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Articles 1 - 6 of 6
Full-Text Articles in Physical Sciences and Mathematics
Dielectronic Recombination And Stability Of Warm Gas In Active Galactic Nuclei, Susmita Chakravorty, Ajit K. Kembhavi, Martin Elvis, Gary J. Ferland, N. R. Badnell
Dielectronic Recombination And Stability Of Warm Gas In Active Galactic Nuclei, Susmita Chakravorty, Ajit K. Kembhavi, Martin Elvis, Gary J. Ferland, N. R. Badnell
Physics and Astronomy Faculty Publications
Understanding the thermal equilibrium (stability) curve may offer insights into the nature of the warm absorbers often found in active galactic nuclei. Its shape is determined by factors such as the spectrum of the ionizing continuum and the chemical composition of the gas. We find that the stability curves obtained under the same set of the above-mentioned physical factors, but using recently derived dielectronic recombination rates, give significantly different results, especially in the regions corresponding to warm absorbers, leading to different physical predictions. Using the current rates we find a larger probability of having a thermally stable warm absorber at …
The H Ii Region/Pdr Connection: Self-Consistent Calculations Of Physical Conditions In Star-Forming Regions, Nicholas Paul Abel, Gary J. Ferland, G. Shaw, Peter A. M. Van Hoof
The H Ii Region/Pdr Connection: Self-Consistent Calculations Of Physical Conditions In Star-Forming Regions, Nicholas Paul Abel, Gary J. Ferland, G. Shaw, Peter A. M. Van Hoof
Physics and Astronomy Faculty Publications
We have performed a series of calculations designed to reproduce infrared diagnostics used to determine physical conditions in star-forming regions. We self-consistently calculate the thermal and chemical structure of an H II region and photodissociation region (PDR) that are in pressure equilibrium. This differs from previous work, which used separate calculations for each gas phase. Our calculations span a wide range of stellar temperatures, gas densities, and ionization parameters. We describe improvements made to the spectral synthesis code Cloudy that made these calculations possible. These include the addition of a molecular network with ~1000 reactions involving 68 molecular species and …
Temperature Variations From Hubble Space Telescope Spectroscopy Of The Orion Nebula, R. H. Rubin, P. G. Martin, R. J. Dufour, Gary J. Ferland, K. P. M. Blagrave, X.-W. Liu, J. F. Nguyen, J. A. Baldwin
Temperature Variations From Hubble Space Telescope Spectroscopy Of The Orion Nebula, R. H. Rubin, P. G. Martin, R. J. Dufour, Gary J. Ferland, K. P. M. Blagrave, X.-W. Liu, J. F. Nguyen, J. A. Baldwin
Physics and Astronomy Faculty Publications
We present Hubble Space Telescope (HST)/STIS long-slit spectroscopy of NGC 1976. Our goal is to measure the intrinsic line ratio [O III] 4364/5008 and thereby evaluate the electron temperature (Te) and the fractional mean-square Te variation (t2A)across the nebula. We also measure the intrinsic line ratio [N II] 5756/6585 in order to estimate Te and t2A in the N+region. The interpretation of the [N II] data is not as clear cut as the [O III] data because of a higher sensitivity to knowledge …
Temperature Variations From Hubble Space Telescope Imagery And Spectroscopy Of Ngc 7009, R. H. Rubin, N. J. Bhatt, R. J. Dufour, B. A. Buckalew, M. J. Barlow, X.-W. Liu, P. J. Storey, B. Balick, Gary J. Ferland, J. P. Harrington, P. G. Martin
Temperature Variations From Hubble Space Telescope Imagery And Spectroscopy Of Ngc 7009, R. H. Rubin, N. J. Bhatt, R. J. Dufour, B. A. Buckalew, M. J. Barlow, X.-W. Liu, P. J. Storey, B. Balick, Gary J. Ferland, J. P. Harrington, P. G. Martin
Physics and Astronomy Faculty Publications
We present new Hubble Space Telescope (HST)/WFPC2 imagery and STIS long-slit spectroscopy of the planetary nebula NGC 7009. The primary goal was to obtain high spatial resolution of the intrinsic line ratio [O III] 4364/5008 and thereby evaluate the electron temperature (Te) and the fractional mean-square Te variation (tA2)across the nebula. The WFPC2 Temap is rather uniform; almost all values are between 9000–11 000 K, with the higher Te values closely coinciding with the inner He++ zone. The results indicate very small values–≲0.01– for …
Numerical Simulations Of Fe Ii Emission Spectra, E. M. Verner, D. A. Verner, K. T. Korista, Jason W. Ferguson, F. Hamann, Gary J. Ferland
Numerical Simulations Of Fe Ii Emission Spectra, E. M. Verner, D. A. Verner, K. T. Korista, Jason W. Ferguson, F. Hamann, Gary J. Ferland
Physics and Astronomy Faculty Publications
This paper describes the techniques that we have used to incorporate a large-scale model of the Fe+ ion and resulting Fe IIemission into CLOUDY, a spectral synthesis code designed to simulate conditions within a plasma and model the resulting spectrum. We describe the numerical methods we use to determine the level populations, mutual line overlap fluorescence, collisional effects, and the heating-cooling effects of the atom on its environment. As currently implemented, the atom includes the lowest 371 levels (up to 11.6 eV) and predicts intensities of 68,635 lines. We describe our data sources, which include the most recent transition …
Physical Conditions In Low-Ionization Regions Of The Orion Nebula, J. A. Baldwin, A. Crotts, R. J. Dufour, Gary J. Ferland, S. Heathcote, J. J. Hester, K. T. Korista, P. G. Martin, C. R. O'Dell, R. H. Rubin, A. G. G. M. Tielens, D. A. Verner, D. K. Walter, Z. Wen
Physical Conditions In Low-Ionization Regions Of The Orion Nebula, J. A. Baldwin, A. Crotts, R. J. Dufour, Gary J. Ferland, S. Heathcote, J. J. Hester, K. T. Korista, P. G. Martin, C. R. O'Dell, R. H. Rubin, A. G. G. M. Tielens, D. A. Verner, D. K. Walter, Z. Wen
Physics and Astronomy Faculty Publications
We reexamine the spectroscopic underpinnings of recent suggestions that [O I] and [Fe II] lines from the Orion H II region are produced in gas where the iron-carrying grains have been destroyed and the electron density is surprisingly high. Our new observations show that previous detections of [O I] 5577 were dominated by telluric emission. Our limits are consistent with a moderate density (≈ 104 cm-3) photoionized gas. We show that a previously proposed model of the Orion H II region reproduces the observed [O I] and [Fe II] spectrum. These lines are fully consistent with formation …