28966631
The pulsation of χ cygni imaged by optical interferometry: A novel technique to derive distance and mass of mira stars
We present infrared interferometric imaging of the S-type Mira star χ Cygni. The object was observed at four different epochs in 2005-2006 with the Infrared-Optical Telescope Array optical interferometer (H band). Images show up to 40% variation in the stellar diameter, as well as significant changes in the limb darkening and stellar inhomogeneities. Model fitting gave precise time-dependent values of the stellar diameter, and reveals presence and displacement of a warm molecular layer. The star radius, corrected for limb darkening, has a mean value of 12.1 mas and shows a 5.1 mas amplitude pulsation. Minimum diameter was observed at phase 0.94 ± 0.01. Maximum temperature was observed several days later at phase 1.02 ± 0.02. We also show that combining the angular acceleration of the molecular layer with CO (Δ_v = 3) radial velocity measurements yields a 5.9 ± 1.5 mas parallax. The constant acceleration of the CO molecules—during 80% of the pulsation cycle—lead us to argument for a free-falling layer. The acceleration is compatible with a gravitational field produced by a 2.1^(+1.5)_(–0.7) solar mass star. This last value is in agreement with fundamental mode pulsator models. We foresee increased development of techniques consisting in combining radial velocity with interferometric angular measurements, ultimately allowing total mapping of the speed, density, and position of the diverse species in pulsation-driven atmospheres.
55468019
Estimating the phase in groundbased interferometry: performance comparison between singlemode and multimode schemes
Aims. In this paper we compare the performance of multi and single-mode interferometry for the estimation of the phase of the complex visibility. Methods. We provide a theoretical description of the interferometric signal which enables to derive the phase error in presence of detector, photon and atmospheric noises, for both multi and single-mode cases. Results. We show that, despite the loss of ux occurring when injecting the light in the single-mode component (i.e. single-mode bers, integrated optics), the spatial ltering properties of such single-mode devices often enable higher performance than multimode concepts. In the high ux regime speckle noise dominated, single-mode interferometry is always more ecient, and its performance is signicantly better when the correction provided by adaptive optics becomes poor, by a factor of 2 and more when the Strehl ratio is lower than 10%. In low light level cases (detector noise regime), multimode interferometry reaches better performance, yet the gain never exceeds 20%, which corresponds to the percentage of photon loss due to the injection in the guides. Besides, we demonstrate that single-mode interferometry is also more robust to the turbulence in both cases of fringe tracking and phase referencing, at the exception of narrow eld of views ( < 1 00 ). Conclusions. Our conclusion is therefore that, from a theoretical point of view and contrarily to a widespread opinion, fringe trackers built using single-mode optics should be considered as a solution both practical and competitive.
119296696
GRAVITY: getting to the event horizon of Sgr A*
We present the second-generation VLTI instrument GRAVITY, which currently is in the preliminary design phase. GRAVITY is specifically designed to observe highly relativistic motions of matter close to the event horizon of Sgr A*, the massive black hole at center of the Milky Way. We have identified the key design features needed to achieve this goal and present the resulting instrument concept. It includes an integrated optics, 4-telescope, dual feed beam combiner operated in a cryogenic vessel; near infrared wavefront sensing adaptive optics; fringe tracking on secondary sources within the field of view of the VLTI and a novel metrology concept. Simulations show that the planned design matches the scientific needs; in particular that 10µas astrometry is feasible for a source with a magnitude of K=15 like Sgr A*, given the availability of suitable phase reference sources.
10981233
Milli-arcsecond images of the Herbig Ae star HD 163296
Context. The very close environments of young stars are the hosts of fundamental physical processes, such as planet formation, stardisk interactions, mass accretion, and ejection. The complex morphological structure of these environments has been confirmed by the now quite rich data sets obtained for a few objects by near-infrared long-baseline interferometry. Aims. We gathered numerous interferometric measurements for the young star HD 163296 with various interferometers (VLTI, IOTA, KeckI and CHARA), allowing for the first time an image independent of any a priori model to be reconstructed. Methods. Using the Multi-aperture image Reconstruction Algorithm (MiRA), we reconstruct images of HD 163296 in the H and K bands. We compare these images with reconstructed images obtained from simulated data using a physical model of the environment of HD 163296. Results. We obtain model-independent H and K-band images of the surroundings of HD 163296. The images present several significant features that we can relate to an inclined asymmetric flared disk around HD 163296 with the strongest intensity at about 4-5 mas. Because of the incomplete spatial frequency coverage, we cannot state whether each of them individually is peculiar in any way. Conclusions. For the first time, milli-arcsecond images of the environment of a young star are produced. These images confirm that the morphology of the close environment of young stars is more complex than the simple models used in the literature so far.
118375766
Imaging the heart of astrophysical objects with optical long-baseline interferometry
The number of publications of aperture-synthesis images based on optical long-baseline interferometry measurements has recently increased due to easier access to visible and infrared interferometers. The interferometry technique has now reached a technical maturity level that opens new avenues for numerous astrophysical topics requiring milli-arcsecond model-independent imaging. In writing this paper our motivation was twofold: (1) review and publicize emblematic excerpts of the impressive corpus accumulated in the field of optical interferometry image reconstruction; (2) discuss future prospects for this technique by selecting four representative astrophysical science cases in order to review the potential benefits of using optical long-baseline interferometers.For this second goal we have simulated interferometric data from those selected astrophysical environments and used state-of-the-art codes to provide the reconstructed images that are reachable with current or soon-to-be facilities. The image-reconstruction process was “blind” in the sense that reconstructors had no knowledge of the input brightness distributions. We discuss the impact of optical interferometry in those four astrophysical fields. We show that image-reconstruction software successfully provides accurate morphological information on a variety of astrophysical topics and review the current strengths and weaknesses of such reconstructions.We investigate how to improve image reconstruction and the quality of the image possibly by upgrading the current facilities. We finally argue that optical interferometers and their corresponding instrumentation, existing or to come, with six to ten telescopes, should be well suited to provide images of complex sceneries.
7357373
Few Skewed Disks Found in First Closure-Phase Survey of Herbig Ae/Be Stars
Using the three-telescope IOTA interferometer on Mount Hopkins, we report results from the first near-infrared (lambda = 1.65 mu m) closure-phase survey of young stellar objects (YSOs). These closure phases allow us to unambiguously detect departures from centrosymmetry (i.e., skew) in the emission pattern from YSO disks on the scale of similar to 4 mas, expected from generic "flared disk'' models. Six of 14 targets showed small, yet statistically significant nonzero closure phases, with largest values from the young binary system MWC 361-A and the (pre-main-sequence?) Be star HD 45677. Our observations are quite sensitive to the vertical structure of the inner disk, and we confront the predictions of the "puffed-up inner wall'' models of Dullemond, Dominik, & Natta (DDN). Our data support disk models with curved inner rims because the expected emission appears symmetrically distributed around the star over a wide range of inclination angles. In contrast, our results are incompatible with the models possessing vertical inner walls because they predict extreme skewness (i.e., large closure phases) from the near-IR disk emission that is not seen in our data. In addition, we also present the discovery of mysterious H-band "halos'' (similar to 5%-10% of light on scales 0."01-0."50) around a few objects, a preliminary "parametric imaging'' study for HD 45677, and the first astrometric orbit for the young binary MWC 361-A.
125088636
Performance of Jets and Missing Transverse Energy in CMS
A summary of the measurements of jet energy calibration and missing transverse energy calibration and resolution is presented. The jet energy calibration is performed with data samples collected in proton-proton collisions at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 1.6 fb−1. The final jet energy calibration is based on dijet, γ+jet and Z+jet events. The results are presented for the “Particle Flow” approach, which attempts to reconstruct all stable particles in the event individually, prior to the jet clustering, based on information from all relevant subdetectors. We discuss the effect of pile-up interactions and the state of the art mitigation techniques used in CMS. Furthermore, we describe the main uncertainty sources for the jet energy calibration. Finally, the results of comprehensive studies of the missing transverse energy are presented, performed with 0.7 fb−1 of Z(→ μμ)+jets events collected at 8 TeV.
122779026
NONLINEAR EVOLUTION AT SMALL x WITH IMPACT PARAMETER DEPENDENCE
Nonlinear evolution at small x was evaluated numerically with full dependence on impact parameter using the BK equation. several distinct behaviors were found and are presented for the leading logarithmic kernel in the BK evolution equation with both fixed and running coupling. The value of the saturation scale at various dipole sizes was found to agree with analytic expectations. Calculation of the F2 structure function from the numerical solution of the evolution with running coupling were then compared to the HERA data and qualitative agreement found. The agreement is improved with inclusion of soft contributions and these are discussed.
118876778
Use of W-boson longitudinal–transverse interference in top quark spin-correlation functions: II
This continuation of the derivation of general beam-referenced stage-two spin-correlation functions is for the analysis of top–antitop pair-production at the Tevatron and at the Large Hadron Collider. Both the gluon-production and the quark-production contributions are included for the charged-lepton-plus-jets reaction pp or $p\bar{p}\rightarrow t\bar{t}\rightarrow(W^+b)(W^-\bar{b})\rightarrow(l^+\nu b)(W^-\bar{b})$. There is a simple 4-angle beam-referenced spin-correlation function for determination of the relative sign of or for measurement of a possible non-trivial phase between the two dominant $\lambda_b=-1/2$ helicity amplitudes for the $t\rightarrow W^+b$ decay mode. There is an analogous function and tests for $\bar{t}\rightarrow W^-\bar{b}$ decay. This signature requires use of the $(t\bar{t})_{\text{c.m.}}$ energy of the hadronically decaying W-boson, or the kinematically equivalent cosine of the polar angle of $W^\mp$ emission in the antitop (top) decay frame. Spinors and their outer-products are constructed so that the helicity-amplitude phase convention of Jacob and Wick can be used throughout for the fixing of the signs associated with this large W-boson longitudinal–transverse interference effect.
73531680
Diffractive vector meson cross sections from BK evolution with impact parameter
The solution of the Balitsky-Kovchegov evolution equation with impact parameter dependence is used to compute cross sections for J/Ψ, ρ and φ vector meson production. These calculations are then compared with data from HERA and good agreement is found for the J/Ψ and φ mesons while the ρ has a low normalization. The phenomenological corrections needed to bring the calculations into agreement with the data are discussed. The work presented here may be found in the publication [1].