Near-UV Observations of CS29497-030: New Constraints on Neutron-Capture Nucleosynthesis Processes

Employing spectra obtained with the new Keck I HIRES near-UV sensitive detector, we have performed a comprehensive chemical composition analysis of the binary blue metal-poor star CS29497-030. Abundances for 29 elements and upper limits for an additional seven have been derived, concentrating on elements largely produced via neutron-capture nucleosynthesis. Included in our analysis are the two elements that define the termination point of the slow neutron-capture process, lead and bismuth. We determine an extremely high value of [Pb/Fe] = +3.65 +/- 0.07 (sigma = 0.13) from three features, supporting the single-feature result obtained in previous studies. We also detect Bi for the first time in a metal-poor star. Our derived Bi/Pb ratio is in accord with those predicted from the most recent FRANEC calculations of the slow neutron-capture process in low-mass AGB stars. We find that the neutron-capture elemental abundances of CS29497-030 are best explained by an AGB model that also includes very significant amounts of pre-enrichment of rapid neutron-capture process material in the protostellar cloud out of which the CS29497-030 binary system formed. Thus, CS29497-030 is both an ``r+s'' and ``extrinsic AGB'' star. Furthermore, we find that the mass of the AGB model can be further constrained by the abundance of the light odd-element [Na/Fe] which is sensitive to the neutron excess.Comment: 7 pages = 4 + 2 colour encapsulated postscript figures + 1 table; to appear in ApJ Letters; additional jpeg figure available at ftp://www.astro.caltech.edu/users/iii/cs2949703

Point-contact Andreev-reflection spectroscopy in segregation-free Mg_{1-x}Al_{x}B_2 single crystals up to x=0.32

We present new results of point-contact Andreev-reflection (PCAR) spectroscopy in single-phase Mg_{1-x}Al_{x}B_{2} single crystals with x up to 0.32. Fitting the conductance curves of our point contacts with the two-band Blonder-Tinkham-Klapwijk model allowed us to extract the gap amplitudes Delta_{sigma} and Delta_{pi}. The gap values agree rather well with other PCAR results in Al-doped crystals and polycrystals up to x=0.2 reported in literature, and extend them to higher Al contents. In the low-doping regime, however, we observed an increase in the small gap Delta_{pi} on increasing x (or decreasing the local critical temperature of the junctions, T_{c}^{A}) which is not as clearly found in other samples. On further decreasing T_{c}^{A} below 30 K, both the gaps decrease and, up to the highest doping level x=0.32 and down to T_{c}^{A}= 12 K, no gap merging is observed. A detailed analysis of the data within the two-band Eliashberg theory shows that this gap trend can be explained as being mainly due to the band filling and to an increase in the interband scattering which is necessary to account for the increase in Delta_{pi} at low Al contents (x < 0.1). We suggest to interpret the following decrease of Delta_{pi} for T_{c}^{A} < 30 K as being governed by the onset of inhomogeneity and disorder in the Al distribution that partly mask the intrinsic effects of doping and is not taken into account in standard theoretical approaches.Comment: 22 pages, 9 eps figures, Elsevier style. Theoretical details added in appendix. Characterization of crystals include

Predictions for low-metallicity s-process Lead stars showing peculiar r-process enhancements

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Triterpenoid saponins from the root bark of haplocoelum congolanum

peer reviewedTwo undescribed triterpenoid saponins together with 5 known ones were isolated from the root bark of Haplocoelum congolanum Hauman. Their structures were elucidated by spectroscopic methods including one-dimensional and two-dimensional nuclear magnetic resonance experiments in combination with mass spectrometry as 3-O-(4-O-[3-hydroxy-3-methylglutaryl])-α-l-arabinopyranosyl-(1→3)-α-l-rhamnopyranosyl-(1→2)-[β-d-glucopyranosyl-(1→4)]-α-l-arabinopyranosyloleanolic acid and 3-O-α-l-arabinofuranosyl-(1→3)-α-l-rhamnopyranosyl-(1→2)-[β-d-glucopyranosyl-(1→4)]-α-l-arabinopyranosyloleanolic acid. © The Author(s) 201

Triterpenoid saponins from the stem bark of pentaclethra eetveldeana

Two previously undescribed triterpenoid saponins together with 4 known ones were isolated from the stem bark of Pentaclethra eetveldeana De Wild. & Th. Dur. Their structures were elucidated by spectroscopic methods including 1D and 2D NMR experiments in combination with mass spectrometry as 3- O-β- d -glucopyranosyl- (1→2)- [β- d -glucopyranosyl- (1→3)]-β- d -glucopyranosyl- (1→4)- β- d -glucopyranosyl- (1→3)-α- l -rhamnopyranosyl- (1→2)-[β- d-glucopyranosyl- (1→4)]-α- l -arabinopyranosyloleanolic acid and 3- O -β- d -glucopyranosyl- (1→2)-[β- d -glucopyranosyl- (1→3)]-β- d -glucopyranosyl- (1→4)-β- d -glucopyranosyl- (1→3)- α -l -rhamnopyranosyl- (1→2)-[β- d -glucopyranosyl- (1→4)]-α- l -arabinopyranosylhederagenin. © The Author(s) 2019

Lead and s-process elements in stars of various metallicities : AGB predictions and observations

Peer reviewe