An Atlas of K-line Spectra for Cool Magnetic CP Stars: The Wing-Nib Anomaly (WNA)

We present a short atlas illustrating the unusual Ca {\sc ii} K-line profiles in upper main sequence stars with anomalous abundances. Slopes of the profiles for 10 cool, magnetic chemically peculiar (CP) stars change abruptly at the very core, forming a deep "nib." The nibs show the same or nearly the same radial velocity as the other atomic lines. The near wings are generally more shallow than in normal stars. In three magnetic CP stars, the K-lines are too weak to show this shape, though the nibs themselves are arguably present. The Ca {\sc ii} H-lines also show deep nibs, but the profiles are complicated by the nearby, strong H$\epsilon$ absorption. The K-line structure is nearly unchanged with phase in $\beta$ CrB and $\alpha$ Cir. Calculations, including NLTE, show that other possibilities in addition to chemical stratification may yield nib-like cores.Comment: 6 pages, 2 figures, and 8 figures; accepted for publication in ApJ

Focusing by blocking: repeatedly generating central density peaks in self-propelled particle systems by exploiting diffusive processes

Over the past few years the displacement statistics of self-propelled particles has been intensely studied, revealing their long-time diffusive behavior. Here, we demonstrate that a concerted combination of boundary conditions and switching on and off the self-propelling drive can generate and afterwards arbitrarily often restore a non-stationary centered peak in their spatial distribution. This corresponds to a partial reversibility of their statistical behavior, in opposition to the above-mentioned long-time diffusive nature. Interestingly, it is a diffusive process that mediates and makes possible this procedure. It should be straightforward to verify our predictions in a real experimental system.Comment: 6 pages, 6 figure

Soft coronal X-rays from \beta{} Pictoris

A type stars are expected to be X-ray dark, yet weak emission has been detected from several objects in this class. We present new Chandra/HRC-I observations of the A5 V star \beta{} Pictoris. It is clearly detected with a flux of 9+-2 10^{-4} counts/s. In comparison with previous data this constrains the emission mechanism and we find that the most likely explanation is an optically thin, collisionally dominated, thermal emission component with a temperature around 1.1 MK. We interpret this component as a very cool and dim corona, with \log L_X/L_{bol}=-8.2 (0.2-2.0 keV). Thus, it seems that \beta{} Pictoris shares more characteristics with cool stars than previously thought.Comment: accepted by ApJ, 5 pages, 2 figure

Design of Multistep Aging Treatments of 2099 (C458) Al-Li Alloy

Multistep artificial aging treatments coupled with various natural aging times for aluminum lithium 2099 alloy (previously called C458) are discussed to obtain mechanical tensile properties in the T6 condition that match those in the T861 condition, having a yield strength in the range of 414-490 MPa (60-71 ksi), an ultimate strength in the range of 496-538 MPa (72-78 ksi), and 10-13% elongation. Yield and ultimate tensile strengths from 90-100% of the strength of the as-received material (in the T861 condition) were obtained. The highest tensile strengths were consistently obtained with two-step, low-to-high temperature artificial aging treatments consisting of a first step at 120 degrees C (248 degrees F) for 12-24 h followed by a second step between 165 and 180 degrees C (329-356 degrees F) for 48-100 h. These T6-type heat treatments produced average yield and ultimate strengths in the longitudinal direction in the range of 428-472 MPa (62.1-68.5 ksi) and 487-523 MPa (70.6-75.9 ksi), respectively, as well as lower yield strength anisotropy when compared with the as-received material in the T861 condition

Stratification and Isotope Separation in CP Stars

We investigate the elemental and isotopic stratification in the atmospheres of selected chemically peculiar (CP) stars of the upper main sequence. Reconfiguration of the UVES spectrograph in 2004 has made it possible to examine all three lines of the Ca II infrared triplet. Much of the material analyzed was obtained in 2008. We support the claim of Ryabchikova, Kochukhov & Bagnulo (RKB) that the calcium isotopes have distinct stratification profiles for the stars 10 Aql, HR 1217, and HD 122970, with the heavy isotope concentrated toward the higher layers. Better observations are needed to learn the extent to which Ca-40 dominates in the deepest layers of all or most CP stars that show the presence of Ca-48. There is little evidence for Ca-40 in the spectra of some HgMn stars, and the infrared triplet in the magnetic star HD 101065 is well fit by pure Ca-48. In HR 5623 (HD 133792) and HD 217522 it is likely that the heavy isotope dominates, though models are possible where this is not the case. While elemental stratification is surely needed in many cases, we point out the importance of including adjustments in the assumed Teff and log(g) values, in attempts to model stratification. We recommend emphasis on profiles of the strongest lines, where the influence of stratification is most evident. Isotopic mixtures, involving the 4 stable calcium nuclides with masses between 40 and 48 are plausible, but are not emphasized.Comment: 16 Pages, 20 Figures, 10 Tables. Accepted for publication in Monthly Notices of the RA

X-ray Variability in the Young Massive Triple theta2 Ori A

Massive stars rarely show intrinsic X-ray variability. The only O-stars credited to be intrinsically variable are theta1 Ori C due to effects from magnetic confinement of its wind, and theta2 Ori A suspected of similar activity. Early Chandra observations have shown that the most massive star system in the Orion Trapezium Cluster, theta2 Ori A, shows rapid variability on time scales of hours. We determine X-ray fluxes and find that the star shows very strong variability over the last 5 years. We observed a second large X-ray outburst in November 2004 with the high resolution transmission grating spectrometer on-board Chandra. In the low state X-ray emissivities indicate temperatures well above 25 MK. In the high state we find an extended emissivity distribution with high emissivities in the range from 3 MK to over 100 MK. The outburst event in stellar terms is one of the most powerful ever observed and the most energetic one in the ONC with a lower total energy limit of 1.5x10^37 ergs. The line diagnostics show that under the assumption that the line emitting regions in the low states are as close as within 1 -- 2 stellar radii from the O-star's photosphere, whereas the hard states suggest a distance of 3 -- 5 stellar radii. The two outbursts are very close to the periastron passage of the stars. We argue that the high X-ray states are possibly the result of reconnection events from magnetic interactions of the primary and secondary stars of the spectroscopic binary. Effects from wind collisions seem unlikely for this system. The low state emissivity and R-ratios strengthen the predicament that the X-ray emission is enhanced by magnetic confinement of the primary wind. We also detect Fe fluorescence indicative of the existence of substantial amounts of neutral Fe in the vicinity of the X-ray emission.Comment: 11 pages, 8 figures, accepted for publication in The Astrophysical Main Journa

Chandra HETGS Multi-Phase Spectroscopy of the Young Magnetic O Star theta^1 Orionis C

We report on four Chandra grating observations of the oblique magnetic rotator theta^1 Ori C (O5.5 V) covering a wide range of viewing angles with respect to the star's 1060 G dipole magnetic field. We employ line-width and centroid analyses to study the dynamics of the X-ray emitting plasma in the circumstellar environment, as well as line-ratio diagnostics to constrain the spatial location, and global spectral modeling to constrain the temperature distribution and abundances of the very hot plasma. We investigate these diagnostics as a function of viewing angle and analyze them in conjunction with new MHD simulations of the magnetically channeled wind shock mechanism on theta^1 Ori C. This model fits all the data surprisingly well, predicting the temperature, luminosity, and occultation of the X-ray emitting plasma with rotation phase.Comment: 52 pages, 14 figures (1 color), 6 tables. To appear in the Astrophysical Journal, 1 August 2005, v628, issue 2. New version corrects e-mail address, figure and table formatting problem

X-ray Emission from Young Stellar Objects in the \epsilon Chamaeleontis Group: the Herbig Ae Star HD 104237 and Associated Low-Mass Stars

We present Chandra-HETGS observations of the Herbig Ae star HD 104237 and the associated young stars comprising lower mass stars, in the 0.15-1.75\msol mass range, in their pre-main sequence phase. The brightest X-ray source in the association is the central system harboring the Herbig Ae primary, and a K3 companion. Its X-ray variability indicates modulation possibly on time scales of the rotation period of the Herbig Ae star, and this would imply that the primary significantly contributes to the overall emission. The spectrum of the Herbig Ae+K3 system shows a soft component significantly more pronounced than in other K-type young stars. This soft emission is reminiscent of the unusually soft spectra observed for the single Herbig Ae stars HD 163296 and AB Aur, and therefore we tentatively attribute it to the Herbig Ae of the binary system. The HETGS spectrum shows strong emission lines corresponding to a wide range of plasma temperatures. The He-like triplet of MgXI and NeIX suggest the presence of plasma at densities of about $10^{12}$ cm$^{-3}$, possibly indicating accretion related X-ray production mechanism. The analysis of the zero-order spectra of the other sources indicates X-ray emission characteristics typical of pre-main sequence stars of similar spectral type, with the exception of the T Tauri HD104237-D, whose extremely soft emission is very similar to the emission of the classical T Tauri star TW Hya, and suggests X-ray production by shocked accreting plasma.Comment: accepted for publication on the Astrophysical Journa

Lower bounds for several online variants of bin packing

We consider several previously studied online variants of bin packing and prove new and improved lower bounds on the asymptotic competitive ratios for them. For that, we use a method of fully adaptive constructions. In particular, we improve the lower bound for the asymptotic competitive ratio of online square packing significantly, raising it from roughly 1.68 to above 1.75.Comment: WAOA 201

The Rigidly Rotating Magnetosphere of Sigma Ori E

We attempt to characterize the observed variability of the magnetic helium-strong star sigma Ori E in terms of a recently developed rigidly rotating magnetosphere model. This model predicts the accumulation of circumstellar plasma in two co-rotating clouds, situated in magnetohydrostatic equilibrium at the intersection between magnetic and rotational equators. We find that the model can reproduce well the periodic modulations observed in the star's light curve, H alpha emission-line profile, and longitudinal field strength, confirming that it furnishes an essentially correct, quantitative description of the star's magnetically controlled circumstellar environment.Comment: 4 pages, 3 figures, accepted by Ap