천문학회지 (Journal of The Korean Astronomical Society)

  • 제55권5호
  • /
  • Pages.173-194
  • /
  • 2022
  • /
  • 1225-4614(pISSN)
  • /
  • 2288-890X(eISSN)
한국천문학회 (The Korean Astronomical Society)
권호 표지
DOI QR코드

DOI QR Code

FREE-FLOATING PLANETS, THE EINSTEIN DESERT, AND 'OUMUAMUA

  • Gould, Andrew (Max-Planck-Institute for Astronomy) ;
  • Jung, Youn Kil (Korea Astronomy and Space Science Institute) ;
  • Hwang, Kyu-Ha (Korea Astronomy and Space Science Institute) ;
  • Dong, Subo (Kavli Institute for Astronomy and Astrophysics, Peking University) ;
  • Albrow, Michael D. (University of Canterbury, Department of Physics and Astronomy) ;
  • Chung, Sun-Ju (Korea Astronomy and Space Science Institute) ;
  • Han, Cheongho (Department of Physics, Chungbuk National University) ;
  • Ryu, Yoon-Hyun (Korea Astronomy and Space Science Institute) ;
  • Shin, In-Gu (Department of Physics, Chungbuk National University) ;
  • Shvartzvald, Yossi (Department of Particle Physics and Astrophysics, Weizmann Institute of Science) ;
  • Yang, Hongjing (Department of Astronomy, Tsinghua University) ;
  • Yee, Jennifer C. (Center for Astrophysics | Harvard & Smithsonian) ;
  • Zang, Weicheng (Department of Astronomy, Tsinghua University) ;
  • Cha, Sang-Mok (Korea Astronomy and Space Science Institute) ;
  • Kim, Dong-Jin (Korea Astronomy and Space Science Institute) ;
  • Kim, Seung-Lee (Korea Astronomy and Space Science Institute) ;
  • Lee, Chung-Uk (Korea Astronomy and Space Science Institute) ;
  • Lee, Dong-Joo (Korea Astronomy and Space Science Institute) ;
  • Lee, Yongseok (Korea Astronomy and Space Science Institute) ;
  • Park, Byeong-Gon (Korea Astronomy and Space Science Institute) ;
  • Pogge, Richard W. (Department of Astronomy, Ohio State University)
  • 투고 : 2022.04.11
  • 심사 : 2022.09.19
  • 발행 : 2022.10.31
PDF 다운로드
⟨ 이전 논문 다음 논문 ⟩

초록

We complete the survey for finite-source/point-lens (FSPL) giant-source events in 2016-2019 KMTNet microlensing data. The 30 FSPL events show a clear gap in Einstein radius, 9 𝜇as < 𝜃E < 26 𝜇as, which is consistent with the gap in Einstein timescales near tE ~ 0.5 days found by Mróz et al. (2017) in an independent sample of point-source/point-lens (PSPL) events. We demonstrate that the two surveys are consistent. We estimate that the 4 events below this gap are due to a power-law distribution of free-floating planet candidates (FFPs) dNFFP/d log M = (0.4 ± 0.2) (M/38 M⊕)-p/star, with 0.9 ≲ p ≲ 1.2. There are substantially more FFPs than known bound planets, implying that the bound planet power-law index 𝛾 = 0.6 is likely shaped by the ejection process at least as much as by formation. The mass density per decade of FFPs in the Solar neighborhood is of the same order as that of 'Oumuamua-like objects. In particular, if we assume that 'Oumuamua is part of the same process that ejected the FFPs to very wide or unbound orbits, the power-law index is p = 0.89 ± 0.06. If the Solar System's endowment of Neptune-mass objects in Neptune-like orbits is typical, which is consistent with the results of Poleski et al. (2021), then these could account for a substantial fraction of the FFPs in the Neptune-mass range.

키워드

과제정보

We thank Quanzhi Ye for valuable discussions. This research has made use of the KMTNet system operated by the Korea Astronomy and Space Science Institute (KASI) and the data were obtained at three host sites of CTIO in Chile, SAAO in South Africa, and SSO in Australia. Work by C.H. was supported by the grant (2017R1A4A101517) of National Research Foundation of Korea. J.C.Y. acknowledges support from US N.S.F. Grant No. AST-2108414. Y.S. acknowledges support from BSF Grant No. 2020740. S.D., H.Y., and W.Z. acknowledge support by the National Science Foundation of China (Grant No. 12133005). Work by S.D. was supported by the Xplorer Prize.

참고문헌

  1. Alard, C., & Lupton, R. H. 1998, A Method for Optimal Image Subtraction, ApJ, 503, 325 https://doi.org/10.1086/305984
  2. Albrow, M. D. 2017, MichaelDAlbrow/pyDIA: Initial release on github. (v1.0.0), Zenodo:268049
  3. Albrow, M. D., Horne, K., Bramich, D. M., et al. 2009, Difference imaging photometry of blended gravitational microlensing events with a numerical kernel, MNRAS, 397, 2099 https://doi.org/10.1111/j.1365-2966.2009.15098.x
  4. Bensby, T., Yee, J. C., Feltzing, S., et al. 2013, Chemical evolution of the Galactic bulge as traced by microlensed dwarfs and subgiant stars. V. Evidence for a wide age distribution and a complex MDF, A&A, 549, A147 https://doi.org/10.1051/0004-6361/201220678
  5. Bessell, M. S., & Brett, J. M. 1988, JHKLM Photometry - Standard Systems, Passbands, and Intrinsic Colors, PASP, 100, 1134 https://doi.org/10.1086/132281
  6. Bovy, J. 2017, Stellar inventory of the solar neighbourhood using Gaia DR1, MNRAS, 470, 1360 https://doi.org/10.1093/mnras/stx1277
  7. Clanton, C., & Gaudi, B. S. 2014a, Synthesizing Exoplanet Demographics from Radial Velocity and Microlensing Surveys. I. Methodology, ApJ, 791, 90 https://doi.org/10.1088/0004-637X/791/2/90
  8. Clanton, C., & Gaudi, B. S. 2014b, Synthesizing Exoplanet Demographics from Radial Velocity and Microlensing Surveys. II. The Frequency of Planets Orbiting M Dwarfs, ApJ, 791, 91 https://doi.org/10.1088/0004-637X/791/2/91
  9. Clanton, C., & Gaudi, B. S. 2016, Synthesizing Exoplanet Demographics: A Single Population of Long-period Planetary Companions to M Dwarfs Consistent with Microlensing, Radial Velocity, and Direct Imaging Surveys, ApJ, 819, 125 https://doi.org/10.3847/0004-637X/819/2/125
  10. Chabrier, G. 2005, The Initial Mass Function From Salpeter 1955 to 2005, Astrophysics and Space Science Library, 327, 41 https://doi.org/10.1007/978-1-4020-3407-7_5
  11. Do, A., Tucker, M. A., & Tonry, J. 2018, Interstellar Interlopers: Number Density and Origin of 'Oumuamua-like Objects, ApJ, 855, L10 https://doi.org/10.3847/2041-8213/aaae67
  12. Gomes, R., Levison, H. F., Tsiganis, K., & Morbidelli, A. 2005, Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets, Nature, 435, 466 https://doi.org/10.1038/nature03676
  13. Gonzalez, O. A., Rejkuba, M., Zoccali, M., et al. 2012, Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS. II. The complete high resolution extinction map and implications for Galactic bulge studies, A&A, 543, A13 https://doi.org/10.1051/0004-6361/201219222
  14. Gould, A. 1996, Theory of Pixel Lensing, ApJ, 470, 201 https://doi.org/10.1086/177861
  15. Gould, A. 2016, Microlensing by Kuiper, Oort, and Free-Floating Planets, JKAS, 49, 123
  16. Gould, A. 2022, MASADA: From Microlensing Planet Mass-Ratio Function to Planet Mass Function, arXiv:2209.12501
  17. Gould, A., & Yee, J. C. 2013, Microlens Terrestrial Parallax Mass Measurements: A Rare Probe of Isolated Brown Dwarfs and Free-floating Planets, ApJ, 764, 107 https://doi.org/10.1088/0004-637X/764/1/107
  18. Gould, A., Zang, W.-C., Mao, S., & Dong, S. 2021, Masses for free-floating planets and dwarf planets, RAA, 21, 133
  19. Groenewegen, M. A. T. 2004, Improved Baade-Wesselink surface brightness relations, MNRAS, 353, 903 https://doi.org/10.1111/j.1365-2966.2004.08121.x
  20. Han, C., Lee, Udalski, A., Gould, A., et al. 2020a, OGLE-2016-BLG-1227L: A Wide-separation Planet from a Very Short-timescale Microlensing Event, AJ, 159, 91 https://doi.org/10.3847/1538-3881/ab6a9f
  21. Han, C., Lee, C.-U., Udalski, A., et al. 2020b, Candidate Brown-dwarf Microlensing Events with Very Short Timescales and Small Angular Einstein Radii, AJ, 159, 134 https://doi.org/10.3847/1538-3881/ab6f66
  22. Higuchi, A., & Kokubo, E. 2020, Hyperbolic Orbits in the Solar System: Interstellar Origin or Perturbed Oort Cloud Comets?, MNRAS, 492, 268
  23. Jewitt, D., Kim, Y., Mutchler, M., et al. 2020, Outburst and Splitting of Interstellar Comet 2I/Borisov, ApJL, 896, L39 https://doi.org/10.3847/2041-8213/ab99cb
  24. Kervella, P., Thevenin, F., Di Folco, E., & Segransan, D. 2004, The angular sizes of dwarf stars and subgiants. Surface brightness relations calibrated by interferometry, A&A, 426, 297 https://doi.org/10.1051/0004-6361:20035930
  25. Kim, S.-L., Lee, C.-U., Park, B.-G., et al. 2016, KMTNet; A Network of 1.6 m Wide-Field Optical Telescopes Installed at Three Southern Observatories, JKAS, 49, 37
  26. Kim, D.-J., Kim, H.-W., Hwang, K.-H., et al., 2018a, Korea Microlensing Telescope Network Microlensing Events from 2015: Event-finding Algorithm, Vetting, and Photometry, AJ, 155, 76 https://doi.org/10.3847/1538-3881/aaa47b
  27. Kim, H.-W., Hwang, K.-H., Shvartzvald, Y., et al. 2018b, The Korea Microlensing Telescope Network (KMTNet) Alert Algorithm and Alert System, arXiv:1806.07545
  28. Kim, H.-W., Hwang, K.-H., Gould, A., et al. 2021, KMT-2019-BLG-2073: Fourth Free-floating-Planet Candidate with θE < 10 µas, AJ, 162, 15 https://doi.org/10.3847/1538-3881/abfc4a
  29. Li, S., Zang, W., Udalski, A., et al. 2019, OGLE-2017-BLG-1186: first application of asteroseismology and Gaussian processes to microlensing, MNRAS, 488, 3308 https://doi.org/10.1093/mnras/stz1873
  30. Loeb, A., 2021, On the Possibility of an Artificial Origin for 'Oumuamua, arXiv:2110.15213
  31. Minniti, D., Lucas, P., VVV Team. 2017, VizieR Online Data Catalog: VISTA Variable in the Via Lactea Survey DR2 (Minniti+, 2017), yCAT, II/348, 0
  32. Morbidelli, A., Levison, H. F., Tsiganis, K., & Gomes, R. 2005, Chaotic capture of Jupiter's Trojan asteroids in the early Solar System, Nature, 435, 462 https://doi.org/10.1038/nature03540
  33. Mroz, P., Udalski, A., Skowron, J., et al. 2017, No large population of unbound or wide-orbit Jupiter-mass planets, Nature, 548, 183 https://doi.org/10.1038/nature23276
  34. Mroz, P., Ryu, Y.-H., Skowron, J., et al. 2018, A Neptune-mass Free-floating Planet Candidate Discovered by Microlensing Surveys, AJ, 155, 121 https://doi.org/10.3847/1538-3881/aaaae9
  35. Mroz, P., Udalski, A., Bennett, D. P., et al. 2019, Two new free-floating or wide-orbit planets from microlensing, A&A, 622, A201 https://doi.org/10.1051/0004-6361/201834557
  36. Mroz, P., Poleski, R., Han, C., et al. 2020, A Free-floating or Wide-orbit Planet in the Microlensing Event OGLE-2019-BLG-0551, AJ, 159, 262 https://doi.org/10.3847/1538-3881/ab8aeb
  37. Mroz, P., Poleski, R., Gould, A., et al. 2020, A Terrestrial-mass Rogue Planet Candidate Detected in the Shortest-timescale Microlensing Event, ApJ, 903, L11 https://doi.org/10.3847/2041-8213/abbfad
  38. Nataf, D. M., Gould, A., Fouque, P., et al. 2013, Reddening and Extinction toward the Galactic Bulge from OGLE-III: The Inner Milky Way's Rv ~ 2.5 Extinction Curve, ApJ, 769, 88 https://doi.org/10.1088/0004-637X/769/2/88
  39. Paczynski, B. 1986, Gravitational Microlensing by the Galactic Halo, ApJ, 304, 1 https://doi.org/10.1086/164140
  40. Poleski, R., Skowron, J., Udalski, A., et al. 2014, Triple Microlens OGLE-2008-BLG-092L: Binary Stellar System with a Circumprimary Uranus-type Planet, ApJ, 795, 42 https://doi.org/10.1088/0004-637X/795/1/42
  41. Poleski, R., Gaudi, B. S., Udalski, A., et al. 2018, An Ice Giant Exoplanet Interpretation of the Anomaly in Microlensing Event OGLE-2011-BLG-0173, AJ, 156, 104 https://doi.org/10.3847/1538-3881/aad45e
  42. Poleski, R., Skowron, J., Mroz, P., et al. 2021, Wide-Orbit Exoplanets are Common. Analysis of Nearly 20 Years of OGLE Microlensing Survey Data, Acta Astron., 71, 1 https://doi.org/10.1016/j.actaastro.2011.08.009
  43. Rafikov, R. R. 2018, 1I/2017 'Oumuamua-like Interstellar Asteroids as Possible Messengers from Dead Stars, ApJ, 861, 35 https://doi.org/10.3847/1538-4357/aac5ef
  44. Ryu, Y.-H., Mroz, P., Gould, A., et al. 2021, KMT-2017-BLG-2820 and the Nature of the Free-floating Planet Population, AJ, 161, 126 https://doi.org/10.3847/1538-3881/abd55f
  45. Shin, I.-G., Udalski, A., Yee, J. C., et al. 2018, OGLE-2016-BLG-1045: A Test of Cheap Space-based Microlens Parallaxes, ApJ, 863, 23 https://doi.org/10.3847/1538-4357/aacdf4
  46. Shvartzvald, Y., Maoz, D., Udalski, A., et al. 2016, The frequency of snowline-region planets from four years of OGLE-MOA-Wise second-generation microlensing, MNRAS, 457, 4089 https://doi.org/10.1093/mnras/stw191
  47. Shvartzvald, Y., Yee, J. C., Skowron, J., et al. 2019, Spitzer Microlensing Parallax for OGLE-2017-BLG-0896 Reveals a Counter-rotating Low-mass Brown Dwarf, AJ, 157, 106 https://doi.org/10.3847/1538-3881/aafe12
  48. Sumi, T., Kamiya, K., Bennett, D. P., et al. 2011, Unbound or distant planetary mass population detected by gravitational microlensing, Nature, 473, 349 https://doi.org/10.1038/nature10092
  49. Suzuki, D., Bennett, D. P., Sumi, T., et al. 2016, The Exoplanet Mass-ratio Function from the MOA-II Survey: Discovery of a Break and Likely Peak at a Neptune Mass, ApJ, 833, 145 https://doi.org/10.3847/1538-4357/833/2/145
  50. Tsiganis, K., Gomes, R., Morbidelli, A., & Levison, H. F. 2005, Origin of the orbital architecture of the giant planets of the Solar System, Nature, 435, 459 https://doi.org/10.1038/nature03539
  51. Tomaney, A. B., & Crotts, A. P. S. 1996, Expanding the Realm of Microlensing Surveys with Difference Image Photometry, AJ, 112, 2872 https://doi.org/10.1086/118228
  52. Yee, J. C., Gould, A., & Beichman, C. 2015, Criteria for Sample Selection to Maximize Planet Sensitivity and Yield from Space-Based Microlens Parallax Surveys, ApJ, 810, 155 https://doi.org/10.1088/0004-637X/810/2/155
  53. Yoo, J., DePoy, D. L., Gal-Yam, A., et al. 2004, OGLE-2003-BLG-262: Finite-Source Effects from a Point-Mass Lens, ApJ, 603, 139 https://doi.org/10.1086/381241
  54. Zang, W., Shvartzvald, Y., Wang, T., et al. 2020, Spitzer Microlensing Parallax Reveals Two Isolated Stars in the Galactic Bulge, ApJ, 891, 3 https://doi.org/10.3847/1538-4357/ab6ff8
  55. Zhu, W., Calchi Novati, S., Gould, A., et al. 2016, Mass Measurements of Isolated Objects from Space-based Microlensing, ApJ, 825, 60 https://doi.org/10.3847/0004-637X/825/1/60
  56. Zhu, W., & Dong, S., 2021, Exoplanet Statistics and Theoreitical Implications, ARA&A, 59, 291 https://doi.org/10.1146/annurev-astro-112420-020055