1,573 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
Anelastic Phenomena in Mg-Al Alloys
Cyclic loading-unloading in tension and compression has been used to quantify the anelastic behaviour, in the form of hysteresis loops, of pure Mg and three Mg-Al alloys (0.5, 2, and 9 at.% Al). The effect reached a maximum at a plastic strain of approximate to 0.02 for all of the materials, and decreased at higher strains. The amount of anelasticity at any given strain was smaller for the dilute alloys in comparison with the pure Mg whereas it increased above that of pure Mg for the most concentrated alloy. Possible reasons for this behaviour are discussed in terms of reversible twinning, solid solution softening, and hardening and short range order
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
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
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
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
Constraining the mass of the planet(s) sculpting a disk cavity. The intriguing case of 2MASS J16042165-2130284
The large cavities observed in the dust and gas distributions of transition
disks may be explained by planet-disk interactions. At ~145 pc, 2MASS
J16042165-2130284 (J1604) is a 5-12 Myr old transitional disk with different
gap sizes in the mm- and m-sized dust distributions (outer edges at ~79
and at ~63 au, respectively). Its CO emission shows a ~30 au cavity.
This radial structure suggests that giant planets are sculpting this disk. We
aim to constrain the masses and locations of plausible giant planets around
J1604. We observed J1604 with the Spectro-Polarimetric High-contrast Exoplanet
REsearch (SPHERE) at the Very Large Telescope (VLT), in IRDIFS\_EXT,
pupil-stabilized mode, obtaining YJH- band images with the integral field
spectrograph (IFS) and K1K2-band images with the Infra-Red Dual-beam Imager and
Spectrograph (IRDIS). The dataset was processed exploiting the angular
differential imaging (ADI) technique with high-contrast algorithms. Our
observations reach a contrast of ~12 mag from 0.15" to 0.80"
(~22 to 115 au), but no planet candidate is detected. The disk is directly
imaged in scattered light at all bands from Y to K, and it shows a red color.
This indicates that the dust particles in the disk surface are mainly
m-sized grains. We confirm the sharp dip/decrement in
scattered light in agreement with polarized light observations. Comparing our
images with a radiative transfer model we argue that the southern side of the
disk is most likely the nearest. This work represents the deepest search yet
for companions around J1604. We reach a mass sensitivity of from ~22 to ~115 au according to a hot start scenario. We propose
that a brown dwarf orbiting inside of ~15 au and additional Jovian planets at
larger radii could account for the observed properties of J1604 while
explaining our lack of detection.Comment: 10 pages, 7 Figures. Accepted for publication in A&A . Abridged
abstrac
Disks around T Tauri Stars with SPHERE (DARTTS-S):I. SPHERE/IRDIS Polarimetric Imaging of Eight Prominent T Tauri Disks
We present the first part of our DARTTS-S (Disks ARound TTauri Stars with
SPHERE) survey: Observations of 8 TTauri stars which were selected based on
their strong (sub-)mm excesses using SPHERE / IRDIS polarimetric differential
imaging (PDI) in the J and H bands. All observations successfully detect the
disks, which appear vastly different in size, from 80 au in scattered
light to 400 au, and display total polarized disk fluxes between 0.06% and
0.89% of the stellar flux. For five of these disks, we are able to determine
the three-dimensional structure and the flaring of the disk surface, which
appears to be relatively consistent across the different disks, with flaring
exponents between 1.1 and 1.6. We also confirm
literature results w.r.t. the inclination and position angle of several of our
disk, and are able to determine which side is the near side of the disk in most
cases. While there is a clear trend of disk mass with stellar ages (1
Myr to 10 Myr), no correlations of disk structures with age were found.
There are also no correlations with either stellar mass or sub-mm flux. We do
not detect significant differences between the J and H bands. However, we note
that while a high fraction (7/8) of the disks in our sample show ring-shaped
sub-structures, none of them display spirals, in contrast to the disks around
more massive Herbig Ae/Be stars, where spiral features are common.Comment: 31 pages, 12 figure
- …