Browsing by Author "Carey S"

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    Analysis of the Full Spitzer Microlensing Sample. I. Dark Remnant Candidates and Gaia Predictions
    (American Astronomical Society, 2024-11-10) Rybicki KA; Shvartzvald Y; Yee JC; Novati SC; Ofek EO; Bond IA; Beichman C; Bryden G; Carey S; Henderson C; Zhu W; Fausnaugh MM; Wibking B; Udalski A; Poleski R; Mróz P; Szymański MK; Soszyński I; Pietrukowicz P; Kozłowski S; Skowron J; Ulaczyk K; Iwanek P; Wrona M; Ryu Y-H; Albrow MD; Chung S-J; Gould A; Han C-H; Hwang K-H; Jung YK; Shin I-G; Yang H; Zang W; Cha S-M; Kim D-J; Kim H-W; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge RW; Abe F; Barry R; Bennett DP; Bhattacharya A; Fukui A; Hamada R; Hamada S; Hamasaki N; Hirao Y; Ishitani Silva S; Itow Y; Kirikawa R; Koshimoto N; Matsubara Y; Miyazaki S; Muraki Y; Nagai T; Nunota K; Olmschenk G; Ranc C; Rattenbury NJ; Satoh YK; Sumi T; Suzuki D; Tristram PJ; Vandorou A; Yama H; Wyrzykowski Ł; Howil K; Kruszyńska K
    In the pursuit of understanding the population of stellar remnants within the Milky Way, we analyze the sample of ∼950 microlensing events observed by the Spitzer Space Telescope between 2014 and 2019. In this study we focus on a subsample of nine microlensing events, selected based on their long timescales, small microlensing parallaxes, and joint observations by the Gaia mission, to increase the probability that the chosen lenses are massive and the mass is measurable. Among the selected events we identify lensing black holes and neutron star candidates, with potential confirmation through forthcoming release of the Gaia time-series astrometry in 2026. Utilizing Bayesian analysis and Galactic models, along with the Gaia Data Release 3 proper-motion data, four good candidates for dark remnants were identified: OGLE-2016-BLG-0293, OGLE-2018-BLG-0483, OGLE-2018-BLG-0662, and OGLE-2015-BLG-0149, with lens masses of 3.0-1.3+1.8M☉, 4.7-2.1+3.2 M☉, 3.15-0.64+0..66 M☉ and 1.40-0.55+0.75 M☉, respectively. Notably, the first two candidates are expected to exhibit astrometric microlensing signals detectable by Gaia, offering the prospect of validating the lens masses. The methodologies developed in this work will be applied to the full Spitzer microlensing sample, populating and analyzing the timescale (tE) versus parallax (πE) diagram to derive constraints on the population of lenses in general and massive remnants in particular.
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    OGLE-2015-BLG-0845L: a low-mass M dwarf from the microlensing parallax and xallarap effects
    (Oxford University Press, 2024-09-01) Hu Z; Zhu W; Gould A; Udalski A; Sumi T; Chen P; Calchi Novati S; Yee JC; Beichman CA; Bryden G; Carey S; Fausnaugh M; Scott Gaudi B; Henderson CB; Shvartzvald Y; Wibking B; Mroz P; Skowron J; Poleski R; Szymanski MK; Soszynski I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Wrona M; Gromadzki MG; Abe F; Barry R; Bennett DP; Bhattacharya A; Bond IA; Fujii H; Fukui A; Hamada R; Hirao Y; Silva SI; Itow Y; Kirikawa R; Koshimoto N; Matsubara Y; Miyazaki S; Muraki Y; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Suzuki D; Tomoyoshi M; Tristram PJ; Vandorou A; Yama H; Yamashita K
    We present the analysis of the microlensing event OGLE-2015-BLG-0845, which was affected by both the microlensing parallax and xallarap effects. The former was detected via the simultaneous observations from the ground and Spitzer, and the latter was caused by the orbital motion of the source star in a relatively close binary. The combination of these two effects led to a mass measurement of the lens object, revealing a low-mass (0.14 ± 0.05 M) M dwarf at the bulge distance (7.6 ± 1.0 kpc). The source binary consists of a late F-type subgiant and a K-type dwarf of ∼ 1.2 and ∼ 0.9M, respectively, and the orbital period is 70 ± 10 d. OGLE-2015-BLG-0845 is the first single-lens event in which the lens mass is measured via the binarity of the source. Given the abundance of binary systems as potential microlensing sources, the xallarap effect may not be a rare phenomenon. Our work thus highlights the application of the xallarap effect in the mass determination of microlenses, and the same method can be used to identify isolated dark lenses.