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41 results on '"Benz, A. O."'

3. Electron Densities in Solar Flare Loops, Chromospheric Evaporation Upflows, and Acceleration Sites

Author

Aschwanden, Markus J and Benz, Arnold O

Subjects
Solar Physics
Abstract

We compare electron densities measured at three different locations in solar flares: (1) in Soft X-Ray (SXR) loops, determined from SXR emission measures and loop diameters from Yohkoh Soft X-Ray Telescope maps (n(sub e, sup SXR) = (0.2-2.5) x 10(exp 11)/ cu cm); (2) in chromospheric evaporation upflows, inferred from plasma frequency cutoffs of decimetric radio bursts detected with the 0.1-3 GHz spectrometer Phoenix of ETH Zuerich (n(sub e, sup upflow) = (0.3-11) x 10(exp 10)/cu cm; and (3) in acceleration sites, inferred from the plasma frequency at the separatrix between upward-accelerated (type III bursts) and downward-accelerated (reverse-drift bursts) electron beams [n(sub e, sup acc) = (0.6-10) x 10(exp 9)/cu cm]. The comparison of these density measurements, obtained from 44 flare episodes (during 14 different flares), demonstrates the compatibility of flare plasma density diagnostics with SXR and radio methods. The density in the upflowing plasma is found to be somewhat lower than in the filled loops, having ratios in a range n(sub e, sup upflow)/n(sub e, sup SXR) = 0.02-1.3, and a factor of 3.6 higher behind the upflow front. The acceleration sites are found to have a much lower density than the SXR-bright flare loops, i.e., n(sub e, sup acc)/n(sub e, sup SXR) = 0.005- 0.13, and thus must be physically displaced from the SXR-bright flare loops. The scaling law between electron time-of-flight distances l' and loop half-lengths s, l'/s = 1.4 +/- 0.3, recently established by Aschwanden et al. suggests that the centroid of the acceleration region is located above the SXR-bright flare loop, as envisioned in cusp geometries (e.g., in magnetic reconnection models).

Published
1996
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4. Chromospheric Evaporation and Decimetric Radio Emission in Solar Flares

Author

Aschwanden, Markus J and Benz, Arnold O

Subjects
Solar Physics
Abstract

We have discovered decimetric signatures of the chromospheric evaporation process. Evidence for the radio detection of chromospheric evaporation is based on the radio-inferred values of (1) the electron density, (2) the propagation speed, and (3) the timing, which are found to be in good agreement with statistical values inferred from the blueshifted Ca xix soft X-ray line. The physical basis of our model is that free-free absorption of plasma emission is strongly modified by the steep density gradient and the large temperature increase in the upflowing flare plasma. The steplike density increase at the chromospheric evaporation front causes a local discontinuity in the plasma frequency, manifested as almost infinite drift rate in decimetric type III bursts. The large temperature increase of the upflowing plasma considerably reduces the local free-free opacity (due to the T-(exp -3/2) dependence) and thus enhances the brightness of radio bursts emitted at the local plasma frequency near the chromospheric evaporation front, while a high-frequency cutoff is expected in the high-density regions behind the front, which can be used to infer the velocity of the upflowing plasma. From model calculations we find strong evidence that decimetric bursts with a slowly drifting high-frequency cutoff are produced by fundamental plasma emission, contrary to the widespread belief that decimetric bursts are preferentially emitted at the harmonic plasma level. We analyzed 21 flare episodes from 1991-1993 for which broadband (100-3000 MHz) radio dynamic spectra from Phoenix, hard X-ray data from BATSE/CGRO, and soft X-ray data from GOES were available. We detected slowly drifting high-frequency cutoffs between 1.1 and 3.0 GHz, with drift rates of -41 +/- 32 MHz/s, extending over time intervals of 24 +/- 23 s. Developing a density model for type III-emitting flare loops based on the statistically observed drift rate of type III bursts by Alvarez & Haddock, we infer velocities of up to 360 km/s for the upflowing plasma, with an average of v(sub CE) = 236 +/- 130 km /s for episodes with 5-15 s duration. The mean electron density of the upflowing plasma is n(sub e) = 5.2(+/-3.1) x 10(exp 10) /cu cm when it is first detected in radio, at coronal altitudes of h(sub 0) = 9.2 +/- 2.3 Mm.

Published
1995
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5. HERSCHELSURVEY OF GALACTIC OH+, H2O+, AND H3O+: PROBING THE MOLECULAR HYDROGEN FRACTION AND COSMIC-RAY IONIZATION RATE

Author

Indriolo, Nick, primary, Neufeld, D. A., additional, Gerin, M., additional, Schilke, P., additional, Benz, A. O., additional, Winkel, B., additional, Menten, K. M., additional, Chambers, E. T., additional, Black, John H., additional, Bruderer, S., additional, Falgarone, E., additional, Godard, B., additional, Goicoechea, J. R., additional, Gupta, H., additional, Lis, D. C., additional, Ossenkopf, V., additional, Persson, C. M., additional, Sonnentrucker, P., additional, van der Tak, F. F. S., additional, van Dishoeck, E. F., additional, Wolfire, Mark G., additional, and Wyrowski, F., additional

Published
2015
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8. HERSCHELOBSERVATIONS OF INTERSTELLAR CHLORONIUM

Author

Neufeld, David A., primary, Roueff, Evelyne, additional, Snell, Ronald L., additional, Lis, Dariusz, additional, Benz, Arnold O., additional, Bruderer, Simon, additional, Black, John H., additional, De Luca, Massimo, additional, Gerin, Maryvonne, additional, Goldsmith, Paul F., additional, Gupta, Harshal, additional, Indriolo, Nick, additional, Le Bourlot, Jacques, additional, Le Petit, Franck, additional, Larsson, Bengt, additional, Melnick, Gary J., additional, Menten, Karl M., additional, Monje, Raquel, additional, Nagy, Zsófia, additional, Phillips, Thomas G., additional, Sandqvist, Aage, additional, Sonnentrucker, Paule, additional, van der Tak, Floris, additional, and Wolfire, Mark G., additional

Published
2012
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10. HERSCHELMEASUREMENTS OF MOLECULAR OXYGEN IN ORION

Author

Goldsmith, Paul F., primary, Liseau, René, additional, Bell, Tom A., additional, Black, John H., additional, Chen, Jo-Hsin, additional, Hollenbach, David, additional, Kaufman, Michael J., additional, Li, Di, additional, Lis, Dariusz C., additional, Melnick, Gary, additional, Neufeld, David, additional, Pagani, Laurent, additional, Snell, Ronald, additional, Benz, Arnold O., additional, Bergin, Edwin, additional, Bruderer, Simon, additional, Caselli, Paola, additional, Caux, Emmanuel, additional, Encrenaz, Pierre, additional, Falgarone, Edith, additional, Gerin, Maryvonne, additional, Goicoechea, Javier R., additional, Hjalmarson, Åke, additional, Larsson, Bengt, additional, Le Bourlot, Jacques, additional, Le Petit, Franck, additional, De Luca, Massimo, additional, Nagy, Zsofia, additional, Roueff, Evelyne, additional, Sandqvist, Aage, additional, van der Tak, Floris, additional, van Dishoeck, Ewine F., additional, Vastel, Charlotte, additional, Viti, Serena, additional, and Yıldız, Umut, additional

Published
2011
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11. STAR-FORMING DENSE CLOUD CORES IN THE TeV GAMMA-RAY SNR RX J1713.7–3946

Author

Sano, H., primary, Sato, J., additional, Horachi, H., additional, Moribe, N., additional, Yamamoto, H., additional, Hayakawa, T., additional, Torii, K., additional, Kawamura, A., additional, Okuda, T., additional, Mizuno, N., additional, Onishi, T., additional, Maezawa, H., additional, Inoue, T., additional, Inutsuka, S., additional, Tanaka, T., additional, Matsumoto, H., additional, Mizuno, A., additional, Ogawa, H., additional, Stutzki, J., additional, Bertoldi, F., additional, Anderl, S., additional, Bronfman, L., additional, Koo, B.-C., additional, Burton, M. G., additional, Benz, A. O., additional, and Fukui, Y., additional

Published
2010
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