Research Article
Modeling Galactic Oxygen Enrichment via the NOFNe Cycle in Halo and Disk Stars
Issue:
Volume 14, Issue 1, March 2026
Pages:
1-13
Received:
5 December 2025
Accepted:
22 December 2025
Published:
20 January 2026
Abstract: We present a theoretical analysis of oxygen abundances in a sample of 67 metal-poor field stars belonging to the Galactic halo and disk populations. The primary objective of this study is to investigate whether proton-capture nucleosynthesis pathways can reproduce the observed oxygen abundance trends in metal-poor stellar environments. Oxygen abundances,[O/H]LTE, are derived under the assumption of local thermodynamic equilibrium. The NOFNe nuclear reaction cycle is modelled under advanced stellar burning conditions, spanning temperatures of 1 × 108–3.5 × 108 K and a characteristic density of 102 g cm−3. Enhanced stellar atmosphere models and refined abundance calculations yield excellent agreement with reported values, with mean absolute deviations in the range 0.00–0.02 dex. The calculations further reveal subtle but systematic variations in oxygen abundance associated with changes in hydrogen (XH) and oxygen (XO) mass fractions. For the full sample, we obtain a mean oxygen abundance of <[O/H]> = −0.49 dex with a mean absolute deviation of 0.19 dex, consistent with expectations for metal-poor stellar populations. Distinct abundance signatures are identified among thick-disk, high-α, and low-α halo stars, reflecting differences in their nucleosynthetic histories and formation pathways. These results provide important constraints on oxygen synthesis in massive stars and supernovae and support a role for proton-capture reactions within the NOFNe cycle, together with rotationally induced mass loss, in shaping the observed surface oxygen abundances. Overall, this study offers new insights into Galactic chemical evolution and the assembly history of the stellar halo.
Abstract: We present a theoretical analysis of oxygen abundances in a sample of 67 metal-poor field stars belonging to the Galactic halo and disk populations. The primary objective of this study is to investigate whether proton-capture nucleosynthesis pathways can reproduce the observed oxygen abundance trends in metal-poor stellar environments. Oxygen abund...
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Research Article
Polarity Dependence of the Diurnal Anisotropy of Cosmic Rays Intensity
Ambika Singh*
Issue:
Volume 14, Issue 1, March 2026
Pages:
14-19
Received:
2 January 2026
Accepted:
14 January 2026
Published:
30 January 2026
DOI:
10.11648/j.ijass.20261401.12
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Abstract: The diurnal anisotropy of galactic cosmic ray intensity provides an important diagnostic of solar modulation processes operating in the heliosphere. In the present work, a comprehensive long-term investigation of the diurnal anisotropy has been carried out using pressure-corrected hourly neutron monitor data from two high-latitude stations, Moscow and Kiel, covering a period of 52 years (1965–2016) corresponding to solar cycles 20 to 24. Daily values of the first harmonic diurnal amplitude and phase were obtained through harmonic analysis, from which annual mean values were derived. The long-term relationship between the diurnal amplitude and phase has been examined on annual, solar-cycle, and solar magnetic polarity bases. While day-to-day variations of amplitude and phase are found to be statistically independent, their annual averages exhibit clear solar-cycle-dependent behavior. A weak positive correlation between the diurnal amplitude and phase is observed when all years are considered together. However, a pronounced odd–even solar cycle asymmetry emerges when the data are segregated into odd and even cycles. Strong and statistically significant positive correlations characterize the odd solar cycles, whereas even solar cycles display weak and insignificant correlations. Furthermore, a clear dependence on solar magnetic polarity is observed, with large positive correlations during positive polarity epochs (A > 0) and reduced or reversed correlations during negative polarity epochs (A < 0). These results provide strong observational evidence that long-term variations of cosmic ray diurnal anisotropy are governed not only by solar activity but also by heliospheric magnetic polarity and particle drift effects.
Abstract: The diurnal anisotropy of galactic cosmic ray intensity provides an important diagnostic of solar modulation processes operating in the heliosphere. In the present work, a comprehensive long-term investigation of the diurnal anisotropy has been carried out using pressure-corrected hourly neutron monitor data from two high-latitude stations, Moscow ...
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