The Milky Way dark matter halo is formed from the accretion of smaller subhalos. These sub-units also harbor stars---typically old and metal-poor---that are deposited in the Galactic inner regions by disruption events. In this Letter, we show that the dark matter and metal-poor stars in the Solar neighborhood share similar kinematics due to their common origin. Using the high-resolution Eris simulation, which traces the evolution of both the dark matter and baryons in a realistic Milky-Way analog galaxy, we demonstrate that metal-poor stars are indeed effective tracers for the local, virialized dark matter velocity distribution. The local dark matter velocities can therefore be inferred from observations of the stellar halo made by the Sloan Digital Sky Survey within 4 kpc of the Sun. This empirical distribution differs from the Standard Halo Model in important ways and suggests that the bounds on the spin-independent scattering cross section may be weakened for dark matter masses below $\sim$10 GeV. Data from Gaia will allow us to further refine the expected distribution for the smooth dark matter component, and to test for the presence of local substructure.
The dark matter velocity distribution in the Solar neighbourhood is an important astrophysical input which enters in the predicted event rate of dark matter direct detection experiments. It has been recently suggested that the local dark matter velocity distribution can be inferred from that of old or metal-poor stars in the Milky Way. We investigate this potential relation using six high resolution magneto-hydrodynamical simulations of Milky Way-like galaxies of the Auriga project. We do not find any correlation between the velocity distributions of dark matter and old stars in the Solar neig…
We present radial velocities for stars in the field of the open star clusters Berkeley 44, Berkeley 81, and NGC 6802 from spectra obtained using the Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5 m telescope. These clusters are of intermediate age (1-3 Gyr), located within the solar Galactocentric radius, and have no previous radial velocity measurements. We find mean radial velocities of -9.6 +/- 3.0 km s^-1, 48.1 +/- 2.0 km s^-1, and 12.4 +/- 2.8 km s^-1 for Be 44, Be 81, and NGC 6802, respectively. We present an analysis of radial velocities of 134 open clusters of a wide range of ages using data o…
We conducted a long-slit spectrophotometry analysis to obtain the chemical abundances of seven metal-poor HII regions in three galaxies: UM 160, UM 420, and TOL 0513-393. The data have been taken with the Focal Reducer Low Dispersion Spectrograph 1 (FORS1) at the 8.2-m Very Large Telescope. We derived the physical conditions and the chemical abundances of N, O, Ne, S, Ar, and Cl. We also performed a detailed analysis that involves abundance determinations using the $t^2$ formalism. Based on HeI recombination line intensity ratios, together with the Helio14 code, we derived the abundance of He.…
We propose a method to determine the galactic constants R_0 (distance to the Galactic Center) and V_0 (rotation velocity of the Sun) from measurements of distances, radial velocities and proper motions of objects near the solar circle. This is a modification of the solar-circle method to a more practical observational method. We apply the method to determine R_0 using data from the literature with known distances and radial velocities, and obtain R_0 = 7.54 +/- 0.77 kpc.
We present a review on the determination of the primordial helium abundance Yp, based on the study of hydrogen and helium recombination lines in extragalactic HII regions. We also discuss the observational determinations of the increase of helium to the increase of oxygen by mass Delta Y / Delta O, and compare them with predictions based on models of galactic chemical evolution.
We present chemical abundances and radial velocities of six HII regions in the extremely metal-poor star-forming dwarf galaxy DDO 68. They are derived from deep spectra in the wavelength range 3500 - 10,000 Å, acquired with the Multi Object Double Spectrograph (MODS) at the Large Binocular Telescope (LBT). In the three regions where the [O III]$λ$4363 Å line was detected, we inferred the abundance of He, N, O, Ne, Ar, and S through the "direct" method. We also derived the oxygen abundances of all the six regions adopting indirect method calibrations. We confirm that DDO 68 is an extremely meta…
Currently, the primordial helium abundance is best estimated through spectroscopic observations of H II regions in metal-poor galaxies. However these determinations are limited by several systematic uncertainties which ultimately limit our ability to accurately ascertain the primordial abundance. In this study, we improve the methodologies for solving for the reddening, the emission contributions from collisional excitation of the H I atoms, the effects underlying absorption in the H I and He I emission lines, and the treatment of the blended H I and He I emission at $λ$3889 with the aim of lo…
The ages of the oldest and most metal-poor stars in the Milky Way bear important information on the age of the Universe and its standard model. We analyze a sample of 28 extremely metal-poor field stars in the solar vicinity culled from the literature and carefully determine their ages. To this aim, we critically make use of Gaia data to derive their distances and associated uncertainties. Particular attention has been paid to the estimate of the reddening and its effect on the derivation of stellar ages. We employed different reddenings and super-impose isochrones from different sources in th…
The orbital motions of halo stars in the Milky Way reflect the orbital motions of the progenitor systems in which they formed, making it possible to trace the mass-assembly history of the Galaxy. Direct measurement of three-dimensional velocities, based on accurate proper motions and line-of-sight velocities, has revealed that the majority of halo stars in the inner-halo region move on eccentric orbits. However, our understanding of the motions of distant, in-situ halo-star samples is still limited, due to the lack of accurate proper motions for these stars. Here we explore a model-independent…
Context: Open clusters are ideal laboratories to investigate a variety of astrophysical topics, from the properties of the Galactic disc to stellar evolution models. For this purpose, we need to know their chemical composition in detail. Unfortunately, the number of systems with chemical abundances determined from high resolution spectroscopy remains small. Aims: Our aim is to increase the number of open clusters with radial velocities and chemical abundances determined from high resolution spectroscopy by sampling a few stars in clusters not studied previously. Methods: We obtained high resol…
An independent determination of $H_0$ is crucial given the growing tension between the Hubble constant, $H_0$, derived locally and that determined from the modeling of the cosmic microwave background (CMB) originating in the early universe. In this work, we present a new determination of $H_0$ using velocities and tip of the red giant branch (TRGB) distances to 33 galaxies located between the Local Group and the Virgo cluster. We use a model of the infall pattern of the local Hubble flow modified by the Virgo mass, which is given as a function of the cosmological constants ($H_0$, $Ω_Λ$), the …
We report new branching fraction measurements for 199 UV and optical transitions of Hf II. These transitions range in wavelength (wavenumber) from 2068- 6584 A (48322-15183 cm-1) and originate in 17 odd-parity upper levels ranging in energy from 38578-53227 cm-1. The branching fractions are combined with radiative lifetimes reported in an earlier study to produce a set of transition probabilities and log(gf) values with accuracy ranging from 5-25%. Comparison is made to transition probabilities from the literature where such data exist. We use these new transition probabilities to derive impro…
(Abridged) Extremely metal-poor stars contain the fossil records of the chemical composition of the early Galaxy. The NLTE profiles of the calcium lines were computed in a sample of 53 extremely metal-poor stars with a modified version of the program MULTI. With our new model atom we are able to reconcile the abundance of Ca deduced from the Ca I and Ca II lines in Procyon. -We find that [Ca/Fe] = 0.50 $\pm$ 0.09 in the early Galaxy, a value slightly higher than the previous LTE estimations. -The scatter of the ratios [X/Ca] is generally smaller than the scatter of the ratio [X/Mg] where X is …
The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is an unbiased, massively multiplexed spectroscopic survey, designed to measure the expansion history of the universe through low-resolution ($R\sim750$) spectra of Lyman-Alpha Emitters. In its search for these galaxies, HETDEX will also observe a few 10$^{5}$ stars. In this paper, we present the first stellar value-added catalog within the internal second data release of the HETDEX Survey (HDR2). The new catalog contains 120,571 low-resolution spectra for 98,736 unique stars between $10 < G < 22$ spread across the HETDEX footprint at …
Context: Open clusters are key to studying the formation and evolution of the Galactic disc. However, there is a deficiency of radial velocity and chemical abundance determinations for open clusters in the literature. Aims: We intend to increase the number of determinations of radial velocities and metallicities from spectroscopy for open clusters. Methods: We acquired medium-resolution spectra (R~8000) in the infrared region Ca II triplet lines (~8500 AA) for several stars in five open clusters with the long-slit IDS spectrograph on the 2.5~m Isaac Newton Telescope (Roque de los Muchachos Obs…
We present 947 radial velocities of RR Lyrae variable stars in four fields located toward the Galactic bulge, observed within the data from the ongoing Bulge RR Lyrae Radial Velocity Assay (BRAVA-RR). We show that these RR Lyrae stars exhibit hot kinematics and null or negligible rotation and are therefore members of a separate population from the bar/pseudobulge that currently dominates the mass and luminosity of the inner Galaxy. Our RR Lyrae stars predate these structures, and have metallicities, kinematics, and spatial distribution that are consistent with a "classical" bulge, although we …
The primordial He abundance $Y_\mathrm{P}$ is a powerful probe of cosmology. Currently, $Y_\mathrm{P}$ is best determined by observations of metal-poor galaxies, while there are only a few known local extremely metal-poor ($<0.1 Z_\odot$) galaxies (EMPGs) having reliable He/H measurements with HeI$λ$10830 near-infrared (NIR) emission. Here we present deep Subaru NIR spectroscopy for 10 EMPGs. Combining the existing optical data, He/H values of 5 out of the 10 EMPGs are reliably derived by the Markov chain Monte Carlo algorithm. Adding the existing 3 EMPGs and 51 moderately metal-poor ($0.1-0.4…
We derive the metallicity (traced by the O/H abundance) of the Narrow Line Region ( NLR) of 108 Seyfert galaxies as well as radial metallicity gradients along their galaxy disks and of these of a matched control sample of no active galaxies. In view of that, observational data from the SDSS-IV MaNGA survey and strong emission-line calibrations taken from the literature were considered. The metallicity obtained for the NLRs %each Active Galactic Nucleus (AGN) was compared to the value derived from the extrapolation of the radial oxygen abundance gradient, obtained from \ion{H}{ii} region estima…
We consider three samples of O- and B-type stars from the solar neighborhood 0.6--4 kpc for which we have taken the distances, line-of-sight velocities, and proper motions from published sources. The first sample contains 120 massive spectroscopic binaries. O stars with spectroscopic distances from Patriarchi et al. constitute the second sample. The third sample consists of 168 OB3 stars whose distances have been determined from interstellar calcium lines. The angular velocity of Galactic rotation at the solar distance $Ω_0,$ its two derivatives $Ω'_0$ and $Ω"_0,$ and the peculiar velocity com…
We report the discovery of 34 stars in the Hamburg/ESO Survey for metal-poor stars and the Sloan Digital Sky Survey that have [Fe/H] < -3.0. Their median and minimum abundances are [Fe/H] = -3.1 and -4.1, respectively, while 10 stars have [Fe/H] < -3.5. High-resolution, high-S/N spectroscopic data - equivalent widths and radial velocities - are presented for these stars, together with an additional four objects previously reported or currently being investigated elsewhere. We have determined the atmospheric parameters, effective temperature (Teff) and surface gravity (logg), which are critical…
We report the discovery of 30 stars with extreme space velocities ($>$ 480 km/s) in the Gaia-DR2 archive. These stars are a subset of 1743 stars with high-precision parallax, large tangential velocity ($v_{tan}>$ 300 km/s), and measured line-of-sight velocity in DR2. By tracing the orbits of the stars back in time, we find at least one of them is consistent with having been ejected by the supermassive black hole at the Galactic Center. Another star has an orbit that passed near the Large Magellanic Cloud (LMC) about 200 Myr ago. Unlike previously discovered blue hypervelocity stars, our sample…
We present a sample of 22 blue ($(B-V)_{AB}<0.45$), luminous ($M_{B,AB}<-18.9$), metal-poor galaxies in the $0.69<z<0.88$ redshift range, selected from the DEEP2 galaxy redshift survey. Their spectra contain the $[OIII]\lambda4363$ auroral line, the $[OII]λ\lambda3726,3729$ doublet and the strong nebular $[OIII]λλ4959,5007$ emission lines. The ionised gas-phase oxygen abundances of these galaxies lie between $7.62<12+\log O/H < 8.19$, i.e. between $1/10 Z_{\odot}$ and $1/3 Z_{\odot}$. We find that galaxies in our sample have comparable metallicities to other intermediate-redshift samples, but …
Determination of kinematic distances of WISE & SMGPS H II regions in the Galactic plane using SEDIGISM cloud association
Technical University of Kenya（肯尼亚科技大学）；University of Leeds（利兹大学）；Aberystwyth University（阿伯里斯特威斯大学）；INAF-Osservatorio Astrofisico di Catania（意大利国家天体物理研究所卡塔尼亚天文台）；University of South Africa（南非大学）
该研究提出通过云关联确定银道面WISE和SMGPS H II区运动学距离的方法，将其与SEDIGISM分子云关联，通过空间和速度建立联系，验证了方法有效性，解决部分速度模糊问题，提供了距离目录并建立研究框架。
Detailed Abundance Determination of Metal-Poor Stars with X-Shooter I. Unusual Chemistry in Halo Stars
Research School of Astronomy and Astrophysics, Australian National University（澳大利亚国立大学天体物理学与天文学研究学院）；Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University（乌普萨拉大学物理与天文学系理论天体物理学）；Zentrum für Astronomie der Universität Heidelberg, Landessternwarte（海德堡大学天文中心州立天文台）
Almost every helium atom in the Universe was created just a few minutes after the Big Bang through a process commonly referred to as Big Bang Nucleosynthesis. The amount of helium that was made during Big Bang Nucleosynthesis is determined by the combination of particle physics and cosmology. The current leading measures of the primordial helium abundance (Y_P) are based on the relative strengths of H I and He I emission lines emanating from star-forming regions in local metal-poor galaxies. As the statistical errors on these measurements improve, it is essential to test for systematics by dev…
We introduce a new methodology to robustly determine the mass profile, as well as the overall distribution, of Local Group satellite galaxies. Specifically we employ a statistical multilevel modelling technique, Bayesian hierarchical modelling, to simultaneously constrain the properties of individual Local Group Milky Way satellite galaxies and the characteristics of the Milky Way satellite population. We show that this methodology reduces the uncertainty in individual dwarf galaxy mass measurements up to a factor of a few for the faintest galaxies. We find that the distribution of Milky Way s…
Photometric Distances for Metal-poor Giants and a Search for Hypervelocity Stars with LAMOST DR13 and Gaia DR3
Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究院）；School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）
We present O, Na, and Fe abundances, as well as radial velocities, for 113 red giant branch (RGB) and asymptotic giant branch (AGB) stars in the globular cluster M13. The abundances and velocities are based on spectra obtained with the WIYN-Hydra spectrograph, and the observations range in luminosity from the horizontal branch (HB) to RGB-tip. The results are examined in the context of recent globular cluster formation scenarios. We find that M13 exhibits many key characteristics that suggest its formation and chemical enrichment are well-described by current models. Some of these observations…
Detailed Abundance Determination of Metal-Poor Stars with X-Shooter II. - Chemically Disentangling the Halo, Disk and GSE
Research School of Astronomy and Astrophysics, Australian National University（澳大利亚国立大学天体物理与天文学研究学院）；Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University（乌普萨拉大学物理学与天文学系理论天体物理学）；Zentrum für Astronomie der Universität Heidelberg, Landessternwarte（海德堡大学天文中心，州立天文台）
Recently, an increasing number of wide binaries has been discovered. Their chemical and dynamical properties are studied through extensive surveys and pointed observations. However, the formation of these wide binaries is far from clear, although several scenarios have been suggested. In order to investigate the chemical compositions of these systems, we analysed high-resolution spectroscopy of three wide binary pairs belonging to the Galactic halo. In total, another three candidates from our original sample of 11 candidates observed at various resolutions with various instruments were refuted…
Orbital characteristics based on Gaia Early Data Release 3 astrometric parameters are analyzed for ${\sim} 8,000$ metal-poor stars ([Fe/H] $\leq -0.8$) compiled from the RAdial Velocity Experiment (RAVE) Data Release 6. Selected as metal-poor candidates based on broadband photometry, RAVE collected moderate-resolution ($R \sim 7,500$) spectra in the region of the Ca triplet for these stars. About $20\%$ of the stars in this sample also have medium-resolution ($1,200 \lesssim R \lesssim 2,000$) validation spectra obtained over a four-year campaign from $2014$ to $2017$ with a variety of telesco…
Context. The study of old, metal-poor stars deepens our knowledge on the early stages of the universe. In particular, the study of these stars gives us a valuable insight into the masses of the first massive stars and their emission of ionising photons. Aims. We present a detailed chemical analysis and determination of the kinematic and orbital properties of a sample of 11 dwarf stars. These are metal-poor stars, and a few of them present a low lithium content. We inspected whether the other elements also present anomalies. Methods. We analysed the high-resolution UVES spectra of a few metal-p…
Globular clusters (GCs) are excellent tracers of the formation and early evolution of the Milky Way. The bulge GCs (BGCs) are particularly important because they can reveal vital information about the oldest, in-situ component of the Milky Way. We aim at deriving mean metallicities and radial velocities for 13 GCs that lie towards the bulge and are generally associated with this component. We use near infrared low resolution spectroscopy with the FORS2 instrument on the VLT to measure the wavelengths and equivalent widths of the CaII triplet (CaT) lines for a number of stars per cluster. We de…
Orbital characteristics based on Gaia Early Data Release 3 astrometric parameters are analyzed for ${\sim} 4000$ metal-poor stars ([Fe/H] $\leq -0.8$) compiled from the Best $\&$ Brightest survey. Selected as metal-poor candidates based on broadband near- and far-IR photometry, $43\%$ of these stars had medium-resolution ($1200 \lesssim R \lesssim 2000$) validation spectra obtained over a seven-year campaign from $2014$ to $2020$ with a variety of telescopes. The remaining stars were chosen based on photometric metallicity determinations from the Huang et al. recalibration of the Sky Mapper So…
We re-examine the extremely metal-poor (XMP) dwarf galaxy AGC 198691 using a high quality spectrum obtained by the LBT's MODS instrument. Previous spectral observations obtained from KOSMOS on the Mayall 4-m and the Blue Channel spectrograph on the MMT 6.5-m telescope did not allow for the determination of sulfur, argon, or helium abundances. We report an updated and full chemical abundance analysis for AGC 198691, including confirmation of the extremely low "direct" oxygen abundance with a value of 12 + log(O/H) = 7.06 $\pm$ 0.03. AGC 198691's low metallicity potentially makes it a high value…
Andromeda X (And X) is a newly discovered low-luminosity M31 dwarf spheroidal galaxy (dSph) found by Zucker et al. (2007) in the Sloan Digital Sky Survey (SDSS - York et al. 2000). In this paper, we present the first spectroscopic study of individual red giant branch stars in And X, as a part of the SPLASH Survey (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo). Using the Keck II telescope and multiobject DEIMOS spectrograph, we target two spectroscopic masks over the face of the galaxy and measure radial velocities for ~100 stars with a median accuracy of sigma_v ~ 3 km/s…
We present new radial velocity measurements for 82 stars, members of the Galactic globular cluster NGC 6388, obtained from ESO-VLT KMOS spectra acquired during the instrument Science Verification. The accuracy of the wavelength calibration is discussed and a number of tests of the KMOS response are presented. The cluster systemic velocity obtained (81.3 +/- 1.5 km/sec) is in very good agreement with previous determinations. While a hint of ordered rotation is found between 9'' and 20'' from the cluster centre, where the distribution of radial velocities is clearly bimodal, more data are needed…
We present a direct determination of the stellar metallicity in the close pair galaxy NGC~4038 (D = 20 Mpc) based on the quantitative analysis of moderate resolution KMOS/VLT spectra of three super star clusters (SSCs). The method adopted in our analysis has been developed and optimised to measure accurate metallicities from atomic lines in the $J$-band of single red supergiant (RSG) or RSG-dominated star clusters. Hence, our metallicity measurements are not affected by the biases and poorly understood systematics inherent to strong line HII methods which are routinely applied to massive data …
We provide *lambda*6708 Li 1 measurements in 37 metal-poor stars, most of which are poorly-studied or have no previous measurements, from high-resolution and high-S/N spectroscopy obtained with the McDonald Observatory 2.1m and 2.7m telescopes. The typical line strength and abundance uncertainties, confirmed by the thinness of the Spite plateau manifested by our data and by comparison with previous measurements, are <=4 mAng and <=0.07-0.10 dex respectively. Two rare moderately metal-poor solar-Teff dwarfs, HIP 36491 and 40613, with significantly depleted but still detectable Li are identified…
We present and discuss radial velocity and the very first metallicity measurements for nine evolved stars in the poorly known old open cluster NGC 7762. We isolated eight radial velocity cluster members and one interloper. Radial velocities are in good agreement with previous studies. NGC 7762 turns out to be of solar metallicity within the uncertainties ([Fe/H]=0.04$\pm$0.12). For this metallicity, the cluster age is 2.5$\pm$0.2 Gyr, and falls in a age range where only a few old open clusters are known. With respect to previous studies, we find a larger distance, implying the cluster to be lo…
We present a study of nearby dwarf galaxies selected from the ALFALFA blind HI survey. A primary goal of the project was to utilize a non-standard selection method with the hope of detecting previously unrecognized extremely metal-poor (XMP) galaxies. The study was motivated by the recent discovery of two XMP galaxies $-$ Leo P and Leoncino $-$ which were both originally found via the ALFALFA survey. We have obtained narrowband H$α$ images for 42 dwarf systems, many of which are located in the local void in front of the Pisces-Perseus Supercluster. Spectra for eleven of the best candidates res…
University of Utah（犹他大学）；Space Telescope Science Institute（太空望远镜科学研究所）；Rutgers University（罗格斯大学）；Christian-Albrechts-Universität zu Kiel（基尔大学）；Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut（海德堡大学天文学计算中心）；The University of Texas at Austin（德克萨斯大学奥斯汀分校）
