ABSTRACT We report the discovery of an excess of main-sequence turnoff stars in the direction of the constellations of Eridanus and Phoenix from the first-year data of the Dark Energy Survey (DES). ...The Eridanus-Phoenix (EriPhe) overdensity is centered around and and spans at least 30° in longitude and 10° in latitude. The Poisson significance of the detection is at least . The stellar population in the overdense region is similar in brightness and color to that of the nearby globular cluster NGC 1261, indicating that the heliocentric distance of EriPhe is about . The extent of EriPhe in projection is therefore at least ∼4 kpc by ∼3 kpc. On the sky, this overdensity is located between NGC 1261 and a new stellar stream discovered by DES at a similar heliocentric distance, the so-called Phoenix Stream. Given their similar distance and proximity to each other, it is possible that these three structures may be kinematically associated. Alternatively, the EriPhe overdensity is morphologically similar to the Virgo overdensity and the Hercules-Aquila cloud, which also lie at a similar Galactocentric distance. These three overdensities lie along a polar plane separated by ∼120° and may share a common origin. Spectroscopic follow-up observations of the stars in EriPhe are required to fully understand the nature of this overdensity.
We announce the discovery of a new satellite of the Milky Way in the constellation of Bootes at a distance of 660 kpc. It was found in a systematic search for stellar overdensities in the north ...Galactic cap using Sloan Digital Sky Survey Data Release 5. The color-magnitude diagram shows a well-defined turnoff, red giant branch, and extended horizontal branch. Its absolute magnitude is M sub(v) 6 -5.8 mag, which makes it one of the faintest galaxies known. The half-light radius is 6220 pc. The isodensity contours are elongated and have an irregular shape, suggesting that Boo may be a disrupted dwarf spheroidal galaxy.
In this Letter, we study a localized stellar overdensity in the constellation of Ursa Major, first identified in Sloan Digital Sky Survey (SDSS) data and subsequently followed up with Subaru imaging. ...Its color-magnitude diagram (CMD) shows a well-defined subgiant branch, main sequence, and turnoff, from which we estimate a distance of 630 kpc and a projected size of 6250 x 125 pc super(2). The CMD suggests a composite population with some range in metallicity and/or age. Based on its extent and stellar population, we argue that this is a previously unknown satellite galaxy of the Milky Way, hereby named Ursa Major II (UMa II) after its constellation. Using SDSS data, we find an absolute magnitude of Mv6-3.8, which would make it the faintest known satellite galaxy. UMall's isophotes are irregular and distorted with evidence for multiple concentrations; this suggests that the satellite is in the process of disruption.
An orphan in the field of streams BELOKUROV, V; EVANS, N. W; HEWETT, P. C ...
The Astrophysical journal,
03/2007, Volume:
658, Issue:
1
Journal Article
The present study is aimed at investigating the role of two biologically important cations, cobalt (Co2+) and strontium (Sr2+) doped into carbonated hydroxyapatite (CHA) crystal structure. Four ...different compositions of Co-Sr CHA powders were synthesized via nanoemulsion method at ambient temperature. Among the as-synthesized powders, Co-Sr CHA 1 (0.0082wt% Co, 0.0547wt% Sr) and Co-Sr CHA 2 (0.0085wt% Co, 0.0261wt% Sr) were chosen as the optimum compositions and used for fabrication of dense products. Sintering was then performed on the Co-Sr CHA compacted samples at 900°C in air, followed by cooled down in dry CO2 atmosphere at temperature of 200°C. Regardless of their compositions, the sintered samples remained as single phase B-type CHA. Co-Sr CHA 1 has the optimum mechanical properties where the relative density and diametral tensile strength (DTS) values obtained were 89.15% and 7.67 MPa, respectively. In vitro bioactivity test revealed that the formation of apatite layer were detected on the surface of all sintered samples after soaking in SBF solution for 7 days, with Co-Sr CHA 1 showing the fastest apatite formation as compared to CHA and Co-Sr CHA 2. Results obtained indicate that simultaneous doping of Co2+ and Sr2+ into CHA structure gives rise to improved mechanical strength as well as enhanced the bioactivity of the apatite.
β-TCP is bioresorbable ceramic which has excellent osteoinduction and osteoconduction properties for using as bone cement and bone implant material. However, their natural brittleness and ...insufficient compaction after sintering under the transformation phase from β- to α-TCP limit their utility for clinical performance. The purpose of this work is to investigate the effect of magnesium ion as the doping element on the β-TCP. The experiment was conducted by introduced 1.0wt% of MgO into the β-TCP structure via simultaneous balls milling and mixing method. Afterward, the powders were pressed into pellets and went through conventional sintering method. The sintered samples were examined by powder X-ray diffraction (XRD), density and biological test for investigation.
We have compiled an extensive data set on potential parts of the Monoceros tidal stream and performed an exhaustive survey of dwarf galaxy semianalytic orbits in order to constrain its orbital ...properties. The best-fit orbits are subsequently realized as self-consistent N-body simulations in order to reproduce the spatial and velocity distribution of satellite debris. We find that all kinematic and geometric constraints can be fit by a single stream allowing for multiple wraps. The orbital eccentricity and inclination of the progenitor are strongly constrained to be e = 0.10 c 0.05 and i = 25 c 5. Ten new estimates of proper motions from the Sloan Digital Sky Survey clearly exclude all retrograde orbits. Particles lost by the satellite populate two nearly concentric rings, naturally explaining the detection of stream stars at both 6-8 kpc (Ibata et al.; Newberg et al.) and 12-18 kpc (the Tri/And stream; Rocha-Pinto et al.) from the Sun. We have attempted to predict the present location of the Monoceros stream progenitor using different information: (1) the kinematical and spatial distribution of detections, and (2) the different mean metallicity in the inner and the outer rings. Because of the lack of observational data in the whole range of Galactic latitudes, the geometrical/kinematical constraints lead to a wide range of possible locations. By associating older parts of the model stream with lower metallicity parts of the observed data, we argue in favor of a current location of l 6 245, b 6 -18, with a distance to the Sun r sub(s) 15 kpc. The mass of the progenitor has been poorly constrained because of the slow orbital decay. Similar fits have been obtained for masses (3-9) x 10 super(8) M sub( ). We have analyzed the possible common origin of the Canis Major dwarf and the Monoceros stream. The Canis Major dwarf moves on a prograde, nearly circular orbit (e 0.16) in the Milky Way disk (i 4 super(+) sub(-) super(1) sub(4) super(4) deg). This orbital inclination is too low to account for the large vertical dispersion of stream stars. However, the bimodal distribution of radial velocities in the central region found by Martin et al. probably indicates that their selection criteria for identifying dwarf stars lead to a contamination of background stars. In that case, the kinematical data outlined above might result in an underestimate of the orbital inclination. Finally, the distance estimation to Canis Major dwarf is around a factor of 2 smaller than that obtained from our model. Unfortunately, the possible identification of the Monoceros stream progenitor in Canis Major remains unclear.
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