Trace element geochemistry of ordinary chondrite chondrules: the type I/type II chondrule dichotomy

We report trace element concentrations of silicate phases in chondrules from LL3 ordinary chondrites Bishunpur and Semarkona. Results are similar to previously reported data for carbonaceous chondrites, with rare earth element (REE) concentrations increasing in the sequence olivine < pyroxene < mesostasis, and heavy REE (HREE) being enriched by 1-2 orders of magnitude (CI-normalized) relative to light REE (LREE) in ferromagnesian silicates, although no single olivine with very large LREE/HREE fractionation has been found. On average, olivine in type II chondrules is poorer in refractory lithophile incompatible elements (such as REE) than its type I counterpart by a factor of ~2. This suggests that olivine in type I and II chondrules formed by batch and fractional crystallization, respectively, implying that type II chondrules formed under faster cooling rates (> ~ 10 K/h) than type I chondrules. Appreciable Na concentrations (3-221 ppm) are measured in olivine from both chondrule types; type II chondrules seem to have behaved as closed systems, which may require chondrule formation in the vicinity of protoplanets or planetesimals. At any rate, higher solid concentrations in type II chondrule forming regions may explain the higher oxygen fugacities they record compared to type I chondrules. Type I and type II chondrules formed in different environments and the correlation between high solid concentrations and/or oxygen fugacities with rapid cooling rates is a key constraint that chondrule formation models must account for.Comment: 46 pages, 7 figure

The formation conditions of enstatite chondrites: Insights from trace element geochemistry of olivine-bearing chondrules in Sahara 97096 (EH3)

We report in situ LA-ICP-MS trace element analyses of silicate phases in olivine-bearing chondrules in the Sahara 97096 (EH3) enstatite chondrite. Most olivine and enstatite present rare earth element (REE) patterns comparable to their counterparts in type I chondrules in ordinary chondrites. They thus likely share a similar igneous origin, likely under similar redox conditions. The mesostasis however frequently shows negative Eu and/or Yb (and more rarely Sm) anomalies, evidently out of equilibrium with olivine and enstatite. We suggest that this reflects crystallization of oldhamite during a sulfidation event, already inferred by others, during which the mesostasis was molten, where the complementary positive Eu and Yb anomalies exhibited by oldhamite would have possibly arisen due to a divalent state of these elements. Much of this igneous oldhamite would have been expelled from the chondrules, presumably by inertial acceleration or surface tension effects, and would have contributed to the high abundance of opaque nodules found outside them in EH chondrites. In two chondrules, olivine and enstatite exhibit negatively sloped REE patterns, which may be an extreme manifestation of a general phenomenon (possibly linked to near-liquidus partitioning) underlying the overabundance of light REE observed in most chondrule silicates relative to equilibrium predictions. The silicate phases in one of these two chondrules show complementary Eu, Yb and Sm anomalies providing direct evidence for the postulated occurrence of the divalent state for these elements at some stage in the formation reservoir of enstatite chondrites. Our work supports the idea that the peculiarities of enstatite chondrites may not require a condensation sequence at high C/O ratios as has long been believed.Comment: 30 pages, 7 figure

Comparative molecular modeling of Amphioxus calcium vector protein with calmodulin and troponin C

Calcium vector protein (CaVP), a new protein isolated from Amphioxus muscle, binds in a Ca2+ -rgulated manner to a 27 kd target protein, named CaVPT, whose function has not been elucidated yet. CaVP bears significant sequence homology to both calmodulin and skeletal muscle troponin C, especially in the C-tenninal half of the molecule, which presumably contains the two functional Ca2+ sites. The N-terminal half contains two abortive EF-hands and is intramolecularly crosslinked with a disulfide bond. Using the crystallographic structures of calmodulin and striated muscle troponin C as a framework, we constructed two different three-dimensional models of CaVP and modeled the intramolecular disulfide bridge. The modeling based upon the coordinates of calmodulin yields a Ca2+ -filled sites configuration in the N-terminal half of the molecule, even though no Ca2+ is bound in this half, whereas the troponin C-derived model generates a Ca2+ -empty sites configuration. The models predict that neither in the Ca2+ nor in the Ca2+ -empty sites conformation is there any steric and/or energetic obstacle for the formation of the disulfide bridge and that the disulfide bond is poorly accessible to reducing reagents. The optical properties of the Trp and Tyr residues of CaVP indicate that the calmodulin-derived model represents the most plausible predictio

Autoantibodies to Endothelial Cell Surface ATP Synthase, the Endogenous Receptor for Hsp60, Might Play a Pathogenic Role in Vasculatides

International audienceBACKGROUND: Heat shock protein (hsp) 60 that provides "danger signal" binds to the surface of resting endothelial cells (EC) but its receptor has not yet been characterized. In mitochondria, hsp60 specifically associates with adenosine triphosphate (ATP) synthase. We therefore examined the possible interaction between hsp60 and ATP synthase on EC surface. METHODOLOGY/PRINCIPAL FINDINGS: Using Far Western blot approach, co-immunoprecipitation studies and surface plasmon resonance analyses, we demonstrated that hsp60 binds to the β-subunit of ATP synthase. As a cell surface-expressed molecule, ATP synthase is potentially targeted by anti-EC-antibodies (AECAs) found in the sera of patients suffering vasculitides. Based on enzyme-linked immunosorbent assay and Western blotting techniques with F1-ATP synthase as substrate, we established the presence of anti-ATP synthase antibodies at higher frequency in patients with primary vasculitides (group I) compared with secondary vasculitides (group II). Anti-ATP synthase reactivity from group I patients was restricted to the β-subunit of ATP synthase, whereas those from group II was directed to the α-, β- and γ-subunits. Cell surface ATP synthase regulates intracellular pH (pHi). In low extracellular pH medium, we detected abnormal decreased of EC pHi in the presence of anti-ATP synthase antibodies, irrespective of their fine reactivities. Interestingly, soluble hsp60 abrogated the anti-ATP synthase-induced pHi down-regulation. CONCLUSIONS/SIGNIFICANCE: Our results indicate that ATP synthase is targeted by AECAs on the surface of EC that induce intracellular acidification. Such pathogenic effect in vasculitides can be modulated by hsp60 binding on ATP synthase which preserves ATP synthase activity

Oxygen- and carbon-rich variable red giant populations in the Magellanic Clouds from EROS, OGLE, MACHO, and 2MASS photometry

The carbon-to-oxygen (C/O) ratio of asymptotic giant branch (AGB) stars constitutes an important index of evolutionary and environment/metallicity factor. We develop a method for mass C/O classification of AGBs in photometric surveys without using periods. For this purpose we rely on the slopes in the tracks of individual stars in the colour-magnitude diagram. We demonstrate that our method enables the separation of C-rich and O-rich AGB stars with little confusion. For the Magellanic Clouds we demonstrate that this method works for several photometric surveys and filter combinations. As we rely on no period identification, our results are relatively insensitive to the phase coverage, aliasing, and time-sampling problems that plague period analyses. For a subsample of our stars, we verify our C/O classification against published C/O catalogues. With our method we are able to produce C/O maps of the entire Magellanic Clouds. Our purely photometric method for classification of C- and O-rich AGBs constitutes a method of choice for large, near-infrared photometric surveys. Because our method depends on the slope of colour-magnitude variation but not on magnitude zero point, it remains applicable to objects with unknown distances.Comment: 14 pages, 16 figures, 1 table, accepted for publication in Astronomy & Astrophysic

Long-term photometry and periods for 261 nearby pulsating M giants

We present the results of a 5.5-year CCD photometric campaign that monitored 261 bright, southern, semi-regular variables with relatively precise Hipparcos parallaxes. The data are supplemented with independent photoelectric observations of 34 of the brightest stars, including 11 that were not part of the CCD survey, and a previously unpublished long time-series of VZ Cam. Pulsation periods and amplitudes are established for 247 of these stars, the majority of which have not been determined before. All M giants with sufficient observations for period determination are found to be variable, with 87% of the sample (at S/N >= 7.5) exhibiting multi-periodic behaviour. The period ratios of local SRVs are in excellent agreement with those in the Large Magellanic Cloud. Apparent K-band magnitudes are extracted from multiple NIR catalogues and analysed to determine the most reliable values. We review the effects of interstellar and circumstellar extinction and calculate absolute K-band magnitudes using revised Hipparcos parallaxes.Comment: 18 pages, 15 figures; accepted for publication in Monthly Notices of the Royal Astronomical Societ

Long Period Variables in the Magellanic Clouds: OGLE + 2MASS + DENIS

(abridged) The 68000 I-band light curves of variable stars detected by the OGLE survey in the Large and Small Magellanic Clouds (MCs) are fitted by Fourier series, and also correlated with the DENIS and 2MASS databases and with lists of spectroscopically confirmed M-, S- and C-stars. Lightcurves and the results of the lightcurve fitting (periods and amplitudes) and DENIS and 2MASS magnitudes are presented for 2277 M-,S-,C-stars in the MCs. The following aspects are discussed: the K-band period-luminosity relations for the spectroscopically confirmed AGB stars, period changes over a timespan of about 17 years in a subset of about 400 LPVs, and candidate obscured AGB stars.Comment: Astronomy and Astrophysics, accepte

Mira Variables in the OGLE Bulge fields

(abridged) The 222000 I-band light curves of variable stars detected by the OGLE-II survey in the direction of the Galactic Bulge have been fitted and have also been correlated with the DENIS and 2MASS databases. Results are presented for 2691 objects with I-band semi-amplitude larger than 0.45 magnitude, corresponding to classical Mira variables. The Mira period distribution of 6 fields at similar longitude but spanning latitudes from -1.2 to -5.8 degrees are statistically indistinguisable indicating similar populations with initial masses of 1.5-2 \msol (corresponding to ages of 1-3 Gyr). A field at similar longitude at b = -0.05 from Glass et al. (2001) does show a significantly different period distribution, indicating the presence of a younger population of 2.5-3 \msol and ages below 1 Gyr. The K-band period-luminosity relation is presented for the whole sample, and for sub-fields. The zero point depends on Galactic longitude. Simulations are carried out to show that the observed dependence of the zero point with $l$, and the number of stars per field are naturally explained using the model of disk and bulge stars of Binney et al. (1997), for a viewing angle of 43 +/- 17 degrees. A comparison is made with similar objects in the Magellanic Clouds, studied in a previous paper. The slope of the PL-relation in the Bulge and the MCs agree within the errorbars. A distance to the Galactic Centre between 8.6 and 9.0 kpc is derived (for an assumed DM of 18.50 to the LMC).Comment: accepted for publication in Astronomy and Astrophysic