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1. Titanium abundances in late-type stars: II. Grid of departure coefficients and application to a sample of 70 000 stars.

Author

Mallinson, J. W. E., Lind, K., Amarsi, A. M., and Youakim, K.

Subjects
COOL stars (Astronomy), LOCAL thermodynamic equilibrium, STARS, STELLAR spectra, GALACTIC evolution
Abstract

Context. Rapidly growing datasets from stellar spectroscopic surveys are providing unprecedented opportunities to analyse the chemical evolution history of our Galaxy. However, spectral analysis requires accurate modelling of synthetic stellar spectra for late-type stars, for which the assumption of local thermodynamic equilibrium (LTE) has been shown to be insufficient in many cases. Errors associated with LTE can be particularly large for Ti I, which is susceptible to over-ionisation, particularly in metal-poor stars. Aims. The aims of this work are to study and quantify the 1D non-LTE effects on titanium abundances across the Hertzsprung-Russell diagram for a large sample of stars. Methods. A large grid of departure coefficients, βν, were computed on standard MARCS model atmospheres. The grid extends from 3000 K to 8000 K in Teff, −0.5 dex to +5.5 dex in log g, and −5.0 to +1.0 in [Fe/H], with non-LTE effects in this grid reaching up to 0.4 dex. This was used to compute abundance corrections that were subsequently applied to the LTE abundances of over 70 000 stars selected from the GALAH survey in addition to a smaller sample of literature Keck data for metal-poor dwarfs. Results. The non-LTE effects grow towards lower [Fe/H], lower log g, and higher Teff, with a minimum and maximum ΔA(Ti)Ti I of 0.02 and 0.19 in the GALAH sample. For metal-poor giants, the non-LTE modelling reduces the average ionisation imbalance (ΔI−II) from −0.11 dex to −0.01 dex at [Fe/H] = −1.7, and the enhancement in titanium abundances from Ti I lines results in a [Ti/Fe] versus [Fe/H] trend that more closely resembles the behaviour of Ti II at low metallicities. At higher metallicities, the results are limited by the precision of the GALAH DR3 LTE abundances and the effects are within the errors. For the most metal-poor dwarfs from the Keck sample, the average ionisation imbalance increases from −0.1 dex to +0.2 dex, a shortcoming that is consistent with previous 1D non-LTE studies and which we speculate could be related to 3D effects. Conclusions. Non-LTE effects on titanium abundances are significant. Neglecting them may alter our understanding of Galactic chemical evolution. We have made our grid of departure coefficients publicly available, with the caveat that the Ti abundances of metal-poor dwarfs need further study in 3D non-LTE. [ABSTRACT FROM AUTHOR]

Published
2024
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2. Beyond Gaia DR3: Tracing the [α/M] – [M/H] bimodality from the inner to the outer Milky Way disc with Gaia-RVS and convolutional neural networks.

Author

Guiglion, G., Nepal, S., Chiappini, C., Khoperskov, S., Traven, G., Queiroz, A. B. A., Steinmetz, M., Valentini, M., Fournier, Y., Vallenari, A., Youakim, K., Bergemann, M., Mészáros, S., Lucatello, S., Sordo, R., Fabbro, S., Minchev, I., Tautvaišienė, G., Mikolaitis, Š., and Montalbán, J.

Subjects
CONVOLUTIONAL neural networks, MILKY Way, STARS, STELLAR spectra, MACHINE learning
Abstract

Context. In June 2022, Gaia DR3 provided the astronomy community with about one million spectra from the Radial Velocity Spectrometer (RVS) covering the CaII triplet region. In the next Gaia data releases, we anticipate the number of RVS spectra to successively increase from several 10 million spectra to eventually more than 200 million spectra. Thus, stellar spectra are projected to be produced on an 'industrial scale', with numbers well above those for current and anticipated ground-based surveys. However, one-third of the published spectra have 15 ≤ S /N ≤ 25 per pixel such that they pose problems for classical spectral analysis pipelines, and therefore, alternative ways to tap into these large datasets need to be devised. Aims. We aim to leverage the versatility and capabilities of machine learning techniques for supercharged stellar parametrisation by combining Gaia-RVS spectra with the full set of Gaia products and high-resolution, high-quality ground-based spectroscopic reference datasets. Methods. We developed a hybrid convolutional neural network (CNN) that combines the Gaia DR3 RVS spectra, photometry (G, G_BP, G_RP), parallaxes, and XP coefficients to derive atmospheric parameters (Teff, log(g) as well as overall [M/H]) and chemical abundances ([Fe/H] and [α/M]). We trained the CNN with a high-quality training sample based on APOGEE DR17 labels. Results. With this CNN, we derived homogeneous atmospheric parameters and abundances for 886 080 RVS stars that show remarkable precision and accuracy compared to external datasets (such as GALAH and asteroseismology). The CNN is robust against noise in the RVS data, and we derive very precise labels down to S/N =15. We managed to characterise the [α/M] - [M/H] bimodality from the inner regions to the outer parts of the Milky Way, which has never been done using RVS spectra or similar datasets. Conclusions. This work is the first to combine machine learning with such diverse datasets and paves the way for large-scale machine learning analysis of Gaia-RVS spectra from future data releases. Large, high-quality datasets can be optimally combined thanks to the CNN, thereby realising the full power of spectroscopy, astrometry, and photometry. [ABSTRACT FROM AUTHOR]

Published
2024
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3. The Pristine Inner Galaxy Survey (PIGS) I: tracing the kinematics of metal-poor stars in the Galactic bulge.

Author

Arentsen, A, Starkenburg, E, Martin, N F, Hill, V, Ibata, R, Kunder, A, Schultheis, M, Venn, K A, Zucker, D B, Aguado, D, Carlberg, R, González Hernández, J I, Lardo, C, Longeard, N, Malhan, K, Navarro, J F, Sánchez-Janssen, R, Sestito, F, Thomas, G, and Youakim, K

Subjects
GALACTIC bulges, MILKY Way, KINEMATICS, GALAXIES, SWINE, STARS
Abstract

Our Galaxy is known to contain a central boxy/peanut-shaped bulge, yet the importance of a classical, pressure-supported component within the central part of the Milky Way is still being debated. It should be most visible at low metallicity, a regime that has not yet been studied in detail. Using metallicity-sensitive narrow-band photometry, the Pristine Inner Galaxy Survey (PIGS) has collected a large sample of metal-poor (⁠|$\rm {[Fe/H]}\, \lt -1.0$|⁠) stars in the inner Galaxy to address this open question. We use PIGS to trace the metal-poor inner Galaxy kinematics as function of metallicity for the first time. We find that the rotational signal decreases with decreasing [Fe/H] , until it becomes negligible for the most metal-poor stars. Additionally, the velocity dispersion increases with decreasing metallicity for |$-3.0 \lt \rm {[Fe/H]}\, \lt -0.5$|⁠ , with a gradient of −44 ± 4 km s−1 dex−1. These observations may signal a transition between Galactic components of different metallicities and kinematics, a different mapping on to the boxy/peanut-shaped bulge for former disc stars of different metallicities and/or the secular dynamical and gravitational influence of the bar on the pressure-supported component. Our results provide strong constraints on models that attempt to explain the properties of the inner Galaxy. [ABSTRACT FROM AUTHOR]

Published
2020
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4. The Pristine survey IV: approaching the Galactic metallicity floor with the discovery of an ultra-metal-poor star

Author

Piercarlo Bonifacio, D. S. Aguado, A. Arentsen, Eline Tolstoy, Rubén Sánchez-Janssen, Patrick Côté, Elisabetta Caffau, Kim A. Venn, Vanessa Hill, Julio F. Navarro, Nicolas Longeard, Carlos Allende Prieto, Morgan Fouesneau, Pascale Jablonka, Raymond G. Carlberg, Marc Gentile, Federico Sestito, Else Starkenburg, Collin Kielty, Helmer H. Koppelman, Jonay I. González Hernández, Nicolas F. Martin, Kris Youakim, Carmela Lardo, Alan W. McConnachie, Astronomy, Starkenburg E., Aguado D.S., Bonifacio P., Caffau E., Jablonka P., Lardo C., Martin N., Sanchez-Janssen R., Sestito F., Venn K.A., Youakim K., Prieto C.A., Arentsen A., Gentile M., Hernandez J.I.G., Kielty C., Koppelman H.H., Longeard N., Tolstoy E., Carlberg R.G., Cote P., Fouesneau M., Hill V., McConnachie A.W., Navarro J.F., Galaxies, Etoiles, Physique, Instrumentation (GEPI), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Franche-Comté Électronique Mécanique, Thermique et Optique - Sciences et Technologies (UMR 6174) (FEMTO-ST), Université de Technologie de Belfort-Montbeliard (UTBM)-Ecole Nationale Supérieure de Mécanique et des Microtechniques (ENSMM)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS), National Research Council of Canada (NRC), Observatoire astronomique de Strasbourg (ObAS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Max-Planck-Institut für Astronomie (MPIA), Max-Planck-Gesellschaft, Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
photometry, stars: abundances, Metallicity, media_common.quotation_subject, 1st stars, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, telescope, Star (graph theory), 01 natural sciences, Galactic halo, Metal, hamburg/eso survey, 0103 physical sciences, Galaxy formation and evolution, Astrophysics::Solar and Stellar Astrophysics, 010306 general physics, 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, media_common, [PHYS]Physics [physics], Physics, Galaxy: evolution, abundance, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astronomy and Astrophysics, stars: abundances, Galaxy: abundances, Galaxy: evolution, Galaxy: formation, Galaxy: halo, Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Astrophysics of Galaxies, model atmospheres, Astrophysics - Astrophysics of Galaxies, chemical-compositions, Universe, sky survey, Galaxy: halo, Galaxy: abundance, Stars, Astrophysics - Solar and Stellar Astrophysics, lithium, 13. Climate action, Space and Planetary Science, Galaxy: formation, Astrophysics of Galaxies (astro-ph.GA), visual_art, visual_art.visual_art_medium, Galaxy: abundances, Astrophysics::Earth and Planetary Astrophysics, halo-stars
Abstract

The early Universe presented a star formation environment that was almost devoid of heavy elements. The lowest metallicity stars thus provide a unique window into the earliest Galactic stages, but are exceedingly rare and difficult to find. Here we present the discovery of an ultra-metal-poor star, Pristine_221.8781+9.7844, using narrow-band Ca H&K photometry from the Pristine survey. Follow-up medium and high-resolution spectroscopy confirms the ultra-metal-poor nature of Pristine_221.8781+9.7844 ([Fe/H] = -4.66 +/- 0.13 in 1D LTE) with an enhancement of 0.3-0.4 dex in alpha-elements relative to Fe, and an unusually low carbon abundance. We derive an upper limit of A(C) = 5.6, well below typical A(C) values for such ultra metal-poor stars. This makes Pristine_221.8781+9.7844 one of the most metal-poor stars; in fact, it is very similar to the most metal-poor star known (SDSS J102915+172927). The existence of a class of ultra metal-poor stars with low(er) carbon abundances suggest that there must have been several formation channels in the early Universe through which long-lived, low-mass stars were formed., Re-submitted to MNRAS after minor revisions

Published
2018

5. The Pristine survey – IX. CFHT ESPaDOnS spectroscopic analysis of 115 bright metal-poor candidate stars

Author

Carmela Lardo, Christopher Sneden, Nicolas F. Martin, Else Starkenburg, Federico Sestito, Julio F. Navarro, Rubén Sánchez Janssen, Jonay I. Gonzalez-Hernandez, Collin Kielty, Pascale Jablonka, Anke Arentsen, K. Youakim, Raymond G. Carlberg, Lyudmilla Mashonkina, Piercarlo Bonifacio, Kim A. Venn, Vanessa Hill, G. F. Thomas, Elisabetta Caffau, David Aguado, Khyati Malhan, Department of Physics and Astronomy [Victoria], University of Victoria [Canada] (UVIC), Observatoire astronomique de Strasbourg (ObAS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Leibniz Institute for Astrophysics Potsdam (AIP), Institute of Astronomy [Cambridge], University of Cambridge [UK] (CAM), Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), EPFL Laboratoire d’astrophysique, Ecole Polytechnique Fédérale de Lausanne (EPFL), Institute of Astronomy of the Russian Academy of Sciences (INASAN), Russian Academy of Sciences [Moscow] (RAS), Department of Astronomy [Austin], University of Texas at Austin [Austin], National Research Council Herzberg Astronomy and Astrophysics, Instituto de Astrofisica de Canarias (IAC), Departamento de Astrofísica [La laguna], Universidad de La Laguna [Tenerife - SP] (ULL), UK Astronomy Technology Centre (UK ATC), Science and Technology Facilities Council (STFC), Department of Astronomy and Astrophysics [Universty of Toronto], University of Toronto, The Oskar Klein Centre for Cosmoparticle Physics and Department of Physics, Stockholm University, Venn K.A., Kielty C.L., Sestito F., Starkenburg E., Martin N., Aguado D.S., Arentsen A., Bonifacio P., Caffau E., Hill V., Jablonka P., Lardo C., Mashonkina L., Navarro J.F., Sneden C., Thomas G., Youakim K., Gonzalez-Hernandez J.I., Janssen R.S., Carlberg R., Malhan K., University of British Columbia (UBC), Institute of Astronomy, University of Cambridge, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA), and Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France.

Subjects
Star, stars: abundances, Milky Way, stars: kinematics and dynamics, 1st stars, Stellar content -Galaxy, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, fe, lte line formation, hamburg/eso survey, Abundance, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010306 general physics, Spectroscopy, 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, milky-way, Astrophysics::Galaxy Astrophysics, Population II, Physics, stellar halo, [PHYS]Physics [physics], Galaxy: stellar content, galactic bar, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Galactic Center, Astronomy and Astrophysics, stars: Population II, Kinematics and dynamic, model atmospheres, Galaxy, Stars, Narrow band, Hamburg/ESO Survey, 13. Climate action, Space and Planetary Science, Galaxy: abundances, chemical-composition, Astrophysics::Earth and Planetary Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Galaxy: kinematics and dynamics
Abstract

A chemo-dynamical analysis of 115 metal-poor candidate stars selected from the narrow-band Pristine photometric survey is presented based on CFHT high-resolution ESPaDOnS spectroscopy. We have discovered 28 new bright (V < 15) stars with [Fe/H] < −2.5 and 5 with [Fe/H] < −3.0 for success rates of 40 (28/70) and 19 per cent (5/27), respectively. A detailed model atmosphere analysis is carried out for the 28 new metal-poor stars. Stellar parameters were determined from SDSS photometric colours, Gaia DR2 parallaxes, MESA/MIST stellar isochrones, and the initial Pristine survey metallicities, following a Bayesian inference method. Chemical abundances are determined for 10 elements (Na, Mg, Ca, Sc, Ti, Cr, Fe, Ni, Y, and Ba). Most stars show chemical abundance patterns that are similar to the normal metal-poor stars in the Galactic halo; however, we also report the discoveries of a new r-process-rich star, a new CEMP-s candidate with [Y/Ba] > 0, and a metal-poor star with very low [Mg/Fe]. The kinematics and orbits for all of the highly probable metal-poor candidates are determined by combining our precision radial velocities with Gaia DR2 proper motions. Some stars show unusual kinematics for their chemistries, including planar orbits, unbound orbits, and highly elliptical orbits that plunge deeply into the Galactic bulge (Rperi < 0.5 kpc); also, eight stars have orbital energies and actions consistent with the Gaia-Enceladus accretion event. This paper contributes to our understanding of the complex chemo-dynamics of the metal-poor Galaxy, and increases the number of known bright metal-poor stars available for detailed nucleosynthetic studies.

Published
2020

6. The Pristine survey VIII: The metallicity distribution function of the Milky Way halo down to the extremely metal-poor regime

Author

G. F. Thomas, Vanessa Hill, Julio F. Navarro, Else Starkenburg, Nicolas F. Martin, Anke Arentsen, Georges Kordopatis, J. I. González Hernández, R. Sánchez Janssen, K. Youakim, C. Allende Prieto, David Aguado, K. A. Venn, Pascale Jablonka, Carmela Lardo, R. G. Carlberg, Federico Sestito, Gal Matijevic, Piercarlo Bonifacio, Youakim, K., Starkenburg, E., Martin, N. F., Matijevič, G., Aguado, D. S., Allende Prieto, C., Arentsen, A., Bonifacio, P., Carlberg, R. G., González Hernández, J. I., Hill, V., Kordopatis, G., Lardo, C., Navarro, J. F., Jablonka, P., Sánchez Janssen, R., Sestito, F., Thomas, G. F., Venn, K., Observatoire astronomique de Strasbourg (ObAS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), University of Toronto, Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Ecole Polytechnique Fédérale de Lausanne (EPFL), Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), and Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)

Subjects
stars, stars: abundances, Metallciity, galaxy: evolution, Metallicity, Milky Way, FOS: Physical sciences, dwarf galaxy, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, galaxy: formation, Photometry (optics), Galactic halo, galaxy: halo, evolution, 0103 physical sciences, Galaxy formation and evolution, 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, Astrophysics::Galaxy Astrophysics, merger, [PHYS]Physics [physics], stellar halo, search, Physics, abundance, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], galaxy: abundances, 010308 nuclear & particles physics, sagittarius, Near-field cosmology, Astronomy and Astrophysics, galaxies: dwarf, Metal-poor star, streams, Astrophysics - Astrophysics of Galaxies, sky survey, Stars, 13. Climate action, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Globular cluster, Halo, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

The Pristine survey uses narrow-band photometry to derive precise metallicities down to the extremely metal-poor regime ([Fe/H] < -3), and currently consists of over 4 million FGK-type stars over a sky area of $\sim 2~500\, \mathrm{deg}^2$. We focus our analysis on a subsample of $\sim 80~000$ main sequence turnoff stars with heliocentric distances between 6 and 20 kpc, which we take to be a representative sample of the inner halo. The resulting metallicity distribution function (MDF) has a peak at [Fe/H] = -1.6, and a slope of $��$(LogN)/$��[Fe/H] = 1.0 \pm 0.1$ in the metallicity range of -3.4 < [Fe/H] < -2.5. This agrees well with a simple closed-box chemical enrichment model in this range, but is shallower than previous spectroscopic MDFs presented in the literature, suggesting that there may be a larger proportion of metal-poor stars in the inner halo than previously reported. We identify the Monoceros/TriAnd/ACS/EBS/A13 structure in metallicity space in a low latitude field in the anticenter direction, and also discuss the possibility that the inner halo is dominated by a single, large merger event, but cannot strongly support or refute this idea with the current data. Finally, based on the MDF of field stars, we estimate the number of expected metal-poor globular clusters in the Milky Way halo to be 5.4 for [Fe/H] < -2.5 and 1.5 for [Fe/H] < -3, suggesting that the lack of low metallicity globular clusters in the Milky Way is not due simply to statistical undersampling., 17 pages, 12 figures, 5 tables, accepted for publication in MNRAS

Published
2020

7. The Pristine Inner Galaxy Survey (PIGS) I: Tracing the kinematics of metal-poor stars in the Galactic bulge

Author

Mathias Schultheis, Jeffrey D. Simpson, Zhen Wan, Anke Arentsen, G. F. Thomas, Nicolas F. Martin, K. A. Venn, Rodrigo A. Ibata, K. Youakim, Daniel B. Zucker, Nicolas Longeard, J. I. González Hernández, Vanessa Hill, Julio F. Navarro, Andrea Kunder, R. G. Carlberg, Carmela Lardo, Khyati Malhan, Geraint F. Lewis, Rubén Sánchez-Janssen, David Aguado, Federico Sestito, Else Starkenburg, Arentsen A., Starkenburg E., Martin N.F., Hill V., Ibata R., Kunder A., Schultheis M., Venn K.A., Zucker D.B., Aguado D., Carlberg R., Gonzalez Hernandez J.I., Lardo C., Longeard N., Malhan K., Navarro J.F., Sanchez-Janssen R., Sestito F., Thomas G., Youakim K., Lewis G.F., Simpson J.D., Wan Z., Observatoire astronomique de Strasbourg (ObAS), Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France., Centre International de Hautes Etudes Agronomiques Méditerranéennes - Institut Agronomique Méditerranéen de Montpellier (CIHEAM-IAMM), Centre International de Hautes Études Agronomiques Méditerranéennes (CIHEAM), Laboratoire de Cosmologie, Astrophysique Stellaire & Solaire, de Planétologie et de Mécanique des Fluides (CASSIOPEE), Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire de la Côte d'Azur (OCA), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), University of Toronto, Ecole Polytechnique Fédérale de Lausanne (EPFL), Facultad de Matematicas, Universidad de Murcia, CLRC Daresbury, SFTC, Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), and COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)

Subjects
photometry, Milky Way, Metallicity, bulge -Galaxy, kinematics and dynamics -Galaxy, formation -Galaxy, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Galaxy: Structure, Galactic halo, Galaxy: Evolution, Bulge, 0103 physical sciences, Galaxy formation and evolution, structure, 010303 astronomy & astrophysics, Galaxy: Halo, halo -Galaxy, milky-way, ComputingMilieux_MISCELLANEOUS, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, Physics, Galaxy: Kinematics and dynamic, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 010308 nuclear & particles physics, [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], stellar populations, Velocity dispersion, Astronomy and Astrophysics, Galaxy: Formation, argos, Galaxy: Bulge, Astrophysics - Astrophysics of Galaxies, Galaxy, evolution -Galaxy, [SDU.ASTR.IM]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Instrumentation and Methods for Astrophysic [astro-ph.IM], Stars, [PHYS.ASTR.GA]Physics [physics]/Astrophysics [astro-ph]/Galactic Astrophysics [astro-ph.GA], Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), galaxy: kinematics and dynamics, [SDU.ASTR.GA]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Galactic Astrophysics [astro-ph.GA], [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

Our Galaxy is known to contain a central boxy/peanut-shaped bulge, yet the importance of a classical, pressure-supported component within the central part of the Milky Way is still being debated. It should be most visible at low metallicity, a regime that has not yet been studied in detail. Using metallicity-sensitive narrow-band photometry, the Pristine Inner Galaxy Survey (PIGS) has collected a large sample of metal-poor ([Fe/H] < -1.0) stars in the inner Galaxy to address this open question. We use PIGS to trace the metal-poor inner Galaxy kinematics as function of metallicity for the first time. We find that the rotational signal decreases with decreasing [Fe/H], until it becomes negligible for the most metal-poor stars. Additionally, the velocity dispersion increases with decreasing metallicity for -3.0 < [Fe/H] < -0.5, with a gradient of -44 $\pm$ 4 km$\,$s$^{-1}\,$dex$^{-1}$. These observations may signal a transition between Galactic components of different metallicities and kinematics, a different mapping onto the boxy/peanut-shaped bulge for former disk stars of different metallicities and/or the secular dynamical and gravitational influence of the bar on the pressure-supported component. Our results provide strong constraints on models that attempt to explain the properties of the inner Galaxy., 5 pages + appendices, accepted to MNRAS Letters

Published
2020

8. The Pristine survey VI. The first three years of medium-resolution follow-up spectroscopy of Pristine EMP star candidates

Author

Carmela Lardo, K. Youakim, Nicolas F. Martin, Rafael Garcia-Dias, Thomas G. Wilson, Luis Peralta de Arriba, Julio F. Navarro, Vanessa Hill, Pascale Jablonca, Pedro A. Palicio, Georges Kordopatis, Nicholas J. Fantin, Federico Sestito, Carlos Allende Prieto, Else Starkenburg, R. Lucchesi, Jonay I. González Hernández, Yeisson Osorio, Farbod Jahandar, Kim A. Venn, Rubén Sánchez-Janssen, David Aguado, Nicolas Longeard, Anke Arentsen, Collin Kielty, Elisabetta Caffau, Guillaume F. Thomas, Patrick Côté, Eline Tolstoy, Piercarlo Bonifacio, Institute of Astronomy, University of Cambridge, Universidad de La Laguna [Tenerife - SP] (ULL), Leibniz Institute for Astrophysics Potsdam (AIP), Observatoire astronomique de Strasbourg (ObAS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Cosmological Impact of the First Stars (CIFIST), Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Peralta de Arriba, Luis [0000-0002-3084-084X], Apollo - University of Cambridge Repository, Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Astronomy, Aguado D.S., Youakim K., Gonzalez Hernandez J.I., Prieto C.A., Starkenburg E., Martin N., Bonifacio P., Arentsen A., Caffau E., de Arriba L.P., Sestito F., Garcia-Dias R., Fantin N., Hill V., Jablonca P., Jahandar F., Kielty C., Longeard N., Lucchesi R., Sanchez-Janssen R., Osorio Y., Palicio P.A., Tolstoy E., Wilson T.G., Cote P., Kordopatis G., Lardo C., Navarro J.F., Thomas G.F., and Venn K.

Subjects
stars: abundances, galaxy: evolution, Milky Way, first stars, Dark age, halo, FOS: Physical sciences, Astrophysics, 01 natural sciences, local group, galaxy: formation, First star, 0103 physical sciences, evolution, Galaxy formation and evolution, William Herschel Telescope, dark ages, reionization, first stars, metal-poor stars, dark ages, Spectroscopy, 010303 astronomy & astrophysics, Reionization, ComputingMilieux_MISCELLANEOUS, milky-way, Physics, [PHYS]Physics [physics], search, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 010308 nuclear & particles physics, abundances, carbon, Astronomy and Astrophysics, oldest, Astrophysics - Astrophysics of Galaxies, early universe, Medium resolution, Stars, classification, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), reionization, discovery
Abstract

We present the results of a 3-year long, medium-resolution spectroscopic campaign aimed at identifying very metal-poor stars from candidates selected with the CaHK, metallicity-sensitive Pristine survey. The catalogue consists of a total of 1007 stars, and includes 146 rediscoveries of metal-poor stars already presented in previous surveys, 707 new very metal-poor stars with [Fe/H] < -2.0, and 95 new extremely metal-poor stars with [Fe/H] < -3.0. We provide a spectroscopic [Fe/H] for every star in the catalogue, and [C/Fe] measurements for a subset of the stars (10% with [Fe/H] < -3 and 24% with -3 < [Fe/H] < -2) for which a carbon determination is possible, contingent mainly on the carbon abundance, effective temperature and S/N of the stellar spectra. We find an average carbon enhancement fraction ([C/Fe] >= +0.7) of 41 +- 4% for stars with -3 < [Fe/H] < -2 and 58 +- 14% for stars with [Fe/H] < -3, and report updated success rates for the Pristine survey of 56 % and 23 % to recover stars with [Fe/H] < -2.5 and [Fe/H] < -3, respectively. Finally, we discuss the current status of the survey and its preparation for providing targets to upcoming multi-object spectroscopic surveys such as WEAVE., 13 pages 6 figures, accepted for publication in MNRAS

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