Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We present here a combined analysis of four high spectral resolution observations of the Diffuse X-ray Background, made using the University of Wisconsin-Madison/Goddard Space Flight Center X-ray Quantum Calorimeter sounding rocket payload. The observed spectra support the existence of a ∼0.1 keV Local Hot Bubble and a ∼0.2 keV Hot Halo, with discrepancies between repeated observations compatible with expected contributions of time-variable emission from Solar Wind Charge Exchange. An additional component of ∼0.9 keV emission observed only at low galactic latitudes can be consistently explained by unresolved dwarf M stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Our heliosphere’s innermost boundary—the termination shock—slows and heats the supersonic solar wind and energizes anomalous cosmic rays (ACRs). We show that in addition to their termination shock crossings, the <jats:italic>Voyager 1</jats:italic> and <jats:italic>2</jats:italic> spacecraft measurements identify additional points on the termination shock when they magnetically disconnect from the ACR source. These four points define a spherical approximation of the termination shock with radius 117 au, offset ∼32 au tailward, ∼27 au north, and ∼12 au to the port side of the Sun. <jats:italic>Interstellar Boundary Explorer</jats:italic> (<jats:italic>IBEX</jats:italic>) spacecraft observations independently confirm these general offsets, with the closest region of the termination shock ∼ 20° south of the interstellar inflow direction and a minimum distance ∼74 au. The maximum distance is ∼161 au, consistent with required ACR acceleration times. Thus, <jats:italic>Voyager</jats:italic> and <jats:italic>IBEX</jats:italic> spacecraft observations have directly revealed the global size and location of our heliosphere’s termination shock for the first time.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present calculated cross sections and rate coefficients for the formation of the dicarbon cation (<jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{C}}}_{2}^{+}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab43cbieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) by the radiative association process in collisions of a <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{C}}{(}^{3}P)$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab43cbieqn2.gif" xlink:type="simple" /> </jats:inline-formula> atom and a <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{C}}}^{+}{(}^{2}{P}^{o})$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab43cbieqn3.gif" xlink:type="simple" /> </jats:inline-formula> ion. Molecular structure calculations for a number of low-lying doublet and quartet states of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{C}}}_{2}^{+}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab43cbieqn4.gif" xlink:type="simple" /> </jats:inline-formula> are used to obtain the potential energy surfaces and transition dipole moments coupling the states of interest, substantially increasing the available molecular data for <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{C}}}_{2}^{+}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab43cbieqn5.gif" xlink:type="simple" /> </jats:inline-formula>. Using a quantum-mechanical method, we explore a number of allowed transitions and determine those contributing to the radiative association process. The calculations extend the available data for this process down to the temperature of 100 K, where the rate coefficient is found to be about <jats:inline-formula> <jats:tex-math> <?CDATA $2\times {10}^{-18}\,{\mathrm{cm}}^{3}\,{{\rm{s}}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab43cbieqn6.gif" xlink:type="simple" /> </jats:inline-formula>. We provide analytical fits suitable for incorporation into astrochemical reaction databases.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Measurements of elemental abundances hold important clues to how mass and energy flow through the solar atmosphere. Variations in abundances are organized by an element’s first ionization potential (FIP), and many previous studies have assumed that low FIP (less than 10 eV) elements are enriched by a factor of 3–4 in the corona. In this paper, we use spatially resolved observations from the Extreme-ultraviolet Imaging Telescope on board the <jats:italic>Hinode</jats:italic> spacecraft to examine the spatial variability of elemental abundance in and around active regions. We find substantial variations within some active regions. In general, however, we find that the enrichment of low FIP elements is limited to bright, active region structures. In faint active region structures and in the dark, quiet regions around active regions, the measured abundances are close to photospheric. These measurements use the ratio of low FIP Si to high FIP S. Similar conclusions concerning quiet Sun regions have been reached recently by Del Zanna using full-Sun spectra. He has found that the coronal quiet Sun (at temperatures greater than 1 MK) has photospheric abundances. Transition region abundances (at temperatures less than 1 MK in the solar atmosphere) have been found to be photospheric. These results and results from this paper suggest that a coronal composition is not a general property of million-degree plasma, but is limited to bright active region loops, and is variable.</jats:p>