The Spatial Evolution of Stellar Structures in the LMC/SMC

We present an analysis of the spatial distribution of various stellar populations within the Large and Small Magellanic Clouds. We use optically selected stellar samples with mean ages between ~9 and ~1000 Myr, and existing stellar cluster catalogues to investigate how stellar structures form and evolve within the LMC/SMC. We use two statistical techniques to study the evolution of structure within these galaxies, the $Q$-parameter and the two-point correlation function (TPCF). In both galaxies we find the stars are born with a high degree of substructure (i.e. are highly fractal) and that the stellar distribution approaches that of the 'background' population on timescales similar to the crossing times of the galaxy (~80/150 Myr for the SMC/LMC respectively). By comparing our observations to simple models of structural evolution we find that 'popping star clusters' do not significantly influence structural evolution in these galaxies. Instead we argue that general galactic dynamics are the main drivers, and that substructure will be erased in approximately the crossing time, regardless of spatial scale, from small clusters to whole galaxies. This can explain why many young Galactic clusters have high degrees of substructure, while others are smooth and centrally concentrated. We conclude with a general discussion on cluster 'infant mortality', in an attempt to clarify the time/spatial scales involved.Comment: 6 pages, conference contribution to IAU Symposium 256, van Loon J.T. & Oliviera J.M., ed

An Anomalous Extinction Law in the Cep OB3b Young Cluster: Evidence for dust processing during gas dispersal

We determine the extinction law through Cep OB3b, a young cluster of 3000 stars undergoing gas dispersal. The extinction is measured toward 76 background K giants identified with MMT/Hectospec spectra. Color excess ratios were determined toward each of the giants using $V$ and $R$ photometry from the literature, $g$,$r$,$i$ and $z$ photometry from SDSS and $J$, $H$, and $K_{s}$ photometry from 2MASS. These color excess ratios were the used to construct the extinction law through the dusty material associated with Cep OB3b. The extinction law through Cep OB3b is intermediate between the $R_{V} = 3.1$ and $R_{V} = 5$ laws commonly used for the diffuse atomic ISM and dense molecular clouds, respectively. The dependence of the extinction law on line-of-sight $A_{V}$ is investigated and we find the extinction law becomes shallower for regions with $A_{V} > 2.5$ magnitudes. We speculate that the intermediate dust law results from dust processing during the dispersal of the molecular cloud by the cluster.Comment: 31 pages, 10 Figures, 3 Tables, accepted for publication in Ap

Shoot chloride exclusion and salt tolerance in grapevine is associated with differential ion transporter expression in roots

BACKGROUND: Salt tolerance in grapevine is associated with chloride (Cl-) exclusion from shoots; the rate-limiting step being the passage of Cl- between the root symplast and xylem apoplast. Despite an understanding of the physiological mechanism of Cl- exclusion in grapevine, the molecular identity of membrane proteins that control this process have remained elusive. To elucidate candidate genes likely to control Cl- exclusion, we compared the root transcriptomes of three Vitis spp. with contrasting shoot Cl- exclusion capacities using a custom microarray. RESULTS: When challenged with 50 mM Cl-, transcriptional changes of genotypes 140 Ruggeri (shoot Cl- excluding rootstock), K51-40 (shoot Cl- including rootstock) and Cabernet Sauvignon (intermediate shoot Cl- excluder) differed. The magnitude of salt-induced transcriptional changes in roots correlated with the amount of Cl- accumulated in shoots. Abiotic-stress responsive transcripts (e.g. heat shock proteins) were induced in 140 Ruggeri, respiratory transcripts were repressed in Cabernet Sauvignon, and the expression of hypersensitive response and ROS scavenging transcripts was altered in K51-40. Despite these differences, no obvious Cl- transporters were identified. However, under control conditions where differences in shoot Cl- exclusion between rootstocks were still significant, genes encoding putative ion channels SLAH3, ALMT1 and putative kinases SnRK2.6 and CPKs were differentially expressed between rootstocks, as were members of the NRT1 (NAXT1 and NRT1.4), and CLC families. CONCLUSIONS: These results suggest that transcriptional events contributing to the Cl- exclusion mechanism in grapevine are not stress-inducible, but constitutively different between contrasting varieties. We have identified individual genes from large families known to have members with roles in anion transport in other plants, as likely candidates for controlling anion homeostasis and Cl- exclusion in Vitis species. We propose these genes as priority candidates for functional characterisation to determine their role in chloride transport in grapevine and other plants.Sam W Henderson, Ute Baumann, Deidre H Blackmore, Amanda R Walker, Rob R Walker and Matthew Gilliha

Spectra of Massive Young Stars in the Cygnus-X Complex

2008sptz.prop50045FWe propose to use the IRS to obtain 5-40 um spectra of a sample of massive stars that are forming in the Cygnus-X region. Cygnus-X is the richest known region in IR-luminous and IR-quiet massive protostars within 2 kpc, and thus is a unique laboratory to study the poorly constrained early stages of massive star formation. The sample will be selected mainly from MSX sources and IR-quiet millimeter continuum sources, and will contain objects with a range of masses and at various stages of evolution. These data will enable us to determine how the properties of these massive stars change as they evolve towards the main sequence. We will also be able to examine the effects that these stars are having on their surroundings, including outflows into the nearby ISM and also in triggering further star formation

Infrared Observations of Massive Star Forming Regions

We have observed NGC 6334 with NASA's Spitzer Space Telescope, using the IRAC infrared imager at wavelengths of 3.6 - 8.0 microns, and NEWFIRM, a ground based near-infrared imager at wavelengths of 1.1 - 2.4 microns. NGC 6334 is a giant molecular cloud with a complex history of star formation located approximately 1.6 kpc away in the plane of the Milky Way Galaxy. NGC 6334's high cloud mass (>10^5 Mo) and bright far-infrared luminosity identify it as a local analog to the unresolved sites of star formation found in other galaxies. Observing high mass Galactic regions such as NGC 6334 will provide the missing link necessary to match empirical relations between the efficiency / rate of star formation and the global properties of the molecular cloud derived from nearby, lower mass star forming regions to results from external galaxies. Our preliminary results reveal that NGC 6334 contains several hundred Class I YSOs and several thousand Class II (older) YSOs concentrated at multiple sites of star formation across the molecular cloud complex

W43 - Extreme Star Formation in the Galactic Bar

Spitzer Proposal ID #80058 2011We propose to extend Spitzer's study of massive star formation to the W43 massive star-forming complex, located in the 5 kpc molecular ring, which is the most active region of star formation in our Galaxy. Star formation may be different in this region due to a higher overall density of massive molecular clouds and star formation, higher radiation fields and supernova rates, and a higher metallicity. Thus, the proposed observations will allow us to compare star formation in this massive inner Galaxy region to star formation near the Sun, and in the outer Galaxy (coming from the studies of W5, the Cycle-5 SMOG project, and GLIMPSE360), and therefore to complete a more representative view of star formation in the Galaxy