Short- and long-term near-infrared spectroscopic variability of eruptive protostars from VVV

ABSTRACT Numerous eruptive variable young stellar objects (YSOs), mostly Class I systems, were recently detected by the near-infrared Vista Variables in the Via Lactea (VVV) survey. We present an exploratory near-infrared spectroscopic variability study of 14 eruptive YSOs. The variations were sampled over one-day and one-to-two-year intervals and analysed in combination with VVV light curves. CO overtone absorption features are observed on three objects with FUor-like spectra: all show deeper absorption when they are brighter. This implies stronger emission from the circumstellar disc with a steeper vertical temperature gradient when the accretion rate is higher. This confirms the nature of fast VVV FUor-like events, in line with the accepted picture for classical FUors. The absence of Brγ emission in a FUor-like object declining to pre-outburst brightness suggests that reconstruction of the stellar magnetic field is a slow process. Within the one-day time-scale, 60 per cent of H2-emitting YSOs show significant but modest variation, and 2/6 sources have large variations in Brγ. Over year-long time-scales, H2 flux variations remain modest despite up to 1.8 mag variation in Ks. This indicates that emission from the molecular outflow usually arises further from the protostar and is unaffected by relatively large changes in accretion rate on year-long time-scales. Two objects show signs of on/off magnetospheric accretion traced by Brγ emission. In addition, a 60 per cent inter-night brightening of the H2 outflow is detected in one YSO.

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Optical images of star-formation regions

Canadian Journal of Physics ◽

10.1139/p86-069 ◽

1986 ◽

Vol 64 (4) ◽

pp. 387-391

Author(s):

Bel Campbell ◽

S. E. Persson

Keyword(s):

Optical Imaging ◽

Near Infrared ◽

Scattered Light ◽

Position Angle ◽

Small Sample ◽

Young Stellar Objects ◽

Image Size ◽

Radio Image ◽

Stellar Objects ◽

Molecular Outflow

New and sensitive optical imaging of a small sample of young stellar objects is presented. The observations are part of a continuing program of deep, red optical imaging of star-forming regions performed with the 4Shooter charge-coupled-device (CCD) system on the Palomar 5-m telescope. Each of the sources presented is of moderately high luminosity [Formula: see text] and is associated with a bipolar outflow of molecular gas. The results on the source GL490 are discussed in some detail. We find the source core to be well resolved and elongated orthogonal to the outflow direction despite an unresolved image size (< 0.3″) in the near infrared; in addition, there is an extended (> 0.8 pc) cone of diffuse emission out from the core source in the direction of the blue-shifted portion of the molecular outflow. From astrometry of the CCD frame, we find that the center of the optical position is displaced from the radio-image centroid by approximately 1.5″ to the southwest, also in the direction of the blue-shifted outflow. It is proposed that the optical image is totally due to scattered light from a source that is entirely obscured from direct view. Owing to inconsistencies in the orientations of the radio image and polarization position angle with the other source orientations, we conclude that a simple disk plus an orthogonal-outflow scenario is no longer supportable for this object and that continued observations may reveal many equally complex cases.

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Near-infrared Spectroscopic Observation of Ices around Extragalactic Young Stellar Objects

10.1063/1.3215829 ◽

2009 ◽

Author(s):

Takashi Shimonishi ◽

Takashi Onaka ◽

Daisuke Kato ◽

Itsuki Sakon ◽

Yoshifusa Ita ◽

...

Keyword(s):

Near Infrared ◽

Spectroscopic Observation ◽

Young Stellar Objects ◽

Stellar Objects ◽

Infrared Spectroscopic

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Near-infrared spectroscopic observations of young stellar objects

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/239.1.139 ◽

1989 ◽

Vol 239 (1) ◽

pp. 139-151 ◽

Cited By ~ 3

Author(s):

H. Suto ◽

K. Mizutani ◽

T. Maihara

Keyword(s):

Near Infrared ◽

Young Stellar Objects ◽

Stellar Objects ◽

Spectroscopic Observations ◽

Infrared Spectroscopic

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Investigating episodic accretion in a very low-mass young stellar object

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038897 ◽

2020 ◽

Vol 643 ◽

pp. A181

Author(s):

C. Stock ◽

A. Caratti o Garatti ◽

P. McGinnis ◽

R. Garcia Lopez ◽

S. Antoniucci ◽

...

Keyword(s):

Near Infrared ◽

Accretion Rate ◽

Photometric Data ◽

Class I ◽

Young Stellar Objects ◽

Line Of Sight ◽

Stellar Objects ◽

Steep Decrease ◽

Order Of Magnitude ◽

Low Mass

Context. Very low-mass Class I protostars have been investigated very little thus far. Variability of these young stellar objects (YSOs) and whether or not they are capable of strong episodic accretion is also left relatively unstudied. Aims. We investigate accretion variability in IRS 54 (YLW52), a Class I very low-mass protostar with a mass of M⋆ ∼ 0.1 − 0.2 M⊙. Methods. We obtained spectroscopic and photometric data with VLT/ISAAC and VLT/SINFONI in the near-infrared (J, H, and K bands) across four epochs (2005, 2010, 2013, and 2014). We used accretion-tracing lines (Paβ and Brγ) and outflow-tracing lines (H2 and [Fe II]) to examine physical properties and kinematics of the object. Results. A large increase in luminosity was found between the 2005 and 2013 epochs of more than 1 magnitude in the K band, followed in 2014 by a steep decrease. Consistently, the mass accretion rate (Ṁacc) rose by an order of magnitude from ∼10−8 M⊙ yr−1 to ∼10−7 M⊙ yr−1 between the two early epochs. The visual extinction (AV) has also increased from ∼15 mag in 2005 to ∼24 mag in 2013. This rise in AV in tandem with the increase in Ṁacc is explained by the lifting up of a large amount of dust from the disc of IRS 54, following the augmented accretion and ejection activity in the YSO, which intersects our line of sight due to the almost edge-on geometry of the disc. Because of the strength and timescales involved in this dramatic increase, this event is believed to have been an accretion burst possibly similar to bursts of EXor-type objects. IRS 54 is the lowest mass Class I source observed to have an accretion burst of this type, and therefore potentially one of the lowest mass EXor-type objects known so far.

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A Near-Infrared Search for Companions around Very Low Luminosity Young Stellar Objects in Taurus

The Astronomical Journal ◽

10.1086/300782 ◽

1999 ◽

Vol 117 (3) ◽

pp. 1471-1484 ◽

Cited By ~ 17

Author(s):

Yoichi Itoh ◽

Motohide Tamura ◽

Tadashi Nakajima

Keyword(s):

Near Infrared ◽

Young Stellar Objects ◽

Stellar Objects

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab358 ◽

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.

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