H2 shocks and mass accretion rate in high mass young stellar objects (HMYSOs)

Determining the mechanisms that drive the evolution of protoplanetary disks is a necessary step toward understanding how planets form. For this work, we measured the mass accretion rate for young stellar objects with disks at age > 5 Myr, a critical test for the current models of disk evolution. We present the analysis of the spectra of 36 targets in the ∼5–10 Myr old Upper Scorpius star-forming region for which disk masses were measured with ALMA. We find that the mass accretion rates in this sample of old but still surviving disks are similarly high as those of the younger (∼1−3 Myr old) star-forming regions of Lupus and Chamaeleon I, when considering the dependence on stellar and disk mass. In particular, several disks show high mass accretion rates ≳10−9 M⊙ yr−1 while having low disk masses. Furthermore, the median values of the measured mass accretion rates in the disk mass ranges where our sample is complete at a level ∼60−80% are compatible in these three regions. At the same time, the spread of mass accretion rates at any given disk mass is still > 0.9 dex, even at age > 5 Myr. These results are in contrast with simple models of viscous evolution, which would predict that the values of the mass accretion rate diminish with time, and a tighter correlation with disk mass at age > 5 Myr. Similarly, simple models of internal photoevaporation cannot reproduce the observed mass accretion rates, while external photoevaporation might explain the low disk masses and high accretion rates. A possible partial solution to the discrepancy with the viscous models is that the gas-to-dust ratio of the disks at ∼5–10 Myr is significantly different and higher than the canonical 100, as suggested by some dust and gas disk evolution models. The results shown here require the presence of several interplaying processes, such as detailed dust evolution, external photoevaporation, and possibly MHD winds, to explain the secular evolution of protoplanetary disks.

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732196 ◽

2018 ◽

Vol 616 ◽

pp. A100 ◽

Cited By ~ 7

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.

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

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319002060 ◽

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.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3374 ◽

2019 ◽

Vol 492 (1) ◽

pp. 294-314 ◽

Cited By ~ 3

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.

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