10,406 research outputs found
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
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