Simulation of a method to directly image exoplanets around multiple stars systems

Direct imaging of extra-solar planets has now become a reality, especially with the deployment and commissioning of the first generation of specialized ground-based instruments such as the GPI, SPHERE, P1640 and SCExAO. These systems will allow detection of planets 1e7 times fainter than their host star. For space-based missions, such as EXCEDE, EXO-C, EXO-S, WFIRST-AFTA, different teams have shown in laboratories contrasts reaching 1e-10 within a few diffraction limits from the star using a combination of a coronagraph to suppress light coming from the host star and a wavefront control system. These demonstrations use a deformable mirror (DM) to remove residual starlight (speckles) created by the imperfections of telescope. However, all these current and future systems focus on detecting faint planets around a single host star or unresolved binaries/multiples, while several targets or planet candidates are located around nearby binary stars such as our neighbor star Alpha Centauri. Until now, it has been thought that removing the light of a companion star is impossible with the current technology, excluding binary star systems from target lists of direct imaging missions. Direct imaging around binaries or multiples systems at a level of contrast allowing Earth-like planets detection is challenging because the region of interest, where a dark zone is essential, is contaminated by the light coming from the host star's companion. We propose a method to simultaneously correct aberration sand diffraction of light coming from the target star. This method works even if the companion star is outside the control region of the DM (beyond its half-Nyquist frequency), by taking advantage of aliasing effects.Comment: 8 pages, 13 figures, SPIE Astronomical Telescope and Instrumentation conferenc

TPC tracking and particle identification in high-density environment

Track finding and fitting algorithm in the ALICE Time projection chamber (TPC) based on Kalman-filtering is presented. Implementation of particle identification (PID) using d$E$/d$x$ measurement is discussed. Filtering and PID algorithm is able to cope with non-Gaussian noise as well as with ambiguous measurements in a high-density environment. The occupancy can reach up to 40% and due to the overlaps, often the points along the track are lost and others are significantly displaced. In the present algorithm, first, clusters are found and the space points are reconstructed. The shape of a cluster provides information about overlap factor. Fast spline unfolding algorithm is applied for points with distorted shapes. Then, the expected space point error is estimated using information about the cluster shape and track parameters. Furthermore, available information about local track overlap is used. Tests are performed on simulation data sets to validate the analysis and to gain practical experience with the algorithm.Comment: 9 pages, 5 figure

The EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE)

We present an overview of the EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE), selected by NASA for technology development and maturation. EXCEDE will study the formation, evolution and architectures of exoplanetary systems, and characterize circumstellar environments into stellar habitable zones. EXCEDE provides contrast-limited scattered-light detection sensitivities ~ 1000x greater than HST or JWST coronagraphs at a much smaller effective inner working angle (IWA), thus enabling the exploration and characterization of exoplanetary circumstellar disks in currently inaccessible domains. EXCEDE will utilize a laboratory demonstrated high-performance Phase Induced Amplitude Apodized Coronagraph (PIAA-C) integrated with a 70 cm diameter unobscured aperture visible light telescope. The EXCEDE PIAA-C will deliver star-to-disk augmented image contrasts of < 10E-8 and a 1.2 L/D IWA or 140 mas with a wavefront control system utilizing a 2000-element MEMS DM and fast steering mirror. EXCEDE will provide 120 mas spatial resolution at 0.4 microns with dust detection sensitivity to levels of a few tens of zodis with two-band imaging polarimetry. EXCEDE is a science-driven technology pathfinder that will advance our understanding of the formation and evolution of exoplanetary systems, placing our solar system in broader astrophysical context, and will demonstrate the high contrast technologies required for larger-scale follow-on and multi-wavelength investigations on the road to finding and characterizing exo-Earths in the years ahead

No Indications of Axion-Like Particles From Fermi

As very high energy (~100 GeV) gamma rays travel over cosmological distances, their flux is attenuated through interactions with the extragalactic background light. Observations of distant gamma ray sources at energies between ~200 GeV and a few TeV by ground-based gamma ray telescopes such as HESS, however, suggest that the universe is more transparent to very high energy photons than had been anticipated. One possible explanation for this is the existence of axion-like-particles (ALPs) which gamma rays can efficiently oscillate into, enabling them to travel cosmological distances without attenuation. In this article, we use data from the Fermi Gamma Ray Space Telescope to calculate the spectra at 1-100 GeV of two gamma ray sources, 1ES1101-232 at redshift z=0.186 and H2356-309 at z=0.165, and use this in conjunction with the measurements of ground-based telescopes to test the ALP hypothesis. We find that the observations can be well-fit by an intrinsic power-law source spectrum with indices of -1.72 and -2.1 for 1ES1101-232 and H2356-309, respectively, and that no ALPs or other exotic physics is necessary to explain the observed degree of attenuation.Comment: 7 pages, 4 figures. v3: Matches published version, the analysis of H2356-309 is revised, no change in conclusion

K0s and \Lambda\ production in Pb--Pb collisions with the ALICE experiment

We present the study of K0s and Lambda production performed with the ALICE experiment at the LHC in Pb--Pb collisions at \sqrt{s_NN}=2.76 TeV and pp collisions at \sqrt{s}=0.9 and 7 TeV. The K0s and Lambda particles are reconstructed via their V0 decay topology allowing their identification up to high transverse momenta. The corresponding baryon/meson ratios as a function of transverse momentum are extracted for Pb--Pb collisions in centrality bins and in the transverse momentum range from 1 to 6 GeV/c. They are also compared with those measured in pp events at the LHC energies of 0.9 and 7 TeV as well as in Au--Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV from RHIC.Comment: 4 pages, 4 figures, proceedings of Quark Matter 2011 (May 23rd-28th 2011, Annecy, France

Experimental study of a low-order wavefront sensor for the high-contrast coronagraphic imager EXCEDE

The mission EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer), selected by NASA for technology development, is designed to study the formation, evolution and architectures of exoplanetary systems and characterize circumstellar environments into stellar habitable zones. It is composed of a 0.7 m telescope equipped with a Phase-Induced Amplitude Apodization Coronagraph (PIAA-C) and a 2000-element MEMS deformable mirror, capable of raw contrasts of 1e-6 at 1.2 lambda/D and 1e-7 above 2 lambda/D. One of the key challenges to achieve those contrasts is to remove low-order aberrations, using a Low-Order WaveFront Sensor (LOWFS). An experiment simulating the starlight suppression system is currently developed at NASA Ames Research Center, and includes a LOWFS controlling tip/tilt modes in real time at 500 Hz. The LOWFS allowed us to reduce the tip/tilt disturbances to 1e-3 lambda/D rms, enhancing the previous contrast by a decade, to 8e-7 between 1.2 and 2 lambda/D. A Linear Quadratic Gaussian (LQG) controller is currently implemented to improve even more that result by reducing residual vibrations. This testbed shows that a good knowledge of the low-order disturbances is a key asset for high contrast imaging, whether for real-time control or for post processing.Comment: 12 pages, 20 figures, proceeding of the SPIE conference Optics+Photonics, San Diego 201