An analysis of the peculiar A star HD 204411.
Model atmosphere analysis of line identifications and equivalent width data for relatively cool Ap star HD 204411, discussing atmospheric composition
Sargent, W. L. W.↗
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OSCILLATION-DRIVEN MAGNETOSPHERIC ACTIVITY IN PULSARS
We study the magnetospheric activity in the polar cap region of pulsars under stellar oscillations. The toroidal oscillation of the star propagates into the magnetosphere, which provides additional voltage due to unipolar induction, changes Goldreich-Julian charge density from the traditional value due to rotation, and hence influences particle acceleration. We present a general solution of the effect of oscillations within the framework of the inner vacuum gap model and consider three different inner gap modes controlled by curvature radiation, inverse Compton scattering, and two-photon annihilation, respectively. With different pulsar parameters and oscillation amplitudes, one of three modes would play a dominant role in defining the gap properties. When the amplitude of oscillation exceeds a critical value, mode changing occurs. Oscillations also lead to a change of the size of the polar cap. As applications, we show the inner gap properties under oscillations in both normal pulsars and anomalous X-ray pulsars/soft gamma-ray repeaters (AXPs/SGRs). We interpret the onset of radio emission after glitches/flares in AXPs/SGRs as due to oscillation-driven magnetic activities in these objects, within the framework of both the magnetar model and the solid quark star model. Within the magnetar model, radio activation may be caused by the enlargement of the effective polar cap angle and the radio emission beam due to oscillation, whereas within the solid quark star angle, it may be caused by activation of the pulsar inner gap from below the radio emission death line due to an oscillation-induced voltage enhancement. The model can also explain the glitch-induced radio profile change observed in PSR J1119–6127.
79 ASTRONOMY AND ASTROPHYSICS↗
OPTICAL SPECTROSCOPY OF H{alpha} FILAMENTS IN COOL CORE CLUSTERS: KINEMATICS, REDDENING, AND SOURCES OF IONIZATION
We have obtained deep, high spatial and spectral resolution, long-slit spectra of the H{alpha} nebulae in the cool cores of nine galaxy clusters. This sample provides a wealth of information on the ionization state, kinematics, and reddening of the warm gas in the cool cores of galaxy clusters. We find evidence for only small amounts of reddening in the extended, line-emitting filaments, with the majority of filaments having E(B - V) < 0.2. We find, in agreement with previous works, that the optical emission in cool core clusters has elevated low-ionization line ratios. The combination of [O III]/H{beta}, [N II]/H{alpha}, [S II]/H{alpha}, and [O I]/H{alpha} allow us to rule out collisional ionization by cosmic rays, thermal conduction, and photoionization by intracluster medium (ICM) X-rays and active galactic nuclei as strong contributors to the ionization in the bulk of the optical line-emitting gas in both the nuclei and filaments. The data are adequately described by a composite model of slow shocks and star formation. This model is further supported by an observed correlation between the line widths and low-ionization line ratios which becomes stronger in systems with more modest star formation activity based on far-ultraviolet observations. We find that the more extended, narrow filaments tend to have shallower velocity gradients and narrower line widths than the compact filamentary complexes. We confirm that the widths of the emission lines decrease with radius, from FWHM {approx}600 km s{sup -1} in the nuclei to FWHM {approx}100 km s{sup -1} in the most extended filaments. The variation of line width with radius is vastly different than what is measured from stellar absorption lines in a typical giant elliptical galaxy, suggesting that the velocity width of the warm gas may in fact be linked to ICM turbulence and, thus, may provide a glimpse into the amount of turbulence in cool cores. In the central regions (r < 10 kpc) of several systems the warm gas shows kinematic signatures consistent with rotation, consistent with earlier work. We find that the kinematics of the most extended filaments in this sample are broadly consistent with both infall and outflow, and recommend further studies linking the warm gas kinematics to both radio and X-ray maps in order to further understand the observed kinematics.
79 ASTRONOMY AND ASTROPHYSICS↗
ON THE ROLE OF FAST MAGNETIC RECONNECTION IN ACCRETING BLACK HOLE SOURCES
We attempt to explain the observed radio and gamma-ray emission produced in the surroundings of black holes by employing a magnetically dominated accretion flow model and fast magnetic reconnection triggered by turbulence. In earlier work, a standard disk model was used and we refine the model by focusing on the sub-Eddington regime to address the fundamental plane of black hole activity. The results do not change substantially with regard to previous work, ensuring that the details of accretion physics are not relevant in the magnetic reconnection process occurring in the corona. Rather, our work puts fast magnetic reconnection events as a powerful mechanism operating in the core region near the jet base of black hole sources on more solid ground. For microquasars and low-luminosity active galactic nuclei, the observed correlation between radio emission and the mass of the sources can be explained by this process. The corresponding gamma-ray emission also seems to be produced in the same core region. On the other hand, emission from blazars and gamma-ray bursts cannot be correlated to core emission based on fast reconnection.
79 ASTRONOMY AND ASTROPHYSICS↗
On the nature of the ionizing agents of the interstellar medium.
The ionization structure of the interstellar trace elements predicted by the steady-state cosmic-ray, X-ray, and ultraviolet star ionization models, even when allowance is made for the stellar H II region, is in disagreement with satellite observations of at least two stars. The conclusion is reached that, in some regions of the Galaxy, the flux of cosmic rays or X-rays is much smaller than was thought previously.
Meszaros, P.↗
Evolution and detectability of comet clouds during post-main-sequence stellar evolution
The destruction of volatile-rich comet disks and Oort-type clouds around luminous post-main-sequence stars is modeled. The models are in agreement with several aspects of existing observations of water and complex molecules in the envelopes of giant and supergiant stars. If confirmed, these results would establish the common existence of Oort-type clouds around other stars and would constitute indirect evidence for sites of past planetary formation.
Stern, S. Alan↗
MULTI-ZONE MODELS OF SUPERBURSTS FROM ACCRETING NEUTRON STARS
Superbursts are rare and energetic thermonuclear carbon flashes observed to occur on accreting neutron stars. We create the first multi-zone models of series of superbursts using a stellar evolution code. We self-consistently build up the fuel layer at different rates, spanning the entire range of observed mass accretion rates for superbursters. For all models light curves are presented. They generally exhibit a shock breakout, a precursor burst due to shock heating, and a two-component power-law decay. Shock heating alone is sufficient for a bright precursor that follows the shock breakout on a short dynamical timescale due to the fallback of expanded layers. Models at the highest accretion rates, however, lack a shock breakout, precursor, and the first power-law decay component. The ashes of the superburst that form the outer crust are predominantly composed of iron, but a superburst leaves a silicon-rich layer behind in which the next one ignites. Comparing the model light curves to an observed superburst from 4U 1636-53, we find for our accretion composition the best agreement with a model at three times the observed accretion rate. We study the dependence on crustal heating of observables such as the recurrence time and the decay timescale. It remains difficult, however, to constrain crustal heating if there is no good match with the observed accretion rate, as we see for 4U 1636-53.
79 ASTRONOMY AND ASTROPHYSICS↗
The Detectability of Exo-Earths and Super-Earths via Resonant Signatures in Exozodiacal Clouds
Directly imaging extrasolar terrestrial planets necessarily means contending with the astrophysical noise of exozodiacal dust and the resonant structures created by these planets in exozodiacal clouds. Using a custom tailored hybrid symplectic integrator we have constructed 120 models of resonant structures created by exo-Earths and super-Earths on circular orbits interacting with collisionless steady-state dust clouds around a Sun-like star. Our models include enough particles to overcome the limitations of previous simulations that were often dominated by a handful of long-lived particles, allowing us to quantitatively study the contrast of the resulting ring structures. We found that in the case of a planet on a circular orbit, for a given star and dust source distribution, the morphology and contrast of the resonant structures depend on only two parameters: planet mass and (square root)ap/Beta, where ap is the planet's semi-major axis and Beta is the ratio of radiation pressure force to gravitational force on a grain. We constructed multiple-grain-size models of 25,000 particles each and showed that in a collisionless cloud, a Dohnanyi crushing law yields a resonant ring whose optical depth is dominated by the largest grains in the distribution, not the smallest. We used these models to estimate the mass of the lowest-mass planet that can be detected through observations of a resonant ring for a variety of assumptions about the dust cloud and the planet's orbit. Our simulations suggest that planets with mass as small as a few times Mars' mass may produce detectable signatures in debris disks at ap greater than or approximately equal to 10 AU.
Stark, Christopher C.↗
Quantum crystals in neutron stars
Using the many-body techniques appropriate for quantum crystals it is shown that the deep interior of a neutron star is most likely an orderly arrangement of neutrons, protons and hyperons forming a solid. It is shown that a liquid or gas arrangement would produce higher energy. If so, a neutron star can be viewed as two solids (crust and core) permeated by a layer of ordinary or (perhaps) superfluid liquid. Astronomical evidence is in favor of such a structure: the sudden jumps in the periods of the Crab and Vela pulsars that differ by a factor of about 100 can be easily explained by the star-quake model. If the Crab is less massive than Vela (i.e., if it is not dense enough to have a solid core), the star-quakes take place in the crust whereas for Vela they occur in the core.
Canuto, V.↗
KELT-22Ab: A Massive, Short-Period Hot Jupiter Transiting a Near-solar Twin
We present the discovery of KELT-22Ab, a hot Jupiter from the KELT-South survey. KELT-22Ab transits the moderately bright (V11.1) Sun-like G2V star TYC 7518-468-1. The planet has an orbital period of P = 1.3866529 0.0000027 days, a radius of = -R 1.285+ R P 0.071 J 0.12 , and a relatively large mass of = - M 3.47+ M P 0.14 J 0.15 . The star has = - + R 1.099 0.046 R 0.079 , = - + M 1.092 0.041 M 0.045 , = - T 5767+ eff 49 50 K, = - log g 4.393+0.0600.039 (cgs), and [m/H]=+ -0.259+0.0830.085; thus other than its slightly super-solar metallicity, it appears to be a near-solar twin. Surprisingly, KELT-22A exhibits kinematics and a Galactic orbit that are somewhat atypical for thin-disk stars. Nevertheless, the star is rotating rapidly for its estimated age, and shows evidence of chromospheric activity. Imaging reveals a slightly fainter companion to KELT-22A that is likely bound, with a projected separation of 6″ (∼1400 au). In addition to the orbital motion caused by the transiting planet, we detect a possible linear trend in the radial velocity of KELT-22A, suggesting the presence of another relatively nearby body that is perhaps non-stellar. KELT-22Ab is highly irradiated (as a consequence of the small semimajor axis of a R = 4.97), and is mildly inflated. At such small separations, tidal forces become significant. The configuration of this system is optimal for measuring the rate of tidal dissipation within the host star. Our models predict that, due to tidal forces, the semimajor axis is decreasing rapidly, and KELT-22Ab is predicted to spiral into the star within the next Gyr.
Knicole Colon↗
Nonequilibrium effects on stability of hybrid stars with first-order phase transitions
The stability of hybrid stars with first-order phase transitions as determined by calculating fundamental radial oscillation modes is known to differ from the predictions of the widely used Bardeen-Thorne-Meltzer criterion. We consider the effects of out-of-chemical-equilibrium physics on the radial modes and hence stability of these objects. For a barotropic equation of state, this is done by allowing the adiabatic sound speed to differ from the equilibrium sound speed. We show that doing so extends the stable branches of stellar models, allowing stars with rapid phase transitions to support stable higher-order stellar multiplets similarly to stars with multiple slow phase transitions. We also derive a new junction condition to impose on the oscillation modes at the phase transition. Termed the reactive condition, it is physically motivated, consistent with the generalized junction conditions between two phases, and has the common rapid and slow conditions as limiting cases. Unlike the two common cases, it can only be applied to nonbarotropic stars. Here, we apply this junction condition to hybrid stellar models generated using a two-phase equation of state consisting of nuclear matter with unpaired quark matter at high densities joined by a first-order phase transition and show that, like in the slow limiting case, stars that are classically unstable are stabilized by a finite chemical reaction speed.
79 ASTRONOMY AND ASTROPHYSICS↗
Stellar chromospheres
The interpretation of stellar chromospheric line intensities and widths is discussed, and semiempirical chromospheric models of single stars are reviewed. Theoretical chromospheric models based on the short period acoustic wave theory are shown to have promise for explaining the heating of the lower chromospheres of quiet chromosphere stars, but are inadequate to explain the heating of transition regions and coronae of active chromosphere stars and solar plages. Attention is given to the Wilson-Bappu (1957) relation between the widths of the Ca II H and K line emission cores and stellar absolute luminosity, while an examination of the calculations of Basri (1979) reveals that it is essential to solve the transfer equation properly before studying the physical basis of width-luminosity relations. Also considered are theoretical calculations of profiles of optically thick chromospheric lines in the presence of systematic flow patterns.
Linsky, J. L.↗
A COMBINED VERY LARGE TELESCOPE AND GEMINI STUDY OF THE ATMOSPHERE OF THE DIRECTLY IMAGED PLANET, β PICTORIS b
We analyze new/archival VLT/NaCo and Gemini/NICI high-contrast imaging of the young, self-luminous planet β Pictoris b in seven near-to-mid IR photometric filters, using advanced image processing methods to achieve high signal-to-noise, high precision measurements. While β Pic b's near-IR colors mimic those of a standard, cloudy early-to-mid L dwarf, it is overluminous in the mid-infrared compared to the field L/T dwarf sequence. Few substellar/planet-mass objects—i.e., κ And b and 1RXJ 1609B—match β Pic b's JHK{sub s}L' photometry and its 3.1 μm and 5 μm photometry are particularly difficult to reproduce. Atmosphere models adopting cloud prescriptions and large (∼60 μm) dust grains fail to reproduce the β Pic b spectrum. However, models incorporating thick clouds similar to those found for HR 8799 bcde, but also with small (a few microns) modal particle sizes, yield fits consistent with the data within the uncertainties. Assuming solar abundance models, thick clouds, and small dust particles ((a) = 4 μm), we derive atmosphere parameters of log (g) = 3.8 ± 0.2 and T{sub eff} = 1575-1650 K, an inferred mass of 7{sup +4}{sub -3} M{sub J} , and a luminosity of log(L/L{sub ☉}) ∼–3.80 ± 0.02. The best-estimated planet radius, ≈1.65 ± 0.06 R{sub J} , is near the upper end of allowable planet radii for hot-start models given the host star's age and likely reflects challenges constructing accurate atmospheric models. Alternatively, these radii are comfortably consistent with hot-start model predictions if β Pic b is younger than ≈7 Myr, consistent with a late formation well after its host star's birth ∼12{sup +8}{sub -4} Myr ago.
79 ASTRONOMY AND ASTROPHYSICS↗
Numerical Simulation of Irradiation Induced Swelling for STAR 4.1 Blanket
Here, this article presents the preliminary results of FEM implementation of irradiation-induced swelling, hardening, and creep effect using ANSYS user programmable features (UPFs) applied to material properties. The first liquid metal breeding blanket model for STAR 4.1 tokamak as a part of the virtual prototyping system is under development at Princeton Plasma Physics Laboratory (PPPL). Intense neutron irradiation produces significant changes in the physical and mechanical properties of Fe-(8%–9%)Cr-based reduced activation ferritic martensitic (RAFM) steels. An ANSYS model of the breeding blanket was built to involve these irradiation-induced material property changes with neutron fluence distribution mapped from the MCNP model. Simulation results show that significant structure deformation forms from nuclear swelling, stress, and plastic strain arising from DPA gradient through wall thickness. The material degradation effect is not negligible. This modeling feature can either assist in analyzing the structural behaviors with the influence of nuclear swelling or provide guidance to design the structure to withstand irradiation.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Radiative transfer in spherical circumstellar dust envelopes. III - Dust envelope models of some well known infrared stars
The radiative transfer techniques described elsewhere by the author have been employed to construct dust envelope models of several well known infrared stars. The resulting calculations indicate that the infrared emissivity of circumstellar grains generally must be higher than that which many calculations of small nonsilicate grains yield. This conclusion is dependent to some degree on the (unknown) size of the stellar envelopes considered, but is quite firm in the case of the spatially resolved envelope of IRC + 10216. Further observations of the spatial distribution of the infrared radiation from stellar envelopes will be invaluable in deciphering the properties of the circumstellar grains.
Apruzese, J. P.↗
Maximum mass of hyperon stars with the Nijmegen ESC08 model
We perform Brueckner-Hartree-Fock calculations of hypernuclear matter employing the recent Nijmegen ESC08 hyperon-nucleon potentials, provide useful parametrizations of the numerical results, and compute the structure of hyperon (neutron) stars within this approach. Very low maximum masses below 1.4 solar masses are found.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
CNO abundances and hydrodynamic models of the nova outburst. III - 0.5 solar mass models with enhanced carbon, oxygen, and nitrogen
Consideration of the evolution of thermonuclear runaways in the hydrogen-rich envelopes of 0.5 solar mass carbon-oxygen white dwarfs. The larger radii of these stars, compared with the 1.00 solar mass white dwarfs, results in a lesser degree of degeneracy at the same depth in the star. Four models of luminosity with .00355 solar luminosity, differing only in the initial abundances of C-12, N-14, and O-16, are presented. The degree of enhancement required to produce mass ejection, and thereby a nova-type outburst, is greater than for the 1.00 solar mass model. Nevertheless, the evolution of the 0.5 solar mass model that ejected material is very similar to that of the 1.00 solar mass models, and it also ejects significant amounts of C-13, N-15, and O-17 into the interstellar medium. The 0.5 solar mass outburst is considerably less intense than the 1.00 solar mass outburst (even under optimum conditions), and this lower mass behavior is interpreted as associated with the observed outburst of the slowest novae.
Starrfield, S.↗
SN 2010LP—A TYPE IA SUPERNOVA FROM A VIOLENT MERGER OF TWO CARBON-OXYGEN WHITE DWARFS
SN 2010lp is a subluminous Type Ia supernova (SN Ia) with slowly evolving lightcurves. Moreover, it is the only subluminous SN Ia observed so far that shows narrow emission lines of [O I] in late-time spectra, indicating unburned oxygen close to the center of the ejecta. Most explosion models for SNe Ia cannot explain the narrow [O I] emission. Here, we present hydrodynamic explosion and radiative transfer calculations showing that the violent merger of two carbon-oxygen white dwarfs of 0.9 and 0.76 M {sub ☉} adequately reproduces the early-time observables of SN 2010lp. Moreover, our model predicts oxygen close to the center of the explosion ejecta, a pre-requisite for narrow [O I] emission in nebular spectra as observed in SN 2010lp.
79 ASTRONOMY AND ASTROPHYSICS↗