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arXiv · 2512.04477

The Binary Fraction of Stars in the Dwarf Galaxy Ursa Minor via Dark Energy Spectroscopic Instrument

Tian Qiu·Wenting Wang·Sergey Koposov·Ting S. Li·Nathan R. Sandford·Joan Najita·Songting Li·Jiaxin Han·Arjun Dey·Constance Rockosi·Boris Gaensicke·Jesse Han·Benjamin Alan Weaver·Adam Myers·Jessica Nicole Aguilar·Steven Ahlen·Carlos Allende Prieto·Davide Bianchi·David Brooks·Todd Claybaugh·Axel de la Macorra·Peter Doel·Andreu Font-Ribera·Jaime Forero-Romero·Enrique Gaztanaga·Satya Gontcho A Gontcho·Gaston Gutierrez·Jorge Jimenez·Dick Joyce·Theodore Kisner·Claire Lamman·Martin Landriau·Laurent Le Guillou·Aaron Meisner·Ramon Miquel·Seshadri Nadathur·Will Percival·Claire Poppett·Francisco Prada·Ignasi Perez-Rafols·Graziano Rossi·Eusebio Sanchez·David Schlegel·Joseph Harry Silber·David Sprayberry·Gregory Tarle·Rongpu Zhou·Hu Zou
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Abstract

We utilize multi-epoch line-of-sight velocity measurements from the Milky Way Survey of the Dark Energy Spectroscopic Instrument to estimate the binary fraction for member stars in the dwarf spheroidal galaxy Ursa Minor. Our dataset comprises 670 distinct member stars, with a total of more than 2,000 observations collected over approximately one year. We constrain the binary fraction for UMi to be $0.61^{+0.16}_{-0.20}$ and $0.69^{+0.19}_{-0.17}$, with the binary orbital parameter distributions based on solar neighborhood observation from Duquennoy & Mayor (1991) and Moe & Di Stefano (2017), respectively. Furthermore, by dividing our data into two subsamples at the median metallicity, we identify that the binary fraction for the metal-rich ([Fe/H]>-2.14) population is slightly higher than that of the metal-poor ([Fe/H]<-2.14) population. Based on the Moe & Di Stefano model, the best-constrained binary fractions for metal-rich and metal-poor populations in UMi are $0.86^{+0.14}_{-0.24}$ and $0.48^{+0.26}_{-0.19}$, respectively. After a thorough examination, we find that this offset cannot be attributed to sample selection effects. We also divide our data into two subsamples according to their projected radius to the center of UMi, and find that the more centrally concentrated population in a denser environment has a lower binary fraction of $0.33^{+0.30}_{-0.20}$, compared with $1.00^{+0.00}_{-0.32}$ for the subsample in more outskirts.

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Tian Qiu, Wenting Wang, Sergey Koposov, Ting S. Li, Nathan R. Sandford, Joan Najita, Songting Li, Jiaxin Han, Arjun Dey, Constance Rockosi, Boris Gaensicke, Jesse Han, Benjamin Alan Weaver, Adam Myers, Jessica Nicole Aguilar, Steven Ahlen, Carlos Allende Prieto, Davide Bianchi, David Brooks, Todd Claybaugh, Axel de la Macorra, Peter Doel, Andreu Font-Ribera, Jaime Forero-Romero, Enrique Gaztanaga, Satya Gontcho A Gontcho, Gaston Gutierrez, Jorge Jimenez, Dick Joyce, Theodore Kisner, Claire Lamman, Martin Landriau, Laurent Le Guillou, Aaron Meisner, Ramon Miquel, Seshadri Nadathur, Will Percival, Claire Poppett, Francisco Prada, Ignasi Perez-Rafols, Graziano Rossi, Eusebio Sanchez, David Schlegel, Joseph Harry Silber, David Sprayberry, Gregory Tarle, Rongpu Zhou, Hu Zou. 2025-12-04. The Binary Fraction of Stars in the Dwarf Galaxy Ursa Minor via Dark Energy Spectroscopic Instrument. https://doi.org/10.3847/1538-4357/ae422d

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