Article
Astronomy & Astrophysics
Louise Welsh, Ryan Cooke, Michele Fumagalli
Summary: This study investigates the intrinsic scatter in the chemical abundances of metal-poor Milky Way halo stars and suggests that the most metal-poor stars were enriched by Population III stars. The model used for the enrichment is sensitive to small changes in the stellar sample, particularly in the [Mg/Ca] abundance. The method has the potential to constrain the multiplicity of the first generation of stars but requires a well-understood stellar sample with documented uncertainties associated with nucleosynthetic yields.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
D. Yong, G. S. Da Costa, M. S. Bessell, A. Chiti, A. Frebel, X. Gao, K. Lind, A. D. Mackey, A. F. Marino, S. J. Murphy, T. Nordlander, M. Asplund, A. R. Casey, C. Kobayashi, J. E. Norris, B. P. Schmidt
Summary: The study presents chemical abundance results for 21 elements in metal-poor Galactic stars and reveals a power-law slope in the metallicity distribution function. It also suggests that the selection of metal-poor stars based on SkyMapper filters may be biased.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
J. E. Norris, D. Yong, A. Frebel, S. G. Ryan
Summary: This study investigates the distribution of lithium abundances in metal-poor dwarf and subgiant stars by analyzing literature data for approximately 200 stars. The study addresses the issue of varying effective temperatures and their impact on uncertainty in lithium abundances, and suggests a method of anchoring the effective temperature to overcome this issue. The study identifies patterns in the behavior of lithium abundances with respect to metallicity, indicating destruction of primordial lithium and the formation of a plateau at a metallicity of -3.0.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Boyuan Liu, Yves Sibony, Georges Meynet, Volker Bromm
Summary: Stellar winds from fast-rotating Population III stars, combined with supernovae feedback, can result in chemical signatures in the enriched medium. Predicted carbon and iron abundances match observations of CEMP-no stars, indicating a pathway for the formation of carbon-rich, iron-free second-generation stars in systems dominated by wind enrichment. Further detailed modeling of wind feedback from Pop III spinstars is warranted in early cosmic structure formation.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Ondrej Jaura, Simon C. O. Glover, Katharina M. J. Wollenberg, Ralf S. Klessen, Sam Geen, Lionel Haemmerle
Summary: The ionizing radiation from massive Pop III stars is trapped in the surrounding accretion disc, thus having no significant impact on the number or total mass of protostars formed. The difference from previous studies lies in the way the radiation is injected into the simulation.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
P. Riviere-Marichalar, A. Fuente, G. Esplugues, V. Wakelam, R. le Gal, C. Baruteau, A. Ribas, E. Macias, R. Neri, D. Navarro-Almaida
Summary: This study investigates the abundance of sulfuretted species and their contribution to the sulfur budget in the region surrounding AB Aur. The results show that H2S is an important sulfur carrier in the protoplanetary disk. The observed abundances are still far from the cosmic sulfur abundance, indicating the need for further research.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
L. Cavallo, G. Cescutti, F. Matteucci
Summary: In this paper, the authors investigate the origin of the large star-to-star variation in the [Eu/Fe] ratios in extremely metal-poor stars. By considering the chemical enrichment of Eu in the building blocks of the Galactic halo, they find that the dynamics of binary systems in the gravitational potential of the host galaxy play a role in the enrichment from neutron star mergers.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
G. Nandakumar, N. Ryde, L. Casagrande, G. Mace
Summary: This study develops a method for determining the stellar parameters of M giants from NIR spectra. The accuracy and precision of the method are validated through observations of nearby well-studied M giants and comparisons with existing data. The results show good agreement and provide insights into the abundance trends of alpha-elements in solar neighborhood M giants.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
D. S. Aguado, S. Salvadori, A. Skuladottir, E. Caffau, P. Bonifacio, I Vanni, V Gelli, I Koutsouridou, A. M. Amarsi
Summary: In this study, a new method called PISN-explorer was proposed to identify stars with dominant PISN enrichment. Through analyzing data from large spectroscopic surveys, the researchers built a catalog with 166 candidates of PISN descendants and found a candidate with a complete chemical signature. High-resolution observations are needed to confirm the selected candidates.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Luis E. Padilla, Juan Carlos Hidalgo, Karim A. Malik
Summary: The study focuses on the formation of boson stars and primordial black holes in the scalar field dark matter model, discussing the criteria for collapse and its relevance to the abundance of PBHs.
Article
Astronomy & Astrophysics
C. Saffe, P. Miquelarena, J. Alacoria, M. Flores, M. Jaque Arancibia, D. Calvo, G. Martin Girardi, M. Grosso, A. Collado
Summary: The study explores the chemical pattern of early-type stars with planets, focusing on a potential link between the λ Bootis chemical pattern and the presence of giant planets. However, no unique chemical pattern was found for early-type stars with giant planets, suggesting the presence of other mechanisms to account for the λ Bootis pattern. Additionally, the formation of planets around λ Bootis stars may also occur through core accretion, not just gravitational instability.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Partha Pratim Goswami, Rajeev Singh Rathour, Aruna Goswami
Summary: The enhanced abundance of s- and r-process elements in a subclass of CEMP stars, known as CEMP-r/s stars, remains poorly understood. The i-process nucleosynthesis is suggested as a promising mechanism for the origin of these stars. By conducting a detailed systematic follow-up spectroscopic study, the researchers aim to better understand the chemical signatures and formation mechanisms of five potential CH star candidates.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
C. Fanelli, L. Origlia, E. Oliva, E. Dalessandro, A. Mucciarelli, N. Sanna
Summary: In this study, high-resolution optical and near-infrared spectra of young red supergiant stars in the Perseus complex were obtained to determine their radial velocities, stellar parameters, and chemical abundances. The results showed that the chemical abundances of these stars are consistent with older stellar populations at a similar galactocentric distance. It was also observed that mixing processes in the stellar interiors lead to an enhancement of nitrogen and a depletion of carbon.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
T. M. Sitnova, L. Mashonkina, A. M. Tatarnikov, O. V. Voziakova, M. A. Burlak, Yu Pakhomov, P. Jablonka, M. D. Neretina, A. Frebel
Summary: This study presents atmospheric parameters and abundances of chemical elements in metal-poor stars in three ultrafaint dwarf galaxies. The results indicate the presence of first generation stars and lower abundance ratios of Sr and Ba in the UFDs compared to other types of galaxies. Additionally, a hypothesis of Sr production in metal-poor binaries at the earliest epoch of galactic evolution is suggested.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
G. Nandakumar, N. Ryde, G. Mace
Summary: The aim of this study is to observe and investigate the Galactic chemical evolution of fluorine in metal-rich stars. Based on the analysis of HF lines, it confirms the enrichment trend of fluorine in the metallicity range of -1.0 < [Fe/H] < 0.0 dex, but fails to confirm the upward trend at [Fe/H] > 0.25 dex. More observations are needed to confirm the changes in fluorine abundance in metal-rich stars.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Sal Wanying Fu, Daniel R. Weisz, Else Starkenburg, Nicolas Martin, Alexander P. Ji, Ekta Patel, Michael Boylan-Kolchin, Patrick Cote, Andrew E. Dolphin, Nicolas Longeard, Mario L. Mateo, Nathan R. Sandford
Summary: By using deep Hubble Space Telescope (HST) CaHK imaging, this study measures the metallicity distribution function (MDF) of the dwarf galaxy Eridanus II (Eri II) in the Local Group. The results show that Eri II has a consistent metallicity with spectroscopic MDFs, and the study identifies extremely metal-poor star candidates. The orbital history of Eri II is also computed, suggesting it is on its first infall into the Milky Way. The study emphasizes the power of HST CaHK imaging for MDF measurements of ultra-faint dwarf galaxies (UFDs).
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Mithi A. C. de los Reyes, Evan N. Kirby, Alexander P. Ji, Evan H. Nunez
Summary: Using up to seven stellar abundance ratios, this study places observational constraints on the star formation histories of Local Group dSphs, with Sculptor dSph as a test case. The best-fit model suggests Sculptor dSph has an ancient SFH with a relatively short total star formation duration of around 0.9 Gyr, compared to previous estimates. The study also explores the nucleosynthesis of individual elements and finds consistency with sub-M (Ch) Type Ia supernova models and the requirement of prompt and delayed r-process events to reproduce observed trends.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Sydney A. Jenkins, Ting S. Li, Andrew B. Pace, Alexander P. Ji, Sergey E. Koposov, Burcin Mutlu-Pakdil
Summary: In this study, we performed consistent reductions and measurements for three ultra-faint dwarf galaxies using VLT/GIRAFFE spectrograph data. We identified new members, refined physical parameters, and conducted a comparative analysis of previously discovered members. Additionally, we found new binary stars in Leo IV and Leo V, and reanalyzed the metallicity distribution function in Bootes I, leading to insights that will contribute to future dark matter studies.
ASTROPHYSICAL JOURNAL
(2021)
Article
Astronomy & Astrophysics
Ting S. Li, Alexander P. Ji, Andrew B. Pace, Denis Erkal, Sergey E. Koposov, Nora Shipp, Gary S. Da Costa, Lara R. Cullinane, Kyler Kuehn, Geraint F. Lewis, Dougal Mackey, Jeffrey D. Simpson, Daniel B. Zucker, Peter S. Ferguson, Sarah L. Martell, Joss Bland-Hawthorn, Eduardo Balbinot, Kiyan Tavangar, Alex Drlica-Wagner, Gayandhi M. De Silva, Joshua D. Simon
Summary: We report the kinematic, orbital, and chemical properties of 12 stellar streams with no evident progenitors. This data set provides the largest homogeneously analyzed set of streams with full 6D kinematics and metallicities.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Kaitlin C. Rasmussen, Matteo Brogi, Fahin Rahman, Hayley Beltz, Miles Currie, Emily Rauscher, Alexander P. Ji
Summary: Spectroscopic studies of exoplanets play a crucial role in understanding their formation, evolution, and atmospheric properties. This paper demonstrates the effectiveness of novel normalization and smoothing methods in extracting atmospheric information from ground-based spectroscopy. By applying SPORK and iterative smoothing, the detection significance for two examples is significantly increased. These methods can be applied to various scenarios, including archival data sets and future spectrographs.
ASTRONOMICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Tilman Hartwig, Mattis Magg, Li-Hsin Chen, Yuta Tarumi, Volker Bromm, Simon C. O. Glover, Alexander P. Ji, Ralf S. Klessen, Muhammad A. Latif, Marta Volonteri, Naoki Yoshida
Summary: A-SLOTH is the first public code that connects the formation of the first stars and galaxies to observables. It is based on dark matter merger trees and applies analytical methods to simulate the formation of metal-free and metal-poor stars and the transition between them. A-SLOTH is calibrated based on six observables and can be used to constrain the properties of the first stars and high-z galaxies, predict the properties of the oldest and most metal-poor stars in the Milky Way, serve as a subgrid model for larger cosmological simulations, and predict next-generation observables of the early universe.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Anirudh Chiti, Joshua D. Simon, Anna Frebel, Andrew B. Pace, Alexander P. Ji, Ting S. Li
Summary: In this study, a chemodynamical analysis of the Grus I ultra-faint dwarf galaxy (UFD) was conducted using medium-resolution Magellan/IMACS spectra. The results show that Grus I is a metal-poor UFD dominated by dark matter, with a low central density.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Kaley Brauer, Hillary Diane Andales, Alexander P. Ji, Anna Frebel, Mohammad K. Mardini, Facundo A. Gomez, Brian W. O'Shea
Summary: Research shows that clustering algorithms have limited success in recovering accreted UFD remnants in the Milky Way, with only up to 6% of UFD remnants being recoverable. Real clusters tend to have higher median energy and angular momentum, providing a way to distinguish real from fake clusters. Incorporating chemical tagging is recommended to improve clustering results.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Alexander P. Ji, Rohan P. Naidu, Kaley Brauer, Yuan-Sen Ting, Joshua D. Simon
Summary: We provide the first high-resolution chemical abundances of seven stars in the recently discovered high-energy stream Typhon, which has apocentres r greater than or similar to 100 kpc. The chemical abundances of Typhon stars resemble those of a dwarf galaxy rather than a globular cluster, with a dispersion in metallicity and no evidence of multiple stellar populations. The high-alpha abundances suggest a short star formation duration for Typhon, but this contradicts expectations for the distant Milky Way halo and the presence of delayed r-process enrichment. Possible scenarios to explain this contradiction include dynamical interactions, late-time star formation, or group pre-processing before infall into the Milky Way.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Mohammad K. Mardini, Anna Frebel, Rana Ezzeddine, Anirudh Chiti, Yohai Meiron, Alexander P. Ji, Vinicius M. Placco, Ian U. Roederer, Jorge Melendez
Summary: We present detailed observations of the extremely metal-poor star 2MASS J1808-5104. By analyzing its spectroscopic and photometric data, we determined its abundance parameters and measured the ratios of important elements. The abundance pattern of J1808-5104 is consistent with nucleosynthesis models. Through kinematic analysis and orbital history investigation, we found that J1808-5104 is a member of the Galactic thin disc, formed in the early stages of the Milky Way's hierarchical assembly.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Sophia Lilleengen, Michael S. Petersen, Denis Erkal, Jorge Penarrubia, Sergey E. Koposov, Ting S. Li, Lara R. Cullinane, Alexander P. Ji, Kyler Kuehn, Geraint F. Lewis, Dougal Mackey, Andrew B. Pace, Nora Shipp, Daniel B. Zucker, Joss Bland-Hawthorn, Tariq Hilmi
Summary: Recent research shows that the Large Magellanic Cloud (LMC) significantly impacts the Milky Way's stellar halo and stellar streams. This study examines how deformations of the Milky Way and LMC's dark matter haloes affect stellar streams and investigates if these effects can be observed. The Orphan-Chenab (OC) stream, which passes close to the LMC and spans a large portion of the Milky Way's halo, is the main focus. Using a basis function expansion, the Milky Way-LMC system is represented to capture their evolution in an N-body simulation. The study finds that the simulated OC stream is strongly influenced by the deformations of both the Milky Way and LMC, and these effects are larger than current observational errors. The Milky Way dipole has the greatest impact on the stream, followed by the evolution of the LMC's monopole and quadrupole. Detecting these effects would confirm a key prediction of collisionless, cold dark matter and serve as a powerful test for alternative dark matter and alternative gravity models.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Anirudh Chiti, Anna Frebel, Alexander P. Ji, Mohammad K. Mardini, Xiaowei Ou, Joshua D. Simon, Helmut Jerjen, Dongwon Kim, John E. Norris
Summary: Using high-resolution Magellan/MIKE spectroscopy, we provide chemical abundances and velocities of five stars located between 0.3 and 1.1 kpc from the center of the Tucana II ultrafaint dwarf galaxy. The stars exhibit low metal and neutron-capture element abundances, confirming their association with Tucana II. The chemical abundances suggest the dominance of faint core-collapse supernovae in the early evolution of Tucana II, with a decline in [alpha/Fe] indicating the onset of Type Ia supernova enrichment. The lack of a radial velocity gradient implies a lack of tidal disruption, providing insights into the formation scenarios of the extended component of Tucana II.
ASTRONOMICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Alexander P. Ji, Joshua D. Simon, Ian U. Roederer, Ekaterina Magg, Anna Frebel, Christian I. Johnson, Ralf S. Klessen, Mattis Magg, Gabriele Cescutti, Mario Mateo, Maria Bergemann, John I. Bailey
Summary: The ultrafaint dwarf galaxy Renticulum II experienced a rare and prolific r-process event, providing a unique opportunity to study metal mixing in a relic first galaxy. The study found that approximately 72-82% of the stars in Reticulum II were r-process enhanced, indicating bursty star formation in this ultrafaint dwarf galaxy.
ASTRONOMICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Joshua D. Simon, Thomas M. Brown, Burcin Mutlu-Pakdil, Alexander P. Ji, Alex Drlica-Wagner, Roberto J. Avila, Clara E. Martinez-Vazquez, Ting S. Li, Eduardo Balbinot, Keith Bechtol, Anna Frebel, Marla Geha, Terese T. Hansen, David J. James, Andrew B. Pace, M. Aguena, O. Alves, F. Andrade-Oliveira, J. Annis, D. Bacon, E. Bertin, D. Brooks, D. L. Burke, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, M. Costanzi, L. N. da Costa, J. De Vicente, S. Desai, P. Doel, S. Everett, I. Ferrero, J. Frieman, J. Garcia-Bellido, M. Gatti, D. W. Gerdes, D. Gruen, R. A. Gruendl, J. Gschwend, G. Gutierrez, S. R. Hinton, D. L. Hollowood, K. Honscheid, K. Kuehn, N. Kuropatkin, J. L. Marshall, J. Mena-Fernandez, R. Miquel, A. Palmese, F. Paz-Chinchon, M. E. S. Pereira, A. Pieres, A. A. Plazas Malagon, M. Raveri, M. Rodriguez-Monroy, E. Sanchez, B. Santiago, V. Scarpine, I. Sevilla-Noarbe, M. Smith, E. Suchyta, M. E. C. Swanson, G. Tarle, C. To, M. Vincenzi, N. Weaverdyck, R. D. Wilkinson
Summary: The ultra-faint dwarf galaxy Reticulum II (Ret II) has a unique chemical evolution history with r-process elements. Observations with the Hubble Space Telescope reveal that Ret II experienced two bursts of star formation, one before the epoch of reionization and the other about 3 billion years later. The presence of r-process-enhanced stars suggests that the r-process elements in Ret II were synthesized early in its star-forming phase and played no role in delayed events like GW170817.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Sergey E. Koposov, Denis Erkal, Ting S. Li, Gary S. Da Costa, Lara R. Cullinane, Alexander P. Ji, Kyler Kuehn, Geraint F. Lewis, Andrew B. Pace, Nora Shipp, Daniel B. Zucker, Joss Bland-Hawthorn, Sophia Lilleengen, Sarah L. Martell
Summary: We present a 6D map of the Orphan-Chenab (OC) stream by combining the data from S-5 and Gaia, which reveals its properties such as luminosity, metallicity, and physical width. The stream shows a constant line-of-sight velocity dispersion despite drastic changes in its physical width. Our measurements allow us to constrain the mass profiles of the Milky Way and the Large Magellanic Cloud (LMC), revealing the extent of the LMC dark matter halo.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)