Stellar Population Variations in the Milky Way's Stellar Halo

If the stellar halos of disk galaxies are built up from the disruption of dwarf galaxies, models predict highly structured variations in the stellar populations within these halos. We test this prediction by studying the ratio of blue horizontal branch stars (BHB stars; more abundant in old, metal-poor populations) to main-sequence turn-off stars (MSTO stars; a feature of all populations) in the stellar halo of the Milky Way using data from the Sloan Digital Sky Survey. We develop and apply an improved technique to select BHB stars using ugr color information alone, yielding a sample of ~9000 g<18 candidates where ~70% of them are BHB stars. We map the BHB/MSTO ratio across ~1/4 of the sky at the distance resolution permitted by the absolute magnitude distribution of MSTO stars. We find large variations of BHB/MSTO star ratio in the stellar halo. Previously identified, stream-like halo structures have distinctive BHB/MSTO ratios, indicating different ages/metallicities. Some halo features, e.g., the low-latitude structure, appear to be almost completely devoid of BHB stars, whereas other structures appear to be rich in BHB stars. The Sagittarius tidal stream shows an apparent variation in BHB/MSTO ratio along its extent, which we interpret in terms of population gradients within the progenitor dwarf galaxy. Our detection of coherent stellar population variations between different stellar halo substructures provides yet more support to cosmologically motivated models for stellar halo growth.Comment: Astronomical Journal, in press. 10 pages, 5 color figures. Much better printed in colo

Minimum Information about a Biosynthetic Gene cluster

A wide variety of enzymatic pathways that produce specialized metabolites in bacteria, fungi and plants are known to be encoded in biosynthetic gene clusters. Information about these clusters, pathways and metabolites is currently dispersed throughout the literature, making it difficult to exploit. To facilitate consistent and systematic deposition and retrieval of data on biosynthetic gene clusters, we propose the Minimum Information about a Biosynthetic Gene cluster (MIBiG) data standard.Chemistry and Chemical Biolog

Solar irradiation measurements in Jordan and comparisons with Californian and Alpine data

In order to obtain reliable irradiation data for the design, operation and economic assessment of solar power stations, a measurement campaign has been performed in Jordan. As promising sites the desert near Quwairah in the South of Jordan, the stony desert South East of Amman and the elevated plateau near Naqb and also in the South of Jordan were chosen. Measurements were performed during the period of June 1989 to July 1992. The data were evaluated and compared with data of Barstow, California and the Swiss Alps. From the yearly sums of the direct normal irradiation in 1990 and 1991 at Quwairah (2701 and 2436 kWh/m2 respectively) it is concluded that this site is comparably as good for solar thermal power stations as the Barstow site. The global normal irradiation (usable with sun-tracked photovoltaic panels) had the surprisingly high values of 3551 and 3373 kWh/m2 in 1990 and 1991 respectively. Occasionally peak values of the global normal irradiation greater than the solar constant were measured (up to 1500 W/m2). Missing global normal data from other arid sites do not permit comparison. As known before, the corresponding values in the Swiss Alps are considerably lower (1100-1700 kWh/m2 for the direct normal irradiation and 2000-2500 kWh/m2 for the global normal irradiation respectively, depending on the year and site). In addition to the direct normal and global normal irradiation, the global horizontal and global inclined (30° South) irradiation were measured, amounting to 2353 and 2499 kWh/m2 respectively in 1990. Data have also been collected on wind, rainfall, ambient temperature, dew point and surface pressure. All data are available in a computer accessible form, in particular as a yearly set of 5 min mean values of the direct normal irradiation for 1990. Combining the ground measured data with METEOSAT-data resulted in a unique map of the direct normal irradiation for Jordan and surrounding countries, indicating attractive sites for solar power stations. The measurement campaign was made possible by active support from the Ministry of Energy and Mineral Resources, MEMR and the Jordan Electricity Authority, JEA, both at Amman, as well as by generous financial support of the Swiss Committee for Scientific Research, KWF, Berne.