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Full-Text Articles in Physics
Spitzer Reveals What Is Behind Orion's Bar, Robert H. Rubin, Janet P. Simpson, C. R. O'Dell, Ian A. Mcnabb, Sean W. J. Colgan, Scott Y. Zhuge, Gary J. Ferland, Sergio A. Hidalgo
Spitzer Reveals What Is Behind Orion's Bar, Robert H. Rubin, Janet P. Simpson, C. R. O'Dell, Ian A. Mcnabb, Sean W. J. Colgan, Scott Y. Zhuge, Gary J. Ferland, Sergio A. Hidalgo
Physics and Astronomy Faculty Publications
We present Spitzer Space Telescope observations of 11 regions south-east (SE) of the Bright Bar in the Orion Nebula, along a radial from the exciting star θ1 Ori C, extending from 2.6 to 12.1 arcmin. Our Cycle 5 programme obtained deep spectra with matching Infrared Spectrograph (IRS) short-high (SH) and long-high (LH) aperture grid patterns. Most previous IR missions observed only the inner few arcmin (the ‘Huygens’ Region). The extreme sensitivity of Spitzer in the 10–37 μm spectral range permitted us to measure many lines of interest to much larger distances from θ1 Ori C. Orion is the …
Fluorescent Excitation Of Balmer Lines In Gaseous Nebulae: Case D, V. Luridiana, S. Simón-Díaz, M. Cerviño, R. M. González Delgado, R. L. Porter, Gary J. Ferland
Fluorescent Excitation Of Balmer Lines In Gaseous Nebulae: Case D, V. Luridiana, S. Simón-Díaz, M. Cerviño, R. M. González Delgado, R. L. Porter, Gary J. Ferland
Physics and Astronomy Faculty Publications
Nonionizing stellar continua are a potential source of photons for continuum pumping in the hydrogen Lyman transitions. In the environments where these transitions are optically thick, de-excitation occurs through higher series lines. As a result, the emitted flux in the affected lines has a fluorescent contribution in addition to the usual recombination one; in particular, Balmer emissivities are systematically enhanced above case B predictions. The effectiveness of such a mechanism in H II regions and the adequacy of photoionization models as a tool to study it are the two main focuses of this work. We find that photoionization models of …
Properties Of Warm Absorbers In Active Galaxies: A Systematic Stability Curve Analysis, Susmita Chakravorty, Ajit K. Kembhavi, Martin Elvis, Gary J. Ferland
Properties Of Warm Absorbers In Active Galaxies: A Systematic Stability Curve Analysis, Susmita Chakravorty, Ajit K. Kembhavi, Martin Elvis, Gary J. Ferland
Physics and Astronomy Faculty Publications
Signatures of warm absorbers are seen in soft X-ray spectra of about half of all type 1 Seyfert galaxies observed and in some quasars and blazars. We use the thermal equilibrium curve to study the influence of the shape of the ionizing continuum, density and the chemical composition of the absorbing gas on the existence and nature of the warm absorbers. We describe circumstances in which a stable warm absorber can exist as a multiphase medium or one with continuous variation in pressure. In particular, we find the following results: (i) the warm absorber exists only if the spectral index …
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 …
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 …
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 …