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Properties of the Milky Way's Old Populations Based on Photometric Metallicities of the OGLE RR Lyrae Stars

Pietrukowicz, P. and Udalski, A. and Soszyński, I. and Skowron, D. M. and Wrona, M. and Szymański, M. K. and Poleski, R. and Ulaczyk, K. and Kozłowski, S. and Skowron, J. and Mróz, P. and Rybicki, K. and Iwanek, P. and Gromadzki, M. (2020) Properties of the Milky Way's Old Populations Based on Photometric Metallicities of the OGLE RR Lyrae Stars. Acta Astronomica, 70 (2). pp. 121-139. ISSN 0001-5237. https://resolver.caltech.edu/CaltechAUTHORS:20201026-151803750

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Abstract

We have used photometric data on almost 91 000 fundamental-mode RR Lyr stars (type RRab) detected by the OGLE survey to investigate properties of old populations in the Milky Way. Based on their metallicity distributions, we demonstrate that the Galaxy is built from three distinct old components: halo, bulge, and disk. The distributions reach their maxima at approximately [Fe/H]_(J95) = -1.2 dex, -1.0 dex, and -0.6 dex on the Jurcsik's metallicity scale, respectively. We find that, very likely, the entire halo is formed from infalling dwarf galaxies. It is evident that halo stars penetrate the inner regions of the Galactic bulge. We estimate that about one-third of all RR Lyr stars within the bulge area belong in fact to the halo population. The whole old bulge is dominated by two populations, A and B, represented by a double sequence in the period--amplitude (Bailey) diagram. The boundary in iron abundance between the halo and the disk population is at about [Fe/H]_(J95) = -0.8 dex. Using Gaia DR2 for RRab stars in the disk area, we show that the observed dispersion of proper motions along the Galactic latitude decreases smoothly with the increasing metal content excluding a bump around [Fe/H]_(J95) = -1.0 dex.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.32023/0001-5237/70.2.3DOIArticle
https://arxiv.org/abs/2007.05849arXivDiscussion Paper
ORCID:
AuthorORCID
Pietrukowicz, P.0000-0002-2339-5899
Udalski, A.0000-0001-5207-5619
Skowron, D. M.0000-0001-9439-604X
Poleski, R.0000-0002-9245-6368
Ulaczyk, K.0000-0001-6364-408X
Skowron, J.0000-0002-2335-1730
Mróz, P.0000-0001-7016-1692
Iwanek, P.0000-0002-6212-7221
Gromadzki, M.0000-0002-1650-1518
Additional Information:© 2020 Copernicus Foundation for Polish Astronomy. Received: July 10, 2020. We thank OGLE observers for their contribution to the collection of the photometric data over the years. The OGLE project has received funding from the National Science Centre, Poland, grant MAESTRO 2014/14/A/ST9/00121 to A.U. This work has been supported by the National Science Centre, Poland, grants OPUS 2016/23/B/ST9/00655 to P.P. and MAESTRO 2016/22/A/ST9/00009 to I.S. In this research, we used data from the European Space Agency (ESA) mission Gaia, processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
Funders:
Funding AgencyGrant Number
National Science Centre (Poland)MAESTRO 2014/14/A/ST9/00121
National Science Centre (Poland)OPUS 2016/23/B/ST9/00655
National Science Centre (Poland)MAESTRO 2016/22/A/ST9/00009
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:Galaxy: bulge - Galaxy: disk - Galaxy: halo - Stars: variables: RR Lyrae
Issue or Number:2
Record Number:CaltechAUTHORS:20201026-151803750
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20201026-151803750
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106280
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:26 Oct 2020 22:48
Last Modified:26 Oct 2020 22:48

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