The parabolic wave equation in local helioseismology

In recent years methods of time-distance helioseismology have been used to produce maps of local flows in the surface layers of the Sun. Usually, these studies rely on ray theory to describe the propagation of sound waves. Ray theory, however, is a poor approximation of the acoustic wavefield near the surface of the Sun. In particular, it is inappropriate for the study of scattering and diffraction by inhomogeneities. But an exact solution of the acoustic wave equation in the Sun is not trivial. In this paper I present an approximation to the full wave equation, which transforms it into a parabolic equation. The parabolic equation is commonly used in ocean acoustics and geoseismology because it is much simpler to solve numerically. Here I discuss the parabolic approximation, its limitations and potential applications in helioseismology. Finally, I present some numerical results to demonstrate the capabilities of this method.     

The sign of temperature inhomogeneities deduced from time-distance helioseismology

Inhomogeneities in wave propagation conditions near and below the solar surface have been detected by means of time-distance helioseismology. Here we calculate the effect of temperature inhomogeneities on the travel times of sound waves. A temperature increase, e.g., in active regions, not only increases the sound speed but also lengthens the path along which the wave travels because the expansion of the heated layers shifts the upper turning of the waves upward. Using a ray-tracing approximation we find that in many cases the net effect of a temperature enhancement is an increase of the travel times. We argue that the reduced travel times that are observed are caused by a combination of magnetic fields in the active region and reduced subsurface temperatures. Such a reduction may be related to the increased radiative energy loss from small magnetic flux tubes.     

Test of a differential photometer for extinction gradient correction in full-disk helioseismology

The ground based full disk velocity Doppler measurements used in helioseismology suffer from an atmospheric noise component when the sky transparency is not perfect. It is due to the non uniform integration of the line of sight component of the solar rotation produced by the differential atmospheric extinction across the direction of the solar equator. A simple two-channel differential photometer is proposed for measuring this differential extinction. The first laboratory tests of this instrument show that it has the capability of performing the required correction without adding a significant level of new instrumental noise contribution.

     

The stark broadening mechanism in an unstable plasma

We consider a beam driven unstable plasma and estimate the turbulent electric fields which may be excited by this beam. We then estimate the Stark broadening due to such fields. Also with the Department of Physics and Astronomy, University of Maryland, College Park, Maryland.     

The heliometer as a tool for the measure of the Moon

The heliometer has been the only instrument for the measurement of the lunar physical libration for more than a century. Bessel (1839), who introduced the use of the heliometer for the systematic measurement of the relative positions of craters on the lunar disc, has also developed the necessary formulation for the calculation of the lunar physical libration from the heliometric measurements. That methodology is presented, and results obtained by Bessel's students and other investigators who followed Bessel's method, are discussed.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846).     

The IRIS network for full disk helioseismology: Present status of the programme

IRIS (International Research on the Interior of the Sun) is the name of a worldwide network of 8 observing stations for full disk helioseismology. The IRIS scientific community is organizing a yearly workshop in one of the 8 sites. This paper is the introduction to the proceedings of the second IRIS workshop, held at Tashkent, Uzbekistan SSR. It presents a brief history, the structure of the international cooperation, the membership rule, the list of sites and members, the scientific working teams additional structure and, as an appendix, the report of the first meeting of the IRIS Scientific Committee.     

The Yarkovsky effect as a heat engine

We show how the Yarkovsky effect can be understood as a heat engine. The output of the engine, manifested in the rate of change in semimajor axis of the body, has a maximum at an intermediate heat capacity, depending on the rotation rate of the body. This maximum arises because the work output depends on the product of the solar heat absorbed by the body and transported from its morning to evening side (this am-pm heat flux increases with heat capacity) and the Carnot efficiency (which declines with heat capacity).     

The evershed effect as a wave phenomenon

It is suggested that longitudinal compression waves are propagating parallel to the solar surface from the umbra towards the photosphere. It is shown that the line-absorption coefficient is asymmetrical, when integrated over a wavelength of the compression wave. The effect of the waves on the line profile is discussed, and it is shown that asymmetrical line profiles of the type observed in sunspot penumbrae will be produced.With the Evershed effect interpreted as an acoustical wave phenomenon the propagation (of the waves) may also be perpendicular to the magnetic lines of force, whereas material motion is likely to be restricted to the direction along the lines of force.     

Correction of the temperature effect in calibration of a solar radio telescope

This work analyzes the annual fluctuation of the observation data of the Mingantu Solar radio Telescope(MST) in S, C and X bands. It is found that the data vary with local air temperature as the logarithmic attenuation of equipment increases with temperature and frequency. A simplified and effective calibration method is proposed, which is used to calibrate the MST data in 2018–2020, while the correction coefficients are calculated from data in 2018–2019. For S, C and X bands, the root mean square errors of one polarization are 2.7, 5.7 and 20 sfu, and the relative errors are 4%, 6% and 8% respectively. The calibration of MUSER and SBRS spectra is also performed. The relative errors of MUSER at 1700 MHz,SBRS at 2800 MHz, 3050 MHz and 3350 MHz are 8%, 8%, 11% and 10% respectively. We found that several factors may affect the calibration accuracy, especially at X-band. The method is expected to work for other radio telescopes with similar design.     

Doppler weather radar as a meteorite recovery tool

Abstract– We report the use of Doppler weather radar as a tool for locating meteorites, both at the time of a fall and from archived radar data. This asset is especially useful for meteorite recovery as it can provide information on the whereabouts of falling meteorites in “dark flight” portion of their descent where information on their flight paths cannot be discerned from more traditional meteorite location techniques such as eyewitness accounts. Weather radar data can provide information from detection in three distinct regimes: (A) direct detection of the rapidly moving, optically bright fireball by distant radars, (B) detection of falling debris to include hand‐sample sized rocks, and (C) detection of dust produced by detonation events that can occur tens of minutes and many kilometers laterally removed from the actual fireball locality. We present examples of each, as well as comparisons against man‐made debris from a re‐entering Soyuz rocket and the Stardust Sample Return Capsule. The use of Doppler weather radar as a supplement to traditional meteorite recovery methods holds the promise of improving both the speed and total number of meteorite recoveries, thereby increasing the number of freshly fallen meteorites for scientific study.     

Magnetic and thermal phase shifts in the local helioseismology of sunspots

Phase perturbations due to inclined surface magnetic field of active region strength are calculated numerically in quiet Sun and simple sunspot models in order to estimate and compare the direct and indirect (thermal) effects of the fields on helioseismic waves. It is found that the largest direct effects occur in highly inclined field characteristic of penumbrae, and scale roughly linearly with magnetic field strength. The combined effects of sunspot magnetic and thermal anomalies typically yield negative travel-time perturbations in penumbrae. Travel-time shifts in umbrae depend on details of how the thermal and density structure differs from the quiet Sun. The combined shifts are generally not well approximated by the sum of the thermal and magnetic effects applied separately, except at low field strengths of around 1 kG or less, or if the thermal shift is small. A useful rule-of-thumb appears to be that travel-time perturbations in umbrae are predominantly thermal, whereas in penumbrae they are mostly magnetic.     

Zatrikean pre-geometry as a tool for modelling in theoretical astrophysics

In this paper, we present an axiomatic foundation on zatrikean (i.e., chess-like) pre-geometry. Furthermore, we find that rotation can induce such a pre-geometry; and this rotationally induced zatrikean pre-geometry can, in turn, decisively affect all the interrelated physical phenomena, which in their majority are significant for theoretical astrophysics and cosmology.     

The effects of stark broadening in the radio recombination line temperatures

Observations of Orion A, M 17, and W 3 made at the National Radio Astronomy Observatory show Stark broadening in the , , and hydrogen recombination lines at 22 cm. Stark effect has such a large effect on the line profiles that fitted Gaussian profiles cannot be used to measure the area of the line. Theoretical line profiles have been derived from modelHii regions. Voigt profiles fitted to the theoretical line profiles indicate that the areas of the lines derived from the fitted profiles may be systematically too small. Using Voigt profiles fitted by least squares to the observations, we found that the line intensities at 22 cm agree with the intensity ratios predicted by LTE theory.     

Fe Mössbauer spectroscopy as a tool in astrobiology

The element Fe and Fe-bearing minerals occur ubiquitously throughout the field of astrobiology. Cycling between the various oxidation states of Fe provides a source of energy available for life. Banded iron formations may record the rise of oxygenic photosynthesis. The distribution of Fe between Fe-bearing minerals and its oxidation states can help to characterize and understand ancient environments with respect to the suitability for life by constraining the primary rock type and the redox conditions under which it crystallized, the extent of alteration and weathering, the type of alteration and weathering products, and the processes and environmental conditions for alteration and weathering. Fe Mössbauer spectroscopy is a powerful tool to investigate Fe-bearing compounds. It can identify Fe-bearing minerals, determine Fe oxidation states with high accuracy, quantify the distribution of Fe between mineralogical phases, and provide clues about crystallinity and particle sizes. Two miniaturized Mössbauer spectrometers are on board of the NASA Mars Exploration Rovers Spirit and Opportunity. The Fe-bearing minerals goethite, an iron oxide-hydroxide, and jarosite, an iron hydroxide sulfate, were identified by Mössbauer spectroscopy in Gusev Crater and at Meridiani Planum, respectively, providing in situ proof of an aqueous history of the two landing sites and constraints on their habitability. Hematite identified by Mössbauer spectroscopy at both landing sites adds further evidence for an aqueous history. On Earth, Mössbauer spectroscopy was used to monitor possibly microbially-induced changes of Fe-oxidation states in basaltic glass samples exposed at the Loihi Seamount, a deep sea hydrothermal vent system, which might be analogous to possible extraterrestrial habitats on ancient Mars or the Jovian moon Europa today.     

Analytical signal as a tool for studying solar p-modes

A technique for analyzing periodic processes based on the introduction of an analytical signal is described. This technique allows the instantaneous frequency, amplitude, and phase of oscillations to be obtained. The data on solar brightness fluctuations collected with the DIFOS multichannel photometer onboard the CORONAS-F satellite are processed. The p-mode spectral lines are broadened mainly by amplitude fluctuations, while the frequency stability appears to be high (～10^?4). A method for separating signals with close frequencies is developed. The p-mode with l = 0 and n = 21 is used as an example to show that the separation of signals with close frequencies is possible when the conventional spectral methods are inefficient. Analysis of the phase shifts between the oscillations observed in various optical channels of the DIFOS photometer has revealed that the five-minute oscillations travel from the upper and deep photospheric layers toward the middle photospheric layers. This effect directly proves that the evanescent p-modes in the photosphere are nonadiabatic.     

The Sunyaev–Zel'dovich effect as a cosmological discriminator

We show how future measurements of the Sunyaev–Zel'dovich effect (SZE) can be used to constrain the cosmological parameters. We combine the SZ information expected from the Planck full-sky survey, N ( S ), where no redshift information is included, with the N ( z ) obtained from an optically identified SZ-selected survey covering less than 1 per cent of the sky. We demonstrate how with a small subsample (≈300 clusters) of the whole SZ catalogue observed optically it is possible to reduce the degeneracy among the cosmological parameters drastically. We have studied the requirements for performing the optical follow-up and we show the feasibility of such a project. Finally, we have compared the cluster expectations for Planck with those expected for Newton–XMM during their lifetimes. It is shown that, owing to its larger sky coverage, Planck will detect a factor of ∼5 times more clusters than Newton–XMM and also provide a larger redshift coverage.     

The Herschel-PACS photometer calibration

This paper provides an overview of the PACS photometer flux calibration concept, in particular for the principal observation mode, the scan map. The absolute flux calibration is tied to the photospheric models of five fiducial stellar standards (α Boo, α Cet, α Tau, β And, γ Dra). The data processing steps to arrive at a consistent and homogeneous calibration are outlined. In the current state the relative photometric accuracy is ～2 % in all bands. Starting from the present calibration status, the characterization and correction for instrumental effects affecting the relative calibration accuracy is described and an outlook for the final achievable calibration numbers is given. After including all the correction for the instrumental effects, the relative photometric calibration accuracy (repeatability) will be as good as 0.5 % in the blue and green band and 2 % in the red band. This excellent calibration starts to reveal possible inconsistencies between the models of the K-type and the M-type stellar calibrators. The absolute calibration accuracy is therefore mainly limited by the 5 % uncertainty of the celestial standard models in all three bands. The PACS bolometer response was extremely stable over the entire Herschel mission and a single, time-independent response calibration file is sufficient for the processing and calibration of the science observations. The dedicated measurements of the internal calibration sources were needed only to characterize secondary effects. No aging effects of the bolometer or the filters have been found. Also, we found no signs of filter leaks. The PACS photometric system is very well characterized with a constant energy spectrum νF _ν = λF _λ = const as a reference. Colour corrections for a wide range of sources SEDs are determined and tabulated.     

Gravitational lensing time delays as a tool for testing Lorentz-invariance violation

It is generally expected that quantum gravity theory should yield the model of a space–time foam at short distances leading to Lorentz-invariance violation (LIV) manifested e.g. by energy-dependent modification of the standard relativistic dispersion relation. One direction of research, pursued intensively, is to measure the energy-dependent time-of-arrival delays in photons emitted by astrophysical sources located at cosmological distances. This is tempered, however, by our ignorance of intrinsic emission delays in different energy channels.
In this paper we discuss a test based on gravitational lensing. Monitoring time delays between images obtained in different energy channels, for example optical (low-energy) and TeV photons, may reveal extra delays due to the distorted dispersion relation typical in LIV theories, a test that is free from the systematics inherent in other settings.     

Multiparametric infrared Tully-Fisher relation as a tool for mapping cosmic flows

The peculiar velocity field for 907 galaxies with heliocentric radial velocities V_H ≤ 3000 km/s is examined. The data are divided into three samples, organized according to the principles behind the method for determining the distance to the galaxies: the luminosity of the tip of the red giant branch (TRGB), fluctuations in the surface brightness, and the infrared Tully-Fisher relation for spiral galaxies viewed edge-on. The latter sample includes 410 galaxies. For determining the distance to the galaxies in this sample, additional regressors were introduced into the Tully-Fisher relation, in particular the “color index” K-m₂₁, which make it possible significantly to reduce the dispersion with respect to the regression curve. All three samples showed good agreement in the peculiar velocity distribution. Based on each of these samples, as well as on the combined sample, detailed maps of the field of peculiar velocities of the galaxies are constructed for V_H ≤ 3000 km/s. An analysis shows that most of the observed features of this map can be explained by large-scale density variations in the galactic distribution. __________ Translated from Astrofizika, Vol. 51, No. 3, pp. 409–422 (August 2008).