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NASA NTRS1986

Temperature, radius, and rotational velocity of Sirius B

The interrelationships between radius, rotational velocity, and effective temperature for Sirius B are derived. The radius, which is between 0.76 and 0.81 in hundredths of solar radii, places Sirius B somewhat above the Hamada-Salpeter mass-radius relation by about one or two sigma. The rotational velocity of Sirius B is predicted to be between 0 and 600 km/s. Only radii which place a white dwarf above the mass-radius line are allowed. Better determinations of T(eff) and magnitude are needed in order to further limit the rotational velocity and the radius of Sirius B.

Thejll, Peter↗

NASA NTRS1994

Asteroseismology: Theory and phenomenology

Seismic studies of the Sun have succeeded in mapping the variation of sound speed with depth in the Sun, and variation of angular velocity with both depth and latitude. Many stars besides the Sun may also be amenable to asteroseismic analysis. Stars of roughly solar type should of course behave in ways similar to the sun, and stars of this sort form a large fraction of the potential targets for asteroseismology. But several other types of stars (delta scuti stars, roAP stars, and the pulsating white dwarfs) also have the desired pulsation characteristics. Pulsations in some of these stars are, for various reasons, much easier to observe than in the Sun-like stars. Virtually all unambiguous observations of multi-mode pulsators relate to these other categories of stars. Since oscillation mode frequencies are arguably the most precise measurement relating to a star that we can make, a few tens of such frequencies may still be of great importance to our understanding of the stellar structure and evolution.

Brown, Timothy M.↗

NASA NTRSDate not supplied

Extending the Life of NASA’s Tracking and Data Relay Satellite (TDRS)-8: TDRS-8 Power Challenges And Planning for End of Mission

The United States National Aeronautics and Space Administration (NASA) Near Space Network’s Space Relay (SR) System provides communication relay services to a number of scientific and manned space missions with its Tracking and Data Relay Satellite (TDRS) constellation. NASA’s eighth Tracking and Data Relay Satellite (TDRS) has been experiencing a decline in the health of its power subsystem, and recent reliability analyses indicate that the end of its mission serving the Space Relay is imminent. Launched in 2000, TDRS-8 is the oldest TDRS built upon a Boeing 601 platform, and as such it is the first TDRS to experience these age-related failures. The most prevalent elements of the power subsystem to decline are the solar array circuitry and the Bus Voltage Limiters (BVLs), which prevent too much power from the solar arrays being transferred to the bus by shunting excess current. This means that while the loss of solar array circuits introduces concerns that the solar arrays will continue providing the spacecraft with enough current to remain power positive, the loss of BVLs introduces a concern that the bus may not be adequately protected from overvoltage events. Spacecraft engineers at the TDRS primary ground terminal, the White Sands Complex (WSC) in Las Cruces, New Mexico, and at NASA's Goddard Space Flight Center (GSFC) have also been working in collaboration with Boeing to develop innovative techniques to extend the serviceable life of TDRS-8.

tdrs↗

NASA NTRS1984

Modelling Solar Spectral Irradiance Variations at Ultraviolet Wavelengths

Solar UV irradiance variations with solar activity are examined using a three component model of the CaII K chromospheric emission. This model, developed from ground based observations of the location, area and relative intensity of CaII K plage, in conjunction with measurements throughout solar cycle 21 of the full disc CaII K emission, includes the contributions to the ultraviolet flux from both plage and active network emission. The model successfully replicates changes in the Lyman alpha flux related to the 27 day rotation of solar plage, outbreaks (or rounds) of activity over periods of a year or more, and the growth and accumulation of active regions over the eleven year solar activity cycles. Estimates of the magnitude of the solar cycle variability of the UV emission between 200 and 300 nm are presented but cannot currently be verified by available observations.

Lean, J. L.↗

NASA NTRS1986

Origins of the solar wind in the corona

The coronal origins of the solar wind are considered. Potential sources of low-speed wind which are consistent with current data, including streamers and the interfaces between them and other coronal regions, await mass flow measurements for confirmation. A Doppler-dimming technique utilizing a white-light coronagraph and UV coronal spectrometer is to be employed aboard the Space Shuttle SPARTAN program, and its usage on Ulysses may provide information on mass flows in streamers and their surroundings.

Withbroe, G. L.↗

NASA NTRS1991

UV observations of the cool DBQA5 white dwarf LDS 678A - Limits on the atmospheric composition, pressure shift, and gravitational redshift derived from C I 2479

A high-resolution ultraviolet spectrum of the helium-rich degenerate LDS 678A, obtained with the International Ultraviolet Explorer (IUE) satellite, is presented. LDS 678A is the coolest metallic line degenerate (DQ or DZ) yet observed with the IUE echelle. These observations provide a detailed line profile of the strong C I 2479 absorption line and equivalent width W2479 = 2.35 + or - 0.06 A from which theoretical profile fits yield a carbon abundance of log C/He = (-6.7 + or- 0.2). The presence of carbon in a He-rich atmosphere lends credence to the notion that LDS 678A is a transitional case between the DB white dwarfs with nearly pure helium atmospheres and the helium-rich DQ white dwarfs which exhibit carbon bands. Corrected for an inferred pressure shift Vp = + 38 + or - 4 km/s for the C I 2479 line, a gravitational redshift of Vrs = + 26 + or - 13 km/s is deduced from which a most probable mass of 0.55 solar mass is derived.

Oswalt, Terry D.↗

NASA NTRS1993

Classical novae - Contributions to the interstellar medium

Theoretical results predicting yields of various isotopes in nova outbursts are reviewed. Emphasis is placed on the stardust and gas-phase chemical anomalies that may be contributed to the Galactic ISM by classic novae. It is concluded that most of the heavy isotope anomalies are produced by about 25 percent of novae that occur in systems containing massive O-Ne-Mg white dwarfs. The dust-production scenario for novae is summarized, and it is argued that explosions on O-Ne-Mg white dwarfs may lead to the formation of dust grains that carry the Ne-E and Mg-26 anomalies. Quantitative constraints are placed on the degree to which classical novae participate in the production of chemical anomalies, both in the primitive solar system and on a Galactic scale.

Gehrz, Robert D.↗

NASA NTRS2002

Long-term Trends in Interplanetary Magnetic Field Strength and Solar Wind Structure during the 20th Century

Lockwood et al have recently reported an approximately 40% increase in the radial component of the interplanetary magnetic field (IMF) at Earth between 1964 and 1996. We argue that this increase does not constitute a secular trend but is largely the consequence of lower than average fields during solar cycle 20 (1964-1976) in comparison with surrounding cycles. For times after 1976 the average IMF strength has actually decreased slightly. Examination of the cosmic ray intensity, an indirect measure of the IMF strength, over the last five solar cycles (19-23) also indicates that cycle averages of the IMF strength have been relatively constant since approximately 1954. We also consider the origin of the well-documented increase in the geomagnetic alphaalpha index that occurred primarily during the first half of the twentieth century. We surmise that the coronal mass ejection (CME) rate for recent solar cycles was approximately twice as high as that for solar cycles 100 years ago. However, this change in the CME rate and the accompanying increase in 27-day recurrent storm activity reported by others are unable to account completely for the increase in alphaalpha. Rather, the CMEs and recurrent high-speed streams at the beginning of the twentieth century must have been embedded in a background of slow solar wind that was less geoeffective (having, for example, lower IMF strength and/or flow speed) than its modern counterpart.

Richardson, I. G.↗

NASA NTRS2003

Dot-Projection Photogrammetry and Videogrammetry of Gossamer Space Structures

This paper documents the technique of using hundreds or thousands of projected dots of light as targets for photogrammetry and videogrammetry of gossamer space structures. Photogrammetry calculates the three-dimensional coordinates of each target on the structure, and videogrammetry tracks the coordinates versus time. Gossamer structures characteristically contain large areas of delicate, thin-film membranes. Examples include solar sails, large antennas, inflatable solar arrays, solar power concentrators and transmitters, sun shields, and planetary balloons and habitats. Using projected-dot targets avoids the unwanted mass, stiffness, and installation costs of traditional retroreflective adhesive targets. Four laboratory applications are covered that demonstrate the practical effectiveness of white-light dot projection for both static-shape and dynamic measurement of reflective and diffuse surfaces, respectively. Comparisons are made between dot-projection videogrammetry and traditional laser vibrometry for membrane vibration measurements. The paper closes by introducing a promising extension of existing techniques using a novel laser-induced fluorescence approach.

Pappa, Richard S.↗

NASA NTRS2016

Coronal Magnetic Field Profiles from Shock-CME Standoff Distances

Coronagraphs observe coronal mass ejections (CMEs) and driven shocks in white light images.From these observations the shocks speed and the shocks standoff distance from the CMEs leading edge can be derived. Using these quantities, theoretical relationships between the shocks Alfvenic Mach number MA and standoff distance, and empirical radial profiles for the solar wind velocity and number density, the radial magnetic field profile upstream of the shock can be calculated. These profiles cannot be measured directly. We test the accuracy of this method for estimating the radial magnetic field profile upstream of the shock by simulating a sample CME that occurred on 29 November 2013 using the three-dimensional (3-D) magnetohydrodynamic Block-Adaptive-Tree-Solar wind-Roe-Upwind-Scheme code, retrieving shock-CME standoff distances from the simulation, and comparing the estimated and simulated radial magnetic field profiles. We find good agreement between the two profiles (within +/-30%) between 1.8 and 10R.Our simulations confirm that a linear relationship exists between the standoff distance and the inverse compression ratio at the shock. We also find very good agreement between the empirical and simulated radial profiles of the number density and speed of the solar wind and inner corona.

Schmidt, J. M.↗

NASA NTRS2019

GOES-R Solar UltraViolet Imager Extended Coronal Imaging

GOES-16 and GOES-17 each hosts a Solar UltraViolet Imager (SUVI) that images the Sun in six extreme ultraviolet (EUV) wavelengths: 9.4 nm, 13.1nm, 17.1nm, 19.5nm, 28.4nm, and 30.4nm. The SUVI is nominally Sun-pointed and has a four-minute imaging sequence covering all the channels and meeting the dynamic range requirements. Based on the SUVI capabilities observed on-orbit, a campaign to image the extended solar corona was undertaken in 2018. This was performed by off-pointing the SUVI line-of-sight to the left and right of the Sun and producing a composite image by stitching together the off-pointed and the Sun-centered images. The imaging area in the composite is about three times the nominal image area in the East-West direction (about 5 RSun versus 1.8 RSun for nominal images). The campaign was conducted in February (4 hours), June (72 hours), and August-September of 2018 (5 weeks). Results from the campaign indicated the presence of solar corona to three solar radii, even in the quiet Sun part of the solar cycle. NOAA can operationalize this concept by tasking the SUVI on one of GOES-E and GOES-W. Such long-term operation will provide data that is needed to establish the much needed connectivity between the EUV and white light coronagraph data for the CME events.

Extended Coronal↗

NASA NTRSDate not supplied

Preliminary Results from the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS)

The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a sounding rocket mission that aims to observe the soft x-ray solar spectrum (0.6 – 2.5 nm) with both spatial and spectral resolution over a substantial field of view. This wavelength range has several high temperature and abundance diagnostics that can be used to assist in diagnosing the coronal heating mechanism. MaGIXS launched from White Sands Missile Range on July 30, 2021 and successfully observed the Sun through a 4’ x 33’ effective slot, producing ``overlappograms’’, where the spatial and spectral information are overlapped and must be unfolded. In this presentation, I will report on the MaGIXS launch and data collection and provide preliminary analysis of MaGIXS data.

Amy Winebarger↗

NASA NTRSDate not supplied

Preliminary Results from the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS)

Amy Winebarger↗

NASA NTRS2007

"Bursty" Reconnection Following Solar Eruptions: MHD Simulations and Comparison with Observations

Posteruptive arcades are frequently seen in the aftermath of coronal mass ejections (CMEs). The formation of these loops at successively higher altitudes, coupled with the classic "two-ribbon" flare seen in H-alpha, are interpreted as reconnection of the coronal magnetic field that has been dragged outward by the CME. White-light observations of "rays," which have been interpreted as being coincident with the current sheet at the reconnection site underneath the erupting CME, also provide evidence for its occurrence. "Blobs" occasionally seen within these rays suggest an even richer level of structure. In this report, we present numerical simulations that reproduce both the observed rays and the formation and evolution of the blobs. We compare their properties with SOHO/LASCO observations of similar structures, and relate their formation to standard theories of reconnection,

Riley, Pete↗

NASA NTRS1978

Magnetohydrodynamics of atmospheric transients. II - Two-dimensional numerical results for a model solar corona

A systematic study of dynamic response of the inner solar corona is made within the context of two-dimensional, time-dependent plane hydromagnetics. The governing equations are written in r-phi coordinates (i.e., in the solar equatorial plane), and numerical solutions are obtained by introducing an impulsive temperature enhancement within a rectangular region (i.e., 'box') in an initially isothermal corona in magnetohydrostatic equilibrium. Effects of the magnetic field configuration are illustrated for initially open (radial) and closed (azimuthal) magnetic fields by comparison with the nonmagnetic response. The channeling or blocking effects by the magnetic fields on the mass motion of solar plasma as the consequence of the evolution of fast and slow mode MHD shock waves are demonstrated. Some physically significant applications of the results, useful for the interpretation of observations, are discussed. It is noted, for example, that coronal transients observed in white light probably occur within essentially radial field topologies.

Wu, S. T.↗

NASA NTRS1983

Combined ultraviolet studies of astronomical sources

Ultraviolet spectra of non-radiataive shock waves grain destruction and elemental abundances in interstellar shocks, carbon abundance in M33 and M31 from supernova remnants, determination of the mass function in the large Magellanic cloud, UV spectra of white dwarf pulsars, stellar flares, availability of the double quasar Q 0957 + 56' AB, spectra of late-F dwarfs and their relation to rotation, dynamics of hot gas surrounding hybrid stars, high resolution study of epsilon coronae Austriual, active regions on solar-type dwarfs as a function of rotation rate and age, coordinated chromospheric synoptic observations of selected late-type stars, the two-component atmosphere of Lambda Andromedae, and activity in Hyades giants are discussed.

Dupree, A. K.↗

NASA NTRS1995

Evaluation of Thermal Control Coatings and Polymeric Materials Exposed to Ground Simulated Atomic Oxygen and Vacuum Ultraviolet Radiation

Numerous thermal control and polymeric samples with potential International Space Station applications were evaluated for atomic oxygen and vacuum ultraviolet radiation effects in the Princeton Plasma Physics Laboratory 5 eV Neutral Atomic Oxygen Facility and in the MSFC Atomic Oxygen Drift Tube System. Included in this study were samples of various anodized aluminum samples, ceramic paints, polymeric materials, and beta cloth, a Teflon-impregnated fiberglass cloth. Aluminum anodizations tested were black duranodic, chromic acid anodize, and sulfuric acid anodize. Paint samples consisted of an inorganic glassy black paint and Z-93 white paint made with the original PS7 binder and the new K2130 binder. Polymeric samples evaluated included bulk Halar, bulk PEEK, and silverized FEP Teflon. Aluminized and nonaluminized Chemfab 250 beta cloth were also exposed. Samples were evaluated for changes in mass, thickness, solar absorptance, and infrared emittance. In addition to material effects, an investigation was made comparing diffuse reflectance/solar absorptance measurements made using a Beckman DK2 spectroreflectometer and like measurements made using an AZ Technology-developed laboratory portable spectroreflectometer.

Kamenetzky, R. R.↗

NASA NTRS1972

Thermal characteristics of the lunar surface layer.

The thermophysical properties of the fines from the Apollo 12 landing site have been determined as a function of their relevant parameters. These properties include the thermal conductivity, thermal diffusivity, directional reflectance and emittance. The density used was the same as that observed from the returned core-tube samples and so should be close to the true density of the surface layer at the Apollo 12 site. The measured properties are used to calculate the diurnal temperature variation of the moon's surface as well as for several depths below the surface. The maximum surface of 389 K is obtained at lunar noon while the minimum temperature of 86.1 K is obtained at sunrise. It is shown that the most significant effects on temperature, as compared with previous calculations, are caused by using the directional reflectance which controls the amount of solar energy absorption during the day in place of a constant hemispherical reflectance. The results are compared with previous analyses and remote measurements.

Cremers, C. J.↗