1,329 research outputs found
Disk Evolution in Young Binaries: from Observations to Theory
The formation of a binary system surrounded by disks is the most common
outcome of stellar formation. Hence studying and understanding the formation
and the evolution of binary systems and associated disks is a cornerstone of
star formation science. Moreover, since the components within binary systems
are coeval and the sizes of their disks are fixed by the tidal truncation of
their companion, binary systems provide an ideal "laboratory" in which to study
disk evolution under well defined boundary conditions.
In this paper, we review observations of several inner disk diagnostics in
multiple systems, including hydrogen emission lines (indicative of ongoing
accretion), and color excesses (evidence of warm inner disks), and
polarization (indicative of the relative orientations of the disks around each
component). We examine to what degree these properties are correlated within
binary systems and how this degree of correlation depends on parameters such as
separation and binary mass ratio. These findings will be interpreted both in
terms of models that treat each disk as an isolated reservoir and those in
which the disks are subject to re-supply from some form of circumbinary
reservoir, the observational evidence for which we will also critically review.
The planet forming potential of multiple star systems is discussed in terms of
the relative lifetimes of disks around single stars, binary primaries and
binary secondaries. Finally, we summarize several potentially revealing
observational problems and future projects that could provide further insight
into disk evolution in the coming decadeComment: 16 pages, 7 figures, chapter in Protostars and Planets
Cumulant ratios in fully developed turbulence
In the context of random multiplicative cascade processes, we derive
analytical solutions for one- and two-point cumulants with restored
translational invariance. On taking ratios of cumulants in ln epsilon,
geometrical effects due to spatial averaging cancel out. These ratios can
successfully distinguish between splitting functions while multifractal scaling
exponents and multiplier distributions cannot.Comment: 9th Workshop on Multiparticle Production (Torino), 9 pages latex,
incl 9 figs and espcrc2.st
Universal dissipation scaling for non-equilibrium turbulence
It is experimentally shown that the non-classical high Reynolds number energy
dissipation behaviour, ,
observed during the decay of fractal square grid-generated turbulence is also
manifested in decaying turbulence originating from various regular grids. For
sufficiently high values of the global Reynolds numbers , .Comment: 5 pages, 6 figure
Statistically Preserved Structures and Anomalous Scaling in Turbulent Active Scalar Advection
The anomalous scaling of correlation functions in the turbulent statistics of
active scalars (like temperature in turbulent convection) is understood in
terms of an auxiliary passive scalar which is advected by the same turbulent
velocity field. While the odd-order correlation functions of the active and
passive fields differ, we propose that the even-order correlation functions are
the same to leading order (up to a trivial multiplicative factor). The leading
correlation functions are statistically preserved structures of the passive
scalar decaying problem, and therefore universality of the scaling exponents of
the even-order correlations of the active scalar is demonstrated.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
NICMOS Images of the GG Tau Circumbinary Disk
We present deep, near-infrared images of the circumbinary disk surrounding
the pre-main-sequence binary star, GG Tau A, obtained with NICMOS aboard the
Hubble Space Telescope. The spatially resolved proto-planetary disk scatters
roughly 1.5% of the stellar flux, with a near-to-far side flux ratio of ~1.4,
independent of wavelength, and colors that are comparable to the central
source; all of these properties are significantly different from the earlier
ground-based observations. New Monte Carlo scattering simulations of the disk
emphasize that the general properties of the disk, such as disk flux, near side
to far side flux ratio and integrated colors, can be approximately reproduced
using ISM-like dust grains, without the presence of either circumstellar disks
or large dust grains, as had previously been suggested. A single parameter
phase function is fitted to the observed azimuthal variation in disk flux,
providing a lower limit on the median grain size of 0.23 micron. Our analysis,
in comparison to previous simulations, shows that the major limitation to the
study of grain growth in T Tauri disk systems through scattered light lies in
the uncertain ISM dust grain properties. Finally, we use the 9 year baseline of
astrometric measurements of the binary to solve the complete orbit, assuming
that the binary is coplanar with the circumbinary ring. We find that the
estimated 1 sigma range on disk inner edge to semi-major axis ratio, 3.2 <
Rin/a < 6.7, is larger than that estimated by previous SPH simulations of
binary-disk interactions.Comment: 40 pages, 8 postscript figures, accepted for publication in Ap
The Taurus Boundary of Stellar/Substellar (TBOSS) Survey I: far-IR disk emission measured with Herschel
With Herschel/PACS 134 low mass members of the Taurus star-forming region
spanning the M4-L0 spectral type range and covering the transition from low
mass stars to brown dwarfs were observed. Combining the new Herschel results
with other programs, a total of 150 of the 154 M4-L0 Taurus members members
have observations with Herschel. Among the 150 targets, 70um flux densities
were measured for 7 of the 7 ClassI objects, 48 of the 67 ClassII members, and
3 of the 76 ClassIII targets. For the detected ClassII objects, the median 70um
flux density level declines with spectral type, however, the distribution of
excess relative to central object flux density does not change across the
stellar/substellar boundary in the M4-L0 range. Connecting the 70um TBOSS
values with the results from K0-M3 ClassII members results in the first
comprehensive census of far-IR emission across the full mass spectrum of the
stellar and substellar population of a star-forming region, and the median flux
density declines with spectral type in a trend analogous to the flux density
decline expected for the central objects. SEDs were constructed for all TBOSS
targets covering the optical to far-IR range and extending to the submm/mm for
a subset of sources. Based on an initial exploration of the impact of different
physical parameters; inclination, scale height and flaring have the largest
influence on the PACS flux densities. From the 24um to 70um spectral index of
the SEDs, 5 new candidate transition disks were identified. The steep 24um to
70um slope for a subset of 8 TBOSS targets may be an indication of truncated
disks in these systems.Two examples of mixed pair systems that include
secondaries with disks were measured. Finally, comparing the TBOSS results with
a Herschel study of Ophiuchus brown dwarfs reveals a lower fraction of disks
around the Taurus substellar population.Comment: 64 pages, 33 figures, 12 tables, accepted for publication in A&
CO Line Emission and Absorption from the HL Tau Disk: Where is all the dust?
We present high-resolution infrared spectra of HL Tau, a heavily embedded
young star. The spectra exhibit broad emission lines of hot CO gas as well as
narrow absorption lines of cold CO gas. The column density for this cooler
material (7.5+/-0.2 x 10^18 cm-2) indicates a large column of absorbing gas
along the line of sight. In dense interstellar clouds, this column density of
CO gas is associated with Av~52 magnitudes. However, the extinction toward this
source (Av~23) suggests that there is less dust along the line of sight than
inferred from the CO absorption data. We discuss three possibilities for the
apparent paucity of dust along the line of sight through the flared disk: 1)
the dust extinction has been underestimated due to differences in circumstellar
grain properties, such as grain agglomeration; 2) the effect of scattering has
been underestimated and the actual extinction is much higher; or (3) the line
of sight through the disk is probing a gas-rich, dust-depleted region, possibly
due to the stratification of gas and dust in a pre-planetary disk.Comment: To be published in The Astrophysical Journa
Noncommutative Metafluid Dynamics
In this paper we define a noncommutative (NC) Metafluid Dynamics
\cite{Marmanis}. We applied the Dirac's quantization to the Metafluid Dynamics
on NC spaces. First class constraints were found which are the same obtained in
\cite{BJP}. The gauge covariant quantization of the non-linear equations of
fields on noncommutative spaces were studied. We have found the extended
Hamiltonian which leads to equations of motion in the gauge covariant form. In
addition, we show that a particular transformation \cite{Djemai} on the usual
classical phase space (CPS) leads to the same results as of the
-deformation with . Besides, we will shown that an additional
term is introduced into the dissipative force due the NC geometry. This is an
interesting feature due to the NC nature induced into model.Comment: 11 page
Destruction of a metastable string by particle collisions
We calculate the probability of destruction of a metastable string by
collisions of the Goldstone bosons, corresponding to the transverse waves on
the string. We find a general formula that allows to determine the probability
of the string breakup by a collision of arbitrary number of the bosons. We find
that the destruction of a metastable string takes place only in collisions of
even number of the bosons, and we explicitly calculate the energy dependence of
such process in a two-particle collision for an arbitrary relation between the
energy and the largest infrared scale in the problem, the length of the
critical gap in the string.Comment: 15 pages, 1 figur
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