207 research outputs found
Spectrophotometric Resolution of Stellar Atmospheres with Microlensing
Microlensing is a powerful tool for studying stellar atmospheres because as
the source crosses regions of formally infinite magnification (caustics) the
surfaceof the star is resolved, thereby allowing one to measure the radial
intensity profile, both photometrically and spectroscopically. However, caustic
crossing events are relatively rare, and monitoring them requires intensive
application of telescope resources. It is therefore essential that the
observational parameters needed to accurately measure the intensity profile are
quantified. We calculate the expected errors in the recovered radial intensity
profile as a function of the unlensed flux, source radius, spatial resolution
the recovered intensity profile, and caustic crossing time for the two
principle types of caustics: point-mass and binary lenses. We demonstrate that
for both cases there exist simple scaling relations between these parameters
and the resultant errors. We find that the error as a function of the spatial
resolution of the recovered profile, parameterized by the number of radial
bins, increases as , considerably faster than the naive
expectation. Finally, we discuss the relative advantages of binary
caustic-crossing events and point-lens events. Binary events are more common,
easier to plan for, and provide more homogeneous information about the stellar
atmosphere. However, a sub-class of point-mass events with low impact
parameters can provide dramatically more information provided that they can be
recognized in time to initiate observations.Comment: 20 pages, 5 figures, submitted to the Astrophysical Journa
Principles And Practices Fostering Inclusive Excellence: Lessons From The Howard Hughes Medical Institute’s Capstone Institutions
Best-practices pedagogy in science, technology, engineering, and mathematics (STEM) aims for inclusive excellence that fosters student persistence. This paper describes principles of inclusivity across 11 primarily undergraduate institutions designated as Capstone Awardees in Howard Hughes Medical Institute’s (HHMI) 2012 competition. The Capstones represent a range of institutional missions, student profiles, and geographical locations. Each successfully directed activities toward persistence of STEM students, especially those from traditionally underrepresented groups, through a set of common elements: mentoring programs to build community; research experiences to strengthen scientific skill/identity; attention to quantitative skills; and outreach/bridge programs to broaden the student pool. This paper grounds these program elements in learning theory, emphasizing their essential principles with examples of how they were implemented within institutional contexts. We also describe common assessment approaches that in many cases informed programming and created traction for stakeholder buy-in. The lessons learned from our shared experiences in pursuit of inclusive excellence, including the resources housed on our companion website, can inform others’ efforts to increase access to and persistence in STEM in higher education
Synthetic Spectra and Color-Temperature Relations of M Giants
As part of a project to model the integrated spectra and colors of elliptical
galaxies through evolutionary synthesis, we have refined our synthetic spectrum
calculations of M giants. After critically assessing three effective
temperature scales for M giants, we adopted the relation of Dyck et al. (1996)
for our models. Using empirical spectra of field M giants as a guide, we then
calculated MARCS stellar atmosphere models and SSG synthetic spectra of these
cool stars, adjusting the band absorption oscillator strengths of the TiO bands
to better reproduce the observational data. The resulting synthetic spectra are
found to be in very good agreement with the K-band spectra of stars of the
appropriate spectral type taken from Kleinmann & Hall (1986) as well. Spectral
types estimated from the strengths of the TiO bands and the depth of the
bandhead of CO near 2.3 microns quantitatively confirm that the synthetic
spectra are good representations of those of field M giants. The broad-band
colors of the models match the field relations of K and early-M giants very
well; for late-M giants, differences between the field-star and synthetic
colors are probably caused by the omission of spectral lines of VO and water in
the spectrum synthesis calculations. Here, we present four grids of K-band
bolometric corrections and colors -- Johnson U-V and B-V; Cousins V-R and V-I;
Johnson-Glass V-K, J-K and H-K; and CIT/CTIO V-K, J-K, H-K and CO -- for models
having 3000 K < Teff < 4000 K and -0.5 < log g < 1.5. These grids, which have
[Fe/H] = +0.25, 0.0, -0.5 and -1.0, extend and supplement the color-temperature
relations of hotter stars presented in a companion paper (astro-ph/9911367).Comment: To appear in the March 2000 issue of the Astronomical Journal. 60
pages including 15 embedded postscript figures (one page each) and 6 embedded
postscript tables (10 pages total
Classification of fibroglandular tissue distribution in the breast based on radiotherapy planning CT
Accurate segmentation of breast tissues is required for a number of applications such as model based deformable registration in breast radiotherapy. The accuracy of breast tissue segmentation is affected by the spatial distribution (or pattern) of fibroglandular tissue (FT). The goal of this study was to develop and evaluate texture features, determined from planning computed tomography (CT) data, to classify the spatial distribution of FT in the breas
Легенди та перекази кінця ХVI - початку ХVІІ ст. в записах Петра Могили
For the first time in the history of the Ukrainian folkloristics the author researches the records of legends made by sanctifier Petro Mohyla at the beginning of the 17th century mainly in Kyiv suburbs. The author focuses on authenticity of the texts, their links to the traditional legendry and hagiography as well as methods of recording
Field Blue Stragglers and Related Mass Transfer Issues
This chapter contains my impressions and perspectives about the current state
of knowledge about field blue stragglers (FBS) stars, drawn from an extensive
literature that I searched. I conclude my review of issues that attend FBS and
mass transfer, by a brief enumeration of a few mildly disquieting observational
facts.Comment: Chapter 4, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
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