17 research outputs found
A New Look at T Tauri Star Forbidden Lines: MHD Driven Winds from the Inner Disk
Magnetohydrodynamic (MHD) and photoevaporative winds are thought to play an
important role in the evolution and dispersal of planet-forming disks. We
report the first high-resolution (6\kms) analysis of [S II]
4068, [O I] 5577, and [O I] 6300 lines from a sample
of 48 T Tauri stars. Following Simon et al. (2016), we decompose them into
three kinematic components: a high-velocity component (HVC) associated with
jets, and a low-velocity narrow (LVC-NC) and broad (LVC-BC) components. We
confirm previous findings that many LVCs are blueshifted by more than 1.5
kms thus most likely trace a slow disk wind. We further show that the
profiles of individual components are similar in the three lines. We find that
most LVC-BC and NC line ratios are explained by thermally excited gas with
temperatures between 5,00010,000 K and electron densities
cm. The HVC ratios are better reproduced by shock
models with a pre-shock H number density of cm.
Using these physical properties, we estimate for the LVC and for the HVC. In
agreement with previous work, the mass carried out in jets is modest compared
to the accretion rate. With the likely assumption that the NC wind height is
larger than the BC, the LVC-BC is found
to be higher than the LVC-NC. These results suggest that most of the mass loss
occurs close to the central star, within a few au, through an MHD driven wind.
Depending on the wind height, MHD winds might play a major role in the
evolution of the disk mass.Comment: 45 pages, 23 figures, and 7 tables, accepted by Ap
A New Look at T Tauri Star Forbidden Lines: MHD-driven Winds from the Inner Disk
Magnetohydrodynamic (MHD) and photoevaporative winds are thought to play an important role in the evolution and dispersal of planet-forming disks. We report the first high-resolution (∆v ∼ 6 km s−1 ) analysis of [S II] λ4068, [O I] λ5577, and [O I] λ6300 lines from a sample of 48 T Tauri stars. Following Simon et al. (2016), we decompose them into three kinematic components: a high-velocity component (HVC) associated with jets, and a low-velocity narrow (LVC-NC) and broad (LVC-BC) components. We confirm previous findings that many LVCs are blueshifted by more than 1.5 km s−1 thus most likely trace a slow disk wind. We further show that the profiles of individual components are similar in the three lines. We find that most LVC-BC and NC line ratios are explained by thermally excited gas with temperatures between 5,000−10,000 K and electron densities ∼ 107 −108 cm−3 . The HVC ratios are better reproduced by shock models with a pre-shock H number density of ∼ 106 − 107 cm−3 . Using these physical properties, we estimate M˙ wind/M˙ acc for the LVC and M˙ jet/M˙ acc for the HVC. In agreement with previous work, the mass carried out in jets is modest compared to the accretion rate. With the likely assumption that the NC wind height is larger than the BC, the LVC-BC M˙ wind/M˙ acc is found to be higher than the LVC-NC. These results suggest that most of the mass loss occurs close to the central star, within a few au, through an MHD driven wind. Depending on the wind height, MHD winds might play a major role in the evolution of the disk mass
Accretion, Outflows, and Winds of Magnetized Stars
Many types of stars have strong magnetic fields that can dynamically
influence the flow of circumstellar matter. In stars with accretion disks, the
stellar magnetic field can truncate the inner disk and determine the paths that
matter can take to flow onto the star. These paths are different in stars with
different magnetospheres and periods of rotation. External field lines of the
magnetosphere may inflate and produce favorable conditions for outflows from
the disk-magnetosphere boundary. Outflows can be particularly strong in the
propeller regime, wherein a star rotates more rapidly than the inner disk.
Outflows may also form at the disk-magnetosphere boundary of slowly rotating
stars, if the magnetosphere is compressed by the accreting matter. In isolated,
strongly magnetized stars, the magnetic field can influence formation and/or
propagation of stellar wind outflows. Winds from low-mass, solar-type stars may
be either thermally or magnetically driven, while winds from massive, luminous
O and B type stars are radiatively driven. In all of these cases, the magnetic
field influences matter flow from the stars and determines many observational
properties. In this chapter we review recent studies of accretion, outflows,
and winds of magnetized stars with a focus on three main topics: (1) accretion
onto magnetized stars; (2) outflows from the disk-magnetosphere boundary; and
(3) winds from isolated massive magnetized stars. We show results obtained from
global magnetohydrodynamic simulations and, in a number of cases compare global
simulations with observations.Comment: 60 pages, 44 figure
A 'Rosetta Stone' for protoplanetary disks:the synergy of multi-wavelength observations
The recent progress in instrumentation and telescope development has brought
us different ways to observe protoplanetary disks, including interferometers,
space missions, adaptive optics, polarimetry, and time- and spectrally-resolved
data. While the new facilities have changed the way we can tackle the existing
open problems in disk structure and evolution, there is a substantial lack of
interconnection between different observing techniques and their user
communities. Here, we explore the complementarity of some of the
state-of-the-art observing techniques, and how they can be brought together in
a collective effort to understand how disks evolve and disperse at the time of
planet formation.
This paper was born at the "Protoplanetary Discussions" meeting in Edinburgh,
2016. Its goal is to clarify where multi-wavelength observations of disks
converge in unveiling disk structure and evolution, and where they diverge and
challenge our current understanding. We discuss caveats that should be
considered when linking results from different observations, or when drawing
conclusions based on limited datasets (in terms of wavelength or sample). We
focus on disk properties that are currently being revolutionized by
multi-wavelength observations. Specifically: the inner disk radius, holes and
gaps and their link to large-scale disk structures, the disk mass, and the
accretion rate. We discuss how the links between them, as well as the apparent
contradictions, can help us to disentangle the disk physics and to learn about
disk evolution.Comment: Accepted for publication in PASA. 37 pages, 9 figures, 1 table.
Revised version: corrected problem in Fig
Interplay between n-3 and n-6 long-chain polyunsaturated fatty acids and the endocannabinoid system in brain protection and repair.
The brain is enriched in arachidonic acid (ARA) and docosahexaenoic acid (DHA), long-chain polyunsaturated fatty acids (LCPUFA) of the n-6 and n-3 series, respectively. Both are essential for optimal brain development and function. Dietary enrichment with DHA and other long-chain n-3 PUFA, such as eicosapentaenoic acid (EPA) have shown beneficial effects on learning and memory, neuroinflammatory processes and synaptic plasticity and neurogenesis. ARA, DHA and EPA are precursors to a diverse repertoire of bioactive lipid mediators, including endocannabinoids. The endocannabinoid system comprises cannabinoid receptors, their endogenous ligands, the endocannabinoids, and their biosynthetic and degradation enzymes. Anandamide (AEA) and 2-archidonoylglycerol (2-AG) are the most widely studied endocannabinoids, and are both derived from phospholipid-bound ARA. The endocannabinoid system also has well established roles in neuroinflammation, synaptic plasticity and neurogenesis, suggesting an overlap in the neuroprotective effects observed with these different classes of lipids. Indeed, growing evidence suggests a complex interplay between n-3 and n-6 LCPUFA and the endocannabinoid system. For example, long-term DHA and EPA supplementation reduces AEA and 2-AG levels, with reciprocal increases in levels of the analogous endocannabinoid-like DHA and EPA-derived molecules. This review summarises current evidence of this interplay and discusses the therapeutic potential for brain protection and repair
A tale of two transition disks: alma long-baseline observations of iso-oph 2 reveal two closely packed nonaxisymmetric rings and a similar to 2 au cavity
ISO-Oph 2 is a wide-separation (240 au) binary system where the primary star harbors a massive (M-dust similar to 40M(circle plus)) ring-like disk with a dust cavity similar to 50 au in radius and the secondary hosts a much lighter (M-dust similar to 0.8M(circle plus)) disk. As part of the high-resolution follow-up of the "Ophiuchus Disk Survey Employing ALMA" (ODISEA) project, we present 1.3 mm continuum and(12)CO molecular line observations of the system at 002 (3 au) resolution. We resolve the disk around the primary into two nonaxisymmetric rings and find that the disk around the secondary is only similar to 7 au across and also has a dust cavity (r similar to 2.2 au). Based on the infrared flux ratio of the system and the M0 spectral type of the primary, we estimate the mass of the companion to be close to the brown-dwarf limit. Hence, we conclude that the ISO-Oph 2 system contains the largest and smallest cavities, the smallest measured disk size, and the resolved cavity around the lowest-mass object (M similar to 0.08M) in Ophiuchus. From the(12)CO data, we find a bridge of gas connecting both disks. While the morphology of the rings around the primary might be due to an unseen disturber within the cavity, we speculate that the bridge might indicate an alternative scenario in which the secondary has recently flown by the primary star causing the azimuthal asymmetries in its disk. The ISO-Oph 2 system is therefore a remarkable laboratory to study disk evolution, planet formation, and companion-disk interactions.Joint China-Chile Committee fund
European Research Council (ERC)
European Commission
757957
ANID-FONDECYT grant
1191934
11190837
ESO-Chile Joint Committee
Alexander von Humboldt Foundation
Australian Research Council
DP180104235
FT13010003