Physical Sciences and Mathematics | Open Access Articles

Structure And Feedback In 30 Doradus. I. Observations, E. W. Pellegrini, J. A. Baldwin, Gary J. Ferland

Physics and Astronomy Faculty Publications

We have completed a new optical imaging and spectrophotometric survey of a 140 × 80 pc² region of 30 Doradus centered on R136, covering key optical diagnostic emission lines including Hα, Hβ, Hγ, [O III] λλ4363, 4959, 5007, [N II] λλ6548, 6584, [SII] λλ6717, 6731 [S III] λ6312, and in some locations [S III] λ9069. We present maps of fluxes and intensity ratios for these lines, and catalogs of isolated ionizing stars, elephant-trunk pillars, and edge-on ionization fronts. The final science-quality spectroscopic data products are available to the public. Our analysis of the new data finds that, while stellar …

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Tuning The Morphology Of Au/Cds Nanocomposites Through Temperature-Controlled Reduction Of Gold-Oleate Complexes, Elena Khon, Nishshanka N. Hewa-Kasakarage, Ian Nemitz, Krishna Acharya, Mikhail Zamkov

Physics and Astronomy Faculty Publications

A general synthetic strategy for controlling the shape of gold domains grown onto CdS semiconductor nanocrystals is presented. The colloidal growth of Au nanoparticles is based on the temperature-controlled reduction of Au-oleate complexes on the surface of CdS and allows for precise tuning of nanoparticle diameters from 2.5 to 16 nm simply by adjusting the temperature of the growth solution, whereas the shape of Au/CdS nanocomposites can be controllably switched between matchsticks and barbells via the reaction rate. Depending on the exact morphology of Au and CdS domains, fabricated nanocomposites can undergo evaporation-induced self-assembly on a substrate either through end-to-end …

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On The Disappearance Of The Broad-Line Region In Low-Luminosity Active Galactic Nuclei, Moshe Elitzur, Luis C. Ho

Physics and Astronomy Faculty Publications

The disk-wind scenario for the broad-line region (BLR) and toroidal obscuration in active galactic nuclei (AGNs) predicts the disappearance of the BLR at low luminosities. In accordance with the model predictions, data from a nearly complete sample of nearby AGNs show that the BLR disappears at luminosities lower than 5 × 10³⁹(M/10⁷ M_⊙)^2/3 erg s^-1, where M is the black hole mass. The radiative efficiency of accretion onto the black hole is ≲10^-3 for these sources, indicating that their accretion is advection-dominated.

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Herschel Photometry Of Brightest Cluster Galaxies In Cooling Flow Clusters, A. C. Edge, J. B. R. Oonk, R. Mittal, S. W. Allen, S. A. Baum, H. Böhringer, J. N. Bregman, M. N. Bremer, F. Combes, C. S. Crawford, M. Donahue, E. Egami, A. C. Fabian, Gary J. Ferland, S. L. Hamer, N. A. Hatch, W. Jaffe, R. M. Johnstone, B. R. Mcnamara, C. P. O'Dea, P. Popesso, A. C. Quillen, P. Salomé, C. L. Sarazin, G. M. Voit, R. J. Wilman, M. W. Wise

Physics and Astronomy Faculty Publications

The dust destruction timescales in the cores of clusters of galaxies are relatively short given their high central gas densities. However, substantial mid-infrared and sub-mm emission has been detected in many brightest cluster galaxies. In this letter we present Herschel PACS and SPIRE photometry of the brightest cluster galaxy in three strong cooling flow clusters, A1068, A2597 and Zw3146. This photometry indicates that a substantial mass of cold dust is present (> 3×10⁷ M⊙) at temperatures significantly lower (20–28 K) than previously thought based on limited MIR and/or sub-mm results. The mass and temperature of the dust appear …

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A Sea Change In Eta Carinae, Andrea Mehner, Kris Davidson, Roberta M. Humphreys, John C. Martin, Kazunori Ishibashi, Gary J. Ferland, Nolan R. Walborn

Physics and Astronomy Faculty Publications

Major stellar-wind emission features in the spectrum of η Car have recently decreased by factors of order 2 relative to the continuum. This is unprecedented in the modern observational record. The simplest, but unproven, explanation is a rapid decrease in the wind density.

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Herschel Observations Of Fir Emission Lines In Brightest Cluster Galaxies, A. C. Edge, J. B. R. Oonk, R. Mittal, S. W. Allen, S. A. Baum, H. Böhringer, J. N. Bregman, M. N. Bremer, F. Combes, C. S. Crawford, M. Donahue, E. Egami, A. C. Fabian, Gary J. Ferland, S. L. Hamer, N. A. Hatch, W. Jaffe, R. M. Johnstone, B. R. Mcnamara, C. P. O'Dea, P. Popesso, A. C. Quillen, P. Salomé, C. L. Sarazin, G. M. Voit, R. J. Wilman, M. W. Wise

Physics and Astronomy Faculty Publications

The question of how much gas cools in the cores of clusters of galaxies has been the focus of many, multiwavelength studies in the past 30 years. In this letter we present the first detections of the strongest atomic cooling lines, [Cii], [Oi] and [Nii] in two strong cooling flow clusters, A1068 and A2597, using Herschel-PACS. These spectra indicate that the substantial mass of cold molecular gas (> 10⁹ M_⊙) known to be present in these systems is being irradiated by intense UV radiation, most probably from young stars. The line widths of these FIR lines …

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Herschel Images Of Ngc 6720: H2 Formation On Dust Grain, P. A. M. Van Hoof, G. C. Van De Steene, M. J. Barlow, K. M. Exter, B. Sibthorpe, T. Ueta, V. Peris, M. A. T. Groenewegen, J. A. D. L. Blommaert, M. Cohen, W. De Meester, Gary J. Ferland, W. K. Gear, H. L. Gomez, P. C. Hargrave, E. Huygen, R. J. Ivison, C. Jean, S. J. Leeks, T. L. Lim, G. Olofsson, E. T. Polehampton, S. Regibo, P. Royer, B. M. Swinyard, B. Vandenbussche, H. Van Winckel, C. Waelkens, H. J. Walker, R. Wesson

Physics and Astronomy Faculty Publications

Herschel PACS and SPIRE images have been obtained of NGC 6720 (the Ring nebula). This is an evolved planetary nebula with a central star that is currently on the cooling track, due to which the outer parts of the nebula are recombining. From the PACS and SPIRE images we conclude that there is a striking resemblance between the dust distribution and the H₂ emission, which appears to be observational evidence that H₂ forms on grain surfaces. We have developed a photoionization model of the nebula with the Cloudy code which we used to determine the physical conditions of …

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A Bright Molecular Core In A Crab Nebula Filament, E. D. Loh, J. A. Baldwin, Gary J. Ferland

Physics and Astronomy Faculty Publications

In a sub-arcsec near-infrared survey of the Crab Nebula using the new Spartan Infrared Camera, we have found several knots with high surface brightness in the H2 2.12 μm line and a very large H₂ 2.12 μm to Brγ ratio. The brightest of these knots has an intensity ratio I(H₂ 2.12 μm)/I(Brγ) = 18 ± 9, which we show sets a lower limit on the ratio of masses in the molecular and recombination (i.e., ionized) zones M _mol/M _rec ≥ 0.9, and a total molecular mass within this single knot M _mol ≥ …

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A Bare Molecular Cloud At Z ~ 0.45*, Therese M. Jones, Toru Misawa, Jane C. Charlton, Andrew C. Mshar, Gary J. Ferland

Physics and Astronomy Faculty Publications

Several neutral species (Mg I, Si I, Ca I, Fe I) have been detected in a weak Mg II absorption line system (W_r (2796) ~ 0.15 Å) at z ~ 0.45 along the sightline toward HE0001-2340. These observations require extreme physical conditions, as noted in D'Odorico. We place further constraints on the properties of this system by running a wide grid of photoionization models, determining that the absorbing cloud that produces the neutral absorption is extremely dense (~100-1000 cm^-3), cold (< 100 K), and has significant molecular content (~72%-94%). Structures of this size and temperature have been detected in Milky Way CO surveys and have been predicted in hydrodynamic simulations of turbulent gas. In order to explain the observed line profiles in all neutral and singly ionized chemical transitions, the lines must suffer from unresolved saturation and/or the absorber must partially cover the broad emission line region of the background quasar. In addition to this highly unusual cloud, three other ordinary weak Mg II clouds (within densities of ~0.005 cm^-3 and temperatures of ~10, 000 K) lie within 500 km s^-1 along the …

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Luminosity-Variation Independent Location Of The Circum-Nuclear, Hot Dust In Ngc 4151, Jorg-Uwe Pott, Matt A. Malkan, Moshe Elitzur, Andrea M. Ghez, Tom M. Herbst, Rainer Schödel, Julien Woillez

Physics and Astronomy Faculty Publications

After recent sensitivity upgrades at the Keck Interferometer (KI), systematic interferometric 2 μm studies of the innermost dust in nearby Seyfert nuclei are within observational reach. Here, we present the analysis of new interferometric data of NGC 4151, discussed in context of the results from recent dust reverberation, spectro-photometric, and interferometric campaigns. The complete data set gives a complex picture, in particular the measured visibilities from now three different nights appear to be rather insensitive to the variation of the nuclear luminosity. KI data alone indicate two scenarios: the K-band emission is either dominated to ~90% by size …

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A Balloon Sounding Technique For Measuring So2 Plumes, Gary A. Morris, Walter D. Komhyr, Jun Hirokawa, James Flynn, Barry Lefer, Nicholay Krotokov, Fong Ngan

Physics and Astronomy Faculty Publications

This paper reports on the development of a new technique for inexpensive measurements of SO2 profiles using a modified dual-ozonesonde instrument payload. The presence of SO2 interferes with the standard electrochemical cell (ECC) ozonesonde measurement, resulting in –1 molecule of O3 reported for each molecule of SO2 present (provided [O3].[SO2]). In laboratory tests, an SO2 filter made with CrO3 placed on the inlet side of the sonde removes nearly 100% of the SO2 present for concentrations up to 60 ppbv and remained effective after exposure to 2.8 3 1016 molecules of SO2 [equivalent to a column ;150 DU (1 DU …

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High-Excitation Emission Lines Near Eta Carinae, And Its Likely Companion Star, Andrea Mehner, Kris Davidson, Gary J. Ferland, Roberta M. Humphreys

Physics and Astronomy Faculty Publications

In order to study the distribution of gas and ionizing radiation around η Car and their implications for its likely companion star, we have examined high-excitation emission lines of [Ne III], [Fe III], etc., in spectra obtained with the Hubble Space Telescope/Space Telescope Imaging Spectrograph instrument during 1998-2004. Our principal results, some of them unexpected, are as follows. (1) The high-excitation fluxes varied systematically and non-trivially throughout η Car's 5.5 year spectroscopic cycle. Instead of rising to a plateau after the 1998 ''event,'' they changed continuously with a maximum in mid-cycle. (2) At one significant location a brief, strong …

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Observations Of Ozone Production In A Dissipating Tropical Convective Cell During Tc4, Gary A. Morris, A. M. Thompson, K. E. Pickering, S. Chen, E. J. Bucsela, P. A. Kucera

Physics and Astronomy Faculty Publications

From 13 July–9 August 2007, 25 ozonesondes were launched from Las Tablas, Panama as part of the Tropical Composition, Cloud, and Climate Coupling (TC4) mission. On 5 August, a strong convective cell formed in the Gulf of Panama. World Wide Lightning Location Network (WWLLN) data indicated 563 flashes (09:00–17:00 UTC) in the Gulf. NO2 data from the Ozone Monitoring Instrument (OMI) show enhancements, suggesting lightning production of NOx. At 15:05 UTC, an ozonesonde ascended into the southern edge of the now dissipating convective cell as it moved west across the Azuero Peninsula. The balloon oscillated from 2.5–5.1 km five times …

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Distance To U Pegasi By The Dde Algorithm, Todd R. Vaccaro, Dirk Terrell, Robert E. Wilson

Physics and Astronomy Faculty Publications

A distance is found for the W UMa type binary U Pegasi, with a newly modified version of the Wilson-Devinney program (W-D) that makes use of the direct distance estimation (DDE) algorithm. The reported distance of d=123.6pc is an average based on solutions for B and V data and a primary star temperature of 5800K. Standardized light curves (not differential), radial velocities, and a spectroscopic primary star temperature are input to the program. Differential corrections were performed for each light curve band along with the velocities for two primary temperatures that span 100K. Log₁₀d is a model parameter …

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Full-Text Articles in Physical Sciences and Mathematics

Structure And Feedback In 30 Doradus. I. Observations, E. W. Pellegrini, J. A. Baldwin, Gary J. Ferland

Physics and Astronomy Faculty Publications

Tuning The Morphology Of Au/Cds Nanocomposites Through Temperature-Controlled Reduction Of Gold-Oleate Complexes, Elena Khon, Nishshanka N. Hewa-Kasakarage, Ian Nemitz, Krishna Acharya, Mikhail Zamkov

Physics and Astronomy Faculty Publications

On The Disappearance Of The Broad-Line Region In Low-Luminosity Active Galactic Nuclei, Moshe Elitzur, Luis C. Ho

Physics and Astronomy Faculty Publications

Physics and Astronomy Faculty Publications

A Sea Change In Eta Carinae, Andrea Mehner, Kris Davidson, Roberta M. Humphreys, John C. Martin, Kazunori Ishibashi, Gary J. Ferland, Nolan R. Walborn

Physics and Astronomy Faculty Publications

Physics and Astronomy Faculty Publications

Physics and Astronomy Faculty Publications

A Bright Molecular Core In A Crab Nebula Filament, E. D. Loh, J. A. Baldwin, Gary J. Ferland

Physics and Astronomy Faculty Publications

A Bare Molecular Cloud At Z ~ 0.45*, Therese M. Jones, Toru Misawa, Jane C. Charlton, Andrew C. Mshar, Gary J. Ferland

Physics and Astronomy Faculty Publications

Luminosity-Variation Independent Location Of The Circum-Nuclear, Hot Dust In Ngc 4151, Jorg-Uwe Pott, Matt A. Malkan, Moshe Elitzur, Andrea M. Ghez, Tom M. Herbst, Rainer Schödel, Julien Woillez

Physics and Astronomy Faculty Publications

A Balloon Sounding Technique For Measuring So2 Plumes, Gary A. Morris, Walter D. Komhyr, Jun Hirokawa, James Flynn, Barry Lefer, Nicholay Krotokov, Fong Ngan

Physics and Astronomy Faculty Publications

High-Excitation Emission Lines Near Eta Carinae, And Its Likely Companion Star, Andrea Mehner, Kris Davidson, Gary J. Ferland, Roberta M. Humphreys

Physics and Astronomy Faculty Publications

Observations Of Ozone Production In A Dissipating Tropical Convective Cell During Tc4, Gary A. Morris, A. M. Thompson, K. E. Pickering, S. Chen, E. J. Bucsela, P. A. Kucera

Physics and Astronomy Faculty Publications

Distance To U Pegasi By The Dde Algorithm, Todd R. Vaccaro, Dirk Terrell, Robert E. Wilson

Physics and Astronomy Faculty Publications