Astronomy Experiment Research Articles

The PILOT optical alignment for its first flight

PILOT is a balloon-borne astronomy experiment designed to study the polarization of dust emission in the diffuse interstellar medium in our Galaxy at wavelengths 240 and 550 µm with an angular resolution of about two arc-min. PILOT optics is composed of an off-axis Gregorian telescope and a refractive re-imager system. All these optical elements, except the primary mirror, are in a cryostat cooled to 3K. We used optical and 3D measurements combined with thermo-elastic modeling to perform the optical alignment. This paper describes the system analysis, the alignment procedure, and finally the performances obtained during the first flight in September 2015

The optical performance of the PILOT instrument from ground end-to-end tests

The Polarized Instrument for Long-wavelength Observation of the Tenuous interstellar medium (PILOT) is a balloon-borne astronomy experiment designed to study the linear polarization of thermal dust emission in two photometric bands centred at wavelengths 240 μm (1.2 THz) and 550 μm (545 GHz), with an angular resolution of a few arcminutes. Several end-to-end tests of the instrument were performed on the ground between 2012 and 2014, in order to prepare for the first scientific flight of the experiment that took place in September 2015 from Timmins, Ontario, Canada. This paper presents the results of those tests, focussing on an evaluation of the instrument’s optical performance. We quantify image quality across the extent of the focal plane, and describe the tests that we conducted to determine the focal plane geometry, the optimal focus position, and sources of internal straylight. We present estimates of the detector response, obtained using an internal calibration source, and estimates of the background intensity and background polarization.

A smartphone-based introductory astronomy experiment: Seasons investigation

Light sensor probes are useful in experiments that investigate seasonal variations and the nature of light. However, having a dedicated light probe is not always possible or even convenient for many instructors. Modern smartphone technology gives instructors the ability to use built-in light sensors as an inexpensive alternative. This introductory experiment will have students use a smartphone loaded with a light detection app to quantitatively determine how changing latitude on Earth changes flux received. The purpose is to have students discover how the different seasons arise from the Earth-Sun system. While performing the experiment and analyzing the data, students will also discover the following important and relevant physical relationships: distance from light source and light brightness (flux), latitude and flux, and Earth’s orientation and location (latitude) of maximum flux. By piecing all of these relationships together, students are able to explain the origins of the different seasons based on the data they collected.

Parametric analysis of cherenkov light LDF from EAS for high energy gamma rays and nuclei: Ways of practical application

In this paper we propose a 'knee-like' approximation of the lateral distribution of the Cherenkov light from extensive air showers in the energy range 30-3000 TeV and study a possibility of its practical application in high energy ground-based gamma-ray astronomy experiments (in particular, in TAIGA-HiSCORE). The approximation has a very good accuracy for individual showers and can be easily simplified for practical application in the HiSCORE wide angle timing array in the condition of a limited number of triggered stations.

Parametric analysis of cherenkov light LDF from EAS for high energy gamma rays and nuclei: Ways of practical application

In this paper we propose a ‘knee-like’ approximation of the lateral distribution of the Cherenkov light from extensive air showers in the energy range 30–3000 TeV and study a possibility of its practical application in high energy ground-based gamma-ray astronomy experiments (in particular, in TAIGA-HiSCORE). The approximation has a very good accuracy for individual showers and can be easily simplified for practical application in the HiSCORE wide angle timing array in the condition of a limited number of triggered stations.

A high performance cost-effective digital complex correlator for an X-band polarimetry survey.

The detailed knowledge of the Milky Way radio emission is important to characterize galactic foregrounds masking extragalactic and cosmological signals. The update of the global sky models describing radio emissions over a very large spectral band requires high sensitivity experiments capable of observing large sky areas with long integration times. Here, we present the design of a new 10 GHz (X-band) polarimeter digital back-end to map the polarization components of the galactic synchrotron radiation field of the Northern Hemisphere sky. The design follows the digital processing trends in radio astronomy and implements a large bandwidth (1 GHz) digital complex cross-correlator to extract the Stokes parameters of the incoming synchrotron radiation field. The hardware constraints cover the implemented VLSI hardware description language code and the preliminary results. The implementation is based on the simultaneous digitized acquisition of the Cartesian components of the two linear receiver polarization channels. The design strategy involves a double data rate acquisition of the ADC interleaved parallel bus, and field programmable gate array device programming at the register transfer mode. The digital core of the back-end is capable of processing 32 Gbps and is built around an Altera field programmable gate array clocked at 250 MHz, 1 GSps analog to digital converters and a clock generator. The control of the field programmable gate array internal signal delays and a convenient use of its phase locked loops provide the timing requirements to achieve the target bandwidths and sensitivity. This solution is convenient for radio astronomy experiments requiring large bandwidth, high functionality, high volume availability and low cost. Of particular interest, this correlator was developed for the Galactic Emission Mapping project and is suitable for large sky area polarization continuum surveys. The solutions may also be adapted to be used at signal processing subsystem levels for large projects like the square kilometer array testbeds.

A laser-lock concept to reach cm s-1-precision in Doppler experiments with Fabry-Pérot wavelength calibrators

State-of-the-art Doppler experiments require wavelength calibration with precision at the cm/s level. A low-finesse Fabry-Perot interferometer (FPI) can provide a wavelength comb with a very large bandwidth as required for astronomical experiments, but unavoidable spectral drifts are difficult to control. Instead of actively controlling the FPI cavity, we propose to passively stabilize the interferometer and track the time-dependent cavity length drift externally. A dual-finesse cavity allows drift tracking during observation. The drift of the cavity length is monitored in the high-finesse range relative to an external standard: a single narrow transmission peak is locked to an external cavity diode laser and compared to an atomic frequency. Following standard locking schemes, tracking at sub-mm/s precision can be achieved. This is several orders of magnitude better than currently planned high-precision Doppler experiments. It allows freedom for relaxed designs rendering this approach particularly interesting for upcoming Doppler experiments. We also show that the large number of interference modes used in an FPI allows us to unambiguously identify the interference mode of each FPI transmission peak defining its absolute wavelength solution. The accuracy reached in each resonance with the laser concept is then defined by the cavity length that is determined from the one locked peak and by the group velocity dispersion. The latter can vary by several 100m/s over the relevant frequency range and severely limits the accuracy of individual peak locations. A potential way to determine the absolute peak positions is to externally measure the frequency of each individual peak with a laser frequency comb (LFC). Thus, the concept of laser-locked FPIs may be useful for applying the absolute accuracy of an LFC to astronomical spectrographs without the need for an LFC at the observatory.

Irregular time series in astronomy and the use of the Lomb–Scargle periodogram

Detection of a signal hidden by noise within a time series is an important problem in many astronomical searches, i.e. for light curves containing the contributions of periodic/semi-periodic components due to rotating objects and all other astrophysical time-dependent phenomena. One of the most popular tools for use in such studies is the "periodogram", whose use in an astronomical context is often not trivial. The "optimal" statistical properties of the periodogram are lost in the case of irregular sampling of signals, which is a common situation in astronomical experiments. Parts of these properties are recovered by the "Lomb-Scargle" (LS) technique, but at the price of theoretical difficulties, that can make its use unclear, and of algorithms that require the development of dedicated software if a fast implementation is necessary. Such problems would be irrelevant if the LS periodogram could be used to significantly improve the results obtained by approximated but simpler techniques. In this work we show that in many astronomical applications simpler techniques provide results similar to those obtainable with the LS periodogram. The meaning of the "Nyquist frequency" is also discussed in the case of irregular sampling.

China’s Space Astronomy and Solar Physics in 2011-2012

In the first part of this paper, we describe briefly the mid and long-term plan of Chinese space astronomy, its preliminary study program, the current status of satellite missions undertaken, and the current status of astronomy experiments in China’s manned space flight program. In the second part, the recent research progress made in the fields of solar physics is summarized briefly, including solar vector magnetic field, solar flares, CME and filaments, solar radio and nonthermal processes, EUV waves, MHD waves and coronal waves, solar model and helioseismology, solar wind and behavior of solar cycle.

A Broadband W-Band Polarization Rotator With Very Low Cross Polarization

We present a 82-100 GHz circular waveguide polarization rotator based on a broadband rotating half-wave retarder. The device was designed for astrophysics experiments aimed to characterize the polarization of the cosmic microwave background radiation. The device is based on a Pancharatnam recipe used in optics and has a very low intrinsic cross polarization, very flat phase response across the band and very low losses. It can be used in astronomical experiments where very high performance is required but also as a variable polarization source for instrument calibrations. The design was manufactured and then tested using a millimeter-wave vector network analyzer. The average measured RL, IL and cross polarization across a 30% bandwidth were, respectively, -38 dB, -0.27 dB, and -36.5 dB.

Surpassing human nature: Reinventions of and for the body as a consequence of astronomical experiments in the seventeenth and eighteenth centuries

Surpassing human nature: Reinventions of and for the body as a consequence of astronomical experiments in the seventeenth and eighteenth centuries

Mansouri-Sexl Test for Light Speed Anisotropy via Cosmic Aberration~!2010-02-11~!2010-02-26~!2010-06-30~!

The Mansouri-Sexl theory is a well known test theory of relativity. In the current paper we will derive the Man- souri-Sexl formalism for the light aberration and we will show how to improve on the theoretical and experimental basis by constraining both the Mansouri-Sexl parameter a(!) and the parameter b(!) . In the process of constraining the Man- souri parameters we devise a novel experiment for measuring and constraining light speed anisotropy as well. An over- whelming number of experiments dealing with light speed anisotropy are laboratory-bound and they are limited to con- straining only parameter a(!) ; we will also take the approach of setting up an astronomical experiment instead of a lab- based one as it befits the relativistic aberration effect. Our paper is organized as follows: in the first section we give a new and more complete derivation of the Mansouri-Sexl aberration effect. In the second part, we apply the newly expanded Mansouri-Sexl aberration formalism in order to devise an astronomical experiment used for constraining both the parame- ter a(!) and the parameter b(!) . This turns the Mansouri-Sexl aberration experiment into a very powerful tool for con- straining light speed anisotropy. 1. THE ROBERTSON-MANSOURI-SEXL TEST THEORY The test theories of special relativity differ in their as- sumptions about the form of the Lorentz transforms. The main test theories of special relativity (SR) are named after their authors, Robertson (1), Mansouri and Sexl (2-4) (RMS). These test theories can also be used to examine po- tential alternate theories to SR - such alternate theories pre- dict particular values of the parameters of the test theory, which can easily be compared to values determined by ex- periments analyzed with the test theory (5-20). The existing experiments put rather strong experimental constraints on any alternative theory. RMS starts by admitting by reduction to absurd that there is a preferential inertial frame Σ in which the light propagates isotropically with the speed c 0 . All other frames in motion with respect to Σ are considered non- preferential and the light speed is anisotropic. The light speed in the non-preferential frames can be deduced via sim- ple calculations described in (3). We start with the Mansouri- Sexl transforms: x=b(v)(X!vT) y=d(v)Y z=d(v)Z t=a(v)T+(v)x=(a!bv)T+bX

Current Developments and Future Plans at NBF@Hyderabad and Prospects for Long Duration Balloon Flights

Established in 1971, National Balloon Facility at Hyderabad is a unique centre which offers complete solution in scientific ballooning for near space access using high altitude balloons. It combines both, in house balloon production and complete flight and recovery support to the experimenters. The balloon facility is also mandated to perform necessary research and development to meet future needs in scientific ballooning and lighter than air systems. The balloon flights conducted by the facility during the last few years are of two types (a) Large volume balloons up to 740,000 m3 with heavy payloads for astronomy experiments and (b) Smaller balloons using lighter payloads for atmospheric sciences and the wind sounding flights up to 43 km altitude. At present, we are involved in the development of a portable telemetry, tracking and telecommand sub-system for remote operation and data link for long duration flights over the continent or the polar missions. Efforts are also on for the design and development of material and envelope design for high altitude platforms for the study of aerosols and trace gases. In this paper I will present details of our present activities and also outline our plans for the future directions.

Telescopes don’t make catalogues!

Astronomical instruments make intensity measurements; any precise astronomical experiment ought to involve modeling those measurements. People make catalogues, but because a catalogue requires hard decisions about calibration and detection, no catalogue can contain all of the information in the raw pixels relevant to most scientific investigations. Here we advocate making catalogue-like data outputs that permit investigators to test hypotheses with almost the power of the original image pixels. The key is to provide users with approximations to likelihood tests against the raw image pixels. We advocate three options, in order of increasing difficulty: The first is to define catalogue entries and associated uncertainties such that the catalogue contains the parameters of an approximate description of the image-level likelihood function. The second is to produce a K-catalogue sampling in "catalogue space" that samples a posterior probability distribution of catalogues given the data. The third is to expose a web service or equivalent that can re-compute on demand the full image-level likelihood for any user-supplied catalogue.

Exotic UV astronomy

After considering a number of historical but somewhat “forgotten” UV astronomy experiments, I discuss a number of ways of non-conventional astronomy in the ultraviolet that, on first considerations, could be viable alternatives and valuable complements to classical space observations. These are (a) UV astronomy from the Antarctic or the Arctic regions that take advantage of the “ozone hole”, (b) the use of high-altitude stratospheric balloon-borne telescopes, and (c) the operation of UV telescopes on the Moon. The advantages of these options are discussed and evaluated against the costs of each option and, one by one, are mostly rejected as not fully justifying the specific alternative. The possibility to achieve valuable (but limited) UV science, such as imaging at ∼2000 A, using long-duration stratospheric balloons is described. The option of lunar UV observatories is retained to be implemented for the case of a UV interferometer, where the stability of the lunar regolith is seen as a significant advantage in comparison to free-flying interferometers. A location beyond the main asteroid belt, where the background due zodiacal light may be negligible, is advocated as an ideal location for a UV observatory in the Solar System.

Materials for cutting-edge experiments in astronomy and particle physics

Progress in fields such as astronomy and fundamental physics can require increasingly complex instrumentation operating at millikelvin temperatures. Such instruments often have demands on materials and components which have not been seen previously, particularly for space based instrumentation. The large scale of these projects and tight timescales forces as conservative design as possible. However, building these instruments with conventional techniques and materials is often impractical and sometimes impossible. It is therefore common for the design stage of such instruments to include test and measurement programmes. This adds risk to the development schedule, and such programmes also suffer from the problem that they are tightly focused on the exact needs of one particular instrument. We are setting up a laboratory to measure material properties and develop cryogenic components for general use in future large millikelvin instruments. By decoupling these measurements from a particular instrument programme, we have the freedom to make more speculative measurements, such as measuring new polymers whose cryogenic properties are completely unknown. We describe our set-up and the results of initial work.

INTER-DIVISION IX-X WORKING GROUP ENCOURAGING THE INTERNATIONAL DEVELOPMENT OF ANTARCTIC ASTRONOMY

Two major astronomical experiments are underway at the US Amundsen-Scott South Pole Station. The first is the South Pole Telescope, a 10m sub-millimetre telescope designed to measure primary and secondary anisotropies in the CMBR, with the aim of placing constraints on the equation of state for dark energy. The second is the IceCube neutrino observatory, which will be a cubic kilometre array designed to image sources of high energy neutrinos.

X-ray emission from solar flares

Solar X-ray Spectrometer (SOXS), the first space-borne solar astronomy experiment of India was designed to improve our current understanding of X-ray emission from the Sun in general and solar flares in particular. SOXS mission is composed of two solid state detectors, viz., Si and CZT semiconductors capable of observing the full disk Sun in X-ray energy range of 4–56 keV. The X-ray spectra of solar flares obtained by the Si detector in the 4–25 keV range show evidence of Fe and Fe/Ni line emission and multi-thermal plasma. The evolution of the break energy point that separates the thermal and non-thermal processes reveals increase with increasing flare plasma temperature. Small scale flare activities observed by both the detectors are found to be suitable to heat the active region corona; however their location appears to be in the transition region.

Very low frequency interferometry for the Chang’E-2 project

Very low frequency interferometry among two astronomical experiments has been proposed and accepted for further study for the second phase of China’s lunar exploration programme (the Chang’E Programme), which is envisaged to operate a lander and a rover on the surface of the moon. This experiment is an interferometer experiment in the very low frequency (VLF, f < 15 MHz) regime of radio frequencies with at least degree-level angular resolution. The goals include observing solar storm activities, Coronal Mass Ejections, Auroral Kilometric Radiation, and planetary radiation in the solar system, studying the origin of Cosmic Rays, spectral properties of pulsars, surveying ionized hydrogen in the Galaxy, and exploring coherent radio emissions.

Telescope and instrument robotization at Dome C

AbstractThis article reviews the situation for robotization of telescopes and instruments at the Antarctic station Concordia on Dome C. A brain‐storming meeting was held in Tenerife in March 2007 from which this review emerged.We describe and summarize the challenges for night‐time operations of various astronomical experiments at conditions “between Earth and Space” and conclude that robotization is likely a prerequisite for continuous astronomical data taking during the 2000‐hour night at Dome C. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)