Spacecraft attitude detection system by stellar reference Patent

Attitude detection system using stellar references for three-axis control and spin stabilized spacecraf

Temporal evolution of the Evershed flow in sunspots. I. Observational characterization of Evershed clouds

[Abridged] The magnetic and kinematic properties of the photospheric Evershed flow are relatively well known, but we are still far from a complete understanding of its nature. The evolution of the flow with time, which is mainly due to appearance of velocity packets called Evershed clouds (ECs), may provide information to further constrain its origin. Here we undertake a detailed analysis of the evolution of the Evershed flow by studying the properties of ECs. In this first paper we determine the sizes, proper motions, location in the penumbra, and frequency of appearance of ECs, as well as their typical Doppler velocities, linear and circular polarization signals, Stokes V area asymmetries, and continuum intensities. High-cadence, high-resolution, full vector spectropolarimetric measurements in visible and infrared lines are used to derive these parameters. We find that ECs appear in the mid penumbra and propage outward along filaments with large linear polarization signals and enhanced Evershed flows. The frequency of appearance of ECs varies between 15 and 40 minutes in different filaments. ECs exhibit the largest Doppler velocities and linear-to-circular polarization ratios of the whole penumbra. In addition, lines formed deeper in the atmosphere show larger Doppler velocities, much in the same way as the ''quiescent'' Evershed flow. According to our observations, ECs can be classified in two groups: type I ECs, which vanish in the outer penumbra, and type II ECs, which cross the outer penumbral boundary and enter the sunspot moat. Most of the observed ECs belong to type I. On average, type II ECs can be detected as velocity structures outside of the spot for only about 14 min. Their proper motions in the moat are significantly reduced with respect to the ones they had in the penumbra.Comment: Accepted for publication in A&

Photoheliograph requirements for a spectrograph, November 1967 - June 1968

Preliminary design requirements and constraints for ATM photoheliograp

Dual color plasmonic pixels create a polarization controlled nano color palette

Color filters based upon nanostructured metals have garnered significant interest in recent years, having been positioned as alternatives to the organic dye-based filters which provide color selectivity in image sensors, as nonfading “printing” technologies for producing images with nanometer pixel resolution, and as ultra-high-resolution, small foot-print optical storage and encoding solutions. Here, we demonstrate a plasmonic filter set with polarization-switchable color properties, based upon arrays of asymmetric cross-shaped nanoapertures in an aluminum thin-film. Acting as individual color-emitting nanopixels, the plasmonic cavity-apertures have dual-color selectivity, transmitting one of two visible colors, controlled by the polarization of the white light incident on the rear of the pixel and tuned by varying the critical dimensions of the geometry and periodicity of the array. This structural approach to switchable optical filtering enables a single nanoaperture to encode two information states within the same physical nanoaperture, an attribute we use here to create micro image displays containing duality in their optical information states

Preliminary design of the Visible Spectro-Polarimeter for the Advanced Technology Solar Telescope

The Visible Spectro-Polarimeter (ViSP) is one of the first light instruments for the Advanced Technology Solar Telescope (ATST). It is an echelle spectrograph designed to measure three different regions of the solar spectrum in three separate focal planes simultaneously between 380 and 900 nm. It will use the polarimetric capabilities of the ATST to measure the full Stokes parameters across the line profiles. By measuring the polarization in magnetically sensitive spectral lines the magnetic field vector as a function of height in the solar atmosphere can be obtained, along with the associated variation of the thermodynamic properties. The ViSP will have a spatial resolution of 0.04 arcsec over a 2 arcmin field of view (at 600 nm). The minimum spectral resolving power for all the focal planes is 180,000. The spectrograph supports up to 4 diffraction gratings and is fully automated to allow for rapid reconfiguration.Comment: 8 pages, 5 figures, proceedings of SPIE Astronomical Telescopes + Instrumentation 2012 Conference 8446 (1-5 July 2012

A Study of H2 Emission in Three Bipolar Proto-Planetary Nebulae: IRAS 16594-4656, Hen 3-401, and Rob 22

We have carried out a spatial-kinematical study of three proto-planetary nebulae, IRAS 16594-4656, Hen 3-401, and Rob 22. High-resolution H2 images were obtained with NICMOS on the HST and high-resolution spectra were obtained with the Phoenix spectrograph on Gemini-South. IRAS 16594-4656 shows a "peanut-shaped" bipolar structure with H2 emission from the walls and from two pairs of more distant, point-symmetric faint blobs. The velocity structure shows the polar axis to be in the plane of the sky, contrary to the impression given by the more complex visual image and the visibility of the central star, with an ellipsoidal velocity structure. Hen 3-401 shows the H2 emission coming from the walls of the very elongated, open-ended lobes seen in visible light, along with a possible small disk around the star. The bipolar lobes appear to be tilted 10-15 deg with respect to the plane of the sky and their kinematics display a Hubble-like flow. In Rob 22, the H2 appears in the form of an "S" shape, approximately tracing out the similar pattern seen in the visible. H2 is especially seen at the ends of the lobes and at two opposite regions close to the unseen central star. The axis of the lobes is nearly in the plane of the sky. Expansion ages of the lobes are calculated to be approximately 1600 yr (IRAS 16594-4656), 1100 yr (Hen 3-401), and 640 yr (Rob 22), based upon approximate distances

Anomalous circular polarization profiles in the He I 1083.0 nm multiplet from solar spicules

We report Stokes vector observations of solar spicules and a prominence in the He I 1083 nm multiplet carried out with the Tenerife Infrared Polarimeter. The observations show linear polarization profiles that are produced by scattering processes in the presence of a magnetic field. After a careful data reduction, we demonstrate the existence of extremely asymmetric Stokes V profiles in the spicular material that we are able to model with two magnetic components along the line of sight, and under the presence of atomic orientation in the energy levels that give rise to the multiplet. We discuss some possible scenarios that can generate the atomic orientation in spicules. We stress the importance of spectropolarimetric observations across the limb to distinguish such signals from observational artifacts.Comment: accepted for publication in Ap