The long period classical cepheid RZ Vel (HD 73502) is known to be a member of an OB association, Vel OB1 in Vela, and a high metallicity is ascribed to it by the photometric work of Eggen (1982). We have done an abundance analysis for this long period (P = 20.4 days) and hence young (age ≈ 1.80×10⁷ yr) classical cepheid using high resolution CCD spectra with good S/N ratio. We have used a detailed model atmosphere method to derive the abundances of the light elements C, O, A1, S and of many Fe-peak elements and a few s-process elements. Our present work indicates near solar abundance for most of the elements for RZ Vel and hence we do not confirm the high metallicity derived photometrically by Eggen (1982) for this star

The origin of the abundance pattern and also the (anti)correlation present among the elements found in stars of globular clusters (GCs) remains unimproved until date. The proton-capture reactions are presently recognised in concert of the necessary candidates for that sort of observed behaviour in the second generation stars. We tend to propose a reaction network of a nuclear cycle namely carbon–nitrogen–oxygen–fluorine (CNOF) at evolved stellar condition since fluorine (¹⁹F) is one such element which gets plagued by proton capture reactions. The stellar temperature thought about here ranges from 2×10⁷ to 10×10⁷ K and there has been an accretion occuring, with material density being 10² g/cm³ and 10³ g/cm³. Such kind of temperature density conditions are probably going to be prevailing within the H-burning shell of evolved stars. The estimated abundances of ¹⁹F are then matched with the info that has been determined for a few some metal-poor giants of GC M4, M22,47 Tuc as well as NGC 6397. As far as the comparison between the observed and calculated abundances is concerned, it is found that the abundance of ¹⁹F have shown an excellent agreement with the observed abundances with a correlation coefficent above 0.9, supporting the incidence of that nuclear cycle at the adopted temperature density conditions.

Understanding nucleosynthesis in and evolution of asymptotic giant branch (AGB) stars is of primary importance as these stars are the main producers of some of the key elements in the Universe. They are the predominant sites for slow-neutron-capture nucleosynthesis (s-process). The exact physical conditionsand nucleosynthetic processes occurring in the interior of AGB stars are not clearly understood, and that hinders better understanding of the contribution of these stars to the Galactic chemical enrichment. Extrinsic-variable stars that are known to have received products of AGB phase of evolution via binary masstransfer mechanisms are vital tools in tracing AGB nucleosynthesis. The [Rb/Zr] ratio is an important diagnostic to understand the average neutron density at the s-process site and provides important clues to the mass of companion AGB stars in binaries. In this work we have presented estimates of [Rb/Zr] ratios based on high-resolution spectroscopic analysis for a sample of Ba stars, and discussed how the ratio can be used to understand the characteristics of the AGB star. Results from an analysis based on a parametric model toconfirm the mass of the companion AGB star are also presented.

All the elements heavier than Fe are produced either by the slow (-s) or rapid (-r) neutroncapture process. The neutron density prevailing in the stellar sites is one of the major factors that determines the type of neutron-capture processes. We present the results based on the estimates of corrected value of absolute carbon abundance, [C/N] ratio, carbon isotopic ratio and [hs/ls] ratio obtained from the highresolution spectral analysis of six stars that include both CH stars and CEMP stars. All the stars show enhancement of neutron-capture elements. Location of these objects in the A(C) vs. [Fe/H] diagram shows that they are Group I objects, with external origin of carbon and neutron-capture elements. Low values of carbon isotopic ratios estimated for these objects may also be attributed to some external sources. As the carbon isotopic ratio is a good indicator of mixing, we have used the estimates of ${}^{12}$C/${}^{13}$C ratios to examine the occurrence of mixing in the stars. While the object HD 30443 might have experienced an extra mixing process that usually occurs after red giant branch (RGB) bump for stars with log(L/L$_{\odot}$)>2.0, the remainingobjects do not show any evidence of having undergone any such mixing process. The higher values of [C/N] ratios obtained for these objects also indicate that none of these objects have experienced any strong internal mixing processes. Based on the estimated abundances of carbon and the neutron-capture elements, and the abundance ratios, we have classified the objects into different groups. While the objects HE 0110-0406, HD 30443 and CD-38 2151 are found to be CEMP-s stars, HE 0308-1612 and HD 176021 show characteristicproperties of CH stars with moderate enhancement of carbon. The object CD-28 1082 with enhancement of both r- and s-process elements is found to belong to the CEMP-r/s group.

The surface chemical compositions of a large fraction of carbon-enhanced metal-poor (CEMP) stars, the so-called CEMP-r/s stars, are known to exhibit enhancement of both s-process and r-process elements. For these stars, the heavy-element abundances cannot be explained either by s-process or r-processnucleosynthesis alone, as the production sites of s-process and r-process elements are very different, and these two processes produce distinct abundance patterns. Thus, the observational evidence of the doubleenhancement seen in CEMP-r/s stars remains a puzzle as far as the origin of the elements is concerned. In this work, we have critically analysed the observed abundances of heavy elements in a sample of eight CEMP-r/s stars from the literature to trace the origin of the observed double enhancement. Towards this, we have conducted a parametric-model-based analysis to delineate the contributions of s-process and r-process nucleosynthesis to the observed elemental abundances. We have further examined if the i-process (intermediate-process) nucleosynthesis that occurs at high neutron density (${\rm n} \sim 10^{15}$ cm$^{-3}$) produced during proton ingestion from a H-rich envelope to the intershell region of an AGB star, which is capable of producing both r-process and s-process elements in a single stellar site, could explain the observed abundance patterns of the sample stars. Our analysis shows that the observed abundance patterns of the selected sample of CEMP-r/s stars could be fairly well reproduced using the i-process model yields.