Astronomy Research Works
Permanent URI for this collectionhttp://hdl.handle.net/1903/1587
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Item Spectral Dependent Degradation of the Solar Diffuser on Suomi-NPP VIIRS Due to Surface Roughness-Induced Rayleigh Scattering(MDPI, 2016-06-17) Shao, Xi; Cao, Changyong; Liu, Tung-ChangThe Visible Infrared Imaging Radiometer Suite (VIIRS) onboard Suomi National Polar Orbiting Partnership (SNPP) uses a solar diffuser (SD) as its radiometric calibrator for the reflective solar band calibration. The SD is made of Spectralon™ (one type of fluoropolymer) and was chosen because of its controlled reflectance in the Visible/Near-Infrared/Shortwave-Infrared region and its near-Lambertian reflectance property. On-orbit changes in VIIRS SD reflectance as monitored by the Solar Diffuser Stability Monitor showed faster degradation of SD reflectance for 0.4 to 0.6 µm channels than the longer wavelength channels. Analysis of VIIRS SD reflectance data show that the spectral dependent degradation of SD reflectance in short wavelength can be explained with a SD Surface Roughness (length scale << wavelength) based Rayleigh Scattering (SRRS) model due to exposure to solar UV radiation and energetic particles. The characteristic length parameter of the SD surface roughness is derived from the long term reflectance data of the VIIRS SD and it changes at approximately the tens of nanometers level over the operational period of VIIRS. This estimated roughness length scale is consistent with the experimental result from radiation exposure of a fluoropolymer sample and validates the applicability of the Rayleigh scattering-based model. The model is also applicable to explaining the spectral dependent degradation of the SDs on other satellites. This novel approach allows us to better understand the physical processes of the SD degradation, and is complementary to previous mathematics based models.Item Unveiling the Origin of the Fermi Bubbles(MDPI, 2018-02-28) Yang, H.-Y. Karen; Ruszkowski, Mateusz; Zweibel, Ellen G.The Fermi bubbles, two giant structures above and below the Galactic center (GC), are among the most important discoveries of the Fermi Gamma-ray Space Telescope. Studying their physical origin has been providing valuable insights into cosmic-ray transport, the Galactic magnetic field, and past activity at the GC in the Milky Way galaxy. Despite their importance, the formation mechanism of the bubbles is still elusive. Over the past few years, there have been numerous efforts, both observational and theoretical, to uncover the nature of the bubbles. In this article, we present an overview of the current status of our understanding of the bubbles’ origin, and discuss possible future directions that will help to distinguish different scenarios of bubble formation.Item Astrophotonic Spectrographs(MDPI, 2019-01-15) Gatkine, Pradip; Veilleux, Sylvain; Dagenais, MarioAstrophotonics is the application of photonic technologies to channel, manipulate, and disperse light from one or more telescopes to achieve scientific objectives in astronomy in an efficient and cost-effective way. Utilizing photonic advantage for astronomical spectroscopy is a promising approach to miniaturizing the next generation of spectrometers for large telescopes. It can be primarily attained by leveraging the two-dimensional nature of photonic structures on a chip or a set of fibers, thus reducing the size of spectroscopic instrumentation to a few centimeters and the weight to a few hundred grams. A wide variety of astrophotonic spectrometers is currently being developed, including arrayed waveguide gratings (AWGs), photonic echelle gratings (PEGs), and Fourier-transform spectrometer (FTS). These astrophotonic devices are flexible, cheaper to mass produce, easier to control, and much less susceptible to vibrations and flexure than conventional astronomical spectrographs. The applications of these spectrographs range from astronomy to biomedical analysis. This paper provides a brief review of this new class of astronomical spectrographs.Item Questions Related to the Equation of State of High-Density Matter(MDPI, 2019-04-30) Miller, M. ColemanAstronomical data about neutron stars can be combined with laboratory nuclear data to give us a strong base from which to infer the equation of state of cold catalyzed matter beyond nuclear density. However, the nuclear and astrophysical communities are largely distinct; each has their own methods, which means that there is often imperfect communication between the communities regarding caveats about claimed measurements and constraints. Here we present a brief summary from one astronomer’s perspective of relevant observations of neutron stars, with warnings as appropriate, followed by a set of questions that are intended to help enhance the dialog between nuclear physicists and astrophysicists.Item Terrestrial Scanning LiDAR of Kilbourne Hole Maar, Potrillo Volcanic Field, New Mexico(2019-10-23) Whelley, Patrick; Enriquez, Frankie; Richardson, Jacob; Hurtado, José; Young, Kelsey; Bleacher, JacobArchived are point clouds collected using the Goddard Instrument Filed Team's Riegl VZ-400, a Terrestrial Scanning LiDAR.Item PIC simulation data for "Magnetic reconnection in a quasi-parallel shock: two-dimensional local particle-in-cell simulation"(2019) Bessho, Naoki; Chen, Li-Jen; Wang, Shan; Hesse, Michael; Wilson, Lynn, III2-dimensional particle-in-cell simulation data for a paper "Fully kinetic simulations of magnetic reconnection in the Earth’s quasi-parallel bow shock" Data for fig.1(a): by1250-fig1a.txt, by1563-fig1a.txt, by1875-fig1a.txt, format: x/d_i, B_y/B_0. For fig.1(b)(c)(d): az1250.txt, az1563.txt, az1875.txt, format: x/d_i, y/d_i, A_z/(B_0d_i). For fig1(e)(f)(g)(h)(i)(j): ex1875.txt, cuz1875.txt, bz1875.txt, ne1875.txt, vxe1875.txt, vye1875.txt, format: x/d_i, y/d_i, Q, where Q is each normalized field quantity (E_x, J_z, B_z, N_e, V_ex, V_ey). Normalization is given in the figure. Data for fig.2(a) for J_z, fig.2(b) for B_z, fig.2(d) for V_ex, fig.2(e) for V_ey are the same as given in fig1. For fig.2(c): cde1875.txt. For fig.2(g)(h): vxi1875.txt, vyi1875.txt. For contour of A_z for each plot, use az1875.txt. For vector plot of fluid velocities, use vxe1875.txt, vye1875.txt, vxi1875.txt, vyi1875.txt. For fig.2(f)(i): az1888.txt, az1900.txt. Format is the same as other 2-D plots. Data for fig.3(a), use ne1875.txt. For fig.3(b): ez1875.txt. For vector plot of fluid velocities, use vxe1875.txt, vye1875.txt. For vector plot of E-field: exav1875.txt, eyav1875.txt. Format is the same as other 2-D plots. For contour of A_z for each plot, use az1875.txt. For fig.3(c)(d)(e): bjc#.txt, ejc#.txt, cujc#.txt, vjec#.txt, vjic#.txt, nec#.txt, cdec#.txt, where the letter j represents a component of the field (x, y, z), and # represents a number (1, 2, or 3), format: y/d_i, Q. For fig.3(f)(g)(h)(i): fj-fig3-?#.txt, where the letter j represents e (electron) or i (ion), ? represents a figure alphabet (f, g, h, or i), and # represents a number 1 (left panel) or 2 (right panel), format: v_k/v_A, v_l/v_A, count, where v_k is the x axis of the velocity and v_l is the y axis of the velocity. Data for fig.4(a): vyi1797.txt, az1797.txt, the same format as other 2-D plots. For fig.4(b), use vyi1875.txt and az1875.txt. For fig.4(c)(d), use vyi1875.txt, vye1875.txt, for A_z contour az1875.txt, and for velocity vectors, also use vxi1875.txt and vxe1875.txt. For fig.4(e), viin-x1875.txt, for velocity vector: vxi-x1875.txt, vyi-x1875.txt, and use az1875.txt for A_z contour. For fig.4(f), vein-x1875.txt, for velocity vector: vxe-x1875.txt, vye-x1875.txt, and use az1875.txt for A_z contour. For fig.4(g)(h): bjc#.txt, ejc#.txt, cujc#.txt, vjec#.txt, vjic#.txt, nec#.txt, cdec#.txt, where the letter j represents a component of the field (x, y, z), and # represents a number (4 or 5), format: x/d_i, Q. For fig.4(i), viinc4.txt, viinc5.txt, format x/d_i, |v_i-xy|/v_A. For fig.4(j), veinc4.txt, veinc5.txt, format x/d_i, |v_e-xy|/v_A. For fig4.(k): fj-fig4-k#.txt, where the letter j represents e or i, and # represents a number 1 (top panel), 2 (middle panel), or 3 (bottom panel), format: v_k/v_A, v_l/v_A, count, where v_k is the x axis of the velocity and v_l is the y axis of the velocity.Item Reduced data for the Swift Intensive Accretion Disk Reverberation Mapping Survey(arXiv.org, 2018-11-19) Edelson, R; Gelbord, J.; Cackett, E.; Peterson, B. M.; Horne, K.; Barth, A. J.; Starkey, D. A.; Bentz, M.; Brandt, W. N.; Goad, M.; Joner, M.; Korista, K.; Netzer, H.; Page, K.; Uttley, P.; Vaughan, S.; Breeveld, A.; Cenko, S. B.; Done, C.; Evans, P.; Fausnaugh, M.; Ferland, G.; Gonzalez-Buitrago, D.; Gropp, J.; Grupe, D.; Kaastra, J.; Kennea, J.; Kriss, G.; Mathur, S.; Mehdipour, M.; Nousek, J.; Schmidt, T.; Vestergaard, M.; Villforth, C.Since 2014, the Niel Gehrels Swift observatory has conducted a series of intensive accretion disk reverberation mapping (IDRM) campaigns of bright AGN. This archive contains reduced data from the first four of these campaigns. We are making the data publicly available to facilitate uniform modeling and analysis of these data. Please feel free to download and use the data as you wish. This table will be updated as more IDRM campaigns are published and as the data reduction (mostly dropout filtering) improves. If these data result in publications, please cite the source paper: "The First Swift Intensive AGN Accretion Disk Reverberation Mapping Survey" by Edelson et al. (2019 ApJ 870 123; available at http://iopscience.iop.org/article/10.3847/1538-4357/aaf3b4/meta). Also please note: © AAS. Reproduced with permission. TABLE NOTES: Column 1: Object name. Column 2: Filter/band used to measure the data point. Column 3: Cadence number, where the most significant digit refers to the object and the next three refer to the visit number for that object. Column 4: Modified Julian Day at the midpoint of the exposure. Column 5: Duration of the integration in that filter/band, in seconds. Column 6: Mean flux of the data point. UVOT fluxes are given in units of 10^-{14} erg/cm2/s/A and X-ray fluxes in units of ct/s. Column 7: Uncertainty on the flux, in the same units as Column 6.Item PIC simulation data for "Effect of the reconnection electric field on electron distribution functions in the diffusion region of magnetotail reconnection"(2018) Bessho, Naoki; Chen, Li-Jen; Wang, Shan; Hesse, Michael2-dimensional particle-in-cell simulation data for a paper, "Effect of the reconnection electric field on electron distribution functions in the diffusion region of magnetotail reconnection".Item The CARMA 3 mm Survey of the Inner 0.7 x 0.4 degrees of the Central Molecular Zone(2017) Pound, Marc; Yusef-Zadeh, FarhadThe Central Molecular Zone (CMZ) of the Galactic Center has to date only been fully mapped at mm wavelengths with singledish telescopes, with resolution about 30 arcseconds (1.2 pc). Using the Combined Array for Research in Millimeter Astronomy (CARMA), we mapped the innermost 0.25 square degrees of the CMZ over the region between -0.2 < l < 0.5 degrees and -0.2 < b < 0.2 degrees (90 x 50 pc) with spatial and spectral resolution of 10 arcseconds (0.4 pc) and 2.5 km/s, respectively. We provide a catalog of 3 mm continuum sources as well as spectral line images of SiO(J=2-1), HCO+(J=1-0), HCN(J=1-0), N2H+(J=1-0), and CS(J=2-1) , with velocity coverage VLSR= -200 to 200 km/s To recover the large scale structure resolved out by the interferometer, the continuum-subtracted spectral line images were combined with data from the Mopra 22-m telescope survey, thus providing maps containing all spatial frequencies down to the resolution limit. We find that integrated intensity ratio of I(HCN)/I(HCO+) is anti-correlated with the intensity of the 6.4 keV Fe Kalpha, which is excited either by high energy photons or low energy cosmic rays, and the gas velocity dispersion as traced by HCO+ is correlated with Fe Kalpha intensity. The intensity ratio and velocity dispersion patterns are consistent with variation expected from the interaction of low energy cosmic rays with molecular gas.Item Two Dimensional Velocity Fields of Low Surface Brightness Galaxies(EDP Sciences, 2005) Kuzio de Naray, R.; McGaugh, S. S.; de Blok, W. J. G.; Bosma, A.We present high resolution two dimensional velocity fields from integral field spectroscopy along with derived rotation curves for nine low surface brightness galaxies. This is a positive step forward in terms of both data quality and number of objects studied. We fit NFW and pseudo-isothermal halo models to the observations. We find that the pseudo-isothermal halo better represents the data in most cases than the NFW halo, as the resulting concentrations are lower than would be expected for CDM.
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