Heating mechanisms in accretion disks around young stellar objects

2018 ◽  
Vol 14 (S345) ◽  
pp. 255-256
Author(s):  
Natália F.S. Andrade ◽  
Rafael Rechiche de Campos ◽  
Vera Jatenco-Pereira
Keyword(s):  
Accretion Disks ◽  
Alfven Waves ◽  
Young Stellar Objects ◽  
Alfvén Waves ◽  
Rotational Instability ◽  
Mhd Turbulence ◽  
Stellar Objects ◽  
Heating Source ◽  
Order Of Magnitude ◽  
Magnetic Filed

AbstractAccretion disks are observed around young stellar objects such as T Tauri stars. In order to complete the star formation, particles in the disk need to loose angular momentum in order to be accreted into the central object. The magneto-rotational instability (MRI) is probably the mechanism responsible for a magneto-hydrodynamic (MHD) turbulence that leads to disk accretion, which implies the disk particles to be coupled with the magnetic filed lines. As the temperature in the disk is low, we considered, besides the viscous heating mechanism often included in the models by means of the α - prescription, the damping of Alfvén waves as an additional heating source. In particular, we show that the mechanism derived that couples the turbulent and non-linear damping mechanisms of Alfvén waves proved to be very efficient, generating temperatures almost one order of magnitude higher than those mechanisms considered independently.

scholarly journals Models of Accretion Disks Around Young Stars

2004 ◽  
Vol 221 ◽  
pp. 403-410 ◽  
Author(s):  
Paola D'Alessio ◽  
Nuria Calvet ◽  
Lee Hartmann ◽  
James Muzerolle ◽  
Michael Sitko
Keyword(s):  
Accretion Disks ◽  
Young Stars ◽  
Stellar Surface ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Disk Structure ◽  
Accretion Rates ◽  
Accretion Shocks

We discuss the importance of accretion in calculating disk models for young stellar objects. In particular, we show that a disk inner rim, irradiated by both the star and the accretion shocks at the stellar surface, can naturally explain recent observations of DG Tau with the Keck interferometer. We present models for two objects, with mass accretion rates differing by almost two orders of magnitude, to illustrate the effects of accretion on the overall disk structure and emission.

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.

Molecular Clouds and Star Formation in the Southern H II Regions

1999 ◽  
Vol 51 (6) ◽  
pp. 791-818 ◽  
Author(s):  
Reiko Yamaguchi ◽  
Hiro Saito ◽  
Norikazu Mizuno ◽  
Yoshihiro Mine ◽  
Akira Mizuno ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Formation Rate ◽  
Point Sources ◽  
Young Stellar Objects ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Order Of Magnitude ◽  
Formation Efficiency ◽  
Active Formation

Abstract We have carried out extensive 13CO(J = 1−0) observations toward 23 southern H II regions associated with bright-rimmed clouds. In total, 95 molecular clouds have been identified to be associated with the H II regions. Among the 95, 57 clouds \ are found to be associated with 204 IRAS point sources which are candidates for young stellar objects. There is a significant increase of star-formation efficiency on the side facing to the H II regions; the luminosity-to-mass ratio, defined as the ratio of the stellar luminosity to the molecular cloud mass, is higher by an order of magnitude on the near side of the H II regions than that on the far side. This indicates that molecular gas facing to the H II regions is more actively forming massive s\ tars whose luminosity is ≳103L⊙. In addition, the number density of the IRAS point sources increases by a factor of 2 on the near side of the H II regions compared with on the far side. These results strongly suggest that the active formation of massive stars on the near side of the H II regions is due to the effects of the H II regions, such as the compression of molecular material by the ionization/shock fronts. For the whole Galaxy, we estimate that the present star-formation rate under such effects is at least 0.2−0.4 M⊙ yr-1, corresponding to a few 10% by mass.

scholarly journals Massive Star Formation: Observational Constraints

1997 ◽  
Vol 182 ◽  
pp. 525-536
Author(s):  
Ed Churchwell
Keyword(s):  
Star Formation ◽  
Accretion Disks ◽  
Massive Star ◽  
Young Stellar Objects ◽  
Mass Star ◽  
Structure And Properties ◽  
Low Mass Stars ◽  
Stellar Objects ◽  
The Past ◽  
Low Mass

Observations during the past several years strongly imply that virtually every star, independent of final mass, goes through a phase of rapid outflow simultaneously with rapid accretion during formation. The structure and properties of outflows and accretion disks associated with low-mass star formation has received intensive observational attention during the past several years (see the reviews and references in Lada 1985; Edwards, Ray, and Mundt 1993; Fukui et al. 1993; and this symposium). Young stellar objects (YSOs) with Lbol < 103 L⊘ will be referred to as “low-mass” stars in this review. The range of physical properties of CO outflows associated with YSOs of all masses are enormous, see Fukui et al. (1993). I will focus attention in this review on what we know about massive YSOs and their environments.

scholarly journals Activity and Kinematics of Late M, L, and T Dwarfs

2003 ◽  
Vol 211 ◽  
pp. 437-442
Author(s):  
James Liebert
Keyword(s):  
Spectral Type ◽  
Young Stellar Objects ◽  
Evolutionary Models ◽  
M Dwarfs ◽  
Stellar Objects ◽  
Order Of Magnitude ◽  
Hα Emission ◽  
L Dwarfs ◽  
Larger Sample ◽  
Rule Out

The kinematics of late M and certainly L dwarfs indicate that they have a mean age of no more than a few Gyr. This result does not rule out a mix of young brown dwarfs and ZAMS stars. Relative Hα emission strengths begin to decline in the late M dwarfs, even though about 100% of the M7-8 dwarfs show the weaker emission. Both the frequency and likely strength of this emission declines with spectral type among the L's and T's. A larger sample of late M and L dwarfs, which may provide more definitive tests of the kinematic and activity properties, is being assembled from our NStars project.Two unusual objects, one an M9.5e and the other a T6e, show persistent Hα emission at least an order of magnitude stronger than their counterparts of similar spectral type. If these are hypothesized to be very young stellar objects (≲10 Myr) like some observed in Rho Oph, Sigma Ori and Taurus – evolutionary models would require them to have very low masses: In particular, for an entity to fade to a late T dwarf temperature and luminosity within 10 Myr, its mass should be no more than several Jupiters. This seems implausible for an isolated object not near any obvious site of recent star formation. However, our attempt to show that the emission might be due to accretion in a binary system was unsuccessful.

Small scale structures in the footprint tails of the Galilean moons observed by JIRAM

2021 ◽  
Author(s):  
Alessandro Moirano ◽  
Alessandro Mura ◽  
Alberto Adriani ◽  
Roberto Sordini ◽  
Alessandra Migliorini ◽  
...  
Keyword(s):  
Alfven Waves ◽  
Alfvén Waves ◽  
Small Scale ◽  
Potential Candidate ◽  
Orbital Parameters ◽  
Auroral Emission ◽  
Galilean Moons ◽  
Order Of Magnitude ◽  
Scale Structures ◽  
Small Scale Structures

&lt;p&gt;The Jovian Infrared Auroral Mapper (JIRAM) on board Juno is a spectro-imager which is observing the&lt;br&gt;atmosphere of Jupiter and its auroral emission using its two imagers in the L (3.3-3.6&amp;#956;m) and M bands (4.5-&lt;br&gt;5.0&amp;#956;m) and a spectrometer (2-5 &amp;#956;m spectral range).&lt;br&gt;The highly elliptic orbit of Juno and the unprecedented resolution of the JIRAM imager allowed to retrieve&lt;br&gt;wealth of details about the morphology of moon-related aurorae. This phenomenon is due to the jovian magnetic&lt;br&gt;field sweeping past the Galiean moons, which generate Alfven waves travelling towards the ionosphere and set&lt;br&gt;up field aligned currents. When the associated electrons reach the ionosphere, they interact with the hydrogen&lt;br&gt;and make it to glow. In particular, the tails of the footprints showed a spot-like substructure consistently, which&lt;br&gt;were investigated using the L-band of the imager from perijove 4 to perijove 30. This feature was observed close&lt;br&gt;to the footprints, where the the typical distance between spots lies between 250km and 500km. This distance&lt;br&gt;decreases to 150km in a group of three observations in the northern emisphere when each moon is close to 250 &amp;#9702;&lt;br&gt;west longitude. No correlation with orbital parameters such as the longitude of the moons was found so far,&lt;br&gt;which suggests that such morphology is almost purely due to ionospheric processes.&lt;br&gt;Moreover, during PJ 13 a long sequence of images of the Io footprint was shot and it revealed that the&lt;br&gt;secondary spots appears to corotate with Jupiter. This behaviour is observed also during orbits 14 and 26.&lt;br&gt;During these sequences JIRAM clearly observed the Io footprint leaving behind a trail of &amp;#8221;footsteps&amp;#8221; as bright&lt;br&gt;spots.&lt;br&gt;The characteristics of these spots are incompatible with multiple reflection of Alfven waves between the two&lt;br&gt;emispheres. Instead, we are currently investigating ionospheric processes like the feedback instability (FI) as a&lt;br&gt;potential candidate to explain the generation of the observed small scale structure. This process relies on local&lt;br&gt;enhacement of conductivity in the ionosphere, which is affected by electron precipitation. Order of magnitude&lt;br&gt;estimates from the FI are compatible with the inter-spot distance and the stillness of the spots.&lt;/p&gt;

scholarly journals Alfvén waves damping in protostellar disks providing a way to expand the action of the magneto-rotational instability

2006 ◽  
Vol 2 (S237) ◽  
pp. 491-491
Author(s):  
A. A. Vidotto ◽  
V. Jatenco-Pereira
Keyword(s):  
Viscous Dissipation ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Rotational Instability ◽  
Dust Grains ◽  
Heating Mechanism ◽  
Protostellar Disks

AbstractIn order for the magneto-rotational instability to take place, we need a sufficiently ionized disk. Here, we study, besides viscous dissipation, another heating mechanism for the disk that involves the damping of Alfvén waves due to its interaction with dust grains.

scholarly journals A movie of accretion/ejection of material in a high-mass YSO in Orion BN/KL at radii comparable to the Solar System

2009 ◽  
Vol 5 (H15) ◽  
pp. 750-750 ◽  
Author(s):  
C. Goddi ◽  
L. Greenhill ◽  
E. Humphreys ◽  
L. Matthews ◽  
C. Chandler
Keyword(s):  
Accretion Disks ◽  
Gas Flow ◽  
Dynamical Evolution ◽  
Young Stellar Objects ◽  
High Mass ◽  
Mass Star ◽  
Proper Motions ◽  
Compact Disk ◽  
Stellar Objects ◽  
Circumstellar Gas

Around high-mass Young Stellar Objects (YSOs), outflows are expected to be launched and collimated by accretion disks inside radii of 100 AU. Strong observational constraints on disk-mediated accretion in this context have been scarce, largely owing to difficulties in probing the circumstellar gas at scales 10-100 AU around high-mass YSOs, which are on average distant (>1 Kpc), form in clusters, and ignite quickly whilst still enshrouded in dusty envelopes. Radio Source I in Orion BN/KL is the nearest example of a high-mass YSO, and only one of three YSOs known to power SiO masers. Using VLA and VLBA observations of different SiO maser transitions, the KaLYPSO project (http://www.cfa.harvard.edu/kalypso/) aims to overcome past observational limitations by mapping the structure, 3-D velocity field, and dynamical evolution of the circumstellar gas within 1000 AU from Source I. Based on 19 epochs of VLBA observations of v=1,2 SiO masers over ~2 years, we produced a movie of bulk gas flow tracing the compact disk and the base of the protostellar wind at radii < 100 AU from Source I. In addition, we have used the VLA to map 7mm SiO v=0 emission and track proper motions over 10 years. We identify a narrowly collimated outflow with a mean motion of 18 km/s at radii 100-1000 AU, along a NE-SW axis perpendicular to that of the disk traced by the v=1,2 masers. The VLBA and VLA data exclude alternate models that place outflow from Source I along a NW-SE axis. The analysis of the complete (VLBA and VLA) dataset provides the most detailed evidence to date that high-mass star formation occurs via disk-mediated accretion.

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