scholarly journals Blinded by the light: on the relationship between CO first overtone emission and mass accretion rate in massive young stellar objects

2018 ◽  
Vol 477 (3) ◽  
pp. 3360-3368 ◽  
Author(s):  
J D Ilee ◽  
R D Oudmaijer ◽  
H E Wheelwright ◽  
R Pomohaci
Keyword(s):  
Accretion Rate ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Mass Accretion Rate ◽  
The Relationship

scholarly journals Stellar masses and disk properties of Lupus young stellar objects traced by velocity-aligned stacked ALMA 13CO and C18O spectra

2018 ◽  
Vol 616 ◽  
pp. A100 ◽  
Author(s):  
Hsi-Wei Yen ◽  
Patrick M. Koch ◽  
Carlo F. Manara ◽  
Anna Miotello ◽  
Leonardo Testi
Keyword(s):  
Accretion Rate ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
Integration Time ◽  
High Signal ◽  
Molecular Line ◽  
Stellar Objects ◽  
Mass Accretion Rate ◽  
Molecular Lines ◽  
Stellar Masses

Aims. Large samples of protoplanetary disks have been observed in recent ALMA surveys. The gas distributions and velocity structures of most of the disks can still not be imaged at high signal to noise ratios (S/Ns) because of the short integration time per source in these surveys. In this work, we apply the velocity-aligned stacking method to extract more information from molecular-line data of these ALMA surveys and to study the kinematics and disk properties traced by molecular lines. Methods. We re-analyzed the ALMA 13CO (3–2) and C18O (3–2) data of 88 young stellar objects (YSOs) in Lupus with the velocity-aligned stacking method. This method aligns spectra at different positions in a disk based on the projected Keplerian velocities at their positions and then stacks them. This method enhances the S/Ns of molecular-line data and allows us to obtain better detections and to constrain dynamical stellar masses and disk orientations. Results. We obtain 13CO detections in 41 disks and C18O detections in 18 disks with 11 new detections in 13CO and 9 new detections in C18O after applying the method. We estimate the disk orientations and the dynamical masses of the central YSOs from the 13CO data. Our estimated dynamical stellar masses correlate with the spectroscopic stellar masses, and in a subsample of 16 sources, where the inclination angles are better constrained, the two masses are in good agreement within the uncertainties and with a mean difference of 0.15 M⊙. With more detections of fainter disks, our results show that high gas masses derived from the 13CO and C18O lines tend to be associated with high dust masses estimated from the continuum emission. Nevertheless, the scatter is large and is estimated to be 0.9 dex, implying large uncertainties in deriving the disk gas mass from the line fluxes. We find that with such large uncertainties it is expected that there is no correlation between the disk gas mass and the mass accretion rate with the current data. Deeper observations to detect disks with gas masses <10−5 M⊙ in molecular lines are needed to investigate the correlation between the disk gas mass and the mass accretion rate.

scholarly journals Episodic accretion in focus: revealing the environment of FU Orionis-type stars

2018 ◽  
Vol 14 (S345) ◽  
pp. 87-90
Author(s):  
O. Fehér ◽  
Á. Kóspál ◽  
P. Ábrahám ◽  
M. R. Hogerheijde ◽  
Ch. Brinch ◽  
...  
Keyword(s):  
Accretion Disks ◽  
Accretion Rate ◽  
Central Star ◽  
Systematic Investigation ◽  
Young Stars ◽  
Young Stellar Objects ◽  
Circumstellar Disk ◽  
Stellar Objects ◽  
Evolutionary Phase ◽  
Intense Mass

AbstractThe earliest phases of star formation are characterised by intense mass accretion from the circumstellar disk to the central star. One group of young stellar objects, the FU Orionis-type stars exhibit accretion rate peaks accompanied by bright eruptions. The occurance of these outbursts might solve the luminosity problem of protostars, play a key role in accumulating the final star mass, and have a significant effect on the parameters of the envelope and the disk. In the framework of the Structured Accretion Disks ERC project, we are conducting a systematic investigation of these sources with millimeter interferometry to examine whether they represent normal young stars in exceptional times or they are unusual objects. Our results show that FU Orionis-type stars can be similar to both Class I and Class II systems and may be in a special evolutionary phase between the two classes with their infall-driven episodic eruptions being the main driving force of the transition.

scholarly journals Kinematics around the B335 protostar down to au scales

2019 ◽  
Vol 631 ◽  
pp. A64 ◽  
Author(s):  
Per Bjerkeli ◽  
Jon P. Ramsey ◽  
Daniel Harsono ◽  
Hannah Calcutt ◽  
Lars E. Kristensen ◽  
...  
Keyword(s):  
Morphological Properties ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
Small Scale ◽  
Short Baseline ◽  
Stellar Objects ◽  
Spatially Resolved ◽  
Long Baseline ◽  
The Relationship ◽  
The Continuum

Context. The relationship between outflow launching and the formation of accretion disks around young stellar objects is still not entirely understood, which is why spectrally and spatially resolved observations are needed. Recently, the Atacama Large Millimetre/sub-millimetre Array (ALMA) carried out long-baseline observations towards a handful of young sources, revealing connections between outflows and the inner regions of disks. Aims. Here we aim to determine the small-scale kinematical and morphological properties of the outflow from the isolated protostar B335 for which no Keplerian disk has, so far, been observed on scales down to 10 au. Methods. We used ALMA in its longest-baseline configuration to observe emission from CO isotopologues, SiO, SO2, and CH3OH. The proximity of B335 provides a resolution of ~3 au (0.03′′). We also combined our long-baseline data with archival observations to produce a high-fidelity image covering scales up to 700 au (7′′). Results. 12CO has an X-shaped morphology with arms ~50 au in width that we associate with the walls of an outflow cavity, similar to what is observed on larger scales. Long-baseline continuum emission is confined to <7 au from the protostar, while short-baseline continuum emission follows the 12CO outflow and cavity walls. Methanol is detected within ~30 au of the protostar. SiO is also detected in the vicinity of the protostar, but extended along the outflow. Conclusions. The 12CO outflow does not show any clear signs of rotation at distances ≳30 au from the protostar. SiO traces the protostellar jet on small scales, but without obvious rotation. CH3OH and SO2 trace a region <16 au in diameter, centred on the continuum peak, which is clearly rotating. Using episodic, high-velocity, 12CO features, we estimate the launching radius of the outflow to be <0.1 au and dynamical timescales of the order of a few years.

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

2019 ◽  
Vol 492 (1) ◽  
pp. 294-314 ◽  
Author(s):  
Zhen Guo (郭震) ◽  
P W Lucas ◽  
C Contreras Peña ◽  
R G Kurtev ◽  
L C Smith ◽  
...  
Keyword(s):  
Time Scales ◽  
Near Infrared ◽  
Accretion Rate ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Molecular Outflow ◽  
Infrared Spectroscopic ◽  
Long Time ◽  
The One ◽  
H2 Flux

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.

scholarly journals The effects of ionization feedback on star formation: a case study of the M 16 H II region

2019 ◽  
Vol 627 ◽  
pp. A27 ◽  
Author(s):  
Jin-Long Xu ◽  
Annie Zavagno ◽  
Naiping Yu ◽  
Xiao-Lan Liu ◽  
Ye Xu ◽  
...  
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Young Stellar Objects ◽  
Ionized Gas ◽  
Stellar Objects ◽  
Multi Wavelength ◽  
The Mean ◽  
The Impact ◽  
The Relationship

Aims. We aim to investigate the impact of the ionized radiation from the M 16 H II region on the surrounding molecular cloud and on its hosted star formation. Methods. To present comprehensive multi-wavelength observations towards the M 16 H II region, we used new CO data and existing infrared, optical, and submillimeter data. The 12CO J = 1−0, 13CO J = 1−0, and C18O J = 1−0 data were obtained with the Purple Mountain Observatory (PMO) 13.7 m radio telescope. To trace massive clumps and extract young stellar objects (YSOs) associated with the M 16 H II region, we used the ATLASGAL and GLIMPSE I catalogs, respectively. Results. From CO data, we discern a large-scale filament with three velocity components. Because these three components overlap with each other in both velocity and space, the filament may be made of three layers. The M 16 ionized gas interacts with the large-scale filament and has reshaped its structure. In the large-scale filament, we find 51 compact cores from the ATLASGAL catalog, 20 of them being quiescent. The mean excitation temperature of these cores is 22.5 K, while this is 22.2 K for the quiescent cores. This high temperature observed for the quiescent cores suggests that the cores may be heated by M 16 and do not experience internal heating from sources in the cores. Through the relationship between the mass and radius of these cores, we obtain that 45% of all the cores are massive enough to potentially form massive stars. Compared with the thermal motion, the turbulence created by the nonthermal motion is responsible for the core formation. For the pillars observed towards M 16, the H II region may give rise to the strong turbulence.

scholarly journals A 1.3 mm SMA survey of 29 variable young stellar objects

2018 ◽  
Vol 612 ◽  
pp. A54 ◽  
Author(s):  
Hauyu Baobab Liu ◽  
Michael M. Dunham ◽  
Ilaria Pascucci ◽  
Tyler L. Bourke ◽  
Naomi Hirano ◽  
...  
Keyword(s):  
Angular Resolution ◽  
Accretion Rate ◽  
Dust Emission ◽  
Young Stellar Objects ◽  
Mass Star ◽  
Gas Reservoirs ◽  
Stellar Objects ◽  
Star Forming ◽  
Low Mass ◽  
One Year

Context. Young stellar objects (YSOs) may undergo periods of active accretion (outbursts), during which the protostellar accretion rate is temporarily enhanced by a few orders of magnitude. Whether or not these accretion outburst YSOs possess similar dust and gas reservoirs to each other, and whether or not their dust and gas reservoirs are similar as quiescent YSOs, are issues yet to be clarified. Aims. The aim of this work is to characterize the millimeter thermal dust emission properties of a statistically significant sample of long and short duration accretion outburst YSOs (i.e., FUors and EXors) and the spectroscopically identified candidates of accretion outbursting YSOs (i.e., FUor-like objects). Methods. We have carried out extensive Submillimeter Array (SMA) observations mostly at ~225 GHz (1.33 mm) and ~272 GHz (1.10 mm), from 2008 to 2017. We covered accretion outburst YSOs located at <1 kpc distances from the solar system. Results. We analyze all the existing SMA data of such objects, both published and unpublished, in a coherent way to present a millimeter interferometric database of 29 objects. We obtained 21 detections at >3σ significance. Detected sources except for the two cases of V883 Ori and NGC 2071 MM3 were observed with ~1″ angular resolution. Overall our observed targets show a systematically higher millimeter luminosity distribution than those of the M* > 0.3 M⊙ Class II YSOs in the nearby (≲400 pc) low-mass star-forming molecular clouds (e.g., Taurus, Lupus, Upp Scorpio, and Chameleon I). In addition, at 1 mm our observed confirmed binaries or triple-system sources are systematically fainter than the rest of the sources even though their 1 mm fluxes are broadly distributed. We may have detected ~30−60% millimeter flux variability from V2494 Cyg and V2495 Cyg, from the observations separated by approximately one year.

scholarly journals The W51 Main/South SFR complex seen through 6-GHz OH and methanol masers

2012 ◽  
Vol 8 (S287) ◽  
pp. 171-175 ◽  
Author(s):  
Sandra Etoka ◽  
Malcolm D. Gray ◽  
Gary A. Fuller
Keyword(s):  
Young Stellar Objects ◽  
High Mass ◽  
Mass Star ◽  
Stellar Objects ◽  
Maser Emission ◽  
Star Forming ◽  
Methanol Maser ◽  
Star Forming Regions ◽  
Relationship Of ◽  
The Relationship

AbstractW51 Main/South is one of the brightest and richest high-mass star-forming regions (SFR) in the complex W51. It is known to host many ultra-compact HII (UCHII) regions thought to be the site of massive young stellar objects. Maser emission from various species is also found in the region. We have performed MERLIN astrometric observations of excited-OH maser emission at 6.035 GHz and Class II methanol maser emission at 6.668 GHz towards W51 to investigate the relationship between the maser emission and the compact continuum sources in this SFR complex. Here we present the astrometric distributions of both 6.668-GHz methanol and 6.035-GHz excited-OH maser emission in the W51 Main/South region. The location of maser emission in the two lines is compared with that of previously published OH groundstate emission. The interesting coherent velocity and spatial structure observed in the methanol maser distribution as well as the relationship of the masers to infall or outflow in the region are discussed. It appears that the masers are excited by multiple objects potentially at different stages of evolution.

scholarly journals Long-term variability of H2O masers in YSOs

2002 ◽  
Vol 206 ◽  
pp. 51-54 ◽  
Author(s):  
Riccardo Valdettaro ◽  
Francesco Palla ◽  
Jan Brand ◽  
Riccardo Cesaroni ◽  
Giovanni Comoretto ◽  
...  
Keyword(s):  
Stellar Mass ◽  
Young Stellar Objects ◽  
Frequency Of Occurrence ◽  
Velocity Range ◽  
Stellar Objects ◽  
Spectral Components ◽  
The Relationship ◽  
Maser Sources ◽  
Water Maser

A sample of 14 water maser sources associated with young stellar objects (YSOs) has been monitored over 13 years with the Medicina 32-m antenna. The YSOs have been selected with bolometric luminosities from 20 L⊙ to 2 × 106 L⊙ with the aim of investigating the relationship between H2O maser variability and stellar mass. The results are presented in various graphical forms which allow to follow the variation of the different spectral components. In particular, four quantities have been considered in our analysis: the intensity of the maser lines as a function of time and velocity; the flux integrated over the observed velocity range as a function of time; the maximum flux ever observed at each velocity; and the frequency of occurrence of the maser emission at any given velocity.

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

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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