The Cepheid impostor HD 18391 and its anonymous parent cluster

New and existing photometry for the G0 Ia supergiant HD 18391 is analyzed in order to confirm the nature of the variability previously detected in the star, which lies off the hot edge of the Cepheid instability strip. Small‐amplitude variability at a level of δV = 0.016 ± 0.002 is indicated, with a period of P = 123^d.04 ± 0^d.06. A weaker second signal may be present at P = 177^d.84 ± 0^d.18 with δV = 0.007 ± 0.002, likely corresponding to fundamental mode pulsation if the primary signal represents overtone pulsation (123.04/177.84 = 0.69). The star, with a spectroscopic reddening of E_B–V = 1.02 ± 0.003, is associated with heavily‐reddened B‐type stars in its immediate vicinity that appear to be outlying members of an anonymous young cluster centered ∼10′ to the west and 1661 ± 73 pc distant. The cluster has nuclear and coronal radii of r_n = 3.5′ and R_c = 14′, respectively, while the parameters for HD 18391 derived from membership in the cluster with its outlying B stars are consistent with those implied by its Cepheid‐like pulsation, provided that it follows the semi‐period‐luminosity relation expected of such objects. Its inferred luminosity as a cluster member is M_V = –7.76 ± 0.10, its age (9 ± 1) × 10⁶ years, and its evolutionary mass ∼19 M_⊙. HD 18391 is not a classical Cepheid, yet it follows the Cepheid period‐luminosity relation closely, much like another Cepheid impostor, V810 Cen (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photometric observations of Cepheids from the ASAS-3 catalog: Photoelectric <Emphasis Type="Italic">BV I</Emphasis><Subscript>c</Subscript> observations of 33 classical Cepheids

Cepheids, the principal distance indicators, point to the existence of two inner Galactic spiral arms in the immediate solar neighborhood (within 5 kpc). However, the available Cepheids are clearly insufficient for a detailed study of the structure of these arms. Fortunately, southern-sky monitoring (the ASAS project) has led to the discovery of many new variable stars, more than one thousand of which have been identified as possible Cepheids. To improve the classification and to construct reliable light curves for new Cepheids, we have begun their regular photometric observations. Here, we present the first results: 1192 photoelectricBV I _c observations were performed for 33 classical Cepheidswith the 76-cm telescope of the South-African Astronomical Observatory (SAAO, the South-African Republic) from December 2006 to January 2008. We provide tables of observations and V light and B-V and V-I _c color curves. The new observations together with ASAS-3 data have been used to improve the elements of the light variations.     

A transmission electron microscope study of Chassigny: Evidence for strong shock metamorphism

Abstract— Chassigny is a shock-metamorphosed dunite of probable Martian origin. In order to determine its degree of shock metamorphism and to define the starting conditions prior to its ejection from Mars, the shock signature of Chassigny has been carefully examined by optical and electronoptical techniques. Dominant shock effects are the conversion of feldspars to diaplectic glass (maskelynite), the clino-/orthoenstatite inversion, strong mosaicism of olivine, and the activation of numerous planar fractures and c dislocations in olivine. High-resolution transmission electron microscopy (TEM) reveals additionally the coexistance of planar fractures with, so far, unknown discontinuous fractures in olivine. These findings point to a shock pressure of 35 GPa. Chassigny has thus experienced a high and similar degree of shock metamorphism as the shergottites. The results of this study suggest that Chassigny was at a shallow target position, close to the point of impact, when it was ejected.     

Particle–water interactions of 2,2′,5,5′-tetrachlorobiphenyl under simulated estuarine conditions

A batch sorption technique for the determination of particle–water interactions of hydrophobic organic micropollutants under simulated estuarine conditions is described. Results are presented for the behaviour of 2,2′,5,5′-tetrachlorobiphenyl (2,2′,5,5′-TCB) in river and sea waters, both in the presence and absence of estuarine suspended particles. Adsorption onto particles in sea water was enhanced compared with adsorption in river water owing to salting out of the compound, and possibly of the particulate organic matter, in the presence of high concentrations of dissolved ions. The particle–water distribution coefficient, K_D, decreased from about 120×10³ to 10×10³ ml g⁻¹, and from about 150×10³ to 20×10³ ml g⁻¹, in river water and sea water, respectively, over a particle concentration range of 10–1000 mg l⁻¹. Incomplete recovery of compound from the reactor walls is partly responsible for a particle concentration effect, while artefacts relating to inadequate sediment and water phase separation were ruled out following further experiments. The particle concentration effect, which is replicated in many field studies of hydrophobic organic micropollutants, including 2,2′,5,5′-TCB, is incorporated into a simple partitioning model and is discussed in the context of the likely estuarine behaviour of such compounds.     

Petrogenesis of an 800 m lava sequence in eastern Uruguay: insights into magma chamber processes beneath the Paraná flood basalt province

Major and trace element along with representative Sr, Nd and Pb isotope data are presented for drill core samples which intersect an 800 m lava pile in eastern Uruguay. The lavas form part of the Paraná flood basalt province, are low-Ti in composition but distinct from the low-Ti Gramado magma type, and have been termed the Treinte Y Trés magma type. The lava pile overlies a large positive gravity anomaly inferred to reflect an east–west trending, mid-crustal mafic intrusive body with a calculated volume of 35,000 km³. Smooth up-section compositional variations in the basalts are interpreted to record magma evolution within this mid-crustal magma chamber. ⁸⁷Sr/⁸⁶Sr and ²⁰⁶Pb/²⁰⁴Pb increase throughout the sequence yet Mg remains relatively constant in the lower 200 m of the sequence, suggesting a role for magma chamber recharge. Above this the lavas show a regular, up-section decrease in Mg coupled with increasing ⁸⁷Sr/⁸⁶Sr and ²⁰⁶Pb/²⁰⁴Pb and this is interpreted to reflect crystal fractionation combined with crustal contamination. The data provide further evidence that contamination of flood basalt magmas in crustal magma chambers is a common phenomenon and calculations suggest that the amount of crustal addition may be as high as 60–70%. Nevertheless, the effects of this crustal contamination do not appear able to account for the discrepancy between key incompatible trace element ratios and isotope ratios of the lavas and those of any putative mantle plume. In fact, La/Ta decreases with decreasing Mg and increasing ⁸⁷Sr/⁸⁶Sr indicating that the effects of crustal contamination were actually to reduce La/Ta and implying that the parental magmas had very high La/Ta (90). These constraints are clearly inconsistent with an asthenospheric origin for the parental magmas and so, consistent with mass balance calculations, it is inferred that they were derived from the lithospheric mantle.