nu Octantis

{{Short description|Brightest star in the constellation Octans}}

{{Starbox begin

| name = ν Octantis

}}

{{Starbox image

|image=

{{Location mark

|image=Octans constellation map.svg|alt=|float=center|width=280

|label=|position=right

|mark=Red circle.svg|mark_width=10|mark_link=Nu Octantis

|x=536|y=334

}}

|caption=Location of ν Octantis in Octans (circled)

}}

{{Starbox observe

| epoch = J2000

| constell = Octans

| ra = {{RA|21|41|28.64977}}{{cite journal | arxiv=0708.1752 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 | title=Validation of the new Hipparcos reduction | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–664 | year=2007 | last1=Van Leeuwen | first1=F. | s2cid=18759600 }} [http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HIP%20107089 Vizier catalog entry]

| dec = {{DEC|-77|23|24.1563}}

| appmag_v = 3.73{{cite journal | bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015 | arxiv=1108.4971 | title=XHIP: An extended hipparcos compilation | journal=Astronomy Letters | volume=38 | issue=5 | pages=331 | year=2012 | last1=Anderson | first1=E. | last2=Francis | first2=Ch. | s2cid=119257644 }} [http://vizier.u-strasbg.fr/viz-bin/VizieR-4?-source=V/137D/XHIP&HIP=107089 Vizier catalog entry]

}}

{{Starbox character

| component1= A

| type= Giant star

| class= K1III{{cite journal

| display-authors=1

| last1=Gray | first1=R. O.

| last2=Corbally | first2=C. J.

| last3=Garrison | first3=R. F.

| last4=McFadden | first4=M. T.

| last5=Bubar | first5=E. J. | last6=McGahee | first6=C. E.

| last7=O'Donoghue | first7=A. A.

| last8=Knox | first8=E. R.

| title=Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample

| journal=The Astronomical Journal

| volume=132 | issue=1 | pages=161–170 | date=July 2006

| doi=10.1086/504637

| bibcode=2006AJ....132..161G

| arxiv=astro-ph/0603770

| s2cid=119476992 }}

| b-v = +1.00{{cite journal | bibcode=2014JAVSO..42..443M | title=Sloan Magnitudes for the Brightest Stars | journal=The Journal of the American Association of Variable Star Observers | volume=42 | pages=443 | last1=Mallama | first1=A. | year=2014 | issue=2 }}[http://vizier.u-strasbg.fr/viz-bin/VizieR-4?-source=J/other/JAVSO/42.443/ugriz&HD=205478 Vizier catalog entry]

| u-b = +0.89

| component2=B

| type2=Either a main sequence star or a white dwarf

| class2=K7–M0V or WD

}}

{{Starbox astrometry

| radial_v = +34.40{{cite journal | last=Wilson | first=R. E. | year=1953 | title=General Catalogue of Stellar Radial Velocities | journal=Carnegie Institute Washington D.C. Publication | publisher=Carnegie Institution for Science | bibcode=1953GCRV..C......0W | lccn=54001336 }}

| prop_mo_ra = +66.41

| prop_mo_dec = −239.10

| pm_footnote =

| parallax = 45.25

| p_error = 0.25

| parallax_footnote =

| absmag_v = {{val|2.3|0.16}}

}}

{{Starbox orbit

|reference={{cite journal|title=The conjectured S-type retrograde planet in ν Octantis: more evidence including four years of iodine-cell radial velocities|author1=Ramm, D. J.|display-authors=etal|journal=Monthly Notices of the Royal Astronomical Society|volume=460|issue=4|pages=3706–3719|date=2016|bibcode=2016MNRAS.460.3706R|doi=10.1093/mnras/stw1106|doi-access=free |arxiv=1605.06720}}

|period_unitless={{val|1050.69|+0.05|-0.07}} d

|eccentricity={{val|0.23680|0.00007}}

|axis_unitless={{val|2.62959|+0.00009|-0.00011}} AU

|periarg={{val|74.970|0.016}}

|inclination={{val|70.8|0.9}}

|node={{val|87|1.2}}

|k1={{val|7.032|0.003}}

}}

{{Starbox detail

| component1 = Nu Octantis A

| mass = 1.61

| radius =

{{val|5.81|0.12}}

| temperature = {{val|4860|40|fmt=commas}}

| luminosity = 17.53

| rotational_velocity = 2.0

| gravity = {{val|3.12|0.10}}

| metal_fe={{val|+0.18|0.04}}

| age_gyr = ~2.5-3

| component2 = Nu Octantis B

| mass2 = 0.585

}}

{{Starbox catalog

| names = nu Oct, CD−77 1079, CCDM J21415-7723, FK5 810, GC 30289, GJ 835.1, GJ 9744, HIP 107089, HR 8254, HD 205478, SAO 257948, WDS J21415-7723

}}

{{Starbox reference

| Simbad = HD+205478

}}

{{Starbox end}}

ν Octantis, Latinised as Nu Octantis, is a star in the constellation of Octans. Unusually for having such a late greek letter in its name, it is the brightest star in this faint constellation at apparent magnitude +3.7. It is a spectroscopic binary{{cite journal

| last1=Eggleton | first1=P. P.

| last2=Tokovinin | first2=A. A.

| title=A catalogue of multiplicity among bright stellar systems

| journal=Monthly Notices of the Royal Astronomical Society

| volume=389 | issue=2 | pages=869–879 | date=September 2008

| doi=10.1111/j.1365-2966.2008.13596.x

| doi-access=free

| bibcode=2008MNRAS.389..869E

| arxiv=0806.2878

| s2cid=14878976

}} star with a period around 2.9 years. Parallax measurements place it at {{convert|22.1|pc|ly}} from Earth.

The primary has a spectral type of K1III, with the luminosity class III indicating that it is a giant star that has burned up the hydrogen at its core and has expanded. Nu Octantis A has 1.6 times the mass of the Sun, but has expanded to 5.8 times the radius of the Sun. Its photosphere has cooler to an effective temperature of 4,860 K and now is radiating 18 times as much luminosity as the Sun. It possibly hosts an extrasolar planet, a jovian planet on a retograde orbit.

The secondary star is likely either a red dwarf or a white dwarf, from its relatively low mass. This star is estimated to have around 60% the mass of the Sun. It shares a center of mass with the primary, completing an orbit around it every 2 years and 11 months. The orbit has an eccentricity of 0.24 and a semi-major axis of 2.63 au.