Complete spectral energy distribution of the hot, helium-rich white dwarf RX J0503.9-2854

In the line-of-sight toward the DO-type white dwarf RX J0503.9-2854, the density of the interstellar medium (ISM) is very low, and thus the contamination of the stellar spectrum almost negligible. This allows us to identify many metal lines in a wide wavelength range from the extreme ultraviolet to the near infrared. In previous spectral analyses, many metal lines in the ultraviolet spectrum of RX J0503.9-2854 have been identified. A complete line list of observed and identified lines is presented here. We compared synthetic spectra that had been calculated from model atmospheres in non-local thermodynamical equilibrium, with observations. In total, we identified 1272 lines (279 of them were newly assigned) in the wavelength range from the extreme ultraviolet to the near infrared. 287 lines remain unidentified. A close inspection of the EUV shows that still no good fit to the observed shape of the stellar continuum flux can be achieved although He, C, N, O, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Cr, Ni Zn, Ga, Ge, As, Kr, Zr, Mo, Sn, Xe, and Ba are included in the stellar atmosphere models. There are two possible reasons for the deviation between observed and synthetic flux in the EUV. Opacities from hitherto unconsidered elements in the model-atmosphere calculation may be missing and/or the effective temperature is slightly lower than previously determined.Comment: 92 pages, 45 figure

The virtual observatory service TheoSSA: Establishing a database of synthetic stellar flux standards. II. NLTE spectral analysis of the OB-type subdwarf Feige 110

In the framework of the Virtual Observatory (VO), the German Astrophysical Virtual Observatory (GAVO) developed the registered service TheoSSA (Theoretical Stellar Spectra Access). It provides easy access to stellar spectral energy distributions (SEDs) and is intended to ingest SEDs calculated by any model-atmosphere code, generally for all effective temperature, surface gravities, and elemental compositions. We will establish a database of SEDs of flux standards that are easily accessible via TheoSSA's web interface. The OB-type subdwarf Feige 110 is a standard star for flux calibration. State-of-the-art non-local thermodynamic equilibrium (NLTE) stellar-atmosphere models that consider opacities of species up to trans-iron elements will be used to provide a reliable synthetic spectrum to compare with observations. In case of Feige 110, we demonstrate that the model reproduces not only its overall continuum shape from the far-ultraviolet (FUV) to the optical wavelength range but also the numerous metal lines exhibited in its FUV spectrum. We present a state-of-the-art spectral analysis of Feige 110. We determined $T_\mathrm{eff} = 47\,250 \pm 2000\,\mathrm{K}$, $\log g = 6.00 \pm 0.20$ and the abundances of He, N, P, S, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, and Ge. Ti, V, Mn, Co, Zn, and Ge were identified for the first time in this star. Upper abundance limits were derived for C, O, Si, Ca, and Sc. The TheoSSA database of theoretical SEDs of stellar flux standards guarantees that the flux calibration of astronomical data and cross-calibration between different instruments can be based on models and SEDs calculated with state-of-the-art model-atmosphere codes.Comment: 19 pages, 7 figure

Stellar laboratories. IX. New Se V, Sr IV - VII, Te VI, and I VI oscillator strengths and the Se, Sr, Te, and I abundances in the hot white dwarfs G191-B2B and RE 0503-289

To analyze spectra of hot stars, advanced non-local thermodynamic equilibrium (NLTE) model-atmosphere techniques are mandatory. Reliable atomic data is for the calculation of such model atmospheres. We aim to calculate new Sr IV - VII oscillator strengths to identify for the first time Sr spectral lines in hot white dwarf (WD) stars and to determine the photospheric Sr abundances. o measure the abundances of Se, Te, and I in hot WDs, we aim to compute new Se V, Te VI, and I VI oscillator strengths. To consider radiative and collisional bound-bound transitions of Se V, Sr IV - VII, Te VI, and I VI in our NLTE atmosphere models, we calculated oscillator strengths for these ions. We newly identified four Se V, 23 Sr V, 1 Te VI, and three I VI lines in the ultraviolet (UV) spectrum of RE0503-289. We measured a photospheric Sr abundance of 6.5 +3.8/-2.4 x 10**-4 (mass fraction, 9500 - 23800 times solar). We determined the abundances of Se (1.6 +0.9/-0.6 x 10**-3, 8000 - 20000), Te (2.5 +1.5/-0.9 x 10**-4, 11000 - 28000), and I (1.4 +0.8/-0.5 x 10**-5, 2700 - 6700). No Se, Sr, Te, and I line was found in the UV spectra of G191-B2B and we could determine only upper abundance limits of approximately 100 times solar. All identified Se V, Sr V, Te VI, and I VI lines in the UV spectrum of RE0503-289 were simultaneously well reproduced with our newly calculated oscillator strengths.Comment: 26 pages, 5 figure

Energy Flow in Acoustic Black Holes

We present the results of an analysis of superradiant energy flow due to scalar fields incident on an acoustic black hole. In addition to providing independent confirmation of the recent results in [5], we determine in detail the profile of energy flow everywhere outside the horizon. We confirm explicitly that in a suitable frame the energy flow is inward at the horizon and outward at infinity, as expected on physical grounds.Comment: 8 pages, 9 figures, Comments added to discussion of energy flow and introductory section abbreviate

Magnetic properties of iron cluster/chromium matrix nanocomposites

A custom-designed apparatus was used for the fine-tuned co-deposition of preformed Fe clusters into antiferromagnetic Cr matrices. Three series of samples with precisely defined cluster sizes, with accuracy to a few atoms, and controlled concentrations were fabricated, followed by a complete characterization of structure and magnetic performance. Relevant magnetic characteristics, reflecting the ferromagnetic/antiferromagnetic coupling between Fe clusters and the Cr matrix, i.e., blocking temperature, coercivity field, and exchange bias were measured and their dependence on cluster size and cluster concentration in the matrix was analyzed. It is evident that the blocking temperatures are clearly affected by both the cluster size and their concentration in the Cr matrix. In contrast the coercivity shows hardly any dependence on size or inter-cluster distance. The exchange bias was found to be strongly sensitive to the cluster size but not to the inter-cluster distances. Therefore, it was concluded to be an effect that is purely localized at the interfaces

Tornadic Behavior Related to Land-Falling Tropical Cyclones in the United States

The 2004 and 2005 North Atlantic hurricane seasons were among the most active and economically devastating for the United States, during which 18 tropical cyclones (TCs) made landfall. These TCs were analyzed using the International Best Tracks Archive for Climate Stewardship (IBTrACS) and Local Storm Reports (LSR) datasets to determine whether they produced tornadoes within a preferred quadrant and distance from the center of circulation of the TC. The land-falling TCs were tracked and analyzed through their weakening stages with tornado reports being classified based on the strength of the TC at the time of occurrence. Tornado reports were not included after the TC was classified as extratropical in the IBTrACS dataset. Over half of all tornado reports occurred when the TCs were rated at or below tropical storm strength. As expected, the northeast quadrant was the most dominate area where tornadic activity occurred. In addition, there were three distinct peaks in tornadic activity at distances of 75-100nm, 175-200nm, and 325-375nm from the center of the circulation. Another emphasis of this work used NEXRAD data to determine the best method of identifying potential tornadic storms within land-falling TCS. The most reliable radar product for the three TCs investigated was velocity couplets

Tornadic Behavior Related to Land-Falling Tropical Cyclones in the United States

The 2004 and 2005 North Atlantic hurricane seasons were among the most active and economically devastating for the United States, during which 18 tropical cyclones (TCs) made landfall. These TCs were analyzed using the International Best Tracks Archive for Climate Stewardship (IBTrACS) and Local Storm Reports (LSR) datasets to determine whether they produced tornadoes within a preferred quadrant and distance from the center of circulation of the TC. The land-falling TCs were tracked and analyzed through their weakening stages with tornado reports being classified based on the strength of the TC at the time of occurrence. Tornado reports were not included after the TC was classified as extratropical in the IBTrACS dataset. Over half of all tornado reports occurred when the TCs were rated at or below tropical storm strength. As expected, the northeast quadrant was the most dominate area where tornadic activity occurred. In addition, there were three distinct peaks in tornadic activity at distances of 75-100nm, 175-200nm, and 325-375nm from the center of the circulation. Another emphasis of this work used NEXRAD data to determine the best method of identifying potential tornadic storms within land-falling TCS. The most reliable radar product for the three TCs investigated was velocity couplets