Intracluster age gradients in numerous young stellar clusters

This is the final version of the article.Available from Oxford University Press via the DOI in this record.The pace and pattern of star formation leading to rich young stellar clusters is quite uncertain. In this context, we analyse the spatial distribution of ages within 19 young (median t ≲ 3 Myr on the Siess et al. time-scale), morphologically simple, isolated, and relatively rich stellar clusters. Our analysis is based on young stellar object (YSO) samples from the Massive Young Star-Forming Complex Study in Infrared and X-ray and Star Formation in Nearby Clouds surveys, and a new estimator of pre-main sequence (PMS) stellar ages, AgeJX, derived from X-ray and near-infrared photometric data. Median cluster ages are computed within four annular subregions of the clusters. We confirm and extend the earlier result of Getman et al. (2014): 80 per cent of the clusters show age trends where stars in cluster cores are younger than in outer regions. Our cluster stacking analyses establish the existence of an age gradient to high statistical significance in several ways. Time-scales vary with the choice of PMS evolutionary model; the inferred median age gradient across the studied clusters ranges from 0.75 to 1.5 Myr pc−1. The empirical finding reported in the present study – late or continuing formation of stars in the cores of star clusters with older stars dispersed in the outer regions – has a strong foundation with other observational studies and with the astrophysical models like the global hierarchical collapse model of Vázquez-Semadeni et al.The MYStIX project is now supported by the Chandra archive grant AR7-18002X. The SFiNCs project is supported at Penn State by NASA grant NNX15AF42G, Chandra GO grant SAO AR5-16001X, Chandra GO grant GO2-13012X, Chandra GO grant GO3-14004X, Chandra GO grant GO4-15013X, and the Chandra ACIS Team contract SV474018 (G. Garmire & L. Townsley, Principal Investigators), issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. The Guaranteed Time Observations (GTO) data used here were selected by the ACIS Instrument Principal Investigator, Gordon P. Garmire, of the Huntingdon Institute for X-ray Astronomy, LLC, which is under contract to the Smithsonian Astrophysical Observatory; Contract SV2-82024. This research has made use of NASA's Astrophysics Data System Bibliographic Services and SAOImage DS9 software developed by Smithsonian Astrophysical Observatory

Young star clusters in nearby molecular clouds

This is the final version of the article. Available from Oxford University Press via the DOI in this record.The SFiNCs (Star Formation in Nearby Clouds) project is an X-ray/infrared study of the young stellar populations in 22 star-forming regions with distances ≲1  kpc designed to extend our earlier MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray) survey of more distant clusters. Our central goal is to give empirical constraints on cluster formation mechanisms. Using parametric mixture models applied homogeneously to the catalogue of SFiNCs young stars, we identify 52 SFiNCs clusters and 19 unclustered stellar structures. The procedure gives cluster properties including location, population, morphology, association with molecular clouds, absorption, age (AgeJX), and infrared spectral energy distribution (SED) slope. Absorption, SED slope, and AgeJX are age indicators. SFiNCs clusters are examined individually, and collectively with MYStIX clusters, to give the following results. (1) SFiNCs is dominated by smaller, younger, and more heavily obscured clusters than MYStIX. (2) SFiNCs cloud-associated clusters have the high ellipticities aligned with their host molecular filaments indicating morphology inherited from their parental clouds. (3) The effect of cluster expansion is evident from the radius–age, radius–absorption, and radius–SED correlations. Core radii increase dramatically from ∼0.08 to ∼0.9 pc over the age range 1–3.5 Myr. Inferred gas removal time-scales are longer than 1 Myr. (4) Rich, spatially distributed stellar populations are present in SFiNCs clouds representing early generations of star formation. An appendix compares the performance of the mixture models and non-parametric minimum spanning tree to identify clusters. This work is a foundation for future SFiNCs/MYStIX studies including disc longevity, age gradients, and dynamical modelling.The MYStIX project is now supported by the Chandra archive grant AR7-18002X. The SFiNCs project is supported at Penn State by NASA grant NNX15AF42G, Chandra GO grant SAO AR5- 16001X, Chandra GO grant GO2-13012X, Chandra GO grant GO3-14004X, Chandra GO grant GO4-15013X, and the Chandra ACIS Team contract SV474018 (G. Garmire and L. Townsley, Principal Investigators), issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060

Circumstellar disc lifetimes in numerous galactic young stellar clusters

This is the final version of the article. Available from Oxford University Press via the DOI in this record.Photometric detections of dust circumstellar discs around pre-main sequence (PMS) stars, coupled with estimates of stellar ages, provide constraints on the time available for planet formation. Most previous studies on disc longevity, starting with Haisch, Lada & Lada, use star samples from PMS clusters but do not consider data sets with homogeneous photometric sensitivities and/or ages placed on a uniform time-scale. Here we conduct the largest study to date of the longevity of inner dust discs using X-ray and 1–8 µm infrared photometry from the MYStIX and SFiNCs projects for 69 young clusters in 32 nearby star-forming regions with ages t ≤ 5 Myr. Cluster ages are derived by combining the empirical AgeJX method with PMS evolutionary models, which treat dynamo-generated magnetic fields in different ways. Leveraging X-ray data to identify disc-free objects, we impose similar stellar mass sensitivity limits for disc-bearing and disc-free young stellar objects while extending the analysis to stellar masses as low as M ∼ 0.1 M⊙. We find that the disc longevity estimates are strongly affected by the choice of PMS evolutionary model. Assuming a disc fraction of 100 per cent at zero age, the inferred disc half-life changes significantly, from t1/2 ∼ 1.3–2 Myr to t1/2 ∼ 3.5 Myr when switching from non-magnetic to magnetic PMS models. In addition, we find no statistically significant evidence that disc fraction varies with stellar mass within the first few Myr of life for stars with masses <2 M⊙, but our samples may not be complete for more massive stars. The effects of initial disc fraction and star-forming environment are also explored.We thank the referee for his/her very helpful comments. We thank K. Luhman, E. Mamajek, M. Pecaut, G. Somers, and R. Jeffries for stimulating discussions. The MYStIX project is now supported by the Chandra archive grant AR7-18002X. The SFiNCs project is supported at Penn State by NASA grant NNX15AF42G, Chandra GO grant SAO AR5-16001X, Chandra GO grant GO2-13012X, Chandra GO grant GO3-14004X, Chandra GO grant GO4-15013X, and the Chandra ACIS Team contract SV474018 (G. Garmire and L. Townsley, Principal Investigators), issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. The Guaranteed Time Observations (GTO) data used here were selected by the ACIS Instrument Principal Investigator, Gordon P. Garmire, of the Huntingdon Institute for X-ray Astronomy, LLC, which is under contract to the Smithsonian Astrophysical Observatory; Contract SV2-82024. This research has made use of NASA’s Astrophysics Data System Bibliographic Services and SAOImage DS9 software developed by Smithsonian Astrophysical Observatory

Star Formation in Nearby Clouds (SFiNCs): X-Ray and Infrared Source Catalogs and Membership

This is the final version of the article. Available from American Astronomical Society via the DOI in this record.The Star Formation in Nearby Clouds (SFiNCs) project is aimed at providing a detailed study of the young stellar populations and of star cluster formation in the nearby 22 star-forming regions (SFRs) for comparison with our earlier MYStIX survey of richer, more distant clusters. As a foundation for the SFiNCs science studies, here, homogeneous data analyses of the Chandra X-ray and Spitzer mid-infrared archival SFiNCs data are described, and the resulting catalogs of over 15,300 X-ray and over 1,630,000 mid-infrared point sources are presented. On the basis of their X-ray/infrared properties and spatial distributions, nearly 8500 point sources have been identified as probable young stellar members of the SFiNCs regions. Compared to the existing X-ray/mid-infrared publications, the SFiNCs member list increases the census of YSO members by 6%-200% for individual SFRs and by 40% for the merged sample of all 22 SFiNCs SFRs.The SFiNCs project is supported at Penn State by NASA grant NNX15AF42G, Chandra GO grant SAO AR5-16001X, Chandra GO grant GO2-13012X, Chandra GO grant GO3-14004X, Chandra GO grant GO4-15013X, Spitzer GO program 90179, and the Chandra-ACIS Team contract SV474018 (G. Garmire & L. Townsley, Principal Investigators), issued by the Chandra X-Ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. he Guaranteed Time Observations (GTO) included here were selected by the ACIS Instrument Principal Investigator, Gordon P. Garmire, of the Huntingdon Institute for X-Ray Astronomy, LLC, which is under contract to the Smithsonian Astrophysical Observatory; Contract SV2-82024. This research made use of data products from the Chandra Data Archive and the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory (California Institute of Technology) under a contract with NASA. This research used data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research has also made use of NASA's Astrophysics Data System Bibliographic Services and SAOImage DS9 software developed by Smithsonian Astrophysical Observatory, and the SIMBAD database (operated at CDS, Strasbourg, France)

Overview of the Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) project

The Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) seeks to characterize 20 OB-dominated young clusters and their environs at distances d ≤ 4 kpc using imaging detectors on the Chandra X-ray Observatory, Spitzer Space Telescope, and the United Kingdom InfraRed Telescope. The observational goals are to construct catalogs of star-forming complex stellar members with well-defined criteria and maps of nebular gas (particularly of hot X-ray-emitting plasma) and dust. A catalog of MYStIX Probable Complex Members with several hundred OB stars and 31,784 low-mass pre-main sequence stars is assembled. This sample and related data products will be used to seek new empirical constraints on theoretical models of cluster formation and dynamics, mass segregation, OB star formation, star formation triggering on the periphery of H II regions, and the survivability of protoplanetary disks in H II regions. This paper gives an introduction and overview of the project, covering the data analysis methodology and application to two star-forming regions: NGC 2264 and the Trifid Nebula. © 2013. The American Astronomical Society. All rights reserved.We thank J. Forbrich and P. Teixeira (Univ. Vienna) for useful discussion about NGC 2264. The MYStIX project is supported at Penn State by NASA grant NNX09AC74G, NSF grant AST-0908038, and theChandra ACIS Team contract SV4- 74018 (PIs: G. Garmire & L. Townsley), issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. M. S. Povich was supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-0901646. This research made use of data products from the Chandra Data Archive and the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory (California Institute of Technology) under a contract with NASA. The United Kingdom Infrared Telescope is operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the U.K. This work is based in part on data obtained as part of the UKIRT Infrared Deep Sky Survey and in part on data obtained in UKIRT Director’s Discretionary Time. This research used data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. The HAWK-I near-infrared observations were collected with the High Acuity Wide-field K-band Imager instrument on the ESO 8 m Very Large Telescope at Paranal Observatory, Chile, under ESO programme 60.A-9284(K). This research has also made use of NASA’s Astrophysics Data System Bibliographic Services, the SIMBAD database operated at the Centre de Donnees ´ Astronomique de Strasbourg, and SAOImage DS9 software developed by Smithsonian Astrophysical Observatory

The malaria testing and treatment landscape in mainland Tanzania, 2016

Abstract Background Understanding the key characteristics of malaria testing and treatment is essential to the control of a disease that continues to pose a major risk of morbidity and mortality in mainland Tanzania, with evidence of a resurgence of the disease in recent years. The introduction of artemisinin combination therapy (ACT) as the first-line treatment for malaria, alongside policies to promote rational case management following testing, highlights the need for evidence of anti-malarial and testing markets in the country. The results of the most recent mainland Tanzania ACTwatch outlet survey are presented here, including data on the availability, market share and price of anti-malarials and malaria diagnosis in 2016. Methods A nationally-representative malaria outlet survey was conducted between 18th May and 2nd July, 2016. A census of public and private outlets with potential to distribute malaria testing and/or treatment was conducted among a representative sample of administrative units. An audit was completed for all anti-malarials, malaria rapid (RDT) diagnostic tests and microscopy. Results A total of 5867 outlets were included in the nationally representative survey, across both public and private sectors. In the public sector, availability of malaria testing was 92.3% and quality-assured (QA) ACT was 89.1% among all screened outlets. Sulfadoxine–pyrimethamine (SP) was stocked by 51.8% of the public sector and injectable artesunate was found in 71.4% of all screened public health facilities. Among anti-malarial private-sector stockists, availability of testing was 15.7, and 65.1% had QA ACT available. The public sector accounted for 83.4% of the total market share for malaria diagnostics. The private sector accounted for 63.9% of the total anti-malarial market, and anti-malarials were most commonly distributed through accredited drug dispensing outlets (ADDOs) (39.0%), duka la dawa baridi (DLDBs) (13.3%) and pharmacies (6.7%). QA ACT comprised 33.1% of the national market share (12.2% public sector and 20.9% private sector). SP accounted for 53.3% of the total market for anti-malarials across both private and public sectors (31.3 and 22.0% of the total market, respectively). The median price per adult equivalent treatment dose (AETD) of QA ACT in the private sector was $1.40, almost 1.5 times more expensive than the median price per AETD of SP ($1.05). In the private sector, 79.3% of providers perceived ACT to be the most effective treatment for uncomplicated malaria for adults and 88.4% perceived this for children. Conclusions While public sector preparedness for appropriate malaria testing and case management is showing encouraging signs, QA ACT availability and market share in the private sector continues to be sub-optimal for most outlet types. Furthermore, it is concerning that SP continues to predominate in the anti-malarial market. The reasons for this remain unclear, but are likely to be in part related to price, availability and provider knowledge or preferences. Continued efforts to implement government policy around malaria diagnosis and case management should be encouraged

Turbulence and galactic structure

Interstellar turbulence is driven over a wide range of scales by processes including spiral arm instabilities and supernovae, and it affects the rate and morphology of star formation, energy dissipation, and angular momentum transfer in galaxy disks. Star formation is initiated on large scales by gravitational instabilities which control the overall rate through the long dynamical time corresponding to the average ISM density. Stars form at much higher densities than average, however, and at much faster rates locally, so the slow average rate arises because the fraction of the gas mass that forms stars at any one time is low, ~10^{-4}. This low fraction is determined by turbulence compression, and is apparently independent of specific cloud formation processes which all operate at lower densities. Turbulence compression also accounts for the formation of most stars in clusters, along with the cluster mass spectrum, and it gives a hierarchical distribution to the positions of these clusters and to star-forming regions in general. Turbulent motions appear to be very fast in irregular galaxies at high redshift, possibly having speeds equal to several tenths of the rotation speed in view of the morphology of chain galaxies and their face-on counterparts. The origin of this turbulence is not evident, but some of it could come from accretion onto the disk. Such high turbulence could help drive an early epoch of gas inflow through viscous torques in galaxies where spiral arms and bars are weak. Such evolution may lead to bulge or bar formation, or to bar re-formation if a previous bar dissolved. We show evidence that the bar fraction is about constant with redshift out to z~1, and model the formation and destruction rates of bars required to achieve this constancy.Comment: in: Penetrating Bars through Masks of Cosmic Dust: The Hubble Tuning Fork strikes a New Note, Eds., K. Freeman, D. Block, I. Puerari, R. Groess, Dordrecht: Kluwer, in press (presented at a conference in South Africa, June 7-12, 2004). 19 pgs, 5 figure

The Drosophila neural lineages: a model system to study brain development and circuitry

In Drosophila, neurons of the central nervous system are grouped into units called lineages. Each lineage contains cells derived from a single neuroblast. Due to its clonal nature, the Drosophila brain is a valuable model system to study neuron development and circuit formation. To better understand the mechanisms underlying brain development, genetic manipulation tools can be utilized within lineages to visualize, knock down, or over-express proteins. Here, we will introduce the formation and development of lineages, discuss how one can utilize this model system, offer a comprehensive list of known lineages and their respective markers, and then briefly review studies that have utilized Drosophila neural lineages with a look at how this model system can benefit future endeavors

Srf1 Is a Novel Regulator of Phospholipase D Activity and Is Essential to Buffer the Toxic Effects of C16:0 Platelet Activating Factor

During Alzheimer's Disease, sustained exposure to amyloid-β42 oligomers perturbs metabolism of ether-linked glycerophospholipids defined by a saturated 16 carbon chain at the sn-1 position. The intraneuronal accumulation of 1-O-hexadecyl-2-acetyl-sn-glycerophosphocholine (C16:0 PAF), but not its immediate precursor 1-O-hexadecyl-sn-glycerophosphocholine (C16:0 lyso-PAF), participates in signaling tau hyperphosphorylation and compromises neuronal viability. As C16:0 PAF is a naturally occurring lipid involved in cellular signaling, it is likely that mechanisms exist to protect cells against its toxic effects. Here, we utilized a chemical genomic approach to identify key processes specific for regulating the sensitivity of Saccharomyces cerevisiae to alkyacylglycerophosphocholines elevated in Alzheimer's Disease. We identified ten deletion mutants that were hypersensitive to C16:0 PAF and five deletion mutants that were hypersensitive to C16:0 lyso-PAF. Deletion of YDL133w, a previously uncharacterized gene which we have renamed SRF1 (Spo14 Regulatory Factor 1), resulted in the greatest differential sensitivity to C16:0 PAF over C16:0 lyso-PAF. We demonstrate that Srf1 physically interacts with Spo14, yeast phospholipase D (PLD), and is essential for PLD catalytic activity in mitotic cells. Though C16:0 PAF treatment does not impact hydrolysis of phosphatidylcholine in yeast, C16:0 PAF does promote delocalization of GFP-Spo14 and phosphatidic acid from the cell periphery. Furthermore, we demonstrate that, similar to yeast cells, PLD activity is required to protect mammalian neural cells from C16:0 PAF. Together, these findings implicate PLD as a potential neuroprotective target capable of ameliorating disruptions in lipid metabolism in response to accumulating oligomeric amyloid-β42

Positional Cues in the Drosophila Nerve Cord: Semaphorins Pattern the Dorso-Ventral Axis

Positional cues target sensory axons to appropriate volumes of the developing nervous system independently of their synaptic partners