Accretion Streamers in the Class 0 Protostar IRAS 16544-1604 in CB 68
基于 ALMA eDisk 项目对 CB 68 中 0 类原恒星 IRAS 16544-1604 的观测，研究揭示了其具有耀展和非轴对称结构的 ~30 au 开普勒旋转盘，并发现了连接盘面的 ~1500 au 吸积流及伴随的吸积激波与外流。
We present SOFIA+ALMA continuum and spectral-line polarisation data on the massive molecular cloud BYF 73, revealing important details about the magnetic field morphology, gas structures, and energetics in this unusual massive star formation laboratory. The 154$μ$m HAWC+ polarisation map finds a highly organised magnetic field in the densest, inner 0.55$\times$0.40 pc portion of the cloud, compared to an unremarkable morphology in the cloud's outer layers. The 3mm continuum ALMA polarisation data reveal several more structures in the inner domain, including a pc-long, $\sim$500 M$_{\odot}$ "St…
Early Planet Formation in Embedded Disks (eDisk) XVII: A Compact but Structured Keplerian Disk and Large-scale Streamers Revealed in the Class I Protostellar System IRAS 04169+2702
针对 Class I 原恒星 IRAS 04169+2702 的高分辨率观测揭示了半径约 21 天文单位的开普勒盘、毫米/厘米级尘埃颗粒，以及延伸至 1400 天文单位的吸积流丝，并发现与螺旋臂吸积相关的激波证据。
A large fraction of stars is found to be part of binary or higher-order multiple systems. The ubiquity of planets found around single stars raises the question if and how planets in binary systems may form. Protoplanetary disks are the birthplaces of planets, and their characterization is crucial in order to understand the planet formation process. Our aim is to characterize the morphology of the GG Tau A disk, one of the largest and most massive circumbinary disks, and trace evidence for binary-disk interactions. We obtained observations in polarized scattered light of GG Tau A using the SPHE…
Deuterium fractionation can constrain the physical and chemical conditions at the early stage of brown dwarf formation. We present IRAM 30m observations over a wide frequency range of 213-279 GHz of singly and doubly deuterated species of formaldehyde (HDCO and D$_{2}$CO) towards Class 0/I proto-brown dwarfs (proto-BDs). Multiple low-excitation HDCO and D$_{2}$CO transition lines with upper energy level $\leq$ 40 K are detected. The D$_{2}$CO/HDCO, HDCO/H$_{2}$CO, D$_{2}$CO/H$_{2}$CO abundance ratios range between 0.01 and 2.5 for the proto-BDs, similar to the range seen in low-mass protostars…
We present 3D hydrodynamical models of the HD142527 protoplanetary disc, a bright and well studied disc that shows spirals and shadows in scattered light around a 100 au gas cavity, a large horseshoe dust structure in mm continuum emission, together with mysterious fast radial flows and streamers seen in gas kinematics. By considering several possible orbits consistent with the observed arc, we show that all of the main observational features can be explained by one mechanism - the interaction between the disc and the observed binary companion. We find that the spirals, shadows and horseshoe a…
We present results from a study of nitrogen chemistry in Class 0/I proto-brown dwarfs (proto-BDs). We have used the IRAM 30 m telescope to observe the CN (2-1), HCN (3-2), and HNC (3-2) lines in 7 proto-BDs. All proto-BDs show a large CN/HCN abundance ratio of >20, and a HNC/HCN abundance ratio close to or larger than unity. The enhanced CN/HCN ratios can be explained by high UV flux originating from an active accretion zone in the proto-BDs. The larger than unity HNC/HCN ratio for the proto-BDs is likely caused by a combination of low temperature and high density. Both CN and HNC show a flat …
We present results from a deep sub-millimeter survey in the Serpens Main and Serpens/G3-G6 clusters, conducted with the Submillimetre Common-User Bolometer Array (SCUBA-2) at the James Clerk Maxwell Telescope. We have combined Herschel PACS far-infrared photometry, sub-millimeter continuum and molecular gas line observations, with the aim to conduct a detailed multi-wavelength characterization of `proto-brown dwarf' candidates in Serpens. We have performed continuum and line radiative transfer modeling, and have considered various classification schemes to understand the structure and the evol…
We present a near-infrared study of accretion and outflow activity in 6 Class 0/I proto-brown dwarfs (proto-BDs) using VLT/SINFONI spectroscopy and spectro-imaging observations. The spectra show emission in several [FeII] and H$_{2}$ lines associated with jet/outflow activity, and in the accretion diagnostics of Pa$β$ and Br$γ$ lines. The peak velocities of the [FeII] lines ($>$100 km s$^{-1}$) are higher than the H$_{2}$ lines. The Class 0 proto-BDs show strong emission in the H$_{2}$ lines but the [FeII] lines are undetected, while the Class I objects show emission in both [FeII] and H$_{2}$…
We report the first detection in the ${\it J}_{\it K}$ = 1$_{0}$ - 0$_{0}$ rotational transition line of CH$_{3}$D towards three Class 0/I proto-brown dwarfs (proto-BDs) from IRAM 30 m observations. Assuming a rotational temperature of 25 K, the CH$_{3}$D abundances (relative to H$_{2}$) are in the range of (2.3--14.5) $\times$ 10$^{-7}$. The CH$_{4}$ abundances derived from the CH$_{3}$D abundances and assuming the DCO$^+$/HCO$^+$ ratios are in the range of (0.05--4.8) $\times $10$^{-5}$. The gas-phase formation of CH$_{3}$D via CH$_2$D$^+$ is enhanced at high densities of 10$^{8}$--10$^{10}$…
We have conducted the first extensive observational survey of several deuterated species in 16 Class 0/I proto-brown dwarfs (proto-BDs) and 4 Class Flat/Class II brown dwarfs. Observations were obtained with the IRAM 30m telescope in the DCO$^{+}$ (3-2), DCN (3-2), DNC (3-2), and N$_{2}$D$^{+}$ (3-2) lines. The DCO$^{+}$/H$^{13}$CO$^{+}$, DCN/H$^{13}$CN, and DNC/HN$^{13}$C ratios are comparatively higher and show a narrower range than the DCO$^{+}$/HCO$^{+}$, DCN/HCN, and DNC/HNC ratios, respectively. The mean D/H ratios for the proto-BDs derived from these molecules are in the range of $\sim$…
We present a study of the CO isotopologues and the high-density tracers H$_{2}$CO, HCO$^{+}$, and CS in Class 0/I proto-brown dwarfs (proto-BDs). We have used the IRAM 30m telescope to observe the $^{12}$CO (2-1), $^{13}$CO (2-1), C$^{18}$O (2-1), C$^{17}$O (2-1), H$_{2}$CO (3-2), HCO$^{+}$ (3-2), and CS (5-4) lines in 7 proto-BDs. The hydrogen column density for the proto-BDs derived from the CO gas emission is $\sim$2-15 times lower than that derived from the dust continuum emission, indicating CO depletion from the gas-phase. The mean H$_{2}$CO ortho-to-para ratio is $\sim$3 for the proto-B…
We present the observational evidence of a pseudo-disc around the proto-brown dwarf Mayrit 1701117, the driving source of the large-scale HH~1165 jet. Our analysis is based on ALMA $^{12}$CO (2-1) line and 1.37 mm continuum observations at an angular resolution of $\sim$0.4$^{\prime\prime}$. The pseudo-disc is a bright feature in the CO position-velocity diagram (PVD), elongated in a direction perpendicular to the jet axis, with a total (gas+dust) mass of $\sim$0.02 M$_{\odot}$, size of 165-192 AU, and a velocity spread of $\pm$2 km s$^{-1}$. The large velocity gradient is a combination of inf…
On the basis of various data such as ALMA, JVLA, Chandra, {\it Herschel}, and {\it Spitzer}, we confirmed that two protostellar candidates in Oph-A are bona fide protostars or proto-brown dwarfs (proto-BDs) in extremely early evolutionary stages. Both objects are barely visible across infrared (IR, i.e., near-IR to far-IR) bands. The physical nature of the cores is very similar to that expected in first hydrostatic cores (FHSCs), objects theoretically predicted in the evolutionary phase prior to stellar core formation with gas densities of $\sim$ 10$^{11-12}$ cm$^{-3}$. This suggests that the …
The formation mechanism of brown dwarfs (BDs) is one of the long-standing problems in star formation because the typical Jeans mass in molecular clouds is too large to form these substellar objects. To answer this question, it is crucial to study a BD at the embedded phase. IRAS 16253-2429 is classified as a very low luminosity object (VeLLO) with internal luminosity 0.1 Lsun. VeLLOs are believed to be very low-mass protostars or even proto-BDs. We observed the jet/outflow driven by IRAS 16253-2429 in CO (2-1), (6-5), and (7-6) using the IRAM 30 m and APEX telescopes and the SMA in order to st…
We are performing a series of observations with ground-based telescopes toward Planck Galactic cold clumps (PGCCs) in the $λ$ Orionis complex in order to systematically investigate the effects of stellar feedback. In the particular case of PGCC G192.32-11.88, we discovered an extremely young Class 0 protostellar object (G192N) and a proto-brown dwarf candidate (G192S). G192N and G192S are located in a gravitationally bound bright-rimmed clump. The velocity and temperature gradients seen in line emission of CO isotopologues indicate that PGCC G192.32-11.88 is externally heated and compressed. G…
In this letter a near-infrared integral field study of a proto-brown dwarf candidate is presented. A $\sim$ 0\farcs5 blue-shifted outflow is detected in both H$_{2}$ and [Fe II] lines at V$_{sys}$ = (-35~$\pm$ 2)~km~s$^{-1}$ and V$_{sys}$ = (-51~$\pm$ 5)~km~s$^{-1}$ respectively. In addition, slower ($\sim$ $\pm$~10~km~s$^{-1}$) H$_{2}$ emission is detected out to $<$ 5\farcs4, in the direction of both the blue and red-shifted outflow lobes but along a different position angle to the more compact faster emission. It is argued that the more compact emission is a jet and the extended H$_{2}$ emi…
This paper presents our observational attempts to precisely measure the central mass of a proto-brown dwarf candidate, L328-IRS, in order to investigate whether L328-IRS is in the substellar mass regime. Observations were made for the central region of L328-IRS with the dust continuum and CO isotopologue line emission at ALMA band 6, discovering the detailed outflow activities and a deconvolved disk structure of a size of $\sim$87 AU $\times$ 37 AU. We investigated the rotational velocities as a function of the disk radius, finding that its motions between 130 AU and 60 AU are partially fitted…
We report the discovery of a new Herbig-Haro jet, HH 1165, in SOAR narrow-band imaging of the vicinity of the sigma Orionis cluster. HH 1165 shows a spectacular extended and collimated spatial structure, with a projected length of 0.26 pc, a bent C-shaped morphology, multiple knots, and fragmented bow-shocks at the apparent ends of the flow. The Halpha image shows a bright halo with a clumpy distribution of material seen around the driving source, and curved reflection nebulosity tracing the outflow cavities. The driving source of HH 1165 is a Class I proto-brown dwarf, Mayrit 1701117 (M170111…
IRAM 04191+1522: a compact proto-brown dwarf binary candidate
Centro de Astrobiología (CAB), CSIC-INTA（天体生物学中心）；European Southern Observatory（欧洲南方天文台）；Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México（墨西哥国立自治大学无线电天文学与天体物理研究所）；Institute of Astronomy, University of Cambridge（剑桥大学天文学研究所）；Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS（波尔多大学天体物理实验室）；Department of Physics, Maynooth University（梅努斯大学物理系）
In this paper we examine a low-energy SEP event observed by IS$\odot$IS's Energetic Particle Instrument-Low (EPI-Lo) inside 0.18 AU on September 30, 2020. This small SEP event has a very interesting time profile and ion composition. Our results show that the maximum energy and peak in intensity is observed mainly along the open radial magnetic field. The event shows velocity dispersion, and strong particle anisotropies are observed throughout the event showing that more particles are streaming outward from the Sun. We do not see a shock in the in-situ plasma or magnetic field data throughout t…
We present ALMA $^{12}$CO (2-1), $^{13}$CO (2-1), C$^{18}$O (2-1) molecular line observations of a very young proto-brown dwarf system, ISO-OPH 200. We have conducted physical+chemical modelling of the complex internal structure for this system using the core collapse simulations for brown dwarf formation. The model at an age of $\sim$6000 yr can provide a good fit to the observed kinematics, spectra, and reproduce the complex structures seen in the moment maps. Results from modelling indicate that $^{12}$CO emission is tracing an extended ($\sim$1000 au) molecular outflow and a bright shock k…
Spiral formation caused by late infall onto protoplanetary disks
Institut für Theoretische Astrophysik, Zentrum für Astronomie der Universität Heidelberg（海德堡大学天文中心理论天体物理研究所）；Dipartimento di Fisica, Università degli Studi di Milano（米兰大学物理系）
Measuring the properties of protoplanetary disks around brown dwarfs is central to understanding the formation of brown dwarfs and their planetary companions. We present modeling of CFHT Tau 4 and 2M0444, two brown dwarfs with protoplanetary disks in the Taurus Molecular Cloud. By combining modeling of the spectral energy distributions and ALMA images, we obtain disk radii and masses for these objects; these parameters can be used to constrain brown dwarf formation and planet formation, respectively. We find that the disk around CFHT Tau 4 has a mass of 0.42 M$_{Jup}$ and a radius of 80 au; we…
Context. Chamaeleon II molecular cloud is an active star forming region that offers an excellent opportunity for studying the formation of brown dwarfs in the southern hemisphere. Aims. Our aims are to identify a population of pre- and proto- brown dwarfs (5 sigma mass limit threshold of ~0.015 Msun) and provide information on the formation mechanisms of substellar objects. Methods. We performed high sensitivity observations at 870 microns using the LABOCA bolometer at the APEX telescope towards an active star forming region in Chamaeleon II. The data are complemented with an extensive multiwa…
First Direct Simulation of Brown Dwarf Formation in a Compact Cloud Core
利用嵌套网格模拟研究了棕矮星的形成和恒星形成效率，覆盖了空间尺度上的五个数量级（10^4 - 0.1AU）。从一个质量为0.22M_sun的旋转磁化致密云开始，我们跟踪云的演化，直到主吸积阶段结束。大约5公里/秒的外流出现约100年前的原恒星形成，并没有消失，直到计算结束。在原恒星形成后的短时间内（约10^4年），质量吸积速率从10^-6 M_sun/yr下降到10^-8 - 10^-12 M_sun/yr。这是因为：（1）大部分的物质被原恒星流出物从宿主云中喷射出来;（2）气体在热压力的作用下从宿主云中逃逸。计算结束时，原恒星总质量（225 M Jup）的74%（167 M Jup）是从原恒星流出的，其中34%（77 M Jup）是由原恒星流出物以超音速喷出的，40%（90 M Jup）是以亚音速逃逸的。另一方面，20%（45 M_Jup）转化为原恒星，6%（13 M_Jup）保留为星周盘。因此，恒星的形成效率为0.2。由此产生的原恒星质量在棕矮星的质量范围内。我们的研究结果表明，棕矮星可以形成在紧凑的核心，在相同的方式，氢燃烧的恒星，和磁场和原恒星外流是必不可少的，在决定恒星形成效率和恒星质量。
We conduct a pebble-driven planet population synthesis study to investigate the formation of planets around very low-mass stars and brown dwarfs, in the (sub)stellar mass range between $0.01 \ M_{\odot}$ and $0.1 \ M_{\odot}$. Based on the extrapolation of numerical simulations of planetesimal formation by the streaming instability, we obtain the characteristic mass of the planetesimals and the initial masses of the protoplanets (largest bodies from the planetesimal size distributions), in either the early self-gravitating phase or the later non-self-gravitating phase of the protoplanetary dis…
