scholarly journals Circumstellar disks of the most vigorously accreting young stars

2016 ◽  
Vol 2 (2) ◽  
pp. e1500875 ◽  
Author(s):  
Hauyu Baobab Liu ◽  
Michihiro Takami ◽  
Tomoyuki Kudo ◽  
Jun Hashimoto ◽  
Ruobing Dong ◽  
...  
Keyword(s):  
Large Scale ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Circumstellar Disks ◽  
Young Stars ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Disk Formation ◽  
Gravitational Instabilities ◽  
Disk Evolution

Stars may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. Our high-resolution near-infrared imaging has verified the presence of the key associated features, large-scale arms and arcs surrounding four young stellar objects undergoing luminous outbursts. Our hydrodynamics simulations and radiative transfer models show that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation phase. The effect of those tempestuous episodes of disk evolution on star and planet formation remains to be understood.

scholarly journals Principal component analysis tomography in near-infrared integral field spectroscopy of young stellar objects – I. Revisiting the high-mass protostar W33A

2021 ◽  
Vol 503 (1) ◽  
pp. 270-291
Author(s):  
F Navarete ◽  
A Damineli ◽  
J E Steiner ◽  
R D Blum
Keyword(s):  
Large Scale ◽  
Near Infrared ◽  
Rotation Axis ◽  
Principal Component ◽  
Young Stellar Objects ◽  
High Mass ◽  
Continuum Emission ◽  
Rotating Disc ◽  
Stellar Objects ◽  
K Band

ABSTRACT 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 0.1 arcsec (∼250 au) from the central source, suggesting a structure about four times more compact than previously reported. We derived a dynamical mass of 10.0$^{+4.1}_{-2.2}$ $\rm {M}_\odot$ for the ‘disc + protostar’ system, about ∼33 per cent smaller than previously reported, but still compatible with high-mass protostar status. A relatively compact H2 wind was identified at the base of the large-scale outflow of W33A, with a mean visual extinction of ∼63 mag. By taking advantage of supplementary near-infrared maps, we identified at least two other point-like objects driving extended structures in the vicinity of W33A, suggesting that multiple active protostars are located within the cloud. The closest object (Source B) was also identified in the NIFS field of view as a faint point-like object at a projected distance of ∼7000 au from W33A, powering extended K-band continuum emission detected in the same field. Another source (Source C) is driving a bipolar $\rm {H}_2$ jet aligned perpendicular to the rotation axis of W33A.

First Near-infrared Imaging Polarimetry of Young Stellar Objects in the Circinus Molecular Cloud

2018 ◽  
Vol 234 (2) ◽  
pp. 42 ◽  
Author(s):  
Jungmi Kwon ◽  
Takao Nakagawa ◽  
Motohide Tamura ◽  
James H. Hough ◽  
Minho Choi ◽  
...  
Keyword(s):  
Molecular Cloud ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Young Stellar Objects ◽  
Near Infrared Imaging ◽  
Stellar Objects ◽  
Imaging Polarimetry

scholarly journals CS Lines and Dust Continuum Observations of the OMC2 Infrared Cluster

1994 ◽  
Vol 140 ◽  
pp. 245-246
Author(s):  
T. Umemoto ◽  
N. Ohashi ◽  
Y. Murata ◽  
K. Tatematsu ◽  
M. Suzuki
Keyword(s):  
Formation Process ◽  
Molecular Clouds ◽  
Large Scale ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Cluster Formation ◽  
Young Stars ◽  
Ir Sources ◽  
Near Ir ◽  
Molecular Core

It is known that stars in GMCs are often born as clusters. Recently, near infrared imaging has enabled us to study the young stars within molecular clouds (e.g., Lada & Lada 1991). Orion Molecular Cloud 2 (OMC2) is located 12' north of the Trapezium cluster in the Orion A cloud, and contains a cluster of about 20 near-IR sources and several FIR sources distributed within a diameter of 0.2 pc (Rayner et al... 1989; Johnson et al. 1990; Mezger, Wink, & Zylka 1990). By large scale mapping observations using the NRO 45 m telescope, this infrared cluster is found to be associated with a dense molecular core (Tatematsu et al. 1993, Umemoto et al. 1993). The region was observed using the Nobeyama Millimeter Array (NMA) to elucidate the structure and cluster formation process within a core.

scholarly journals The accretion disk paradigm for young stars

2007 ◽  
Vol 3 (S243) ◽  
pp. 1-12 ◽  
Author(s):  
Claude Bertout
Keyword(s):  
Accretion Disk ◽  
Indirect Evidence ◽  
Circumstellar Disks ◽  
T Tauri Stars ◽  
Young Stars ◽  
Young Stellar Objects ◽  
Recent Attempt ◽  
Disk Model ◽  
Stellar Objects ◽  
T Tauri

AbstractAccretion and magnetic fields play major roles in several of the many models put forward to explain the properties of T Tauri stars since their discovery by Alfred Joy in the 1940s. Early investigators already recognized in the 1950s that a source of energy external to the star was needed to account for the emission properties of these stars in the optical range.The opening of new spectral windows from the infrared to the ultraviolet in the 1970s and 1980s showed that the excess emission of T Tauri stars and related objects extends into all wavelength domains, while evidence of outflow and/or infall in their circumstellar medium was accumulating.Although the disk hypothesis had been put forward by Merle Walker as early as 1972 to explain properties of YY Orionis stars and although Lynden-Bell and Pringle worked out the accretion disk model and applied it specifically to T Tauri stars in 1974, the prevailing model for young stellar objects until the mid-1980s assumed that they experienced extreme solar-type activity. It then took until the late 1980s before the indirect evidence of disks presented by several teams of researchers became so compelling that a paradigm shift occurred, leading to the current consensual picture.I briefly review the various models proposed for explaining the properties of young stellar objects, from their discovery to the direct observations of circumstellar disks that have so elegantly confirmed the nature of young stars. I will go on to discuss more modern issues concerning their accretion disk properties and conclude with some results obtained in a recent attempt to better understand the evolution of Taurus-Auriga young stellar objects.

Magnetic field structures in star-forming regions revealed by imaging polarimetry at multi-wavelengths

2018 ◽  
Vol 14 (A30) ◽  
pp. 102-102
Author(s):  
Jungmi Kwon
Keyword(s):  
Magnetic Fields ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Young Stellar Objects ◽  
High Mass ◽  
Mass Star ◽  
Stellar Objects ◽  
Star Forming ◽  
Star Forming Regions ◽  
Imaging Polarimetry

AbstractMagnetic fields are ubiquitous in various scales of astronomical objects, and they are considered as playing significant roles from star to galaxy formations. However, the role of the magnetic fields in star forming regions is less well understood because conventional optical polarimetry is hampered by heavy extinction by dust. We have been conducting extensive near-infrared polarization survey of various star-forming regions from low- and intermediate-mass to high-mass star-forming regions, using IRSF/SIRPOL in South Africa. Not only linear but also circular polarizations have been measured for more than a dozen of regions. Both linear and circular polarimetric observations at near-infrared wavelengths are useful tools to study the magnetic fields in star forming regions, although infrared circular polarimetry has been less explored so far. In this presentation, we summarize our results of the near-infrared polarization survey of star forming regions and its comparison with recent submillimeter polarimetry results. Such multi-wavelength approaches can be extended to the polarimetry using ALMA, SPICA in future, and others. We also present our recent results of the first near-infrared imaging polarimetry of young stellar objects in the Circinus molecular cloud, which has been less studied but a very intriguing cluster containing numerous signs of active low-mass star formation.

scholarly journals High Angular Resolution Observations of Protostellar Disks

1994 ◽  
Vol 158 ◽  
pp. 387-390
Author(s):  
J.-L. Monin ◽  
J. Bouvier ◽  
F. Malbet
Keyword(s):  
Near Infrared ◽  
Angular Resolution ◽  
Circumstellar Disks ◽  
Physical Structure ◽  
Young Stellar Objects ◽  
High Angular Resolution ◽  
Stellar Objects ◽  
Star Forming ◽  
T Tauri ◽  
Chromatic Properties

The existence of circumstellar disks around young stellar objects like T Tauri stars is now well accepted. Such disks would have solar system sizes and, at the distance of the nearest star forming cloud, an angular diameter of 0.01 to 1 arcsecond at most, requiring very high angular resolution to be detected. Due to the nature of the emission process in circumstellar disks and to chromatic properties of ground based observations, disk imaging is expected to be more efficient in the near infrared. Also, multi-aperture interferometry in this wavelength range (1 – 10 μm) is expected to bring considerable insight into the disks properties and evolution in revealing their inner physical structure.In this paper, we present synthetic images of circumstellar accretion disks. The images have been computed from a complete disk vertical structure model.

scholarly journals Optical and Near-Infrared Imaging of Jets and Outflows

2000 ◽  
Vol 197 ◽  
pp. 213-222
Author(s):  
Ji Yang ◽  
Yongqiang Yao
Keyword(s):  
Large Scale ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Early Stage ◽  
Young Stellar Objects ◽  
High Mass ◽  
Jets And Outflows ◽  
Nir Imaging ◽  
Bow Shocks ◽  
Hh Objects

Jets and outflows are typical manifestations of the stellar mass loss process during the early stage of star formation. Optical and near-infrared (NIR) imaging of jets and outflows has become extremely popular recently, especially concerning large-scale surveys of Herbig-Haro (HH) objects, NIR imaging of jets and outflows driven by both low- and high-mass stars, and detailed imaging of jets and bow shocks at sub-arcsec resolution.Optical and IR observations of jets and outflows have revealed (1) cavities evacuated by the outflow motion; (2) bow shocks inside and near the surface of the jets and outflows; (3) exciting sources; (4) circumstellar disks responsible for collimating the jets and outflows; (5) sometimes a cluster instead of a single source from which the jets and outflows initiate; (6) bursts of jets and outflows in some regions. Large-scale surveys of HH objects and outflows have been done in a number of nearby regions including Taurus, Orion, and Perseus. The prominent results of these studies range from the discovery of parsec-scale jets and outflows to their large-scale distribution. These studies also begin to reveal the relation between outflow activity and the large-scale distribution of young stellar objects.

scholarly journals Magnetized Accretion Disks and the Origin of Bipolar Outflows

1997 ◽  
Vol 163 ◽  
pp. 551-560 ◽  
Author(s):  
Arieh Königl
Keyword(s):  
Accretion Disks ◽  
Rapid Heating ◽  
Circumstellar Disks ◽  
Young Stellar Objects ◽  
Large Momentum ◽  
Flux Transport ◽  
Bipolar Outflows ◽  
Stellar Objects ◽  
Disk Formation

AbstractCentrifugally driven winds from the surfaces of magnetized accretion disks are an attractive mechanism for removing the angular momentum of the accreted matter and of producing bipolar outflows and jets in compact astronomical objects. In this contribution, I first review steady–state disk–wind models that have been constructed for the different density regimes of circumstellar disks and comment on their expected stability. I then consider several nonsteady effects, including disk formation in molecular cloud-core collapse, magnetic flux transport through the disk, and the role of magnetic fields in the FU Orionis outburst phenomenon. I conclude with a discussion of some of the unique observational properties of disk-driven outflows in young stellar objects and in active galactic nuclei. These characteristics are a consequence of the highly stratified density and velocity structures of centrifugally driven outflows, their large momentum discharges (which result in the efficient uplifting of dust from the disk), and, in the case of molecular disks around lowluminosity objects, their comparatively low initial degrees of ionization (which can lead to rapid heating by ambipolar diffusion).

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