We combine V I photometry from OGLE-III with V V V and 2MASS measurements of E(J − K s ) to resolve the longstanding problem of the non-standard optical extinction toward the Galactic bulge. We show that the extinction is wellfit by the relation. The optical and near-IR reddening law toward the inner Galaxy approximately follows an R V ≈ 2.5 extinction curve with a dispersion σ R V ≈ 0.2, consistent with extragalactic investigations of the hosts of type Ia SNe. Differential reddening is shown to be significant on scales as small as as our mean field size of 6 . The intrinsic luminosity parameters of the Galactic bulge red clump (RC) are derived to be (M I,RC , σ I,RC,0 , (V − I) RC,0 , σ (V −I) RC , (J − K s ) RC,0 ) = (−0.12, 0.09, 1.06, 0.121, 0.66). Our measurements of the RC brightness, brightness dispersion and number counts allow us to estimate several Galactic bulge structural parameters. We estimate a distance to the Galactic center of 8.20 kpc. We measure an upper bound on the tilt α ≈ 40 • between the bulge's major axis and the Sun-Galactic center line of sight, though our brightness peaks are consistent with predictions of -2an N-body model oriented at α ≈ 25 • . The number of RC stars suggests a total stellar mass for the Galactic bulge of ∼ 2.3×10 10 M if one assumes a canonical Salpeter IMF, or ∼ 1.6×10 10 M if one assumes a bottom-light Zoccali IMF.We adopt (M I,RC , σ I,RC,0 , (V −I) RC,0 , σ (V −I) RC , (J −K s ) RC,0 ) = (−0.12, 0.09, 1.06, 0.121, 0.66) for the mean absolute magnitude and magnitude dispersion in I, intrinsic (V −I) color,

The Galactic Archaeology with HERMES (GALAH) survey is a large-scale stellar spectroscopic survey of the Milky Way and designed to deliver chemical information complementary to a large number of stars covered by the Gaia mission. We present the GALAH second public data release (GALAH DR2) containing 342,682 stars. For these stars, the GALAH collaboration provides stellar parameters and abundances for up to 23 elements to the community. Here we present the target selection, observation, data reduction and detailed explanation of how the spectra were analysed to estimate stellar parameters and element abundances. For the stellar analysis, we have used a multi-step approach. We use the physics-driven spectrum synthesis of Spectroscopy Made Easy (SME) to derive stellar labels (T eff , log g, [Fe/H], [X/Fe], v mic , v sin i, A K S ) for a representative training set of stars. This information is then propagated to the whole survey with the data-driven method of The Cannon. Special care has been exercised in the spectral synthesis to only consider spectral lines that have reliable atomic input data and are little affected by blending lines. Departures from local thermodynamic equilibrium (LTE) are considered for several key elements, including Li, O, Na, Mg, Al, Si, and Fe, using 1D stellar atmosphere models. Validation tests including repeat observations, Gaia benchmark stars, open and globular clusters, and K2 asteroseismic targets lend confidence to our methods and results. Combining the GALAH DR2 catalogue with the kinematic information from Gaia will enable a wide range of Galactic Archaeology studies, with unprecedented detail, dimensionality, and scope.

The GALAH survey is a large high-resolution spectroscopic survey using the newly commissioned HERMES spectrograph on the Anglo-Australian Telescope. The HER-MES spectrograph provides high-resolution (R ∼28,000) spectra in four passbands for 392 stars simultaneously over a 2 degree field of view. The goal of the survey is to unravel the formation and evolutionary history of the Milky Way, using fossil remnants of ancient star formation events which have been disrupted and are now dispersed throughout the Galaxy. Chemical tagging seeks to identify such dispersed remnants solely from their common and unique chemical signatures; these groups are unidentifiable from their spatial, photometric or kinematic properties. To carry out chemical tagging, the GALAH survey will acquire spectra for a million stars down to V ∼14. The HERMES spectra of FGK stars contain absorption lines from 29 elements including light proton-capture elements, α-elements, odd-Z elements, iron-peak elements and n-capture elements from the light and heavy s-process and the r-process. This paper describes the motivation and planned execution of the GALAH survey, and presents some results on the first-light performance of HERMES.

The red clump is found to be split into two components along several sightlines toward the Galactic Bulge. This split is detected with high significance toward the areas (−3.5 < l < 1, b < −5) and (l, b) = (0, +5.2), i.e., along the Bulge minor axis and at least 5 degrees off the plane. The fainter (hereafter "main") component is the one that more closely follows the distance-longitude relation of the Bulge red clump. The main component is ∼0.5 magnitudes fainter than the secondary component and with an overall approximately equal population. For sightlines further from the plane, the difference in brightness increases, and more stars are found in the secondary component than in the main component. The two components have very nearly equal (V − I) color.

The ensemble of chemical element abundance measurements for stars, along with precision distances and orbit properties, provides high-dimensional data to study the evolution of the Milky Way. With this third data release of the Galactic Archaeology with HERMES (GALAH) survey, we publish 678 423 spectra for 588 571 mostly nearby stars (81.2% of stars are within &lt; 2 kpc), observed with the HERMES spectrograph at the Anglo-Australian Telescope. This release (hereafter GALAH+ DR3) includes all observations from GALAH Phase 1 (bright, main, and faint survey, 70%), K2-HERMES (17%), TESS-HERMES (5%), and a subset of ancillary observations (8%) including the bulge and &gt; 75 stellar clusters. We derive stellar parameters Teff, log g, [Fe/H], vmic, vbroad, and vradusing our modified version of the spectrum synthesis code Spectroscopy Made Easy (sme) and 1D marcs model atmospheres. We break spectroscopic degeneracies in our spectrum analysis with astrometry from Gaia DR2 and photometry from 2MASS. We report abundance ratios [X/Fe] for 30 different elements (11 of which are based on non-LTE computations) covering five nucleosynthetic pathways. We describe validations for accuracy and precision, flagging of peculiar stars/measurements and recommendations for using our results. Our catalogue comprises 65% dwarfs, 34% giants, and 1% other/unclassified stars. Based on unflagged chemical composition and age, we find 62% young low-α, 9% young high-α, 27% old high-α, and 2% stars with [Fe/H] ≤ −1. Based on kinematics, 4% are halo stars. Several Value-Added-Catalogues, including stellar ages and dynamics, updated after GaiaeDR3, accompany this release and allow chrono-chemodynamic analyses, as we showcase.

We report evidence from APOGEE for the presence of a new metal-poor stellar structure located within ∼4 kpc of the Galactic Centre. Characterized by a chemical composition resembling those of low-mass satellites of the Milky Way, this new inner Galaxy structure (IGS) seems to be chemically and dynamically detached from more metal-rich populations in the inner Galaxy. We conjecture that this structure is associated with an accretion event that likely occurred in the early life of the Milky Way. Comparing the mean elemental abundances of this structure with predictions from cosmological numerical simulations, we estimate that the progenitor system had a stellar mass of ∼5 × 108 M⊙, or approximately twice the mass of the recently discovered Gaia-Enceladus/Sausage system. We find that the accreted:in situ ratio within our metal-poor ([Fe/H] &lt; –0.8) bulge sample is somewhere between 1:3 and 1:2, confirming predictions of cosmological numerical simulations by various groups.

There is growing evidence that the Galactic Center Excess identified in the Fermi-LAT gamma-ray data arises from a population of faint astrophysical sources. We provide compelling supporting evidence by showing that the morphology of the excess traces the stellar over-density of the Galactic bulge. By adopting a template of the bulge stars obtained from a triaxial 3D fit to the diffuse near-infrared emission, we show that it is detected at high significance. The significance deteriorates when either the position or the orientation of the template is artificially shifted, supporting the correlation of the gamma-ray data with the Galactic bulge. In deriving these results, we have used more sophisticated templates at low-latitudes for the Fermi bubbles compared to previous work and the three-dimensional Inverse Compton (IC) maps recently released by the GALPROP team. Our results provide strong constraints on Millisecond Pulsar (MSP) formation scenarios proposed to explain the excess. We find that an admixture formation scenario, in which some of the relevant binaries are primordial and the rest are formed dynamically, is preferred over a primordial-only formation scenario at 7.6σ confidence level. Our detailed morphological analysis also disfavors models of the disrupted globular clusters scenario that predict a spherically symmetric distribution of MSPs in the Galactic bulge. For the first time, we report evidence of a high energy tail in the nuclear bulge spectrum that could be the result of IC emission from electrons and positrons injected by a population of MSPs and star formation activity from the same site. pulsars, in the form of either old "recycled" millisecond pulsars [13,18], or young pulsar remnants from Galactic Center supernovae [19,20]. The gamma-ray spectra of known pulsars are similar to the GCE, and the capture of pulsars onto the Galactic Center region by Globular Cluster disruptions could explain the GCE's quasi-spherical spatial distribution [21,22]. Other explanations for the GCE discussed in the literature include outbursts of cosmic-ray production by the central supermassive black hole (e.g., [23]).While pulsars are a natural astrophysical candidate, there is ongoing debate regarding the consistency of the luminosity function required to explain the GCE with that measured for the pulsar population observed elsewhere as point sources [24][25][26][27]. Nevertheless, there are strengthening indications that the GCE may have an astrophysical origin. Cosmic-ray interactions in the Galactic Center region are notoriously complex to model. New analyses have cast doubt on some of the main properties claimed previously for the GCE. First, the energy spectrum of the GCE is subject to large systematic uncertainties arising from the incomplete understanding of cosmic-ray interactions in the Galactic Center region (e.g., [13][14][15]17]). A variety of scenarios might, therefore, describe the GCE based on the energy spectrum alone. Second, it has been argued that the photon count distribution of the GCE is ...

We combine high-resolution spectroscopic data from APOGEE-2 survey Data Release 16 (DR16) with broad-band photometric data from several sources as well as parallaxes from Gaia Data Release 2 (DR2). Using the Bayesian isochrone-fitting code StarHorse, we derived the distances, extinctions, and astrophysical parameters for around 388 815 APOGEE stars. We achieve typical distance uncertainties of ∼6% for APOGEE giants, ∼2% for APOGEE dwarfs, and extinction uncertainties of ∼0.07 mag, when all photometric information is available, and ∼0.17 mag if optical photometry is missing. StarHorse uncertainties vary with the input spectroscopic catalogue, available photometry, and parallax uncertainties. To illustrate the impact of our results, we show that thanks to Gaia DR2 and the now larger sky coverage of APOGEE-2 (including APOGEE-South), we obtain an extended map of the Galactic plane. We thereby provide an unprecedented coverage of the disc close to the Galactic mid-plane (|ZGal| < 1 kpc) from the Galactic centre out to RGal ∼ 20 kpc. The improvements in statistics as well as distance and extinction uncertainties unveil the presence of the bar in stellar density and the striking chemical duality in the innermost regions of the disc, which now clearly extend to the inner bulge. We complement this paper with distances and extinctions for stars in other public released spectroscopic surveys: 324 999 in GALAH DR2, 4 928 715 in LAMOST DR5, 408 894 in RAVE DR6, and 6095 in GES DR3.