Introduction to the Theory of Stellar Evolution

In this chapter we briefly review the basics of the theory of stellar evolution.Comment: Chapter 1, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G. Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe

A population of binaries in the Asymptotic Giant Branch of 47 Tucanae?

We have used a set of archived Hubble Space Telescope/ACS images to probe the evolved populations of the globular cluster 47 Tucanae. We find an excess of Asymptotic Giant Branch (AGB) stars in the cluster core. We interpret this feature as the signature of an extra-population likely made by the progeny of massive stars originated by the evolution of binary systems. Indeed the comparison with theoretical tracks suggests that the AGB population of 47 Tuc can be significantly contaminated by more massive stars currently experiencing the first ascending Red Giant Branch.Comment: 14 pages, 4 figures, in press on ApJ Letter

Time domain reflectometry applied to MMIC passive component modeling

The time domain facilities of a network analyzer, combined with the tools of network synthesis, were recently used for experimental modeling of discontinuities in an S-parameter measurement set, so as to allow the instrument calibration directly to the ports of the device under test. The technique proved to be very useful in those cases where the discontinuities, that lie before the unknown device, cannot be isolated by the usual calibration methods, and therefore, since network synthesis deals only with frequency domain information, it is impossible to optimize the model's parameters, since they are affected by errors due to discontinuities. This paper describes a procedure which allows to isolate the response of the device under test, and to derive its complete model; when it to reach a reasonable accuracy it gives anyway a topology, which is a good starting point for other optimization routines that can be used for obtaining a better match, on a broad frequency band. This can be accomplished by optimzing the first approach topology to which other circuit elements have been added, so as to take into account second order effects especially at the higher frequencies. The technique was applied to model and characterize passive discrete components used in MMIC. The experimental results show the validity of the approac

Piecewise Extended Chebyshev Spaces: a numerical test for design

Given a number of Extended Chebyshev (EC) spaces on adjacent intervals, all of the same dimension, we join them via convenient connection matrices without increasing the dimension. The global space is called a Piecewise Extended Chebyshev (PEC) Space. In such a space one can count the total number of zeroes of any non-zero element, exactly as in each EC-section-space. When this number is bounded above in the global space the same way as in its section-spaces, we say that it is an Extended Chebyshev Piecewise (ECP) space. A thorough study of ECP-spaces has been developed in the last two decades in relation to blossoms, with a view to design. In particular, extending a classical procedure for EC-spaces, ECP-spaces were recently proved to all be obtained by means of piecewise generalised derivatives. This yields an interesting constructive characterisation of ECP-spaces. Unfortunately, except for low dimensions and for very few adjacent intervals, this characterisation proved to be rather difficult to handle in practice. To try to overcome this difficulty, in the present article we show how to reinterpret the constructive characterisation as a theoretical procedure to determine whether or not a given PEC-space is an ECP-space. This procedure is then translated into a numerical test, whose usefulness is illustrated by relevant examples