5,329 research outputs found

    Predicting Stellar Angular Diameters from VV, ICI_C, HH, KK Photometry

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    Determining the physical properties of microlensing events depends on having accurate angular sizes of the source star. Using long-baseline optical interferometry we are able to measure the angular sizes of nearby stars with uncertainties 2%\leq 2\%. We present empirically derived relations of angular diameters that are calibrated using both a sample of dwarfs/subgiants and a sample of giant stars. These relations are functions of five color indices in the visible and near-infrared, and have uncertainties of 1.8-6.5% depending on the color used. We find that a combined sample of both main-sequence and evolved stars of A-K spectral types is well fit by a single relation for each color considered. We find that in the colors considered, metallicity does not play a statistically significant role in predicting stellar size, leading to a means of predicting observed sizes of stars from color alone.Comment: 8 pages, 1 figure, accepted for publication in MNRA

    An Extinction Map and Color Magnitude Diagram for the Globular Cluster NGC 3201

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    Differential EVIE_{V-I} variations of up to 0.2\sim 0.2 mag on a scale of arcminutes across NGC 3201 are presented in the form of an extinction map. This map, created by calculating average EVIE_{V-I} values for stars in small subregions of the field with respect to a fiducial region, greatly improves the appearance of the CMD of the cluster. We describe how we implemented this technique in detail with our data for NGC 3201. A comparison between our map and that of the same region extracted from the COBE/DIRBE reddening maps published by Schlegel, Finkbeiner, & Davis (1998) (SFD) displays larger-scale similarities between the two maps as well as smaller-scale features which show up in our map but not in the SFD map. Several methods of determining an EVIE_{V-I} zeropoint to add to our differential extinction map are presented. Isochrone fitting proved to be the most successful one, but it produces an average EVIE_{V-I} for the cluster which is smaller than previously published values by 1.5σ\sim 1.5\sigma. Finally, our results seem to support the statement by Arce & Goodman (1999) that the SFD maps overestimate the reddening in regions of high extinction.Comment: 19 pages, 12 figures, 1 table, accepted for publication in AJ (March 2001). Full resolution version may be obtained at http://www.astro.lsa.umich.edu/users/kaspar/html/ngc3201.pdf (PDF) and at http://www.astro.lsa.umich.edu/users/kaspar/html/ngc3201.ps.gz (PS

    Agriculture, food security, nutrition and the Millennium Development Goals

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    "...Today, 1.1 billion people live on less than one US dollar per day (the internationally recognized poverty threshold)—430 million in South Asia, 325 million in Sub-Saharan Africa, 260 million in East Asia and the Pacific, and 55 million in Latin America. Too many children live lives characterized by hunger and illness, and all too often succumb to early death. Moreover, another 1.6 billion people live on between one and two dollars per day, often sliding temporarily below the one dollar per day threshold. To enable all these people to live in dignity, the eight goals to achieve by 2015 are: 1. Eradicate extreme poverty and hunger 2. Achieve universal primary education 3. Promote gender equality and empower women 4. Reduce child mortality 5. Improve maternal health 6. Combat HIV/AIDS, malaria, and other diseases 7. Ensure environmental sustainability 8. Develop a global partnership for development." from TextMillenium Development Goals ,HIV/AIDS ,Gender issues ,Equality ,Nutrition ,Impact ,

    First Results from the Transit Ephemeris Refinement and Monitoring Survey (TERMS)

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    Transiting planet discoveries have yielded a plethora of information towards understanding the structure and atmospheres of extra-solar planets. These discoveries have been restricted to the short-period or low-periastron distance regimes due to the bias inherent in the geometric transit probability. Through the refinement of planetary orbital parmaters, and hence reducing the size of transit windows, long-period planets become feasible targets for photometric follow-up. Here we describe the TERMS project which is monitoring these host stars at predicted transit times

    Polymorphisms in the bradykinin B2 receptor gene and childhood asthma

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    Bradykinin has been suggested as one of the key mediators of bronchial asthma. Polymorphisms with a potential functional relevance have been described in the B2 bradykinin receptor gene. Study of these polymorphisms in 77 children with asthma and 73 controls revealed no association. However, when comparing the asthmatics according to their age at onset (before and after age 4), the exon 1 allele BE1-2G was significantly associated with late-onset asthma (p <0.05). Since BE1-2G has previously been shown to lead to a higher transcription rate of the B2 receptor, this result warrants further investigation of the role of bradykinin in conferring susceptibility to pediatric asthma

    Lessons learned from the dragon (China) and the elephant (India): Essays from IFPRI's 2004-2005 Annual Report

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    "The world made significant progress on reducing poverty between 1981 and 2001 — the number of people in developing countries living on less than US$1 a day fell from 1.5 billion to 1.1 billion, or from 40 to 21 percent of the world's population. In fact, however, nearly all this progress reflects gains made in reducing poverty in China and India, two of the world's fastest-growing economies. The rapid economic growth and enormous poverty reduction achieved by China, and to a lesser extent India, are remarkable accomplishments that bear closer investigation. What do the experiences of these two countries reveal about how to sequence reforms and about what kinds of reforms are most effective in stimulating growth and combating poverty? These three essays compare the experiences of China and India to learn what steps each country took and what lessons they each have to offer." from TextPoverty reduction, economic growth, Economic reform, Governance, Food policy, Food systems, Agriculture, Rural development Asia,

    The LAEX and NASA portals for CoRoT public data

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    * Aims. We describe here the main functionalities of the LAEX (Laboratorio de Astrofisica Estelar y Exoplanetas/Laboratory for Stellar Astrophysics and Exoplanets) and NASA portals for CoRoT Public Data. The CoRoT archive at LAEX was opened to the community in January 2009 and is managed in the framework of the Spanish Virtual Observatory. NStED (NASA Star and Exoplanet Database) serves as the CoRoT portal for the US astronomical community. NStED is a general purpose stellar and exoplanet archive with the aim of providing support for NASA planet finding and characterisation goals, and the planning and support of NASA and other space missions. CoRoT data at LAEX and NStED can be accessed at http://sdc.laeff.inta.es/corotfa/ and http://nsted.ipac.caltech.edu,respectively. * Methods. Based on considerable experience with astronomical archives, the aforementioned archives are designed with the aim of delivering science-quality data in a simple and efficient way. * Results. LAEX and NStED not only provide access to CoRoT Public Data but furthermore serve a variety of observed and calculated astrophysical data. In particular, NStED provides scientifically validated information on stellar and planetary data related to the search for and characterization of extrasolar planets, and LAEX makes any information from Virtual Observatory services available to the astronomical community.Comment: Accepted for publication in Astronomy & Astrophysic

    Stellar diameters and temperatures. IV. Predicting stellar angular diameters

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    The number of stellar angular diameter measurements has greatly increased over the past few years due to innovations and developments in the field of long baseline optical interferometry. We use a collection of high-precision angular diameter measurements for nearby, main-sequence stars to develop empirical relations that allow the prediction of stellar angular sizes as a function of observed photometric color. These relations are presented for a combination of 48 broadband color indices. We empirically show for the first time a dependence on metallicity of these relations using Johnson (B-V) and Sloan (g-r) colors. Our relations are capable of predicting diameters with a random error of less than 5% and represent the most robust and empirical determinations of stellar angular sizes to date. © 2014. The American Astronomical Society. All rights reserved.
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