Stellar populations in the Magellanic Clouds: looking through the dust

We present the first results of our study of stellar populations in the Large and Small Magellanic Clouds based on multi-band WFPC2 observations of "random" fields taken as part of the "pure parallel" programme carried out with the HST as a service to the community.Comment: Two pages, one figure, to appear in the proceedings of IAU Symposium 241 "Stellar Populations as Building Blocks of Galaxies", eds. A. Vazdekis and R. Peletie

RULES FOR AN EMERGENT MARKET: Selling paintings in late seventeenth-century London

Conditions of sale were a feature of the Roman auction, and probably published along with the written public announcement, the proscriptio , that preceded a sale. When such conditions appeared on the front pages of printed sale catalogues for paintings, prints and drawings in late seventeenth-century London, then, this was nothing new; but the rules themselves were almost certainly modified to fit the circumstances then prevailing. Here I wish to examine those rules and explore the rationale for either modifying traditional elements among them or introducing some for - it seems - the first time. I will also use the exploration as an occasion to conduct two additional probes. One of these will be into the likely level and structure of prices in these early London sales, the inquiry into structure revealing that many sales were two-in-one, appealing to dual audiences. The other probe will show that the market was also segmented by quality and location, which must have restricted the possibilities for immediate profitable resale and thus the likelihood that individuals' bids were influenced by those of others.

NGC2298: a globular cluster on its way to disruption

We have studied the stellar main sequence (MS) of the globular cluster NGC2298 using deep HST/ACS observations in the F606W and F814W bands covering an area of 3.4' x 3.4' around the cluster centre or about twice the cluster's half-mass radius. The colour-magnitude diagram that we derive in this way reveals a narrow and well defined MS extending down to the 10 sigma detection limit at m_606~26.5, m_814~25, corresponding to stars of ~0.2 Msolar. The luminosity function (LF) obtained with these data, once corrected for the limited effects of photometric incompleteness, reveals a remarkable deficiency of low-mass stars as well as a radial gradient, in that the LF becomes progressively steeper with radius. Using the mass-luminosity relation appropriate for the metallicity of NGC2298, we derive the cluster's global mass function (GMF) by using a multi-mass Michie-King model. Over the range 0.8 - 0.2 Msolar, the number of stars per unit mass decreases following a power-law distribution of the type dN/dm \propto m^(0.5), where, for comparison, typical halo clusters have dN/dm \propto m^(-1.5). If the IMF of NGC2298 was similar to that of other metal poor halo clusters, like e.g. NGC6397, the present GMF that we obtain implies that this object must have lost of order 85% of its original mass, at a rate much higher than that suggested by current models based on the available cluster orbit. The latter may, therefore, need revision.Comment: 9 pages, 6 figures, accepted for publication in Astronomy and Astrophysic

The Luminosity Function of Omega Centauri

Deep HST-WFPC2 observations of the stellar population in the globular cluster Omega Cen (NGC 5139) have been used to measure the luminosity function of main sequence stars at the low-mass end. Two fields have been investigated, located respectively ~4.6' and ~7' away from the cluster center, or near the half-light radius of this cluster (~4.8'). The color-magnitude diagrams derived from these data show the cluster main sequence extending to the detection limit at I ~ 24. Information on both color and magnitude is used to build the luminosity functions of main sequence stars in these fields and the two independent determinations are found to agree very well with each other within the observational uncertainty. Both functions show a peak in the stellar distribution around M_I ~ 9 followed by a drop at fainter magnitudes well before photometric incompleteness becomes significant, as is typical of other globular clusters observed with the HST. This result is at variance with previous claims that the luminosity function of Omega Cen stays flat at low masses, but is in excellent agreement with recent near-IR NICMOS observations of the same cluster.Comment: To appear in The Astronomical Journal. Contains 7 pages, 4 figures, prepared with the AAS LaTeX macr

The elusive half-pole in the transfer function of Peltier thermoelectric devices

it is shown that the transfer function of thermoelectric devices includes a half pole, which could be useful in precisione control loop

On the Lebesgue constant of the trigonometric Floater-Hormann rational interpolant at equally spaced nodes

It is well known that the classical polynomial interpolation gives bad approximation if the nodes are equispaced. A valid alternative is the family of barycentric rational interpolants introduced by Berrut in [4], analyzed in terms of stability by Berrut and Mittelmann in [5] and their extension done by Floater and Hormann in [8]. In this paper firstly we extend them to the trigonometric case, then as in the Floater-Hormann classical interpolant, we study the growth of the Lebesgue constant on equally spaced points. We show that the growth is logarithmic providing a stable interpolation operato