Abundance Ratios in the Galactic Bulge and Super Metal-Rich Type II Nucle osynthesis

We present abundance results from our Keck/HIRES observations of giants in the Galactic Bulge. We confirm that the metallicity distribution of giants in the low-reddening bulge field Baade's Window can be well-fit by a closed-box enrichment model. We also confirm previous observations that find enhanced [Mg/Fe], [Si/Fe] and [Ca/Fe] for all bulge giants, including those at super-solar metallicities. However, we find that the [O/Fe] ratios of metal-rich bulge dwarfs decrease with increasing metallicity, contrary to what is expected if the enhancements of the other $\alpha$-elements is due to Type II supernovae enrichment. We suggest that the decrease in oxygen production may be due to mass loss in the pre-supernova evolution of metal-rich progenitors.Comment: Conference proceeding to Nuclei in the Cosmos VIII, Vancouver, BC, July, 2004. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundatio

Characterization and Performance of the Suomi-NPP VIIRS Solar Diffuser Stability Monitor

We describe the on-orbit characterization and performance of the Solar Diffuser Stability Monitor (SDSM) on-board Suomi-NPP/VIIRS. This description includes the observing procedure of each SDSM event, the algorithms used to generate the Solar Diffuser degradation corrective factors, and the results for the mission to date. We will also compare the performance of the VIIRS SDSM and SD to the similar components operating on the MODIS instrument on the EOS Terra and Aqua satellite

Alpha Enhancement and the Metallicity Distribution Function of Plaut's Window

We present Fe, Si, and Ca abundances for 61 giants in Plaut's Window (l=-1,b=-8.5) and Fe abundances for an additional 31 giants in a second, nearby field (l=0,b=-8) derived from high resolution (R~25,000) spectra obtained with the Blanco 4m telescope and Hydra multifiber spectrograph. The median metallicity of red giant branch (RGB) stars in the Plaut field is ~0.4 dex lower than those in Baade's Window, and confirms the presence of an iron abundance gradient along the bulge minor axis. The full metallicity range of our (biased) RGB sample spans -1.5<[Fe/H]<+0.3, which is similar to that found in other bulge fields. We also derive a photometric metallicity distribution function for RGB stars in the (l=-1,b=-8.5) field and find very good agreement with the spectroscopic metallicity distribution. The radial velocity and dispersion data for the bulge RGB stars are in agreement with previous results of the BRAVA survey, and we find evidence for a decreasing velocity dispersion with increasing [Fe/H]. The [alpha/Fe] enhancement in Plaut field stars is nearly identical to that observed in Baade's window, and suggests that an [alpha/Fe] gradient does not exist between b=-4 and -8. Additionally, a subset of our sample (23 stars) appear to be foreground red clump stars that are very metal--rich, exhibit small metallicity and radial velocity dispersions, and are enhanced in alpha elements. While these stars likely belong to the Galactic inner disk population, they exhibit [alpha/Fe] ratios that are enhanced above the thin and thick disk.Comment: Accepted for publication in ApJ. 38 pages, 11 figures, and 2 tables. Requests for higher resolution figures and electronic versions of tables 1 and/or 2 in advance of publication may be sent to cijohnson[at]astro.ucla.ed

Initial On-Orbit Radiometric Calibration of the Suomi NPP VIIRS Reflective Solar Bands

The on-orbit radiometric response calibration of the VISible/Near InfraRed (VISNIR) and the Short-Wave InfraRed (SWIR) bands of the Visible/Infrared Imager/Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership (NPP) satellite is carried out through a Solar Diffuser (SD). The transmittance of the SD screen and the SD's Bidirectional Reflectance Distribution Function (BRDF) are measured before launch and tabulated, allowing the VIIRS sensor aperture spectral radiance to be accurately determined. The radiometric response of a detector is described by a quadratic polynomial of the detector?s digital number (dn). The coefficients were determined before launch. Once on orbit, the coefficients are assumed to change by a common factor: the F-factor. The radiance scattered from the SD allows the determination of the F-factor. In this Proceeding, we describe the methodology and the associated algorithms in the determination of the F-factors and discuss the results

MODIS and VIIRS Lunar Observations and Applications

Terra and Aqua MODIS have successfully operated for more than 13 and 11 years since their launch in 1999 and 2002, respectively. The VIIRS instrument on-board the S-NPP launched in 2011 has also operated for nearly 2 years. Both MODIS and VIIRS make observations in the reflective solar and thermal emissive regions and their on-orbit calibration and characterization are provided by a set of on-board calibrators (OBC). In addition, lunar observations have been made on a regular basis to support sensor on-orbit calibration. This paper provides a brief overview of MODIS and VIIRS instrument on-orbit calibration and characterization activities. It describes the approaches and strategies developed to schedule and perform on-orbit lunar observations. Specific applications of MODIS and VIIRS lunar observations discussed in this paper include radiometric calibration stability monitoring and performance assessment of sensor spatial characterization. Results derived from lunar observations, such as sensor response (or gain) trending and band-to-band registration, are compared with that derived from sensor OBC. The methodologies and applications presented in this paper can also be applied to other earth observing sensors

An Extremely Lithium-Rich Bright Red Giant in the Globular Cluster M3

We have serendipitously discovered an extremely lithium-rich star on the red giant branch of the globular cluster M3 (NGC 5272). An echelle spectrum obtained with the Keck I HIRES reveals a Li I 6707 Angstrom resonance doublet of 520 milli-Angstrom equivalent width, and our analysis places the star among the most Li-rich giants known: log[epsilon(Li)] ~= +3.0. We determine the elemental abundances of this star, IV-101, and three other cluster members of similar luminosity and color, and conclude that IV-101 has abundance ratios typical of giants in M3 and M13 that have undergone significant mixing. We discuss mechanisms by which a low-mass star may be so enriched in Li, focusing on the mixing of material processed by the hydrogen-burning shell just below the convective envelope. While such enrichment could conceivably only happen rarely, it may in fact regularly occur during giant-branch evolution but be rarely detected because of rapid subsequent Li depletion.Comment: 7-page LaTeX file, including 2 encapsulated ps figures + 1 table; accepted for publication in the Astrophysical Journal Letter

Abundances and Kinematics of Field Stars II: Kinematics and Abundance Relationships

As an investigation of the origin of ``$\alpha$-poor'' halo stars, we analyze kinematic and abundance data for 73 intermediate metallicity stars ($-1 >$ [Fe/H] $\geq -2$) selected from Paper I of this series. We find evidence for a connection between the kinematics and the enhancement of certain element-to-iron ([X/Fe]) ratios in these stars. Statistically significant correlations were found between [X/Fe] and galactic rest-frame velocities (\vrf{}) for Na, Mg, Al, Si, Ca and Ni, with marginally significant correlations existing for Ti and Y as well. We also find that the [X/Fe] ratios for these elements all correlate with a similar level of significance with [Na/Fe]. Finally, we compare the abundances of these halo stars against those of stars in nearby dSph galaxies. We find significant differences between the abundance ratios in the dSph stars and halo stars of similar metallicity. From this result, it is unlikely that the halo stars in the solar neighborhood, including even the ``$\alpha$-poor'' stars, were once members of disrupted dSph galaxies similar to those studied to date.Comment: Accepted for publication in January 2002 AJ. 29 pages, 12 figures, 2 table