Galaxies

18 pages, 5685 KiB

Open AccessArticle

Analysis of Habitability and Stellar Habitable Zones from Observed Exoplanets

by Jonathan H. Jiang, Philip E. Rosen, Christina X. Liu, Qianzhuang Wen and Yanbei Chen

Galaxies 2024, 12(6), 86; https://doi.org/10.3390/galaxies12060086 - 3 Dec 2024

The investigation of exoplanetary habitability is integral to advancing our knowledge of extraterrestrial life potential and detailing the environmental conditions of distant worlds. In this analysis, we explore the properties of exoplanets situated with respect to circumstellar habitable zones by implementing a sophisticated [...] Read more.

The investigation of exoplanetary habitability is integral to advancing our knowledge of extraterrestrial life potential and detailing the environmental conditions of distant worlds. In this analysis, we explore the properties of exoplanets situated with respect to circumstellar habitable zones by implementing a sophisticated filtering methodology on data from the NASA Exoplanet Archive. This research encompasses a thorough examination of 5595 confirmed exoplanets listed in the Archive as of 10 March 2024, systematically evaluated according to their calculated average surface temperatures and stellar classifications of their host stars, taking into account the biases implicit in the methodologies used for their discovery. Machine learning, in the form of a Random Forest classifier and an XGBoost classifier, is applied in the classification with high accuracies. The feature importance analysis indicates that our approach captures the most important parameters for habitability classification. Our findings elucidate distinctive patterns in exoplanetary attributes, which are significantly shaped by the spectral classifications and mass of the host stars. The insights garnered from our study both inform refinement of existing models for managing burgeoning exoplanetary datasets, and lay foundational groundwork for more in-depth explorations of the dynamic relationships between exoplanets and their stellar environments. Full article

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6 pages, 256 KiB

Open AccessCommunication

Insight on AGB Mass-Loss and Dust Production from PNe

by Silvia Tosi

Galaxies 2024, 12(6), 85; https://doi.org/10.3390/galaxies12060085 - 2 Dec 2024

Abstract

The asymptotic giant branch (AGB) phase, experienced by low- and intermediate-mass stars (LIMSs), plays a crucial role in galaxies due to its significant dust production. Planetary nebulae (PNe) offer a novel perspective, providing valuable insights into the dust production mechanisms and the evolutionary [...] Read more.

The asymptotic giant branch (AGB) phase, experienced by low- and intermediate-mass stars (LIMSs), plays a crucial role in galaxies due to its significant dust production. Planetary nebulae (PNe) offer a novel perspective, providing valuable insights into the dust production mechanisms and the evolutionary history of LIMSs. We selected a sample of nine PNe from the Large Magellanic Cloud (LMC), likely originating from single stars. By modeling their spectral energy distributions (SEDs) with photoionization techniques, we successfully reproduced the observed photometric data, spectra, and chemical abundances. This approach enabled us to constrain key characteristics of the central stars (CSs), dust, and gaseous nebulae, which were then compared with predictions from stellar evolution models. By integrating observational data across ultraviolet (UV) to infrared (IR) wavelengths, we achieved a comprehensive understanding of the structure of the PNe in our sample. The results of the SED analysis are consistent with evolutionary models and previous studies that focus on individual components of the PN, such as dust or the gaseous nebula. Our analysis enabled us to determine the metallicity, the progenitor mass of the CSs, and the amount of dust and gas surrounding the CSs, linking these properties to the previous AGB phase. The PN phase provides critical insights into the physical processes active during earlier evolutionary stages. Additionally, we found that higher progenitor masses are associated with greater amounts of dust in the surrounding nebulae but lower amounts of gaseous material compared to sources with lower progenitor masses. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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9 pages, 7780 KiB

Open AccessArticle

On the Ionization Tolerance of C₂₀ Fullerene in Ground and Excited Electronic States in Planetary Nebulae

by SeyedAbdolreza Sadjadi and Quentin Andrew Parker

Galaxies 2024, 12(6), 84; https://doi.org/10.3390/galaxies12060084 - 30 Nov 2024

Abstract

As the smallest member of the fullerene family,

C_{20}

is yet to be discovered in planetary nebulae. In this work, we present a quantum chemical study via density functional theory (DFT) and partially by the MP2 on the ionization tolerance of this [...] Read more.

As the smallest member of the fullerene family,

C_{20}

is yet to be discovered in planetary nebulae. In this work, we present a quantum chemical study via density functional theory (DFT) and partially by the MP2 on the ionization tolerance of this molecule in the space environment. Considering that the ionization and excitation phenomena play key roles in demonstrating the lifetime of a molecule, we examined both ground and excited electronic-state potential energy surfaces (PES) of

C_{20}

and its cations

{C_{20}}^{q +}

. Our theoretical results indicate that the

C_{20}

cage tolerates a positive charge as high as

13 +

by characterizing local minimum geometries on both the abovementioned electronic states. The results are backed by characterizing both

{C_{20}}^{12 +}

and

{C_{20}}^{13 +}

as local minimum geometries at the MP2 level of computations. We also explored, theoretically and systematically, scenarios in which the electronic structure of neutral

C_{20}

is excited to very high spin multiplicity (beyond triplet state), and local minimum molecular geometries with cage structures are well characterized. We anticipate that such structural resistance to excitation and ionization delivers a prolonged lifetime necessary for the spectroscopic detection of this interesting molecule and its cations in space and potentially in planetary nebulae (PN). Full article

(This article belongs to the Special Issue Origins and Models of Planetary Nebulae)

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32 pages, 3308 KiB

Open AccessReview

Primer on Formation and Evolution of Hydrogen-Deficient Central Stars of Planetary Nebulæ and Related Objects

by Marcelo M. Miller Bertolami

Galaxies 2024, 12(6), 83; https://doi.org/10.3390/galaxies12060083 - 29 Nov 2024

Abstract

We present a brief review of the formation and evolution of hydrogen-deficient central stars of planetary nebulae. We include a detailed description of the main observable features of both the central stars and their surrounding nebulae and review their main classifications. We also [...] Read more.

We present a brief review of the formation and evolution of hydrogen-deficient central stars of planetary nebulae. We include a detailed description of the main observable features of both the central stars and their surrounding nebulae and review their main classifications. We also provide a brief description of the possible progenitor systems of hydrogen-deficient central stars as well as of transients, which are closely connected to the formation of these stars. In particular, we offer a detailed theoretical explanation of the main evolutionary scenarios, both single and binary, which is devised to explain these stars and nebulae. Particular emphasis is made in the description of the so-called born again scenario, their quantitative predictions, and uncertainties. Finally, we discuss the pros and cons of both binary and single evolution channels, draw some conclusions, and discuss open questions in the field. Full article

(This article belongs to the Special Issue Origins and Models of Planetary Nebulae)

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8 pages, 888 KiB

Open AccessArticle

Dusty Common Envelope Evolution

by Lionel Siess, Luis C. Bermúdez-Bustamante, Orsola De Marco, Daniel J. Price, Miguel González-Bolívar, Chunliang Mu, Mike Y. M. Lau, Ryosuke Hirai and Taïssa Danilovich

Galaxies 2024, 12(6), 82; https://doi.org/10.3390/galaxies12060082 - 29 Nov 2024

Abstract

We present the first hydrodynamical simulations of common envelope evolution that include the formation of dust and the effect of radiation pressure on dust grains. We performed smoothed particle hydrodynamics simulations of the CE evolution for two systems made of a 1.7 [...] Read more.

We present the first hydrodynamical simulations of common envelope evolution that include the formation of dust and the effect of radiation pressure on dust grains. We performed smoothed particle hydrodynamics simulations of the CE evolution for two systems made of a 1.7

M_{⊙}

and 3.7

M_{⊙}

AGB star primary with a 0.6

M_{⊙}

binary companion. The results of our calculations indicate that dust formation has a negligible impact on the gas dynamics essentially because dust forms in the already unbound material. The expansion and cooling of the envelope yield very early and highly efficient production of dust. In our formalism, which does not consider dust destruction, almost 100% of the available carbon that is not locked in CO condensates in dust grains. This massive dust production, thus, strongly depends on the envelope mass and composition, in particular, its C/O ratio, and has a considerable impact on the observational aspect of the object, resulting in a photospheric radius that is approximatively one order of magnitude larger than that of a non-dusty system. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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14 pages, 565 KiB

Open AccessArticle

A Parameter Study of 1D Atmospheric Models of Pulsating AGB Stars

by Henry A. Prager, Lee Anne M. Willson, Joyce A. Guzik, Michelle J. Creech-Eakman and Qian Wang

Galaxies 2024, 12(6), 81; https://doi.org/10.3390/galaxies12060081 - 29 Nov 2024

Abstract

Using the atmospheric pulsation code written by George Bowen, we have performed a parameter study examining the effects of modifying various parameters of models of oxygen-rich AGB atmospheres pulsating in the fundamental and first-overtone modes. For each pulsation mode, we have examined the [...] Read more.

Using the atmospheric pulsation code written by George Bowen, we have performed a parameter study examining the effects of modifying various parameters of models of oxygen-rich AGB atmospheres pulsating in the fundamental and first-overtone modes. For each pulsation mode, we have examined the effects of adjusting the dust condensation temperature, dust condensation temperature range, pulsation amplitude, dust opacity, and metallicity. Our model grids are generated with the constraint that their luminosities are chosen to span the range of observed mass loss rates at a chosen mass. The dust condensation temperature, pulsation amplitude, and dust opacity have strong effects on the ultimate location and shape of the final model grids in the mass luminosity plane. The mass loss rate evolution of the fundamental and first-overtone mode models show a significant difference in behavior. While the fundamental mode models exhibit the typically assumed power–law relation with mass and luminosity, the first-overtone mode models show significant non-power law behavior at observed mass loss rates. Effectively, models in the first-overtone mode require somewhat higher luminosities to reach the same mass loss rates seen in fundamental mode models of the same mass, consistent with observed AGB stars. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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19 pages, 1396 KiB

Open AccessReview

Fifty Years After the Discovery of the First Stellar-Mass Black Hole: A Review of Cyg X-1

by Jiachen Jiang

Galaxies 2024, 12(6), 80; https://doi.org/10.3390/galaxies12060080 - 21 Nov 2024

Abstract

Around 50 years ago, the famous bet between Stephen Hawking and Kip Thorne on whether Cyg X-1 hosts a stellar-mass black hole became a well-known story in the history of black hole science. Today, Cyg X-1 is widely recognised as hosting a stellar-mass [...] Read more.

Around 50 years ago, the famous bet between Stephen Hawking and Kip Thorne on whether Cyg X-1 hosts a stellar-mass black hole became a well-known story in the history of black hole science. Today, Cyg X-1 is widely recognised as hosting a stellar-mass black hole with a mass of approximately 20 solar masses. With the advancement of X-ray telescopes, Cyg X-1 has become a prime laboratory for studies in stellar evolution, accretion physics, and high-energy plasma physics. In this review, we explore the latest results from X-ray observations of Cyg X-1, focusing on its implications for black hole spin, its role in stellar evolution, the geometry of the innermost accretion regions, and the plasma physics insights derived from its X-ray emissions. This review primarily focuses on Cyg X-1; however, the underlying physics applies to other black hole X-ray binaries and, to some extent, to AGNs. Full article

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10 pages, 3558 KiB

Open AccessArticle

The New Deep-Underground Direct Measurement of ²²Ne(α, γ)²⁶Mg with EASγ: A Feasibility Study

by Daniela Mercogliano, Andreas Best and David Rapagnani

Galaxies 2024, 12(6), 79; https://doi.org/10.3390/galaxies12060079 - 20 Nov 2024

Abstract

²²Ne(α, γ)²⁶Mg is pivotal in the understanding of several open astrophysical questions, as the nucleosynthesis beyond Fe through the s-process, but its stellar reaction rate is still subject to large uncertainties. These mainly arise from its extremely low rate in [...] Read more.

²²Ne(α, γ)²⁶Mg is pivotal in the understanding of several open astrophysical questions, as the nucleosynthesis beyond Fe through the s-process, but its stellar reaction rate is still subject to large uncertainties. These mainly arise from its extremely low rate in the Gamow energy region, whose measurement is hampered by the unavoidable presence of the cosmic ray background noise. A possibility to overcome this issue is to perform the measurement in a quasi background-free environment, such as that offered by the underground Bellotti Ion Beam Facility at LNGS. This is the key idea of EASγ experiment. In this study, the signal from the de-excitation of the compound nucleus ²⁶Mg has been simulated and its detection has been investigated both on surface and deep-underground laboratories. The simulation results show the enhancement in sensitivity achieved by performing the measurement deep underground and with an additional shielding, yielding to unprecedented sensitivity. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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16 pages, 3064 KiB

Open AccessArticle

TOrsion-Bar Antenna: A Ground-Based Detector for Low-Frequency Gravity Gradient Measurement

by Satoru Takano, Tomofumi Shimoda, Yuka Oshima, Ching Pin Ooi, Perry William Fox Forsyth, Mengdi Cao, Kentaro Komori, Yuta Michimura, Ryosuke Sugimoto, Nobuki Kame, Shingo Watada, Takaaki Yokozawa, Shinji Miyoki, Tatsuki Washimi and Masaki Ando

Galaxies 2024, 12(6), 78; https://doi.org/10.3390/galaxies12060078 - 20 Nov 2024

Abstract

The Torsion-Bar Antenna (TOBA) is a torsion pendulum-based gravitational detector developed to observe gravitational waves in frequencies between 1 mHz and 10 Hz. The low resonant frequency of the torsion pendulum enables observation in this frequency band on the ground. The final target [...] Read more.

The Torsion-Bar Antenna (TOBA) is a torsion pendulum-based gravitational detector developed to observe gravitational waves in frequencies between 1 mHz and 10 Hz. The low resonant frequency of the torsion pendulum enables observation in this frequency band on the ground. The final target of TOBA is to observe gravitational waves with a 10 m detector and expand the observation band of gravitational waves. In this paper, an overview of TOBA, including the previous prototype experiments and the current ongoing development, is presented. Full article

(This article belongs to the Special Issue Challenges for Third-Generation Gravitational Wave Detectors and Beyond)

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19 pages, 3178 KiB

Open AccessReview

Exploring the Components of Cosmogenic UHECR, Neutrino, and Diffuse Gamma Ray from High-Energy Astrophysical Objects

by Fangsheng Min, Hong Lu and Yiqing Guo

Galaxies 2024, 12(6), 77; https://doi.org/10.3390/galaxies12060077 - 18 Nov 2024

Abstract

The development of multimessenger astrophysics allows us to probe various background particles from the distant early universe. Up to now, much effort has been made researching the emission and radiation of diverse steady or transient astrophysical sources. We review the potential accelerating, escaping, [...] Read more.

The development of multimessenger astrophysics allows us to probe various background particles from the distant early universe. Up to now, much effort has been made researching the emission and radiation of diverse steady or transient astrophysical sources. We review the potential accelerating, escaping, propagating, and radiation process of high-energy particles under specific circumstances for regular astrophysical sources and briefly discuss the underlying contribution from their emissions to the intensity of ultrahigh-energy cosmic ray, TeV-PeV cosmic neutrino, and the diffuse gamma-ray background, aiming to find a possible common origin. Full article

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5 pages, 600 KiB

Open AccessCommunication

Stellar Ages of TESS Stars, Adopting Spectroscopic Data from Gaia GSP-Spec

by Elisa Denis, Patrick de Laverny, Andrea Miglio, Alejandra Recio-Blanco, Pedro Alonso Palicio, Josefina Montalban and Carlos Abia

Galaxies 2024, 12(6), 76; https://doi.org/10.3390/galaxies12060076 - 14 Nov 2024

Abstract

The Gaia DR3 GSP-spec/TESS (GST) catalog combines asteroseismic data from NASA’s TESS mission with spectroscopic data from ESA’s Gaia mission, and contains about 116,000 Red Clump and Red Giant Branch stars, surpassing previous datasets in size and precision. The Bayesian [...] Read more.

The Gaia DR3 GSP-spec/TESS (GST) catalog combines asteroseismic data from NASA’s TESS mission with spectroscopic data from ESA’s Gaia mission, and contains about 116,000 Red Clump and Red Giant Branch stars, surpassing previous datasets in size and precision. The Bayesian tool PARAM is used to estimate stellar ages using MESA models for, currently, 30,297 stars. This GST catalog, which includes kinematics and chemical information, is adopted for studying the Milky Way’s structure and evolution, in particular its thin and thick disk components. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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13 pages, 1877 KiB

Open AccessArticle

Classification of Variable Star Light Curves with Convolutional Neural Network

by Almat Akhmetali, Timur Namazbayev, Gulnur Subebekova, Marat Zaidyn, Aigerim Akniyazova, Yeskendyr Ashimov and Nurzhan Ussipov

Galaxies 2024, 12(6), 75; https://doi.org/10.3390/galaxies12060075 - 12 Nov 2024

Abstract

The classification of variable stars is essential for understanding stellar evolution and dynamics. With the growing volume of light curve data from extensive surveys, there is a need for automated and accurate classification methods. Traditional methods often rely on manual feature extraction and [...] Read more.

The classification of variable stars is essential for understanding stellar evolution and dynamics. With the growing volume of light curve data from extensive surveys, there is a need for automated and accurate classification methods. Traditional methods often rely on manual feature extraction and selection, which can be time-consuming and less adaptable to large datasets. In this work, we present an approach using a convolutional neural network (CNN) to classify variable stars using only raw light curve data and their known periods, without the need for manual feature extraction or hand-selected data preprocessing. Our method utilizes phase-folding to organize the light curves and directly learns the variability patterns crucial for classification. Trained and tested on the Optical Gravitational Lensing Experiment (OGLE) dataset, our model demonstrates an average accuracy of 88% and an F1 score of 0.89 across five well-known classes of variable stars. We also compared our classification model with the Random Forest (RF) classifier and showed that our model gives better results across all of the classification metrics. By leveraging CNN, our approach does not need manual feature extraction and can handle diverse light curve shapes and sampling cadences. This automated, data-driven method offers a powerful tool for classifying variable stars, enabling efficient processing of large datasets from current and future sky surveys. Full article

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19 pages, 637 KiB

Open AccessReview

An Objective Classification Scheme for Solar-System Bodies Based on Surface Gravity

by Dimitris M. Christodoulou, Silas G. T. Laycock and Demosthenes Kazanas

Galaxies 2024, 12(6), 74; https://doi.org/10.3390/galaxies12060074 - 6 Nov 2024

Abstract

We introduce succinct and objective definitions of the various classes of objects in the solar system. Unlike the formal definitions adopted by the International Astronomical Union in 2006, group separation is obtained from measured physical properties of the objects. Thus, this classification scheme [...] Read more.

We introduce succinct and objective definitions of the various classes of objects in the solar system. Unlike the formal definitions adopted by the International Astronomical Union in 2006, group separation is obtained from measured physical properties of the objects. Thus, this classification scheme does not rely on orbital/environmental factors that are subject to debate—the physical parameters are intrinsic properties of the objects themselves. Surface gravity g is the property that single-handedly differentiates (a) planets from all other objects (and it leaves no room for questioning the demotion of Pluto), and (b) the six largest (

g > 1

m

s^{- 2}

) of the large satellites from dwarf planets. Large satellites are separated from small satellites by their sizes and masses/densities, which may serve as higher-order qualifiers for class membership. Size considerations are also sufficient for the classification of (i) main-belt asteroids (except possibly Ceres) as small solar-system bodies similar in physical properties to the small satellites; and (ii) a group of large Kuiper-belt objects as dwarf planets similar in physical properties to the large (but not the largest) satellites in our solar system. The selection criteria are simple and clear and reinforce the argument that body shape and environmental factors need not be considered in stipulating class membership of solar as well as extrasolar bodies. Full article

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8 pages, 1261 KiB

Open AccessCommunication

Spectroscopy of a Sample of RV Tauri Stars Without IR Excess

by Kārlis Puķītis and Karina Korenika

Galaxies 2024, 12(6), 73; https://doi.org/10.3390/galaxies12060073 - 6 Nov 2024

Abstract

We observed high-resolution optical spectra of 11 RV Tauri stars without IR excess, with the primary goal of searching for chemical depletion patterns. Using equivalent widths of absorption lines, we calculated the photospheric parameters and chemical element abundances for five stars in the [...] Read more.

We observed high-resolution optical spectra of 11 RV Tauri stars without IR excess, with the primary goal of searching for chemical depletion patterns. Using equivalent widths of absorption lines, we calculated the photospheric parameters and chemical element abundances for five stars in the sample: HD 172810, V399 Cyg, AA Ari, V457 Cyg, and V894 Per. Only the abundance pattern of V457 Cyg suggests depletion. In the spectrum of this star, TiO lines are also observed in the emission, in addition to metal emissions. V457 Cyg is likely a binary system that was once surrounded by a circumbinary disc. In the spectrum of V894 Per, we find a set of spectral lines that appear to belong to another star, corroborating that it is an eclipsing variable rather than an RV Tauri star. The high overabundance of sodium may result from mass transfer within the binary system. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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14 pages, 1078 KiB

Open AccessArticle

A “Wonderful” Reference Dataset of Mira Variables

by Dana K. Baylis-Aguirre, Michelle J. Creech-Eakman and Gerard T. van Belle

Galaxies 2024, 12(6), 72; https://doi.org/10.3390/galaxies12060072 - 31 Oct 2024

Abstract

The conditions in Mira variable atmospheres make them wonderful laboratories to study a variety of stellar physics such as molecule–grain formation, dust production, shock chemistry, stellar winds, mass loss, opacity-driven pulsation, and shocks. We were awarded an NSF grant to analyze over a [...] Read more.

The conditions in Mira variable atmospheres make them wonderful laboratories to study a variety of stellar physics such as molecule–grain formation, dust production, shock chemistry, stellar winds, mass loss, opacity-driven pulsation, and shocks. We were awarded an NSF grant to analyze over a decade of synoptic observations from the Palomar Testbed Interferometer (PTI) of 106 Miras to curate a Mira Reference Dataset. The Miras included in this dataset include M-types, S-types, and C-types, and span a wide range of pulsation periods. PTI measured K-band angular sizes that when combined with a distance allow us to directly determine fundamental stellar parameters such as effective temperature, radial size, and bolometric flux. Supplementing observations with interferometric measurements of the stars opens the Mira laboratory to a wealth of different experiments. We provide two case studies to serve as examples of the power of the Mira Reference Dataset. The first case study describes combining PTI measurements with Spitzer IRS spectra of M-type Miras, which allowed us to fully characterize

{CO}_{2}

gas in their atmospheres. The second case study examines how PTI narrow-band data can be used to study phase-dependent pulsation effects on the stellar atmosphere. We provide a list of all the Miras (with coordinates) included in the set for anyone who would like to add them to their observing programs. All the data we produce and collate for this Mira Reference Dataset will be hosted and curated on a website open to the public so that other researchers and citizen scientists can participate in expanding the utility and body of knowledge on this set of “wonderful” stars. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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7 pages, 288 KiB

Open AccessCommunication

¹⁷O Destruction Rate in Stars

by David Rapagnani, Oscar Straniero and Gianluca Imbriani

Galaxies 2024, 12(6), 71; https://doi.org/10.3390/galaxies12060071 - 29 Oct 2024

Abstract

In recent years, several laboratory studies of CNO cycle-related nuclear reactions have been carried out. Nevertheless, extant models of stellar nucleosynthesis still adopt CNO reaction rates reported in old compilations, such as NACRE or CF88. In order to update these rates, we performed [...] Read more.

In recent years, several laboratory studies of CNO cycle-related nuclear reactions have been carried out. Nevertheless, extant models of stellar nucleosynthesis still adopt CNO reaction rates reported in old compilations, such as NACRE or CF88. In order to update these rates, we performed new calculations based on a Monte Carlo R-Matrix analysis. In more detail, a method was developed that is based on the collection of all the available data, including recent low-energy measurements obtained by the LUNA collaboration in the reduced background environment of the INFN-LNGS underground laboratory, on R-Matrix cross-section calculations with the AZURE2 code and on uncertainty evaluations with a Monte Carlo analysis. As a first scientific benchmark case, the reactions ¹⁷O

(p, γ)

¹⁸F and ¹⁷O

(p, α)

¹⁴N were investigated. Among the different stellar scenarios they can influence, the ¹⁶O/¹⁷O abundance ratio in RGB and AGB stars is the one that can be directly confirmed from spectroscopic measurements. The aim is to reduce the nuclear physics uncertainties, thus providing a useful tool to constrain deep mixing processes eventually taking place in these stars. In this work, we present the procedure we followed to calculate the ¹⁷O

(p, γ)

¹⁸F and the ¹⁷O

(p, α)

¹⁴N reaction stellar rates and preliminary comparisons with similar rates reported in widely used nuclear physics libraries are discussed. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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10 pages, 457 KiB

Open AccessArticle

The ¹⁷O/¹⁸O Ratio of Post-AGB Sources: Canonical and Non-Canonical Populations

by Javier Alcolea, Elisa Masa, Theo Khouri, Miguel Santander-García, Iván Gallardo Cava, Hans Olofsson, Carmen Sánchez Contreras, Valentín Bujarrabal, Wouter H. T. Vlemmings and Daniel Tafoya

Galaxies 2024, 12(6), 70; https://doi.org/10.3390/galaxies12060070 - 25 Oct 2024

Abstract

Stellar evolution models serve as tools to derive stellar parameters from elemental and isotopic abundance ratios. For low-to-intermediate mass evolved stars, C/O, ¹²C/¹³C, and ¹⁷O/¹⁸O ratios are proxies of the initial mass, a largely unknown parameter in [...] Read more.

Stellar evolution models serve as tools to derive stellar parameters from elemental and isotopic abundance ratios. For low-to-intermediate mass evolved stars, C/O, ¹²C/¹³C, and ¹⁷O/¹⁸O ratios are proxies of the initial mass, a largely unknown parameter in post-AGB sources, yet fundamental to establish correlations with the main properties of their post-AGB envelopes, progressing in understanding their formation and evolution. In these sources, the C/O ratio can be constrained from the detection of C- or O-bearing species in addition to CO, while the ¹⁷O/¹⁸O ratio is straightforwardly determined from the C¹⁷O-to-C¹⁸O intensity ratio of rotational lines. However, the theory is at odds with the observations. We review the status of the question, including new accurate ¹⁷O/¹⁸O ratios for 11 targets (totaling 29). Comparing the results for the ¹⁷O/^$18$O ratios and C-rich/O-rich chemical composition, we find that ∼45% of the cases are canonical, i.e., the observations align with standard model predictions. O-rich non-canonical sources, with ^$17$O/^$18$O ratios above the expected, can be explained by a premature interruption of their AGB evolution as a consequence of a quasi-explosive ejection of a large fraction of the initial mass. For non-canonical C-rich sources, with ^$17$O/^$18$O ratios below predictions, we suggest the possibility they are extrinsic C-rich stars. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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10 pages, 1402 KiB

Open AccessArticle

Calibration of Luminosity Correlations of Gamma-Ray Bursts Using Quasars

by Sarveshkumar Purohit and Shantanu Desai

Galaxies 2024, 12(6), 69; https://doi.org/10.3390/galaxies12060069 - 25 Oct 2024

Abstract

In order to test the efficacy of gamma-ray bursts (GRBs) as cosmological probes, we characterize the scatter in the correlations between six pairs of GRB observables. However, some of these observables depend on the luminosity distance, for which one needs to assume an [...] Read more.

In order to test the efficacy of gamma-ray bursts (GRBs) as cosmological probes, we characterize the scatter in the correlations between six pairs of GRB observables. However, some of these observables depend on the luminosity distance, for which one needs to assume an underlying cosmological model. In order to circumvent this circularity problem, we use X-ray and UV fluxes of quasars as distance anchors to calculate the luminosity distance in a model-independent manner, which, in turn, is used to calculate the GRB-related quantities. We find that all six pairs of regression relations show high intrinsic scatter for both low- and high-redshift samples. This implies that these GRB observables cannot be used as model-independent high-precision cosmological probes. Full article

(This article belongs to the Special Issue Gamma-Ray Bursts in Multiwavelength: Theory, Observational Correlations and GRB Cosmology)

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6 pages, 2267 KiB

Open AccessArticle

The Ongoing Deep Underground Measurement of ²²Ne(α,n)²⁵Mg at the Ion Beam Facility of the INFN-LNGS

by Andreas Best, David Rapagnani and Daniela Mercogliano

Galaxies 2024, 12(6), 68; https://doi.org/10.3390/galaxies12060068 - 24 Oct 2024

Abstract

The ²²

Ne

(α, n)

²⁵

Mg

reaction is of major importance in nuclear astrophysics. It is the main neutron source for the weak s-process and as such is responsible for the nucleosynthesis of 60 < A < 90 elements. [...] Read more.

The ²²

Ne

(α, n)

²⁵

Mg

reaction is of major importance in nuclear astrophysics. It is the main neutron source for the weak s-process and as such is responsible for the nucleosynthesis of 60 < A < 90 elements. In addition, it provides a strong neutron burst during the later, hottest phases of the main s-process, which modifies the final nucleosynthesis products, especially at so-called branch points, which can be used to provide insight into the stellar interior at that time. The reaction rate needs to be known below ca. 900 keV, and due to the low cross-section at these energies, a direct measurement has so far proven to be severely hampered by external neutron background at the surface of the Earth. To solve this problem, a measurement campaign (the ERC-funded SHADES project) was recently started at the deep underground Gran Sasso National Laboratory (LNGS) in Italy. We provide an overview of the experiment status and an outlook into the near future. Full article

(This article belongs to the Special Issue Nucleosynthesis and Dust Production in AGB Stars: Open Issues and Future Perspectives)

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