MAXIPOL: a balloon-borne experiment for measuring the polarization anisotropy of the cosmic microwave background radiation

We discuss MAXIPOL, a bolometric balloon-borne experiment designed to measure the E-mode polarization anisotropy of the cosmic microwave background radiation (CMB) on angular scales of 10^′ to 2°. MAXIPOL is the first CMB experiment to collect data with a polarimeter that utilizes a rotating half-wave plate and fixed wire-grid polarizer. We present the instrument design, elaborate on the polarimeter strategy and show the instrument performance during flight with some time domain data. Our primary dataset was collected during a 26 h turnaround flight that was launched from the National Scientific Ballooning Facility in Ft. Sumner, New Mexico in May 2003. During this flight five regions of the sky were mapped. Data analysis is in progress.     

The GEM project: An international collaboration to survey galactic radiation emission

The GEM (Galactic Emission Mapping) project is an international collaboration established with the aim of surveying the full sky at long wavelengths with a multi-frequency radio telescope. A total of 745 hours of observation at 408 MHz were completed from an Equatorial site in Colombia. The observations cover the celestial band 0 ^h <<24 ^h , and –24° 22<<+35° 37. Preliminary results of this partial survey will be discussed. A review of the instrumental setup and a 10° resolution sky map at 408 MHz is presented.Presented by S. Torres at the UN/ESA Workshop on Basic Space Sciences: From Small Telescopes to Space Missions, Colombo, Sri Lanka 11–14 January 1996     

The Darwin Rise demise: the western Pacific guyot heights trace the trans-Pacific Mendocino fracture zone

The Darwin Rise has been proposed so many times and in so many forms and places that the time has come to make a more comprehensive examination of the region. Lying on the NW Pacific Plate between the Geisha Guyots, the Mid-Pacific Mountains, the equator, and the trenches, the region is roughly bounded by magnetic anomaly M20 (147 Ma). It was subjected to a massive outpouring of lava about 105 to 120 Ma, which created the guyots and seamounts in that region. Guyots are excellent tools for studying events of long ago because they eroded in the same lowstand in the Cretaceous and guyot relief, therefore, is a surrogate for paleo-sealevel. The relief is derived by subtracting the break depth of the summit plateau of a guyot from the regional depth. Guyot relief would necessarily be less in the center than to the periphery if the feature formed on a pre-existing rise, as has been postulated. The existence of a paleo-Darwin Rise would give concentric contours for the region in question. Of the sixty guyots used in this study, thirty-seven of these guyots were surveyed using SASS multibeam in the Marcus-Wake seamount group. Twenty-three guyots were surveyed using random track single-beam sonar surveys. An entirely different scenario is shown. Data revealed a major fracture passing through the area coevally or after the guyots formed. Because the depths to the summit are not the same now, vertical tectonics occurred after subaerial erosion. This means the fracture formed during and after the erosion (roughly 105 Ma) and influenced the normal sequence of events in guyot formation. Depending on how one deciphers trends through the Hess Rise morass, SASS bathymetry shows a continuation of the Surveyor/Mendocino fracture zone swarm inside the M20 region to the NE of these data. The fracture swarm continues to the western Pacific trench system. Based on this information, if the Darwin Rise ever existed, it had to have done so elsewhere.     

Radiocarbon Ages and Environments of Deposition of the Wono and Trego Hot Springs Tephra Layers in the Pyramid Lake Subbasin, Nevada

Uncalibrated radiocarbon data from core PLC92B taken from Wizards Cove in the Pyramid Lake subbasin indicate that the Trego Hot Springs and Wono tephra layers were deposited 23,200 ± 300 and 27,300 ± 300¹⁴C yr B.P. (uncorrected for reservoir effect). Sedimentological data from sites in the Pyramid Lake and Smoke Creek–Black Rock Desert subbasins indicate that the Trego Hot Springs tephra layer was deposited during a relatively dry period when Pyramid Lake was at or below its spill point (1177 m) to the Winnemucca Lake subbasin. The Wono tephra layer was deposited when lake depth was controlled by spill across Emerson Pass sill (1207 m) to the Smoke Creek–Black Rock Desert subbasin.¹⁸O data from core PLC92B also support the concept that the Trego Hot Springs tephra fell into a relatively shallow Pyramid Lake and that the Wono tephra fell into a deeper spilling lake.     

Observations on Gulf of Alaska seamount chains by multi-beam sonar

Geomorphic and age data are presented for the Dellwood, Denson, Dickins, Giacomini, and Ely seamounts, the Tsimshian Seachannel, and the southern Juan de Fuca Ridge with Brown Bear, Bear Cub, Grizzly Bear, and Cobb seamounts. Formational speculations extrapolated to a regional scale allow the strikes and outer limits of the seamount chains to be interpreted. Six of these chains are shown in the Gulf of Alaska, none of which conform to the Pratt-Welker or Kodiak-Bowie in the literature. Different strikes show the chains/plate to have rotated 23° about 17 m.y. ago. Morphology also shows that there are four less guyots in the Gulf than previously thought, and that, at least in the Gulf of Alaska, guyot heights do not necessarily reflect sealevel during erosion.     

A research program to map the Galactic Emission at low frequencies

The need for accurate and complete maps of the galaxy at radio frequencies is made evident not only by the importance of the data in the study of galactic dynamics and structure formation but also in the analysis of cosmic background radiation data. A summary of the existing radio surveys of our galaxy is presented along with their limitations. A new program, the Galactic Emission Mapping (GEM) project, to obtain calibrated and complete maps of the galaxy in the 400 to 1400 MHz range, is outlined.Presented at the 2nd UN/ESA Workshop, held in Bogotá, Colombia, 9-13 November, 1992.     

The large-scale polarization of the microwave foreground

Most of the useful information about inflationary gravitational waves and reionization is on large angular scales where Galactic foreground contamination is the worst, so a key challenge is to model, quantify and remove polarized foregrounds. We use the Leiden radio surveys to quantify the polarized synchrotron radiation at large angular scales, which is likely to be the most challenging polarized contaminant for the WMAP satellite. We find that the synchrotron E- and B-contributions are equal to within 10% from 408–820 MHz with a hint of E-domination at higher frequencies. We quantify Faraday rotation and depolarization effects and show that they cause the synchrotron polarization percentage to drop both towards lower frequencies and towards lower multipoles.     

Site evaluation and RFI spectrum measurements in Portugal at the frequency range 0.408–10 GHz for a GEM polarized galactic radio emission experiment

We probed for radio frequency interference (RFI) at three potential galactic emission mapping experiment (GEM) sites in Portugal using custom made omnidirectional disconic antennas and directional pyramidal horn antennas. For the installation of a 10-m dish dedicated to the mapping of polarized galactic emission foreground planned for 2005–2007 in the 5–10 GHz band, the three sites chosen as suitable to host the antenna were surveyed for local radio pollution in the frequency range 0.01–10 GHz. Tests were done to look for radio broadcasting and mobile phone emission lines in the radio spectrum. The results show one of the sites to be almost entirely RFI clean and showing good conditions to host the experiment.     

Digital complex correlator for a C-band polarimetry survey

The international Galactic Emission Mapping project aims to map and characterize the polarization field of the Milky Way. In Portugal it will map the sky polarized emission of the Northern Hemisphere in C-band and provide templates for map calibration and foreground control of microwave space data to be provided by ESA Planck Surveyor mission and later missions. The receiver system is equipped with a novel receiver with a full digital back-end using a low-cost Field Programmable Gate Array without compromising its performance relation. This new digital backend comprises a base-band complex cross-correlator outputting the four Stokes parameters of the incoming polarized radiation. In this document we describe the design and implementation of the complex correlator using the FPGA and the dedicated digitizers at each receiver arm, detailing the method applied at the several algorithm stages. This correlator is suitable for large sky area polarization continuum surveys.     

Orthogonal intersections of megatrends in the Western Pacific ocean basin: a case study of the Mid-Pacific mountains

Present-day tectonic concepts of events on the western paleo-Pacific lithosphere must be assessed relative to new data. Data collected by the newer techniques of geophysical surveying reveal leaky fracture zones, trending NNW–SSE and WSW–ENE; non-sequential in-line ages on most seamount chains; and orthogonal intersections of fracture zones. The fracture zones meander, braid, merge, splay, start and stop at any place, and are generally aligned with, or contain, linear chains of seamount. The combination of these in-line features is called megatrends. When the GEOSAT data are compared to the available bathymetry, this seemingly jumbled tectonic structure is verified. As the pole of rotation changes, the stress field changes alignment to agree with the Chandler wobble of Earth. Younger megatrends, propagating ever eastward, cross the older, already imprinted megatrends. During the Cretaceous, the voluminous outpouring of igneous rock created the large Pacific plateaus and rises where the megatrends, active and inactive, orthogonally intersected. The magma floods at the intersections flowed outwardly, and the outward flooding accounts for the fanning magnetic lineations around the Manihiki, Magellan, Shatskiy, and Hess rises. A case study of the Mid-Pacific Mountains (MPM), lying in the north-central Pacific Ocean basin, shows that the MPM formed about 125–110-Ma by overprinting the orthogonal intersections of fracture zones at the Molokai and Easter/Krusenstern–Emperor megatrends and the Murray and Tubai/Mamua megatrends. The MPM have been undergoing distortion into a vortex structure, a feature which has been confirmed by updated bathymetry, GEOSAT altimetry data, and drillsite information.