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Millisecond pulsars are very likely the main source of gamma-ray emission from globular clusters. However, the relative contributions of two separate emission processes--curvature radiation from millisecond pulsar magnetospheres vs. inverse Compton emission from relativistic pairs launched into the globular cluster environment by millisecond pulsars--have long been unclear. To address this, we search for evidence of inverse Compton emission in 8-year $\textit{Fermi}$-LAT data from the directions of 157 Milky Way globular clusters. We find a mildly statistically significant (3.8$\sigma$) correlation between the measured globular cluster gamma-ray luminosities and their photon field energy densities. However, this may also be explained by a hidden correlation between the photon field densities and the stellar encounter rates of globular clusters. Analysed $\textit{in toto}$, we demonstrate that the gamma-ray emission of globular clusters can be resolved spectrally into two components: i) an exponentially cut-off power law and ii) a pure power law. The latter component--which we uncover at a significance of 8.2$\sigma$--has a power index of 2.79 $\pm$ 0.25. It is most naturally interpreted as inverse Compton emission by cosmic-ray electrons and positrons injected by millisecond pulsars. We find the luminosity of this power-law component is comparable to, or slightly smaller than, the luminosity of the curved component, suggesting the fraction of millisecond pulsar spin-down luminosity into relativistic leptons is similar to the fraction of the spin-down luminosity into prompt magnetospheric radiation., Comment: 16+9 pages, 13+4 figures, 4+1 tables. match the published version in MNRAS

Millisecond pulsars are very likely the main source of gamma-ray emission from globular clusters. However, the relative contributions of two separate emission processes-curvature radiation from millisecond pulsar magnetospheres vs. inverse Compton emission from relativistic pairs launched into the globular cluster environment by millisecond pulsars-has long been unclear. To address this, we search for evidence of inverse Compton emission in 8-year Fermi-LAT data from the directions of 157 Milky Way globular clusters. We find a mildly statistically significant (3.8$\sigma$) correlation between the measured globular cluster gamma-ray luminosities and their photon field energy densities. However, this may also be explained by a hidden correlation between the photon field densities and the stellar encounter rates of globular clusters. Analysed in toto, we demonstrate that the gamma-ray emission of globular clusters can be resolved spectrally into two components: i) an exponentially cut-off power law and ii) a pure power law. The latter component-which we uncover at a significance of 8.2$\sigma$-is most naturally interpreted as inverse Compton emission by cosmic-ray electrons and positrons injected by millisecond pulsars. We find the luminosity of this inverse Compton component is comparable to, or slightly smaller than, the luminosity of the curved component, suggesting the fraction of millisecond pulsar spin-down luminosity into relativistic leptons is similar to the fraction of the spin-down luminosity into prompt magnetospheric radiation.

It has been proposed that the globular cluster-like system Terzan 5 is the surviving remnant of a primordial building block of the Milky Way bulge, mainly due to the age/metallicity spread and the distribution of its stars in the $\alpha$-Fe plane. We employ Sloan Digital Sky Survey (SDSS-IV) data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE 2) to test this hypothesis. Adopting a random sampling technique, we contrast the abundances of 10 elements in Terzan 5 stars with those of their bulge field counterparts with comparable atmospheric parameters, finding that they differ at statistically significant levels. Abundances between the two groups differ by more than 1$\sigma$ in Ca, Mn, C, O, and Al, and more than 2$\sigma$ in Si and Mg. Terzan 5 stars have lower [$\alpha$/Fe] and higher [Mn/Fe] than their bulge counterparts. Given those differences, we conclude that Terzan 5 is not the remnant of a $major$ building block of the bulge. We also estimate the stellar mass of the Terzan 5 progenitor based on predictions by the Evolution and Assembly of GaLaxies and their Environments (EAGLE) suite of cosmological numerical simulations, concluding that it may have been as low as $\sim3\times10^8$ M$_\odot$ so that it was likely unable to significantly influence the mean chemistry of the bulge/inner disk, which is significantly more massive ($\sim10^{10}$ M$_\odot$). We briefly discuss existing scenarios for the nature of Terzan 5 and propose an observational test that may help elucidate its origin., Comment: 15 pages, 10 figures, accepted for publication by MNRAS

Globular cluster progenitors may have been detected by \textit{HST}, and are predicted to be observable with \textit{JWST} and ground-based extremely-large telescopes with adaptive optics. This has the potential to elucidate the issue of globular cluster formation and the origins of significantly helium-enriched subpopulations, a problem in Galactic astronomy with no satisfactory theoretical solution. Given this context, we use model stellar tracks and isochrones to investigate the predicted observational properties of helium-enriched stellar populations in globular cluster progenitors. We find that, relative to helium-normal populations, helium-enriched (${\Delta}Y=+0.12$) stellar populations similar to those inferred in the most massive globular clusters, are expected, modulo some rapid fluctuations in the first $\sim$30 Myr, to be brighter and redder in the rest frame. At fixed age, stellar mass, and metallicity, a helium-enriched population is predicted to converge to being $\sim$0.40 mag brighter at $\lambda \approx 2.0\, {\mu}m$, and to be 0.30 mag redder in the \textit{JWST}-NIRCam colour $(F070W-F200W)$, and to actually be fainter for $\lambda \lesssim 0.50 \, {\mu}m$. Separately, we find that the time-integrated shift in ionizing radiation is a negligible $\sim 5\%$, though we show that the Lyman-$\alpha$ escape fraction could end up higher for helium-enriched stars., Comment: Accepted for publication in MNRAS on 13 May, 2020 Replaced to update some bibliographic information

Studies of the kinematics and chemical compositions of Galactic globular clusters (GCs) enable the reconstruction of the history of star formation, chemical evolution, and mass assembly of the Galaxy. Using the latest data release (DR16) of the SDSS/APOGEE survey, we identify 3,090 stars associated with 46 GCs. Using a previously defined kinematic association, we break the sample down into eight separate groups and examine how the kinematics-based classification maps into chemical composition space, considering only $\alpha$ (mostly Si and Mg) elements and Fe. Our results show that: (i) The loci of both in situ and accreted subgroups in chemical space match those of their field counterparts; (ii) GCs from different individual accreted subgroups occupy the same locus in chemical space. This could either mean that they share a similar origin or that they are associated with distinct satellites which underwent similar chemical enrichment histories; (iii) The chemical compositions of the GCs associated with the low orbital energy subgroup defined by Massari and collaborators is broadly consistent with an in situ origin. However, at the low metallicity end, the distinction between accreted and in situ populations is blurred; (iv) Regarding the status of GCs whose origin is ambiguous, we conclude the following: the position in Si-Fe plane suggests an in situ}origin for Liller 1 and a likely accreted origin for NGC 5904 and NGC 6388. The case of NGC 288 is unclear, as its orbital properties suggest an accretion origin, its chemical composition suggests it may have formed in situ., Comment: 18 pages, 10 figures, 3 tables. Accepted for publication in MNRAS

Asteroseismology is a promising tool to study Galactic structure and evolution because it can probe the ages of stars. Earlier attempts comparing seismic data from the {\it Kepler} satellite with predictions from Galaxy models found that the models predicted more low-mass stars compared to the observed distribution of masses. It was unclear if the mismatch was due to inaccuracies in the Galactic models, or the unknown aspects of the selection function of the stars. Using new data from the K2 mission, which has a well-defined selection function, we find that an old metal-poor thick disc, as used in previous Galactic models, is incompatible with the asteroseismic information. We show that spectroscopic measurements of [Fe/H] and [$\alpha$/Fe] elemental abundances from the GALAH survey indicate a mean metallicity of $\log (Z/Z_{\odot})=-0.16$ for the thick disc. Here $Z$ is the effective solar-scaled metallicity, which is a function of [Fe/H] and [$\alpha$/Fe]. With the revised disc metallicities, for the first time, the theoretically predicted distribution of seismic masses show excellent agreement with the observed distribution of masses. This provides an indirect verification of the asteroseismic mass scaling relation is good to within five percent. Using an importance-sampling framework that takes the selection function into account, we fit a population synthesis model of the Galaxy to the observed seismic and spectroscopic data. Assuming the asteroseismic scaling relations are correct, we estimate the mean age of the thick disc to be about 10 Gyr, in agreement with the traditional idea of an old $\alpha$-enhanced thick disc., Comment: 21 pages, submitted to MNRAS

This work explores the detailed chemistry of the Milky Way bulge using the HERMES spectrograph on the Anglo-Australian Telescope. Here we present the abundance ratios of 13 elements for 832 red giant branch and clump stars along the minor bulge axis at latitudes $b=-10^{\circ}, -7.5$ and $-5^{\circ}$. Our results show that none of the abundance ratios vary significantly with latitude. We also observe {\color{red}disk-like} [Na/Fe] abundance ratios, which indicates the bulge does not contain helium-enhanced populations as observed in some globular clusters. Helium enhancement is therefore not the likely explanation for the double red-clump observed in the bulge. We confirm that bulge stars mostly follow abundance trends observed in the disk. However, this similarity is not confirmed across for all elements and metallicity regimes. The more metal-poor bulge population at [Fe/H] $\lesssim -0.8$ is enhanced in the elements associated with core collapse supernovae (SNeII). In addition, the [La/Eu] abundance ratio suggests higher $r$-process contribution, and likely higher star formation in the bulge compared to the disk. This highlights the complex evolution in the bulge, which should be investigated further, both in terms of modelling; and with additional observations of the inner Galaxy., Comment: 14 pages, 9 figures. Submitted to MNRAS July 2018; revised version. Online data access

We discuss a meta-analysis of the association of abundance variations in globular cluster stars with the present-day stellar mass and metallicity of globular clusters. Using data for 42 globular clusters that are well-sampled from either or both of prior literature studies and the APOGEE survey, we confirm prior findings that increasing aluminum abundance variations in globular clusters are positively correlated with increasing present-day stellar mass or decreasing metallicity. We also demonstrate that the ratio of aluminum abundance variations to either nitrogen abundance variations or sodium abundance variations is itself positively correlated with decreasing metallicity and increasing stellar mass of globular clusters. This suggests that there were at least two non-supernovae chemical polluters that were active in the early universe.

We present a study using the second data release of the GALAH survey of stellar parameters and elemental abundances of 15 pairs of stars identified by Oh et al 2017. They identified these pairs as potentially co-moving pairs using proper motions and parallaxes from Gaia DR1. We find that 11 very wide (>1.7 pc) pairs of stars do in fact have similar Galactic orbits, while a further four claimed co-moving pairs are not truly co-orbiting. Eight of the 11 co-orbiting pairs have reliable stellar parameters and abundances, and we find that three of those are quite similar in their abundance patterns, while five have significant [Fe/H] differences. For the latter, this indicates that they could be co-orbiting because of the general dynamical coldness of the thin disc, or perhaps resonances induced by the Galaxy, rather than a shared formation site. Stars such as these, wide binaries, debris of past star formation episodes, and coincidental co-orbiters, are crucial for exploring the limits of chemical tagging in the Milky Way., 14 pages, 9 figures, submitted to MNRAS. Updated for Gaia DR2 values

We compare abundance ratio trends in a sample of $\sim 11,000$ Milky Way bulge stars ($R_{\rm GC} < 3$ kpc) from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) to those of APOGEE stars in the Galactic disk ($5$ kpc $< R_{\rm GC} < 11$ kpc). We divide each sample into low-Ia (high-[Mg/Fe]) and high-Ia (low-[Mg/Fe]) populations, and in each population we examine the median trends of [X/Mg] vs. [Mg/H] for elements X = Fe, O, Na, Al, Si, P, S, K, Ca, V, Cr, Mn, Co, Ni, Cu, and Ce. To remove small systematic trends of APOGEE abundances with stellar $\log(g)$, we resample the disk stars to match the $\log(g)$ distributions of the bulge data. After doing so, we find nearly identical median trends for low-Ia disk and bulge stars for all elements. High-Ia trends are similar for most elements, with noticeable (0.05-0.1 dex) differences for Mn, Na, and Co. The close agreement of abundance trends (with typical differences $\lesssim 0.03$ dex) implies that similar nucleosynthetic processes enriched bulge and disk stars despite the different star formation histories and physical conditions of these regions. For example, we infer that differences in the high mass slope of the stellar initial mass function (IMF) between disk and bulge must have been $\lesssim 0.30$. This agreement, and the generally small scatter about the median sequences, means that one can predict all of a bulge star's APOGEE abundances with good accuracy knowing only its measured [Mg/Fe] and [Mg/H] and the observed trends of disk stars., 32 pages, 22 figures, 5 tables

The contribution of dissolved globular clusters (GCs) to the stellar content of the Galactic halo is a key constraint on models for GC formation and destruction, and the mass assembly history of the Milky Way. Earlier results from APOGEE pointed to a large contribution of destroyed GCs to the stellar content of the inner halo, by as much as 25$\%$, which is an order of magnitude larger than previous estimates for more distant regions of the halo. We set out to measure the ratio between N-rich and normal halo field stars, as a function of distance, by performing density modelling of halo field populations in APOGEE DR16. Our results show that at 1.5 kpc from the Galactic Centre, N-rich stars contribute a much higher 16.8$^{+10.0}_{-7.0}$$\%$ fraction to the total stellar halo mass budget than the 2.7$^{+1.0}_{-0.8}$$\%$ ratio contributed at 10 kpc. Under the assumption that N-rich stars are former GC members that now reside in the stellar halo field, and assuming the ratio between first-and second-population GC stars being 1:2, we estimate a total contribution from disrupted GC stars of the order of 27.5$^{+15.4}_{-11.5}$$\%$ at r = 1.5 kpc and 4.2$^{+1.5}_{-1.3}$$\%$ at r = 10 kpc. Furthermore, since our methodology requires fitting a density model to the stellar halo, we integrate such density within a spherical shell from 1.5-15 kpc in radius, and find a total stellar mass arising from dissolved and/or evaporated GCs of $M_{\mathrm{GC,total}}$ = 9.6$^{+4.0}_{-2.6}$ $\times$ 10$^{7}$ M$\odot$., Paper accepted for Publication in MNRAS, correction of Fig 7

We report evidence from APOGEE for the presence of a new metal-poor stellar structure located within $\sim$4~kpc of the Galactic centre. Characterised 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 $\sim5\times10^8M_\odot$, or approximately twice the mass of the recently discovered Gaia-Enceladus/Sausage system. We find that the accreted:{\it in situ} ratio within our metal-poor ([Fe/H]$, Comment: Accepted for publication in MNRAS. 22 pages, 13 Figures

We explore the fundamental relations governing the radial and vertical velocity dispersions of stars in the Milky Way, from combined studies of complementary surveys including GALAH, LAMOST, APOGEE, the NASA $Kepler$ and K2 missions, and $Gaia$ DR2. We find that different stellar samples, even though they target different tracer populations and employ a variety of age estimation techniques, follow the same set of fundamental relations. We provide the clearest evidence to date that, in addition to the well-known dependence on stellar age, the velocity dispersions of stars depend on orbital angular momentum $L_z$, metallicity and height above the plane $|z|$, and are well described by a multiplicatively separable functional form. The dispersions have a power-law dependence on age with exponents of 0.441$\pm 0.007$ and 0.251$\pm 0.006$ for $\sigma_z$ and $\sigma_R$ respectively, and the power law is valid even for the oldest stars. For the solar neighborhood stars, the apparent break in the power law for older stars, as seen in previous studies, is due to the anti-correlation of $L_z$ with age. The dispersions decrease with increasing $L_z$ until we reach the Sun's orbital angular momentum, after which $\sigma_z$ increases (implying flaring in the outer disc) while $\sigma_R$ flattens. The dispersions increase with decreasing metallicity, suggesting that the dispersions increase with birth radius. The dispersions also increase linearly with $|z|$. The same set of relations that work in the solar neighborhood also work for stars between $3, Comment: 19 pages, 15 figures, submitted to MNRAS

The zero point of the reddening toward the Large Magellanic Cloud (LMC) has been the subject of some dispute. Its uncertainty propagates as a systematic error for methods which measure the extragalactic distance scale through knowledge of the absolute extinction of LMC stars. In an effort to resolve this issue, we used three different methods to calibrate the most widely-used metric to predict LMC extinction, the intrinsic color of the red clump, $(V-I)_{RC,0}$, for the inner $\sim$3 degrees of that galaxy. The first approach was to empirically calibrate the color zeropoints of the BaSTI isochrones over a wide metallicity range of ${\Delta}\rm{[Fe/H]} \approx 1.10$ using measurements of red clump stars in 47 Tuc, the Solar Neighborhood, and NGC 6791. From these efforts we also measure these properties of the Solar Neighborhood red clump, ($V-I$, $G_{BP}-K_{s}$, $G-K_{s}$, $G_{RP}-K_{s}$, $J-K_{s}$, $H-K_{s}$, $M_{I}$, $M_{Ks}$)$_{RC,0} =$ (1.02, 2.75, 2.18, 1.52, 0.64, 0.15, $-$0.23, $-$1.63). The second and third methods were to compare the observed colors of the red clump to those of Cepheids and RR Lyrae in the LMC. With these three methods, we estimated the intrinsic color of the red clump of the LMC to be $(V-I)_{RC,0,\rm{LMC}} = \{ \approx 0.93,0.91 \pm 0.02,0.89 \pm 0.02\}$ respectively, and similarly using the first and third method we estimated $ (V-I)_{RC,0,\rm{SMC}} = \{\approx 0.85,0.84 \pm 0.02 \}$ respectively for the Small Magellanic Cloud. We estimate the luminosities to be $M_{I,RC,\rm{LMC}}=-0.26$ and $M_{I,RC,\rm{SMC}}=-0.37$. We show that this has important implications for recent calibrations of the tip of the red giant branch in the Magellanic Clouds used to measure $H_0$., Comment: 20 pages, 5 figures, 4 tables. Accepted for Publication in The Astrophysical Journal as of February 9th, 2021

Radial velocities of 2768 fundamental mode RR Lyrae stars (RRLs) toward the Southern Galactic bulge are presented, spanning the southern bulge from -8 < l < +8 and -3 < b 500 km/s and find that the majority of these high-velocity stars are halo interlopers; it is unclear if a sub-sample of these stars with similar space velocities have a common origin. Once the 25% of the sample represented by halo interlopers is cleaned, we can clearly discern two populations of bulge RRLs in the inner Galaxy. One population of RRLs is not as tightly bound to the Galaxy (but is still confined to the inner ~3.5 kpc), and is both spatially and kinematically consistent with the barred bulge. The second population is more centrally concentrated and does not trace the bar. One possible interpretation is that this population was born prior to bar formation, as its spatial location, kinematics and pulsation properties suggest, possibly from an accretion event at high redshift., Comment: accepted for publication in the Astronomical Journal

We present stellar age distributions of the Milky Way (MW) bulge region using ages for $\sim$6,000 high-luminosity ($\log(g) < 2.0$), metal-rich ($\rm [Fe/H] \ge -0.5$) bulge stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Ages are derived using {\it The Cannon} label-transfer method, trained on a sample of nearby luminous giants with precise parallaxes for which we obtain ages using a Bayesian isochrone-matching technique. We find that the metal-rich bulge is predominantly composed of old stars ($>$8 Gyr). We find evidence that the planar region of the bulge ($|Z_{\rm GC}| \le 0.25$ kpc) enriched in metallicity, $Z$, at a faster rate ($dZ/dt \sim$ 0.0034 ${\rm Gyr^{-1}}$) than regions farther from the plane ($dZ/dt \sim$ 0.0013 ${\rm Gyr^{-1}}$ at $|Z_{\rm GC}| > 1.00$ kpc). We identify a non-negligible fraction of younger stars (age $\sim$ 2--5 Gyr) at metallicities of $\rm +0.2 < [Fe/H] < +0.4$. These stars are preferentially found in the plane ($|Z_{\rm GC}| \le 0.25$ kpc) and between $R_{\rm cy} \approx 2-3$ kpc, with kinematics that are more consistent with rotation than are the kinematics of older stars at the same metallicities. We do not measure a significant age difference between stars found in and outside of the bar. These findings show that the bulge experienced an initial starburst that was more intense close to the plane than far from the plane. Then, star formation continued at super-solar metallicities in a thin disk at 2 kpc $\lesssim R_{\rm cy} \lesssim$ 3 kpc until $\sim$2 Gyr ago., 21 pages, 15 figures, accepted for publication in ApJ

We present an overview of, and first science results from, the Magellanic Edges Survey (MagES), an ongoing spectroscopic survey mapping the kinematics of red clump and red giant branch stars in the highly substructured periphery of the Magellanic Clouds. In conjunction with Gaia astrometry, MagES yields a sample of ~7000 stars with individual 3D velocities that probes larger galactocentric radii than most previous studies. We outline our target selection, observation strategy, data reduction and analysis procedures, and present results for two fields in the northern outskirts ($>10^{\circ}$ on-sky from the centre) of the Large Magellanic Cloud (LMC). One field, located in the vicinity of an arm-like overdensity, displays apparent signatures of perturbation away from an equilibrium disk model. This includes a large radial velocity dispersion in the LMC disk plane, and an asymmetric line-of-sight velocity distribution indicative of motions vertically out of the disk plane for some stars. The second field reveals 3D kinematics consistent with an equilibrium disk, and yields $V_{\text{circ}}=87.7\pm8.0$km s$^{-1}$ at a radial distance of ~10.5kpc from the LMC centre. This leads to an enclosed mass estimate for the LMC at this radius of $(1.8\pm0.3)\times10^{10}\text{M}_{\odot}$., 23 pages, 10 figures. Accepted by MNRAS

We investigate the Fe, C, N, O, Mg, Al, Si, K, Ca, Ce and Nd abundances of 2283 red giant stars in 31 globular clusters from high-resolution spectra observed in both the northern and southern hemisphere by the SDSS-IV APOGEE-2 survey. This unprecedented homogeneous dataset, largest to date, allows us to discuss the intrinsic Fe spread, the shape and statistics of Al-Mg and N-C anticorrelations as a function of cluster mass, luminosity, age and metallicity for all 31 clusters. We find that the Fe spread does not depend on these parameters within our uncertainties including cluster metallicity, contradicting earlier observations. We do not confirm the metallicity variations previously observed in M22 and NGC 1851. Some clusters show a bimodal Al distribution, while others exhibit a continuous distribution as has been previously reported in the literature. We confirm more than 2 populations in $\omega$ Cen and NGC 6752, and find new ones in M79. We discuss the scatter of Al by implementing a correction to the standard chemical evolution of Al in the Milky Way. After correction, its dependence on cluster mass is increased suggesting that the extent of Al enrichment as a function of mass was suppressed before the correction. We observe a turnover in the Mg-Al anticorrelation at very low Mg in $\omega$ Cen, similar to the pattern previously reported in M15 and M92. $\omega$ Cen may also have a weak K-Mg anticorrelation, and if confirmed, it would be only the third cluster known to show such a pattern., Comment: Published in MNRAS, 31 pages, 24 figures, 7 tables. Further typos are corrected, now identical in text, figures and tables to the published paper

GALAH is a large-scale magnitude-limited southern stellar spectroscopic survey. Its second data release (GALAH DR2) provides values of stellar parameters and abundances of 23 elements for 342,682 stars (Buder et al.). Here we add a description of the public release of radial velocities with a typical accuracy of 0.1 km/s for 336,215 of these stars, achievable due to the large wavelength coverage, high resolving power and good signal to noise ratio of the observed spectra, but also because convective motions in stellar atmosphere and gravitational redshift from the star to the observer are taken into account. In the process we derive medians of observed spectra which are nearly noiseless, as they are obtained from between 100 and 1116 observed spectra belonging to the same bin with a width of 50 K in temperature, 0.2 dex in gravity, and 0.1 dex in metallicity. Publicly released 1181 median spectra have a resolving power of 28,000 and trace the well-populated stellar types with metallicities between -0.6 and +0.3. Note that radial velocities from GALAH are an excellent match to the accuracy of velocity components along the sky plane derived by Gaia for the same stars. The level of accuracy achieved here is adequate for studies of dynamics within stellar clusters, associations and streams in the Galaxy. So it may be relevant for studies of the distribution of dark matter., Comment: Accepted to MNRAS, compared to the initial submission it now reports radial velocities for more stars (336,215 instead of 199,628) and all radial velocities have been recalculated

We report the serendipitous discovery of a nitrogen-rich, mildly metal-poor ([Fe/H]=-1.08) giant star in a single-lined spectroscopic binary system found in the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) survey, Data Release 14 (DR14). Previous work has assumed that the two percent of halo giants with unusual elemental abundances have been evaporated from globular clusters, but other origins for their abundance signatures, including binary mass transfer, must also be explored. We present the results of an abundance re-analysis of the APOGEE-2 high-resolution near-infrared spectrum of 2M12451043+1217401 with the Brussels Automatic Stellar Parameter (BACCHUS) automated spectral analysis code, and re-derive manually the main element families, namely the light elements (C, N), elements (O, Mg, Si), iron-peak element (Fe), \textit{s}-process element (Ce), and the light odd-Z element (Al). Our analysis confirm the N-rich nature of 2M12451043+1217401, which has a [N/Fe] ratio of $+0.69$, and shows that the abundances of C and Al are slightly discrepant from that of a typical mildly metal-poor RGB star, but exhibit Mg, Si, O and \textit{s}-process abundances (Ce) of typical field stars. We also detect a particularly large variability in its radial velocity over the period of the APOGEE-2 observations, and the most likely orbit fit to the radial velocity data has a period of $730.89\pm106.86$ days, a velocity semi-amplitude of $9.92 \pm 0.14$ km s$^{-1}$, and an eccentricity of $\sim 0.1276 \pm0.1174$, which support the hypothesis of a binary companion, and that has probably been polluted by a now-extinct AGB star., Comment: Accepted for publication in A&A, 13 pages, 8 figures, 7 tables

The technique of chemical tagging uses the elemental abundances of stellar atmospheres to 'reconstruct' chemically homogeneous star clusters that have long since dispersed. The GALAH spectroscopic survey - which aims to observe one million stars using the Anglo-Australian Telescope - allows us to measure up to 30 elements or dimensions in the stellar chemical abundance space, many of which are not independent. How to find clustering reliably in a noisy high-dimensional space is a difficult problem that remains largely unsolved. Here, we explore t-distributed stochastic neighbour embedding (t-SNE) - which identifies an optimal mapping of a high-dimensional space into fewer dimensions - whilst conserving the original clustering information. Typically, the projection is made to a 2D space to aid recognition of clusters by eye. We show that this method is a reliable tool for chemical tagging because it can: (i) resolve clustering in chemical space alone, (ii) recover known open and globular clusters with high efficiency and low contamination, and (iii) relate field stars to known clusters. t-SNE also provides a useful visualization of a high-dimensional space. We demonstrate the method on a data set of 13 abundances measured in the spectra of 187 000 stars by the GALAH survey. We recover seven of the nine observed clusters (six globular and three open clusters) in chemical space with minimal contamination from field stars and low numbers of outliers. With chemical tagging, we also identify two Pleiades supercluster members (which we confirm kinematically), one as far as 6 degrees-one tidal radius away from the cluster centre.

Radial velocities of fifteen double-mode bulge RR Lyrae (RR01) stars are presented, six of which belong to a compact group of RR01 stars in pulsation space, with the ratio of first-overtone period to fundamental-mode period, P_{fo}/P_{f}~0.74, and P_{f}~0.44. It has been suggested that these pulsationally clumped RR01 stars are a relic of a disrupted dwarf galaxy or stellar cluster, as they also appear to be spatially coherent in a vertical strip across the bulge. However, the radial velocities of the stars presented here, along with proper motions from Gaia DR2, show a large range of radial velocities, proper motions and distances for the bulge RR01 stars in the pulsation clump, much larger than the RR01 stars in the Sagittarius dwarf galaxy (Sgr). Therefore, in contrast to the kinematics of the RRL stars belonging to Sgr, and those in and surrounding the bulge globular cluster NGC~6441, there is no obvious kinematic signature within the pulsationally clumped RR01 stars. If the pulsationally clumped RR01 stars belonged to the same system in the past and were accreted, their accretion in the inner Galaxy was not recent, as the kinematic signature of this group has been lost (i.e., these stars are now well-mixed within the inner Galaxy). We show that the apparent spatial coherence reported for these stars could have been caused by small number statistics. The orbits of the RR01 stars in the inner Galaxy suggest they are confined to the innermost ~4~kpc of the Milky Way., accepted to ApJL

We investigate aluminum abundance variations in the stellar populations of globular clusters using both literature measurements of sodium and aluminum and APOGEE measurements of nitrogen and aluminum abundances. For the latter, we show that the Payne is the most suitable of the five available abundance pipelines for our purposes. Our combined sample of 42 globular clusters spans approximately 2 dex in [Fe/H] and 1.5 dex in $\log{M_{GC}/M_{\odot}}$. We find no fewer than five globular clusters with significant internal variations in nitrogen and/or sodium with little-to-no corresponding variation in aluminum, and that the minimum present-day cluster mass for aluminum enrichment in metal-rich systems is $\log{M_{GC}/M_{\odot}} \approx 4.50 + 2.17(\rm{[Fe/H]}+1.30)$. We demonstrate that the slopes of the [Al/Fe] vs [Na/Fe] and [Al/Fe] vs [N/Fe] relations for stars without field-like abundances are approximately log-linearly dependent on both the metallicity and the stellar mass of the globular clusters. In contrast, the relationship between [Na/Fe] and [N/Fe] shows no evidence of such dependencies. This suggests that there were (at least) two classes of non-supernovae chemical polluters that were common in the early universe, and that their relative contributions within globular clusters somehow scaled with the metallicity and mass of globular clusters. The first of these classes is predominantly responsible for the CNO and NeNa abundance variations, and likewise the second for the MgAl abundance variations. 47 Tuc and M4 are particularly striking examples of this dichotomy. As an auxiliary finding, we argue that abundance variations among Terzan 5 stars are consistent with it being a normal globular cluster., Comment: 39 pages, 24 figures, 8 tables, accepted for publication in The Astronomical Journal

There is growing evidence that the Galactic Center Excess identified in the $\textit{Fermi}$-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 $\textit{Fermi}$ bubbles compared to previous work and the three-dimensional Inverse Compton (IC) maps recently released by the ${\tt GALPROP}$ team. Our results provide strong constraints on Millisecond Pulsar (MSP) formation scenarios proposed to explain the excess. We find that an $\textit{admixture formation}$ scenario, in which some of the relevant binaries are $\textit{primordial}$ and the rest are formed $\textit{dynamically}$, is preferred over a primordial-only formation scenario at $7.6\sigma$ 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., Comment: 21 pages, 13 figures, V2: Minor changes to match submitted version, V3: matches JCAP published version

The overlap between the spectroscopic Galactic Archaeology with HERMES (GALAH) survey & $Gaia$ provides a high-dimensional chemodynamical space of unprecedented size. We present a first analysis of a subset of this overlap, of 7066 dwarf, turn-off, & sub-giant stars. [...] We investigate correlations between chemical compositions, ages, & kinematics for this sample. Stellar parameters & elemental abundances are derived from the GALAH spectra with the spectral synthesis code SME. [...] We report Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, as well as Ba & we note that we employ non-LTE calculations for Li, O, Al, & Fe. We show that the use of astrometric & photometric data improves the accuracy of the derived spectroscopic parameters, especially $\log g$. [...] we recover the result that stars of the high-$\alpha$ sequence are typically older than stars in the low-$\alpha$ sequence, the latter spanning $-0.78$ Gyr have lower angular momenta $L_z$ than the Sun, which implies that they are on eccentric orbits & originate from the inner disk. Contrary to some previous smaller scale studies we find a continuous evolution in the high-$\alpha$-sequence up to super-solar [Fe/H] rather than a gap, which has been interpreted as a separate "high-$\alpha$ metal-rich" population. Stars in our sample that are younger than 10 Gyr, are mainly found on the low $\alpha$-sequence & show a gradient in $L_z$ from low [Fe/H] ($L_z>L_{z,\odot}$) towards higher [Fe/H] ($L_z, Comment: Revised paper resubmitted to A&A, 20 pages (+10 pages appendix), 25 figures, 2 tables, 1 catalog

Over half of disk galaxies are barred, yet the mechanisms for bar formation and the life-time of bar buckling remain poorly understood. In simulations, a thin bar undergoes a rapid (, 22 pages, 12 figures. Accepted for publication in ApJ

The first stars are predicted to have formed within 200 million years after the Big Bang, initiating the cosmic dawn. A true first star has not yet been discovered, although stars with tiny amounts of elements heavier than helium ('metals') have been found in the outer regions ('halo') of the Milky Way. The first stars and their immediate successors should, however, preferentially be found today in the central regions ('bulges') of galaxies, because they formed in the largest over-densities that grew gravitationally with time. The Milky Way bulge underwent a rapid chemical enrichment during the first 1-2 billion years, leading to a dearth of early, metal-poor stars. Here we report observations of extremely metal-poor stars in the Milky Way bulge, including one star with an iron abundance about 10,000 times lower than the solar value without noticeable carbon enhancement. We confirm that the most metal-poor bulge stars are on tight orbits around the Galactic Centre, rather than being halo stars passing through the bulge, as expected for stars formed at redshifts greater than 15. Their chemical compositions are in general similar to typical halo stars of the same metallicity although intriguing differences exist, including lower abundances of carbon., Published in Nature on 11/11/15, see http://dx.doi.org/10.1038/nature15747

If the Galaxy is axisymmetric and in dynamical equilibrium, we expect negligible fluctuations in the residual line-of-sight velocity field. Recent results using the \apg{} survey find significant fluctuations in velocity for stars in the midplane ($|z, Comment: 20 pages, 16 figures, accepted for publication in MNRAS

Detailed elemental abundance patterns of metal-poor ([Fe/H] ~ -1~dex) stars in the Galactic bulge indicate that a number of them are consistent with globular cluster (GC) stars and may be former members of dissolved GCs. This would indicate that a few per cent of the Galactic bulge was built up from destruction and/or evaporation of globular clusters. Here an attempt is made to identify such presumptive stripped stars originating from the massive, inner Galaxy globular cluster NGC~6441 using its rich RR Lyrae variable star (RRL) population. We present radial velocities of forty RRLs centered on the globular cluster NGC~6441. All of the 13 RRLs observed within the cluster tidal radius have velocities consistent with cluster membership, with an average radial velocity of 24 +- 5~km/s and a star-to-star scatter of 11~km/s. This includes two new RRLs that were previously not associated with the cluster. Eight RRLs with radial velocities consistent with cluster membership but up to three time the distance from the tidal radius are also reported. These potential extra-tidal RRLs also have exceptionally long periods, which is a curious characteristic of the NGC~6441 RRL population that hosts RRLs with periods longer than seen anywhere else in the Milky Way. As expected of stripped cluster stars, most are inline with the cluster's orbit. Therefore, either the tidal radius of NGC~6441 is underestimated and/or we are seeing dissolving cluster stars stemming from NGC~6441 that are building up the old spheroidal bulge., accepted to AJ

We report the discovery of a giant planet in event UKIRT-2017-BLG-001, detected by the UKIRT microlensing survey. The mass ratio between the planet and its host is $q=1.50_{-0.14}^{+0.17}\times10^{-3}$, about 1.5 times the Jupiter/Sun mass ratio. The event lies 0.35$^{\circ}$ from the Galactic center and suffers from high extinction of $A_K=1.68$. Therefore, it could be detected only by a near-infrared survey. The field also suffers from large spatial differential extinction, which makes it difficult to estimate the source properties required to derive the angular Einstein radius. Nevertheless, we find evidence suggesting that the source is located in the far disk. If correct, this would be the first source star of a microlensing event to be identified as belonging to the far disk. We estimate the lens mass and distance using a Bayesian analysis to find that the planet's mass is $1.28^{+0.37}_{-0.44}\,M_{J}$, and it orbits a $0.81^{+0.21}_{-0.27}\,M_{\odot}$ star at an instantaneous projected separation of $4.18^{+0.96}_{-0.88}$ AU. The system is at a distance of $6.3^{+1.6}_{-2.1}$ kpc, and so likely resides in the Galactic bulge. In addition, we find a non-standard extinction curve in this field, in agreement with previous results toward high-extinction fields near the Galactic center., 27 pages, 8 figures, 2 tables. Accepted for publication in ApJ Letters

Using GALAH survey data of nearby stars, we look at how structure in the planar (u,v) velocity distribution depends on metallicity and on viewing direction within the Galaxy. In nearby stars, with distance d < 1 kpc, the Hercules stream is most strongly seen in higher metallicity stars [Fe/H] > 0.2. The Hercules stream peak v value depends on viewed galactic longitude, which we interpret as due to the gap between the stellar stream and more circular orbits being associated with a specific angular momentum value of about 1640 km/s kpc. The association of the gap with a particular angular momentum value supports a bar resonant model for the Hercules stream. Moving groups previously identified in Hipparcos observations are easiest to see in stars nearer than 250 pc, and their visibility and peak velocities in the velocity distributions depends on both viewing direction (galactic longitude and hemisphere) and metallicity. We infer that there is fine structure in local velocity distributions that varies over distances of a few hundred pc in the Galaxy., accepted for publication in MNRAS

Open cluster members are coeval and share the same initial bulk chemical composition. Consequently, differences in surface abundances between members of a cluster that are at different evolutionary stages can be used to study the effects of mixing and internal chemical processing. We carry out an abundance analysis of seven elements (Li, O, Na, Mg, Al, Si, and Fe) in 66 stars belonging to the open cluster M67, based on high resolution GALAH spectra, 1D MARCS model atmospheres, and non-local thermodynamic equilibrium (non-LTE) radiative transfer. From the non-LTE analysis, we find a typical star-to-star scatter in the abundance ratios of around 0.05 dex. We find trends in the abundance ratios with effective temperature, indicating systematic differences in the surface abundances between turn-off and giant stars; these trends are more pronounced when LTE is assumed. However, trends with effective temperature remain significant for Al and Si also in non-LTE. Finally, we compare the derived abundances with prediction from stellar evolution models including effects of atomic diffusion. We find overall good agreement for the abundance patterns of dwarfs and sub-giant stars, but the abundances of cool giants are lower relative to less evolved stars than predicted by the diffusion models, in particular for Mg.

Swan bands - characteristic molecular absorption features of the C$_2$ molecule - are a spectroscopic signature of carbon-enhanced stars. They can also be used to identify carbon-enhanced metal-poor (CEMP) stars. The GALAH (GALactic Archaeology with Hermes) is a magnitude-limited survey of stars producing high-resolution, high signal-to-noise spectra. We used 627,708 GALAH spectra to search for carbon-enhanced stars with a supervised and unsupervised classification algorithm, relying on the imprint of the Swan bands. We identified 918 carbon-enhanced stars, including 12 already described in the literature. An unbiased selection function of the GALAH survey allows us to perform a population study of carbon-enhanced stars. Most of them are giants, out of which we find 28 CEMP candidates. A large fraction of our carbon-enhanced stars with repeated observations show variation in radial velocity, hinting that there is a large fraction of variables among them. 32 of the detected stars also show strong Lithium enhancement in their spectra., Comment: 13+5 pages, 13 figures, 1 catalog, accepted to MNRAS

We model the split red clump of the Galactic bulge in OGLE-III photometry, and compare the results to predictions from two N-body models. Our analysis yields precise maps of the brightness of the two red clumps, the fraction of stars in the more distant peak, and their combined surface density. We compare the observations to predictions from two N-body models previously used in the literature. Both models correctly predict several features as long as one assumes an angle $\alpha_{\rm{Bar}} \approx 30^{\circ}$ between the Galactic bar's major axis and the line of sight to the Galactic centre. In particular that the fraction of stars in the faint red clump should decrease with increasing longitude. The biggest discrepancies between models and data are in the rate of decline of the combined surface density of red clump stars toward negative longitudes and of the brightness difference between the two red clumps toward positive longitudes, with neither discrepancy exceeding $\sim$25% in amplitude. Our analysis of the red giant luminosity function also yields an estimate of the red giant branch bump parameters toward these high-latitude fields, and evidence for a high rate ($\sim$25%) of disk contamination in the bulge at the colour and magnitude of the red clump, with the disk contamination rate increasing toward sightlines further distant from the plane., Comment: 20 pages, 14 figures, 5 tables, accepted for publication in MNRAS

Our Galaxy hosts the annihilation of a few $\times 10^{43}$ low-energy positrons every second. Radioactive isotopes capable of supplying such positrons are synthesised in stars, stellar remnants, and supernovae. For decades, however, there has been no positive identification of a main stellar positron source leading to suggestions that many positrons originate from exotic sources like the Galaxy's central super-massive black hole or dark matter annihilation. %, but such sources would not explain the recently-detected positron signal from the extended Galactic disk. Here we show that a single type of transient source, deriving from stellar populations of age 3-6 Gyr and yielding ~0.03 $M_\odot$ of the positron emitter $^{44}$Ti, can simultaneously explain the strength and morphology of the Galactic positron annihilation signal and the solar system abundance of the $^{44}$Ti decay product $^{44}$Ca. This transient is likely the merger of two low-mass white dwarfs, observed in external galaxies as the sub-luminous, thermonuclear supernova known as SN1991bg-like., 28 pages main text with 4 figures in preprint style; 26 pages of Supplementary Information

The assembly of the Milky Way bulge is an old topic in astronomy, one now in a period of renewed and rapid development. The dominant scenario for bulge formation is that of the Milky Way as a nearly pure disk galaxy, with the inner disk having formed a bar and buckled. This can potentially explain virtually all bulge stars with [Fe/H] ~ -0.50., Comment: 13 pages, 5 figures, accepted for publication in PASA

ULTIMATE is an instrument concept under development at the AAO, for the Subaru Telescope, which will have the unique combination of ground layer adaptive optics feeding multiple deployable integral field units. This will allow ULTIMATE to probe unexplored parameter space, enabling science cases such as the evolution of galaxies at z ~ 0:5 to 1.5, and the dark matter content of the inner part of our Galaxy. ULTIMATE will use Starbugs to position between 7 and 13 IFUs over a 14 × 8 arcmin field-of-view, pro- vided by a new wide-field corrector. All Starbugs can be positioned simultaneously, to an accuracy of better than 5 milli-arcsec within the typical slew-time of the telescope, allowing for very efficient re-configuration between observations. The IFUs will feed either the near-infrared nuMOIRCS or the visible/ near-infrared PFS spectrographs, or both. Future possible upgrades include the possibility of purpose built spectrographs and incorporating OH suppression using fibre Bragg gratings. We describe the science case and resulting design requirements, the baseline instrument concept, and the expected performance of the instrument.

Cosmological models predict the oldest stars in the Galaxy should be found closest to the centre of the potential well, in the bulge. The EMBLA Survey successfully searched for these old, metal-poor stars by making use of the distinctive SkyMapper photometric filters to discover candidate metal-poor stars in the bulge. Their metal-poor nature was then confirmed using the AAOmega spectrograph on the AAT. Here we present an abundance analysis of 10 bulge stars with -2.8, Comment: 20 pages, 16 figures. Accepted to Monthly Notices of the Royal Astronomical Society. Online tables can be found at http://www.astro.lu.se/~louise/data

We present an analysis of the relative throughputs of the 3.9-metre Anglo-Australian Telescope's 2dF/HERMES system, based upon spectra acquired during the first two years of the GALAH survey. Averaged spectral fluxes of stars were compared to their photometry to determine the relative throughputs of fibres for a range of fibre position and atmospheric conditions. We find that overall the throughputs of the 771 usable fibres have been stable over the first two years of its operation. About 2.5 per cent of fibres have throughputs much lower than the average. There are also a number of yet unexplained variations between the HERMES bandpasses, and mechanically & optically linked fibre groups known as retractors or slitlets related to regions of the focal plane. These findings do not impact the science that HERMES will produce., 14 pages, 10 figures. Accepted for publication in MNRAS

We present the data reduction procedures being used by the GALactic Archeology with Hermes (GALAH) survey, carried out with the HERMES fibre-fed, multi-object spectrograph on the 3.9-m Anglo-Australian Telescope. GALAH is a unique survey, targeting 1 million stars brighter than magnitude V = 14 at a resolution of 28 000 with a goal to measure the abundances of 29 elements. Such a large number of high-resolution spectra necessitate the development of a reduction pipeline optimized for speed, accuracy, and consistency.We outline the design and structure of the IRAF-based reduction pipeline that we developed, specifically for GALAH, to produce fully calibrated spectra aimed for subsequent stellar atmospheric parameter estimation. The pipeline takes advantage of existing IRAF routines and other readily available software so as to be simple to maintain, testable, and reliable. A radial velocity and stellar atmospheric parameter estimator code is also presented, which is used for further data analysis and yields a useful verification of the reduction quality. We have used this estimator to quantify the data quality of GALAH for fibre cross-talk level (≲0.5 per cent) and scattered light (~5 counts in a typical 20 min exposure), resolution across the field, sky spectrum properties, wavelength solution reliability (better than 1 kms-1 accuracy), and radial velocity precision. (Less)

Galah is an ongoing high-resolution spectroscopic survey with the goal of disentangling the formation history of the Milky Way, using the fossil remnants of disrupted star formation sites which are now dispersed around the Galaxy. It is targeting a randomly selected, magnitude limited ($V \leq 14$) sample of stars, with the goal of observing one million objects. To date, 300,000 spectra have been obtained. Not all of them are correctly processed by parameter estimation pipelines and we need to know about them. We present a semi-automated classification scheme which identifies different types of peculiar spectral morphologies, in an effort to discover and flag potentially problematic spectra and thus help to preserve the integrity of the survey's results. To this end we employ a recently developed dimensionality reduction technique t-SNE (t-distributed Stochastic Neighbour Embedding), which enables us to represent the complex spectral morphology in a two-dimensional projection map while still preserving the properties of the local neighbourhoods of spectra. We find that the majority (178,483) of the 209,533 Galah spectra considered in this study represents normal single stars, whereas 31,050 peculiar and problematic spectra with very diverse spectral features pertaining to 28,579 stars are distributed into 10 classification categories: Hot stars, Cool metal-poor giants, Molecular absorption bands, Binary stars, H$\alpha$/H$\beta$ emission, H$\alpha$/H$\beta$ emission superimposed on absorption, H$\alpha$/H$\beta$ P-Cygni, H$\alpha$/H$\beta$ inverted P-Cygni, Lithium absorption, and Problematic. Classified spectra with supplementary information are presented in the catalogue, indicating candidates for follow-up observations and population studies of the short-lived phases of stellar evolution.

I review the literature covering the issue of interstellar extinction toward the Milky Way bulge, with emphasis placed on findings from planetary nebulae, RR Lyrae, and red clump stars. I also report on observations from HI gas and globular clusters. I show that there has been substantial progress in this field in recent decades, most particularly from red clump stars. The spatial coverage of extinction maps has increased by a factor $\sim 100 \times$ in the past twenty years, and the total-to-selective extinction ratios reported have shifted by $\sim$20-25\%, indicative of the improved accuracy and separately, of a steeper-than-standard extinction curve. Problems remain in modelling differential extinction, explaining anomalies involving the planetary nebulae, and understanding the difference between bulge extinction coefficients and "standard" literature values., Comment: 12 pages, 6 figures, 2 Tables, invited article to PASA special review issue on the Galactic Bulge, edited by Beatriz Barbuy. This version includes minor modifications requested by referee prior to being accepted for publication

We investigate interstellar extinction curve variations toward $\sim$4 deg$^{2}$ of the inner Milky Way in $VIJK_{s}$ photometry from the OGLE-III and $VVV$ surveys, with supporting evidence from diffuse interstellar bands and $F435W,F625W$ photometry. We obtain independent measurements toward $\sim$2,000 sightlines of $A_{I}$, $E(V-I)$, $E(I-J)$, and $E(J-K_{s})$, with median precision and accuracy of 2%. We find that the variations in the extinction ratios $A_{I}/E(V-I)$, $E(I-J)/E(V-I)$ and $E(J-K_{s})/E(V-I)$ are large (exceeding 20%), significant, and positively correlated, as expected. However, both the mean values and the trends in these extinction ratios are drastically shifted from the predictions of Cardelli and Fitzpatrick, regardless of how $R_{V}$ is varied. Furthermore, we demonstrate that variations in the shape of the extinction curve has at least two degrees of freedom, and not one (e.g. $R_{V}$), which we conform with a principal component analysis. We derive a median value of $=13.44$, which is $\sim$60% higher than the "standard" value. We show that the Wesenheit magnitude $W_{I}=I-1.61(I-J)$ is relatively impervious to extinction curve variations. Given that these extinction curves are linchpins of observational cosmology, and that it is generally assumed that $R_{V}$ variations correctly capture variations in the extinction curve, we argue that systematic errors in the distance ladder from studies of type Ia supernovae and Cepheids may have been underestimated. Moreover, the reddening maps from the Planck experiment are shown to systematically overestimate dust extinction by $\sim$100%, and lack sensitivity to extinction curve variations., Comment: 16 pages, 13 figures, 3 tables, accepted to MNRAS, small revisions due to editor's comments and suggestions from the international astronomical community