Spitzer Microlensing Parallax for OGLE-2017-BLG-0896 Reveals a Counter-rotating Low-mass Brown Dwarf

Shvartzvald, Yossi; Yee, Jennifer C.; Skowron, J.; Lee, Chung-Uk; Udalski, A.; Novati, S. Calchi; Bozza, V.; Beichman, Charles; Bryden, G.; Carey, Sean; Gaudi, B. Scott; Henderson, Calen B.; Zhu, Wei; Bachelet, E.; Bolt, Greg; Christie, Grant; Maoz, Dan; Natusch, T.; Pogge, Richard W.; Street, R. A.; Tan, T. G.; Tsapras, Y.; Pietrukowicz, P.; Szymański, M. K.; Mróz, P.; Poleski, R.; Ulaczyk, K.; Pawlak, M.; Rybicki, K.; Iwanek, P.; Albrow, M. D.; Cha, Sang-Mok; Chung, Sun-Ju; Gould, Andrew; Han, Cheongho; Hwang, Kyu-Ha; Jung, Youn Kil; Kim, Dong-Jin; Kim, Hyoun-Woo; Kim, Seung‐Lee; Lee, Dong-Joo; Lee, Yongseok; Park, Byeong-Gon; Ryu, Yoon-Hyun; Shin, In-Gu; Zang, Weicheng; Dominik, M.; Helling, Christiane; Hundertmark, M.; Jørgensen, U. G.; Longa-Peña, Penélope; Lowry, S. C.; Sajadian, Sedighe; Burgdorf, M.; Campbell-White, J.; Ciceri, S.; Evans, D. F.; Fujii, Yuri I.; Hinse, T. C.; Rahvar, S.; Rabus, M.; Skottfelt, J.; Snodgrass, C.; Southworth, J.

doi:10.3847/1538-3881/aafe12

Cited by 28 publications

(24 citation statements)

References 55 publications

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“…We note that the limb-darkening effect is a high-order effect in microlensing modelling, hence measurement of its coefficients from light-curve analysis is usually a difficult task. In the cases where dense-coverage and good-quality data are available, the measured coefficients are generally in good agreement with theoretical values (Choi et al 2012;Shvartzvald et al 2019). In other cases, large differences (but with large uncertainties) between the measured results and the theoretical values are common (Fouqué et al 2010).…”

Section: Microlensing Modelmentioning

confidence: 51%

“…Although few, M giants play important roles in single events, as finite-source effects are strongly biased toward large (hence, bright and red) source stars (Shvartzvald et al 2019). In fact, the three free-floating planet candidates with finite-source effects measured all have M-giant sources (Mróz et al 2018;OGLE Collaboration et al 2019).…”

Section: Summary and Discussionmentioning

confidence: 99%

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OGLE-2017-BLG-1186: first application of asteroseismology and Gaussian processes to microlensing

Li¹,

Zang²,

Udalski³

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Abstract We present the analysis of the event OGLE-2017-BLG-1186 from the 2017 Spitzer microlensing campaign. This is a remarkable microlensing event because its source is photometrically bright and variable, which makes it possible to perform an asteroseismic analysis using ground-based data. We find that the source star is an oscillating red giant with average time-scale of ∼9 d. The asteroseismic analysis also provides us source properties including the source angular size (∼27 $\mu$as) and distance (∼11.5 kpc), which are essential for inferring the properties of the lens. When fitting the light curve, we test the feasibility of Gaussian processes (GPs) in handling the correlated noise caused by the variable source. We find that the parameters from the GP model are generally more loosely constrained than those from the traditional χ2 minimization method. We note that this event is the first microlensing system for which asteroseismology and GPs have been used to account for the variable source. With both finite-source effect and microlens parallax measured, we find that the lens is likely a ∼0.045 M⊙ brown dwarf at distance ∼9.0 kpc, or a ∼0.073 M⊙ ultracool dwarf at distance ∼9.8 kpc. Combining the estimated lens properties with a Bayesian analysis using a Galactic model, we find a $\sim 35{{\ \rm per\ cent}}$ probability for the lens to be a bulge object and $\sim 65{{\ \rm per\ cent}}$ to be a background disc object.

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Section: Microlensing Modelmentioning

confidence: 51%

Section: Summary and Discussionmentioning

confidence: 99%

OGLE-2017-BLG-1186: first application of asteroseismology and Gaussian processes to microlensing

Li¹,

Zang²,

Udalski³

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Such discoveries are crucial for testing theories about the origin and evolution of free-floating planets (Veras & Raymond 2012;Pfyffer et al 2015;Ma et al 2016; Barclay et al 2017;Clanton & Gaudi 2017). For more massive objects (i.e., isolated brown dwarfs), five have been discovered by microlensing: OGLE-2007-BLG-224L (Gould et al 2009, OGLE-2015-BLG-1268L (Zhu et al 2016), OGLE-2015-BLG-1482 58 (Chung et al 2017), OGLE-2017-BLG-0896 (Shvartzvald et al 2019), and OGLE-2017-BLG-1186 59 (Li et al 2019). Shvartzvald et al (2019) recently announced the discovery of an isolated, extremely low-mass brown dwarf of M∼19 M J , with proper motion in the opposite direction of disk stars, which indicates that it might be a halo brown dwarf or from a different, unknown counter-rotating population.…”

Section: Introductionmentioning

confidence: 99%

“…For more massive objects (i.e., isolated brown dwarfs), five have been discovered by microlensing: OGLE-2007-BLG-224L (Gould et al 2009, OGLE-2015-BLG-1268L (Zhu et al 2016), OGLE-2015-BLG-1482 58 (Chung et al 2017), OGLE-2017-BLG-0896 (Shvartzvald et al 2019), and OGLE-2017-BLG-1186 59 (Li et al 2019). Shvartzvald et al (2019) recently announced the discovery of an isolated, extremely low-mass brown dwarf of M∼19 M J , with proper motion in the opposite direction of disk stars, which indicates that it might be a halo brown dwarf or from a different, unknown counter-rotating population. At the high-mass end, Gould (2000a) estimated that ∼20% of microlensing events observed toward the Galactic bulge are caused by stellar remnants, and specifically that ∼1% are due to stellar-mass black holes, with another ∼3% due to neutronstar lenses.…”

Section: Introductionmentioning

confidence: 99%

Spitzer Microlensing Parallax Reveals Two Isolated Stars in the Galactic Bulge

Zang¹,

Shvartzvald²,

Udalski³

et al. 2020

ApJ

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We report the mass and distance measurements of two single-lens events from the 2017 Spitzer microlensing campaign. The ground-based observations yield the detection of finite-source effects, and the microlens parallaxes are derived from the joint analysis of ground-based observations and Spitzer observations. We find that the lens of OGLE-2017-BLG-1254 is a 0.60±0.03 M e star with D LS =0.53±0.11 kpc, where D LS is the distance between the lens and the source. The second event, OGLE-2017-BLG-1161, is subject to the known satellite parallax degeneracy, and thus is either a -+ M 0.51 0.10 0.12 star with D LS =0.40±0.12 kpc or a -+ M 0.38 0.12 0.13 star with D LS =0.53±0.19 kpc. Both of the lenses are therefore isolated stars in the Galactic bulge. By comparing the mass and distance distributions of the eight published Spitzer finite-source events with the expectations from a Galactic model, we find that the Spitzer sample is in agreement with the probability of finite-source effects occurring in single-lens events.

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“…40 The CFHT Mircolensing Collaboration. populations, including binary brown dwarfs (Albrow et al 2018), single-mass objects (Zhu et al 2016;Chung et al 2017;Shin et al 2018;Shvartzvald et al 2019), and planetary systems Street et al 2016;Shvartzvald et al 2017b;Calchi Novati et al 2018Ryu et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Spitzer Parallax of OGLE-2018-BLG-0596: A Low-mass-ratio Planet around an M Dwarf

Jung

Gould

Udalski

et al. 2019

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We report the discovery of a Spitzer microlensing planet OGLE-2018-BLG-0596Lb, with preferred planet-host mass ratio q∼2×10 −4 . The planetary signal, which is characterized by a short (∼1 day) "bump" on the rising side of the lensing light curve, was densely covered by ground-based surveys. We find that the signal can be explained by a bright source that fully envelops the planetary caustic, i.e., a "Hollywood" geometry. Combined with the source proper motion measured from Gaia, the Spitzer satellite parallax measurement makes it possible to precisely constrain the lens physical parameters. The preferred solution, in which the planet perturbs the minor image due to lensing by the host, yields a Uranus-mass planet with a mass of M p =13.9±1.6M ⊕ orbiting a mid M-dwarf with a mass of M h =0.23±0.03M e . There is also a second possible solution that is substantially disfavored but cannot be ruled out, for which the planet perturbs the major image. The latter solution yields M p =1.2±0.2M ⊕ and M h =0.15±0.02M e . By combining the microlensing and Gaia data together with a Galactic model, we find in either case that the lens lies on the near side of the Galactic bulge at a distance D L ∼6±1 kpc. Future adaptive optics observations may decisively resolve the major image/minor image degeneracy.

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Spitzer Microlensing Parallax for OGLE-2017-BLG-0896 Reveals a Counter-rotating Low-mass Brown Dwarf

Cited by 28 publications

References 55 publications

OGLE-2017-BLG-1186: first application of asteroseismology and Gaussian processes to microlensing

OGLE-2017-BLG-1186: first application of asteroseismology and Gaussian processes to microlensing

Spitzer Microlensing Parallax Reveals Two Isolated Stars in the Galactic Bulge

Spitzer Parallax of OGLE-2018-BLG-0596: A Low-mass-ratio Planet around an M Dwarf

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