scholarly journals Chemo-dynamics of outer halo dwarf stars, including Gaia-Sausage and Gaia-Sequoia candidates

2020 ◽  
Vol 497 (1) ◽  
pp. 1236-1255 ◽  
Author(s):  
Stephanie Monty ◽  
Kim A Venn ◽  
James M M Lane ◽  
Deborah Lokhorst ◽  
David Yong
Keyword(s):  
Stellar Evolution ◽  
Dwarf Galaxy ◽  
Orbital Energy ◽  
Test Cases ◽  
Dwarf Stars ◽  
Orbital Parameters ◽  
Low Metallicity ◽  
Low Mass ◽  
Star Formation Histories ◽  
Gaia Dr2

ABSTRACT The low-metallicity, kinematically interesting dwarf stars studied by Stephens & Boesgaard (2002, SB02) are re-examined using Gaia DR2 astrometry, and updated model atmospheres and atomic line data. New stellar parameters are determined based on the Gaia DR2 parallactic distances and Dartmouth Stellar Evolution Database isochrones. These are in excellent agreement with spectroscopically determined stellar parameters for stars with [Fe/H] > −2; however, large disagreements are found for stars with [Fe/H] ≤ −2, with offsets as large as ΔTeff ∼ +500 K and Δlog g ∼ +1.0. A subset of six stars (test cases) are analysed ab initio using high-resolution spectra with Keck HIRES and Gemini GRACES. This sub-sample is found to include two α-challenged dwarf stars, suggestive of origins in a low-mass, accreted dwarf galaxy. The orbital parameters for the entire SB02 sample are re-determined using Gaia DR2 data. We find 11 stars that are dynamically coincident with the Gaia-Sausage accretion event and another 17 with the Gaia-Sequoia event in action space. Both associations include low-mass, metal-poor stars with isochrone ages older than 10 Gyr. Two dynamical subsets are identified within Gaia-Sequoia. When these subsets are examined separately, a common knee in [α/Fe] is found for the Gaia-Sausage and low orbital energy Gaia-Sequoia stars. A lower metallicity knee is tentatively identified in the Gaia-Sequoia high orbital energy stars. If the metal-poor dwarf stars in these samples are true members of the Gaia-Sausage and Gaia-Sequoia events, then they present a unique opportunity to probe the earlier star formation histories of these systems.

scholarly journals Lithium and beryllium in the Gaia-Enceladus galaxy

2020 ◽  
Vol 496 (3) ◽  
pp. 2902-2909
Author(s):  
P Molaro ◽  
G Cescutti ◽  
X Fu
Keyword(s):  
Milky Way ◽  
Local Group ◽  
Galactic Halo ◽  
Dwarf Galaxy ◽  
Chemical Abundances ◽  
Dwarf Stars ◽  
Evolution Experiment ◽  
External Galaxies ◽  
Low Metallicity ◽  
Gaia Dr2

ABSTRACT Data from Gaia DR2 and The Apache Point Observatory Galactic Evolution Experiment surveys revealed a relatively new component in the inner Galactic halo, which is likely the dynamical remnant of a disrupted dwarf galaxy named Gaia-Enceladus that collided with the Milky Way about 10 Gyr ago. This merging event offers an extraordinary opportunity to study chemical abundances of elements in a dwarf galaxy, since they are generally hampered in external galaxies. Here, we focus on 7Li and 9Be in dwarf stars that are out of reach even in Local Group galaxies. Searching in GALAH, Gaia-ESO survey and in literature, we found several existing 7Li abundance determinations of stars belonging to the Gaia-Enceladus galaxy. The 7Li abundances of stars at the low metallicity end overlap with those of the Galactic halo. These are effective extragalactic 7Li measurements, which suggest that the 7Li Spite plateau is universal, as is the cosmological 7Li problem. We found a 7Li-rich giant out of 101 stars, which suggests a small percentage similar to that of the Milky Way. We also collect 9Be abundance for a subsample of 25 Gaia-Enceladus stars from literature. Their abundances share the Galactic [Be/H] values at the low metallicity end but grow slower with [Fe/H] and show a reduced dispersion. This suggests that the scatter observed in the Milky Way could reflect the different 9Be evolution patterns of different stellar components that are mixed-up in the Galactic halo.

scholarly journals Jsolated Stars of Low Metallicity

Galaxies ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 89
Author(s):  
Efrat Sabach
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Stellar Evolution ◽  
Planetary Nebula ◽  
Luminosity Function ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Solar Metallicity ◽  
Low Metallicity ◽  
Low Mass

We study the effects of a reduced mass-loss rate on the evolution of low metallicity Jsolated stars, following our earlier classification for angular momentum (J) isolated stars. By using the stellar evolution code MESA we study the evolution with different mass-loss rate efficiencies for stars with low metallicities of Z = 0 . 001 and Z = 0 . 004 , and compare with the evolution with solar metallicity, Z = 0 . 02 . We further study the possibility for late asymptomatic giant branch (AGB)—planet interaction and its possible effects on the properties of the planetary nebula (PN). We find for all metallicities that only with a reduced mass-loss rate an interaction with a low mass companion might take place during the AGB phase of the star. The interaction will most likely shape an elliptical PN. The maximum post-AGB luminosities obtained, both for solar metallicity and low metallicities, reach high values corresponding to the enigmatic finding of the PN luminosity function.

scholarly journals Single metal-poor ultra compact dwarf galaxy at one kiloparsec distance from the low-mass elliptical galaxy FCC 47

2019 ◽  
Vol 625 ◽  
pp. A50 ◽  
Author(s):  
Katja Fahrion ◽  
Iskren Georgiev ◽  
Michael Hilker ◽  
Mariya Lyubenova ◽  
Glenn van de Ven ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Stellar Population ◽  
Dwarf Galaxy ◽  
Elliptical Galaxy ◽  
Population Analysis ◽  
Elliptical Galaxies ◽  
Star Cluster ◽  
High Mass ◽  
Low Metallicity ◽  
Low Mass

Context. Photometric surveys of galaxy clusters have revealed a large number of ultra compact dwarfs (UCDs) around predominantly massive elliptical galaxies. Their origin is still debated as some UCDs are considered to be the remnant nuclei of stripped dwarf galaxies while others seem to mark the high-mass end of the star cluster population. Aims. We aim to characterize the properties of a UCD found at very close projected distance (rwproj = 1.1 kpc) from the centre of the low-mass (M ∼ 1010 M⊙) early-type galaxy FCC 47. This is a serendipitous discovery from MUSE adaptive optics science verification data. We explore the potential origin of this UCD as either a massive cluster or the remnant nucleus of a dissolved galaxy. Methods. We used archival Hubble Space Telescope data to study the photometric and structural properties of FCC 47-UCD1. In the MUSE data, the UCD is unresolved, but we used its spectrum to determine the radial velocity and metallicity. Results. The surface brightness of FCC 47-UCD1 is best described by a single King profile with low concentration C = Rt/Rc ∼ 10 and large effective radius (reff = 24 pc). Its integrated magnitude and blue colour (Mg = −10.55 mag, (g − z) = 1.46 mag) combined with a metallicity of [M/H] = −1.12 ± 0.10 dex and an age > 8 Gyr obtained from the full fitting of the MUSE spectrum suggests a stellar population mass of M* = 4.87 × 106 M⊙. The low S/N of the MUSE spectrum prevents detailed stellar population analysis. Due to the limited spectral resolution of MUSE, we can only give an upper limit on the velocity dispersion (σ <  17 km s−1), and consequently on its dynamical mass (Mdyn <  1.3 × 107 M⊙). Conclusions. The origin of the UCD cannot be constrained with certainty. The low metallicity, old age, and magnitude are consistent with a star cluster origin, whereas the extended size is consistent with an origin as the stripped nucleus of a dwarf galaxy with a initial stellar mass of a few 108 M⊙.

scholarly journals SDSS-IV MaNGA: the ‘G-dwarf problem’ revisited

2021 ◽  
Vol 502 (1) ◽  
pp. L95-L98
Author(s):  
Michael J Greener ◽  
Michael Merrifield ◽  
Alfonso Aragón-Salamanca ◽  
Thomas Peterken ◽  
Brett Andrews ◽  
...  
Keyword(s):  
Milky Way ◽  
High Mass ◽  
Dwarf Stars ◽  
The Galaxy ◽  
Star Formation In Galaxies ◽  
History Of ◽  
Low Metallicity ◽  
Low Mass ◽  
Gas Accretion ◽  
Made In

ABSTRACT The levels of heavy elements in stars are the product of enhancement by previous stellar generations, and the distribution of this metallicity among the population contains clues to the process by which a galaxy formed. Most famously, the ‘G-dwarf problem’ highlighted the small number of low-metallicity G-dwarf stars in the Milky Way, which is inconsistent with the simplest picture of a galaxy formed from a ‘closed box’ of gas. It can be resolved by treating the Galaxy as an open system that accretes gas throughout its life. This observation has classically only been made in the Milky Way, but the availability of high-quality spectral data from SDSS-IV MaNGA and the development of new analysis techniques mean that we can now make equivalent measurements for a large sample of spiral galaxies. Our analysis shows that high-mass spirals generically show a similar deficit of low-metallicity stars, implying that the Milky Way’s history of gas accretion is common. By contrast, low-mass spirals show little sign of a G-dwarf problem, presenting the metallicity distribution that would be expected if such systems evolved as pretty much closed boxes. This distinction can be understood from the differing timescales for star formation in galaxies of differing masses.

scholarly journals The Metal-Poor IMF, Stellar Evolution, and Star Formation Histories

2008 ◽  
Vol 4 (S255) ◽  
pp. 285-296 ◽  
Author(s):  
Evan D. Skillman
Keyword(s):  
Star Formation ◽  
Stellar Evolution ◽  
Low Metallicity ◽  
Star Formation Histories ◽  
The Imf

AbstractI present an introduction to three important subjects relevant to low metallicity star formation: the IMF, stellar evolution, and star formation histories. I will draw on observations from the LCID (Local Cosmology from Isolated Dwarfs) project to illustrate some of these topics.

scholarly journals Neutron Nucleosynthesis in a Low-Mass, Low-Metallicity AGB Star

1989 ◽  
Vol 106 ◽  
pp. 227-227
Author(s):  
David Hollowell ◽  
Icko Iben,
Keyword(s):  
Neutron Source ◽  
Stellar Evolution ◽  
Light Elements ◽  
Convective Envelope ◽  
Thermal Pulse ◽  
Low Metallicity ◽  
Low Mass ◽  
Neutron Exposure ◽  
The Creation ◽  
Filtering Effect

Stellar evolution calculations confirm that semiconvection will occur below the convective envelope of a low-mass, low-metallicity AGB star, after a thermal pulse. These calculations show how semiconvection leads to the creation of a “13C layer” in the star, which can provide a potent source of neutrons (via the 13C[a, n]160 reaction) in a convective shell during later evolution. The rate at which neutrons are released is largely determined by the rate at which the 13C layer is introduced into the convective shell. The 13C neutron source maintains neutron densities of 109-1010 n/cm3 for ∼ 10 years. This provides a neutron exposure r=0.15 mb“1 during most of the pulses calculated. Because of the strong filtering effect by light elements, only 10—20% of the neutrons produced will be captured by iron-seed nuclei, each such nucleus capturing 4–5 neutrons per pulse.

scholarly journals The EBLM Project

2019 ◽  
Vol 625 ◽  
pp. A150 ◽  
Author(s):  
Alexander von Boetticher ◽  
Amaury H. M. J. Triaud ◽  
Didier Queloz ◽  
Sam Gill ◽  
Pierre F. L. Maxted ◽  
...  
Keyword(s):  
Physical Properties ◽  
Stellar Evolution ◽  
Binary Systems ◽  
Close Binary ◽  
Low Mass Stars ◽  
Orbital Parameters ◽  
Eclipse Observations ◽  
Low Mass ◽  
Orbital Periods ◽  
Host Stars

Measurements of the physical properties of stars at the lower end of the main sequence are scarce. In this context we report masses, radii and surface gravities of ten very-low-mass stars in eclipsing binary systems, with orbital periods of the order of several days. The objects probe the stellar mass-radius relation in the fully convective regime, M⋆ ≲ 0.35 M⊙, down to the hydrogen burning mass-limit, MHB ∼ 0.07 M⊙. The stars were detected by the WASP survey for transiting extra-solar planets, as low-mass, eclipsing companions orbiting more massive, F- and G-type host stars. We use eclipse observations of the host stars, performed with the TRAPPIST, Leonhard Euler and SPECULOOS telescopes, and radial velocities of the host stars obtained with the CORALIE spectrograph, to determine the physical properties of the low-mass companions. Surface gravities of the low-mass companions are derived from the eclipse and orbital parameters of each system. Spectroscopic measurements of the host star effective temperature and metallicity are used to infer the host star mass and age from stellar evolution models for solar-type stars. Masses and radii of the low-mass companions are then derived from the eclipse and orbital parameters of the binary systems. The objects are compared to stellar evolution models for low-mass stars, to test for an effect of the stellar metallicity and orbital period on the radius of low-mass stars in close binary systems. Measurements are found to be in good agreement with stellar evolution models; a systematic inflation of the radius of low-mass stars with respect to model predictions is limited to 1.6 ± 1.2%, in the fully convective low-mass regime. The sample of ten objects indicates a scaling of the radius of low-mass stars with the host star metallicity. No correlation between stellar radii and the orbital periods of the binary systems is determined. A combined analysis with thirteen comparable objects from the literature is consistent with this result.

scholarly journals Role of massive stars in the evolution of primitive galaxies

2012 ◽  
Vol 10 (H16) ◽  
pp. 370-370
Author(s):  
Sara Heap
Keyword(s):  
Galaxy Evolution ◽  
Dwarf Galaxy ◽  
Massive Stars ◽  
Stellar Winds ◽  
Stellar Feedback ◽  
Low Metallicity ◽  
Low Mass ◽  
Blue Compact Dwarf Galaxy

AbstractAn important factor controlling galaxy evolution is feedback from massive stars. It is believed that the nature and intensity of stellar feedback changes as a function of galaxy mass and metallicity. At low mass and metallicity, feedback from massive stars is mainly in the form of photoionizing radiation. At higher mass and metallicity, it is in stellar winds. I Zw 18 is a local blue, compact dwarf galaxy that meets the requirements for a primitive galaxy: low halo mass <109M⊙, strong photoionizing radiation, no galactic outflow, and very low metallicity, log(O/H)+12=7.2. We will describe the properties of massive stars and their role in the evolution of I Zw 18, based on analysis of ultraviolet images and spectra obtained with HST.

scholarly journals The GALAH survey and Gaia DR2: Linking ridges, arches, and vertical waves in the kinematics of the Milky Way

2019 ◽  
Vol 489 (4) ◽  
pp. 4962-4979 ◽  
Author(s):  
Shourya Khanna ◽  
Sanjib Sharma ◽  
Thor Tepper-Garcia ◽  
Joss Bland-Hawthorn ◽  
Michael Hayden ◽  
...  
Keyword(s):  
Large Scale ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Elemental Abundance ◽  
Space Distribution ◽  
Orbital Energy ◽  
Small Scale ◽  
Constant Energy ◽  
Third Dimension ◽  
Gaia Dr2

ABSTRACT Gaia DR2 has revealed new small-scale and large-scale patterns in the phase-space distribution of stars in the Milky Way. In cylindrical Galactic coordinates $(R,\phi ,z)$, ridge-like structures can be seen in the $(R,V_\phi)$ plane and asymmetric arch-like structures in the $(V_R,V_\phi)$ plane. We show that the ridges are also clearly present when the third dimension of the $(R,V_\phi)$ plane is represented by $\langle z \rangle$, $\langle V_z \rangle$, $\langle V_R \rangle$, $\langle$[Fe/H]$\rangle$, and $\langle [\alpha /{\rm Fe}]\rangle$. The maps suggest that stars along the ridges lie preferentially close to the Galactic mid-plane ($|z|\lt 0.2$ kpc), and have metallicity and $\alpha$ elemental abundance similar to that of the Sun. We show that phase mixing of disrupting spiral arms can generate both the ridges and the arches. It also generates discrete groupings in orbital energy – the ridges and arches are simply surfaces of constant energy. We identify eight distinct ridges in the Gaia DR2 data: six of them have constant energy while two have constant angular momentum. Given that the signature is strongest for stars close to the plane, the presence of ridges in $\langle z \rangle$ and $\langle V_z \rangle$ suggests a coupling between planar and vertical directions. We demonstrate, using N-body simulations that such coupling can be generated both in isolated discs and in discs perturbed by an orbiting satellite like the Sagittarius dwarf galaxy.

scholarly journals Identifying stellar streams in Gaia DR2 with data mining techniques

2019 ◽  
Vol 492 (1) ◽  
pp. 1370-1384 ◽  
Author(s):  
Nicholas W Borsato ◽  
Sarah L Martell ◽  
Jeffrey D Simpson
Keyword(s):  
Data Mining ◽  
Globular Clusters ◽  
Dwarf Galaxy ◽  
Large Data ◽  
Data Sets ◽  
Integral Of Motion ◽  
Data Mining Techniques ◽  
Orbital Parameters ◽  
Stellar Streams ◽  
Gaia Dr2

ABSTRACT Streams of stars from captured dwarf galaxies and dissolved globular clusters are identifiable through the similarity of their orbital parameters, a fact that remains true long after the streams have dispersed spatially. We calculate the integrals of motion for 31 234 stars, to a distance of 4 kpc from the Sun, which have full and accurate 6D phase space positions in the Gaia DR2 catalogue. We then apply a novel combination of data mining, numerical, and statistical techniques to search for stellar streams. This process returns five high confidence streams (including one which was previously undiscovered), all of which display tight clustering in the integral of motion space. Colour–magnitude diagrams indicate that these streams are relatively simple, old, metal-poor populations. One of these resolved streams shares very similar kinematics and metallicity characteristics with the Gaia-Enceladus dwarf galaxy remnant, but with a slightly younger age. The success of this project demonstrates the usefulness of data mining techniques in exploring large data sets.

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