The Impact of Accurate Extinction Measurements for X-ray Spectral Models

Interstellar extinction includes both absorption and scattering of photons from interstellar gas and dust grains, and it has the effect of altering a source's spectrum and its total observed intensity. However, while multiple absorption models exist, there are no useful scattering models in standard X-ray spectrum fitting tools, such as XSPEC. Nonetheless, X-ray halos, created by scattering from dust grains, are detected around even moderately absorbed sources and the impact on an observed source spectrum can be significant, if modest, compared to direct absorption. By convolving the scattering cross section with dust models, we have created a spectral model as a function of energy, type of dust, and extraction region that can be used with models of direct absorption. This will ensure the extinction model is consistent and enable direct connections to be made between a source's X-ray spectral fits and its UV/optical extinction.Comment: 8 pages, 4 figure

An investigation of teachers\u27 temperament and students\u27 perceptions of teachers: Communication behavior and students\u27 attitudes toward teachers.

This study examined relationships among the way teachers communicate in the classroom, teachers temperaments, and perceptions of teachers by students. Specifically, the first goal was to determine to what extent a teacher\u27s levels of extraversion, neuroticism, and psychoticism can predict students perceptions of task attraction, immediacy, assertiveness, responsiveness, and credibility. The second goal was to determine the relationships between teacher temperament and teacher evaluations, affective learning, and cognitive learning. Self-report surveys of 52 teachers and 1242 students across seven disciplines at West Virginia University were collected. Instructors received measures of extraversion, neuroticism, and psychoticism. Teachers were asked to rate themselves on each item. Students received measures of task attraction, immediacy, assertiveness, responsiveness and credibility, or measures of affective learning, cognitive learning, and teacher evaluations. Students either reported perceptions of their teacher, or their attitudes toward the class. Results indicated a significant relationship between extraversion and student reports of assertiveness, caring, immediacy, and cognitive learning. Hence, teachers who reported themselves as more extraverted had students claim that those teachers were more assertive, caring, immediate, and learned more with that teacher than with an introverted instructor. There was also a significant relationship between teachers psychoticism and students trust. Teachers who self-reported a high level of psychoticism had students state that they trusted those teachers less than those teachers who recorded a low level of psychoticism. This study revealed several important trends as well, and speculative observations are discussed

Effects of Interstellar Dust Scattering on the X-ray Eclipses of the LMXB AX J1745.6-2901 in the Galactic Center

AX J1745.6-2901 is an eclipsing low mass X-ray binary (LMXB) in the Galactic Centre (GC). It shows significant X-ray excess emission during the eclipse phase, and its eclipse light curve shows an asymmetric shape. We use archival XMM-Newton and Chandra observations to study the origin of these peculiar X-ray eclipsing phenomena. We find that the shape of the observed X-ray eclipse light curves depends on both photon energy and the shape of the source extraction region, and also shows differences between the two instruments. By performing detailed simulations for the time-dependent X-ray dust scattering halo, as well as directly modelling the observed eclipse and non-eclipse halo profiles of AX J1745.6-2901, we obtained solid evidence that its peculiar eclipse phenomena are indeed caused by the X-ray dust scattering in multiple foreground dust layers along the line-of-sight (LOS). The apparent dependence on the instruments is caused by different instrumental point-spread-functions. Our results can be used to assess the influence of dust scattering in other eclipsing X-ray sources, and raise the importance of considering the timing effects of dust scattering halo when studying the variability of other X-ray sources in the GC, such as Sgr A*. Moreover, our study of halo eclipse reinforces the existence of a dust layer local to AX J1745.6-2901 as reported by Jin et al. (2017), as well as identifying another dust layer within a few hundred parsecs to Earth, containing up to several tens of percent LOS dust, which is likely to be associated with the molecular clouds in the Solar neighbourhood. The remaining LOS dust is likely to be associated with the molecular clouds located in the Galactic disk in-between.Comment: 25 pages, 18 figures, 5 tables, accepted by MNRA

The extinction properties of reddened Galactic OB sightlines

A solid understanding of dust grains and their extinction properties is needed to better remove the effects of extinction from data and to comprehend the nature of the processes which modify grains. This requires a large sample of Galactic sightlines, extending far beyond the solar neighborhood, sampling not only a large volume of space but also a wide variety of environments. To fulfill this requirement, a database of sightlines toward 426 young, reddened stars was constructed using extinction curves based on IUE spectra. The curves were fit and the Fitzpatrick-Massa (FM) parameters were found. FM parameters allow for a quantitative analysis of curve characteristics. IR photometry was also obtained for these sightlines, and thus R(V) (=A(V)/E(B-V)) was found. Links between the environment and various grain populations responsible for different components of the extinction curve were sought, as were relationships between different FM parameters, especially those which describe the 2175 Angstrom absorption feature (the &quotbump ). A search for sightlines which cannot be described by the R(V)-dependent extinction law of Cardelli, Clayton, & Mathis (1989; hereafter CCM) was also undertaken. The main results are: (1.) The CCM extinction relation is accurate for the vast majority of Galactic sightlines. Thus, processes which lead to a CCM-like extinction curve dominate the ISM and the grain populations responsible for the extinction are modified efficiently and systematically. (2.) The central wavelength of the bump does not shift, and the bump width is environment-dependent, being narrow along diffuse sightlines and broadening with increasing density. These provide constraints on grain mantle materials. (3.) The Galaxy can support environments that lead to Magellanic Cloud-like extinction; this emphasizes the importance of local environment in determining extinction properties. (4.) Reddened Galactic sightlines which do not adhere to the standard extinction relation tend to be dense and molecule-rich

Interstellar Abundances Toward X Per, Revisited

The nearby X-ray binary X Per (HD 24534) provides a useful beacon with which to measure elemental abundances in the local ISM. We examine absorption features of 0, Mg, and Si along this line of sight using spectra from the Chandra Observatory's LETG/ ACIS-S and XMM-Newton's RGS instruments. In general, we find that the abundances and their ratios are similar to those of young F and G stars and the most recent solar values. We compare our results with abundances required by dust grain models

An Analysis of Dust Halo and Extinction Toward X Persei

Interstellar dust grain models are not sufficiently constrained by UV extinction curves to be able to distinguish between them. By testing grain models in the X-ray regime and applying elemental abundance constraints, we show to what extent the models can reproduce the observables in these regimes, and if they are capable of doing so while respecting the abundance limits. We tested the MRN and WD grain models. The fits to the X-ray data do not allow us to distinguish between MRN and WD; both models provide reasonable fits, but cannot do so while respecting the elemental abundance constraints. The situation in the UV regime is similar. Both MRN and WD underestimate the hydrogen column density NH. The model of ZDA provides promising results, as it finds NH much closer to the UV-measured value; further testing of this model is called for