Publications (177)
The R-Process Alliance: Abundance Universality among Some Elements at and between the First and Second R-Process Peaks
Ian U. Roederer, John J. Cowan, Marco Pignatari +11
We present new observational benchmarks of rapid neutron-capture process (r-process) nucleosynthesis for elements at and between the first (A ~ 80) and second (A ~ 130) peaks. Our…
Predicting the locations of possible long-lived low-mass first stars: Importance of satellite dwarf galaxies
Mattis Magg, Tilman Hartwig, Bhaskar Agarwal +4
The search for metal-free stars has so far been unsuccessful, proving that if there are surviving stars from the first generation, they are rare, they have been polluted, or we hav…
Detailed chemical abundances of stars in the outskirts of the Tucana II ultra-faint dwarf galaxy
Anirudh Chiti, Anna Frebel, Alexander P. Ji +6
We present chemical abundances and velocities of five stars between 0.3 kpc to 1.1 kpc from the center of the Tucana II ultra-faint dwarf galaxy (UFD) from high-resolution Magellan…
The R-Process Alliance: A Nearly Complete R-Process Abundance Template Derived from Ultraviolet Spectroscopy of the R-Process-Enhanced Metal-Poor Star HD 222925
Ian U. Roederer, James E. Lawler, Elizabeth A. Den Hartog +9
We present a nearly complete rapid neutron-capture process (r-process) chemical inventory of the metal-poor ([Fe/H] = -1.46 +/- 0.10) r-process-enhanced ([Eu/Fe] = +1.32 +/- 0.08)…
Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
Vinicius M. Placco, Anna Frebel, Timothy C. Beers +1
We revisit the observed frequencies of Carbon-Enhanced Metal-Poor (CEMP) stars as a function of the metallicity in the Galaxy, using data from the literature with available high-re…
The minimum stellar metallicity observable in the Galaxy
Anna Frebel, Jarrett L. Johnson, Volker Bromm
The first stars fundamentally transformed the early Universe through their production of energetic radiation and the first heavy chemical elements. The impact on cosmic evolution s…
Observing the r-Process Signature in the Oldest Stars
Anna Frebel
The abundance patterns of metal-poor stars provide us a wealth of chemical information about various stages of the chemical evolution of the Galaxy. In particular, these stars allo…
Portrait of a Dark Horse: a Photometric and Spectroscopic Study of the Ultra-faint Milky Way Satellite Pegasus III
Dongwon Kim, Helmut Jerjen, Marla Geha +6
Pegasus III (Peg III) is one of the few known ultra-faint stellar systems in the outer halo of the Milky Way. We present the results from a follow-up campaign with Magellan/IMACS a…
The R-Process Alliance: Exploring the cosmic scatter among ten r-process sites with stellar abundances
Mila Racca, Terese T. Hansen, Ian U. Roederer +11
The astrophysical origin of the rapid neutron-capture process (r-process), which produces about half of the elements heavier than iron, remains uncertain. The oldest, most metal-po…
The R-Process Alliance: Hunting for gold in the near-UV spectrum of 2MASS J05383296-5904280
Terese T. Hansen, Ian U. Roederer, Shivani P. Shah +10
Context. Over the past few years, the -Process Alliance (RPA) has successfully carried out a search for stars that are highly enhanced in elements produced via the rapid neutron…
Observations of R-Process Stars in the Milky Way and Dwarf Galaxies
Anna Frebel, Alexander P. Ji
This chapter presents an overview of the recent progress on spectroscopic observations of metal-poor stars with r-process element signatures found in the Milky Way's stellar halo a…
The R-Process Alliance: J1521-3538, a very metal-poor, extremely r-process-enhanced star with [Eu/Fe]=+2.2, and the class of r-III stars
Madelyn Cain, Anna Frebel, Alexander P. Ji +8
We report the discovery of J1521-3538, a bright (V=12.2), very metal-poor ([Fe/H]=-2.8) strongly r-process enhanced field horizontal branch star, based on a high-resolution, high s…
The 300km/s stellar stream near Segue 1: Insights From high-resolution spectroscopy of its brightest star
Anna Frebel, Ragnhild Lunnan, Andrew R. Casey +3
We present a chemical abundance analysis of 300S-1, the brightest likely member star of the 300 km/s stream near the faint satellite galaxy Segue 1. From a high-resolution Magellan…
Discovery of an Star in XP Spectra
Guilherme Limberg, Vinicius M. Placco, Alexander P. Ji +5
We report on the discovery of GDR3_526285 ( DR3 Source ID 5262850721755411072), a star with and one of the lowest metal ($\text{atomic number} >…
The formation of the heaviest elements
Anna Frebel, Timothy C. Beers
The rapid neutron-capture process needed to build up many of the elements heavier than iron seems to take place primarily in neutron-star mergers, not supernova explosions.
The Metal-Poor Metallicity Distribution of the Ancient Milky Way
Anirudh Chiti, Mohammad K. Mardini, Anna Frebel +1
We present a low metallicity map of the Milky Way consisting of 111,000 giants with [Fe/H] 0.75, based on public photometry from the second data r…
Chemical Signatures of the First Galaxies: Criteria for One-Shot Enrichment
Anna Frebel, Volker Bromm
We utilize metal-poor stars in the local, ultra-faint dwarf galaxies (UFDs; L_tot < 10^5 L_sun) to empirically constrain the formation process of the first galaxies. Since UFDs hav…
Chemical Abundance Analysis of the Extremely Metal-Poor Star HE 1300+0157
Anna Frebel, John E. Norris, Wako Aoki +5
We present a detailed chemical abundance analysis of HE 1300+0157, a subgiant with [Fe/H]=-3.9. From a high-resolution, high-S/N Subaru/HDS spectrum we find the star to be enriched…
The Rise of the -Process in the Gaia-Sausage/Enceladus Dwarf Galaxy
Xiaowei Ou, Alexander P. Ji, Anna Frebel +2
Neutron star mergers (NSMs) produce copious amounts of heavy r-process elements after a time delayed inspiral process. Once NSMs are present in a galaxy, r-process elements, such a…
The R-Process Alliance: 2MASS J22132050-5137385, the Star with the Highest-known r-process Enhancement at [Eu/Fe] = +2.45
Ian U. Roederer, Timothy C. Beers, Kohei Hattori +6
We present stellar parameters and chemical abundances of 47 elements detected in the bright (V = 11.63) very metal-poor ([Fe/H] = -2.20 +- 0.12) star 2MASS J22132050-5137385. We ob…
Chemical Abundance Signature of J0023+0307 -- A Second-Generation Main-Sequence Star with [Fe/H]<-6
Anna Frebel, Alexander P. Ji, Rana Ezzeddine +4
We present a chemical abundance analysis of the faint halo metal-poor main-sequence star J0023+0307, with [Fe/H]<-6.3, based on a high-resolution (R~35,000) Magellan/MIKE spectrum.…
High-resolution spectroscopy of extremely metal-poor stars in the least evolved galaxies: Bootes II
Alexander P. Ji, Anna Frebel, Joshua D. Simon +1
We present high-resolution Magellan/MIKE spectra of the four brightest confirmed red giant stars in the ultra-faint dwarf galaxy Bootes II (Boo II). These stars all inhabit the met…
Segue 1 - A Compressed Star Formation History Before Reionization
David Webster, Anna Frebel, Joss Bland-Hawthorn
Segue 1 is the current best candidate for a "first galaxy", a system which experienced only a single short burst of star formation and has since remained unchanged. Here we present…
Stellar metallicities from SkyMapper photometry I: A study of the Tucana II ultra-faint dwarf galaxy
Anirudh Chiti, Anna Frebel, Helmut Jerjen +2
We present a study of the ultra-faint Milky Way dwarf satellite galaxy Tucana II using deep photometry from the 1.3m SkyMapper telescope at Siding Spring Observatory, Australia. Th…
Broadband UBVRI Photometry of Horizontal-Branch and Metal-Poor Candidates from the HK and Hamburg/ESO Surveys. I
Timothy C. Beers, Chris Flynn, Silvia Rossi +17
We report broadband UBV and/or BVRI CCD photometry for a total of 1857 stars in the thick-disk and halo populations of the Galaxy. The majority of our targets were selected as cand…
RAVE J203843.2-002333: The first highly r-process-enhanced star identified in the RAVE survey
Vinicius M. Placco, Erika M. Holmbeck, Anna Frebel +9
We report the discovery of RAVE J203843.2-002333, a bright (V = 12.73), very metal-poor ([Fe/H] = -2.91), r-process-enhanced ([Eu/Fe] = +1.64 and [Ba/Eu] = -0.81) star selected fro…
Detection of the Second r-process Peak Element Tellurium in Metal-Poor Stars
Ian U. Roederer, James E. Lawler, John J. Cowan +6
Using near-ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope, we detect neutral tellurium in three metal-poor stars enri…
The Chemical Abundances of Stars in the Halo (CASH) Project. II. A Sample of 16 Extremely Metal-poor Stars
Julie K. Hollek, Anna Frebel, Ian U. Roederer +5
We present a comprehensive abundance analysis of 20 elements for 16 new low-metallicity stars from the Chemical Abundances of Stars in the Halo (CASH) project. The abundances have…
Enrichment by Extragalactic First Stars in the Large Magellanic Cloud
Anirudh Chiti, Mohammad Mardini, Guilherme Limberg +8
The Large Magellanic Cloud (LMC) is the Milky Way's most massive satellite galaxy, which only recently (~2 billion years ago) fell into our Galaxy. Since stellar atmospheres preser…
Chemical Signatures of the First Supernovae in the Sculptor Dwarf Spheroidal Galaxy
Joshua D. Simon, Heather R. Jacobson, Anna Frebel +3
We present a homogeneous chemical abundance analysis of five of the most metal-poor stars in the Sculptor dwarf spheroidal galaxy. We analyze new and archival high resolution spect…
Spectroscopic Discovery of the Broad-Lined Type Ic Supernova 2010bh Associated with the Low-Redshift GRB 100316D
Ryan Chornock, Edo Berger, Emily M. Levesque +14
We present the spectroscopic discovery of a broad-lined Type Ic supernova (SN 2010bh) associated with the nearby long-duration gamma-ray burst (GRB) 100316D. At z = 0.0593, this is…
The chemical evolution of the Bootes I ultra-faint dwarf galaxy
Anna Frebel, John E. Norris, Gerard Gilmore +1
We present chemical abundance measurements of two metal-poor red giant stars in the ultra-faint dwarf galaxy Bootes I, based on Magellan/MIKE high-resolution spectra. For Boo I-980…
Near-Field Cosmology with Metal-Poor Stars
Anna Frebel, John E. Norris
The oldest, most metal-poor stars in the Galactic halo and satellite dwarf galaxies present an opportunity to explore the chemical and physical conditions of the earliest star form…
Exploring the Universe with Metal-Poor Stars
Anna Frebel
The early chemical evolution of the Galaxy and the Universe is vital to our understanding of a host of astrophysical phenomena. Since the most metal-poor Galactic stars (with metal…
The -Process Alliance: Detailed Composition of an -Process Enhanced Star with UV and Optical Spectroscopy
Shivani P. Shah, Rana Ezzeddine, Ian U. Roederer +8
We present a detailed chemical-abundance analysis of a highly -process enhanced (RPE) star, 2MASS J00512646-1053170, using high-resolution spectroscopic observations with $Hubbl…
The -Process Alliance: Fourth Data Release from the Search for -Process-Enhanced Stars in the Galactic Halo
Erika M. Holmbeck, Terese T. Hansen, Timothy C. Beers +22
This compilation is the fourth data release from the -Process Alliance (RPA) search for -process-enhanced stars, and the second release based on "snapshot" high-resolution ($…
High-Resolution Spectroscopy of Extremely Metal-Poor Stars in the Least Evolved Galaxies: Ursa Major II and Coma Berenices
Anna Frebel, Joshua D. Simon, Marla Geha +1
We present Keck/HIRES observations of six metal-poor stars in two of the ultra-faint dwarf galaxies orbiting the Milky Way, Ursa Major II and Coma Berenices. These observations inc…
New Hubble Space Telescope Observations of Heavy Elements in Four Metal-Poor Stars
Ian U. Roederer, James E. Lawler, Jennifer S. Sobeck +7
Elements heavier than the iron group are found in nearly all halo stars. A substantial number of these elements, key to understanding neutron-capture nucleosynthesis mechanisms, ca…
From actinides to zinc: Using the full abundance pattern of the brightest star in Reticulum II to distinguish between different r-process sites
Alexander P. Ji, Anna Frebel
The ultra-faint dwarf galaxy Reticulum II was enriched by a rare and prolific r-process event, such as a neutron star merger. To investigate the nature of this event, we present hi…
Metal-poor stars observed with the Magellan Telescope. IV. Neutron-capture element signatures in 27 main-sequence stars
Mohammad K. Mardini, Anna Frebel, Leyatt Betre +3
Based on high-resolution spectra obtained with Magellan/MIKE, we present a chemo-dynamical analysis for 27 near main-sequence turnoff metal-poor stars, including 20 stars analyzed…
The Atari Disk, a Metal-Poor Stellar Population in the Disk System of the Milky Way
Mohammad K. Mardini, Anna Frebel, Anirudh Chiti +3
We have developed a chemo-dynamical approach to assign 36,010 metal-poor SkyMapper stars to various Galactic stellar populations. Using two independent techniques (velocity and act…
The Chemical Evolution of Phosphorus
Heather R. Jacobson, Thanawuth Thanathibodee, Anna Frebel +3
Phosphorus is one of the few remaining light elements for which little is known about its nucleosynthetic origin and chemical evolution, given the lack of optical absorption lines…
The \emph{R}-process Alliance: A Bright, Strongly \emph{R}-process-enhanced Extremely Metal-poor Star Observed with GHOST
Mohammad K. Mardini, Anna Frebel, Vinicius M. Placco +8
We present a detailed chemical-abundance and kinematic analysis of four extremely metal-poor (EMP; [Fe/H] ) stars identified from \textit{Gaia} BP/RP data in our ongoing…
Stellar Archaeology -- Exploring the Universe with Metal-Poor Stars
Anna Frebel
The abundance patterns of the most metal-poor stars in the Galactic halo and small dwarf galaxies provide us with a wealth of information about the early Universe. In particular, t…
The black hole low mass X-ray binary V404 Cygni is part of a wide hierarchical triple, and formed without a kick
Kevin B. Burdge, Kareem El-Badry, Erin Kara +7
Evidence suggests that when compact objects such as black holes and neutron stars form, they may receive a ``natal kick,'' where the stellar remnant gains momentum. Observational e…
Astro2020 Science White Paper: Local Dwarf Galaxy Archaeology
Alexander P. Ji, Rachel Beaton, Sukanya Chakrabarti +8
Nearby dwarf galaxies are local analogues of high-redshift and metal-poor stellar populations. Most of these systems ceased star formation long ago, but they retain signatures of t…
The Effects of Patchy Reionization on Satellite Galaxies of the Milky Way
Ragnhild Lunnan, Mark Vogelsberger, Anna Frebel +3
We combine the high-resolution Aquarius simulations with three-dimensional models of reionization based on the initial density field of the Aquarius parent simulation, Millennium-I…
Reconstructing Masses of Merging Neutron Stars from Stellar -Process Abundance Signatures
Erika M. Holmbeck, Anna Frebel, G. C. McLaughlin +5
Neutron star mergers (NSMs) are promising astrophysical sites for the rapid neutron-capture ("-") process, but can their integrated yields explain the majority of heavy-element…
High-Resolution Spectroscopic Study of Extremely Metal-Poor Star Candidates from the SkyMapper Survey
Heather. R. Jacobson, Stefan Keller, Anna Frebel +13
The SkyMapper Southern Sky Survey is carrying out a search for the most metal-poor stars in the Galaxy. It identifies candidates by way of its unique filter set that allows for est…
Carbon Abundances in Metal-Poor Stars Reveal Distinct Galaxy and Star Formation Pathways in the Early Universe
Alexander Yelland, Anna Frebel, Xiaowei Ou +2
Carbon-enhanced metal-poor (CEMP; with and ) stars preserve information about early chemical enrichment, low-mass star formation, and th…
All the Little Things in Abell 2744: 1000 Gravitationally Lensed Dwarf Galaxies at from JWST NIRCam Grism Spectroscopy
Rohan P. Naidu, Jorryt Matthee, Ivan Kramarenko +31
Dwarf galaxies hold the key to crucial frontiers of astrophysics, however, their faintness renders spectroscopy challenging. Here we present the JWST Cycle 2 survey, All the Little…
Tracing the first stars and galaxies of the Milky Way
Brendan F. Griffen, Gregory A. Dooley, Alexander P. Ji +3
We use 30 high-resolution dark matter halos of the simulation suite to probe the first stars and galaxies of Milky Way-mass systems. We quantify the environment of th…
Non-LTE effects on the lead and thorium abundance determinations for cool stars
Lyudmila Mashonkina, Alexander Ryabtsev, Anna Frebel
Knowing accurate Pb abundances of metal-poor stars provides constraints on the Pb production mechanisms in the early Galaxy. Accurately deriving Th abundances permits a nucleo-chro…
The R-Process Alliance: The Peculiar Chemical Abundance Pattern of RAVE J183013.5-455510
Vinicius M. Placco, Rafael M. Santucci, Zhen Yuan +14
We report on the spectroscopic analysis of RAVE J183013.5-455510, an extremely metal-poor star, highly enhanced in CNO, and with discernible contributions from the rapid neutron-ca…
Metal-Poor Stars Observed with the Southern African Large Telescope
Kaitlin C. Rasmussen, Joseph Zepeda, Timothy C. Beers +5
We present the first release of a large-scale study of relatively bright (V < 13.5) metal-poor stars observed with the Southern African Large Telescope (SALT), based on high-resolu…
Enhanced tidal stripping of satellites in the galactic halo from dark matter self-interactions
Gregory A. Dooley, Annika H. G. Peter, Mark Vogelsberger +2
We investigate the effects of self-interacting dark matter (SIDM) on the tidal stripping and evaporation of satellite galaxies in a Milky Way-like host. We use a suite of five zoom…
Possibilities and Limitations of Kinematically Identifying Stars from Accreted Ultra-Faint Dwarf Galaxies
Kaley Brauer, Hillary Diane Andales, Alexander P. Ji +4
The Milky Way has accreted many ultra-faint dwarf galaxies (UFDs), and stars from these galaxies can be found throughout our Galaxy today. Studying these stars provides insight int…
HE 1327-2326, an unevolved star with [Fe/H]<-5.0. II. New 3D-1D corrected abundances from a VLT/UVES spectrum
Anna Frebel, Kjell Eriksson, Remo Collet +2
We present a new abundance analysis of HE 1327-2326, the currently most iron-poor star, based on observational data obtained with VLT/UVES. We correct the 1D LTE abundances for 3D…
Decoding the Galactic Twirl: The Downfall of Milky Way-mass Galaxies Rotation Curves in the FIRE Simulations
Xiaowei Ou, Lina Necib, Andrew Wetzel +3
Recent measurements of the Milky Way rotation curve found a sharp decline at around - kpc from the center of the Galaxy, suggesting that the Galactic dark matter halo is mu…
CD -24_17504 revisited: a new comprehensive element abundance analysis
Heather R. Jacobson, Anna Frebel
With [Fe/H] ~ -3.3, CD -24_17504 is a canonical metal-poor main sequence turn-off star. Though it has appeared in numerous literature studies, the most comprehensive abundance anal…
Cosmological Insights into the Early Accretion of \textit{r}-Process-Enhanced stars. I. A Comprehensive Chemo-dynamical Analysis of LAMOST J1109+0754
Mohammad K. Mardini, Vinicius M. Placco, Yohai Meiron +10
This study presents a comprehensive chemo-dynamical analysis of LAMOST J1109+0754, a bright (V = 12.8), extremely metal-poor (\abund{Fe}{H} = ) star, with a strong \textit{r…
Probing the Formation of the First Low-Mass Stars with Stellar Archaeology
Anna Frebel, Jarrett L. Johnson, Volker Bromm
We investigate the conditions under which the first low-mass stars formed in the universe by confronting theoretical predictions governing the transition from massive Population II…
The R-Process Alliance: Chemo-Dynamically Tagged Groups of Halo -Process-Enhanced Stars Reveal a Shared Chemical-Evolution History
Dmitrii Gudin, Derek Shank, Timothy C. Beers +11
We derive dynamical parameters for a large sample of 446 -process-enhanced (RPE) metal-poor stars in the halo and disk systems of the Milky Way, based on data releases from the…
Segue 1: An Unevolved Fossil Galaxy from the Early Universe
Anna Frebel, Joshua D. Simon, Evan N. Kirby
We present Magellan/MIKE and Keck/HIRES high-resolution spectra of six red giant stars in the dwarf galaxy Segue 1. Including one additional Segue 1 star observed by Norris et al.…
Observational nuclear astrophysics: neutron-capture element abundances in old, metal-poor stars
Heather R. Jacobson, Anna Frebel
The chemical abundances of metal-poor stars provide a great deal of information regarding the individual nucleosynthetic processes that created the observed elements and the overal…
New Detections of Arsenic, Selenium, and Other Heavy Elements in Two Metal-Poor Stars
Ian U. Roederer, Hendrik Schatz, James E. Lawler +6
We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to obtain new high-quality spectra covering the 1900 to 2360 Angstrom wavelength range for two m…
Metal-Poor Stars and the Chemical Enrichment of the Universe
Anna Frebel, John E. Norris
Metal-poor stars hold the key to our understanding of the origin of the elements and the chemical evolution of the Universe. This chapter describes the process of discovery of thes…
High-Resolution Spectroscopy of Extremely Metal-Poor Stars in the Least Evolved Galaxies: Leo IV
Joshua D. Simon, Anna Frebel, Andrew McWilliam +2
We present high-resolution Magellan/MIKE spectroscopy of the brightest star in the ultra-faint dwarf galaxy Leo IV. We measure an iron abundance of [Fe/H] = -3.2, adding to the rap…
An observer's guide to the (Local Group) dwarf galaxies: predictions for their own dwarf satellite populations
Gregory A. Dooley, Annika H. G. Peter, Tianyi Yang +3
A recent surge in the discovery of new ultrafaint dwarf satellites of the Milky Way has inspired the idea of searching for faint satellites, $10^3\, \mathrm{M_{\odot}} < M_* < 10^6…
The End of Nucleosynthesis: Production of Lead and Thorium in the Early Galaxy
Ian U. Roederer, Karl-Ludwig Kratz, Anna Frebel +4
We examine the Pb and Th abundances in 27 metal-poor stars (-3.1 < [Fe/H] < -1.4) whose very heavy metal (Z > 56) enrichment was produced only by the rapid (r-) nucleosynthesis pro…
Dynamically Tagged Groups of Very Metal-poor Halo Stars from the HK and Hamburg/ESO Surveys
Guilherme Limberg, Silvia Rossi, Timothy C. Beers +13
We analyze the dynamical properties of 1500 very metal-poor (VMP; [Fe/H] ) halo stars, based primarily on medium-resolution spectroscopic data from the HK and…
Chemical abundances of metal-poor RR Lyrae stars in the Magellanic Clouds
Raoul Haschke, Eva K. Grebel, Anna Frebel +3
We present for the first time a detailed spectroscopic study of chemical element abundances of metal-poor RR Lyrae stars in the Large and Small Magellanic Cloud (LMC and SMC). Usin…
Detection of Neutral Phosphorus in the Near Ultraviolet Spectra of Late-Type Stars
Ian U. Roederer, Heather R. Jacobson, Thanawuth Thanathibodee +2
We report the detection of several absorption lines of neutral phosphorus (P, Z=15) in archival near ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on b…
Early r-process Enrichment and Hierarchical Assembly Across the Sagittarius Dwarf Galaxy
Xiaowei Ou, Alexander Yelland, Anirudh Chiti +3
Dwarf galaxies like Sagittarius (Sgr) provide a unique window into the early stages of galactic chemical evolution, particularly through their metal-poor stars. By studying the che…
The dark matter profile of the Milky Way inferred from its circular velocity curve
Xiaowei Ou, Anna-Christina Eilers, Lina Necib +1
In this paper, we construct the circular velocity curve of the Milky Way out to kpc, providing an updated model of the dark matter density profile. We derive precise para…
Hunting the Parent of the Orphan Stream II: The First High-Resolution Spectroscopic Study
Andrew Casey, Stefan Keller, Gary Da Costa +2
We present the first high-resolution spectroscopic study on the Orphan Stream for five stream candidates, observed with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph on…
The R-Process Alliance: Discovery of a low-alpha, r-Process-Enhanced Metal-Poor Star in the Galactic Halo
Charli M. Sakari, Ian U. Roederer, Vinicius M. Placco +24
A new moderately r-process-enhanced metal-poor star, RAVE J093730.5-062655, has been identified in the Milky Way halo as part of an ongoing survey by the R-Process Alliance. The te…
Metal-Poor Stars
Anna Frebel
The abundance patterns of metal-poor stars provide us a wealth of chemical information about various stages of the chemical evolution of the Galaxy. In particular, these stars allo…
An Extremely Carbon-rich, Extremely Metal-poor Star in the Segue 1 System
John E. Norris, Gerard Gilmore, Rosemary F. G. Wyse +2
We report the analysis of high-resolution, high-S/N spectra of an extremely metal-poor, extremely C-rich red giant, Seg 1-7, in the Segue 1 system - described in the literature alt…
The -Process Alliance: The -Process Enhancement of Stars from Chemodynamically Tagged Groups in the Milky Way Halo
Jessica Merritt Agnos, Charli M. Sakari, Pedro Silva +9
As part of the ongoing work of the -Process Alliance (RPA), detailed abundance measurements of 29 heavy elements in three metal-poor stars, 2MASS J145929813852558, 2MASS J194…
The Caterpillar Project: A Large Suite of Milky Way Sized Halos
Brendan F. Griffen, Alexander P. Ji, Gregory A. Dooley +4
We present the largest number of Milky Way sized dark matter halos simulated at very high mass ( M/particle) and temporal resolution (5 Myrs/snapshot) don…
The oldest stars with low neutron-capture element abundances and origins in ancient dwarf galaxies
Hillary Diane Andales, Ananda Santos Figueiredo, Casey Gordon Fienberg +2
We present a detailed chemical abundance and kinematic analysis of six extremely metal-poor ( [Fe/H] 2.9) halo stars with very low neutron-capture abundances ([Sr…
Preserving chemical signatures of primordial star formation in the first low-mass stars
Alexander P. Ji, Anna Frebel, Volker Bromm
We model early star forming regions and their chemical enrichment by Population III (Pop III) supernovae with nucleosynthetic yields featuring high [C/Fe] ratios and pair-instabili…
AEOS: Star-by-Star Cosmological Simulations of Early Chemical Enrichment and Galaxy Formation
Kaley Brauer, Andrew Emerick, Jennifer Mead +7
The AEOS project introduces a series of high-resolution cosmological simulations that model star-by-star chemical enrichment and galaxy formation in the early Universe, achieving 1…
An extended halo around an ancient dwarf galaxy
Anirudh Chiti, Anna Frebel, Joshua D. Simon +7
The Milky Way is surrounded by dozens of ultra-faint (< solar luminosities) dwarf satellite galaxies. They are the surviving remnants of the earliest galaxies, as confirmed…
Detection of a population of carbon-enhanced metal-poor stars in the Sculptor dwarf spheroidal galaxy
Anirudh Chiti, Joshua D. Simon, Anna Frebel +6
The study of the chemical abundances of metal-poor stars in dwarf galaxies provides a venue to constrain paradigms of chemical enrichment and galaxy formation. Here we present meta…
Neutron Star Mergers Might not be the Only Source of r-Process Elements in the Milky Way
Benoit Côté, Marius Eichler, Almudena Arcones +8
Probing the origin of r-process elements in the universe represents a multi-disciplinary challenge. We review the observational evidence that probe the properties of r-process site…
R-process enrichment from a single event in an ancient dwarf galaxy
Alexander P. Ji, Anna Frebel, Anirudh Chiti +1
Elements heavier than zinc are synthesized through the (r)apid and (s)low neutron-capture processes. The main site of production of the r-process elements (such as europium) has be…
The R-Process Alliance: Spectroscopic Follow-up of Low-Metallicity Star Candidates from the Best & Brightest Survey
Vinicius M. Placco, Rafael M. Santucci, Timothy C. Beers +17
We present results from an observing campaign to identify low-metallicity stars in the Best & Brightest Survey. From medium-resolution (R ~ 1, 200 - 2, 000) spectroscopy of 857 can…
Formation of an extended stellar halo around an ultra-faint dwarf galaxy following one of the earliest mergers from galactic building blocks
Yuta Tarumi, Naoki Yoshida, Anna Frebel
Ultra-faint dwarf galaxies (UFDs) are promising observable proxies to building blocks of galaxies formed in the early Universe. We study the formation and evolution of UFDs using c…
The Hobby-Eberly Telescope "Chemical Abundances of Stars in the Halo" (CASH) Project. I. The Lithium-, s-, and r-Enhanced Metal-Poor Giant HKII 17435-00532
Ian U. Roederer, Anna Frebel, Matthew D. Shetrone +7
We present the first detailed abundance analysis of the metal-poor giant HKII 17435-00532. This star was observed as part of the University of Texas long-term project "Chemical Abu…
Probing Abundance Variations among Multiple Stellar Populations in the Metal-Poor Globular Cluster NGC 2298 using Gemini-South/GHOST
Avrajit Bandyopadhyay, Rana Ezzeddine, Vinicius M. Placco +3
Studying the abundances in metal-poor globular clusters is crucial for understanding the formation of the Galaxy and the nucleosynthesis processes in the early Universe. We observe…
Evidence for an aspherical Population III supernova explosion inferred from the hyper metal-poor star HE1327-2326
Rana Ezzeddine, Anna Frebel, Ian U. Roederer +6
We present observational evidence that an aspherical supernova explosion could have occurred in the First stars in the early universe. Our results are based on the First determinat…
s-process Enirchment of Ultrafaint Dwarf Galaxies
Yuta Tarumi, Takuma Suda, Freeke van de Voort +3
We study the production of barium (Ba) and strontium (Sr) in ultrafaint dwarf galaxies (UFDs). Both r- and s- processes produce these elements, and one can infer the contribution o…
Discovery of 18 stars with -3.10 < [Fe/H] < -1.45 in the Sagittarius dwarf galaxy
Anirudh Chiti, Kylie Y. Hansen, Anna Frebel
Studies of the early chemical evolution of some larger dwarf galaxies ( solar masses) are limited by the small number of stars known at low metallicities in these systems.…
The Most Metal-Poor Stars. II. Chemical Abundances of 190 Metal-Poor Stars Including 10 New Stars With [Fe/H] < -3.5
David Yong, John E. Norris, M. S. Bessell +6
We present a homogeneous chemical abundance analysis of 16 elements in 190 metal-poor Galactic halo stars (38 program and 152 literature objects). The sample includes 171 stars wit…
Reconstructing the cosmic evolution of the chemical elements
Anna Frebel
The chemical elements are created in nuclear fusion processes in the hot and dense cores of stars. The energy generated through nucleosynthesis allows stars to shine for billions o…
Complete element abundances of nine stars in the r-process galaxy Reticulum II
Alexander P. Ji, Anna Frebel, Joshua D. Simon +1
We present chemical abundances derived from high-resolution Magellan/MIKE spectra of the nine brightest known red giant members of the ultra-faint dwarf galaxy Reticulum II. These…
The Oxygen Abundance of HE 1327-2326
Anna Frebel, Norbert Christlieb, John E. Norris +2
From a newly obtained VLT/UVES spectrum we have determined the oxygen abundance of HE 1327-2326, the most iron-poor star known to date. UV-OH lines yield a 1D LTE abundance of [O/F…
A gravitational wave detectable candidate Type Ia supernova progenitor
Emma T. Chickles, Kevin B. Burdge, Joheen Chakraborty +37
Type Ia supernovae, critical for studying cosmic expansion, arise from thermonuclear explosions of white dwarfs, but their precise progenitor pathways remain unclear. Growing evide…