The Complicated Evolution of the ACIS Contamination Layer over the Mission Life of the Chandra X-ray Observatory

The Chandra X-ray Observatory was launched almost 19 years ago and has been delivering spectacular science over the course of its mission. The Advanced CCD Imager Spectrometer is the prime instrument on the satellite, conducting over 90% of the observations. The CCDs operate at a temperature of -120 C and the optical blocking filter in front of the CCDs is at a temperature of approximately -60C. The surface of the OBF has accumulated a layer of contamination over the course of the mission. We have been characterizing the thickness, chemical composition, and spatial distribution of the contamination layer as a function of time over the mission. All three have exhibited significant changes with time. There has been a dramatic decrease in the accumulation rate of the contaminant starting in 2017. The lower accumulation rate may be due to a decrease in the deposition rate or an increase in the vaporization rate or a combination of the two. We show that the current calibration file which models the additional absorption of the contamination layer is significantly overestimating that additional absorption by using the standard model spectrum for the supernova remnant 1E 0102.2-7219 developed by the International Astronomical Consortium for High Energy Calibration. In addition, spectral data from the cluster of galaxies known as Abell 1795 and the Blazar Markarian 421 are used to generate a model of the absorption produced by the contamination layer. The Chandra X-ray Center calibration team is preparing a revised calibration file that more accurately represents the complex time dependence of the accumulation rate, the spatial dependence, and the chemical composition of the contaminant. Given the rapid changes in the contamination layer over the past year, future calibration observations at a higher cadence will be necessary to more accurately monitor such changes.Comment: 15 pages, 10 figures, SPIE Astronomical Instruments and Telescopes 2018, Conference Series, 1069

Orbital magnetoelectric coupling at finite electric field

We extend the band theory of linear orbital magnetoelectric coupling to treat crystals under finite electric fields. Previous work established that the orbital magnetoelectric response of a generic insulator at zero field comprises three contributions that were denoted as local circulation, itinerant circulation, and Chern-Simons. We find that the expression for each of them is modified by the presence of a dc electric field. Remarkably, the sum of the three correction terms vanishes, so that the total coupling is still given by the same formula as at zero field. This conclusion is confirmed by numerical tests on a tight-binding model, for which we calculate the field-induced change in the linear magnetoelectric coefficient.Comment: 4 pages, 2 figure

Thomas-Fermi versus one- and two-dimensional regimes of a trapped dipolar Bose-Einstein condensate

We derive the criteria for the Thomas-Fermi regime of a dipolar Bose-Einstein condensate in cigar, pancake and spherical geometries. This also naturally gives the criteria for the mean-field one- and two-dimensional regimes. Our predictions, including the Thomas-Fermi density profiles, are shown to be in excellent agreement with numerical solutions. Importantly, the anisotropy of the interactions has a profound effect on the Thomas-Fermi/low-dimensional criteria.Comment: 5 pages, 2 figure

Chemical abundances in the protoplanetary disk LV2 (Orion): clues to the causes of the abundance anomaly in HII regions

Optical integral field spectroscopy of the archetype protoplanetary disk LV2 in the Orion Nebula is presented, taken with the VLT FLAMES/Argus fibre array. The detection of recombination lines of CII and OII from this class of objects is reported, and the lines are utilized as abundance diagnostics. The study is complemented with the analysis of HST Faint Object Spectrograph ultraviolet and optical spectra of the target contained within the Argus field of view. By subtracting the local nebula background the intrinsic spectrum of the proplyd is obtained and its elemental composition is derived for the first time. The proplyd is found to be overabundant in carbon, oxygen and neon compared to the Orion Nebula and the sun. The simultaneous coverage over LV2 of the CIII] 1908-A and [OIII] 5007-A collisionally excited lines (CELs) and CII and OII recombination lines (RLs) has enabled us to measure the abundances of C++ and O++ for LV2 with both sets of lines. The two methods yield consistent results for the intrinsic proplyd spectrum, but not for the proplyd spectrum contaminated by the generic nebula spectrum, thus providing one example where the long-standing abundance anomaly plaguing metallicity studies of HII regions has been resolved. These results would indicate that the standard forbidden-line methods used in the derivation of light metal abundances in HII regions in our own and other galaxies underestimate the true gas metallicity.Comment: Accepted by MNRAS November 8; 16 pages, 9 figs; typos corrected, error in FWHMs in table 4 corrected in this versio

Probiotic Therapy for the Prevention of Recurrent Spontaneous Preterm Birth

Preterm birth is the national leading cause of neonatal morbidity and mortality. Nearly 500,000 infants are born prematurely each year in the United States and the annual cost of prematurity averages over $26 billion dollars. Despite multiple interventions to reduce infection related prematurity many spontaneous preterm births remain attributed infection and inflammation. We hypothesize that prevention of infection and inflammation related spontaneous preterm birth is possible through enrichment, stabilization, and normalization of the vaginal microbiome. To test this hypothesis we will perform a randomized, double blind, placebo-controlled trial of intravaginal Lactobacillus probiotic in women at high-risk for spontaneous preterm birth. Primary outcome will be reduction frequency of spontaneous preterm birth prior to 37 weeks completed gestation. Results of this study will heighten understanding of the role of the normal vaginal flora in pregnancy and potentially uncover a new intervention capable of reducing preterm birth and the complications of prematurity

BOOK REVIEWS: Bumble Bees of North America. Paul H. Williams, Robbin W. Thorp, Leif L. Richardson, and Sheila R. Colla.

Bumblebee identification is generally considered straight- forward, yet mistakes often are made due to the degree of similarity between the color patterns of different species. Bumble Bees of North America aims to improve the accuracy of identifications by both casual observers and professionals through the use of intuitive diagrams, descriptions, and the more technical dichotomous keys. In addition to providing the first complete field guide to North American bumblebees, the authors make efficient use of the reader’s attention by summarizing taxonomic history, favored food plants, and environmental issues concerning bumblebees. Bumble Bees of North America is organized into three distinct sections. The first section of the book details the collective knowledge regarding bumblebees, delving into issues such as taxonomy, conservation, parasites, and host plants. The authors begin by introducing readers to the cultural and economic value of bumblebees, and follow by informing readers of evidence for population decline and extinction in certain bumblebee species. This combination almost perfectly explains why a scientist might study bees, and subsequently why they need to be able to differentiate bumblebee species (i.e., in order to effectively study bees, scientists have to be able to tell them apart). Next, the authors supply a condensed summary of historical publications on North American bumblebees. Unfortunately, some of the historical sources cited in this summary are not included in the “Additional Resources” section at the end of the book, leaving the readers to intuit the titles of those publications if they are interested in reading these historical resources. Salient features of the introduction include eye-opening figures illustrating global and North American bumblebee diversity, the intensity of bumblebee collection on the continent, and finally, the life cycle of bumblebees

Spitzer reveals what's behind Orion's Bar

We present Spitzer Space Telescope observations of 11 regions SE of the Bright Bar in the Orion Nebula, along a radial from the exciting star theta1OriC, extending from 2.6 to 12.1'. Our Cycle 5 programme obtained deep spectra with matching IRS short-high (SH) and long-high (LH) aperture grid patterns. Most previous IR missions observed only the inner few arcmin. Orion is the benchmark for studies of the ISM particularly for elemental abundances. Spitzer observations provide a unique perspective on the Ne and S abundances by virtue of observing the dominant ionization states of Ne (Ne+, Ne++) and S (S++, S3+) in Orion and H II regions in general. The Ne/H abundance ratio is especially well determined, with a value of (1.01+/-0.08)E-4. We obtained corresponding new ground-based spectra at CTIO. These optical data are used to estimate the electron temperature, electron density, optical extinction, and the S+/S++ ratio at each of our Spitzer positions. That permits an adjustment for the total gas-phase S abundance because no S+ line is observed by Spitzer. The gas-phase S/H abundance ratio is (7.68+/-0.30)E-6. The Ne/S abundance ratio may be determined even when the weaker hydrogen line, H(7-6) here, is not measured. The mean value, adjusted for the optical S+/S++ ratio, is Ne/S = 13.0+/-0.6. We derive the electron density versus distance from theta1OriC for [S III] and [S II]. Both distributions are for the most part decreasing with increasing distance. A dramatic find is the presence of high-ionization Ne++ all the way to the outer optical boundary ~12' from theta1OriC. This IR result is robust, whereas the optical evidence from observations of high-ionization species (e.g. O++) at the outer optical boundary suffers uncertainty because of scattering of emission from the much brighter inner Huygens Region.Comment: 60 pages, 16 figures, 10 tables. MNRAS accepte

Physical Conditions in Orion's Veil

Orion's veil consists of several layers of largely neutral gas lying between us and the main ionizing stars of the Orion nebula. It is visible in 21cm H I absorption and in optical and UV absorption lines of H I and other species. Toward the Trapezium, the veil has two remarkable properties, high magnetic field (~100 microGauss) and a surprising lack of molecular hydrogen given its total hydrogen column density. Here we compute photoionization models of the veil to establish its gas density and its distance from the Trapezium. We use a greatly improved model of the hydrogen molecule that determines level populations in ~1e5 rotational/vibrational levels and provides improved estimates of molecular hydrogen destruction via the Lyman-Werner bands. Our best fit photoionization models place the veil 1-3 pc in front of the star at a density of 1e3-1e4 cubic centimeters. Magnetic energy dominates the energy of non-thermal motions in at least one of the 21cm H I velocity components. Therefore, the veil is the first interstellar environment where magnetic dominance appears to exist. We find that the low ratio of molecular to atomic hydrogen (< 1e-4) is a consequence of high UV flux incident upon the veil due to its proximity to the Trapezium stars and the absence of small grains in the region.Comment: 45 pages, 20 figures, accepted for publication in Ap

Psycholinguistics in Fluency Disorders: Prearticulatory Speech Planning In Stuttering and Cluttering

The Covert Repair Hypothesis (CRH) is an account for speech errors in normally fluent speakers, and also hypothesizes errors in the phonological encoding stage in people who stutter (PWS). Previous research has shown that PWS exhibit poorer performance compared to typically fluent adults (TFA) on linguistic tasks designed to tap into the level of phonological encoding, such as phoneme monitoring. Stuttering and cluttering often co-occur, thus the field can benefit from extending this methodology to study people who clutter (PWC). Experiment 1 in Chapter 2 used phoneme monitoring to study phonological encoding in PWS and PWC, with three conclusions: (1) slower performance by PWS; (2) increased errors by PWS compared to TFA; and (3) similar performance by PWC compared to TFA, suggesting that PWC do not exhibit difficultly with phonological encoding at the single word level. One criticism of the CRH is that the cause of errors in the speech plan has not been accounted for. Chapter 3 proposed the Near Neighbor Interference Hypothesis (NNIH) as an account for errors in the speech plan in PWS, which hypothesizes that due to a lifetime of word-substitution behavior to avoid stuttering, semantic neighborhoods of PWS may be organized differently than TFA, with more neighbors and/or stronger connections between neighbors. Chapter 3 tested the NNIH by investigating the effects of the number of associates (NoA) and the degree of relatedness on performance during lexical decision. Previous research shows TFA respond faster to words with a high vs. low NoA, and words preceded by a picture with a high vs. a low degree of relatedness. Following from the NNIH, it was hypothesized that the magnitude of these effects would be greater in PWS. In Experiment 2, both groups responded faster to words with higher NoA, but PWS were slower to respond than TFA overall, regardless of NoA. In Experiment 3, PWS were not overall slower than TFA, and the effect of degree of relatedness was actually stronger for TFA than PWS. Together, these results suggest that rather than experiencing a benefit from more semantic neighbors, it appears PWS may experience interference from these additional neighbors. Overall, results suggest that PWS may have errors in their speech plan that originate prearticulatoraily, potentially at the lexical-semantic level, and are passed down to the phonological encoding level

Integral field spectroscopy of selected areas of the Bright Bar and Orion-S cloud in the Orion Nebula

We present integral field spectroscopy of two selected zones in the Orion Nebula obtained with the Potsdam Multi-Aperture Spectrophotometer (PMAS), covering the optical spectral range from 3500 to 7200 A and with a spatial resolution of 1". The observed zones are located on the prominent Bright Bar and on the brightest area at the northeast of the Orion South cloud, both containing remarkable ionization fronts. We obtain maps of emission line fluxes and ratios, electron density and temperatures, and chemical abundances. We study the ionization structure and morphology of both fields, which ionization fronts show different inclination angles with respect to the plane of the sky. We find that the maps of electron density, O+/H+ and O/H ratios show a rather similar structure. We interpret this as produced by the strong dependence on density of the [OII] lines used to derive the O+ abundance, and that our nominal values of electron density-derived from the [SII] line ratio-may be slightly higher than the appropriate value for the O+ zone. We measure the faint recombination lines of OII in the field at the northeast of the Orion South cloud allowing us to explore the so-called abundance discrepancy problem. We find a rather constant abundance discrepancy across the field and a mean value similar to that determined in other areas of the Orion Nebula, indicating that the particular physical conditions of this ionization front do not contribute to this discrepancy.Comment: 15 pages, 10 figures. Accepted for publication in MNRA