The enigmatic globular cluster UKS 1 obscured by the bulge: H-band discovery of nitrogen-enhanced stars

Author(s):Show less -

Fernandez-Trincado, Jose G. ^{[1, 2]} ; Minniti, Dante ^{[3, 4]} ; Beers, Timothy C. ^{[5, 6]} ; Villanova, Sandro ^[7] ; Geisler, Doug ^{[7, 8, 9]} ; Souza, Stefano O. ^[10] ; Smith, Leigh C. ^[11] ; Placco, Vinicius M. ^[12] ; Vieira, Katherine ^[1] ; Perez-Villegas, Angeles ^[10] ; Barbuy, Beatriz ^[10] ; Alves-Brito, Alan ^[13] ; Moni Bidin, Christian ^[14] ; Alonso-Garcia, Javier ^{[15, 16]} ; Tang, Baitian ^[17] ; Palma, Tali ^{[18, 19]}

Affiliation:Show less -

^[1] Univ Atacama, Inst Astron & Ciencias Planetarias, Copayapu 485, Copiapo - Chile

^[2] Univ Bourgogne Franche Comte, Inst Utinam, CNRS UMR 6213, OSU THETA Franche Comte, Observ Besancon, BP 1615, F-251010 Besancon - France

^[3] Vatican Observ, I-00120 Vatican City - Vatican

^[4] Univ Andres Bello, Dept Cs Fis, Fac Ciencias Exactas, Av Fernandez Concha 700, Santiago - Chile

^[5] Univ Notre Dame, Dept Phys, Notre Dame, IN 46556 - USA

^[6] Univ Notre Dame, JINA Ctr Evolut Elements, Notre Dame, IN 46556 - USA

^[7] Univ Concepcion, Dept Astron, Casilla 160-C, Concepcion - Chile

^[8] Univ La Serena, Dept Astron, Ave Juan Cisternas 1200, La Serena - Chile

^[9] Univ La Serena, Inst Invest Multidisciplinario Ciencia & Tecnol, Benavente 980, La Serena - Chile

^[10] Univ Sao Paulo, IAG, Rua Matao 1226, Cidade Univ, BR-05508900 Sao Paulo - Brazil

^[11] Univ Cambridge, Inst Astron, Madingley Rd, Cambridge CB3 0HA - England

^[12] NSFs Opt Infrared Astron Res Lab, Tucson, AZ 85719 - USA

^[13] Univ Fed Rio Grande do Sul, Inst Fis, Av Bento Goncalves 9500, Porto Alegre, RS - Brazil

^[14] Univ Catolica Norte, Inst Astron, Av Angamos 0610, Antofagasta - Chile

^[15] Millennium Inst Astrophys, Santiago - Chile

^[16] Univ Antofagasta, Ctr Astron CITEVA, Av Angamos 601, Antofagasta - Chile

^[17] Sun Yat Sen Univ, Sch Phys & Astron, Zhuhai 519082 - Peoples R China

^[18] Univ Nacl Cordoba, Observ Astronom Cordoba, Laprida 854, RA-5000 Cordoba - Argentina

^[19] Consejo Nacl Invest Cient & Tecn CONICET, Godoy Cruz 2290, Buenos Aires, DF - Argentina

• Document type: Journal article
• Source: Astronomy & Astrophysics; v. 643, NOV 17 2020.
• Web of Science Citations: 1

Abstract

The presence of nitrogen-enriched stars in globular clusters provides key evidence for multiple stellar populations (MPs), as has been demonstrated with globular cluster spectroscopic data towards the bulge, disk, and halo. In this work, we employ the VVV Infrared Astrometric Catalogue (VIRAC) and the DR16 SDSS-IV release of the APOGEE survey to provide the first detailed spectroscopic study of the bulge globular cluster UKS 1. Based on these data, a sample of six selected cluster members was studied. We find the mean metallicity of UKS 1 to be {[}Fe /H] = 0.98 +/- 0.11, considerably more metal-poor than previously reported, and a negligible metallicity scatter, typical of that observed by APOGEE in other Galactic globular clusters. In addition, we find a mean radial velocity of 66.1 +/- 12.9 km s(-1), which is in good agreement with literature values, within 1 sigma. By selecting stars in the VIRAC catalogue towards UKS1, we also measure a mean proper motion of (mu alpha cos(delta), mu(delta)) = ( 2.77 +/- 0.23, 2.43 +/- 0.16) mas yr(-1). We find strong evidence for the presence of MPs in UKS1, since four out of the six giants analysed in this work have strong enrichment in nitrogen ({[}N /Fe] greater than or similar to +0.95) accompanied by lower carbon abundances ({[}C /Fe]. 0.2). Overall, the light- (C, N), ff- (O, Mg, Si, Ca, Ti), Fe-peak (Fe, Ni), Odd-Z (Al, K), and the s-process (Ce, Nd, Yb) elemental abundances of our member candidates are consistent with those observed in globular clusters at similar metallicity. Furthermore, the overall star-to-star abundance scatter of elements exhibiting the multiple-population phenomenon in UKS 1 is typical of that found in other global clusters (GCs), and larger than the typical errors of some {[}X /Fe] abundances. Results from statistical isochrone fits in the VVV colour-magnitude diagrams indicate an age of 13.10(-1).(+0)(29).(93) Gyr, suggesting that UKS 1 is a fossil relic in the Galactic bulge. (AU)

• FAPESP's process: 17/15893-1 - Globular cluster orbits of bulge: the formation and evolution of the Milky Way
• Grantee: Maria de Los Angeles Perez Villegas
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 18/22044-3 - Bulge globular clusters: relics of the early formation of the galaxy
• Grantee: Stefano Oliveira de Souza
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)