Lithium abundances in red giants of M4: evidence for asymptotic giant branch star pollution in globular clusters?

The determination of Li and proton-capture element abundances in globular cluster (GC) giants allows us to constrain several key questions on the multiple population scenarios in GCs, from formation and early evolution, to pollution and dilution mechanisms. In this Letter, we present our results on Li abundances for a large sample of giants in the intermediate-metallicity GC NGC 6121 (M4), for which Na and O have been already determined by Marino et al. The stars analyzed are both below and above the red giant branch bump luminosity. We found that the first and second generation stars share the same Li content, suggesting that a Li production must have occurred. This is a strong observational evidence providing support for the scenario in which asymptotic giant branch stars are GC polluters.Comment: updated version after proo

The Unique Na:O Abundance Distribution in NGC 6791: The First Open(?) Cluster with Multiple Populations

Almost all globular clusters investigated exhibit a spread in their light element abundances, the most studied being a Na:O anticorrelation. In contrast, open clusters show a homogeneous composition and are still regarded as Simple Stellar Populations. The most probable reason for this difference is that globulars had an initial mass high enough to retain primordial gas and ejecta from the first stellar generation and thus formed a second generation with a distinct composition, an initial mass exceeding that of open clusters. NGC 6791 is a massive open cluster, and warrants a detailed search for chemical inhomogeneities. We collected high resolution, high S/N spectra of 21 members covering a wide range of evolutionary status and measured their Na, O and Fe content. We found [Fe/H]=+0.42$\pm 0.01$, in good agreement with previous values, and no evidence for a spread. However, the Na:O distribution is completely unprecedented. It becomes the first open cluster to show intrinsic abundance variations that cannot be explained by mixing, and thus the first discovered to host multiple populations. It is also the first star cluster to exhibit two subpopulations in the Na:O diagram with one being chemically homogeneous while the second has an intrinsic spread that follows the anticorrelation so far displayed only by globular clusters. NGC 6791 is unique in many aspects, displaying certain characteristics typical of open clusters, others more reminiscent of globulars, and yet others, in particular its Na:O behavior investigated here, that are totally unprecedented. It clearly had a complex and fascinating history.Comment: 16 pages, 4 figures, accepted for publication in the Astrophysical Journal Letter

Aluminum abundances of multiple stellar generations in the globular cluster NGC 1851

We study the distribution of aluminum abundances among red giants in the peculiar globular cluster NGC 1851. Aluminum abundances were derived from the strong doublet Al I 8772-8773 A measured on intermediate resolution FLAMES spectra of 50 cluster stars acquired under the Gaia-ESO public survey. We coupled these abundances with previously derived abundance of O, Na, Mg to fully characterize the interplay of the NeNa and MgAl cycles of H-burning at high temperature in the early stellar generation in NGC 1851. The stars in our sample show well defined correlations between Al,Na and Si; Al is anticorrelated with O and Mg. The average value of the [Al/Fe] ratio steadily increases going from the first generation stars to the second generation populations with intermediate and extremely modified composition. We confirm on a larger database the results recently obtained by us (Carretta et al. 2011a): the pattern of abundances of proton-capture elements implies a moderate production of Al in NGC 1851. We find evidence of a statistically significant positive correlation between Al and Ba abundances in the more metal-rich component of red giants in NGC 1851.Comment: Astronomy and Astrophysics, in pres

A method for predicting the rate and effect of approach to the stall of a microlight aeroplane

The stall and immediately post-stall behaviour of a microlight aeroplane are shown to be a function of the deceleration rate prior to the stall; therefore, it is necessary to use a representative deceleration rate when determining the acceptability of stall and post-stall handling qualities. This research has found means by which the range of deceleration rates likely to be seen in a particular type can be estimated, so that flight test programmes can ensure these rates are included, and thus aircraft are confirmed to have acceptable stalling characteristics. Recommendations are made towards the use of this research for all aircraft type, and of further work which might usefully be carried out

BCAR section S issue 2 - What is possible and a review of existing designs

British Civil Airworthiness Requirements Section S “Small Light Aeroplanes” is a standard based upon the European light aircraft standard JAR-VLA. It is an unusual standard in that it is a UK administered standard that is still in routine use and development, not having been superseded by a Joint Airworthiness Requirement (JAR). Section S applies to the artificially defined class of “Microlight Aircraft” (some of which are also referred to as “SLAs”)

Stalling speeds and determination of manoeuver speed for Rogallo-winged microlight airplanes

Rogallo-winged airplanes can display a non-square law of stall speed versus loading. This Note shows, from experimental data, the form of this relationship and how this has been used during the certification of such airplanes, through operating data and modification of either maneuver speed or the normal acceleration limit

A timed method for the estimation of aeroplane take-off and landing distances

This paper describes a method by which, without the use of external personnel or equipment, take-off and landing distances of an aeroplane may be estimated. An error analysis for the method, allowing determination of outcome accuracy, is also shown. The method is validated through use of flight test results from two certification programmes: one on a light aeroplane, and one on a microlight aeroplane

Safety for non-microlight pilots

Microlight aircraft are some of the safest, cheapest and most fun aircraft flying in the UK. The fatal accident rate, at around 1 per 30,000 flying hours is similar to that of General Aviation overall, and rather better than some parts of it in recent years. However, at the BMAA we see several perfectly serviceable aircraft per year written off by very experienced GA pilots, typically with several thousand hours. Why? - well because they are different, not more difficult or more dangerous, just different. The phrase “it’s only a microlight” has as much validity as “it’s only a jet fighter” all aircraft will treat you back as they are treated