O. H. Bauer

Metal mesh resonant filters for terahertz frequencies

The interest in terahertz photometric and imaging measurements has motivated the development of bandpass resonant filters to be coupled to multiple-pixel devices such as bolometer arrays. Resonant grids are relatively simple to fabricate, exhibiting high transmission at the central frequency, a narrow bandpass, and good rejection of the side frequencies of the spectrum. We have fabricated filters centered at different frequencies between 0.4 and 10 THz, using photolithography and electroforming techniques. Transmission measurements have shown center frequencies and bandwidths close to the design predictions. The performance of the filters was found not to be critically dependent on small physical deformations in the mesh, becoming more noticeable at higher frequencies (i.e., for smaller physical sizes). Wider bandwidths, needed to attain higher sensitivities in the continuum, were obtained by changing the design parameters for filters at 2 and 3 THz.

New Wavelength Determinations of Mid-Infrared Fine-structure Lines by Infrared Space Observatory Short Wavelength Spectrometer

We report accurate new wavelengths for 29 mid-infrared ionic fine-structure lines, based on observations with the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory (ISO). Our results originate from observations of NGC 7027, NGC 6543, NGC 6302, the Circinus galaxy, Sgr A West, and W51 IRS 2. The obtained accuracies (λ/Δλ) range from 3 × 104 to 1 × 105, depending on instrumental mode and uncertainty in radial velocities.

Optical and radar observations of the motion of auroral arcs

Abstract During a nine day observational campaign in February 1992 we used an image-intensified CCD TV camera along with the EISCAT radar to observe auroral arcs in the magnetic zenith above Kiruna. We determine the normal motions of auroral arcs near magnetic zenith and compare them with the plasma velocities measured by EISCAT. Our interest focuses on the relative motions of arcs and ionospheric plasma and the changes of tangential velocity as the plasma traverses the arcs. In all six cases, relative motions of arc and plasma of the order of 200 m s −1 are found. They are interpreted in relation to the current system to which the arc belongs as a trace of an upward-directed field-aligned sheet current. In most cases the arc moves so as to reduce the size and energy content of the current system, but the opposite case is also observed. There is a striking correlation between the N-S motion of arcs and plasma, but the arcs tend to lag behind.

Automatic Solar Flare Detection Using Neural Network Techniques

We present a new method for automatic detection of flare events from images in the optical range. The method uses neural networks for pattern recognition and is conceived to be applied to full-disk Hαimages. Images are analyzed in real time, which allows for the design of automatic patrol processes able to detect and record flare events with the best time resolution available without human assistance. We use a neural network consisting of two layers, a hidden layer of nonlinear neurodes and an output layer of one linear neurode. The network was trained using a back-propagation algorithm and a set of full-disk solar images obtained by HASTA (HαSolar Telescope for Argentina), which is located at the Estación de Altura Ulrico Cesco of OAFA (Observatorio Astronómico Félix Aguilar), El Leoncito, San Juan, Argentina. This method is appropriate for the detection of solar flares in the complete optical classification, being portable to any Hαinstrument and providing unique criteria for flare detection independent of the observer.

Rapid Submillimeter Brightenings Associated with a Large Solar Flare

We present high time resolution observations of Active Region 8910 obtained simultaneously at 212 and 405 GHz during a large Hα flare, which produced a soft X-ray class X1.1 event. Data were obtained with the new solar submillimeter telescope recently installed at the El Leoncito Observatory to explore this poorly known part of the solar emission spectrum. A small slow submillimeter enhancement (≤300 sfu) was associated to bulk emissions at X-rays, Hα, and microwaves. The event exhibited numerous submillimeter-wave 100-300 ms duration spikes, the larger ones with fluxes on the order of 220 and 500 sfu (±20%) at 212 and 405 GHz, respectively. A dramatic increase in the incidence rate of submillimeter spikes sets in as a new large loop system appears in AR 8910, and X-ray emission increases nearly 1 hr before the large flare. The brightening incidence rate (~20 per minute) correlates well with the large flare light curves at X-rays and Hα. The submillimeter spikes may be associated to microflares, waves, or quakes in flaring active regions.

CCD-camera system for stereoscopic optical observations of the aurora

A system of three identical CCD-cameras was developed enabling stereoscopic auroral observations. An image intensifier allows for real-time imaging of auroral arcs with interference or broad-band filters. The combination of a small-angle optics with a CCD-chip of 756 by 580 pixels provides spatial resolutions of auroral small-scale structures down to 20 m. The cameras are controlled by personal computers with integrated global positioning (GPS) modules enabling time synchronization of the cameras and providing the exact geographical position for the portable cameras. Calibration with a standard light source is the basis for quantitative evaluation of images by image processing techniques. The current technical development is the combination with local operating networks (LON) for monitoring camera parameters like voltage and temperature and remote control of parameters like filter positions, mounting tilt angles and camera gain.

First combined observations in the German–Argentinean solar observatory: correlations in quiet and eruptive phenomena at the limb

Abstract This is a first report of combined observations form the solar instruments at the recently inaugurated German–Argentinean Solar-Observatory at El Leoncito, San Juan, Argentina. The Hα telescope (HASTA) and the mirror coronagraph (MICA) daily image the solar disk and the inner solar corona respectively with high temporal and spatial resolution. The excellent weather conditions for solar studies of the Observatory, and its south equatorial location allow a complementary summer-condition data with respect to the majority of the other observatories, mainly located in the northern hemisphere. In this paper, we present four events in order to study possible correlations between observations taken by both telescopes. Since each instrument records data in quite different temperature regimes, correlation between both set of data appears when the phenomena span a broad range of temperatures. This is explicitly shown for two of the four set of data presented here. On the other hand, the four cases are good examples of the contributions the two instruments can provide to the better understanding of the mechanisms at work in the inner solar atmosphere.

Solar Flare Observations at Submm-waves

First 405 GHz and 212 GHz solar flare observations were obtained during short campaigns while the new solar submillimeter-wave telescope (SST) was still undergoing adjustments at the CASLEO EI Leoncito observatory in the Argentina Andes. We show here preliminary results for a large X1.1 class X-ray event occurred on 2000 March 22, which exhibited a small submm-w continuum response to the slow (minutes) bulk flare emission, and numerous subsecond spikes (100-300 ms), the brightest spikes reaching about 180 and 50 s.f.u. at 405 and 212 GHz, respectively. Solar flare observations are nearly unknown in the submm-IR range of wavelengths. Few results limited to time resolution of about one minute have suggested brightness variations of 10-100 K in active regions without clear flare associations (Clark & Park 1970; Hudson 1975). The six SST beams (Kaufmann et al. 1994) are superimposed on a Kitt Peak solar magnetogram (NOAA 2000) shown in Figure 1 (left) at about the time of the event on 2000 March 22. The flare emission light-curves in compressed time scales are shown in Figure 1 (right) for different frequencies. The H-a telescope is described elsewhere (Bagala et al. 1999). The bottom plot of Figure 1 (right) shows the rate of submm-w brightest (~ 20 K) spikes incidence with time. An example of such a bright spike (labeled A in Figure 1 (right)) is shown in Figure 2 (A) in a five seconds time interval, compared to data obtained tracking a quiet solar region, near its center, in Figure 2 (B), labeled B in Figure 1 (right). The spiky incidence increases drastically after about 1730 UT approximately together with the soft X-ray level. There is a pronounced concentration of brightenings in correspondence to the bulk emissions at X-rays and H-a. Clusters of spikes seem to be added at about 1745 UT and 1820 UT coincident to flares occurring in AR

HERSCHEL: TESTING OF CRYOGENICS INSTRUMENTS AT SPACECRAFT LEVEL AND EARLY FLIGHT RESULTS

Herschel cryogenics instrument (HIFI, PACS, SPIRE) flight models have been delivered to ESA & Prime contractor Thales Alenia Space mid 2007, to be integrated and tested on the Herschel spacecraft, for a launch mid May 2009.The instrument integration and test campaign at spacecraft level was performed between mid 2007 and end 2008 in Astrium GmbH, Immenstadt (Gernany) and later in ESA’s test facilities at Estec, Noordwijk (Nederland). The objective of these tests was to demonstrate full operability and performances of the instruments in spacecraft configuration, and their compatibility with the launch and space environment, while maintaining full compliance with the underlying requirements. A set of short functional tests were developed and used repeatedly to quickly check the health of each instrument at key points in the test campaign. Typically, this was after integration of a major component, prior to a major environmental test or before/after movement of the spacecraft. A set of full functional tests ...

Three-dimensional reconstruction of the auroral arc emission from stereoscopic optical observations

The mathematics of emission computed tomography is applied to the three-dimensional reconstruction of the optical emission within an auroral arc. According to general experimental conditions, a very limited angular range and a small number of observers require an iterative back projection method. Parameters for the quantitative correspondence between the original and reconstructed volumes and between the images are defined and using this method, a theoretical arc can be reconstructed with root- mean-square errors of the images of less than 2%. The reconstruction accuracy of the volume can be improved with an increasing number of observers to root-mean-square errors of about 15%. Different geometries are tested but the best results are obtained as long as one observer looks along the magnetic field line through the auroral arc. The calculations confirm the range of suitable observation geometries to within 20 km from the field line through one of the observers.