Identifying Contributions to the Stellar Halo from Accreted, Kicked-Out, and In Situ Populations

[Abridged] We present a medium-resolution spectroscopic survey of late-type giant stars at mid-Galactic latitudes of (30$^{\circ}<|b|<60^{\circ}$), designed to probe the properties of this population to distances of $\sim$9 kpc. Because M giants are generally metal-rich and we have limited contamination from thin disk stars by the latitude selection, most of the stars in the survey are expected to be members of the thick disk ($\sim$-0.6) with some contribution from the metal-rich component of the nearby halo. Here we report first results for 1799 stars. The distribution of radial velocity (RV) as a function of l for these stars shows (1) the expected thick disk population and (2) local metal-rich halo stars moving at high speeds relative to the disk, that in some cases form distinct sequences in RV-$l$ space. High-resolution echelle spectra taken for 34 of these "RV outliers" reveal the following patterns across the [Ti/Fe]-[Fe/H] plane: seventeen of the stars have abundances reminiscent of the populations present in dwarf satellites of the Milky Way; eight have abundances coincident with those of the Galactic disk and more metal-rich halo; and nine of the stars fall on the locus defined by the majority of stars in the halo. The chemical abundance trends of the RV outliers suggest that this sample consists predominantly of stars accreted from infalling dwarf galaxies. A smaller fraction of stars in the RV outlier sample may have been formed in the inner Galaxy and subsequently kicked to higher eccentricity orbits, but the sample is not large enough to distinguish conclusively between this interpretation and the alternative that these stars represent the tail of the velocity distribution of the thick disk. Our data do not rule out the possibility that a minority of the sample could have formed from gas {\it in situ} on their current orbits.Comment: 43 pages, 9 figures, 4 tables, published in the Astrophysical Journa

2017 Research & Innovation Day Program

A one day showcase of applied research, social innovation, scholarship projects and activities.https://first.fanshawec.ca/cri_cripublications/1004/thumbnail.jp

Assessing the influence of genotypic diversity on sulfur dynamics in the seagrass halodule wrightii using stable isotope analysis

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Environmental Science from Texas A&M University-Corpus Christi in Corpus Christi, Texas.Coastal development and other mounting anthropogenic pressures are threatening valuable seagrass habitats. The greatest risks posed to seagrasses are the effects of coastal eutrophication, which stimulates primary productivity and ultimately supplies abundant organic matter to marine sediments. The decomposition of this material is initially facilitated by aerobic microorganisms, depleting dissolved oxygen and generating anoxic conditions. Under these conditions, anaerobic microorganisms such as sulfate-reducing bacteria begin to dominate the degradation process, which reduce sulfate (SO42-) to sulfide (H2S) for energy production. The accumulation of H2S in marine sediments is problematic for seagrasses, as this molecule can be highly toxic. Yet, seagrasses can withstand relatively high concentrations of H2S in their environments. Stable isotope analyses have been used to investigate sulfide intrusion in seagrass meadows, as the unique isotopic signature of sediment-derived sulfur can be used to trace the uptake of H2S and its distribution throughout the plant. This technique has allowed the study of factors that may influence sulfide production and intrusion, such as reduced light availability, organic matter enrichment, and high temperatures. However, few studies have examined the biological or biochemical features that enable seagrasses to withstand relatively high sedimentary sulfide levels. One biological feature that may help confer resistance is population genetic diversity, which has been identified as an important trait in the survival and performance of seagrass meadows under environmental stress. In general, genetic diversity is thought to play an important role in population resistance to environmental disturbance, as a wider assortment of functional traits encoded at the molecular level results in a variety of phenotypes likely to possess morphological and physiological differences that are complementary. This genotypic complementarity may extend to biochemical strategies associated with tolerance to, or detoxification of, H­2S. The purpose of this study was to determine whether sulfide intrusion differs between genotypes of the seagrass Halodule wrightii, a prominent species in the Gulf of Mexico. Further, as the sulfur isotopic composition of marine sediments and seagrass vegetation is known to exhibit high spatial variability, this study also sought to assess sulfide intrusion between populations from distinct sites along the Texas Gulf Coast. Stable isotope data was used to infer the proportion of sulfur in H. wrightii tissues that was derived from sedimentary sulfide, while total sulfur (TS) data was also considered to understand the extent of sulfur accumulation within the plant. H. wrightii genotypes were determined by screening each sample at a series of microsatellite loci previously identified for this species. Although no difference in sulfide intrusion was observed between genotypes, sulfide uptake and distribution was significantly different between the three study sites. The results offer important insight to the effect of local conditions on sulfide intrusion in seagrass meadows and may guide future investigations concerned with the influence of genotypic diversity on H2S metabolism in seagrasses.Physical and Environmental SciencesCollege of Science and Engineerin

Sulfide intrusion in the seagrass Halodule wrightii as assessed by tissue sulfur isotopic composition

Seagrass populations are declining considerably due to anthropogenic pressures, such as nutrient loading into coastal waters. Excessive nutrient availability in these environments can induce eutrophication events that ultimately generate anoxia in marine sediments. This promotes the activity of anaerobic sulfate-reducing bacteria, which reduce sulfate (SO42-) to hydrogen sulfide (H2S) for energy production. When high levels of this bacterial activity persist, H2S accumulates in the sediment. This small molecule can be highly toxic to living cells; yet, seagrasses appear to withstand relatively high concentrations of H2S in their environments. The purpose of this study is to assess sulfide intrusion in the seagrass Halodule wrightii from various locations along the Texas Gulf Coast, and determine whether the uptake and distribution of sulfide-derived sulfur in H. wrightii vegetation differs between locations. Vegetation, sediment, and seawater samples were collected from three H. wrightii meadows within two estuaries near Corpus Christi, TX: two from the Upper Laguna Madre and one from Oso Bay. Root, rhizome, and leaf tissue from vegetation samples were separated, lyophilized, and homogenized into a fine powder. Sediment samples underwent a distillation procedure capable of liberating H2S gas, which was precipitated as Ag2S. Seawater samples were acidified and treated with BaCl2 to precipitate seawater sulfate as BaSO4. Tissue, Ag2S, and BaSO4 samples were analyzed for their sulfur stable isotopic composition by EA-IRMS. 34S values of H. wrightii samples taken from the Upper Laguna Madre, for all tissue types, were lower than those obtained for vegetation from Oso Bay, suggesting that the Upper Laguna Madre populations sourced more sulfur from sedimentary sulfide compared to the Oso Bay population. Results interpreted to date suggest a difference between H. wrightii populations from these two locations in sulfide uptake and assimilation, and allows for future research into the effects of local conditions on seagrass sulfur metabolism

Highlighting the potential of peer-led workshops in training early-career researchers for conducting research with Indigenous communities

For decades, Indigenous voices have called for more collaborative and inclusive research practices. Interest in community-collaborative research is consequently growing among university-based researchers in Canada. However, many researchers receive little formal training on how to collaboratively conduct research with Indigenous communities. This is particularly problematic for early-career researchers (ECRs) whose fieldwork often involves interacting with communities. To address this lack of training, two peer-led workshops for Canadian ECRs were organized in 2016 and 2017 with the following objectives: (i) to cultivate awareness about Indigenous cultures, histories, and languages; (ii) to promote sharing of Indigenous and non-Indigenous ways of knowing; and (iii) to foster approaches and explore tools for conducting community-collaborative research. Here we present these peer-led Intercultural Indigenous Workshops and discuss workshop outcomes according to five themes: scope and interdisciplinarity, Indigenous representation, workshop environment, skillful moderation, and workshop outcomes. Although workshops cannot replace the invaluable experience gained through working directly with Indigenous communities, we show that peer-led workshops can be an effective way for ECRs to develop key skills for conducting meaningful collaborative research. Peer-led workshops are therefore an important but insufficient step toward more inclusive research paradigms in Canada