2,186 research outputs found
An Upper Limit on the Mass of the Circumplanetary Disk for DH Tau b
Indexación: Scopus.DH Tau is a young (sim;1 Myr) classical T Tauri star. It is one of the few young PMS stars known to be associated with a planetary mass companion, DH Tau b, orbiting at large separation and detected by direct imaging. DH Tau b is thought to be accreting based on copious Ha emission and exhibits variable Paschen Beta emission. NOEMA observations at 230 GHz allow us to place constraints on the disk dust mass for both DH Tau b and the primary in a regime where the disks will appear optically thin. We estimate a disk dust mass for the primary, DH Tau A of 17.2 ± 1.7 MÅ, which gives a disk to star mass ratio of 0.014 (assuming the usual gas to dust mass ratio of 100 in the disk). We find a conservative disk dust mass upper limit of 0.42M⊕ for DH Tau b, assuming that the disk temperature is dominated by irradiation from DH Tau b itself. Given the environment of the circumplanetary disk, variable illumination from the primary or the equilibrium temperature of the surrounding cloud would lead to even lower disk mass estimates. A MCFOST radiative transfer model, including heating of the circumplanetary disk by DH Tau b and DH Tau A, suggests that a mass-averaged disk temperature of 22 K is more realistic, resulting in a dust disk mass upper limit of 0.09M⊕ for DH Tau b. We place DH Tau b in context with similar objects and discuss the consequences for planet formation models.http://iopscience.iop.org/article/10.3847/1538-3881/aa74cd/met
New Supergravity Backgrounds Dual to N=1 SQCD-like Theories with N_f=2N_c
We present new supergravity backgrounds generated by N_c D5-branes, wrapping
the S^2 of the resolved conifold, in the presence of N_f = 2 N_c smeared flavor
D5-branes. The smearing allows us to take their backreaction on the geometry
into account. We discuss the consistency, stability, and supersymmetry of these
types of setups. We find near horizon geometries that we expect to be
supergravity duals of SQCD-like theories with N_f= 2N_c. From these backgrounds
we numerically extract rectangular Wilson loops and beta functions of the dual
field theory for the regime where our approximations are valid.Comment: 22+24 pages, 17 figures, Figure 12 replace
The inner environment of Z~CMa: High-Contrast Imaging Polarimetry with NaCo
Context. Z\,CMa is a binary composed of an embedded Herbig Be and an FU Ori
class star separated by au. Observational evidence indicate a complex
environment in which each star has a circumstellar disk and drives a jet, and
the whole system is embedded in a large dusty envelope.
Aims. We aim to probe the circumbinary environment of Z\,CMa in the inner 400
au in scattered light.
Methods. We use high contrast imaging polarimetry with VLT/NaCo at and
bands.
Results. The central binary is resolved in both bands. The polarized images
show three bright and complex structures: a common dust envelope, a sharp
extended feature previously reported in direct light, and an intriguing bright
clump located 0\farcs3 south of the binary, which appears spatially connected
to the sharp extended feature.
Conclusions.We detect orbital motion when compared to previous observations,
and report a new outburst driven by the Herbig star. Our observations reveal
the complex inner environment of Z\,CMa with unprecedented detail and contrast.Comment: Accepted for publication in A&A Letter
Nonextensivity and multifractality in low-dimensional dissipative systems
Power-law sensitivity to initial conditions at the edge of chaos provides a
natural relation between the scaling properties of the dynamics attractor and
its degree of nonextensivity as prescribed in the generalized statistics
recently introduced by one of us (C.T.) and characterized by the entropic index
. We show that general scaling arguments imply that , where and are the
extremes of the multifractal singularity spectrum of the attractor.
This relation is numerically checked to hold in standard one-dimensional
dissipative maps. The above result sheds light on a long-standing puzzle
concerning the relation between the entropic index and the underlying
microscopic dynamics.Comment: 12 pages, TeX, 4 ps figure
Bacterioplankton composition as an indicator of environmental status: proof of principle using indicator value analysis of estuarine communities
Increasing awareness of environmental impacts caused by anthropogenic activities highlights the need to determine indicators of environmental status that can be routinely assessed at large spatial and temporal scales. Microbial communities comprise the greatest share of biological diversity on Earth and can rapidly reflect recent environmental changes while providing a record of past events. However, they have rarely been targeted in the search for ecological indicators of habitat types, environmental conditions, or environmental changes. Here, as a proof of principle, we analysed the bacterioplankton community composition of 4 estuaries in North and South America, Europe, and Asia, and looked for indicators of groups of samples defined using partition techniques, according to primary physicochemical variables typically monitored to infer water quality. Indicator value analysis (IndVal) was conducted to identify indicator operational taxonomic units (OTUs; analogous to species in other fields of ecology) in each group. These bacterioplankton-based indicators exhibited a high capacity to predict the group membership of the samples within each estuary and to correctly assign the samples to the appropriate estuary in a combined data set, employing different machine learning techniques. The indicators were composed of OTUs belonging to several bacterial phyla, which responded significantly and differentially to the environmental variables used to define the groups of samples. Moreover, the predictive values of these bacterial indicators were generally higher than those of other biological assemblages commonly used for environmental monitoring. Therefore, this approach appears to be a promising tool to complement existing strategies for monitoring and conservation of aquatic systems worldwide
The First Science Results from SPHERE: Disproving the Predicted Brown Dwarf around V471 Tau
Variations of eclipse arrival times have recently been detected in several
post common envelope binaries consisting of a white dwarf and a main sequence
companion star. The generally favoured explanation for these timing variations
is the gravitational pull of one or more circumbinary substellar objects
periodically moving the center of mass of the host binary. Using the new
extreme-AO instrument SPHERE, we image the prototype eclipsing post-common
envelope binary V471 Tau in search of the brown dwarf that is believed to be
responsible for variations in its eclipse arrival times. We report that an
unprecedented contrast of 12.1 magnitudes in the H band at a separation of 260
mas was achieved, but resulted in a non-detection. This implies that there is
no brown dwarf present in the system unless it is three magnitudes fainter than
predicted by evolutionary track models, and provides damaging evidence against
the circumbinary interpretation of eclipse timing variations. In the case of
V471 Tau, a more consistent explanation is offered with the Applegate
mechanism, in which these variations are prescribed to changes in the
quadrupole moment within the main-sequence sta
No-Drag String Configurations for Steadily Moving Quark-Antiquark Pairs in a Thermal Bath
We investigate the behavior of stationary string configurations on a
five-dimensional AdS black hole background which correspond to quark-antiquark
pairs steadily moving in an N=4 super Yang-Mills thermal bath. There are many
branches of solutions, depending on the quark velocity and separation as well
as on whether Euclidean or Lorentzian configurations are examined.Comment: references added; statements corrected; eliminated computation of jet
quenching parameter from Wilson loop of [Liu, Rajagopal, Wiedemann,
hep-th/0605178] using Euclidean string configurations since those authors
advocate [hep-th/0607062, footnote 14] the use of spacelike Lorentzian string
configurations instea
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