HD 181068

{{Short description|Star system in the constellation Lyra}}

{{Starbox begin}}

{{Starbox image

| image = 250px

| caption = A light curve for HD 181068, adapted from Derekas et al. (2011)

}}

{{Starbox observe

|constell=Lyra{{cite constellation|HD 181068}}

|epoch=J2000

|ra={{RA|19|17|08.97867}}

|dec={{DEC|+41|15|53.3144}}

|appmag_v=7.09{{cite journal|title=The Tycho-2 catalogue of the 2.5 million brightest stars|author1=Høg, E.|display-authors=etal|date=2000|journal=Astronomy and Astrophysics|volume=355|pages=L27–L30|bibcode=2000A&A...355L..27H}}

}}

{{Starbox character

|class=G8III / G8V / K1V{{cite journal|title=HD 181068: A Red Giant in a Triply Eclipsing Compact Hierarchical Triple System|author1=Derekas, A.|display-authors=etal|journal=Science|volume=332|issue=6026|date=2011|pages=216–218|bibcode=2011Sci...332..216D|doi=10.1126/science.1201762|pmid=21474755|arxiv=1202.2196|s2cid=14180715}}

|variable=Eclipsing binary

}}

{{Starbox astrometry

|radial_v={{val|+2.90|11.04}}{{cite Gaia DR2|2101454419072479488}}

|prop_mo_ra=+1.366

|prop_mo_dec=−8.376

|parallax=4.2065

|p_error=0.0322

|parallax_footnote={{cite Gaia DR3|2101454419072479488}}

|absmag_v=–0.3 / 5.6 / 6.1

}}

{{Starbox orbit

|reference={{cite journal|title=Dynamical masses, absolute radii and 3D orbits of the triply eclipsing star HD 181068 from Kepler photometry|author1=Borkovits, T.|author2=Derekas, A.|author3=Kiss, L. L.|author4=Forgács-Dajka, E.|author5=Bíró, I. B.|author6=Bedding, T. R.|author6-link= Tim Bedding|author7=Bryson, S. T.|author8=Huber, D.|author9=Szabó, R.|journal=Monthly Notices of the Royal Astronomical Society|volume=428|issue=2|pages=1656–1672|date=2013|bibcode=2013MNRAS.428.1656B|doi=10.1093/mnras/sts146|doi-access=free |arxiv=1210.1061}}

|primary=HD 181068 A

|name=HD 181068 B

|period_unitless={{val|45.4711|0.0002|u=d}}

|periastron={{nowrap|T_min {{=}} 2455499.9962}}

|axis_unitless={{val|90.31|0.72|ul=solar radius}}

|eccentricity=0

|inclination={{val|87.5|2}}

}}

{{Starbox orbit

|reference=

|primary=HD 181068 Ba

|name=HD 181068 Bb

|period_unitless={{val|fmt=none|0.9056768|0.0000002|u=d}}

|periastron={{nowrap|T_min {{=}} 2455051.23623}}

|axis_unitless={{val|4.777|0.039|ul=solar radius}}

|eccentricity=0

|inclination={{val|87.6|1.4}}

}}

{{Starbox detail

|source={{cite journal|title=A multiwavelength study of the hierarchical triple HD 181068. A test bed for studying star-planet interaction?|author1=Czesla, S.|author2=Huber, K. F.|author3=Schneider, P. C.|author4=Schmitt, J. H. M. M.|journal=Astronomy & Astrophysics|volume=570|date=2014|pages=A115|bibcode=2014A&A...570A.115C|doi=10.1051/0004-6361/201423879|arxiv=1408.2988|s2cid=119307151}}

|component1=HD 181068 A

|mass={{val|3|0.1}}

|radius={{val|12.46|0.15}}

|temperature={{val|fmt=commas|5100|100}}

|luminosity={{val|92.8|7.6}}

|gravity=2.73

}}

{{Starbox detail|no_heading=y

|component1=HD 181068 Ba

|mass={{val|0.915|0.034}}

|radius={{val|0.865|0.01}}

|temperature={{val|fmt=commas|5100|100}}

|luminosity={{val|0.447|0.037}}

|gravity=4.53

|component2=HD 181068 Bb

|mass2={{val|0.870|0.043}}

|radius2={{val|0.8|0.02}}

|temperature2={{val|fmt=commas|4675|100}}

|luminosity2={{val|0.27|0.027}}

|gravity2=4.58

}}

{{Starbox catalog

|names=HD 181068, BD+41°3292, HIP 94780, SAO 48282, KIC 5952403{{cite simbad|title=HD 181068|access-date=28 February 2017}}

}}

{{Starbox reference

|Simbad=HD+181068

|KIC=5952403

}}

{{Starbox end}}

HD 181068 is a star system in the constellation of Lyra. With an apparent magnitude of 7.09, the system is not visible to the naked eye but may be viewed with a pair of binoculars. Based on parallax measurements made by the Gaia spacecraft, the system is some 775 light years (238 parsecs) away from Earth.

HD 181068 is in the Kepler spacecraft's field of view, and its unique properties were first observed by the satellite's photometer. It consists of a red giant, designated HD 181068 A, along with two main-sequence stars, designated HD 181068 Ba and HD 181068 Bb, respectively. Normal eclipsing binaries have two components that pass in front of each other while eclipsing. However, all three components of HD 181068 orbit each other in such a way that they eclipse each other, forming a rare triply eclipsing system.{{cite web|url=http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=119|archive-url=https://web.archive.org/web/20110510204231/http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=119|url-status=dead|archive-date=May 10, 2011|title=Kepler discovery of a unique triply eclipsing triple star|work=NASA Kepler News|date=April 7, 2011}}

The primary, HD 181068 A, has a spectral type of G8III, meaning it is a red giant that has used up its core hydrogen and has expanded to a radius of {{solar radius|12.46}}. The primary star is also unusual in that it does not exhibit internal seismic oscillations as have been detected in other red giants, although tidal forces from the closer pair may possibly be causing other variability in the light curve of the system.

HD 181068 Ba and Bb have spectral types of G8V and K1V respectively, indicating their location on the main sequence, slightly later than the Sun. They are in a close orbit and complete an orbit once every 0.906 days (about 21.7 hours), while they orbit HD 181068 A every 45.5 days. All three stars have similar surface brightnesses and colors, so when the two companions eclipse the red giant, the change in brightness is very slight and hard to detect.