scholarly journals Weighing the stellar constituents of the galactic halo with APOGEE red giant stars

2020 ◽  
Vol 492 (3) ◽  
pp. 3631-3646 ◽  
Author(s):  
J Ted Mackereth ◽  
Jo Bovy
Keyword(s):  
Milky Way ◽  
Galactic Halo ◽  
Power Laws ◽  
Stellar Mass ◽  
Giant Star ◽  
Giant Stars ◽  
Stellar Halo ◽  
Tentative Evidence ◽  
History Of ◽  
Red Giant

ABSTRACT The stellar mass in the halo of the Milky Way is notoriously difficult to determine, owing to the paucity of its stars in the solar neighbourhood. With tentative evidence from Gaia that the nearby stellar halo is dominated by a massive accretion event – referred to as Gaia-Enceladus or Sausage – these constraints are now increasingly urgent. We measure the mass in kinematically selected mono-abundance populations (MAPs) of the stellar halo between −3 < [Fe/H] < −1 and 0.0 < [Mg/Fe] < 0.4 using red giant star counts from APOGEE DR14. We find that MAPs are well fit by single power laws on triaxial ellipsoidal surfaces, and we show that that the power-law slope α changes such that high [Mg/Fe] populations have α ∼ 4, whereas low [Mg/Fe] MAPs are more extended with shallow slopes, α ∼ 2. We estimate the total stellar mass to be $M_{*,\mathrm{tot}} = 1.3^{+0.3}_{-0.2}\times 10^{9}\ \mathrm{M_{\odot}}$, of which we estimate ${\sim}0.9^{+0.2}_{-0.1} \times 10^{9}\ \mathrm{M_{\odot}}$ to be accreted. We estimate that the mass of accreted stars with e > 0.7 is M*,accreted, e > 0.7 = 3 ± 1 (stat.) ± 1 (syst.) × 108 M⊙, or ${\sim}30{-}50{{\ \rm per\ cent}}$ of the accreted halo mass. If the majority of these stars are the progeny of a massive accreted dwarf, this places an upper limit on its stellar mass, and implies a halo mass for the progenitor of ∼1010.2 ± 0.2 M⊙. This constraint not only shows that the Gaia-Enceladus/Sausage progenitor may not be as massive as originally suggested, but that the majority of the Milky Way stellar halo was accreted. These measurements are an important step towards fully reconstructing the assembly history of the Milky Way.

The evolution of the Milky Way’s radial metallicity gradient as seen by APOGEE, CoRoT, and Gaia

2018 ◽  
Vol 14 (A30) ◽  
pp. 257-257
Author(s):  
Friedrich Anders ◽  
Ivan Minchev ◽  
Cristina Chiappini
Keyword(s):  
Milky Way ◽  
Past History ◽  
Open Clusters ◽  
Dynamical Models ◽  
Giant Stars ◽  
The Past ◽  
The Status ◽  
History Of ◽  
Abundance Profile ◽  
Red Giant

AbstractThe time evolution of the radial metallicity gradient is one of the most important constraints for Milky Way chemical and chemo-dynamical models. In this talk we reviewed the status of the observational debate and presented a new measurement of the age dependence of the radial abundance gradients, using combined asteroseismic and spectroscopic observations of red giant stars. We compared our results to state-of-the-art chemo-dynamical Milky Way models and recent literature results obtained with open clusters and planetary nebulae, and propose a new method to infer the past history of the Galactic radial abundance profile.

scholarly journals Contributions to the Galactic halo from in-situ, kicked-out, and accreted stars

2015 ◽  
Vol 11 (S317) ◽  
pp. 241-246
Author(s):  
Allyson A. Sheffield ◽  
Kathryn V. Johnston ◽  
Katia Cunha ◽  
Verne V. Smith ◽  
Steven R. Majewski
Keyword(s):  
Neutron Capture ◽  
Milky Way ◽  
Galactic Halo ◽  
Galactic Disk ◽  
High Resolution Spectroscopy ◽  
Chemical Abundances ◽  
Giant Stars ◽  
Halo Stars ◽  
Tentative Evidence

AbstractWe report chemical abundances for a sample of 66 M giants with high S/N high-resolution spectroscopy in the inner halo of the Milky Way. The program giant stars have radial velocities that vary significantly from those expected for stars moving on uniform circular orbits in the Galactic disk. Thus, based on kinematics, we expect a sample dominated by halo stars. Abundances are derived for α-elements and neutron capture elements. By analyzing the multi-dimensional abundance space, the formation site of the halo giants – in-situ or accreted – can be assessed. Of particular interest are a class of stars that form in-situ, deep in the Milky Way's gravitational potential well, but are “kicked out” of the disk into the halo due to a perturbation event. We find: (1) our sample is dominated by accreted stars and (2) tentative evidence of a small kicked-out population in our Milky Way halo sample.

scholarly journals Stellar loci IV. red giant stars

2022 ◽  
Vol 21 (12) ◽  
pp. 319
Author(s):  
Ruo-Yi Zhang ◽  
Hai-Bo Yuan ◽  
Xiao-Wei Liu ◽  
Mao-Sheng Xiang ◽  
Yang Huang ◽  
...  
Keyword(s):  
Galactic Halo ◽  
Signal To Noise Ratio ◽  
Sloan Digital Sky Survey ◽  
Red Giants ◽  
Giant Stars ◽  
Sky Survey ◽  
History Of ◽  
Red Giant Stars ◽  
Red Giant ◽  
A New Technique

Abstract In the fourth paper of this series, we present the metallicity-dependent Sloan Digital Sky Survey (SDSS) stellar color loci of red giant stars, using a spectroscopic sample of red giants in the SDSS Stripe 82 region. The stars span a range of 0.55 – 1.2 mag in color g – i, –0.3 – –2.5 in metallicity [Fe/H], and have values of surface gravity log g smaller than 3.5 dex. As in the case of main-sequence (MS) stars, the intrinsic widths of loci of red giants are also found to be quite narrow, a few mmag at maximum. There are however systematic differences between the metallicity-dependent stellar loci of red giants and MS stars. The colors of red giants are less sensitive to metallicity than those of MS stars. With good photometry, photometric metallicities of red giants can be reliably determined by fitting the u – g, g – r, r – i, and i – z colors simultaneously to an accuracy of 0.2 – 0.25 dex, comparable to the precision achievable with low-resolution spectroscopy for a signal-to-noise ratio of 10. By comparing fitting results to the stellar loci of red giants and MS stars, we propose a new technique to discriminate between red giants and MS stars based on the SDSS photometry. The technique achieves completeness of ∼70 per cent and efficiency of ∼80 per cent in selecting metal-poor red giant stars of [Fe/H] ≤ –1.2. It thus provides an important tool to probe the structure and assemblage history of the Galactic halo using red giant stars.

scholarly journals Discovery of s-process enhanced stars in the LAMOST survey

2019 ◽  
Vol 490 (2) ◽  
pp. 2219-2227 ◽  
Author(s):  
Brodie J Norfolk ◽  
Andrew R Casey ◽  
Amanda I Karakas ◽  
Matthew T Miles ◽  
Alex J Kemp ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Selection Bias ◽  
Galactic Halo ◽  
Asymptotic Giant Branch ◽  
The Other ◽  
Data Driven ◽  
Giant Stars ◽  
Show Evidence ◽  
Data Driven Approach ◽  
Red Giant

ABSTRACT Here we present the discovery of 895 s-process-rich candidates from 454 180 giant stars observed by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) using a data-driven approach. This sample constitutes the largest number of s-process enhanced stars ever discovered. Our sample includes 187 s-process-rich candidates that are enhanced in both barium and strontium, 49 stars with significant barium enhancement only and 659 stars that show only a strontium enhancement. Most of the stars in our sample are in the range of effective temperature and log g typical of red giant branch (RGB) populations, which is consistent with our observational selection bias towards finding RGB stars. We estimate that only a small fraction (∼0.5 per cent) of binary configurations are favourable for s-process enriched stars. The majority of our s-process-rich candidates (95 per cent) show strong carbon enhancements, whereas only five candidates (<3  per cent) show evidence of sodium enhancement. Our kinematic analysis reveals that 97 per cent of our sample are disc stars, with the other 3 per cent showing velocities consistent with the Galactic halo. The scaleheight of the disc is estimated to be $z_{\rm h}=0.634 \pm {0.063}\, \mathrm{kpc}$, comparable with values in the literature. A comparison with yields from asymptotic giant branch (AGB) models suggests that the main neutron source responsible for the Ba and Sr enhancements is the 13C(α,n)16O reaction. We conclude that s-process-rich candidates may have received their overabundances via mass transfer from a previous AGB companion with an initial mass in the range $1\!-\!3\, \mathrm{M}_{\odot }$.

scholarly journals Neutron-capture elements in dwarf galaxies

2019 ◽  
Vol 631 ◽  
pp. A171 ◽  
Author(s):  
Á. Skúladóttir ◽  
C. J. Hansen ◽  
S. Salvadori ◽  
A. Choplin
Keyword(s):  
Neutron Capture ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Core Collapse ◽  
Chemical Abundances ◽  
Relative Contribution ◽  
History Of ◽  
Red Giant ◽  
Process Element ◽  
Giant Branch Stars

The heavy elements (Z >  30) are created in neutron (n)-capture processes that are predicted to happen at vastly different nucleosynthetic sites. To study these processes in an environment different from the Milky Way, we targeted the n-capture elements in red giant branch stars in the Sculptor dwarf spheroidal galaxy. Using ESO VLT/FLAMES spectra, we measured the chemical abundances of Y, Ba, La, Nd, and Eu in 98 stars covering the metalliticy range −2.4 < [Fe/H] < −0.9. This is the first paper in a series about the n-capture elements in dwarf galaxies, and here we focus on the relative and absolute timescales of the slow (s)- and rapid (r)-processes in Sculptor. From the abundances of the s-process element Ba and the r-process element Eu, it is clear that the r-process enrichment occurred throughout the entire chemical evolution history of Sculptor. Furthermore, there is no evidence for the r-process to be significantly delayed in time relative to core-collapse supernovae. Neutron star mergers are therefore unlikely the dominant (or only) nucleosynthetic site of the r-process. However, the products of the s-process only become apparent at [Fe/H] ≈ −2 in Sculptor, and the s-process becomes the dominant source of Ba at [Fe/H] ≳ −2. We tested the use of [Y/Mg] and [Ba/Mg] as chemical clocks in Sculptor. Similarly to what is observed in the Milky Way, [Y/Mg] and [Ba/Mg] increase towards younger ages. However, there is an offset in the trends, where the abundance ratios of [Y/Mg] in Sculptor are significantly lower than those of the Milky Way at any given age. This is most likely caused by metallicity dependence of yields from the s-process, as well as by a different relative contribution of the s-process to core-collapse supernovae in these galaxies. Comparisons of our results with data of the Milky Way and the Fornax dwarf spheroidal galaxy furthermore show that these chemical clocks depend on both metallicity and environment.

29. Stellar Spectra (Spectres Stellaires)

1991 ◽  
Vol 21 (1) ◽  
pp. 309-326
Keyword(s):  
Milky Way ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Dynamical Interaction ◽  
Stellar Spectra ◽  
Luminous Blue Variables ◽  
Classical Novae ◽  
Giant Stars ◽  
Red Giant ◽  
Sydney Australia

In the triennium under review, from the late second half of 1987 to the early second half of 1990, Commission 29 has sponsored or cosponsored the following IAU Conferences: Coll. No. 106, “Evolution of Peculiar Red Giant Stars,” Bloomington, Indiana, July 1988; CoU. No. 114, “White Dwarfs,” Hanover, New Hamsphire, August 1988; Coll. No. 113, “Physics of Luminous Blue Variables,” Val Morin, Quebec, August 1988; Coll. No. 122, “Physics of Classical Novae,” Madrid, Spain, June 1989; Symp. No. 143, “Wolf-Rayet Stars and Interrelations with Other Massive Stars in Galaxies,” Denpasar, Indonesia, June 1990; Symp. No 148, “The Magellanic Clouds and their Dynamical Interaction with the Milky Way,” Sydney, Australia, July 1990; Symp. No. 145, “Evolution of Stars: the Photospheric Abundance Connection,” Druzba, Bulgaria. August 1990.

scholarly journals Distance to the nearby dwarf galaxy [TT2009] 25 in the NGC 891 group using the tip of the red giant branch

2019 ◽  
Vol 629 ◽  
pp. L2 ◽  
Author(s):  
Oliver Müller ◽  
Rodrigo Ibata ◽  
Marina Rejkuba ◽  
Lorenzo Posti
Keyword(s):  
Milky Way ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Small Scale ◽  
Accurate Information ◽  
Standard Candle ◽  
Stellar Halo ◽  
Red Giant ◽  
Small Field Of View

Dwarf galaxies are key objects for small-scale cosmological tests like the abundance problems or the planes-of-satellites problem. A crucial task is therefore to get accurate information for as many nearby dwarf galaxies as possible. Using extremely deep, ground-based V and i-band Subaru Suprime Cam photometry with a completeness of i = 27 mag, we measure the distance of the dwarf galaxy [TT2009] 25 using the tip of the red giant branch as a standard candle. This dwarf resides in the field around the Milky Way-analog NGC 891. Using a Bayesian approach, we measure a distance of 10.28−1.73+1.17 Mpc, which is consistent with the distance of NGC 891, and thus confirm it as a member of NGC 891. The dwarf galaxy follows the scaling relations defined by the Local Group dwarfs. We do not find an extended stellar halo around [TT2009] 25. In the small field of view of 100 kpc covered by the survey, only one bright dwarf galaxy and the giant stream are apparent. This is comparable to the Milky Way, where one bright dwarf resides in the same volume, as well as the Sagittarius stream – excluding satellites which are farther away but would be projected in the line-of-sight. It is thus imperative to survey for additional dwarf galaxies in a larger area around NGC 891 to test the abundance of dwarf galaxies and compare this to the number of satellites around the Milky Way.

scholarly journals Kraken reveals itself – the merger history of the Milky Way reconstructed with the E-MOSAICS simulations

2020 ◽  
Vol 498 (2) ◽  
pp. 2472-2491 ◽  
Author(s):  
J M Diederik Kruijssen ◽  
Joel L Pfeffer ◽  
Mélanie Chevance ◽  
Ana Bonaca ◽  
Sebastian Trujillo-Gomez ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Mass Range ◽  
Stellar Mass ◽  
Host Galaxies ◽  
Stellar Halo ◽  
Major Merger ◽  
Virial Mass ◽  
Minor Mergers ◽  
Stellar Masses

ABSTRACT Globular clusters (GCs) formed when the Milky Way experienced a phase of rapid assembly. We use the wealth of information contained in the Galactic GC population to quantify the properties of the satellite galaxies from which the Milky Way assembled. To achieve this, we train an artificial neural network on the E-MOSAICS cosmological simulations of the co-formation and co-evolution of GCs and their host galaxies. The network uses the ages, metallicities, and orbital properties of GCs that formed in the same progenitor galaxies to predict the stellar masses and accretion redshifts of these progenitors. We apply the network to Galactic GCs associated with five progenitors: Gaia-Enceladus, the Helmi streams, Sequoia, Sagittarius, and the recently discovered ‘low-energy’ GCs, which provide an excellent match to the predicted properties of the enigmatic galaxy ‘Kraken’. The five galaxies cover a narrow stellar mass range [M⋆ = (0.6–4.6) × 108 M⊙], but have widely different accretion redshifts ($\mbox{$z_{\rm acc}$}=0.57\!-\!2.65$). All accretion events represent minor mergers, but Kraken likely represents the most major merger ever experienced by the Milky Way, with stellar and virial mass ratios of $\mbox{$r_{M_\star }$}=1$:$31^{+34}_{-16}$ and $\mbox{$r_{M_{\rm h}}$}=1$:$7^{+4}_{-2}$, respectively. The progenitors match the z = 0 relation between GC number and halo virial mass, but have elevated specific frequencies, suggesting an evolution with redshift. Even though these progenitors likely were the Milky Way’s most massive accretion events, they contributed a total mass of only log (M⋆, tot/M⊙) = 9.0 ± 0.1, similar to the stellar halo. This implies that the Milky Way grew its stellar mass mostly by in-situ star formation. We conclude by organizing these accretion events into the most detailed reconstruction to date of the Milky Way’s merger tree.

scholarly journals Formation history of open clusters constrained by detailed asteroseismology of red giant stars observed byKepler

2017 ◽  
Vol 160 ◽  
pp. 05002
Author(s):  
Enrico Corsaro ◽  
Yueh-Ning Lee ◽  
Rafael A. García ◽  
Patrick Hennebelle ◽  
Savita Mathur ◽  
...  
Keyword(s):  
Open Clusters ◽  
Giant Stars ◽  
Formation History ◽  
History Of ◽  
Red Giant Stars ◽  
Red Giant

scholarly journals Constraints on Interactions and Mergers from dSph Galaxies and Globular Clusters

1999 ◽  
Vol 186 ◽  
pp. 52-52
Author(s):  
E.K. Grebel
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Local Group ◽  
Galactic Halo ◽  
Dwarf Galaxies ◽  
Thick Disk ◽  
History Of

Observations at high redshifts are revealing numerous interactions and ongoing mergers. Our own Milky Way is currently merging with the Sagittarius dwarf spheroidal (dSph) galaxy. Past mergers with dwarf galaxies may have contributed significantly to the Galactic halo and possibly to the thick disk. The properties of Local Group dSphs and halo globular clusters impose constraints on the merger history of the Milky Way.

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