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.
119177458
The fringe detection laser metrology for the GRAVITY interferometer at the VLTI
Interferometric measurements of optical path length differences of stars over large baselines can deliver extremely accurate astrometric data. The interferometer GRAVITY will simultaneously measure two objects in the field of view of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO) and determine their angular separation to a precision of 10 μas in only 5 minutes. To perform the astrometric measurement with such a high accuracy, the differential path length through the VLTI and the instrument has to be measured (and tracked since Earth's rotation will permanently change it) by a laser metrology to an even higher level of accuracy (corresponding to 1 nm in 3 minutes). Usually, heterodyne differential path techniques are used for nanometer precision measurements, but with these methods it is difficult to track the full beam size and to follow the light path up to the primary mirror of the telescope. Here, we present the preliminary design of a differential path metrology system, developed within the GRAVITY project. It measures the instrumental differential path over the full pupil size and up to the entrance pupil location. The differential phase is measured by detecting the laser fringe pattern both on the telescopes' secondary mirrors as well as after reflection at the primary mirror. Based on our proposed design we evaluate the phase measurement accuracy based on a full budget of possible statistical and systematic errors. We show that this metrology design fulfills the high precision requirement of GRAVITY.
14528716
FU Orionis Resolved by Infrared Long-Baseline Interferometry at a 2 AU Scale
We present the first infrared interferometric observations of a young stellar object with a spatial projected resolution better than 2 AU. The observations were obtained with the Palomar Testbed Interferometer (PTI). FU Orionis exhibits a visibility of V2=0.72 ± 0.07 for a 103 ± 5 m-projected baseline at λ=2.2 μm. On the spatial scale probed by the PTI, the data are consistent with both a binary system scenario (a maximum magnitude difference of 2.7 ± 0.5 mag and the smallest separation of 0.35 ± 0.05 AU) and a standard luminous accretion disk model ( ~6 × 10−5 M☉ yr-1), where the thermal emission dominates the stellar scattering, and are inconsistent with a single stellar photosphere.
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.
118593802
Imaging the spotty surface of Betelgeuse in the H band
Aims. This paper reports on H-band interferometric observations of Betelgeuse made at the three-telescope interferometer IOTA. We image Betelgeuse and its asymmetries to understand the spatial variation of the photosphere, including its diameter, limb darkening, effective temperature, surrounding brightness, and bright (or dark) star spots. Methods. We used different theoretical simulations of the photosphere and dusty environment to model the visibility data. We made images with parametric modeling and two image reconstruction algorithms: MIRA and WISARD. Results. We measure an average limb-darkened diameter of 44.28 ± 0.15 mas with linear and quadratic models and a Rosseland diameter of 45.03 ± 0.12 mas with a MARCS model. These measurements lead us to derive an updated effective temperature of 3600 ± 66 K. We detect a fully-resolved environment to which the silicate dust shell is likely to contribute. By using two imaging reconstruction algorithms, we unveiled two bright spots on the surface of Betelgeuse. One spot has a diameter of about 11 mas and accounts for about 8.5% of the total flux. The second one is unresolved (diameter < 9 mas) with 4.5% of the total flux. Conclusions. Resolved images of Betelgeuse in the H band are asymmetric at the level of a few percent. The MOLsphere is not detected in this wavelength range. The amount of measured limb-darkening is in good agreement with model predictions. The two spots imaged at the surface of the star are potential signatures of convective cells.
18853087
The limb-darkened Arcturus: imaging with the IOTA/IONIC interferometer
Aims. We undertook an H band interferometric examination of Arcturus, a star frequently used as a spatial and spectral calibrator. 
Methods. Using the IOTA 3 telescope interferometer, we performed spectro-interferometric observations (R ≈ 35) of Arcturus. 
Atmospheric models and prescriptions were fitted to the data to derive the brightness distribution of the photosphere. Image reconstruction 
was performed using two software algorithms: Wisard and Mira. 
Results. An achromatic power law proved to be a good model of the brightness distribution, with a limb darkening compatible with 
the one derived from atmospheric model simulations using our marcs model. A Rosseland diameter of 21.05 ± 0.21 was derived, 
corresponding to an effective temperature of Teff = 4295 ± 26 K. No companion was detected from the closure phases, with an upper 
limit on the brightness ratio of 8 × 10^−4 at 1 AU. The dynamic range at such distance from the photosphere was established as 
1.5 × 10^−4 (1σrms). An upper limit of 1.7×10^−3 was also derived for the level of brightness asymmetries present in the photosphere.
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.
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].
119390534
Use of W-boson longitudinal-transverse interferencein top quark spin-correlation functions
Abstract.Most of this paper consists of the derivation of general beam-referenced stage-two spin-correlation functions for the analysis of top-antitop pair production at the Tevatron, at the Large Hadron Collider, and/or at an International Linear Collider. However, for the charged-lepton plus jets reaction $q \bar{q} \rightarrow t \bar{t} \rightarrow (W^ + b) (W^- \bar{b} ) \rightarrow (l^{ + } \nu b ) (W^- \bar{b} )$, there is a simple three-angle spin-correlation function for the determination of the relative sign of or for the measurement of a possible non-trivial phase between the two dominant λb=-1/2 helicity amplitudes for the t → W+b decay mode. For the CP-conjugate case, there is an analogous function and tests for $\bar{t} \rightarrow W^{-} \bar{b}$ decay. These results make use of W-boson longitudinal-transverse interference.