1,327 research outputs found
Resolved Young Binary Systems And Their Disks
We have conducted a survey of young single and multiple systems in the Taurus–Auriga star-forming region with the Atacama Large Millimeter Array (ALMA), substantially improving both the spatial resolution and sensitivity with which individual protoplanetary disks in these systems have been observed. These ALMA observations can resolve binary separations as small as 25–30 au and have an average 3σ detection level of 0.35 mJy, equivalent to a disk mass of 4 × 10−5 M ⊙ for an M3 star. Our sample was constructed from stars that have an infrared excess and/or signs of accretion and have been classified as Class II. For the binary and higher-order multiple systems observed, we detect λ = 1.3 mm continuum emission from one or more stars in all of our target systems. Combined with previous surveys of Taurus, our 21 new detections increase the fraction of millimeter-detected disks to over 75% in all categories of stars (singles, primaries, and companions) earlier than spectral type M6 in the Class II sample. Given the wealth of other information available for these stars, this has allowed us to study the impact of multiplicity with a much larger sample. While millimeter flux and disk mass are related to stellar mass as seen in previous studies, we find that both primary and secondary stars in binary systems with separations of 30–4200 au have lower values of millimeter flux as a function of stellar mass than single stars. We also find that for these systems, the circumstellar disk around the primary star does not dominate the total disk mass in the system and contains on average 62% of the total mass
Resolved Young Binary Systems And Their Disks
We have conducted a survey of young single and multiple systems in the Taurus–Auriga star-forming region with the Atacama Large Millimeter Array (ALMA), substantially improving both the spatial resolution and sensitivity with which individual protoplanetary disks in these systems have been observed. These ALMA observations can resolve binary separations as small as 25–30 au and have an average 3σ detection level of 0.35 mJy, equivalent to a disk mass of 4 × 10−5 M ⊙ for an M3 star. Our sample was constructed from stars that have an infrared excess and/or signs of accretion and have been classified as Class II. For the binary and higher-order multiple systems observed, we detect λ = 1.3 mm continuum emission from one or more stars in all of our target systems. Combined with previous surveys of Taurus, our 21 new detections increase the fraction of millimeter-detected disks to over 75% in all categories of stars (singles, primaries, and companions) earlier than spectral type M6 in the Class II sample. Given the wealth of other information available for these stars, this has allowed us to study the impact of multiplicity with a much larger sample. While millimeter flux and disk mass are related to stellar mass as seen in previous studies, we find that both primary and secondary stars in binary systems with separations of 30–4200 au have lower values of millimeter flux as a function of stellar mass than single stars. We also find that for these systems, the circumstellar disk around the primary star does not dominate the total disk mass in the system and contains on average 62% of the total mass
Magnetothermodynamics: Measuring equations of state in a relaxed magnetohydrodynamic plasma
We report the first measurements of equations of state of a fully relaxed
magnetohydrodynamic (MHD) laboratory plasma. Parcels of magnetized plasma,
called Taylor states, are formed in a coaxial magnetized plasma gun, and are
allowed to relax and drift into a closed flux conserving volume. Density, ion
temperature, and magnetic field are measured as a function of time as the
Taylor states compress and heat. The theoretically predicted MHD and double
adiabatic equations of state are compared to experimental measurements. We find
that the MHD equation of state is inconsistent with our data.Comment: 4 pages, 4 figure
Spontaneous Interlayer Charge Transfer near the Magnetic Quantum Limit
Experiments reveal that a confined electron system with two equally-populated
layers at zero magnetic field can spontaneously break this symmetry through an
interlayer charge transfer near the magnetic quantum limit. New fractional
quantum Hall states at unusual total filling factors such as \nu = 11/15 (= 1/3
+ 2/5) stabilize as signatures that the system deforms itself, at substantial
electrostatic energy cost, in order to gain crucial correlation energy by
"locking in" separate incompressible liquid phases at unequal fillings in the
two layers (e.g., layered 1/3 and 2/5 states in the case of \nu = 11/15).Comment: 4 pages, 4 figures (1 color) included in text. Related papers at
http://www.ee.princeton.edu/~hari/papers.htm
Magnetic-Field-Induced Hybridization of Electron Subbands in a Coupled Double Quantum Well
We employ a magnetocapacitance technique to study the spectrum of the soft
two-subband (or double-layer) electron system in a parabolic quantum well with
a narrow tunnel barrier in the centre. In this system unbalanced by gate
depletion, at temperatures T\agt 30 mK we observe two sets of quantum
oscillations: one originates from the upper electron subband in the
closer-to-the-gate part of the well and the other indicates the existence of
common gaps in the spectrum at integer fillings. For the lowest filling factors
and , both the common gap presence down to the point of one- to
two-subband transition and their non-trivial magnetic field dependences point
to magnetic-field-induced hybridization of electron subbands.Comment: Major changes, added one more figure, the latest version to be
published in JETP Let
Extrinsic Curvature Embedding Diagrams
Embedding diagrams have been used extensively to visualize the properties of
curved space in Relativity. We introduce a new kind of embedding diagram based
on the {\it extrinsic} curvature (instead of the intrinsic curvature). Such an
extrinsic curvature embedding diagram, when used together with the usual kind
of intrinsic curvature embedding diagram, carries the information of how a
surface is {\it embedded} in the higher dimensional curved space. Simple
examples are given to illustrate the idea.Comment: 22 pages, 4 figure
Quantum Hall effect in single wide quantum wells
We study the quantum Hall states in the lowest Landau level for a single wide
quantum well. Due to a separation of charges to opposite sides of the well, a
single wide well can be modelled as an effective two level system. We provide
numerical evidence of the existence of a phase transition from an
incompressible to a compressible state as the electron density is increased for
specific well width. Our numerical results show a critical electron density
which depends on well width, beyond which a transition incompressible double
layer quantum Hall state to a mono-layer compressible state occurs. We also
calculate the related phase boundary corresponding to destruction of the
collective mode energy gap. We show that the effective tunneling term and the
interlayer separation are both renormalised by the strong magnetic field. We
also exploite the local density functional techniques in the presence of strong
magnetic field at to calculate renormalized . The
numerical results shows good agreement between many-body calculations and local
density functional techniques in the presence of a strong magnetic field at
. we also discuss implications of this work on the
incompressible state observed in SWQW.Comment: 30 pages, 7 figures (figures are not included
Towards a Singularity-Proof Scheme in Numerical Relativity
Progress in numerical relativity has been hindered for 30 years because of
the difficulties of avoiding spacetime singularities in numerical evolution. We
propose a scheme which excises a region inside an apparent horizon containing
the singularity. Two major ingredients of the scheme are the use of a
horizon-locking coordinate and a finite differencing which respects the causal
structure of the spacetime. Encouraging results of the scheme in the spherical
collapse case are given.Comment: 9 page
Half-Integral Spin-Singlet Quantum Hall Effect
We provide numerical evidence that the ground state of a short range
interaction model at is incompressible and spin-singlet for a wide
range of repulsive interactions. Furthermore it is accurately described by a
trial wave function studied earlier. For the Coulomb interaction we find that
this wave function provides a good description of the lowest lying spin-singlet
state, and propose that fractional quantum Hall effect would occur at
if this state became the global ground state.Comment: Latex 13 pages, 3 figures upon reques
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