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NASA NTRS2001

Dips in X-Ray Flux Associated with Superluminal Ejections in the Radio Galaxy 3C 120

We compare the RXTE X-ray light curve of 3C 120 from our late 1997 to early 2000 observations, plus early 1997 archival data, with both the cm-wave light curves (University of Michigan Radio Astronomy Observatory) and the times of ejections of apparent superluminal components (from VLBA observations). There is no correlation between the X-ray and radio light curves. However, the epochs of all four observed superluminal ejections correspond, to within the errors, with pronounced dips in the X-ray light curves (photon energies in the range 2-20 keV). This behavior is similar to that of the binary-system 'microquasar' GRS1915+105 in the Milky Way galaxy, although in 3C 120 there is no evidence for rapid, quasi-periodic fluctuations in X-ray flux. These observations therefore support the notion that in active galactic nuclei eruptions of energetic outflow are related to excess accretion onto a supermassive black hole.

Marscher, A. P.↗
NASA NTRS2001

Rapid Changes in the Structure of the BN Object

The BN/KL region in Orion is the archetypal region of high-mass star formation, radiating approx. 10(sup)5 Lsun and displaying promininent bulk outflows. In particular, there is no certain identification of the sources responsible for the high luminosity and outflows, and is the origin of a major explosive event (Shultz et al. 1999, ApJ, 511, 282). Using 18.7 and 12.5 micron data from observations in December 1999 and October 2000 made at the Keck I telescope, we discovered that the BN Object has a companion previously seen only at radio wavelengths (Menten & Reid 1995, ApJ, 445, L157). We call this companion B2 and it is about 1.5 arcsec West of the bright component. We also see changes in the shape of BN and the emission of "blobs" or "bullets" of material. While B2 remains unchanged and in the same place between the two epochs, there is an additional structure in BN to the South-South-East and the North-East, as well as a finger of material pointing North from B2 itself. Such a change has not been seen before in the infrared. We have looked very carefully at these images, calibrator images taken within a few minutes of the source images, as well as our previous images and cannot find any technical faults with the data. We explore the implications of these results, in particular, can these features be connected with previously observed "bullets" or "fingers" (see Allen & Burton 1993, for example), making BN a source for the bullets, implying they are not from IRc2 as previously thought? Or could they be produced by an interaction between material from BN and other sources such as IRc2?

Danchi, William C.↗
NASA NTRS2002

Extending the ICRF to Higher Radio Frequencies

The ICRF forms the basis for all astrometry including use as the inertial coordinate system for navigating deep space missions. This frame was defined using S/X-band observations over the past 20+ years. In January 2002, the VLBA approved our proposal for observing time to extend the ICRF to K-band (24 GHz) and Q-band (43 GHz). The first step will be observations at K- and Q-bands on a subset of ICRF sources. Eventually, K- and Q-band multi-epoch observations will be used to estimate positions, flux density and source structure for a large fraction of the current S/X-band ICRF source list. This work will benefit the radio astronomy community by extending the VLBA calibrator list at these bands. In the longer term, we would also like to extend the ICRF to Ka-band (32 GHz). A celestial reference frame will be needed at this frequency to support deep space navigation. A navigation demonstration is being considered for NASA's Mars 2005 mission. The initial K- and Q-band work will serve to identify candidate sources at Ka-band for use with that mission.

Jacobs, C. S.↗
NASA NTRS2002

Dynamical Effects on the Escape of H and D: Martian Water Reservoirs

The evolution of water on Mars is dependent on the loss rates of H and D from its atmosphere, where the dominant loss mechanism for these constituents is Jeans escape. Throughout time, preferential escape of H over D has produced a deuterium rich atmosphere with a D/H ratio 5.2 times that of terrestrial water. Motion in the atmosphere of Mars is shown to change the Jeans escape rates of H and D in two important ways: (1) Atmospheric wind and rotation at the exobase increase the escape fluxes of H and D above the corresponding Jeans fluxes. (2) The percentage increase in escape flux due to motion is greatest for D. Recently, several models have been used to estimate the magnitudes of current and ancient crustal water reservoirs on Mars that freely exchange with its atmosphere. Differences in the reservoir sizes are influenced by differences in the composition at the exobase, thermal history of the atmosphere and the D/H ratio of earlier epochs as inferred from meteorites. When motion enhanced Jeans escape is applied to each of these models, it is shown in every case that factors (1) and (2) above lead to current and ancient crustal water reservoirs that are larger than those obtained without motion.

Hartle, Richard E.↗
NASA NTRS2002

Probing Galaxy Formation and Evolution with Space Born Sub-Millimeter Telescopes

A major unresolved question in cosmology is how the complex system of galaxies we see in the present universe evolved from an almost perfectly smooth beginning. Multiwavelength observations of galaxies have revealed that a significant fraction of their UV-visible starlight is absorbed and reradiated by dust at infrared JR) and submillimeter wavelengths. The cumulative IR-submm. emission from galaxies since the epoch of recombination, the cosmic IR background, has recently been recorded by the COBE satellite. The COBE observations in combination with recent submm surveys conducted with the SCUBA on the 15 m JCMT have shown that most of the radiation from star formation that has taken place in the early stages of galaxy evolution is reradiated by dust at submm wavelengths. Therefore, submm telescopes offer a unique probe of the early stages of galaxy formation and evolution. This talk will: (1) consider the impact of telescope diameter on the depth of the survey (what redshift can be probed) at different wavelengths; (2) discuss the relative scientific merits of high-resolution narrow-field surveys versus lower resolution deep surveys; and (3) show how both strategies offer complementary information crucial to our understanding of the structure and evolution of galaxies in the universe.

Dwek, Eli↗
NASA NTRS2002

Broad-Band Continuum and Line Emission of the gamma-Ray Blazar PKS 0537-441

PKS 0537-441, a bright gamma ray emitting blazar was observed at radio, optical, UV and X-ray frequencies during various EGRET paintings, often quasi-simultaneously. In 1995 the object was found in an intense emission state at all wavelengths. BeppoSAX observations made in 1998, non-simultaneously with exposures at other frequencies, allow us to characterize precisely the spectral shape of the high energy blazer component, which we attribute to inverse Compton scatter in The optical-to-gamma-ray spectral energy distributions at the different epochs show that the gamma-ray luminosity dominates the barometric output. This, together with the presence of optical and UV line emission, suggests that, besides the synchrotron self-Compton mechanism, the Compton upscattering of photons external to the jet (e.g., in the broad line region) may have a significant role for high energy radiation. The multiwavelength variability can be reproduced by changes of the plasma bulk Lorentz factor. The spectrum secured by ICE in 1995 appears to be partially absorbed shortward of approximately 1700 Angstroms. However, this signature is not detected in the HST spectrum taker during a lower state of the source. The presence of intervening absorbers is not supported by optical imaging and spectroscopy of the field.

Pian, E.↗
NASA NTRS2002

Spectroscopic Detection of a Stellar-like Photosphere in an Accreting Protostar

We present high-resolution (R is approximately equal to 18,000), high signal-to-noise 2 micron spectra of two luminous, X-ray flaring Class I protostars in the rho Ophiuchi cloud acquired with the NIRSPEC (near infrared spectrograph) of the Keck II telescope. We present the first spectrum of a highly veiled, strongly accreting protostar which shows photospheric absorption features and demonstrates the stellar nature of its central core. We find the spectrum of the luminous (L (sub bol) = 10 solar luminosity) protostellar source, YLW 15, to be stellar-like with numerous atomic and molecular absorption features, indicative of a K5 IV/V spectral type and a continuum veiling r(sub k) = 3.0. Its derived stellar luminosity (3 stellar luminosity) and stellar radius (3.1 solar radius) are consistent with those of a 0.5 solar mass pre-main-sequence star. However, 70% of its bolometric luminosity is due to mass accretion, whose rate we estimate to be 1.7 x 10(exp -6) solar masses yr(exp -1). We determine that excess infrared emission produced by the circumstellar accretion disk, the inner infalling envelope, and accretion shocks at the surface of the stellar core of YLW 15 all contribute significantly to its near-IR (infrared) continuum veiling. Its rotational velocity v sin i = 50 km s(exp -1) is comparable to those of flat-spectrum protostars but considerably higher than those of classical T Tauri stars in the rho Oph cloud. The protostar may be magnetically coupled to its circumstellar disk at a radius of 2 - 3 R(sub *). It is also plausible that this protostar can shed over half its angular momentum and evolve into a more slowly rotating classical T Tauri star by remaining coupled to its circumstellar disk (at increasing radius) as its accretion rate drops by an order of magnitude during the rapid transition between the Class I and Class II phases of evolution. The spectrum of WL 6 does not show any photospheric absorption features, and we estimate that its continuum veiling is r(sub k) is greater than or equal to 4.6. Its low luminosity (2 solar masses) and high veiling dictate that its central protostar is very low mass, M is approx. 0.1 solar masses. We also evaluate multi-epoch X ray data along with these spectra and conclude that the X ray variabilities of these sources are not directly related to their protostellar rotation velocities.

Greene, Thomas P.↗
NASA NTRS1998

Incorporation of Solar Noble Gases from a Nebula-Derived Atmosphere During Magma Ocean Cooling

The presence of solar noble gases in the deep interior of the Earth is inferred from the Ne isotopic compositions of MORB (Mid-ocean Ridge Basalts) and OIB (Oceanic Island Basalt); Ar data may also consistent with a solar component in the deep mantle. Models of the transport and distribution of noble gases in the earth's mantle allow for the presence of solar Ar/Ne and Xe/Ne ratios and permit the calculation of lower mantle noble gas concentrations. These mantle data and models also indicate that the Earth suffered early (0.7 to 2 x 10(exp 8) yr) and large (greater than 99 percent) losses of noble gases from the interior, a result previously concluded for atmospheric Xe. We have pursued the suggestion that solar noble gases were incorporated in the forming Earth from a massive, nebula-derived atmosphere which promoted large-scale melting, so that gases from this atmosphere dissolved in the magma ocean and were mixed downward. Models of a primitive atmosphere captured from the solar nebula and supported by accretion luminosity indicate that pressures at the Earth's surface were adequate (and largely more than the required 100 Atm) to dissolve sufficient gases. We have calculated the coupled evolution of the magma ocean and the overlying atmosphere under conditions corresponding to the cessation (or severe attenuation) of the sustaining accretion luminosity, prior to the complete removal of the solar nebula. Such a condition was likely to obtain, for instance, when most of the unaccumulated mass resided in large bodies which were only sporadically accreted. The luminosity supporting the atmosphere is then that provided by the cooling Earth, consideration of which sets a lower limit to the time required to solidify the mantle and terminate the incorporation of atmospheric gases within it. In our initial calculations, we have fixed the nebula temperature at To = 300K, a value likely to be appropriate for nebular temperatures at lAU in the early planet-building epoch. We treated the background (nebula) pressure as an adjustable, time-dependent parameter. Additional information is contained within the original extended abstract.

Woolum, D. S.↗
NASA NTRS2002

Algorithms for Autonomous GPS Orbit Determination and Formation Flying: Investigation of Initialization Approaches and Orbit Determination for HEO

This report summarizes the efforts to date in processing GPS measurements in High Earth Orbit (HEO) applications by the Colorado Center for Astrodynamics Research (CCAR). Two specific projects were conducted; initialization of the orbit propagation software, GEODE, using nominal orbital elements for the IMEX orbit, and processing of actual and simulated GPS data from the AMSAT satellite using a Doppler-only batch filter. CCAR has investigated a number of approaches for initialization of the GEODE orbit estimator with little a priori information. This document describes a batch solution approach that uses pseudorange or Doppler measurements collected over an orbital arc to compute an epoch state estimate. The algorithm is based on limited orbital element knowledge from which a coarse estimate of satellite position and velocity can be determined and used to initialize GEODE. This algorithm assumes knowledge of nominal orbital elements, (a, e, i, omega, omega) and uses a search on time of perigee passage (tau(sub p)) to estimate the host satellite position within the orbit and the approximate receiver clock bias. Results of the method are shown for a simulation including large orbital uncertainties and measurement errors. In addition, CCAR has attempted to process GPS data from the AMSAT satellite to obtain an initial estimation of the orbit. Limited GPS data have been received to date, with few satellites tracked and no computed point solutions. Unknown variables in the received data have made computations of a precise orbit using the recovered pseudorange difficult. This document describes the Doppler-only batch approach used to compute the AMSAT orbit. Both actual flight data from AMSAT, and simulated data generated using the Satellite Tool Kit and Goddard Space Flight Center's Flight Simulator, were processed. Results for each case and conclusion are presented.

Axelrad, Penina↗
NASA NTRS2002

Coronal Element Abundances of the Post-Common Envelope Binary V471 Tauri with ASCA

We report on ASCA observations of the coronally active companion star in the post-common envelope binary V471 Tau. While it would be prudent to check the following results with grating spectroscopy, we find that a single-temperature plasma model does not fit the data. Two temperature models with variable abundances indicate that Fe is underabundant compared to the Hyades photospheric mean, whereas, the high first ionization potential element Ne is overabundant. This is indicative of the inverse first ionization effect, believed to result from the fractionation of ionized material by the magnetic field in the upper atmosphere of the star. Evolutionary calculations indicate that there should be no peculiar abundances on the companion star resulting from the common envelope epoch. Indeed, we find no evidence for peculiar abundances, although uncertainties are high.

Still, Martin↗
NASA NTRS2002

Conference Summary: First International Conference on Global Warming and the Next Ice Age

The First International Conference on Global Warming and the Next Ice Age was convened in Halifax, Nova Scotia, August 19-24, 2001. The conference program began each day with a 30 minute live classical music performances of truly international quality before the beginning business. Ample time for panel discussions was also scheduled. The general public was invited to attend and participate in a special evening panel session on the last day of the conference. The unusual and somewhat provocative title of the conference was designed to attract diverse views on global climate change. This summary attempts to accurately reflect the tone and flavor of the lively discussions which resulted. Presentations ranged from factors forcing current climate to those in effect across the span of time from the Proterozoic "snowball Earth" epoch to 50,000 years in the future. Although, as should be expected, attendees at the conference arrived with opinions on some of the controversial issues regarding climate change, and no-one openly admitted to a 'conversion' from their initial point of view, the interdisciplinary nature of the formal presentations, poster discussions, panels, and abundant informal discourse helped to place the attendees' personal perspectives into a broader, more diversified context.

Wetzel, Peter J.↗
NASA NTRS2002

Geoscience Laser Altimeter System (GLAS) for the ICESat Mission

The Geoscience Laser Altimeter System (GLAS) is a new generation lidar and is the primary science payload for NASA's ICESat Mission. The GLAS design combines a 10 cm precision surface lidar with a sensitive dual wavelength cloud and aerosol lidar. GLAS will precisely measure the heights of the Earth's polar ice sheets, establish a grid of accurate height profiles of the Earth's land topography, and profile the vertical distribution of clouds and aerosols on a global scale. GLAS will be integrated onto a small spacecraft built by Ball Aerospace, and will be launched into a polar orbit with a 590-630 km altitude at an inclination of 94 degrees. ICESat is is currently planned to launch in winter 2002/03 and GLAS is designed to operate continuously in space for a minimum of 3 years. GLAS will measure the vertical distance from orbit to the Earth's surface with pulses from a ND:YAG laser at a 40 Hz rate. Each 6 nsec wide 1064 nm laser pulse is used to produce a single range measurement. On the surface, the laser footprints have 66 m diameter and approx. 170 m center-center spacings. The GLAS receiver uses a I m diameter telescope to detect laser backscatter and a Si APD to detect the 1064 nm signals. The detector's output is sampled by a digital ranging receiver, which records each transmitted pulse and surface echo waveform with 1 nsec (15 cm) resolution. Each echo pulse is digitized and is reported to ground with a record length of from 200 to 544 samples, depending on the spacecraft's location . The GLAS location and epoch times are measured by a precision GPS receiver carried on the ICESat spacecraft. Initial processing of the echo waveforms within GLAS permits discrimination between cloud and surface echoes for selecting appropriate waveform samples. This selection is guided by an on-board DEM which is used to set the boundaries for the echo pulse search algorithm. Subsequent ground-based echo pulse analysis, along with GPS-based clock frequency estimates, permit final determination of the range to the surface, degree of pulse spreading, and vertical distribution of any vegetation illuminated by the laser. Accurate knowledge of the laser beam's pointing angle is needed to prevent height biases when measuring over tilted surfaces, such as near the boundaries of ice sheets. For surfaces with 2 deg. slopes, knowledge of pointing angle of the beam's centroid angle to better than 10 urad is needed. GLAS uses a stellar reference system (SRS) to measure the pointing angle of each laser firing relative to inertial space. The SRS uses a high precision star camera oriented toward local zenith and a gyroscope to determine the inertial orientation of the SRS optical bench. The far field pattern of each laser is measured pulse relative to the star camera with a laser reference system (LRS). GLAS will also measure the vertical distributions of clouds and aerosols by recording the vertical profiles of laser pulse backscatter at both 1064 and 532 nm. The 1064 rim measurements use the Si APD detector and will be used to measure the height and echo pulse shape from thicker clouds. The lidar receiver at 532 nm uses a narrow bandwidth etalon filter and highly sensitive photon counting detectors. The 532 nm backscatter profiles will be used to measure the vertical extent of thinner clouds and the atmospheric boundary layer. The GLAS instrument component development is complete and the instrument is undergoing final testing and qualification at NASA-Goddard. The GLAS "as-built" characteristics and its expected measurement performance will be discussed.

Abshire, James B.↗
NASA NTRS2002

Unveiling the Engines In QSOS: A Multi-Wavelength Study

In the past year, the project has passed three major milestones: 1. Completed the spectroscopic emission line measurements for the full Hubble preCOSTAR FOS sample, resulting in the publication of "Emission Line Properties of AGN from a pre-COSTAR FOS HST Spectral Atlas" in the ApJ. 2. By compiling narrow absorption line (NAL) and broad emission line (BEL) measurements for the subsample of FOS AGN showing both NV and CIV absorption, we have given the first conclusive evidence that the NAL clouds and BEL clouds have similar metallicity. The resulting paper, just resubmitted to ApJL after a largely congratulatory referee report, is entitled "Evidence for a Strong Abundance Correlation Between Emission and Absorption Lines in AGN". 3) Collaboration with Dr. Crenshaw at GSU has also yielded a complete merged atlas of FOS spectra from the postCOSTAR epoch. These will be analyzed and published in the next year, along with investigations of correlations to high energy (X-ray) emission.

Green, P.↗
NASA NTRS2002

The Winds of B Supergiants

We present the most suitable data sets available in the International Ultraviolet Explorer (IUE) archive for the study of time-dependent stellar winds in early B supergiants. The UV line profile variability in 11 B0 to B3 stars is analyzed, compared and discussed, based on 16 separate data sets comprising over 600 homogeneously reduced high-resolution spectrograms. The targets include 'normal' stars with moderate rotation rates and examples of rapid rotators. A gallery of grey-scale images (dynamic spectra) is presented, which demonstrates the richness and range of wind variability and highlights different structures in the winds of these stars. This work emphasises the suitability of B supergiants for wind studies, under-pinned by the fact that they exhibit unsaturated wind lines for a wide range of ionization. The wind activity of B supergiants is substantial and has highly varied characteristics. The variability evident in individual stars is classified and described in terms of discrete absorption components, spontaneous absorption, bowed structures, recurrence, and ionization variability and stratification. Similar structures can occur in stars of different fundamental parameters, but also different structures may occur in the same star at a given epoch. We discuss the physical phenomena that may be associated with the spectral signatures, and highlight the challenges that these phenomena present to theoretical studies of time-dependent outflows in massive stars. In addition, SEI line-synthesis modelling of the UV wind lines is used to provide further information about the state of the winds in our program stars. Typically the range, implied by the line profile variability, in the product of mass-loss rate and ion fraction (M (dot) q(sub i)) is a factor of approximately 1.5, when integrated between 0.2 and 0.9 v infinity; it can however be several times larger over localized velocity regions. At a given effective temperature the mean relative ion ratios can differ by a factor of 5. The general excess in predicted (forward-scattered) emission in the low velocity regime is discussed in terms of structured outflows. Mean ion fractions are estimated over the B0 to B1 spectral classes, and trends in the ionic ratios as a function of wind velocity are described. The low values obtained for the ion fractions of UV resonance lines may reflect the role of clumping in the wind.

Massa, D.↗
NASA NTRS2002

9.1 Years of All-Sky Hard X-Ray Monitoring with BATSE

The hard X-ray sky was continuously monitored with the BATSE experiment on the Compton Gamma Ray Observatory using the Earth Occultation method. Known sources were monitored twice every orbit and transients could be detected at about the approximately 50 crab level on a daily basis. Long-term, post-processing of the complete BATSE dataset will produce all-sky, hard X-ray maps at a sensitivity level of approximately 5 mCrab in un-crowded regions. For long period pulsars (greater than 1 second), Fourier transforms and epoch-folded searches were used to measure pulse frequency and pulsed flux. Using these methods, 3 black hole candidates and 6 x-ray pulsars were discovered with BATSE during its 9 years in orbit. I will present highlights from BATSE observations of X-ray binaries from 9 years of monitoring the hard X-ray sky.

Wilson, C. A.↗
NASA NTRS2002

Anaerobic Halo-Alkaliphilic Baterial Community of Athalassic, Hypersaline Mono Lake in California

The microorganisms of soda Mono Lake and other similar athalassic hypersaline alkaline soda lakes are of significance to Astrobiology. The microorganisms of these regimes represent the best known terrestrial analogs for microbial life that might have inhabited the hypersaline alkaline lakes and evaporites confined within closed volcanic basins and impact craters during the late Noachian and early Hesperian epochs (3.6 - 4.2 Gya) of ancient Mars. We have investigated the anaerobic microbiota of soda Mono Lake in northern California. In this paper we discuss the astrobiological significance of these ecosystems and describe several interesting features of two novel new species of anaerobic halo-alkaliphilic bacteria (Spirochaeta americana, sp. nov. and Desulfonatronum paiuteum, sp. nov) that we have isolated from Mono Lake.

Pikuta, Elena V.↗
NASA NTRS2002

Thickness Constraints on the Icy Shells of the Galilean Satellites from a Comparison of Crater Shapes

A thin outer ice shell on Jupiter's large moon Europa would imply easy exchange between the surface and any organic or biotic material in its putative subsurface ocean. The thickness of the outer ice shell is poorly constrained, however, with model-dependent estimates ranging from a few kilometers of depths of impact craters on Europa, Ganymede and Callisto that reveal two anomalous transitions in crater shape with diameter. The first transition is probably related to temperature-dependent ductility of the crust at shallow depths (7-8 km on Europa). The second transition is attributed to the influence of subsurface oceans on all three satellites, which constrains Europa's icy shell to be at least 19 km thick. The icy lithospheres of Ganymede and Callisto are equally ice-rich, but Europa's icy shell has a thermal structure about 0.25-0.5 times the thickness of Ganymede's or Callisto's shells, depending on epoch. The appearances of the craters on Europa are inconsistent with thin-ice-shell models and indicate that exchange of oceanic and surface material could be difficult.

Schenk, Paul M.↗
NASA NTRS2003

What can we learn about cosmic structure from gravitational waves?

Observations of low frequency gravitational waves by the space-based LISA mission will open a new observational window on the early universe and the emergence of structure. LISA will observe the dynamical coalescence of massive black hole binaries at high redshifts, giving an unprecedented look at the merger history of galaxies and the reionization epoch. LISA will also observe gravitational waves from the collapse of supermassive stars to form black holes, and will map the spacetime in the central regions of galaxy cusps at high precision.

Centrella, Joan M.↗