144 research outputs found
Mid-infrared observations of the transitional disks around DH Tau, DM Tau, and GM Aur
Aims: We present mid-infrared observations and photometry of the transitional
disks around the young stellar objects DH Tau, DM Tau, and GM Aur, obtained
with VISIR/VLT in N band. Our aim is to resolve the inner region and the
large-scale structures of these transitional disks, carrying potential
signatures of intermediate or later stages of disk evolution and ongoing planet
formation.
Methods: We use the simultaneously observed standard-stars as PSF reference
to constrain the radial flux profiles of our target objects. Subtracting the
obtained standard-star profile from the corresponding science object profile
yields the flux residuals produced by the star-disk system. A detection
threshold takes into account the background standard deviation and also the
seeing variations during the observations to evaluate the significance of these
flux residuals. On the basis of a simple model for the dust re-emission, we
derive constraints on the inner radius of the dust disk.
Results: We spatially resolve the transitional disk around GM Aur and
determine an inner-disk hole radius of 20.5(+1.0,-0.5) AU. The circumstellar
disks around DH Tau and DM Tau are not spatially resolved but we are able to
constrain the inner-disk hole radius to <15.5(+9.0,-2.0) AU and
<15.5(+0.5,-0.5) AU, respectively. The performed photometry yields fluxes of
178+-31 mJy for DH Tau, 56+-6 mJy for DM Tau, and 229+-14 mJy for GM Aur.Comment: Accepted for publication in Astronomy & Astrophysics. (6 pages,
including 7 figures and 5 tables
Low-energy peak structure in strong-field ionization by mid-infrared laser-pulses: two-dimensional focusing by the atomic potential
We analyze the formation of the low-energy structure (LES) in above-threshold
ionization spectra first observed by Quan et al.\ \cite{quan09} and Blaga et
al.\ \cite{blaga09} using both quasi-classical and quantum approaches. We show
this structure to be largely classical in origin resulting from a
two-dimensional focusing in the energy-angular momentum plane of the
strong-field dynamics in the presence of the atomic potential. The peak at low
energy is strongly correlated with high angular momenta of the photoelectrons.
Quantum simulations confirm this scenario. Resulting parameter dependences
agree with experimental findings \cite{quan09,blaga09} and, in part, with other
simulations \cite{liu10,yan10,kast11}.Comment: 12 pages, 6 figure
Enhanced ionization of acetylene in intense laser pulses is due to energy upshift and field coupling of multiple orbitals
Synopsis We describe a new enhanced ionization mechanism for polyatomic molecules. It works via a significant energy up-shift of valence orbitals for stretched bonds and a strong concomitant increase in the coupling between multiple molecular orbitals
Extended X-ray emission in PKS 1718-649
© ESO 2018. PKS 1718-649 is one of the closest and most comprehensively studied candidates of a young active galactic nucleus (AGN) that is still embedded in its optical host galaxy. The compact radio structure, with a maximal extent of a few parsecs, makes it a member of the group of compact symmetric objects (CSO). Its environment imposes a turnover of the radio synchrotron spectrum towards lower frequencies, also classifying PKS 1718-649 as gigahertz-peaked radio spectrum (GPS) source. Its close proximity has allowed the first detection of extended X-ray emission in a GPS/CSO source with Chandra that is for the most part unrelated to nuclear feedback. However, not much is known about the nature of this emission. By co-adding all archival Chandra data and complementing these datasets with the large effective area of XMM-Newton, we are able to study the detailed physics of the environment of PKS 1718-649. Not only can we confirm that the bulk of the kiloparsec-scale environment emits in the soft X-rays, but we also identify the emitting gas to form a hot, collisionally ionized medium. While the feedback of the central AGN still seems to be constrained to the inner few parsecs, we argue that supernovae are capable of producing the observed large-scale X-ray emission at a rate inferred from its estimated star formation rate
Extended X-ray emission in PKS 1718649
PKS 1718649 is one of the closest and most comprehensively studied
candidates of a young active galactic nucleus (AGN) that is still embedded in
its optical host galaxy. The compact radio structure, with a maximal extent of
a few parsecs, makes it a member of the group of compact symmetric objects
(CSO). Its environment imposes a turnover of the radio synchrotron spectrum
towards lower frequencies, also classifying PKS 1718649 as gigahertz-peaked
radio spectrum (GPS) source. Its close proximity has allowed the first
detection of extended X-ray emission in a GPS/CSO source with Chandra that is
for the most part unrelated to nuclear feedback. However, not much is known
about the nature of this emission. By co-adding all archival Chandra data and
complementing these datasets with the large effective area of XMM-Newton, we
are able to study the detailed physics of the environment of PKS 1718649.
Not only can we confirm that the bulk of the kiloparsec-scale
environment emits in the soft X-rays, but we also identify the emitting gas to
form a hot, collisionally ionized medium. While the feedback of the central AGN
still seems to be constrained to the inner few parsecs, we argue that
supernovae are capable of producing the observed large-scale X-ray emission at
a rate inferred from its estimated star formation rate.Comment: 5 pages, 2 figures, 2 tables, accepted for publication by A&
Coherent Excitation of Heterosymmetric Spin Waves with Ultrashort Wavelengths
In the emerging field of magnonics, spin waves are foreseen as signal carriers for future spintronic information processing and communication devices, owing to both the very low power losses and a high device miniaturization potential predicted for short-wavelength spin waves. Yet, the efficient excitation and controlled propagation of nanoscale spin waves remains a severe challenge. Here, we report the observation of high-amplitude, ultrashort dipole-exchange spin waves (down to 80 nm wavelength at 10 GHz frequency) in a ferromagnetic single layer system, coherently excited by the driven dynamics of a spin vortex core. We used time-resolved x-ray microscopy to directly image such propagating spin waves and their excitation over a wide range of frequencies. By further analysis, we found that these waves exhibit a heterosymmetric mode profile, involving regions with anti-Larmor precession sense and purely linear magnetic oscillation. In particular, this mode profile consists of dynamic vortices with laterally alternating helicity, leading to a partial magnetic flux closure over the film thickness, which is explained by a strong and unexpected mode hybridization. This spin-wave phenomenon observed is a general effect inherent to the dynamics of sufficiently thick ferromagnetic single layer films, independent of the specific excitation method employed
Photonic quantum information processing: a review
Photonic quantum technologies represent a promising platform for several
applications, ranging from long-distance communications to the simulation of
complex phenomena. Indeed, the advantages offered by single photons do make
them the candidate of choice for carrying quantum information in a broad
variety of areas with a versatile approach. Furthermore, recent technological
advances are now enabling first concrete applications of photonic quantum
information processing. The goal of this manuscript is to provide the reader
with a comprehensive review of the state of the art in this active field, with
a due balance between theoretical, experimental and technological results. When
more convenient, we will present significant achievements in tables or in
schematic figures, in order to convey a global perspective of the several
horizons that fall under the name of photonic quantum information.Comment: 36 pages, 6 figures, 634 references. Updated version with minor
changes and extended bibliograph
ANTARES constrains a blazar origin of two IceCube PeV neutrino events
Context. The source(s) of the neutrino excess reported by the IceCube Collaboration is unknown. The TANAMI Collaboration recently reported on the multiwavelength emission of six bright, variable blazars which are positionally coincident with two of the most energetic IceCube events. Objects like these are prime candidates to be the source of the highest-energy cosmic rays, and thus of associated neutrino emission. Aims. We present an analysis of neutrino emission from the six blazars using observations with the ANTARES neutrino telescope. Methods. The standard methods of the ANTARES candidate list search are applied to six years of data to search for an excess of muons Âż and hence their neutrino progenitors Âż from the directions of the six blazars described by the TANAMI Collaboration, and which are possibly associated with two IceCube events. Monte Carlo simulations of the detector response to both signal and background particle fluxes are used to estimate the sensitivity of this analysis for different possible source neutrino spectra. A maximum-likelihood approach, using the reconstructed energies and arrival directions of through-going muons, is used to identify events with properties consistent with a blazar origin. Results. Both blazars predicted to be the most neutrino-bright in the TANAMI sample (1653â329 and 1714â336) have a signal flux fitted by the likelihood analysis corresponding to approximately one event. This observation is consistent with the blazar-origin hypothesis of the IceCube event ICâ14 for a broad range of blazar spectra, although an atmospheric origin cannot be excluded. No ANTARES events are observed from any of the other four blazars, including the three associated with IceCube event IC20. This excludes at a 90% confidence level the possibility that this event was produced by these blazars unless the neutrino spectrum is flatter than â2.4
- âŠ