Keele University

About: Keele University is a education organization based out in Newcastle-under-Lyme, United Kingdom. It is known for research contribution in the topics: Population & Stars. The organization has 11318 authors who have published 26323 publications receiving 894671 citations. The organization is also known as: Keele University.

Great Circle Tidal Streams: Evidence for a Nearly Spherical Massive Dark Halo around the Milky Way

Abstract: An all-high-latitude sky survey for cool carbon giant stars in the Galactic halo has revealed 75 such stars, of which the majority are new detections. Of these, more than half are clustered on a great circle on the sky that intersects the center of Sagittarius dwarf galaxy and is parallel to its proper-motion vector, while many of the remainder are outlying Magellanic Cloud carbon stars. Previous numerical experiments regarding the disruption of the Sagittarius dwarf galaxy (the closest of the Galactic satellite galaxies) predicted that the effect of the strong tides, during its repeated close encounters with the Milky Way, would be to slowly disrupt that galaxy. Because of the small velocity dispersion of the disrupted particles, these disperse slowly along (approximately) the orbital path of the progenitor, eventually giving rise to a very long stream of tidal debris surrounding our Galaxy. The more recently disrupted fragments of this stream should contain a mix of stellar populations similar to that found in the progenitor, which includes giant carbon stars. Given the measured position and velocity of the Sagittarius dwarf, we first integrate its orbit assuming a standard spherical model for the Galactic potential and find both that the path of the orbit intersects the position of the stream and that the radial velocity of the orbit, as viewed from the solar position, agrees very well with the observed radial velocities of the carbon stars. We also present a pole-count analysis of the carbon star distribution, which clearly indicates that the great circle stream we have isolated is statistically significant, being a 5-6 σ overdensity. These two arguments strongly support our conclusion that a large fraction of the halo carbon stars originated in the Sagittarius dwarf galaxy. The stream orbits the Galaxy between the present location of the Sagittarius dwarf, 16 kpc from the Galactic center, and the most distant stream carbon star, at ~60 kpc. It follows neither a polar nor a Galactic plane orbit, so that a large range in both Galactic R- and z-distances is probed. That the stream is observed as a great circle indicates that the Galaxy does not exert a significant torque on the stream, so the Galactic potential must be nearly spherical in the regions probed by the stream. Furthermore, the radial mass distribution of the halo must allow a particle at the position and with the velocity of the Sagittarius dwarf galaxy to reach the distance of the furthest stream carbon stars. Thus, the Sagittarius dwarf galaxy tidal stream gives a very powerful means to constrain the mass distribution it resides in, that is, the dark halo. We present N-body experiments simulating this disruption process as a function of the distribution of mass in the Galactic halo. A likelihood analysis shows that, in the Galactocentric distance range 16 kpc < R < 60 kpc, the dark halo is most likely almost spherical. We rule out, at high confidence levels, the possibility that the halo is significantly oblate, with isodensity contours of aspect qm < 0.7. This result is quite unexpected and contests currently popular galaxy formation models.

Variability in use of cut-off scores and formats on the Edinburgh Postnatal Depression Scale: implications for clinical and research practice.

Abstract: Objectives: i) To highlight the increasing use in the literature of unvalidated cut-off scores on the Edinburgh Depression Scale (EDS/EPDS), as well as different wording and formatting in the scale; ii) to investigate and discuss the possible impact of using an unvalidated cut-off score; iii) to highlight possible reasons for these ‘errors’; and iv) to make recommendations to clinicians and researchers who use the EDS/EPDS. Method: A convenience sample of studies that have used unvalidated cut-off scores, or different formatting, are cited as evidence that these types of ‘errors’ are occurring fairly frequently. Examination of previous data from one of the authors is undertaken to determine the effect of using an unvalidated cut-off score. Summary: Many studies report rates of high scorers on the EDS/EPDS using different cut-off scores to the validated ones. The effect of doing this on the overall rate can be substantial. The effect of using different formatting is not known, though excluding items from the EDS/EPDS must also make a substantial difference. Recommendations: We recommend that i) the validated score of 13 or more is used when reporting on probable major depression in postnatal English-speaking women, and 15 or more when reporting on antenatal English-speaking women; ii) that the wording used is “13 or more” (or equivalent), and not other terms that may cause confusion (e.g., ‘>12’; ‘more than 12’; ‘13’ etc), iii) if a different cut-off score to the validated one is used, a clear explanation is given as to why this has been done; and iv) that the scale should be worded and formatted as originally described by its authors.

Sharing Versus Pseudo-Sharing in Web 2.0

Abstract: The Internet has opened up a new era in sharing. There has also been an explosion of studies and writings about sharing via the Internet. This includes a series of books, articles, and web discussi...