Artifacts at 4.5 and 8.0 um in Short Wavelength Spectra from the Infrared Space Observatory

Spectra from the Short Wavelength Spectrometer (SWS) on ISO exhibit artifacts at 4.5 and 8 um. These artifacts appear in spectra from a recent data release, OLP 10.0, as spurious broad emission features in the spectra of stars earlier than ~F0, such as alpha CMa. Comparison of absolutely calibrated spectra of standard stars to corresponding spectra from the SWS reveals that these artifacts result from an underestimation of the strength of the CO and SiO molecular bands in the spectra of sources used as calibrators by the SWS. Although OLP 10.0 was intended to be the final data release, these findings have led to an additional release addressing this issue, OLP 10.1, which corrects the artifacts.Comment: 14 pages, AASTex, including 5 figures. Accepted by ApJ Letter

Stringent Phenomenological Investigation into Heterotic String Optical Unification

For the weakly coupled heterotic string (WCHS) there is a well-known factor of twenty conflict between the minimum string coupling unification scale, Lambda_H ~5x10^(17) GeV, and the projected MSSM unification scale, Lambda_U ~ 2.5x10^(16) GeV, assuming an intermediate scale desert (ISD). Renormalization effects of intermediate scale MSSM-charged exotics (ISME) (endemic to quasi-realistic string models) can resolve this issue, pushing the MSSM scale up to the string scale. However, for a generic string model, this implies that the projected Lambda_U unification under ISD is accidental. If the true unification scale is 5.0x10^(17) GeV, is it possible that illusionary unification at 2.5x10^(17) GeV in the ISD scenario is not accidental? If it is not, then under what conditions would the assumption of ISME in a WCHS model imply apparent unification at Lambda_U when ISD is falsely assumed? Geidt's "optical unification" suggests that Lambda_U is not accidental, by offering a mechanism whereby a generic MSSM scale Lambda_U < Lambda_H is guaranteed. A WCHS model was constructed that offers the possibility of optical unification, depending on the availability of anomaly-cancelling flat directions meeting certain requirements. This paper reports on the systematic investigation of the optical unification properties of the set of stringent flat directions of this model. Stringent flat directions can be guaranteed to be F-flat to all finite order (or to at least a given finite order consistent with electroweak scale supersymmetry breaking) and can be viewed as the likely roots of more general flat directions. Analysis of the phenomenology of stringent flat directions gives an indication of the remaining optical unification phenomenology that must be garnered by flat directions developed from them.Comment: standard latex, 18 pages of tex

Carbon-rich dust production in metal-poor galaxies in the Local Group

We have observed a sample of 19 carbon stars in the Sculptor, Carina, Fornax, and Leo I dwarf spheroidal galaxies with the Infrared Spectrograph on the Spitzer Space Telescope. The spectra show significant quantities of dust around the carbon stars in Sculptor, Fornax, and Leo I, but little in Carina. Previous comparisons of carbon stars with similar pulsation properties in the Galaxy and the Magellanic Clouds revealed no evidence that metallicity affected the production of dust by carbon stars. However, the more metal-poor stars in the current sample appear to be generating less dust. These data extend two known trends to lower metallicities. In more metal-poor samples, the SiC dust emission weakens, while the acetylene absorption strengthens. The bolometric magnitudes and infrared spectral properties of the carbon stars in Fornax are consistent with metallicities more similar to carbon stars in the Magellanic Clouds than in the other dwarf spheroidals in our sample. A study of the carbon budget in these stars reinforces previous considerations that the dredge-up of sufficient quantities of carbon from the stellar cores may trigger the final superwind phase, ending a star's lifetime on the asymptotic giant branch.Comment: ApJ, in press, 21 pages, 12 figures. Replaced Fig 12, corrected two reference

The Nystrom plus Correction Method for Solving Bound State Equations in Momentum Space

A new method is presented for solving the momentum-space Schrodinger equation with a linear potential. The Lande-subtracted momentum space integral equation can be transformed into a matrix equation by the Nystrom method. The method produces only approximate eigenvalues in the cases of singular potentials such as the linear potential. The eigenvalues generated by the Nystrom method can be improved by calculating the numerical errors and adding the appropriate corrections. The end results are more accurate eigenvalues than those generated by the basis function method. The method is also shown to work for a relativistic equation such as the Thompson equation.Comment: Revtex, 21 pages, 4 tables, to be published in Physical Review

On the metallicity dependence of crystalline silicates in oxygen-rich asymptotic giant branch stars and red supergiants

We investigate the occurrence of crystalline silicates in oxygen-rich evolved stars across a range of metallicities and mass-loss rates. It has been suggested that the crystalline silicate feature strength increases with increasing mass-loss rate, implying a correlation between lattice structure and wind density. To test this, we analyse Spitzer IRS and Infrared Space Observatory SWS spectra of 217 oxygen-rich asymptotic giant branch stars and 98 red supergiants in the Milky Way, the Large and Small Magellanic Clouds and Galactic globular clusters. These encompass a range of spectral morphologies from the spectrally-rich which exhibit a wealth of crystalline and amorphous silicate features to 'naked' (dust-free) stars. We combine spectroscopic and photometric observations with the GRAMS grid of radiative transfer models to derive (dust) mass-loss rates and temperature. We then measure the strength of the crystalline silicate bands at 23, 28 and 33 microns. We detect crystalline silicates in stars with dust mass-loss rates which span over 3 dex, down to rates of ~10^-9 solar masses/year. Detections of crystalline silicates are more prevalent in higher mass-loss rate objects, though the highest mass-loss rate objects do not show the 23-micron feature, possibly due to the low temperature of the forsterite grains or it may indicate that the 23-micron band is going into absorption due to high column density. Furthermore, we detect a change in the crystalline silicate mineralogy with metallicity, with enstatite seen increasingly at low metallicity.Comment: Accepted for publication in MNRAS, 24 pages, 16 figure

The Relationships Between School Poverty and Student Achievement in Maine

The goal of this study was to examine the relationships between school level poverty found in Maine schools and student academic performance. The evidence clearly shows that there is a relationship. As the percent of poverty increases in a school, student performance declines. But the poverty level alone does not explain the wide variations in performance found across the state. The level of poverty in a school is the single best predictor of average student performance, but other factors also play a role in influencing student achievement. Some of these factors include the type of school students are enrolled in, years of teaching experience of the school staff, and the education levels of teachers. Evidence was also found for some higher poverty schools that were defying the odds. Even with higher levels of poverty in their schools, these schools were successful in producing higher levels of student performance. Two additional characteristics were discovered for student performance in higher poverty schools. First, overall performance differs in K-8 and middle schools. The negative relationship between poverty levels and performance is weaker for K-8 schools. More of the higher poverty K-8 schools are performing better than higher poverty middle schools. Second, the levels of poverty found in schools not only affected children in poverty but also those not in poverty. Students in higher poverty schools who do not qualify for free or reduced lunches do not perform as well as their cohorts in lower poverty schools. What is unclear are the causes of this lower performance of non-poverty children in higher poverty schools. Without question, the evidence examined in this study indicates that levels of school poverty and average student achievement are related. The magnitude of the relationship varies, and other factors are related to poverty and achievement, but the single best predictor of performance is school poverty level. The bright news is that there are schools at all levels that defy the odds. Student achievement is better than predicted in spite of school poverty levels. These schools may provide good models for other schools to emulate. In addition, the evidence from this study indicates that there is more to learn about the performance of some types of school configurations (i.e., K-8 schools) and the performance of non-poverty children in higher poverty schools. Additional numerical data is included in the appendices. [This study was funded by the Maine State Legislature, and the University of Maine System.

Pathways to Mathematics College Readiness in Maine

The goal of this study was to examine the pathways to being college ready in mathematics. Students who enter high school already having demonstrated mathematics proficiency on a standardized test in the 8th grade have already taken a significant step towards being college ready. The best scenario is to enter high school proficient in mathematics and having already completed Algebra I, then to complete at least Algebra II and Calculus before graduating from high school. Students completing this pathway are virtually guaranteed to be college ready in mathematics. There also is an alternative path to being college ready. Being proficient entering high school, and then completing a course sequence that includes at least Algebra I, Algebra II, and pre-Calculus significantly increased students\u27 chances of being college ready in mathematics. Thus, it appears 8th grade proficiency is key to becoming college ready in mathematics. It affords opportunities for students to complete Algebra I before entering high school and then take higher level mathematics courses in high school. Alternatively, even if students wait to take Algebra I in high school, if they are proficient and complete at least pre-Calculus, they have a high likelihood of being college ready. The key is 8th grade mathematics proficiency. It opens the gate to a successful high school and college experience in mathematics. The typical sequence of courses completed by most high school students is Algebra I, Geometry, and Algebra II. The Common Core State Standards Initiative (2012) has endorsed this three course sequence as preparing students for college. However, the evidence from this study does not support this endorsement. Completing Geometry does not substantially ensure college readiness, nor does completing Algebra II ensure college readiness. Students also need to successfully complete either a pre-Calculus or Calculus course in high school to be college ready