122947911
Reaction rate sensitivity of 44Ti production in massive stars and implications of a thick target yield measurement of 40Ca(alpha,gamma)44Ti
We evaluate two dominant nuclear reaction rates and their uncertainties that affect 44Ti production in explosive nucleosynthesis. Experimentally we develop thick target yields for the 40Ca(α, γ)44Ti reaction at E α = 4.13, 4.54, and 5.36 MeV using γ-ray spectroscopy. At the highest beam energy, we also performed an activation measurement which agrees with the thick target result. From the measured yields a stellar reaction rate was developed that is smaller than current statistical-model calculations and recent experimental results, which would suggest lower 44Ti production in scenarios for the α-rich freezeout. Special attention has been paid to assessing realistic uncertainties of stellar reaction rates produced from a combination of experimental and theoretical cross sections. With such methods, we also develop a re-evaluation of the 44Ti(α, p)47V reaction rate. Using these two rates we carry out a sensitivity survey of 44Ti synthesis in eight expansions representing peak temperature and density conditions drawn from a suite of recent supernova explosion models. Our results suggest that the current uncertainty in these two reaction rates could lead to as large an uncertainty in 44Ti synthesis as that produced by different treatments of stellar physics.
15724697
The Hubble Deep Field South - STIS imaging
We present the imaging observations made with the Space Telescope Imaging Spectrograph (STIS) of the Hubble Deep Field South. The field was imaged in four bandpasses: a clear CCD bandpass for 156 ks, a long-pass filter for 22–25 ks pixel-1 typical exposure, a near-UV bandpass for 23 ks, and a far-UV bandpass for 52 ks. The clear, visible image is the deepest observation ever made in the UV-optical wavelength region, reaching a 10 σ AB magnitude of 29.4 for an object of area 0.2 arcsec2. The field contains QSO J2233-606, the target of the STIS spectroscopy, and extends 50'' × 50'' for the visible images, and 25'' × 25'' for the ultraviolet images. We present the images, catalog of objects, and galaxy counts obtained in the field.
118530564
DISCOVERY OF A RED GIANT WITH SOLAR-LIKE OSCILLATIONS IN AN ECLIPSING BINARY SYSTEM FROM KEPLER SPACE-BASED PHOTOMETRY
Oscillating stars in binary systems are among the most interesting stellar laboratories, as these can provide information on the stellar parameters and stellar internal structures. Here we present a red giant with solar-like oscillations in an eclipsing binary observed with the NASA Kepler satellite. We compute stellar parameters of the red giant from spectra and the asteroseismic mass and radius from the oscillations. Although only one eclipse has been observed so far, we can already determine that the secondary is a main-sequence F star in an eccentric orbit with a semi-major axis larger than 0.5 AU and orbital period longer than 75 days.
119293956
The Kepler Asteroseismic Investigation: Scientific goals and first results
Kepler is a NASA mission designed to detect exoplanets and characterize the properties of exoplanetary systems. Kepler also includes an asteroseismic programme which is being conducted through the Kepler Asteroseismic Science Consortium (KASC), whose 400 members are organized into 13 working groups by type of variable star. So far data have been available from the first 7 month of the mission containing a total of 2937 targets observed at a 1-min cadence for periods between 10 days and 7 months. The goals of the asteroseismic part of the Kepler project is to perform detailed studies of stellar interiors. The first results of the asteroseismic analysis are orders of magnitude better than seen before, and this bodes well for how the future analysis of Kepler data for many types of stars will impact our general understanding of stellar structure and evolution (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
9685561
Hubble Space Telescope and Ground-based Optical and Ultraviolet Observations of GRB 010222
We report on Hubble Space Telescope (HST) Wide Field Planetary Camera 2 optical and Space Telescope Imaging Spectrograph (STIS) near-ultraviolet MAMA observations and ground-based optical observations of GRB 010222, spanning 15 hr to 71 days. The observations are well described by a relativistic blast wave model with a hard electron energy distribution, p = 1.57, and a jet transition at t* = 0.93 days. These values are slightly larger than previously found as a result of a correction for the contribution from the host galaxy to the late-time ground-based observations and the larger temporal baseline provided by the HST observations. The host galaxy is found to contain a very compact core (size <025), which coincides with the position of the optical transient. The STIS near-ultraviolet MAMA observations allow for an investigation of the extinction properties along the line of sight to GRB 010222. We find that the far-ultraviolet curvature component c4 is rather large. In combination with the low optical extinction, AV = 0.110 mag, when compared with the hydrogen column inferred from X-ray observations, we suggest that this is evidence for dust destruction.
119288725
Observational detection of eclipses of J5 Amalthea by the Galilean satellites
Aims. We carried out observations of the small jovian satellite Amalthea (J5) as it was being eclipsed by the Galilean satellites near the 2009 equinox of Jupiter in order to apply the technique of mutual event photometry to the astrometric determination of this satellite’s position. Methods. The observations were carried out during the period 06/2009−09/2009 from the island of Maui, Hawaii and Siding Spring, Australia with the 2m Faulkes Telescopes North and South respectively. We observed in the near-infrared part of the spectrum using a PanStarrs-Z filter with Jupiter near the edge of the field in order to mitigate against the glare from the planet. Frames were acquired at rates >1/min during eclipse times predicted using recent JPL ephemerides for the satellites. Following subtraction of the sky background from these frames, differential aperture photometry was carried out on Amalthea and a nearby field star. Results. We have obtained three lightcurves which show a clear drop in the flux from Amalthea, indicating that an eclipse took place as predicted. These were model-fitted to yield best estimates of the time of maximum flux drop and the impact parameter. These are consistent with Amalthea’s ephemeris but indicate that Amalthea is slightly ahead of, and closer to Jupiter than, its predicted position by approximately half the ephemeris uncertainty in these directions. We argue that a ground-based campaign of higher-cadence photometry accurate at the 5% level or better during the next season of eclipses in 2014-15 should yield positions to within 0. �� 05 and affect a corresponding improvement in Amalthea’s ephemeris.
17530033
UV emission from elliptical galaxies near and far
The far-ultraviolet is the most rapidly evolving portion of the spectrum in both very young galaxies and very old galaxies. The “UV upturn” in the spectra of elliptical galaxies shortward of 2000 A offers a promising probe of the ages and chemical evolution of very old galaxies. In early-type non-active galaxies with the bluest 1550—V colors, the bulk of the emission arises from Extreme Horizontal Branch (EHB) stars, along their evolution from the zero-age HB to the white-dwarf cooling curve. The strength of the UV-upturn is governed by the fraction of stars that evolve through the EHB phase, which is in turn governed by age, metallicity, helium abundance, and other parameters such as stellar rotation and binarity that might influence the amount of mass loss on the RGB. Spectral constraints on the nature of the hot stellar population from Astro-2 are reviewed, and new imaging results from the HST Faint Object Camera are presented. Attempts to measure evolution through observations of high-redshift ellipti...
7045461
Permutations and the loop
We consider the one-loop two-point function for multi-trace operators in the U(2) sector of = 4 supersymmetric Yang-Mills at finite N. We derive an expression for it in terms of U(N) and Sn+1 group theory data, where n is the length of the operators. The Clebsch-Gordan operators constructed in [1], which are diagonal at tree level, only mix at one loop if you can reach the same (n+1)-box Young diagram by adding a single box to each of the n-box Young diagrams of their U(N) representations (which organise their multi-trace structure). Similar results are expected for higher loops and for other sectors of the global symmetry group.
15423004
Halos of Spiral Galaxies. II. Halo Metallicity-Luminosity Relation*
Using the Hubble Space Telescope, we have resolved individual red giant branch stars in the halos of eight nearby spiral galaxies. The fields lie at projected distances between 2 and 13 kpc along the galaxies' minor axes. The data set allows a first look at the systematic trends in halo stellar populations. We have found that bright galaxies tend to have broad red giant branch star color distributions with redder mean colors, suggesting that the heavy-element abundance spread increases with the parent galaxy luminosity. The mean metallicity of the stellar halo, estimated using the mean colors of red giant branch stars, correlates with the parent galaxy luminosity. The metallicity of the Milky Way halo falls nearly 1 dex below this luminosity-metallicity relation, suggesting that the halo of the Galaxy is more the exception than the rule for spiral galaxies; i.e., massive spirals with metal-poor halos are unusual. The luminosity-halo stellar abundance relation is consistent with the scaling relation expected for stellar systems embedded in dominant halos, suggesting that the bulk of the halo stellar population may have formed in situ.
197476756
Stellar Proper Motions in the Galactic Bulge from deep HST ACS/WFC Photometry
We present stellar proper motions in the Galactic bulge from the Sagittarius Window Eclipsing Extrasolar Search (SWEEPS) project using ACS/WFC on HST. Proper motions are extracted for more than 180,000 objects, with >81,000 measured to accuracy better than 0.3 mas/yr in both coordinates. We report several results based on these measurements: 1. Kinematic separation of bulge from disk allows a sample of >15,000 bulge objects to be extracted based on >6-sigma detections of proper motion, with <0.2% contamination from the disk. This includes the first detection of a candidate bulge Blue Straggler population. 2. Armed with a photometric distance modulus on a star by star basis, and using the large number of stars with high-quality proper motion measurements to overcome intrinsic scatter, we dissect the kinematic properties of the bulge as a function of distance along the line of sight. This allows us to extract the stellar circular speed curve from proper motions alone, which we compare with the circular speed curve obtained from radial velocities. 3. We trace the variation of the {l,b} velocity ellipse as a function of depth. 4. Finally, we use the density-weighted {l,b} proper motion ellipse produced from the tracer stars to assess the kinematic membership of the sixteen transiting planet candidates discovered in the Sagittarius Window; the kinematic distribution of the planet candidates is consistent with that of the disk and bulge stellar populations.
119184266
The WFC3 Galactic Bulge Treasury Program: Metallicity Estimates for the Stellar Population and Exoplanet Hosts
We present new UV-to-IR stellar photometry of four low-extinction windows in the Galactic bulge, obtained with the Wide Field Camera 3 on the Hubble Space Telescope (HST). Using our five bandpasses, we have defined reddening-free photometric indices sensitive to stellar effective temperature and metallicity. We find that the bulge populations resemble those formed via classical dissipative collapse: each field is dominated by an old (~10 Gyr) population exhibiting a wide metallicity range (–1.5 [Fe/H] 0.5). We detect a metallicity gradient in the bulge population, with the fraction of stars at super-solar metallicities dropping from 41% to 35% over distances from the Galactic center ranging from 0.3 to 1.2 kpc. One field includes candidate exoplanet hosts discovered in the SWEEPS HST transit survey. Our measurements for 11 of these hosts demonstrate that exoplanets in the distinct bulge environment are preferentially found around high-metallicity stars, as in the solar neighborhood, supporting the view that planets form more readily in metal-rich environments.