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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

High resolution observations of the L1551 bipolar outflow

The nearby dark cloud Lynds 1551 contains one of the closest examples of a well-collimated bipolar molecular outflow. This source has the largest angular size of any known outflow and was the first bipolar outflow to be detected. The outflow originates from a low-luminosity young stellar object, IRS-5. Optical and radio continuum observations show the presence of a highly collimated, ionized stellar wind orginating from close to IRS-5 and aligned with the molecular outflow. However, we have little information on the actual mechanism that generates the stellar wind and collimates it into opposed jets. The Very Large Array (VLA) observations indicate that the winds originate within 10(15) cm of IRS-5, unfortunately at a size scale difficult to resolve. For these reasons, observations of the structure and dynamics of the hypersonic molecular gas may provide valuable information on the origin and evolution of these outflows. In addition, the study of the impact of the outflowing gas on the surrounding molecular material is essential to understand the consequence these outflows have on the evolution and star formation history of the entire cloud. Moriarty-Schieven et al. (1986) obtained a oversampled map of the CO emission of a portion of both the blueshifted and redshifted outflows in LI551 using Five College Radio Astronomy Observatory 14 m telescope. The oversampled maps have been reconstructed to an effective angular resolution of 20 arcsec using a maximum entropy algorithm. A continuation of the study of Moriarty-Schieven et al. is presented. The entire L1551 outflow has now been mapped at 12 arcsec sampling requiring roughly 4000 spectra. This data has been constructed to 20 arcsec resolution to provide the first high resolution picture of the entire L1551 outflow. This new data has shown that the blueshifted lobe is more extended than previously thought and has expanded downstream sufficiently to break out of the dense molecular cloud, but the redshifted outflow is still confined within the molecular cloud. Details of the structure and kinematics of the high velocity gas are used to test the various models of the origin and evolution of outflows.

Snell, R.↗
NASA NTRS2011

Development of the Advanced Energetic Pair Telescope (AdEPT) for Medium-Energy Gamma-Ray Astronomy

Progress in high-energy gamma-ray science has been dramatic since the launch of INTEGRAL, AGILE and FERMI. These instruments, however, are not optimized for observations in the medium-energy (approx.0.3< E(sub gamma)< approx.200 MeV) regime where many astrophysical objects exhibit unique, transitory behavior, such as spectral breaks, bursts, and flares. We outline some of the major science goals of a medium-energy mission. These science goals are best achieved with a combination of two telescopes, a Compton telescope and a pair telescope, optimized to provide significant improvements in angular resolution and sensitivity. In this paper we describe the design of the Advanced Energetic Pair Telescope (AdEPT) based on the Three-Dimensional Track Imager (3-DTI) detector. This technology achieves excellent, medium-energy sensitivity, angular resolution near the kinematic limit, and gamma-ray polarization sensitivity, by high resolution 3-D electron tracking. We describe the performance of a 30x30x30 cm3 prototype of the AdEPT instrument.

Hunter, Stanley D.↗
NASA NTRS1990

Lunar occultations for gamma-ray source measurements

The unambiguous association of discrete gamma-ray sources with objects radiating at other wavelengths, the separation of discrete sources from the extended emission within the Galaxy, the mapping of gamma-ray emission from nearby galaxies and the measurement of structure within a discrete source cannot presently be accomplished at gamma-ray energies. In the past, the detection processes used in high-energy gamma-ray astronomy have not allowed for good angular resolution. This problem can be overcome by placing gamma-ray detectors on the moon and using the horizon as an occulting edge to achieve arcsec resolution. For purposes of discussion, this concept is examined for gamma rays above 100 MeV for which pair production dominates the detection process and locally-generated nuclear gamma rays do not contribute to the background.

Koch, David G.↗
NASA NTRS2002

Two Years of Chandra Observations: Neutron Stars and Pulsars with Emphasis on the Pulsar in the Crab Nebula

The Chandra X-Ray Observatory is entering its third year of operation. The Observatory, the premiere x-ray telescope for high-resolution imaging, has exceeded all expectations. The sub-arc second angular resolution together with other instrumental capabilities has allowed for new insights into the understanding of compact x-ray emitting objects including neutron stars and pulsars. We briefly review the Chandra Program and the first two years of observation with emphasis on these interesting objects. We detail the results of our observations of the pulsar in the Crab Nebula including the first continuum spectrum that is virtually uncontaminated by any dust-scattered radiation.

Weisskopf, Martin C.↗
NASA NTRS2007

Gamma-ray Astronomy and GLAST

The high energy gamma-ray (30 MeV to 100 GeV) sky has been relatively poorly studied. Most of our current knowledge comes from observations made by the Energetic Gamma Ray Experiment Telescope (EGRET) detector on the Compton Gamma Ray Observatory (CGRO), which revealed that the GeV gamma-ray sky is rich and vibrant. Studies of astrophysical objects at GeV energies are interesting for several reasons: The high energy gamma-rays are often produced by a different physical process than the better studied X-ray and optical emission, thus providing a unique information for understanding these sources. Production of such high-energy photons requires that charged particles are accelerated to equally high energies, or much greater. Thus gamma-ray astronomy is the study of extreme environments, with natural and fundamental connections to cosmic-ray and neutrino astrophysics. The launch of GLAST in 2008 will herald a watershed in our understanding of the high energy gamma-ray sky, providing dramatic improvements in sensitivity, angular resolution and energy range. GLAST will open a new avenue to study our Universe as well as to answer scientific questions EGRET observations have raised. In this talk, I will describe the GLAST instruments and capabilities and highlight some of the science we expect to address.

McEnery, Julie↗
NASA NTRS2008

The EXIST Mission Concept Study

EXIST is a mission designed to find and study black holes (BHs) over a wide range of environments and masses, including: 1) BHs accreting from binary companions or dense molecular clouds throughout our Galaxy and the Local Group, 2) supermassive black holes (SMBHs) lying dormant in galaxies that reveal their existence by disrupting passing stars, and 3) SMBHs that are hidden from our view at lower energies due to obscuration by the gas that they accrete. 4) the birth of stellar mass BHs which is accompanied by long cosmic gamma-ray bursts (GRBs) which are seen several times a day and may be associated with the earliest stars to form in the Universe. EXIST will provide an order of magnitude increase in sensitivity and angular resolution as well as greater spectral resolution and bandwidth compared with earlier hard X-ray survey telescopes. With an onboard optical-infra red (IR) telescope, EXIST will measure the spectra and redshifts of GRBs and their utility as cosmological probes of the highest z universe and epoch of reionization. The mission would retain its primary goal of being the Black Hole Finder Probe in the Beyond Einstein Program. However, the new design for EXIST proposed to be studied here represents a significant advance from its previous incarnation as presented to BEPAC. The mission is now less than half the total mass, would be launched on the smallest EELV available (Atlas V-401) for a Medium Class mission, and most importantly includes a two-telescope complement that is ideally suited for the study of both obscured and very distant BHs. EXIST retains its very wide field hard X-ray imaging High Energy Telescope (HET) as the primary instrument, now with improved angular and spectral resolution, and in a more compact payload that allows occasional rapid slews for immediate optical/IR imaging and spectra of GRBs and AGN as well as enhanced hard X-ray spectra and timing with pointed observations. The mission would conduct a 2 year full sky survey in scanning mode, interrupted for several orbits per day by GRB follow-ups, followed by a combined pointing-scanning mission phase for optical/IR spectroscopy and redshifts for the large AGN sample found in the survey as well as GRBs and LSST transients. A Team of university, NASA, and industry investigators will conduct the study to determine the full sensitivity and capabilities of this new configuration for EXIST. It will build on the extensive studies of the prior design for the mission and the HET and will incorporate the optical/IR telescope (hereafter IRT) now fully developed by our ITT partner for the NextView Commercial Remote Sensing mission (early 2008 launch) with a focal plane to be developed at GSFC based in part on JWST/NIRSPEC designs. No new technology is needed for either the IRT or HET instruments. The study will pay close attention to full mission cost and present a design for the Decadal Survey Workshop to ensure this even more capable EXIST mission is once again part of the next Decadal Survey.

Fishman, Gerald J.↗
NASA NTRSDate not supplied

Next Generation X-ray Optics for Astrophysics: High Resolution, Light Weight, and Low Cost

Ready a technology with the following features, compared to Chandra’s. Much better angular resolution: - On-axis: Comparable(~0.5”HPD) by 2026, 5Xbetter by ~2030 - Off-axis: 10Xbetter at 10-arcmin off-axis Much lighter weight per unit area–at least 10Xlighter Much lower cost per unit area–at least 10X lower in real year dollars

Silicon X-ray mirrors↗
NASA NTRS2010

Focusing X-Ray Telescopes

During the half-century history of x-ray astronomy, focusing x-ray telescopes, through increased effective area and finer angular resolution, have improved sensitivity by 8 orders of magnitude. Here, we review previous and current x-ray-telescope missions. Next, we describe the planned next-generation x-ray-astronomy facility, the International X-ray Observatory (IXO). We conclude with an overview of a concept for the next next-generation facility, Generation X. Its scientific objectives will require very large areas (about 10,000 sq m) of highly-nested, lightweight grazing-incidence mirrors, with exceptional (about 0.1-arcsec) resolution. Achieving this angular resolution with lightweight mirrors will likely require on-orbit adjustment of alignment and figure.

O'Dell, Stephen↗
NASA NTRS2000

Galactic Diffuse Gamma Ray Emission Is Greater than 10 Gev

AGILE and Gamma-ray Large Area Telescope (GLAST) are the next high-energy gamma-ray telescopes to be flown in space. These instruments will have angular resolution about 5 times better than Energetic Gamma-Ray Experiment Telescope (EGRET) above 10 GeV and much larger field of view. The on-axis effective area of AGILE will be about half that of EGRET, whereas GLAST will have about 6 times greater effective area than EGRET. The capabilities of ground based very high-energy telescopes are also improving, e.g. Whipple, and new telescopes, e.g. Solar Tower Atmospheric Cerenkov Effect Experiment (STACEE), Cerenkov Low Energy Sampling and Timing Experiment (CELESTE), and Mars Advanced Greenhouse Integrated Complex (MAGIC) are expected to have low-energy thresholds and sensitivities that will overlap the GLAST sensitivity above approximately 10 GeV. In anticipation of the results from these new telescopes, our current understanding of the galactic diffuse gamma-ray emission, including the matter and cosmic ray distributions is reviewed. The outstanding questions are discussed and the potential of future observations with these new instruments to resolve these questions is examined.

Hunter, Stanley D.↗
NASA NTRS1995

A surprise at the bottom of the main sequence: Rapid rotation and NO H-alpha emission

We report Kech Observatory high-resolution echelle spectra from 640-850 nm for eight stars near the faint end of the main sequence. These spectra are the highest resolution spectra of such late-type stars, and clearly resolve the TiO, VO, and atomic lines. The sample includes the field brown-dwarf candidate, BRI 0021-0214 (M9.5+). Very unexpectedly, it shows the most rapid rotation in the entire samples, v sin i approximately 40 km/s, which is 20x faster than typical field nonemission M stars. Equally surprising is that BRI 0021 exhibits no emission or absorptionat H-alpha. We argue that this absence is not simply due to its cool photosphere, but that stellar activity declines in a fundamental way at the end of the main sequence. As it is the first very late M dwarf observed at high spectral resolution, BRI 0021 may be signaling a qualitative change in the angular momentum loss rate among the lowest mass stars. Conventionally, its rapid rotation would have marked BRI 0021 as very young, consistent with the selection effect which arises if the latest-type dwarfs are really brown dwarfs on cooling curves. In any case, it is unprecedented to find no sign of stellar activity in such a rapidly rotating convective star. We also discuss the possible conflict between this observation and the extremely strong H-alpha seen in another very cool star, PC 0025+0447. Extrapolation of M-L relations for BRI 0021 yields M approximately 0.065 solar mass, and the other sample objects have expected masses near the H-burning limit. These include two Pleiades brown-dwarf candidates, four field M6 dwarfs and one late-type T Tauri star. The two Pleiades M6 dwarfs have v sin i of 26 and 37 km/s, H-alpha in emission, and radial velocities consistent with Pleiades M6 dwarfs have v sin i of 26 and 37 km/s, H-alpha in emission, and radial velocities consistent with Pleiades membership. Similarly, the late-type T Tauri star has v sin i approximately 30 km/s and H alpha emission indicate of its youth. Two of the four late-type field dMe star also exhibit rotation above 5 km/s, consistent with expectations. BRI 0021 has no measurable absoprtion due to lithium, indicating that it is likely to be more massive than 0.065 solar mass.

Basri, Gibor↗
NASA NTRS1997

Few arc-minute and keV resolutions with the TIGRE Compton telescope

The tracking and imaging gamma ray experiment (TIGRE) Compton telescope concept can provide an angular resolution of a few arcmin, an energy resolution of a few keV and high sensitivity, while providing the wide field of view necessary for surveying and monitoring observations. Silicon and CdZnTe strip detectors are used to detect Compton pair events and determine their incident directions and energies. Above 400 keV, Compton recoil electrons are tracked through successive layers of thin silicon strip detectors. Compton scattered photons are detected with CdZnTe strip detectors. Pair electrons and positrons are tracked to provide high sensitivity observations in the 10 to 100 MeV range. Polarization studies are performed with large angle Compton scatter events. The TIGRE concept and development status are described.

Zych, A.↗
NASA NTRS2009

Computing Challenges in Coded Mask Imaging

This slide presaentation reviews the complications and challenges in developing computer systems for Coded Mask Imaging telescopes. The coded mask technique is used when there is no other way to create the telescope, (i.e., when there are wide fields of view, high energies for focusing or low energies for the Compton/Tracker Techniques and very good angular resolution.) The coded mask telescope is described, and the mask is reviewed. The coded Masks for the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) instruments are shown, and a chart showing the types of position sensitive detectors used for the coded mask telescopes is also reviewed. Slides describe the mechanism of recovering an image from the masked pattern. The correlation with the mask pattern is described. The Matrix approach is reviewed, and other approaches to image reconstruction are described. Included in the presentation is a review of the Energetic X-ray Imaging Survey Telescope (EXIST) / High Energy Telescope (HET), with information about the mission, the operation of the telescope, comparison of the EXIST/HET with the SWIFT/BAT and details of the design of the EXIST/HET.

Skinner, Gerald↗
NASA NTRS2001

Fabricating High Resolution Mirrors for Hand X-Ray Astronomy

We describe the fabrication process for producing high-resolution conical mirrors for hard x-ray astronomy. When flown aboard stratospheric balloons, these high-resolution reflective mirrors focus hard x-rays (10-70 keV) emitted from cosmic sources such as supernovae, neutron stars, and quasars onto imaging focal plane detectors. Focused hard x-ray images allow scientists to determine the elemental compositions, temperatures, magnetic fields, velocities, and gravitational fields of these celestial bodies. The fabrication process involves generating super-polished mandrels, mandrel metrology, mirror shell nickel electroforming, and mirror testing. Each mandrel is a cylinder consisting of two conical segments; each segment is approximately 305-mm long. Through precision grinding these mandrels before super polishing, we have achieved 30 arc seconds, half power diameter replicated mirrors. During a May 2001 high atmosphere balloon flight, these mirrors focused high energy x-rays from three different celestial sources. However, we seek to improve the angular resolutions of future mirror shells by a factor of two. To achieve this goal, we have begun single point diamond turning the mandrels before super polishing. This has allowed greater precision tolerances on mandrel surface roughness and axial figure errors before super polishing. Surface roughnesses before polishing have been reduced from approximately 60 nm to approximately 15 nm. The peak to valley axial figure profile errors have been reduced from approximately 1.0 micrometers to approximately 0.4 micrometers. We are currently in Phase 2 of the HERO (high energy replicated optics) program which entails the production of sixteen 6-m-focal-length mirror modules, each containing a nested array of 15 mirror shells of diameters ranging from 50-mm to 94-mm. This flight is slated for the fall of 2003.

Speegle, Chet O.↗
NASA NTRS2022

Quantifying Energy Release in Solar Flares and Solar Eruptive Events

Solar flares and the often associated solar eruptive events serve as an outstanding laboratory to study the magnetic reconnection and the associated energy release and conversion processes under plasma conditions difficult to reproduce in the laboratory, and with considerable spatiotemporal details not possible elsewhere in the universe. In the past decade, thanks to advances in multiwavelength imaging spectroscopy, as well as developments in theories and numerical modeling, significant progress has been made in improving our understanding of solar flare/eruption energy release. In particular, broadband imaging spectroscopy at microwave wavelengths offered by the Expanded Owens Valley Solar Array (EOVSA) has enabled the revolutionary capability of measuring the time-evolving coronal magnetic fields at or near the flare reconnection region. However, owing to EOVSA’s limited dynamic range, imaging fidelity, and angular resolution, such measurements can only be done in a region around the brightest source(s) where the signal-to-noise is sufficiently large. In this white paper, after a brief introduction to the outstanding questions and challenges pertinent to magnetic energy release in solar flares and eruptions, we will demonstrate how a next-generation radio facility with many (∼100–200) antenna elements can bring the next revolution by enabling high dynamic range, high fidelity broadband imaging spectropolarimetry along with a sub-second time resolution and arcsecond level angular resolution. We recommend to prioritize the implementation of such a ground-based instrument within this decade. We also call for facilitating multi-wavelength, multi-messenger observations and advanced numerical modeling in order to achieve a comprehensive understanding of the “system science” of solar flares and eruptions.

Bin Chen↗
NASA NTRS2014

The Coldest Object in the Universe: Probing the Mass Distribution of the Ultra-Cold Outflow and Dusty Disk in the Boomerang Nebula

Our Cycle 0 ALMA observations confirmed that the Boomerang Nebula is the coldest known object in the universe, with a massive high-speed outflow that has cooled significantly below the temperature of the cosmic background (CMB). The Boomerang's prodigious mass-loss rate (0.001 solar mass M yr (exp -1) and low-luminosity (300L ) make it a key object for understanding the remarkable transition of the circumstellar envelopes of AGB stars into bipolar planetary nebulae. We have obtained new ACA CO 1-0 data that recover much of the flux lost in the Cycle O data, and reveal heretofore unseen distant regions of the ultra-cold outflow reheated to temperatures above the CMB. Our CO J=3-2 data reveal the precise, highly collimated shape of an inner bipolar structure and its dense central waist, with unprecedented angular resolution (0.4 in). The waist shows a core-halo structure in the thermal dust emission at 0.88 millimeter, and its derived flux at this wavelength, compared with the 3.3, 2.6, and 1.3 millimeter fluxes support the presence of about 5 x 10 (exp -4) solar mass of very large (approximately millimeter-sized), cold (approximately 30K) grains. We also find the unexpected presence of weak SO emission, possibly resulting from the release of S from grains due to high-speed shocks.

Sahai, R.↗
NASA NTRS1983

Coded aperture imaging of X-ray and gamma-ray sources

Coded aperture telescopes employing arrays of a small number of discrete detector elements for hard X-rays or gamma-rays are discussed. Aperture patterns are described that permit a unique reconstruction of the image with high contrast, and that exhibit a specific rotational antisymmetry to suppress systematic distortions. It is shown that high flux sensitivity can be achieved in this fashion as well as good angular resolution.

Kroeger, R.↗
NASA NTRS1995

A test of galaxy evolutionary models via angular sizes

The relationship between angular size, magnitude, and redshift of faint galaxies is explored as a potential tool to distinguish between galaxy evolutionary models. Different models, based on merging, mild luminosity evolution, and no evolution, lead to different predictions of the angular size distribution, redshift- size relation, and magnitude-size relation. The merging model predicts significantly smaller sizes for faint galaxies than the standard model, because of the requirement for more intrinsically small faint objects at high redshift. A dwarf-rich no-evolution model also predicts small sizes for faint galaxies. The mild luminosity evolution model predicts more luminous galaxies of large angular size at high redshift, as does a standard no-evolution model. Prefurbishment Hubble Space Telescope (HST) Medium Deep Survey observations of magnitudes and sizes of faint galaxies indicate an excess of small versus large faint galaxies, favoring the dwarf rich, no evolution model with respect to the merging model; the other two models are more discrepant with the data. While these results cannot yet rule out with certainty any of the proposed models, they demonstrate the potential of angular size to discriminate between models of galaxy evolution, especially with the high-resolution HST wide field/planetary camera-2 (WFPC2) data.

Im, Myungshin↗
NASA NTRS1988

High throughput X-ray optics - An overview

Techniques for the production of high-throughput modular arrays of telescopes with net collecting areas exceeding 10 to the 5th sq cm and 20-arsec angular resolution are discussed. Techniques considered include the automated figuring of flats as parabolic reflectors, the replication of cylindrical shells, the alignment of thin lacquer-coated conical foils, electroforming, and the use of large diamond turning machines. High-throughput programs are described, and it is noted that future missions will emphasize high resolution spectroscopy.

Gorenstein, Paul↗