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  • 1
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    Stationary Planetary Waves in Northern Late Winter: MRO/MARCI Observations and Mars Climate Model Simulations (2014)
    In:  CASI
    Details
    Publication Date: 2019-11-06
    Description: Mars reveals similar, yet also rather different, atmospheric circulation patterns compared to those on Earth. In both atmospheres, solar differential heating drives global Hadley circulation cells. However during solstice on Mars, its Hadley cells are hemispherically asymmetric: an intense, deep, cross-hemisphere single cell dominates with rising motion in the summer hemisphere and sinking motion in the winter hemisphere. Both planets also exhibit thermally indirect (i.e., eddy-driven) Ferrel circulation cells in middle and high latitudes. In addition, Earth and Mars exhibit distinctive large-scale orography and, in a broadly defined context, continentality. For Mars northern midlatitudes, Tharsis in the western hemisphere, and Arabia Terra and Elysium in the eastern hemisphere, are the primary large-scale topographic features. In the southern-midlatitudes, Tharsis and Argyre in the western hemisphere, and Hellas in the eastern hemisphere are the key topographic features which can influence large-scale circulation patterns. Such underlying orographic complexes not only cause significant latitudinal excursions of the seasonal mean westerly circumnavigating polar vortex but also significantly modulate the intensity and preferred geographic regions of traveling baroclinic weather systems.
    Keywords: Astronomy
    Type: ARC-E-DAA-TN15068 , International Conference on Mars; Jul 14, 2014 - Jul 18, 2014; Pasadena, CA; United States
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  • 2
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    A Newly Developed Fluorescence Model for C2H6 v5 and Application to Cometary Spectra Acquired with NIRSPEC at Keck II (2011)
    In:  Other Sources
    Details
    Publication Date: 2019-09-24
    Description: Accurate rotational temperatures are essential for extracting production rates for parent volatiles in comets. Two strong bands of ethane (v7 at 2985.39/cm and v5 at 2895.67/cm) are seen in infrared cometary spectra, but the Q-branches of v7 are not resolved by current instruments and cannot provide an accurate rotational temperature with current models.We developed a fluorescence model for the C2H6 v5 band that can be used to derive a rotational temperature.We applied our C2H6 5 model to high-resolution infrared spectra of the comets C/2004 Q2 Machholz and C/2000 WM1 (LINEAR), acquired with the Near-infrared Echelle Spectrograph on the Keck II telescope. We demonstrate agreement among the rotational temperatures derived from C2H6 v5 and other species, and between mixing ratios derived from C2H6 v5 and C2H6 v7. As a symmetric hydrocarbon, C2H6 is observed only in the infrared, and it is now the fifth molecule (along with H2O, HCN, CO, and H2CO) for which we can derive a reliable rotational temperature from cometary infrared spectra.
    Keywords: Astronomy
    Type: GSFC.JA01232.2012 , The Astrophysical Journal; 729; 2; 135
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  • 3
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    Monolithic afocal telescope (2010)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: An afocal monolithic optical element formed of a shallow cylinder of optical material (glass, polymer, etc.) with fast aspheric surfaces, nominally confocal paraboloids, configured on the front and back surfaces. The front surface is substantially planar, and this lends itself to deposition of multi-layer stacks of thin dielectric and metal films to create a filter for rejecting out-of-band light. However, an aspheric section (for example, a paraboloid) can either be ground into a small area of this surface (for a Cassegrain-type telescope) or attached to the planar surface (for a Gregorian-type telescope). This aspheric section of the surface is then silvered to create the telescope's secondary mirror. The rear surface of the cylinder is figured into a steep, convex asphere (again, a paraboloid in the examples), and also made reflective to form the telescope's primary mirror. A small section of the rear surface (approximately the size of the secondary obscuration, depending on the required field of the telescope) is ground flat to provide an unpowered surface through which the collimated light beam can exit the optical element. This portion of the rear surface is made to transmit the light concentrated by the reflective surfaces, and can support the deposition of a spectral filter.
    Keywords: Astronomy
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  • 4
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    Advanced Telescopes and Observatories Capability Roadmap Presentation to the NRC (2005)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: This viewgraph presentation provides an overview of the NASA Advanced Planning and Integration Office (APIO) roadmap for developing technological capabilities for telescopes and observatories in the following areas: Optics; Wavefront Sensing and Control and Interferometry; Distributed and Advanced Spacecraft; Large Precision Structures; Cryogenic and Thermal Control Systems; Infrastructure.
    Keywords: Astronomy
    Type: Capabilities Roadmap Briefings to the National Research Council
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  • 5
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    Characterization of the Morphometry of Impact Craters Hosting Polar Deposits in Mercury's North Polar Region (2012)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: Earth-based radar images of Mercury show radar-bright material inside impact craters near the planet s poles. A previous study indicated that the polar-deposit-hosting craters (PDCs) at Mercury s north pole are shallower than craters that lack such deposits. We use data acquired by the Mercury Laser Altimeter on the MESSENGER spacecraft during 11 months of orbital observations to revisit the depths of craters at high northern latitudes on Mercury. We measured the depth and diameter of 537 craters located poleward of 45 N, evaluated the slopes of the northern and southern walls of 30 PDCs, and assessed the floor roughness of 94 craters, including nine PDCs. We find that the PDCs appear to have a fresher crater morphology than the non-PDCs and that the radar-bright material has no detectable influence on crater depths, wall slopes, or floor roughness. The statistical similarity of crater depth-diameter relations for the PDC and non-PDC populations places an upper limit on the thickness of the radar-bright material (〈 170 m for a crater 11 km in diameter) that can be refined by future detailed analysis. Results of the current study are consistent with the view that the radar-bright material constitutes a relatively thin layer emplaced preferentially in comparatively young craters.
    Keywords: Astronomy
    Type: GSFC-E-DAA-TN6171 , Journal of Geophysical Research-Planets; 117; E12
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  • 6
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    A 200-Second Quasi-Periodicity After the Tidal Disruption of a Star by a Dormant Black Hole (2012)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: Supermassive black holes are known to exist at the center of most galaxies with sufficient stellar mass, In the local Universe, it is possible to infer their properties from the surrounding stars or gas. However, at high redshifts we require active, continuous accretion to infer the presence of the SMBHs, often coming in the form of long term accretion in active galactic nuclei. SMBHs can also capture and tidally disrupt stars orbiting nearby, resulting in bright flares from otherwise quiescent black holes. Here, we report on a approx.200-s X-ray quasi-periodicity around a previously dormant SMBH located in the center of a galaxy at redshift z = 0.3534. This result may open the possibility of probing general relativity beyond our local Universe.
    Keywords: Astronomy
    Type: GSFC.JA.7092.2012 , Science; 337; 6097; 949-951
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  • 7
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    A Giant Radio Flare from Cygnus X-3 with Associated Gamma-Ray Emission (2012)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: With frequent flaring activity of its relativistic jets, Cygnus X-3 (Cyg X-3) is one of the most active microquasars and is the only Galactic black hole candidate with confirmed high energy gamma-ray emission, thanks to detections by Fermi/LAT and AGILE. In 2011, Cyg X-3 was observed to transit to a soft X-ray state, which is known to be associated with high-energy gamma-ray emission. We present the results of a multiwavelength campaign covering a quenched state, when radio emission from Cyg X-3 is at its weakest and the X-ray spectrum is very soft. A giant (approx 20 Jy) optically thin radio flare marks the end of the quenched state, accompanied by rising non-thermal hard X-rays. Fermi/LAT observations (E greater than or equal 100 MeV) reveal renewed gamma-ray activity associated with this giant radio flare, suggesting a common origin for all non-thermal components. In addition, current observations unambiguously show that the gamma-ray emission is not exclusively related to the rare giant radio flares. A 3-week period of gamma-ray emission is also detected when Cyg X-3 was weakly flaring in radio, right before transition to the radio quenched state. No gamma rays are observed during the one-month long quenched state, when the radio flux is weakest. Our results suggest transitions into and out of the ultrasoft X-ray (radio quenched) state trigger gamma-ray emission, implying a connection to the accretion process, and also that the gamma-ray activity is related to the level of radio flux (and possibly shock formation), strengthening the connection to the relativistic jets.
    Keywords: Astronomy
    Type: GSFC.JA.6320.2012
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  • 8
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    Galactic Bulge Giants: Probing Stellar and Galactic Evolution. 1. Catalogue of Spitzer IRAC and MIPS Sources (PREPRINT) (2010)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: Aims. We aim at measuring mass-loss rates and the luminosities of a statistically large sample of Galactic bulge stars at several galactocentric radii. The sensitivity of previous infrared surveys of the bulge has been rather limited, thus fundamental questions for late stellar evolution, such as the stage at which substantial mass-loss begins on the red giant branch and its dependence on fundamental stellar properties, remain unanswered. We aim at providing evidence and answers to these questions. Methods. To this end, we observed seven 15 15 arcmin2 fields in the nuclear bulge and its vicinity with unprecedented sensitivity using the IRAC and MIPS imaging instruments on-board the Spitzer Space Telescope. In each of the fields, tens of thousands of point sources were detected. Results. In the first paper based on this data set, we present the observations, data reduction, the final catalogue of sources, and a detailed comparison to previous mid-IR surveys of the Galactic bulge, as well as to theoretical isochrones. We find in general good agreement with other surveys and the isochrones, supporting the high quality of our catalogue.
    Keywords: Astronomy
    Type: AD-A538716 , ARXIV:1002.5015V1
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  • 9
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    Early MESSENGER Results for Less Abundant or Weakly Emitting Species in Mercury's Exosphere (2011)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: Now that the Messenger spacecraft is in orbit about Mercury, the extended observing time enables searches for exospheric species that are less abundant or weakly emitting compared with those for which emission has previously been detected. Many of these species cannot be observed from the ground because of terrestrial atmospheric absorption. We report here on the status of MESSENGER orbital-phase searches for additional species in Mercury's exosphere.
    Keywords: Astronomy
    Type: GSFC.ABS.5329.2011 , EPSC-DPS Joint Meeting 2011; Oct 02, 2011 - Oct 07, 2011; Nantes; France|EPSC Abstracts; 6
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  • 10
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    Interstellar Magnetic Fields and Polarimetry of Dust Emission (2010)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: Magnetic fields are an important ingredient in the stormy cosmos. Magnetic fields: (1) are intimately involved with winds from Active Galactic Nuclei (AGN) and stars (2) create at least some of the structures observed in the ISM (3) modulate the formation of clouds, cores, and stars within a turbulent medium (4) may be dynamically important in protostellar accretion disks (5) smooth weak shocks (C-shocks).
    Keywords: Astronomy
    Type: 2010 Conference: The Evolving Interstellar Medium: Recent Progress from Space IR/Submm; Nov 01, 2010 - Nov 04, 2010; Pasadena, CA; United States
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