What is written in the stars? A chemical view on the formation of the Milky Way
Final Report Abstract
We can unravel much of the light from our own galaxy, the Milky Way, and the closest surrounding galaxies into individual stars. Because stars keep a chemical fingerprint during their lives, studying present-day stars teaches us about the past, an approach called Galactic Archaeology. In particular, low-mass stars can have very old ages and bring us back to the earliest epochs of star formation in the Universe. The main aim of this Emmy Noether program was to unravel this information contained within a star’s chemical fingerprint and use it to make significant progress in our understanding of the formation of galaxies like our Milky Way. In pursuing this aim we are bringing together information from both observations and cosmological modelling studies. As a Galactic archaeologist, it is particularly intriguing to study most chemically pristine stars that still exist today, as they carry the imprint of very few generations of supernovae and represent our closest approach to studying the very first stars. To find and study these stars, I have designed and am co-leading the Pristine survey, which uses a narrow-band filter on the Canada-France-Hawaii Telescope to search with unprecedented efficiency for these very rare stars among their more numerous and more normal peers. Having already photographed over 6000 square degrees of the sky with this filter, we have an impressive dataset available that we use better characterize the metallicity structure of the Milky Way and its satellites. Some surprising results from our Emmy Noether research group and collaborators have already challenged current models of the formation of our Galaxy. In combination with the exquisite information from the Gaia satellite, we found that, contrary to expectations, a significant fraction of the most pristine stars orbits in the disk plane of our Galaxy. Comparison with state-of-the-art simulations demonstrates that these stars probably track the initial build-up of the Milky Way. In the inner galaxy, we have demonstrated for the first time that very metal-poor stars show no net rotation, in sharp contrast to the more enriched populations. Additionally, we find differences in the carbon-toiron elemental ratios of this population when compared to the Galactic halo, which could also be explained by differences in chemical evolution at very early times. We select the very rare most pristine candidates from our photometric observations for more detailed spectroscopic studies. Many new extremely metal-poor stars have already been uncovered by our efforts, among which one of the most chemically pristine stars known. This star has a very special abundance pattern, providing a unique insight in chemical enrichment at the earliest times. A large leap forward in this field is expected in the coming years when the highly multiplexed spectroscopic 4MOST and WEAVE surveys come on line. In collaboration with the Pristine candidate selection we expect to enhance current samples of well-studied chemically pristine stars at least by a factor of ten.
Publications
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"The oldest and most metal-poor stars in the APOSTLE Local Group simulations", 2017, MNRAS, 465, 2212
Starkenburg, E.; Oman, K. A.; Navarro, J. F.; Crain, R. A.; Fattahi, A.; Frenk, C. S.; Sawala, T.; Schaye, J.
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"The Pristine survey I: Mining the Galaxy for the most metal-poor stars", 2017, MNRAS, 471, 2587
Starkenburg, E.; Martin, N.; Youakim, K.; Aguado, D. S.; Allende Prieto, C.; Arentsen, A.; Bernard, E. J.; Bonifacio, P.; Caffau, E.; Carlberg, R. G.; Cote, P.; Fouesneau, M.; Francois, P.; Franke, O.; Gonzalez Hernandez, J. I.; Gwyn, S. D. J.; Hill, V.; Ibata, R. A.; Jablonka, P.; Longeard, N.; McConnachie, A. W.; Navarro, J. F.; Sanchez-Janssen, R.; Tolstoy, E.; Venn, K. A.
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"The Pristine survey III: Spectroscopic confirmation of an efficient search for extremely metal-poor stars", 2017, MNRAS, 472, 2963
Youakim, K.; Starkenburg, E.; Aguado, D. S.; Martin, N. F.; Fouesneau, M.; Gonzalez Hernandez, J. I.; Allende Prieto, C.; Bonifacio, P.,; Gentile, M.; Kielty, C.; Cote, P.; Jablonka, P.; McConnachie, A.,; Sanchez Janssen, R.; Tolstoy, E.; Venn, K.
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"The Pristine Survey IV: Approaching the Galactic metallicity floor with the discovery of an ultra metal-poor star", 2018, MNRAS, 481, 3838
Starkenburg, E.; Aguado, D. S.; Bonifacio, P.; Caffau, E.; Jablonka, P.; Lardo, C.; Martin, N.; Venn, K. A.; Youakim, K.; Allende Prieto, C.; Arentsen, A.; Gentile, M.; Gonzalez Hernandez, J. I.; Kielty, C.; Koppelman, H. H.; Longeard, N.; Sanchez-Janssen, R.; Tolstoy, E.; Carlberg, R.; Cote, P.; Fouesneau, M.; Hill, V.; McConnachie A. W.; Navarro, J. F.; Sestito, F.
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"Tracing the formation of the Milky Way through ultra metal-poor stars", 2019, MNRAS, 484, 2166
Sestito, F.; Longeard, N.; Martin, N. F.; Starkenburg, E.; Fouesneau, M.; González Hernández, J. I.; Arentsen, A.; Ibata, R.; Aguado, D. S.; Carlberg, R. G.; Jablonka, P.; Navarro, J. F.; Tolstoy, E.; Venn, K. A.
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McConnachie, A. W. "Binarity among CEMP-no stars: an indication of multiple formation pathways?" 2019, A&A, 621, 108
Arentsen, A.; Starkenburg, E.; Shetrone, M. D.; Venn, K. A.; Depagne, É.
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“The Pristine survey - VII. A cleaner view of the Galactic outer halo using blue horizontal branch stars”, 2019, MNRAS, 490, 5757
Starkenburg, E.; Youakim, K.; Martin, N.; Thomas, G.; Aguado, D. S.; Arentsen, A.; Carlberg, R. G.; González Hernández, J. I.; Ibata, R.; Longeard, N.; McConnachie, A. W.; Navarro, J.; Sánchez-Janssen, R.; Venn, K. A.
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The Pristine Inner Galaxy Survey (PIGS) II: Uncovering the most metal-poor populations in the inner Milky Way”, 2020, MNRAS, 496, 4964
Arentsen, A.; Starkenburg, E.; Martin, N. F.; Aguado, D. S.; Zucker, D. B.; Allende Prieto, C.; Hill, V.; Venn, K. A.; Carlberg, R. G.; González Hernández, J. I.; Mashonkina, L. I.; Navarro, J. F.; Sánchez-Janssen, R.; Schultheis, M.; Thomas, G. F.; Youakim, K.; Lewis, G. F.; Simpson, J. D.; Wan, Z.; Cohen, R. E. Geisler, D.; O'Connell, J. E.
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“The Pristine Inner Galaxy Survey (PIGS) I: tracing the kinematics of metal-poor stars in the Galactic bulge”, 2020, MNRAS Letters, 491, L11
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.; Youakim, K.; Lewis, G. F.; Simpson, J. D.; Wan, Z.
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“The Pristine Survey - VIII. The metallicity distribution function of the Milky Way halo down to the extremely metal-poor regime”, 2020, MNRAS, 492, 4986
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.
