OGLE-2015-BLG-1609Lb: a sub-Jovian planet orbiting a low-mass stellar or brown dwarf host

M. J. Mróz; R. Poleski; A. Udalski; T. Sumi; Y. Tsapras; M. Hundertmark; P. Pietrukowicz; M. K. Szymański; J. Skowron; P. Mróz; M. Gromadzki; P. Iwanek; S. Kozłowski; M. Ratajczak; K. A. Rybicki; D. M. Skowron; I. Soszyński; K. Ulaczyk; M. Wrona; F. Abe; K. Bando; D. P. Bennett; A. Bhattacharya; I. A. Bond; A. Fukui; R. Hamada; S. Hamada; N. Hamasaki; Y. Hirao; S. Ishitani Silva; Y. Itow; N. Koshimoto; Y. Matsubara; S. Miyazaki; Y. Muraki; T. Nagai; K. Nunota; G. Olmschenk; C. Ranc; N. J. Rattenbury; Y. Satoh; D. Suzuki; S. K. Terry; P. J. Tristram; A. Vandorou; H. Yama; R. A. Street; M. Dominik; R. Figuera Jaimes; K. Horne

doi:10.1051/0004-6361/202453454

OGLE-2015-BLG-1609Lb: a sub-Jovian planet orbiting a low-mass stellar or brown dwarf host

M. J. Mróz^*, R. Poleski, A. Udalski, T. Sumi, Y. Tsapras, M. Hundertmark, P. Pietrukowicz, M. K. Szymański, J. Skowron, P. Mróz, M. Gromadzki, P. Iwanek, S. Kozłowski, M. Ratajczak, K. A. Rybicki, D. M. Skowron, I. Soszyński, K. Ulaczyk, M. Wrona, F. AbeK. Bando, D. P. Bennett, A. Bhattacharya, I. A. Bond, A. Fukui, R. Hamada, S. Hamada, N. Hamasaki, Y. Hirao, S. Ishitani Silva, Y. Itow, N. Koshimoto, Y. Matsubara, S. Miyazaki, Y. Muraki, T. Nagai, K. Nunota, G. Olmschenk, C. Ranc, N. J. Rattenbury, Y. Satoh, D. Suzuki, S. K. Terry, P. J. Tristram, A. Vandorou, H. Yama, R. A. Street, M. Dominik, R. Figuera Jaimes, K. Horne

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

Abstract

We present a comprehensive analysis of the planetary microlensing event OGLE-2015-BLG-1609. The planetary anomaly was detected by two survey telescopes, OGLE and MOA. Both surveys collected enough data over the planetary anomaly to enable an unambiguous planet detection. Such survey detections of planetary anomalies are needed to build a robust sample of planets, which could improve studies on the microlensing planetary occurrence rate by reducing biases and statistical uncertainties. In this work we examined different methods for modeling microlensing events using individual datasets. In particular, we incorporated a Galactic model prior to better constrain the poorly defined microlensing parallax. Ultimately, we fitted a comprehensive model to all available data, identifying three potential topologies, with two showing comparably high Bayesian evidence. Our analysis indicates that the host of the planet is either a brown dwarf, with a probability of 34%, or a low-mass stellar object (M dwarf), with a probability of 66%. The topology that provides the best fit to the data results in an extraordinary low host mass, M_h = 0.025^+0.050_-0.012M_⊙, accompanied by an Earth-mass planet with M_c = 1.9^+3.9_-1.0M_⊕.

Original language	English
Pages (from-to)	A126
Number of pages	12
Journal	Astronomy & Astrophysics
Volume	698
DOIs	https://doi.org/10.1051/0004-6361/202453454
Publication status	Published - 12 Jun 2025

Keywords

Gravitation
Gravitational lensing: micro
Planets and satellites: detection

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© The Authors 2025. Open Access article, published under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Mróz, M. J., Poleski, R., Udalski, A., Sumi, T., Tsapras, Y., Hundertmark, M., Pietrukowicz, P., Szymański, M. K., Skowron, J., Mróz, P., Gromadzki, M., Iwanek, P., Kozłowski, S., Ratajczak, M., Rybicki, K. A., Skowron, D. M., Soszyński, I., Ulaczyk, K., Wrona, M., ... Horne, K. (2025). OGLE-2015-BLG-1609Lb: a sub-Jovian planet orbiting a low-mass stellar or brown dwarf host. Astronomy & Astrophysics, 698, A126. https://doi.org/10.1051/0004-6361/202453454

@article{d1d49f97442a4b11af37985f77793689,

title = "OGLE-2015-BLG-1609Lb: a sub-Jovian planet orbiting a low-mass stellar or brown dwarf host",

abstract = "We present a comprehensive analysis of the planetary microlensing event OGLE-2015-BLG-1609. The planetary anomaly was detected by two survey telescopes, OGLE and MOA. Both surveys collected enough data over the planetary anomaly to enable an unambiguous planet detection. Such survey detections of planetary anomalies are needed to build a robust sample of planets, which could improve studies on the microlensing planetary occurrence rate by reducing biases and statistical uncertainties. In this work we examined different methods for modeling microlensing events using individual datasets. In particular, we incorporated a Galactic model prior to better constrain the poorly defined microlensing parallax. Ultimately, we fitted a comprehensive model to all available data, identifying three potential topologies, with two showing comparably high Bayesian evidence. Our analysis indicates that the host of the planet is either a brown dwarf, with a probability of 34\%, or a low-mass stellar object (M dwarf), with a probability of 66\%. The topology that provides the best fit to the data results in an extraordinary low host mass, Mh = 0.025+0.050-0.012 M⊙, accompanied by an Earth-mass planet with Mc = 1.9+3.9-1.0 M⊕.",

keywords = "Gravitation, Gravitational lensing: micro, Planets and satellites: detection",

author = "Mr{\'o}z, \{M. J.\} and R. Poleski and A. Udalski and T. Sumi and Y. Tsapras and M. Hundertmark and P. Pietrukowicz and Szyma{\'n}ski, \{M. K.\} and J. Skowron and P. Mr{\'o}z and M. Gromadzki and P. Iwanek and S. Koz{\l}owski and M. Ratajczak and Rybicki, \{K. A.\} and Skowron, \{D. M.\} and I. Soszy{\'n}ski and K. Ulaczyk and M. Wrona and F. Abe and K. Bando and Bennett, \{D. P.\} and A. Bhattacharya and Bond, \{I. A.\} and A. Fukui and R. Hamada and S. Hamada and N. Hamasaki and Y. Hirao and \{Ishitani Silva\}, S. and Y. Itow and N. Koshimoto and Y. Matsubara and S. Miyazaki and Y. Muraki and T. Nagai and K. Nunota and G. Olmschenk and C. Ranc and Rattenbury, \{N. J.\} and Y. Satoh and D. Suzuki and Terry, \{S. K.\} and Tristram, \{P. J.\} and A. Vandorou and H. Yama and Street, \{R. A.\} and M. Dominik and \{Figuera Jaimes\}, R. and K. Horne",

note = "Funding: The work by Rados{\l}aw Poleski was partly supported by the Polish National Agency for Academic Exchange grant “Polish Returns 2019”. The MOA project is supported by JSPS KAKENHI Grant Number JP24253004, JP26247023,JP16H06287 and JP22H00153. YT acknowledges the support of the DFG priority program SPP 1992 “Exploring the Diversity of Extrasolar Planets” (TS 356/3-1). R.F.J. acknowledges support for this project provided by ANID{\textquoteright}s Millennium Science Initiative through grant ICN12\_009, awarded to the Millennium Institute of Astrophysics (MAS), and by ANID{\textquoteright}s Basal project FB210003. L.M. acknowledges financial contribution from PRIN MUR 2022 project 2022J4H55R.",

year = "2025",

month = jun,

day = "12",

doi = "10.1051/0004-6361/202453454",

language = "English",

volume = "698",

pages = "A126",

journal = "Astronomy \& Astrophysics",

issn = "0004-6361",

publisher = "EDP Sciences",

}

Mróz, MJ, Poleski, R, Udalski, A, Sumi, T, Tsapras, Y, Hundertmark, M, Pietrukowicz, P, Szymański, MK, Skowron, J, Mróz, P, Gromadzki, M, Iwanek, P, Kozłowski, S, Ratajczak, M, Rybicki, KA, Skowron, DM, Soszyński, I, Ulaczyk, K, Wrona, M, Abe, F, Bando, K, Bennett, DP, Bhattacharya, A, Bond, IA, Fukui, A, Hamada, R, Hamada, S, Hamasaki, N, Hirao, Y, Ishitani Silva, S, Itow, Y, Koshimoto, N, Matsubara, Y, Miyazaki, S, Muraki, Y, Nagai, T, Nunota, K, Olmschenk, G, Ranc, C, Rattenbury, NJ, Satoh, Y, Suzuki, D, Terry, SK, Tristram, PJ, Vandorou, A, Yama, H, Street, RA, Dominik, M, Figuera Jaimes, R & Horne, K 2025, 'OGLE-2015-BLG-1609Lb: a sub-Jovian planet orbiting a low-mass stellar or brown dwarf host', Astronomy & Astrophysics, vol. 698, pp. A126. https://doi.org/10.1051/0004-6361/202453454

TY - JOUR

T1 - OGLE-2015-BLG-1609Lb

T2 - a sub-Jovian planet orbiting a low-mass stellar or brown dwarf host

AU - Mróz, M. J.

AU - Poleski, R.

AU - Udalski, A.

AU - Sumi, T.

AU - Tsapras, Y.

AU - Hundertmark, M.

AU - Pietrukowicz, P.

AU - Szymański, M. K.

AU - Skowron, J.

AU - Mróz, P.

AU - Gromadzki, M.

AU - Iwanek, P.

AU - Kozłowski, S.

AU - Ratajczak, M.

AU - Rybicki, K. A.

AU - Skowron, D. M.

AU - Soszyński, I.

AU - Ulaczyk, K.

AU - Wrona, M.

AU - Abe, F.

AU - Bando, K.

AU - Bennett, D. P.

AU - Bhattacharya, A.

AU - Bond, I. A.

AU - Fukui, A.

AU - Hamada, R.

AU - Hamada, S.

AU - Hamasaki, N.

AU - Hirao, Y.

AU - Ishitani Silva, S.

AU - Itow, Y.

AU - Koshimoto, N.

AU - Matsubara, Y.

AU - Miyazaki, S.

AU - Muraki, Y.

AU - Nagai, T.

AU - Nunota, K.

AU - Olmschenk, G.

AU - Ranc, C.

AU - Rattenbury, N. J.

AU - Satoh, Y.

AU - Suzuki, D.

AU - Terry, S. K.

AU - Tristram, P. J.

AU - Vandorou, A.

AU - Yama, H.

AU - Street, R. A.

AU - Dominik, M.

AU - Figuera Jaimes, R.

AU - Horne, K.

N1 - Funding: The work by Radosław Poleski was partly supported by the Polish National Agency for Academic Exchange grant “Polish Returns 2019”. The MOA project is supported by JSPS KAKENHI Grant Number JP24253004, JP26247023,JP16H06287 and JP22H00153. YT acknowledges the support of the DFG priority program SPP 1992 “Exploring the Diversity of Extrasolar Planets” (TS 356/3-1). R.F.J. acknowledges support for this project provided by ANID’s Millennium Science Initiative through grant ICN12_009, awarded to the Millennium Institute of Astrophysics (MAS), and by ANID’s Basal project FB210003. L.M. acknowledges financial contribution from PRIN MUR 2022 project 2022J4H55R.

PY - 2025/6/12

Y1 - 2025/6/12

N2 - We present a comprehensive analysis of the planetary microlensing event OGLE-2015-BLG-1609. The planetary anomaly was detected by two survey telescopes, OGLE and MOA. Both surveys collected enough data over the planetary anomaly to enable an unambiguous planet detection. Such survey detections of planetary anomalies are needed to build a robust sample of planets, which could improve studies on the microlensing planetary occurrence rate by reducing biases and statistical uncertainties. In this work we examined different methods for modeling microlensing events using individual datasets. In particular, we incorporated a Galactic model prior to better constrain the poorly defined microlensing parallax. Ultimately, we fitted a comprehensive model to all available data, identifying three potential topologies, with two showing comparably high Bayesian evidence. Our analysis indicates that the host of the planet is either a brown dwarf, with a probability of 34%, or a low-mass stellar object (M dwarf), with a probability of 66%. The topology that provides the best fit to the data results in an extraordinary low host mass, Mh = 0.025+0.050-0.012 M⊙, accompanied by an Earth-mass planet with Mc = 1.9+3.9-1.0 M⊕.

AB - We present a comprehensive analysis of the planetary microlensing event OGLE-2015-BLG-1609. The planetary anomaly was detected by two survey telescopes, OGLE and MOA. Both surveys collected enough data over the planetary anomaly to enable an unambiguous planet detection. Such survey detections of planetary anomalies are needed to build a robust sample of planets, which could improve studies on the microlensing planetary occurrence rate by reducing biases and statistical uncertainties. In this work we examined different methods for modeling microlensing events using individual datasets. In particular, we incorporated a Galactic model prior to better constrain the poorly defined microlensing parallax. Ultimately, we fitted a comprehensive model to all available data, identifying three potential topologies, with two showing comparably high Bayesian evidence. Our analysis indicates that the host of the planet is either a brown dwarf, with a probability of 34%, or a low-mass stellar object (M dwarf), with a probability of 66%. The topology that provides the best fit to the data results in an extraordinary low host mass, Mh = 0.025+0.050-0.012 M⊙, accompanied by an Earth-mass planet with Mc = 1.9+3.9-1.0 M⊕.

KW - Gravitation

KW - Gravitational lensing: micro

KW - Planets and satellites: detection

U2 - 10.1051/0004-6361/202453454

DO - 10.1051/0004-6361/202453454

M3 - Article

SN - 0004-6361

VL - 698

SP - A126

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

ER -

OGLE-2015-BLG-1609Lb: a sub-Jovian planet orbiting a low-mass stellar or brown dwarf host

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