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NASA NTRS2006

Global X-ray Spectral Variation of Eta Carinae through the 2003 X-ray Minimum

We report on the results of the X-ray observing campaign of the massive, evolved star Eta Carinae in 2003 around its recent X-ray Minimum, mainly using data from the XMM-Newton observatory. These imaging observations show that the hard X-ray source associated with the Eta Carinae system does not completely disappear in any of the observations during the Minimum. The variation of the spectral shape revealed two emission components. One newly discovered component did not exhibit any variation on kilo-second to year-long timescales, in a combined analysis with earlier ASCA and ROSAT data, and might represent the collision of a high speed outflow from Eta Carinae with ambient gas clouds. The other emission component was strongly variable in flux but the temperature of the hottest plasma did not vary significantly at any orbital phase. Absorption to the hard emission, was about a factor of three larger than the absorption determined from the cutoff of the soft emission, and reached a maximum of approx.4 x 10(exp 23)/sq cm before the Minimum. The thermal Fe\rm XXV emission line showed significant excesses on both the red and blue sides of the line outside the Minimum and exhibited a large redward excess during the Minimum. This variation in the line profile probably requires an abrupt change in ionization balance in the shocked gas.

Hamaguchi, K.↗

NASA NTRS2007

2-.mu.m fiber amplified spontaneous emission (ASE) source

A 2-.mu.m fiber Amplified Spontaneous Emission (ASE) source provides a wide emission bandwidth and improved spectral stability/purity for a given output power. The fiber ASE source is formed from a heavy metal oxide multicomponent glass selected from germanate, tellurite and bismuth oxides and doped with high concentrations, 0.5-15 wt. %, thulium oxides (Tm.sub.2O.sub.3) or 0.1-5 wt% holmium oxides (Ho.sub.2O.sub.3) or mixtures thereof. The high concentration of thulium dopants provide highly efficient pump absorption and high quantum efficiency. Co-doping of Tm and Ho can broaden the ASE spectrum.

Jiang, Shibin↗

NASA NTRS2012

In-Flight Measurement of the Absolute Energy Scale of the Fermi Large Area Telescope

The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron- plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in the Earth's magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between approx. 6 and approx. 13 GeV with an estimated uncertainty of approx. 2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.

Cosmic-rays↗

NASA NTRS2015

X-Raying the Coronae of HD 155555

We present an analysis of the high-resolution Chandra observation of the multiple system, HD 155555 (an RS CVn type binary system, HD 155555 AB, and its spatially resolved low-mass companion HD 155555 C). This is an intriguing system which shows properties of both an active pre-main sequence star and a synchronised (main sequence) binary. We obtain the emission measure distribution, temperature structures, plasma densities, and abundances of this system and compare them with the coronal properties of other young/active stars. HD 155555 AB and HD 155555 C produce copious X-ray emission with log L(sub x) of 30.54 and 29.30, respectively, in the 0.3-6.0 kiloelectronvolt energy band. The light curves of individual stars show variability on timescales of few minutes to hours. We analyse the dispersed spectra and reconstruct the emission measure distribution using spectral line analysis. The resulting elemental abundances exhibit inverse first ionisation potential effect in both cases. An analysis of He-like triplets yields a range of coronal electron densities 1010 − 1013 per cubic centimeter. Since HD 155555 AB is classified both as an RS CVn and a PMS star, we compare our results with those of other slightly older active main-sequence stars and T Tauri stars, which indicates that the coronal properties of HD 155555 AB closely resemble that of an older RS CVn binary rather than a younger PMS star. Our results also suggests that the properties of HD 155555 C is very similar to those of other active M dwarfs.

stars: coronae↗

NASA NTRS2018

Characterization of CO Thermochemistry in Incident Shockwaves

Incident shock waves in pure CO have been characterized in the Electric Arc Shock Tube facility at NASA Ames Research Center. Spectrally and spatially resolved emission spectra characterize radiative signatures from CO in the VUV (Vacuum Ultra-Violet) and mid-infrared and atomic carbon and C2 in the visible. CO absorption of a single vibrational line is also measured with a tunable diode laser. The experimental data analyzed here are at a pressure of 0.25 Torr in the driven section and span a shock velocity range from 3.4-9.5 km/s. The emission and absorption signals are analyzed to extract temperature relaxation behind the shock which is used to derive the rate of CO dissociation. The emission spectra are compared to results using different kinetic parameters for CO dissociation and C2 dissociation and exchange. Different rates from the literature are found to match the data from 3.4-6.6 km/s and 6.6-9.5 km/s. Areas for improvement in CO and C2 radiation modeling are suggested on the basis of the analysis.

Entry↗

NASA NTRS2022

A Study of Photoionized Gas in Two H װ Regions of the N44 Complex in the LMC Using MUSE Observations

We use the optical integral field observations with Multi-Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope, together with CLOUDY photoionization models, to study ionization structure and physical conditions of two luminous H װ regions in the N44 star-forming complex of the Large Magellanic Cloud. The spectral maps of various emission lines reveal a stratified ionization geometry in N44 D1. The spatial distribution of [O ו] λ6300 emission in N44 D1 indicates a partially covered ionization front at the outer boundary of the H װ region. These observations reveal that N44 D1 is a blister H װ region. The [O ו] λ6300 emission in N44 C does not provide a well-defined ionization front at the boundary, while patches of [S װ] λ6717 and [O ו] λ6300 emission bars are found in the interior. The results of spatially resolved MUSE spectra are tested with the photoionization models for the first time in these H װ regions. A spherically symmetric ionization-bounded model with a partial covering factor, which is appropriate for a blister H װ region, can well reproduce the observed geometry and most of the diagnostic line ratios in N44 D1. Similarly, in N44 C we apply a low-density and optically thin model based on the observational signatures. Our modeling results show that the ionization structure and physical conditions of N44 D1 are mainly determined by the radiation from an O5 V star. However, local X-rays, possibly from supernovae or stellar wind, play a key role. In N44 C, the main contribution is from three ionizing stars.

H II regions↗

NASA NTRSDate not supplied

Revealing the Magnetic Field Geometry of Gamma-Ray Binary PSR B1259-63 Via X-Ray Polarimetry

PSR B1259-63 (PSR 1259) is a radio pulsar with a spin period of ~48 ms, in a binary system with a massive, emission-line star of spectral type O9.5Ve (Figs 1 and 2). The star, LS 2883, is commonly referred to as a Be-type star, with optical spectra revealing a dense equatorial outflow and isotropic wind that forms an equatorial disk, purportedly inclined with respect to the orbital plane. The pulsar is in a highly eccentric orbit (e~0.87, P~3.38 years), around LS 2883, plunging through this circumstellar twice at about 16 days and 13 days before and after periastron, respectively. This interaction of the pulsar wind wind with the stellar outflow, produces TeV gamma rays as a result of highly energetic particles being efficiently accelerated, producing synchrotron radiation in the X-ray and soft gamma-ray bands, in a time-varying shock. X-ray polarization to be aligned perpendicular to the magnetic field for synchrotron radiation.

Oliver J Roberts↗

NASA NTRS1989

Doppler shifted H Ly alpha emission from Jupiter's aurora

High-spectral-resolution IUE observations of the aurora on Jupiter were obtained in order to search for Doppler shifted H-Ly-alpha emission produced through charge exchange by fast precipitating protons. Although no emission has been observed corresponding to proton energies greater than 200 eV, a large fraction of the H-Ly-alpha emission has appeared Doppler shifted, mainly toward the blue, by about 50 km/s. These results show that the acceleration of ionospheric plasma in an H2 atmosphere can lead to bright Ly-alpha emission, setting constraints on the production of the outer planet airglow emissions.

Clarke, John T.↗

NASA NTRS1996

(abstract) An All Sky Cirrus Confusion Noise Map for WIRE

The Wide Field Infrared Explorer (WIRE) is a Small Explorer (SMEX) satellite scheduled for launch in 1998 which will carry out a sky survey of at least 100 square degrees in the wavelength regions of 9-15(micro)m and 21-27(micro)m with spatial resolution of approximately 20 arcsec and sensitivity exceeding 0.6mJy. At this sensitivity level WIRE observations can be seriously affected by the confusion noise contribution from the infrared cirrus emission, so the WIRE survey must be planned with some knowledge of the expected level of cirrus confusion. Production of a cirrus confusion noise map with 0.5 degree resolution based on the spatial power spectral density of the cirrus emission in the IRAS ISSA data is in progess using the method described by Gauthier, et al. Spectrally resolved power spectra density data is obtained from the ISSA maps with a wavelet transform technique.

Wide Field Infrared Explorer WIRE infrared sky sur↗

NASA NTRS1989

IRAS results on outer galaxy star formation

An infrared defined (60 micron) sample of IRAS sources were systematically studied in order to investigate star formation in the outer Galaxy. Five percent of the sample are point sources with IRAS spectra that suggest the emission is from a dust shell surrounding a mature star. Ninety five percent have spectra where flux density strictly rises with wavelength. The sources are extended, and it is shown that Point Source Catalog fluxes seriously underestimate total fluxes. CO kinematic distances were reliably assigned to two thirds of the sources. Most of the infrared luminosities correspond to B spectral types. Six cm continuum emission were detected from all sources inferred to have spectral type B1 or earlier. The combined IRAS/CO/6 cm data show these sources are young, moderately massive stars that are embedded in interstellar clouds. The young embedded sources define a distinct band in an IRAS color-colar diagram. Normal IRAS galaxies fall in the same band, consistent with the interpretation that their infrared emission is due to star formation.

Terebey, Susan↗

NASA NTRS1994

Impulsive behavior in solar soft X-radiation

The Yohkoh soft X-ray telescope has observed impulsive, thermal, soft X-ray emission at the footpoints of magnetic loops during solar flares. The soft X-ray (thermal) time profiles at the footpoints closely match the hard X-ray (nonthermal) time profiles, directly demonstrating the heating of the lower solar atmosphere on short timescales during the interval of nonthermal energy release. This phenomenon is the rule, rather than the exception, occurring in the majority of flares that we have examined with the Yohkoh data. We illustrate the impulsive behavior with data from the major flare of 1992 January 26. For this flare, the soft X-ray peak times matched the hard X-ray peak times within the time resolution of the soft X-ray measurements (about 10 s), and the soft and hard X-ray locations match within the resolution of the hard X-ray imager. The impulsive soft X-ray emission clearly has a thermal spectral signature, but not at the high temperature of a 'superhot' source. We conclude that the impulsive soft X-ray emission comes from material heated by precipitating electrons at loop footpoints and evaporating from the deeper atmosphere into the flaring flux tube.

Hudson, H. S.↗

NASA NTRS2013

Energy Feedback from X-ray Binaries in the Early Universe

X-ray photons, because of their long mean-free paths, can easily escape the galactic environments where they are produced, and interact at long distances with the intergalactic medium, potentially having a significant contribution to the heating and reionization of the early universe. The two most important sources of X-ray photons in the universe are active galactic nuclei (AGNs) and X-ray binaries (XRBs). In this Letter we use results from detailed, large scale population synthesis simulations to study the energy feedback of XRBs, from the first galaxies (z (redshift) approximately equal to 20) until today.We estimate that X-ray emission from XRBs dominates over AGN at z (redshift) greater than or approximately equal to 6-8. The shape of the spectral energy distribution of the emission from XRBs shows little change with redshift, in contrast to its normalization which evolves by approximately 4 orders of magnitude, primarily due to the evolution of the cosmic star-formation rate. However, the metallicity and the mean stellar age of a given XRB population affect significantly its X-ray output. Specifically, the X-ray luminosity from high-mass XRBs per unit of star-formation rate varies an order of magnitude going from solar metallicity to less than 10% solar, and the X-ray luminosity from low-mass XRBs per unit of stellar mass peaks at an age of approximately 300 Myr (million years) and then decreases gradually at later times, showing little variation for mean stellar ages 3 Gyr (Giga years, or billion years). Finally, we provide analytical and tabulated prescriptions for the energy output of XRBs, that can be directly incorporated in cosmological simulations.

galaxies↗

NASA NTRS2006

Prompt and Afterglow Emission Properties of Gamma-Ray Bursts with Spectroscopically Identified Supernovae

We present a detailed spectral analysis of the prompt and afterglow emission of four nearby GRBs (GRBs 980425, 030329, 031203, and 060218) that were spectroscopically found to be associated with type Ib/c supernovae. For each event, we investigated its spectral and luminosity evolution and estimated the total energy budget based on the broadband observations. We discuss the properties of the four events in comparison to general burst population, and infer the physical parameters involved in creation of these nearby GRB-SN events

Kaneko, Yuki↗

NASA NTRS1986

The shapes of the circumstellar silicate features

Around oxygen-rich stars the spectra of most long-period variables (LPV) show an excess infrared emission which is attributed to circumstellar silicate dust grains. It is known that the spectral energy distribution of the 10 micron emissions shows variations from star to star. With the availability of many Infrared Astronomy Satellite (IRAS) Low Resolution Spectra (LRS) in the 8 to 22 micron region, the 10 micron feature can be studied to determine its uniformity (or lack thereof). The excess silicate emissions (10 micron emission), divided into three groups characterized by similar spectral shapes, are discussed.

Little-Marenin, I. R.↗

NASA NTRS2014

Prompt Emission of GRB 121217A from Gamma-Rays to the Near-Infrared

The mechanism that causes the prompt-emission episode of gamma-ray bursts (GRBs) is still widely debated despite there being thousands of prompt detections. The favoured internal shock model relates this emission to synchrotron radiation. However, it does not always explain the spectral indices of the shape of the spectrum, which is often fit with empirical functions, such as the Band function. Multi-wavelength observations are therefore required to help investigate the possible underlying mechanisms that causes the prompt emission. We present GRB 121217A, for which we were able to observe its near-infrared (NIR) emission during a secondary prompt-emission episode with the Gamma-Ray burst Optical Near-infrared Detector (GROND) in combination with the Swift and Fermi satellites, which cover an energy range of 5 orders of magnitude (10(exp −3) keV to 100 keV). We determine a photometric redshift of z = 3.1 +/- 0.1 with a line-of-sight with little or no extinction (AV approx. 0 mag) utilising the optical/NIR SED. From the afterglow, we determine a bulk Lorentz factor of Gamma(sub 0) approx. 250 and an emission radius of R < 1018 cm. The prompt-emission broadband spectral energy distribution is well fit with a broken power law with beta1 = −0.3 +/- 0.1 and beta2 = 0.6 +/- 0.1 that has a break at E = 6.6 +/- 0.9 keV, which can be interpreted as the maximum injection frequency. Self-absorption by the electron population below energies of Ea < 6 keV suggest a magnetic field strength of B approx. 10(exp 5) G. However, all the best fit models underpredict the flux observed in the NIR wavelengths, which also only rebrightens by a factor of approx. 2 during the second prompt emission episode, in stark contrast to the X-ray emission, which rebrightens by a factor of approx. 100. This suggests an afterglow component is dominating the emission. We present GRB 121217A, one of the few GRBs that has multi-wavelength observations of the prompt-emission period and shows that it can be understood with a synchrotron radiation model. However, due to the complexity of the GRB's emission, other mechanisms that result in Band-like spectra cannot be ruled out.

prompt↗

NASA NTRS1985

Microwave observations of late-type stars with the Very Large Array

The Very Large Array was used to search for microwave emission from 32 stars of late spectral type including RS CVn type stars, dwarf M stars, and stars with active chromospheres, coronae, or intense magnetic fields. The RS CVn stars were detected at 6 cm wavelength, and upper limits are established for another six. Radio emission was detected from three dwarf M flare stars, UV Cet, EQ Peg and YZ CMi. Both impulsive (no more than 20 s) and more gradual (at least ten minutes) bursts were observed from the flare star YZ CMi. Radio emission was not confirmed at 6 cm from the solar type star Chi(1) Ori, with an upper limit that is three times lower than the detections reported by other observers. Microwave emission could not be detected from any other solar type star of spectral class F to K. The quiescent radio emission from dwarf M flare stars was interpreted as nonthermal gyrosynchrotron emission by mildly relativistic electrons accelerated more or less continuously in the magnetic fields of starspots.

Pallavicini, R.↗

NASA NTRS2007

Prompt and Afterglow Emission Properties of Gamma-Ray Bursts with Spectroscopically Identified Supernovae

We present a detailed spectral analysis of the prompt and afterglow emission of four nearby long-soft gamma-ray bursts (GRBs 980425,030329,031203, and 060218) that were spectroscopically found to be associated with Type Ic supernovae and compare them to the general GRB population. For each event, we investigate the spectral and luminosity evolution and estimate the total energy budget based on broadband observations. The observational inventory for these events has become rich enough to allow estimates of their energy content in relativistic and subrelativistic form. The result is a global portrait of the effects of the physical processes responsible for producing long-soft GRBs. In particular, we find that the values of the energy released in mildly relativistic outflows appears to have a significantly smaller scatter than those found in highly relativistic ejecta. This is consistent with a picture in which the energy released inside the progenitor star is roughly standard, while the fraction of that energy that ends up in highly relativistic ejecta outside the star can vary dramatically between different events.

Kaneko, Yuki↗

NASA NTRS2012

Quantitative Spectral Radiance Measurements in the HYMETS Arc Jet

Calibrated spectral radiance measurements of gaseous emission spectra have been obtained from the HYMETS (Hypersonic Materials Environmental Test System) 400 kW arc-heated wind tunnel at NASA Langley Research Center. A fiber-optic coupled spectrometer collected natural luminosity from the flow. Spectral radiance measurements are reported between 340 and 1000 nm. Both Silicon Carbide (SiC) and Phenolic Impregnated Carbon Ablator (PICA) samples were placed in the flow. Test gases studied included a mostly-N2 atmosphere (95% nitrogen, 5% argon), a simulated Earth Air atmosphere (75% nitrogen, 20% oxygen, 5% argon) and a simulated Martian atmosphere (71% carbon dioxide, 24% nitrogen, 5% argon). The bulk enthalpy of the flow was varied as was the location of the measurement. For the intermediate flow enthalpy tested (20 MJ/kg), emission from the Mars simulant gas was about 10 times higher than the Air flow and 15 times higher than the mostly-N2 atmosphere. Shock standoff distances were estimated from the spectral radiance measurements. Within-run, run-to-run and day-to-day repeatability of the emission were studied, with significant variations (15-100%) noted.

Danehy, Paul M.↗