The Evolution of Carbon and Oxygen in the Bulge and Disk of the Milky Way

The evolution of C and O abundances in the Milky Way can impose strong constraints on stellar nucleosynthesis and help understanding the formation and evolution of our Galaxy. The aim is to review the measured C and O abundances in the disk and bulge of the Galaxy and compare them with model predictions. We adopt two successful chemical evolution models for the bulge and the disk, which assume the same nucleosynthesis prescriptions but different histories of star formation. The data show a clear distinction between the trend of [C/O] in the thick and thin Galactic disks, while the thick disk and bulge trends are indistinguishable with a large (>0.5 dex) increase in the C/O ratio in the range from -0.1 to +0.4 dex for [O/H]. In our models we consider yields from massive stars with and without the inclusion of metallicity-dependent stellar winds. The observed increase in the [C/O] ratio with metallicity in the bulge and thick disk lies between the predictions utilizing the mass-loss rates of Maeder (1992) and those of Meynet & Maeder (2002). A model without metallicity-dependent yields completely fails to match the observations. Thus, the relative increase in carbon abundance at high metallicity appears to be due to metallicity-dependent stellar winds in massive stars. These results also explain the steep decline of the [O/Fe] ratio with [Fe/H] in the Galactic bulge, while the [Mg/Fe] ratio is enhanced at all [Fe/H]. (abridged)Comment: 18 pages, 6 figures, submitted to Astronomy & Astrophysic

Thin-film cryogenic accelerator targets

Thin-film accelerator targets (0.1 mg/cm2 x 2) produced by condensation of various gases (Ar, Kr, Xe, N2, etc.) onto thin, cryogenically cooled substrates (T = 20 K to 80 K) have been developed and tested in-beam with 35 MeV 4He.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23775/1/0000013.pd

Fundamental Parameters and Abundances of Metal-Poor Stars: The SDSS Standard BD +17 4708

The atmospheric parameters and iron abundance of the Sloan Digital Sky Survey (SDSS) spectrophotometric standard star BD +17 4708 are critically examined using up-to-date Kurucz model atmospheres, LTE line formation calculations, and reliable atomic data. We find Teff = 6141+-50 K, log g = 3.87+-0.08, and [Fe/H]=-1.74+-0.09. The line-of-sight interstellar reddening, bolometric flux, limb-darkened angular diameter, stellar mass, and the abundances of Mg, Si, and Ca are also obtained. This star is a unique example of a moderately metal-poor star for which the effective temperature can be accurately constrained from the observed spectral energy distribution (corrected for reddening). Such analysis leads to a value that is higher than most spectroscopic results previously reported in the literature (~5950 K). We find that the ionization balance of Fe lines is satisfied only if a low Teff (~5950 K) is adopted. With our preferred Teff (6141 K), the mean iron abundance we obtain from the FeII lines is lower by about 0.15 dex than that from the FeI lines, and therefore, the discrepancy between the mean iron abundance from FeI and FeII lines cannot be explained by overionization by UV photons as the main non-LTE effect. We also comment on non-LTE effects and the importance of inelastic collisions with neutral H atoms in the determination of oxygen abundances in metal-poor stars from the 777 nm OI triplet. (Abridged)Comment: A&A in pres

Review of the cultivation program within the National Alliance for Advanced Biofuels and Bioproducts

The cultivation efforts within the National Alliance for Advanced Biofuels and Bioproducts (NAABB)were developed to provide four major goals for the consortium, which included biomass production for downstream experimentation, development of new assessment tools for cultivation, development of new cultivation reactor technologies, and development of methods for robust cultivation. The NAABB consortium test beds produced over 1500 kg of biomass for downstream processing. The biomass production included a number of model production strains, but also took into production some of the more promising strains found through the prospecting efforts of the consortium. Cultivation efforts at large scale are intensive and costly, therefore the consortium developed tools and models to assess the productivity of strains under various environmental conditions, at lab scale, and validated these against scaled outdoor production systems. Two new pond-based bioreactor designs were tested for their ability to minimize energy consumption while maintaining, and even exceeding, the productivity of algae cultivation compared to traditional systems. Also, molecular markers were developed for quality control and to facilitate detection of bacterial communities associated with cultivated algal species, including the Chlorella spp. pathogen, Vampirovibrio chlorellavorus,which was identified in at least two test site locations in Arizona and New Mexico. Finally, the consortium worked on understanding methods to utilize compromised municipal waste water streams for cultivation. This review provides an overview of the cultivation methods and tools developed by the NAABB consortium to produce algae biomass, in robust low energy systems, for biofuel production

Differences in Brain Function and Changes with Intervention in Children with Poor Spelling and Reading Abilities

Previous fMRI studies in English-speaking samples suggested that specific interventions may alter brain function in language-relevant networks in children with reading and spelling difficulties, but this research strongly focused on reading impaired individuals. Only few studies so far investigated characteristics of brain activation associated with poor spelling ability and whether a specific spelling intervention may also be associated with distinct changes in brain activity patterns. We here investigated such effects of a morpheme-based spelling intervention on brain function in 20 children with comparatively poor spelling and reading abilities using repeated fMRI. Relative to 10 matched controls, children with comparatively poor spelling and reading abilities showed increased activation in frontal medial and right hemispheric regions and decreased activation in left occipito-temporal regions prior to the intervention, during processing of a lexical decision task. After five weeks of intervention, spelling and reading comprehension significantly improved in the training group, along with increased activation in the left temporal, parahippocampal and hippocampal regions. Conversely, the waiting group showed increases in right posterior regions. Our findings could indicate an increased left temporal activation associated with the recollection of the new learnt morpheme-based strategy related to successful training

The Apache Point Observatory Galactic Evolution Experiment (APOGEE)

The Apache Point Observatory Galactic Evolution Experiment (APOGEE), one of the programs in the Sloan Digital Sky Survey III (SDSS-III), has now completed its systematic, homogeneous spectroscopic survey sampling all major populations of the Milky Way. After a three-year observing campaign on the Sloan 2.5 m Telescope, APOGEE has collected a half million high-resolution (R ~ 22,500), high signal-to-noise ratio (>100), infrared (1.51–1.70 μm) spectra for 146,000 stars, with time series information via repeat visits to most of these stars. This paper describes the motivations for the survey and its overall design—hardware, field placement, target selection, operations—and gives an overview of these aspects as well as the data reduction, analysis, and products. An index is also given to the complement of technical papers that describe various critical survey components in detail. Finally, we discuss the achieved survey performance and illustrate the variety of potential uses of the data products by way of a number of science demonstrations, which span from time series analysis of stellar spectral variations and radial velocity variations from stellar companions, to spatial maps of kinematics, metallicity, and abundance patterns across the Galaxy and as a function of age, to new views of the interstellar medium, the chemistry of star clusters, and the discovery of rare stellar species. As part of SDSS-III Data Release 12 and later releases, all of the APOGEE data products are publicly available

SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems

Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II), SDSS-III is a program of four spectroscopic surveys on three scientific themes: dark energy and cosmological parameters, the history and structure of the Milky Way, and the population of giant planets around other stars. In keeping with SDSS tradition, SDSS-III will provide regular public releases of all its data, beginning with SDSS DR8 (which occurred in Jan 2011). This paper presents an overview of the four SDSS-III surveys. BOSS will measure redshifts of 1.5 million massive galaxies and Lya forest spectra of 150,000 quasars, using the BAO feature of large scale structure to obtain percent-level determinations of the distance scale and Hubble expansion rate at z<0.7 and at z~2.5. SEGUE-2, which is now completed, measured medium-resolution (R=1800) optical spectra of 118,000 stars in a variety of target categories, probing chemical evolution, stellar kinematics and substructure, and the mass profile of the dark matter halo from the solar neighborhood to distances of 100 kpc. APOGEE will obtain high-resolution (R~30,000), high signal-to-noise (S/N>100 per resolution element), H-band (1.51-1.70 micron) spectra of 10^5 evolved, late-type stars, measuring separate abundances for ~15 elements per star and creating the first high-precision spectroscopic survey of all Galactic stellar populations (bulge, bar, disks, halo) with a uniform set of stellar tracers and spectral diagnostics. MARVELS will monitor radial velocities of more than 8000 FGK stars with the sensitivity and cadence (10-40 m/s, ~24 visits per star) needed to detect giant planets with periods up to two years, providing an unprecedented data set for understanding the formation and dynamical evolution of giant planet systems. (Abridged)Comment: Revised to version published in The Astronomical Journa

The tidal disruption of stars by a massive black hole at the center of a galaxy.

Studies of the luminosity evolution of optical Quasi-Stellar Objects (QSOs) suggest that a large number of normal-looking galaxies today have a central massive black hole. These galaxies once contained Active Galactic Nuclei (AGN), but a dwindling fuel supply forced the central engine to fade. If one of these galaxies happens to be close enough, it might be possible to detect the central black hole by the effects it has on the kinematics and surface density of stars in the galactic nucleus. But, for the majority of galaxies, it is not feasible to observe these effects due to their great distance. Not feasible, that is, until the black hole disrupts a passing star. The debris of the star will form an accretion disk around the black hole. The galactic nucleus will then become a reborn AGN. It is then possible to detect the black hole by the sudden appearance of a compact source of extreme UV and X-ray photons at the center of a galaxy. Broad, double-peaked emission lines may also appear, giving conclusive evidence that an accretion disk has formed around a massive black hole. A survey to detect flares from galactic nuclei resulting from tidally-disrupted stars could possibly answer whether or not most galaxies go through an AGN phase. In this work, we will use Smoothed Particle Hydrodynamics (SPH) simulations to remove much of the uncertainty that existed in previous work on the tidal disruption of stars. These works were forced to assume that stars which passed inside the Roche limit of a black hole were completely accreted by the black hole. We will replace this assumption with the results of our SPH simulations, and find that previous works overestimated the rate at which gas is stripped from stars by a factor of two. We will then review the observational consequences of a disruption event, and consider two cases in which such an event may have been witnessed

Crop protection in industrial algae farming: detecting weedy algae and characterizing bacterial communities

Includes bibliographical references.2015 Fall.Microalgae are a promising source of feedstock for biofuel and bioproducts. Algae have higher rates of biomass production than terrestrial crops, and therefore can use less land for producing equivalent energy compared to other biofuels. Elite algae strains are chosen based on traits such as fast and robust growth, and rapid production of desired biochemical products, including fatty acids and other high-energy compounds. Monocultures of elite strains are grown in large algae production systems. A major challenge algae growers face is consistently growing robust cultures of elite algae. This is due to unwanted organisms invading cultures such as weedy algae that contain less desirable biochemical products, and bacteria that can detract from algae growth, thereby reducing overall system productivity. Historically, algae have not been grown at scales required for biofuels and bioproducts, and thus there is a lack of fundamental pest management knowledge and developed tools. In this work, we developed three polymerase chain reaction (PCR)-based tools for detecting and quantifying weedy and elite algae. We developed a simple and inexpensive CAPS (cleaved amplified polymorphic sequence) assay that can determine the presence of dominant algae species in cultures. Also, we developed and validated qPCR primers were able to detect one weedy algae cell in 108 cells in a culture. Compared to flow cytometry, the qPCR primers were 104 times more sensitive for detecting weedy algae. We validated tools by monitoring industrial algae systems, and exhibited their utility for assisting in culture management decisions. Bacteria are also prevalent in industrial algae cultures yet little is understood about their dynamics or role in the ecosystem of elite algae cultures. We sampled small, medium and large cultures from an industrial algae system growing elite algae Nannochloropsis salina, and sequenced the 16S rDNA gene and used QIIME bioinformatics program to analyze data. In this study, we characterized bacterial communities diversity, richness, and composition in industrial algae bioreactors during the scale-up process, through time and during various algae growth rates. We demonstrate that bacterial diversity richness increases as the size of the algae production system increases in the scale-up process. Therefore, larger cultures are comprised of more complex communities than smaller cultures, thus increasing the probability of detrimental algae-bacteria interactions. We identified a single core bacterium Saprospiraceae that was present in 100% of samples, and was on average the most abundant bacterium in all systems. Further, we identified a Deltaproteobacterium that was detected at abnormally high relative abundances in poorly growing algae cultures. Identifying pest bacteria that can detract from elite algae growth is an important step in developing crop protection strategies. We isolated bacteria from a poorly performing algae system and determined their influence on algae growth. We identified a single isolate, S7 as a growth inhibiting bacteria that was capable of completely inhibiting Nannochloropsis gaditana and N. salina growth. The bacterium was characterized as Bacillus pumilus. Additionally, we identified nutrients and cell concentrations required for inhibition of N. gaditana and N. salina. B. pumilus inhibition effect is species-specific as it did not inhibit weedy algae, Chlorella vulgaris and Tetraselmis striata. Due to this, B. pumilus is capable of manipulating algae population composition and reducing productivity. Contaminating organisms such as bacteria will often be prevalent in algae systems and understanding their influence on culture productivity is essential for successful large-scale cultivation of algae. In summary, we 1) developed molecular tools to monitor weedy algae that can be used by growers, 2) characterized bacterial communities in industrial algae system cultures, and 3) identified a novel pest for elite algae, N. gaditana and N. salina