# HD 139139

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Star system in the constellation Libra

HD 139139 Star field around HD 139139 (north is up, field is approximately 20′ wide) Observation data Epoch J2000 Equinox J2000 Constellation Libra[1] Right ascension 15h 37m 06.215s[2] Declination −19° 08′ 33.08″[2] Apparent magnitude (V) 9.84[3] Characteristics Evolutionary stage main sequence[2] Spectral type G3/G5V[4] Astrometry Radial velocity (Rv) +16.36[5] km/s Proper motion (μ) RA: −67.475[2] mas/yr Dec.: −92.600[2] mas/yr Parallax (π) 9.3455±0.0144 mas[2] Distance 349.0 ± 0.5 ly (107.0 ± 0.2 pc) Details Radius 1.14[5] R☉ Luminosity (bolometric) 1.29[5] L☉ Temperature 5,766[5] K Rotation 14.5 d[6] Age 1.5±0.4[6] Gyr Other designations BD−18°4107, PPM 717808, EPIC 249706694, TIC 70652803, TYC 6193-969-1, GSC 06193-00969, 2MASS J15370623−1908329, DENIS J153706.2−190832, Gaia DR1 6254212216862625024, Gaia DR2 6254212221163830016, Gaia DR3 6254212221163830016, RAVE J153706.2−190833, USNO‑B1.0 0708-00306171 [7] Database references SIMBAD data

**HD 139139** (also known as **EPIC 249706694**) is likely part of a [bound pair](/source/Binary_star) system of [main sequence](/source/Main_sequence) stars about 350 light-years (110 parsecs) away from Earth in the [constellation](/source/Constellation) [Libra](/source/Libra_(constellation)). HD 139139 is a [G-type main-sequence star](/source/G-type_main-sequence_star), a little larger and more luminous than the [Sun](/source/Sun), and at an almost identical temperature. It has an [apparent magnitude](/source/Apparent_magnitude) of 9.8. The companion star is thought to be a K5-K7 [red dwarf](/source/Red_dwarf) 3.3[″](/source/Second_of_arc) away from HD 139139. It is about three magnitudes fainter and has a temperature of between 4,100 and 4,300 [K](/source/Kelvin).[6] Both stars have a similar proper motion, meaning they may form a gravitationally-bound [binary pair](/source/Binary_pair).

A [light curve](/source/Light_curve) for HD 139139 showing the irregularly spaced dimmings, adapted from Rappaport *et al.* (2019)[6]

HD 139139 exhibits dips in brightness similar to those caused by [transiting](/source/Transit_(astronomy)) [Earth-like planets](/source/Earth_analog).[6] The [Kepler space telescope](/source/Kepler_space_telescope) observed 28 dips in their brightness over an 87-day period (23 August – 20 November 2017).[8][9] The dips do not appear to be periodic as would be expected if they were due to [transiting planets](/source/Transiting_planets).[10][11][12]

It is unknown which of the two stars produces the dimming events.[6] Potential explanations that have been investigated include planets transiting a binary star, planets that are perturbing the orbits of each other producing large transit timing variations, a [disintegrating planet](/source/Disrupted_planet), large dust producing [asteroids](/source/Asteroid), and short lived [sunspots](/source/Sunspot).[6][13][14] According to Andrew Vanderburg, one of the researchers of the original studies,

- In astronomy we have a long history of not understanding something, thinking it’s aliens, and later finding out it’s something else ... The odds are pretty good that it’s going to be another one of those.[12][15]

Subsequent observations performed with [CHEOPS](/source/CHEOPS) in two observing campaigns in the years 2021 and 2022 detected no transit-like events. The team estimated 4.8% probability of having missed all of them by chance, assuming that the frequency of the events remained unchanged from the 2017 measurements by Kepler. While it is possible that the events detected by Kepler were real, but inactive during observations by CHEOPS, the team also noted that it is not possible to discard also the possibility that they were caused by unidentified and infrequent instrumentation error.[16]

## Background

HD 139139 was identified as unusual by two independent groups of visual surveyors (citizen scientists) working in collaboration with professional astronomers.

- "But some of these patterns are too complex for computers to tease out; volunteer citizen scientists also comb through the Kepler catalogue, using the human brain's power to uncover surprising signals. In spring 2018 some of these citizen astronomers contacted Vanderburg and told him to check out HD 139139, a sunlike star roughly 350 light-years away."[6][10]

HD 139139 is one of the 0.5% of stars in the sky that can see [Earth transit](/source/Transit_(astronomy)), according to Andrew Vanderburg. "The transit impact parameter would be close to 0.9, so they can just barely see us – the transit duration would be only about 40% the duration we'd expect for a perfectly edge-on transit."[17]

## See also

- [Tabby's Star](/source/Tabby's_Star)

- [List of stars that have unusual dimming periods](/source/List_of_stars_that_have_unusual_dimming_periods)

## References

1. **[^](#cite_ref-DJM-2008_1-0)** ["Finding the constellation which contains given sky coordinates"](http://djm.cc/constellation.html). *DJM.cc*. 2 August 2008. Retrieved 8 June 2019.

1. ^ [***a***](#cite_ref-dr3_2-0) [***b***](#cite_ref-dr3_2-1) [***c***](#cite_ref-dr3_2-2) [***d***](#cite_ref-dr3_2-3) [***e***](#cite_ref-dr3_2-4) [***f***](#cite_ref-dr3_2-5) Vallenari, A.; et al. (Gaia collaboration) (2023). ["*Gaia* Data Release 3. Summary of the content and survey properties"](https://doi.org/10.1051%2F0004-6361%2F202243940). *Astronomy and Astrophysics*. **674**: A1. [arXiv](/source/ArXiv_(identifier)):[2208.00211](https://arxiv.org/abs/2208.00211). [Bibcode](/source/Bibcode_(identifier)):[2023A&A...674A...1G](https://ui.adsabs.harvard.edu/abs/2023A&A...674A...1G). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/202243940](https://doi.org/10.1051%2F0004-6361%2F202243940). [S2CID](/source/S2CID_(identifier)) [244398875](https://api.semanticscholar.org/CorpusID:244398875). [Gaia DR3 record for this source](https://vizier.cds.unistra.fr/viz-bin/VizieR-4?-source=+I%2F355&-from=nav&-nav=cat%3AI%2F355%26tab%3A%7BI%2F355%2Fgaiadr3%7D%26key%3Asource%3D1355%2Fgaiadr3%26HTTPPRM%3A%26-out.add%3D.%26Source%3D%3D%3D6254212221163830016%26-go+%25%23Sesame%23%25%26) at [VizieR](/source/VizieR).

1. **[^](#cite_ref-tycho2_3-0)** Høg, E.; Fabricius, C.; Makarov, V.V.; Urban, S.; Corbin, T.; Wycoff, G.; et al. (2000). "The Tycho 2 catalogue of the 2.5 million brightest stars". *[Astronomy and Astrophysics](/source/Astronomy_and_Astrophysics)*. **355**: L27. [Bibcode](/source/Bibcode_(identifier)):[2000A&A...355L..27H](https://ui.adsabs.harvard.edu/abs/2000A&A...355L..27H).

1. **[^](#cite_ref-Houk-Smith-1988_4-0)** Houk, N.; Smith-Moore, M. (1988). *Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars*. Vol. 4: Declinations −26°.0 to −12°.0. [Bibcode](/source/Bibcode_(identifier)):[1988mcts.book.....H](https://ui.adsabs.harvard.edu/abs/1988mcts.book.....H).

1. ^ [***a***](#cite_ref-dr2_5-0) [***b***](#cite_ref-dr2_5-1) [***c***](#cite_ref-dr2_5-2) [***d***](#cite_ref-dr2_5-3) [Brown, A. G. A.](/source/Anthony_Brown_(scientist)); et al. ([Gaia collaboration](/source/Data_Processing_and_Analysis_Consortium)) (August 2018). ["*Gaia* Data Release 2: Summary of the contents and survey properties"](https://doi.org/10.1051%2F0004-6361%2F201833051). *[Astronomy & Astrophysics](/source/Astronomy_%26_Astrophysics)*. **616**. A1. [arXiv](/source/ArXiv_(identifier)):[1804.09365](https://arxiv.org/abs/1804.09365). [Bibcode](/source/Bibcode_(identifier)):[2018A&A...616A...1G](https://ui.adsabs.harvard.edu/abs/2018A&A...616A...1G). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/201833051](https://doi.org/10.1051%2F0004-6361%2F201833051). [Gaia DR2 record for this source](https://vizier.u-strasbg.fr/viz-bin/VizieR-S?Gaia%20DR2%206254212221163830016) at [VizieR](/source/VizieR).

1. ^ [***a***](#cite_ref-Rappaport-2019_6-0) [***b***](#cite_ref-Rappaport-2019_6-1) [***c***](#cite_ref-Rappaport-2019_6-2) [***d***](#cite_ref-Rappaport-2019_6-3) [***e***](#cite_ref-Rappaport-2019_6-4) [***f***](#cite_ref-Rappaport-2019_6-5) [***g***](#cite_ref-Rappaport-2019_6-6) [***h***](#cite_ref-Rappaport-2019_6-7) Rappaport, S.; Vanderburg, A.; Kristiansen, M.H.; Omohundro, M. R.; Schwengeler, H.M.; Terentev, I.A.; et al. (2019). ["The Random Transiter – EPIC 249706694/HD 139139"](https://doi.org/10.1093%2Fmnras%2Fstz1772). *[Monthly Notices of the Royal Astronomical Society](/source/Monthly_Notices_of_the_Royal_Astronomical_Society)*. **488** (2): 2455–2465. [arXiv](/source/ArXiv_(identifier)):[1906.11268](https://arxiv.org/abs/1906.11268). [Bibcode](/source/Bibcode_(identifier)):[2019MNRAS.488.2455R](https://ui.adsabs.harvard.edu/abs/2019MNRAS.488.2455R). [doi](/source/Doi_(identifier)):[10.1093/mnras/stz1772](https://doi.org/10.1093%2Fmnras%2Fstz1772). [S2CID](/source/S2CID_(identifier)) [195699431](https://api.semanticscholar.org/CorpusID:195699431).

1. **[^](#cite_ref-SIMBAD-HD139139_7-0)** ["Basic data: HD 139139 – high proper-motion star"](http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD_139139). *[SIMBAD](/source/SIMBAD)*. 2019. Retrieved 7 July 2019.

1. **[^](#cite_ref-SciA-20190702_8-0)** Starr, Michelle (2 July 2019). ["Astronomers found a star that dims so erratically, they have no explanation for it"](https://www.sciencealert.com/a-star-with-random-dimming-has-become-one-of-the-most-mysterious-in-the-milky-way). *ScienceAlert.com*. Retrieved 4 July 2019.

1. **[^](#cite_ref-PHY-20190703_9-0)** Yirka, Bob (3 July 2019). ["Binary stars with unexplainable dimming pattern"](https://phys.org/news/2019-07-binary-stars-unexplainable-dimming-pattern.html). *[Phys.org](/source/Phys.org)*. Retrieved 4 July 2019.

1. ^ [***a***](#cite_ref-SA-20190703_10-0) [***b***](#cite_ref-SA-20190703_10-1) Mann, Adam. ["Astronomers don't know what to make of this incredibly bizarre star"](https://www.scientificamerican.com/article/astronomers-dont-know-what-to-make-of-this-incredibly-bizarre-star/). *[Scientific American](/source/Scientific_American)*. Retrieved 3 July 2019.

1. **[^](#cite_ref-GZM-20190703_11-0)** Mandelbaum, Ryan F. (2 July 2019). ["Freaky star seems to dim randomly, and astronomers don't know why"](https://gizmodo.com/freaky-star-seems-to-dim-randomly-and-astronomers-dont-1836045295). *Gizmodo*. Retrieved 3 July 2019.

1. ^ [***a***](#cite_ref-NS-20190702_12-0) [***b***](#cite_ref-NS-20190702_12-1) Crane, Leah (2 July 2019). ["The weirdest stars we've ever seen have astronomers utterly baffled"](https://www.newscientist.com/article/2208275-the-weirdest-stars-weve-ever-seen-have-astronomers-utterly-baffled/). *[New Scientist](/source/New_Scientist)*. Retrieved 4 July 2019.

1. **[^](#cite_ref-HO-20190629_13-0)** Osborn, Hugh (29 June 2019). ["Why the 'Random Transiter' is now the most mysterious star in the Galaxy"](http://www.hughosborn.co.uk/2019/06/29/why-the-random-transiter-is-the-most-mysterious-star-in-the-galaxy/). *HughOsborn.co.uk*. Retrieved 19 July 2019.

1. **[^](#cite_ref-RD-20190630_14-0)** Schirmer, H. (30 June 2019). ["Why the 'Random Transiter' (HD139139) is now the most mysterious star in the Galaxy"](https://www.reddit.com/r/KIC8462852/comments/c70xw2/why_the_random_transiter_hd139139_is_now_the_most/). *[Reddit](/source/Reddit)*. Retrieved 19 July 2019.

1. **[^](#cite_ref-TDG-20190703_15-0)** ["'Something Weird Going On' –'Random-Transiter' Star System Stumps Scientists"](https://web.archive.org/web/20190720020117/https://dailygalaxy.com/2019/07/something-weird-going-on-bizarre-random-transiter-star-system-stumps-scientists/). *The Daily Galaxy*. 3 July 2019. Archived from [the original](https://dailygalaxy.com/2019/07/something-weird-going-on-bizarre-random-transiter-star-system-stumps-scientists/) on 20 July 2019. Retrieved 19 July 2019.

1. **[^](#cite_ref-CHEOPS_16-0)** Alonso, R.; Hoyer, S.; Deleuil, M.; Simon, A. E.; Beck, M.; Benz, W.; Florén, H. -G.; Guterman, P.; Borsato, L.; Brandeker, A.; Gandolfi, D.; Wilson, T. G.; Zingales, T.; et al. (December 2023). ["No random transits in CHEOPS observations of HD 139139"](https://doi.org/10.1051%2F0004-6361%2F202347779). *[Astronomy & Astrophysics](/source/Astronomy_%26_Astrophysics)*. **680** A78. [arXiv](/source/ArXiv_(identifier)):[2310.10332](https://arxiv.org/abs/2310.10332). [Bibcode](/source/Bibcode_(identifier)):[2023A&A...680A..78A](https://ui.adsabs.harvard.edu/abs/2023A&A...680A..78A). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/202347779](https://doi.org/10.1051%2F0004-6361%2F202347779). [S2CID](/source/S2CID_(identifier)) [264145874](https://api.semanticscholar.org/CorpusID:264145874).

1. **[^](#cite_ref-EventHorizons_17-0)** Godier, John Michael; Andrew, Vanderburg. [*The mysterious star HD 139139 with Dr. Andrew Vanderburg*](https://www.youtube.com/watch?v=Ml8BsjSdPWo&t=1492). *[YouTube](/source/YouTube)* (video 30m36s ). Retrieved 13 July 2019.

## External links

- ["EPIC Catalog at MAST"](http://archive.stsci.edu/k2/epic/search.php). *[Space Telescope Science Institute](/source/Space_Telescope_Science_Institute) (stsci.edu)*.

- [HD 139139 summary & related (video 8m57s )](https://www.youtube.com/watch?v=FPcKs3bC-1I) on [YouTube](/source/YouTube_video_(identifier))

- [The mysterious star HD 139139 with Dr. Andrew Vanderburg (video 30m36s )](https://www.youtube.com/watch?v=Ml8BsjSdPWo) on [YouTube](/source/YouTube_video_(identifier))

- [*HD 139139 summary*](https://web.archive.org/web/20190704130729/https://www.kgw.com/video/tech/science/amaze-lab/a-stars-unpredictable-dimming-pattern-is-stumping-scientists/609-fb765204-e679-4251-a83c-0ad4b65aad82). *kgw.com* (video 1m00s ). Archived from [the original](https://www.kgw.com/video/tech/science/amaze-lab/a-stars-unpredictable-dimming-pattern-is-stumping-scientists/609-fb765204-e679-4251-a83c-0ad4b65aad82) on 4 July 2019. Retrieved 4 July 2019.

v t e Constellation of Libra List of stars in Libra Libra in Chinese astronomy Stars Bayer α1 α2 (Zubenelgenubi) β (Zubeneschamali) γ (Zubenelhakrabi) δ ε ζ1 ζ2 ζ3 ζ4 η θ ι1 ι2 κ λ μ ν ξ1 ξ2 ο σ (Brachium) τ υ Flamsteed 2 3 4 5 10 11 12 16 17 18 22 23 26 28 30 36 37 41 42 47 48 49 50 Variable HN HO KU KX HR 5504 5455 HD 133131 134439 134440 135485 137010 139139 140283 141569 141937 Other 2M1510 2MASS 1507−1627 CWISEP J1446−2317 HE 1523−0901 WASP-57 WISE 1534−1043 WISE 1541−2250 Exoplanets 23 Librae b c Gliese 581b c e HD 137010 b (unconfirmed) K2-315b WASP-189b Star clusters NGC 5897 Galaxies NGC 5597 5605 5716 5728 5792 5793 5861 5885 5890 5898 5915 5917 Other AP Librae IC 1059 IRAS 14348−1447 PKS 1510−089 PKS 1519−273 QSO B1524−136 RXC J1504.1−0248 BCG Category

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Adapted from the Wikipedia article [HD 139139](https://en.wikipedia.org/wiki/HD_139139) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/HD_139139?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.