scholarly journals Envelope-to-disk mass transport in the FUor-type young eruptive star V346 Normae

2018 ◽  
Vol 14 (S345) ◽  
pp. 320-321
Author(s):  
Á. Kóspál ◽  
P. Ábrahám ◽  
O. Fehér ◽  
F. Cruz-Sáenz de Miera ◽  
M. Takami
Keyword(s):  
Mass Transport ◽  
Velocity Structure ◽  
Accretion Rate ◽  
Central Star ◽  
Type Star ◽  
Disk Mass ◽  
Disk Material ◽  
Accretion Rates

AbstractHaving disk-to-star accretion rates on the order of 10-4M⊙/yr, FU Orionis-type stars (FUors) are thought to be the visible examples for episodic accretion. FUors are often surrounded by massive envelopes, which replenish the disk material and enable the disk to produce accretion outbursts. We observed the FUor-type star V346 Nor with ALMA at 1.3 mm continuum and in different CO rotational lines. We mapped the density and velocity structure of its envelope and analyzed the results using channel maps, position-velocity diagrams, and spectro-astrometric methods. We discovered a pseudo-disk and a Keplerian disk around a 0.1 M⊙ central star. We determined an infall rate from the envelope onto the disk of 6×10-6M⊙/yr, a factor of few higher than the quiescent accretion rate from the disk onto the star. This hints for a mismatch between the infall and accretion rates as the cause of the eruption.

scholarly journals Effects of photoevaporation on protoplanetary disc ‘isochrones’

2019 ◽  
Vol 492 (1) ◽  
pp. 1120-1126 ◽  
Author(s):  
Alice Somigliana ◽  
Claudia Toci ◽  
Giuseppe Lodato ◽  
Giovanni Rosotti ◽  
Carlo F Manara
Keyword(s):  
Numerical Solutions ◽  
Accretion Rate ◽  
Central Star ◽  
Mass Region ◽  
Self Similar Solution ◽  
Accretion Rates ◽  
Standard Scenario ◽  
Inner Region ◽  
Viscous Transport ◽  
Protoplanetary Discs

ABSTRACT Protoplanetary discs are the site of star and planet formation, and their evolution and consequent dispersal deeply affect the formation of planetary systems. In the standard scenario they evolve on time-scales ∼Myr due to the viscous transport of angular momentum. The analytical self-similar solution for their evolution predicts specific disc isochrones in the accretion rate–disc mass plane. However, photoevaporation by radiation emitted by the central star is likely to dominate the gas disc dispersal of the innermost region, introducing another (shorter) time-scale for this process. In this paper, we include the effect of internal (X and EUV) photoevaporation on the disc evolution, finding numerical solutions for a population of protoplanetary discs. Our models naturally reproduce the expected quick dispersal of the inner region of discs when their accretion rates match the rate of photoevaporative mass loss, in line with previous studies. We find that photoevaporation preferentially removes the lightest discs in the sample. The net result is that, counter-intuitively, photoevaporation increases the average disc mass in the sample, by dispersing the lightest discs. At the same time, photoevaporation also reduces the mass accretion rate by cutting the supply of material from the outer to the inner disc. In a purely viscous framework, this would be interpreted as the result of a longer viscous evolution, leading to an overestimate of the disc age. Our results thus show that photoevaporation is a necessary ingredient to include when interpreting observations of large disc samples with measured mass accretion rates and disc masses. Photoevaporation leaves a characteristic imprint on the shape of the isochrone. Accurate data of the accretion rate–disc mass plane in the low disc mass region therefore give clues on the typical photoevaporation rate.

scholarly journals X-shooter survey of disk accretion in Upper Scorpius

2020 ◽  
Vol 639 ◽  
pp. A58 ◽  
Author(s):  
C. F. Manara ◽  
A. Natta ◽  
G. P. Rosotti ◽  
J. M. Alcalá ◽  
B. Nisini ◽  
...  
Keyword(s):  
Accretion Rate ◽  
Protoplanetary Disks ◽  
Young Stellar Objects ◽  
High Mass ◽  
Star Forming ◽  
Mass Accretion Rate ◽  
Disk Mass ◽  
Accretion Rates ◽  
Disk Evolution ◽  
Simple Models

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.

scholarly journals Multi-epoch monitoring of the AA Tauri-like star V 354 Mon

2018 ◽  
Vol 614 ◽  
pp. A108 ◽  
Author(s):  
P. C. Schneider ◽  
C. F. Manara ◽  
S. Facchini ◽  
H. M. Günther ◽  
G. J. Herczeg ◽  
...  
Keyword(s):  
Accretion Rate ◽  
Central Star ◽  
T Tauri Stars ◽  
Gas Absorption ◽  
Gas Content ◽  
Dust Extinction ◽  
T Tauri ◽  
Disk Material ◽  
A Minor ◽  
High Dust

Disk warps around classical T Tauri stars (CTTSs) can periodically obscure the central star for some viewing geometries. For these so- called AA Tau-like variables, the obscuring material is located in the inner disk and absorption spectroscopy allows one to characterize its dust and gas content. Since the observed emission from CTTSs consists of several components (photospheric, accretion, jet, and disk emission), which can all vary with time, it is generally challenging to disentangling disk features from emission variability. Multi- epoch, flux-calibrated, broadband spectra provide us with the necessary information to cleanly separate absorption from emission variability. We applied this method to three epochs of VLT/X-shooter spectra of the CTTS V 354 Mon (CSI Mon-660) located in NGC 2264 and find that: (a) the accretion emission remains virtually unchanged between the three epochs; (b) the broadband flux evolution is best described by disk material obscuring part of the star, and (c) the Na and K gas absorption lines show only a minor increase in equivalent width during phases of high dust extinction. The limits on the absorbing gas column densities indicate a low gas-to-dust ratio in the inner disk, less than a tenth of the ISM value. We speculate that the evolutionary state of V 354 Mon, rather old with a low accretion rate, is responsible for the dust excess through an evolution toward a dust dominated disk or through the fragmentation of larger bodies that drifted inward from larger radii in a still gas dominated disk.

Time-scales to reach chemical equilibrium in ices at snowline distance around compact objects: the influence of accretion mass in the central object

2021 ◽  
Vol 503 (2) ◽  
pp. 2973-2978
Author(s):  
G A Carvalho ◽  
S Pilling
Keyword(s):  
Time Scales ◽  
Chemical Equilibrium ◽  
Accretion Rate ◽  
Radiation Reaction ◽  
Compact Objects ◽  
Compact Stars ◽  
X Ray ◽  
Accretion Rates ◽  
Central Compact Objects ◽  
Astrophysical Ices

ABSTRACT In this work, we analyse soft X-ray emission due to mass accretion on to compact stars and its effects on the time-scale to reach chemical equilibrium of eventual surrounding astrophysical ices exposed to that radiation. Reaction time-scales due to soft X-ray in water-rich and pure ices of methanol, acetone, acetonitrile, formic acid, and acetic acid were determined. For accretion rates in the range $\dot{m}=10^{-12}\!-\!10^{-8}\,{\rm M}_\odot$ yr−1 and distances in the range 1–3 LY from the central compact objects, the time-scales lie in the range 10–108 yr, with shorter time-scales corresponding to higher accretion rates. Obtained time-scales for ices at snow-line distances can be small when compared to the lifetime (or age) of the compact stars, showing that chemical equilibrium could have been achieved. Time-scales for ices to reach chemical equilibrium depend on X-ray flux and, hence, on accretion rate, which indicates that systems with low accretion rates may not have reached chemical equilibrium.

Effect of Protein accretion rate on reproductive function in the gilt between 50kg and 3rd oestrus

1999 ◽  
Vol 1999 ◽  
pp. 6-6
Author(s):  
J. Cameron ◽  
J. Wiseman ◽  
R. Webb ◽  
M.G. Hunter
Keyword(s):  
Accretion Rate ◽  
Genetic Selection ◽  
Reproductive Function ◽  
Reproductive Failure ◽  
Lean Tissue ◽  
Body Protein ◽  
Protein Mass ◽  
Accretion Rates ◽  
Selection For ◽  
Tissue Accretion

Recent MLC survey data (Pig Year Book, 1995) reports that approximately 0.5 of annual first parity gilt cullings are due to reproductive failure. This high culling rate may be attributed to recent genetic selection for increased lean tissue accretion rates, and as a result a greater mature body weight. However, the gilt attains puberty and is thus mated at a lower age and as a consequence has not reached the target threshold of 35kg body protein mass at farrowing, suggested by Everts (1994),to be necessary for optimal reproductive performance. This, confounded with excessive tissue catabolism over lactation results in the attenuation of the gilt's potential protein accretion curve and hence reproductive failure (Foxcroft et al. 1995). The aim of this experiment was to study the effect of two protein accretion rates (maximum and 0.8 of maximum) on reproductive function in the gilt from 50kg liveweight to 3rd oestrus.

scholarly journals Radiative efficiency of hot accretion flow and the radio/X-ray correlation in X-ray binaries

2014 ◽  
Vol 10 (S312) ◽  
pp. 139-140
Author(s):  
Fu-Guo Xie
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
X Ray ◽  
Radiative Efficiency ◽  
Accretion Flow ◽  
Accretion Rates ◽  
Distinctive Property ◽  
X Ray Binaries

AbstractSignificant progresses have been made since the discovery of hot accretion flow, a theory successfully applied to the low-luminosity active galactic nuclei (LLAGNs) and black hole (BH) X-ray binaries (BHBs) in their hard states. Motivated by these updates, we re-investigate the radiative efficiency of hot accretion flow. We find that, the brightest regime of hot accretion flow shows a distinctive property, i.e. it has a constant efficiency independent of accretion rates, similar to the standard thin disk. For less bright regime, the efficiency has a steep positive correlation with the accretion rate, while for faint regime typical of advection-dominated accretion flow, the correlation is shadower. This result can naturally explain the observed two distinctive correlations between radio and X-ray luminosities in black hole X-ray binaries. The key difference in systems with distinctive correlations could be the viscous parameter, which determines the critical luminosity of different accretion modes.

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 Planet formation by pebble accretion in ringed disks

2020 ◽  
Vol 638 ◽  
pp. A1 ◽  
Author(s):  
A. Morbidelli
Keyword(s):  
Growth Rate ◽  
Upper Bound ◽  
Planet Formation ◽  
Accretion Rate ◽  
Central Star ◽  
Giant Planets ◽  
Type I ◽  
Dust Density ◽  
Dominant Process ◽  
The One

Context. Pebble accretion is expected to be the dominant process for the formation of massive solid planets, such as the cores of giant planets and super-Earths. So far, this process has been studied under the assumption that dust coagulates and drifts throughout the full protoplanetary disk. However, observations show that many disks are structured in rings that may be due to pressure maxima, preventing the global radial drift of the dust. Aims. We aim to study how the pebble-accretion paradigm changes if the dust is confined in a ring. Methods. Our approach is mostly analytic. We derived a formula that provides an upper bound to the growth of a planet as a function of time. We also numerically implemented the analytic formulæ to compute the growth of a planet located in a typical ring observed in the DSHARP survey, as well as in a putative ring rescaled at 5 AU. Results. Planet Type I migration is stopped in a ring, but not necessarily at its center. If the entropy-driven corotation torque is desaturated, the planet is located in a region with low dust density, which severely limits its accretion rate. If the planet is instead near the ring’s center, its accretion rate can be similar to the one it would have in a classic (ringless) disk of equivalent dust density. However, the growth rate of the planet is limited by the diffusion of dust in the ring, and the final planet mass is bounded by the total ring mass. The DSHARP rings are too far from the star to allow the formation of massive planets within the disk’s lifetime. However, a similar ring rescaled to 5 AU could lead to the formation of a planet incorporating the full ring mass in less than 1/2 My. Conclusions. The existence of rings may not be an obstacle to planet formation by pebble-accretion. However, for accretion to be effective, the resting position of the planet has to be relatively near the ring’s center, and the ring needs to be not too far from the central star. The formation of planets in rings can explain the existence of giant planets with core masses smaller than the so-called pebble isolation mass.

scholarly journals Testing viscous disc theory using the balance between stellar accretion and external photoevaporation of protoplanetary discs

2020 ◽  
Vol 497 (1) ◽  
pp. L40-L45
Author(s):  
Andrew J Winter ◽  
Megan Ansdell ◽  
Thomas J Haworth ◽  
J M Diederik Kruijssen
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Central Star ◽  
Outer Edge ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Accretion Rates ◽  
Novel Method ◽  
Viscous Models ◽  
Protoplanetary Discs

ABSTRACT The nature and rate of (viscous) angular momentum transport in protoplanetary discs (PPDs) have important consequences for the formation process of planetary systems. While accretion rates on to the central star yield constraints on such transport in the inner regions of a PPD, empirical constraints on viscous spreading in the outer regions remain challenging to obtain. Here, we demonstrate a novel method to probe the angular momentum transport at the outer edge of the disc. This method applies to PPDs that have lost a significant fraction of their mass due to thermal winds driven by UV irradiation from a neighbouring OB star. We demonstrate that this external photoevaporation can explain the observed depletion of discs in the 3–5 Myr old σ Orionis region, and use our model to make predictions motivating future empirical investigations of disc winds. For populations of intermediate-age PPDs, in viscous models we show that the mass flux outwards due to angular momentum redistribution is balanced by the mass-loss in the photoevaporative wind. A comparison between wind mass-loss and stellar accretion rates therefore offers an independent constraint on viscous models in the outer regions of PPDs.

scholarly journals Tidal disruption event discs around supermassive black holes: disc warp and inclination evolution

2019 ◽  
Vol 487 (4) ◽  
pp. 4965-4984 ◽  
Author(s):  
J J Zanazzi ◽  
Dong Lai
Keyword(s):  
Black Hole ◽  
Equatorial Plane ◽  
Accretion Rate ◽  
Accretion Disc ◽  
Precession Frequency ◽  
Tidal Disruption ◽  
Eigenmode Analysis ◽  
Accretion Rates ◽  
Rigid Disc ◽  
Disruption Event

ABSTRACT After the tidal disruption event (TDE) of a star around a supermassive black hole (SMBH), the bound stellar debris rapidly forms an accretion disc. If the accretion disc is not aligned with the spinning SMBH’s equatorial plane, the disc will be driven into Lense–Thirring precession around the SMBH’s spin axis, possibly affecting the TDE’s light curve. We carry out an eigenmode analysis of such a disc to understand how the disc’s warp structure, precession, and inclination evolution are influenced by the disc’s and SMBH’s properties. We find an oscillatory warp may develop as a result of strong non-Keplarian motion near the SMBH. The global disc precession frequency matches the Lense–Thirring precession frequency of a rigid disc around a spinning black hole within a factor of a few when the disc’s accretion rate is high, but deviates significantly at low accretion rates. Viscosity aligns the disc with the SMBH’s equatorial plane over time-scales of days to years, depending on the disc’s accretion rate, viscosity, and SMBH’s mass. We also examine the effect of fallback material on the warp evolution of TDE discs, and find that the fallback torque aligns the TDE disc with the SMBH’s equatorial plane in a few to tens of days for the parameter space investigated. Our results place constraints on models of TDE emission which rely on the changing disc orientation with respect to the line of sight to explain observations.

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