Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA Blueprint for the Milky Ways Stellar Populations. II. Improved Isochrone Calibration in the SDSS and Pan-STARRS Photometric Systems
232
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We improve the identification and isolation of individual stellar populations in the Galactic halo based on an updated set of empirically calibrated stellar isochrones in the Sloan Digital Sky Survey (SDSS) and Pan-STARRS 1 (PS1) photometric systems. Along the Galactic prime meridian ($l=0^{circ}$ and $180^{circ}$), where proper motions and parallaxes from Gaia DR2 can be used to compute rotational velocities of stars in the rest frame of the Milky Way, we use the observed double color-magnitude sequences of stars having large transverse motions, which are attributed to groups of stars in the metal-poor halo and the thick disk with halo-like kinematics, respectively. The Gaia sequences directly constrain color-magnitude relations of model colors, and help to improve our previous calibration using Galactic star clusters. Based on these updated sets of stellar isochrones, we confirm earlier results on the presence of distinct groups of stars in the metallicity versus rotational-velocity plane, and find that the distribution of the most metal-poor ([Fe/H] $<-2$) stars in our sample can be modeled using two separate groups on prograde and retrograde orbits, respectively. At $4$-$6$ kpc from the Galactic plane, we find approximately equal proportions of the Splashed Disk, and the metal-rich ($langle {rm [Fe/H]} ranglesim-1.6$) and metal-poor ($langle {rm [Fe/H]} ranglesim-2.5$) halos on prograde orbits. The Gaia-Sausage-Enceladus, the metal-weak thick disk, and the retrograde halo structure(s) ($langle {rm [Fe/H]} ranglesim-2.2$) constitute approximately $10%$ of the rest of the stellar populations at these distances.
rate research
Read More
Recent advances from astronomical surveys have revealed spatial, chemical, and kinematical inhomogeneities in the inner region of the stellar halo of the Milky Way Galaxy. In particular, large spectroscopic surveys, combined with Gaia astrometric data, have provided powerful tools for analyzing the detailed abundances and accurate kinematics for individual stars. Despite these noteworthy efforts, however, spectroscopic samples are typically limited by the numbers of stars considered; their analysis and interpretation are also hampered by the complex selection functions that are often employed. Here we present a powerful alternative approach $-$ a synoptic view of the spatial, chemical, and kinematical distributions of stars in the Milky Way based on large photometric survey databases, enabled by a well-calibrated technique for obtaining individual stellar metal abundances from broad-band photometry. We combine metallicities with accurate proper motions from the Gaia mission along the Prime Meridian of the Galaxy, and find that various stellar components are clearly separated from each other in the metallicity versus rotation-velocity space. The observed metallicity distribution of the inner-halo stars deviates from the traditional single-peaked distribution, and exhibits complex substructures comprising varying contributions from individual stellar populations, sometimes with striking double peaks at low metallicities. The substructures revealed from our less-biased, comprehensive maps demonstrate the clear advantages of this approach, which can be built upon by future mixed-band and broad-band photometric surveys, and used as a blueprint for identifying the stars of greatest interest for upcoming spectroscopic studies.
We present the details of the photometric and astrometric calibration of the Pan-STARRS1 $3pi$ Survey. The photometric goals were to reduce the systematic effects introduced by the camera and detectors, and to place all of the observations onto a photometric system with consistent zero points over the entire area surveyed, the ~30,000 square degrees north of $delta$ = -30 degrees. The astrometric calibration compensates for similar systematic effects so that positions, proper motions, and parallaxes are reliable as well. The Pan-STARRS Data Release 2 (DR2) astrometry is tied to the Gaia DR1 release.
We analyze the observed spatial, chemical and dynamical distributions of local metal-poor stars, based on photometrically derived metallicity and distance estimates along with proper motions from the Gaia mission. Along the Galactic prime meridian, we identify stellar populations with distinct properties in the metallicity versus rotational velocity space, including Gaia Sausage/Enceladus (GSE), the metal-weak thick disk (MWTD), and the Splash (sometimes referred to as the in situ halo). We model the observed phase-space distributions using Gaussian mixtures and refine their positions and fractional contributions as a function of distances from the Galactic plane ($|Z|$) and the Galactic center ($R_{rm GC}$), providing a global perspective of the major stellar populations in the local halo. Within the sample volume ($|Z|<6$ kpc), stars associated with GSE exhibit a larger proportion of metal-poor stars at greater $R_{rm GC}$ ($Delta langle{rm[Fe/H]}rangle /Delta R_{rm GC} =-0.05pm0.02$ dex kpc$^{-1}$). This observed trend, along with a mild anticorrelation of the mean rotational velocity with metallicity ($Delta langle v_phi rangle / Delta langle{rm[Fe/H]} rangle sim -10$ km s$^{-1}$ dex$^{-1}$), implies that more metal-rich stars in the inner region of the GSE progenitor were gradually stripped away, while the prograde orbit of the merger at infall became radialized by dynamical friction. The metal-rich GSE stars are causally disconnected from the Splash structure, whose stars are mostly found on prograde orbits ($>94%$) and exhibit a more centrally concentrated distribution than GSE. The MWTD exhibits a similar spatial distribution to the Splash, suggesting earlier dynamical heating of stars in the primordial disk of the Milky Way, possibly before the GSE merger.
We show for the first time, that a fully cosmological hydrodynamical simulation can reproduce key properties of the innermost region of the Milky Way. Our high resolution simulation matches the profile and kinematics of the Milky Ways boxy/peanut-shaped bulge, and hence we can use it to reconstruct and understand the bulge assembly. In particular, the age dependence of the X-shape morphology of the simulated bulge parallels the observed metallicity dependent split in the red clump stars of the inner Galaxy. We use this feature to derive an observational metric that allows us to quantify when the bulge formed from the disk. The metric we propose can be employed with upcoming survey data to constrain the age of the Milky Way bar. From the split in stellar counts we estimate the formation of the 4~kpc scale bar in the simulation to have happened $t^{rm bar}_{rm form}sim8^{+2}_{-2}$ Gyr ago, in good agreement with conventional methods to measure bar formation in simulations. We test the prospects for observationally differentiating the stars that belong to the bulge/bar compared to the surrounding disk, and find that the inner disk and bulge are practically indistinguishable in both chemistry and ages.
We report photometric estimates of effective temperature, $T_{rm eff}$, metallicity, [Fe/H], carbonicity, [C/Fe], and absolute carbon abundances, $A{rm (C)}$, for over 700,000 stars from the Southern Photometric Local Universe Survey (S-PLUS) Data Release 2, covering a substantial fraction of the equatorial Sloan Digital Sky Survey Stripe 82. We present an analysis for two stellar populations: 1) halo main-sequence turnoff stars and 2) K-dwarf stars of mass $0.58 < M/M_{odot} <0.75$ in the Solar Neighborhood. Application of the Stellar Photometric Index Network Explorer (SPHINX) to the mixed-bandwidth (narrow- plus wide-band) filter photometry from S-PLUS produces robust estimates of the metallicities and carbon abundances in stellar atmospheres over a wide range of temperature, $4250 < T_{rm eff} textrm{(K)} < 7000$. The use of multiple narrow-band S-PLUS filters enables SPHINX to achieve substantially lower levels of catastrophic failures (large offsets in metallicity estimates relative to spectroscopic determinations) than previous efforts using a single metallicity-sensitive narrow-band filter. We constrain the exponential slope of the Milky Ways K-dwarf halo metallicity distribution function (MDF), $lambda_{10, textrm{[Fe/H]}} = 0.85 pm 0.21$, over the metallicity range $-2.5 < textrm{[Fe/H]} < -1.0$; the MDF of our local-volume K-dwarf sample is well-represented by a gamma distribution with parameters $alpha=2.8$ and $beta=4.2$. S-PLUS photometry obtains absolute carbon abundances with a precision of $sim 0.35$dex for stars with $T_{rm eff} < 6500$K. We identify 364 candidate carbon-enhanced metal-poor stars, obtain assignments of these stars into the Yoon-Beers morphological groups in the $A$(C)-[Fe/H] space, and derive the CEMP frequencies.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
