Using Astrometry to Deblend Microlensing Events

We discuss the prospect of deblending microlensing events by observing astrometric shifts of the lensed stars. Since microlensing searches are generally performed in very crowded fields, it is expected that stars will be confusion limited rather than limited by photon statistics. By performing simulations of events in crowded fields, we find that if we assume a dark lens and that the lensed star obeys a power law luminosity function, $n(L)\propto L^{-\beta}$, over half the simulated events show a measurable astrometric shift. Our simulations included 20000 stars in a $256\times 256$ Nyquist sampled CCD frame. For $\beta=2$, we found that 58% of the events were significantly blended $(F_{\ast}/F_{tot}\leq 0.9)$, and of those, 73% had a large astrometric shift $(\geq 0.5 pixels)$. Likewise, for $\beta=3$, we found that 85% of the events were significantly blended, and that 85% of those had large shifts. Moreover, the shift is weakly correlated to the degree of blending, suggesting that it may be possible not only to detect the existence of a blend, but also to deblend events statistically using shift information.Comment: 24 pages, 7 postscript Figure

Blood-brain barrier-associated pericytes internalize and clear aggregated amyloid-β42 by LRP1-dependent apolipoprotein E isoform-specific mechanism

Table S1. Demographic and clinical features of human subjects used in this study. Figure S1. Aβ deposition in microvessels in AD patients and APPSw/0 mice. Figure S2. Biochemical analysis of Aβ42 aggregates. Figure S3. Cy3-Aβ42 cellular uptake in wild type mouse brain slices within 30 min. Figure S4. Pericyte coverages in Lrp1lox/lox and Lrp1lox/lox; Cspg4-Cre mice. Figure S5.. LRP1 and apoE suppression with siRNA. (DOCX 1454 kb

Portion Size Influences Intake in Samburu Kenyan People Not Exposed to the Western Obesogenic Environment

For people in the modernized food environment, external factors like food variety, palatability, and ubiquitous learned cues for food availability can overcome internal, homeostatic signals to promote excess intake. Portion size is one such external cue; people typically consume more when served more, often without awareness. Though susceptibility to external cues may be attributed to the modernized, cue-saturated environment, there is little research on people living outside that context, or with distinctly different food norms. We studied a sample of Samburu people in rural Kenya who maintain a traditional, semi-nomadic pastoralist lifestyle, eat a very limited diet, and face chronic food insecurity. Participants (12 male, 12 female, aged 20–74, mean BMI = 18.4) attended the study on two days and were provided in counterbalanced order an individual serving bowl containing 1.4 or 2.3 kg of a familiar bean and maize stew. Amount consumed was recorded along with post-meal questions in their dialect about their awareness of intake amount. Data were omitted from two participants who consumed the entire portion in a session. Even though the ‘smaller’ serving was a very large meal, participants consumed 40% more when given the larger serving, despite being unable to reliably identify which day they consumed more food. This result in the Samburu demonstrates the portion size effect is not a by-product of the modern food environment and may represent a more fundamental feature of human dietary psychology

Accurate photometry of extended spherically symmetric sources

We present a new method to derive reliable photometry of extended spherically symmetric sources from {\it HST} images (WFPC2, ACS/WFC and NICMOS/NIC2 cameras), extending existing studies of point sources and marginally resolved sources. We develop a new approach to accurately determine intrinsic sizes of extended spherically symmetric sources, such as star clusters in galaxies beyond the Local Group (at distances <~ 20 Mpc), and provide a detailed cookbook to perform aperture photometry on such sources, by determining size-dependent aperture corrections (ACs) and taking sky oversubtraction as a function of source size into account. In an extensive Appendix, we provide the parameters of polynomial relations between the FWHM of various input profiles and those obtained by fitting a Gaussian profile (which we have used for reasons of computational robustness, although the exact model profile used is irrelevant), and between the intrinsic and measured FWHM of the cluster and the derived AC. Both relations are given for a number of physically relevant cluster light profiles, intrinsic and observational parameters. AC relations are provided for a wide range of apertures. Depending on the size of the source and the annuli used for the photometry, the absolute magnitude of such extended objects can be underestimated by up to 3 mag, corresponding to an error in mass of a factor of 15. We carefully compare our results to those from the more widely used DeltaMag method, and find an improvement of a factor of 3--40 in both the size determination and the AC.Comment: The paper is accepted for publication in A&A, Section 13 (Observational Techniques, published electronically). The published version contains one example table per appendix. A version of the paper containing all tables as well as all data in electronical form are available http://www.astro.physik.uni-goettingen.de/~galev/panders/Sizes_AC

Extinction Maps Toward The Milky Way Bulge: Two-Dimensional And Three-Dimensional Tests With APOGEE

Galactic interstellar extinction maps are powerful and necessary tools for Milky Way structure and stellar population analyses, particularly toward the heavily reddened bulge and in the midplane. However, due to the difficulty of obtaining reliable extinction measures and distances for a large number of stars that are independent of these maps, tests of their accuracy and systematics have been limited. Our goal is to assess a variety of photometric stellar extinction estimates, including both two-dimensional and three-dimensional extinction maps, using independent extinction measures based on a large spectroscopic sample of stars toward the Milky Way bulge. We employ stellar atmospheric parameters derived from high-resolution H-band Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra, combined with theoretical stellar isochrones, to calculate line-of-sight extinction and distances for a sample of more than 2400 giants toward the Milky Way bulge. We compare these extinction values to those predicted by individual near-IR and near+mid-IR stellar colors, two-dimensional bulge extinction maps, and three-dimensional extinction maps. The long baseline, near+mid-IR stellar colors are, on average, the most accurate predictors of the APOGEE extinction estimates, and the two-dimensional and three-dimensional extinction maps derived from different stellar populations along different sightlines show varying degrees of reliability. We present the results of all of the comparisons and discuss reasons for the observed discrepancies. We also demonstrate how the particular stellar atmospheric models adopted can have a strong impact on this type of analysis, and discuss related caveats.NSF Astronomy & Astrophysics Postdoctoral Fellowship AST-1203017Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA) PHY 08-22648U.S. National Science FoundationAlfred P. Sloan FoundationParticipating InstitutionsU.S. Department of Energy Office of Science ANR-12-BS05-0015-01Astronom

PDS 144: the first confirmed Herbig Ae-Herbig Ae wide binary

PDS 144 is a pair of Herbig Ae stars that are separated by 5.'' 35 on the sky. It has previously been shown to have an A2Ve Herbig Ae star viewed at 83 degrees inclination as its northern member and an A5Ve Herbig Ae star as its southern member. Direct imagery revealed a disk occulting PDS 144 N-the first edge-on disk observed around a Herbig Ae star. The lack of an obvious disk in direct imagery suggested PDS 144 S might be viewed face-on or not physically associated with PDS 144 N. Multi-epoch Hubble Space Telescope imagery of PDS 144 with a 5 year baseline demonstrates PDS 144 N & S are comoving and have a common proper motion with TYC 6782-878-1. TYC 6782-878-1 has previously been identified as a member of Upper Sco sub-association A at d = 145 +/- 2 pc with an age of 5-10 Myr. Ground-based imagery reveals jets and a string of Herbig-Haro knots extending 13' (possibly further) which are aligned to within 7 degrees +/- 6 degrees on the sky. By combining proper motion data and the absence of a dark mid-plane with radial velocity data, we measure the inclination of PDS 144 S to be i = 73 degrees +/- 7 degrees. The radial velocity of the jets from PDS 144 N & S indicates they, and therefore their disks, are misaligned by 25 degrees +/- 9 degrees. This degree of misalignment is similar to that seen in T Tauri wide binaries.Peer reviewe

Argon Abundances in the Solar Neighborhood: Non-LTE Analysis of Orion Association B-type Stars

Argon abundances have been derived for a sample of B main-sequence stars in the Orion association. The abundance calculations are based on NLTE metal line-blanketed model atmospheres calculated with the NLTE code TLUSTY and an updated and complete argon model atom. We derive an average argon abundance for this young population of A(Ar) = 6.66 +- 0.06. While our result is in excellent agreement with a recent analysis of the Orion nebula, it is significantly higher than the currently recommended solar value which is based on abundance measurements in the solar corona. Moreover, the derived argon abundances in the Orion B stars agree very well with a measurement from a solar impulsive flare during which unmodified solar photospheric material was brought to flare conditions. We therefore argue that the argon abundances obtained independently for both the Orion B stars and the Orion nebula are representative of the disk abundance value in the solar neighborhood. The lower coronal abundance may reflect a depletion related to the FIP effect. We propose a new reference value for the abundance of argon in the solar neighborhood, A(Ar) = 6.63 +- 0.10, corresponding to Ar/O = 0.009.Comment: to appear in Astrophysical Journal, 24 pages, 3 figures; minor corrections after referee's repor

Constraining dark energy fluctuations with supernova correlations

We investigate constraints on dark energy fluctuations using type Ia supernovae. If dark energy is not in the form of a cosmological constant, that is if the equation of state is not equal to -1, we expect not only temporal, but also spatial variations in the energy density. Such fluctuations would cause local variations in the universal expansion rate and directional dependences in the redshift-distance relation. We present a scheme for relating a power spectrum of dark energy fluctuations to an angular covariance function of standard candle magnitude fluctuations. The predictions for a phenomenological model of dark energy fluctuations are compared to observational data in the form of the measured angular covariance of Hubble diagram magnitude residuals for type Ia supernovae in the Union2 compilation. The observational result is consistent with zero dark energy fluctuations. However, due to the limitations in statistics, current data still allow for quite general dark energy fluctuations as long as they are in the linear regime.Comment: 18 pages, 6 figures, matches the published versio

The young age of the extremely metal-deficient blue compact dwarf galaxy SBS 1415+437

We use Multiple Mirror Telescope (MMT) spectrophotometry and Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) spectra and Wide Field and Planetary Camera 2 (WFPC2) V and I images to study the properties and evolutionary status of the nearby (D = 11.4 Mpc) extremely metal-deficient blue compact dwarf (BCD) galaxy SBS 1415+437=CG 389. The oxygen abundance in the galaxy is 12+log(O/H)=7.60+/-0.01 or Zsun/21. The helium mass fraction in SBS 1415+437 is Y=0.246+/-0.004 which agrees with the primordial helium abundance determined by Izotov & Thuan using a much larger sample of BCDs. The alpha-elements-to-oxygen abundance ratios (Ne/O, S/O, Ar/O) are in very good agreement with the mean values for other metal-deficient BCDs and are consistent with the scenario that these elements are made in massive stars. The Fe/O abundance ratio is ~2 times smaller than the solar ratio. The Si/O ratio is close to the solar value, implying that silicon is not significantly depleted into dust grains. The values of the N/O and C/O ratios imply that intermediate-mass stars have not had time to evolve in SBS 1415+437 and release their nucleosynthesis products and that both N and C in the BCD have been made by massive stars only. This sets an upper limit of ~100 Myr on the age of SBS 1415+437. The (V-I) color of the low-surface-brightness component of the galaxy is blue (<0.4 mag) indicative of a very young underlying stellar population. The (V-I) - I color-magnitude diagrams of the resolved stellar populations in different regions of SBS 1415+437 suggest propagating star formation from the NE side of the galaxy to the SW. All regions in SBS 1415+437 possess very blue spectral energy distributions (SED). We find that the ages of the stellar populations in SBS 1415+437 to range from a few Myr to 100 Myr.Comment: 25 pages, 12 PS and 5 JPG figures, to appear in Ap