High Mass Triple Systems: The Classical Cepheid Y Car

We have obtained an HST STIS ultraviolet high dispersion Echelle mode spectrum the binary companion of the double mode classical Cepheid Y Car. The velocity measured for the hot companion from this spectrum is very different from reasonable predictions for binary motion, implying that the companion is itself a short period binary. The measured velocity changed by 7 km/ s during the 4 days between two segments of the observation confirming this interpretation. We summarize "binary" Cepheids which are in fact members of triple system and find at least 44% are triples. The summary of information on Cepheids with orbits makes it likely that the fraction is under-estimated.Comment: accepted by A

Preclinical antitumour activity of F 11782, a novel dual catalytic inhibitor of topoisomerases

F 11782 is a novel inhibitor of topoisomerases I and II, with an original mechanism of action (Perrin et al, 2000). This study, aimed to define its anticancer efficacy against a series of murine and human tumour models, has provided evidence of major antitumour activity for F 11782. This was demonstrated as a high level of activity against the P388 leukaemia, as reflected by increased survival of 143–457%, when administered i.p., p.o. or i.v. as single or multiple doses, and proved consistently superior to etoposide or camptothecin tested concurrently. Single or multiple i.p. doses of F 11782 also proved highly active against the s.c. grafted B16 melanoma, significantly increasing survival (P < 0.001) and inhibiting tumour growth (T/C of 0.3%), again superior to etoposide tested concurrently. Furthermore, F 11782 inhibited the number of pulmonary metastatic foci of the B16F10 melanoma by 99%. In human tumour xenograft studies, multiple i.p. doses of F 11782 resulted in major inhibitory activity against MX-1 (breast) tumours (T/C of 0.1%), as well as causing definite tumour regressions, whereas none resulted from similar experimental treatments with etoposide. Significant activity was also recorded with F 11782 against the relatively refractory LX-1 (lung) xenografts, with an optimal T/C value of 19%. It was notable that the antitumour activity of F 11782 was consistently demonstrated over a wide range of 2–6 dose levels, providing evidence of its good overall tolerance. In conclusion, these results emphasize the preclinical interest of this novel molecule and support its further preclinical development. © 2000 Cancer Research Campaign http://www.bjcancer.co

Structure and Evolution of Nearby Stars with Planets. I. Short-Period Systems

Using the Yale stellar evolution code, we have calculated theoretical models for nearby stars with planetary-mass companions in short-period nearly circular orbits: 51 Pegasi, Tau Bootis, Upsilon Andromedae, Rho Cancri, and Rho Coronae Borealis. We present tables listing key stellar parameters such as mass, radius, age, and size of the convective envelope as a function of the observable parameters (luminosity, effective temperature, and metallicity), as well as the unknown helium fraction. For each star we construct best models based on recently published spectroscopic data and the present understanding of galactic chemical evolution. We discuss our results in the context of planet formation theory, and, in particular, tidal dissipation effects and stellar metallicity enhancements.Comment: 48 pages including 13 tables and 5 figures, to appear in Ap

Magnetic Interactions and Transport in (Ga,Cr)As

The magnetic, transport, and structural properties of (Ga,Cr)As are reported. Zincblende Ga$_{1-x}$Cr$_{x}$As was grown by low-temperature molecular beam epitaxy (MBE). At low concentrations, x$\sim$0.1, the materials exhibit unusual magnetic properties associated with the random magnetism of the alloy. At low temperatures the magnetization M(B) increases rapidly with increasing field due to the alignment of ferromagnetic units (polarons or clusters) having large dipole moments of order 10-10$^2$$\mu_B$. A standard model of superparamagnetism is inadequate for describing both the field and temperature dependence of the magnetization M(B,T). In order to explain M(B) at low temperatures we employ a distributed magnetic moment (DMM) model in which polarons or clusters of ions have a distribution of moments. It is also found that the magnetic susceptibility increases for decreasing temperature but saturates below T=4 K. The inverse susceptibility follows a linear-T Curie-Weiss law and extrapolates to a magnetic transition temperature $\theta$=10 K. In magnetotransport measurements, a room temperature resistivity of $\rho$=0.1 $\Omega$cm and a hole concentration of $\sim10^{20}$ cm$^{-3}$ are found, indicating that Cr can also act as a acceptor similar to Mn. The resistivity increases rapidly for decreasing temperature below room temperature, and becomes strongly insulating at low temperatures. The conductivity follows exp[-(T$_1$/T)$^{1/2}$] over a large range of conductivity, possible evidence of tunneling between polarons or clusters.Comment: To appear in PRB 15 Mar 200