{{Short description|Star system in the constellation Libra}} {{use dmy dates|date=July 2019}} {{Starbox begin | name = HD 139139 }} {{Starbox image | image = [[File:EPIC-249706694-context.png|250px]] | caption = {{center|Star field around HD 139139<br/>{{small|(north is up, field is approximately {{val|20|ul='}} wide)}}}} }} {{Starbox observe | epoch = J2000 | constell = [[Libra (constellation)|Libra]]<ref name=DJM-2008/> | ra = {{RA|15|37|06.215}}<ref name=dr3/> | dec = {{DEC|-19|08|33.08}}<ref name=dr3/> | appmag_v = 9.84<ref name=tycho2/> }} {{Starbox character | type = [[main sequence]]<ref name=dr3/> | class = G3/G5V<ref name=Houk-Smith-1988/> | appmag_1_passband = | appmag_1 = | r-i = <!--R−I color--> | v-r = <!--V−R color--> | b-v = <!--B−V color--> | u-b = <!--U−B color--> | j-h = | j-k = }} {{Starbox astrometry | radial_v = +16.36<ref name=dr2/> | prop_mo_ra = −67.475<ref name=dr3/> | prop_mo_dec = −92.600<ref name=dr3/> | parallax = 9.3455 | p_error = 0.0144 | parallax_footnote = <ref name=dr3/> | dist_ly = | dist_pc = | absmag_v = }} {{Starbox detail | mass = | radius = 1.14<ref name=dr2/> | luminosity_bolometric = 1.29<ref name=dr2/> | temperature = 5,766<ref name=dr2/> | rotation = {{val|14.5|ul=days}}<ref name=Rappaport-2019/> | age_gyr = {{val|1.5|0.4}}<ref name=Rappaport-2019/> }} {{Starbox catalog | names = {{odlist |2MASS=J15370623−1908329 |BD=-18°4107 |GSC=06193-00969 |TYC=6193-969-1 |Gaia DR1=6254212216862625024 |Gaia DR2=6254212221163830016 |Gaia DR3=6254212221163830016 |DENIS=J153706.2−190832 |EPIC=249706694 |PPM=717808 |TIC=70652803}}, [[RAVE (survey)|RAVE]] J153706.2−190833, [[United States Naval Observatory|USNO]]{{nbh}}B1.0 0708-00306171 <ref name=SIMBAD-HD139139 /> }} {{Starbox reference | Simbad = HD+139139 }} {{Starbox end}} '''HD 139139''' (also known as '''EPIC 249706694''') is likely part of a [[Binary star|bound pair]] system of [[main sequence]] stars about {{convert|350|ly|pc|abbr=off}} away from Earth in the [[constellation]] [[Libra (constellation)|Libra]]. HD 139139 is a [[G-type main-sequence star]], a little larger and more luminous than the [[Sun]], and at an almost identical temperature. It has an [[apparent magnitude]] of 9.8. The companion star is thought to be a K5-K7 [[red dwarf]] {{val|3.3|ul=arcsec}} away from HD 139139. It is about three magnitudes fainter and has a temperature of between 4,100 and {{val|4,300|fmt=commas|ul=K}}.<ref name=Rappaport-2019/> Both stars have a similar proper motion, meaning they may form a gravitationally-bound [[binary pair]].
[[File:HD139139LightCurve.png|thumb|left|A [[light curve]] for HD 139139 showing the irregularly spaced dimmings, adapted from Rappaport ''et al.'' (2019)<ref name=Rappaport-2019/>]] HD 139139 exhibits dips in brightness similar to those caused by [[Transit (astronomy)|transiting]] [[Earth analog|Earth-like planets]].<ref name=Rappaport-2019/> The [[Kepler space telescope]] observed 28 dips in their brightness over an 87-day period (23 August{{snd}}20 November 2017).<ref name=SciA-20190702/><ref name=PHY-20190703/> The dips do not appear to be periodic as would be expected if they were due to [[transiting planets]].<ref name=SA-20190703/><ref name=GZM-20190703/><ref name=NS-20190702/>
It is unknown which of the two stars produces the dimming events.<ref name=Rappaport-2019/> 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 [[Disrupted planet|disintegrating planet]], large dust producing [[asteroid]]s, and short lived [[sunspot]]s.<ref name=Rappaport-2019/><ref name=HO-20190629/><ref name=RD-20190630/> 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.<ref name=NS-20190702/><ref name=TDG-20190703/>
Subsequent observations performed with [[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.<ref name=CHEOPS />
==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."<ref name=Rappaport-2019/><ref name=SA-20190703/>
HD 139139 is one of the 0.5% of stars in the sky that can see [[Transit (astronomy)|Earth transit]], 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."<ref name=EventHorizons/>
==See also== * [[Tabby's Star]] * [[List of stars that have unusual dimming periods]]
{{clear}} ==References== {{reflist|30em|refs=
<ref name=dr2>{{cite Gaia DR2|6254212221163830016}}</ref>
<ref name=dr3>{{cite Gaia DR3|6254212221163830016}}</ref>
<ref name=DJM-2008>{{cite web |title=Finding the constellation which contains given sky coordinates |date=2 August 2008 |website=DJM.cc |url=http://djm.cc/constellation.html |access-date=8 June 2019 }}</ref>
<ref name=EventHorizons>{{cite AV media |last1=Godier |first1=John Michael |last2=Andrew |first2=Vanderburg |medium=video {{small| 30{{sup|m}}36{{sup|s}} }} |title=The mysterious star HD 139139 with Dr. Andrew Vanderburg |url=https://www.youtube.com/watch?v=Ml8BsjSdPWo&t=1492 |website=[[YouTube]] |access-date=13 July 2019}}</ref>
<ref name=GZM-20190703>{{cite web |last1=Mandelbaum |first1=Ryan F. |date=2 July 2019 |title=Freaky star seems to dim randomly, and astronomers don't know why |website=Gizmodo |url=https://gizmodo.com/freaky-star-seems-to-dim-randomly-and-astronomers-dont-1836045295 |access-date=3 July 2019}}</ref>
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<ref name=NS-20190702>{{cite news |last=Crane |first=Leah |title=The weirdest stars we've ever seen have astronomers utterly baffled |date=2 July 2019 |magazine=[[New Scientist]] |url=https://www.newscientist.com/article/2208275-the-weirdest-stars-weve-ever-seen-have-astronomers-utterly-baffled/ |access-date=4 July 2019 }}</ref>
<ref name=PHY-20190703>{{cite news |last=Yirka |first=Bob |date=3 July 2019 |title=Binary stars with unexplainable dimming pattern |website=[[Phys.org]] |url=https://phys.org/news/2019-07-binary-stars-unexplainable-dimming-pattern.html |access-date=4 July 2019 }}</ref>
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<ref name=SA-20190703>{{cite magazine |last=Mann |first=Adam |title=Astronomers don't know what to make of this incredibly bizarre star |magazine=[[Scientific American]] |url=https://www.scientificamerican.com/article/astronomers-dont-know-what-to-make-of-this-incredibly-bizarre-star/ |access-date=3 July 2019}}</ref>
<ref name=RD-20190630>{{cite web |last=Schirmer |first=H. |title=Why the 'Random Transiter' (HD139139) is now the most mysterious star in the Galaxy |date=30 June 2019 |website=[[Reddit]] |url=https://www.reddit.com/r/KIC8462852/comments/c70xw2/why_the_random_transiter_hd139139_is_now_the_most/ |access-date=19 July 2019 }}</ref>
<ref name="SciA-20190702">{{cite news |last=Starr |first=Michelle |date=2 July 2019 |title=Astronomers found a star that dims so erratically, they have no explanation for it |website=ScienceAlert.com |url=https://www.sciencealert.com/a-star-with-random-dimming-has-become-one-of-the-most-mysterious-in-the-milky-way |access-date=4 July 2019 }}</ref>
<ref name=SIMBAD-HD139139>{{cite web |title=Basic data: HD 139139 – high proper-motion star |year=2019 |website=[[SIMBAD]] |url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD_139139 |access-date=7 July 2019 }}</ref>
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}} <!-- end "refs=" -->
==External links== * {{cite web |title=EPIC Catalog at MAST |website=[[Space Telescope Science Institute]] (stsci.edu) |url=http://archive.stsci.edu/k2/epic/search.php }} * {{YouTube|FPcKs3bC-1I | HD 139139 summary & related (video {{small| 8{{sup|m}}57{{sup|s}} }}) }} * {{YouTube|Ml8BsjSdPWo | The mysterious star HD 139139 with Dr. Andrew Vanderburg (video {{small| 30{{sup|m}}36{{sup|s}} }}) }} * {{cite AV media |title=HD 139139 summary |website=kgw.com |medium=video {{small| 1{{sup|m}}00{{sup|s}} }} |url=https://www.kgw.com/video/tech/science/amaze-lab/a-stars-unpredictable-dimming-pattern-is-stumping-scientists/609-fb765204-e679-4251-a83c-0ad4b65aad82 |access-date=4 July 2019 |archive-date=4 July 2019 |archive-url=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 |url-status=dead }}
{{Stars of Libra|state=collapsed}} {{Sky|15|37|06.215|-|19|08|33.09|350}} <!---please check light year distance---> {{Portal bar|Astronomy|Space}}
[[Category:Binary stars]] [[Category:G-type main-sequence stars]] [[Category:Henry Draper Catalogue objects|139139]] [[Category:Libra (constellation)]] [[Category:Durchmusterung objects|BD-18 4107]] [[Category:DENIS objects|J153706.2-190832]] [[Category:Unsolved problems in astronomy]]