2,524 research outputs found
Nitrogen K-shell photoabsorption
Reliable atomic data have been computed for the spectral modeling of the
nitrogen K lines, which may lead to useful astrophysical diagnostics. Data sets
comprise valence and K-vacancy level energies, wavelengths, Einstein
-coefficients, radiative and Auger widths and K-edge photoionization cross
sections. An important issue is the lack of measurements which are usually
employed to fine-tune calculations so as to attain spectroscopic accuracy. In
order to estimate data quality, several atomic structure codes are used and
extensive comparisons with previous theoretical data have been carried out. In
the calculation of K photoabsorption with the Breit--Pauli -matrix method,
both radiation and Auger damping, which cause the smearing of the K edge, are
taken into account. This work is part of a wider project to compute atomic data
in the X-ray regime to be included in the database of the popular {\sc xstar}
modeling code
Variability of a Stellar Corona on a Time Scale of Days: Evidence for Abundance Fractionation in an Emerging Coronal Active Region
Elemental abundance effects in active coronae have eluded our understanding for almost three decades, since the discovery of the first ionization potential (FIP) effect on the sun. The goal of this paper is to monitor the same coronal structures over a time interval of six days and resolve active regions on a stellar corona through rotational modulation. We report on four iso-phase X-ray spectroscopic observations of the RS CVn binary EI Eri with XMM-Newton, carried out approximately every two days, to match the rotation period of EI Eri. We present an analysis of the thermal and chemical structure of the EI Eri corona as it evolves over the six days. Although the corona is rather steady in its temperature distribution, the emission measure and FIP bias both vary and seem to be correlated. An active region, predating the beginning of the campaign, repeatedly enters into our view at the same phase as it rotates from beyond the stellar limb. As a result, the abundances tend slightly, but consistently, to increase for high FIP elements (an inverse FIP effect) with phase. We estimate the abundance increase of high FIP elements in the active region to be of about 75% over the coronal mean. This observed fractionation of elements in an active region on time scales of days provides circumstantial clues regarding the element enrichment mechanism of non-flaring stellar coronae
Attentional Bias And Training In Individuals With High Dental Anxiety
Dental anxiety is common and associated with negative outcomes. According to information-processing models, anxiety is maintained by maladaptive patterns of processing threatening information. Furthermore, attention training interventions can reduce anxiety in one session. Fifty-three individuals with high levels of dental anxiety completed a Posner reaction-time task. Participants were randomized to attention training or control using a dot-probe task, and then attentional bias was remeasured using another Posner task. Participants then completed a script-driven imaginal exposure task. Results indicated that individuals high in dental anxiety exhibit threat-relevant attentional bias. There was mixed evidence about the efficacy of attention training. On the one hand, training did not eliminate attentional bias and training condition did not predict distress during the imagery task. On the other hand, cue dependency scores in the control group were higher for dental than neutral cues, but did not differ in the training group. In addition, cue dependency scores for both dental and neutral cues predicted subjective anxiety in anticipation of the imagery task. The mixed results of training are considered in terms of the possibility that it enhanced attentional control, rather than reducing bias
Accretion onto the Companion of Eta Carinae During the Spectroscopic Event: II. X-Ray Emission Cycle
We calculate the X-ray luminosity and light curve for the stellar binary
system Eta Carinae for the entire orbital period of 5.54 years. By using a new
approach we find, as suggested before, that the collision of the winds blown by
the two stars can explain the X-ray emission and temporal behavior. Most X-ray
emission in the 2-10 \kev band results from the shocked secondary stellar
wind. The observed rise in X-ray luminosity just before minimum is due to
increase in density and subsequent decrease in radiative cooling time of the
shocked fast secondary wind. Absorption, particularly of the soft X-rays from
the primary wind, increases as the system approaches periastron and the shocks
are produced deep inside the primary wind. However, absorption can not account
for the drastic X-ray minimum. The 70 day minimum is assumed to result from the
collapse of the collision region of the two winds onto the secondary star. This
process is assumed to shut down the secondary wind, hence the main X-ray
source. We show that this assumption provides a phenomenological description of
the X-ray behavior around the minimum.Comment: The Astrophysical Journal, in pres
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