Measured Intensity Variations Research Articles

Atmospheric scintillation noise in ground-based exoplanet photometry

ABSTRACT Atmospheric scintillation caused by optical turbulence in the Earth’s atmosphere can be the dominant source of noise in ground-based photometric observations of bright targets, which is a particular concern for ground-based exoplanet transit photometry. We demonstrate the implications of atmospheric scintillation for exoplanet transit photometry through contemporaneous turbulence profiling and transit observations. We find a strong correlation between measured intensity variations and scintillation determined through optical turbulence profiling. This correlation indicates that turbulence profiling can be used to accurately model the amount of scintillation noise present in photometric observations on another telescope at the same site. We examine the conditions under which scintillation correction would be beneficial for transit photometry through turbulence profiling, and find that for the atmosphere of La Palma, scintillation dominates for bright targets of magnitude above V ∼ 10.1 mag for a 0.5 m telescope, and at V ∼ 11.7 mag for a 4.2 m telescope under median atmospheric conditions. Through Markov-chain Monte Carlo methods we examine the effect of scintillation noise on the uncertainty of the measured exoplanet parameters, and determine the regimes where scintillation correction is especially beneficial. The ability to model the amount of noise in observations due to scintillation, given an understanding of the atmosphere, is a crucial test for our understanding of scintillation and the overall noise budget of our observations.

Highly Sensitive Intensity Detection by a Self-Interference Micro-Ring Resonator

A novel highly sensitive intensity detection method has been proposed based on a self-interference ring resonator, where it is obtained by introducing an additional interference sensing arm between two coupling regions in the conventional planar add-drop micro-ring resonator. By means of dissipative and dispersive coupling mechanisms, optical path length changes of sensing arm not only bring the shift in a resonant wavelength, but also result in the variation of the linewidth and extinction of the spectrum. Using the analytical expression of the transmittance, it is proved that this sensor can monitor optical path length changes of sensing arm with a theoretical detection limit ( $5.6\times 10^{-3}$ nm) by measuring intensity variations at a certain transmission valley.

What are solar faculae?

Results are presented of observations of the facula area near the solar disc center. Observations were performed at the German Vacuum Tower Telescope of the Observatorio del Teide (Tenerife) with the simultaneous use of two instruments, i.e., TESOS in the Ba IIλ 455.4 nm line to measure intensity variations in the photosphere and, at the same time, TIP in the Fe I (λλ 1564.3–1565.8 nm) line to measure Stokes parameters. Using the Fourier filtering technique, we separated the convective and wave components of the intensity field. Stokes parameters Fe I λ 1564.8 nm and λ 1565.2 nm were inverted by the SIR inversion code to estimate the magnetic field strength. We found that the contrast of intergranular lines of the facula in the continuum is almost independent of the magnetic field strengh (in the range from 30 to 160 mT). This result casts doubt on the assertion that solar faculae are a cluster of magnetic flux tubes. Most likely, due to the decrease of transparency of the matter in a strong (approximately 1 kilogauss) magnetic field, we can see the hot walls of granules.

Fiber Optic Pressure Sensor using Multimode Interference

Based on the theory of multimode interference (MMI) and self-image formation, we developed a novel intrinsic optical fiber pressure sensor. The sensing element consists of a section of multimode fiber (MMF) without cladding spliced between two single mode fibers (SMF). The MMI pressure sensor is based on the intensity changes that occur in the transmitted light when the effective refractive index of the MMF is changed. Basically, a thick layer of Polydimethylsiloxane (PDMS) is placed in direct contact with the MMF section, such that the contact area between the PDMS and the fiber will change proportionally with the applied pressure, which results in a variation of the transmitted light intensity. Using this configuration, a good correlation between the measured intensity variations and the applied pressure is obtained. The sensitivity of the sensor is 3 μV/psi, for a range of 0-60 psi, and the maximum resolution of our system is 0.25 psi. Good repeatability is also observed with a standard deviation of 0.0019. The key feature of the proposed pressure sensor is its low fabrication cost, since the cost of the MMF is minimal.

Microbolometer-infrared imaging Stokes polarimeter

A long-wave infrared division of amplitude imaging Stokes polarimeter is presented. For the first time, to our knowledge, application of microbolometer focal plane array (FPA) technology to polarimetry is demonstrated. The sensor utilizes a wire-grid beamsplitter with imaging systems positioned at each output to analyze two orthogonal linear polarization states simultaneously. Combined with a form birefringent wave plate, the system is capable of snapshot imaging polarimetry in any one Stokes parameter (S1, S2, or S3). Radiometric and polarimetric calibration procedures for the instrument are provided, and the reduction matrices from the calibration are compared to rigorous coupled wave analysis and ray-tracing simulations. Image registration techniques for the sensor are discussed, and data from the instrument are presented, demonstrating the ability to measure intensity variations corresponding to polarized emission in natural environments. As such, emission polarimetry can be exploited at significantly reduced cost, sensor size, and power consumption over instruments based on more expensive mercury-cadmium telluride FPAs.

Characterization of Intensity Variations Along Fe XIV Coronal Loops – A Case Study

We discuss a method, and corresponding results, to analyze the dynamics of localized small-scale coronal (post-flare) loops observed with the MICA (Mirror Coronagraph for Argentina) telescope in the well-known green coronal line at 530.3 nm. In particular, we designed a procedure to measure intensity variations along the structure of a loop, both in space and time. The method was applied to a loop on the southwest limb on green-line images taken on October 1st, 2001 with a cadence of about one per minute. Significant coronal variability was detected in a compact loop system suggesting different types of plasma flow. One of them shows a brightening at the top, which moves down along the axis of the loop with mean velocities that suggest scenarios of high-speed plasma flows. The results obtained allow the flow inside coronal structures to be characterized and theoretical descriptions related to different physical scenarios to be compared.

Electric field induced charge density variations in partially-ionic compounds

Using a modulation technique and synchrotron radiation, we investigated the charge density variations in cubic ZnSe and trigonal SiO 2 induced by an external high-electric field E applied along the [111] and [11.0] direction, respectively. Selecting particularly weak reflections, we observed an almost linear variation of the integrated intensity versus E changing by up to 2% at | E|=3 kV/mm. For both crystals, the displacements of the relative ion positions within the unit cell exceed the piezoelectric induced variation of the unit cell parameters by at least one order of magnitude. The measured intensity variations of ZnSe can be explained by the opposite displacement of the zinc and selenium ions towards the field direction breaking the stiff tetrahedral coordination of the chemical bond. For quartz, the electric field initiates a displacement of those oxygen ions only where the O–Si bond is directed oblique to the field direction. The other oxygen ions and the silicon positions remain nearly unchanged. Thus, the ionic arrangement is described mainly by a change in the O–Si–O bonding angles.

Profiling with tritium imaging

The tritium imaging technique focuses secondary electrons produced by β-particles emerging from a surface as a means of mapping the distribution of tritium in that surface. The short range of β-particles makes this technique sensitive to the depth of the tritium. The effect of tritium depth on the intensity of tritium images was investigated by several means. Specimens of different materials were implanted with 20 keV tritium ions, and imaged. The depth of the implanted tritium was decreased by sputtering the surface, while monitoring variations in image intensity. In graphite the image intensity increased as the depth of tritium was reduced, then decreased as sputtering began to remove the tritium itself. In aluminum, rapid tritium diffusion and large changes in surface conditioning had a strong effect on image intensity. It was, however, possible to measure intensity variations in one of the graphite specimens as increasingly thicker layers of aluminum were evaporated onto the surface. In this case surface conditioning effects were minimized by making measurements immediately after deposition. The results of both sets of experiments are interpreted using a theoretical curve which was based on the transport of primary beta particles to the surface. By introducing a light source, the imaging apparatus could be made to function as a photoelectron microscope. In this mode, changes in surface conditioning of deposited aluminum surfaces were observed.

The use of metal-halide discharge lamps for film lighting (Part 2)

Intensity variations of light from a discharge lamp, occurring at twice the alternating supply frequency, can lead to a cyclic variation in frame-to-frame exposure if such lamps are used as light sources in motion picture film work. The visibility of picture luminance fluctuations brought about by such exposure variations is discussed, and limits of film exposure variation are recommended. Practical magnitudes of exposure variation are examined. Using these factors, relationships are derived between camera frame frequency and shutter angle, and lamp supply frequency and intensity variation magnitude, such that practical picture luminance variations are not perceptible. An assessment of a 'safe' lamp supply frequency is described, above which the appearance of picture luminance fluctuations may be discounted. The effect of ripple asymmetry (differing magnitudes of successive intensity maxima) is discussed. Experimental techniques for measuring intensity variations under standardized conditions are described, and the characteristics of two currently-available metal-halide discharge lamps are examined.

The use of metal-halide discharge lamps for film lighting (Part 1)

Intensity variations of light from a discharge lamp, occurring at twice the alternating supply frequency, can lead to a cyclic variation in frame-to-frame exposure if such lamps are used as light sources in motion picture film work. The visibility of picture luminance fluctuations brought about by such exposure variations is discussed, and limits of film exposure variation are recommended. Practical magnitudes of exposure variation are examined. Using these factors, relationships are derived between camera frame frequency and shutter angle, and lamp supply frequency and intensity variation magnitude, such that practical picture luminance variations are not perceptible. An assessment of a 'safe' lamp supply frequency is described, above which the appearance of picture luminance fluctuations may be discounted. The effect of ripple asymmetry (differing magnitudes of successive intensity maxima) is discussed. Experimental techniques for measuring intensity variations under standardized conditions are described, and the characteristics of two currently-available metal-halide discharge lamps are examined.

Gamma rays from resonance neutron capture in 115In

Gamma rays in the range 5.4–6.7 MeV have been studied for 31 s-wave neutron resonances of 115In, selected by time of flight in the range 3–430 eV. In a subsidiary experiment, spin J = 5 has been assigned to 17 and J = 4 to 14 resonances by measuring intensity variations of some strong low-energy transitions. The reduced widths averaged over all initial states of the same spin have been estimated for 41 primary transitions: these values have provided information on the spin and parity of the corresponding 116In final states. Overall mean values of E1 and M1 radiative strength have been calculated. The width distribution has been fitted with a χ2 function with ν = 1.10+0.27−0.09 degrees of freedom for M1 and ν = 1.42 + 0.014−0.08 for E1 radiation. An estimate of the spin cut-off parameter σ = 3.6−0.4 + 0.8 has been derived. A non-statistical effect already evidenced in previous measurements has been confirmed, consisting of a strong modulation of the radiative strength against resonance energy, correlated also with the local neutron strength function. In addition, it has now been shown that this structure is due to E1 radiation only.

Pulse technique for measuring intensity variations of continuous lights in comparison with reference scintillation flashes

A technique is described for measuring both a continuous light and reference scintillation flashes simultaneously by means of gated operation of a single photomultiplier tube. The technique enables us to measure intensity variations of continuous lights with very high accuracy.