Kapteyn's Star#Search for planets

{{Starbox begin

| name=Kapteyn's Star

}}

{{Starbox image

| image={{Location map|100x100

|AlternativeMap=Pictor constellation map.svg

|caption=

|width=300

|lat=83.6| long=67.1

|position=left|label=Kapteyn's Star

|float=center

}}|caption=Location of Kapteyn's Star in the constellation Pictor

}}

{{Starbox observe

| epoch = J2000

| constell = Pictor

| ra = {{RA|05|11|40.58984}}

| dec = {{DEC|-45|01|06.3617}}

| appmag_v = {{val|8.853|0.008}}

}}

{{Starbox character

| class = sdM1 or M1.5V

| b-v = {{val|1.57|0.012}}

| u-b = +1.21

| variable = BY Dra

}}

{{Starbox astrometry

| radial_v = {{val|245.05|0.13}}

| prop_mo_ra = {{val|+6491.223|fmt=commas}}

| prop_mo_dec = {{val|−5708.614|fmt=commas}}

| pm_footnote =

| parallax = 254.1986

| p_error = 0.0168

| parallax_footnote =

| absmag_v = 10.89

}}

{{Starbox detail

| source =

| mass = {{val|0.281|0.014}}

| radius = {{val|0.291|0.025}}

| luminosity = 0.012

| gravity = {{val|4.96|0.13}}

| temperature = {{val|3570|80|fmt=commas}}

| metal_fe = {{val|−0.86|0.05}}

| rotation = {{val|124.71|0.19|ul=d}}

| rotational_velocity = ~0.2

| age_gyr = {{val|11.5|0.5|1.5}}

}}

{{Starbox catalog

| names = {{odlist | V=VZ Pictoris | GJ=191 | HD=33793 | CD=-45°1841, CP(D)-44°612 | SAO=217223 | LHS=29 | LTT=2200 | LFT=395 | GCTP=1181 | HIP=24186 }}

}}

{{Starbox reference

| Simbad = NAME+Kapteyn's+star|sn=The star

| Simbad2 = GJ+191+b|sn2=planet b

| Simbad3 = GJ+191+c|sn3=planet c

| NSTED = Kapteyn

| ARICNS =

}}

Kapteyn's Star is a class M1 red subdwarf about 12.83 light-years from Earth in the southern constellation Pictor; it is the closest halo star to the Solar System. With an apparent magnitude of nearly 9, it is visible through binoculars or a telescope.

Its diameter is 30% of the Sun's, but its luminosity just 1.2% that of the Sun. It may have once been part of the globular cluster Omega Centauri, itself the likely core of a dwarf galaxy swallowed up by the Milky Way in the distant past. The discovery of two planets—Kapteyn b and Kapteyn c—was announced in 2014, but had a mixed history of rejections and confirmations, until a 2021 study refuted both planets. The "planets" are in fact artifacts of the star's rotation and activity.

History of observations

Attention was first drawn to what is now known as Kapteyn's Star by the Dutch astronomer Jacobus Kapteyn in 1898. Under the name CPD-44 612 it was included in the Cape photographic Durchmusterung for the equinox 1875 (−38 to −52) by David Gill and Jacobus Cornelius Kapteyn in 1897.{{r|CPD}} This catalogue was based on Gill's observations from the Cape Observatory in 1885–1889 and was created in collaboration with Kapteyn. While he was reviewing star charts and photographic plates, Kapteyn noted that a star, previously catalogued in 1873 by B. A. Gould as C.Z. V 243, seemed to be missing. However, Robert T. A. Innes found an uncatalogued star about 15 arcseconds away from the absent star's position. It became clear that the star had a very high proper motion of more than 8 arcseconds per year and had moved significantly.

Later, CPD-44 612 came to be referred to as Kapteyn's Star although equal credit should be accorded to Robert Innes. At the time of its discovery it had the highest proper motion of any star known, dethroning Groombridge 1830. In 1916, Barnard's Star was found to have an even larger proper motion. In 2014, two super-Earth planet candidates in orbit around the star were announced, but later refuted.

Characteristics

Based upon parallax measurements, Kapteyn's Star is {{Convert|12.83|ly|pc|abbr=off|lk=on}} from the Earth. It came within {{cvt|2.144|pc|ly|1|adj=ri1|order=flip}} of the Sun about 10,900 years ago and has been moving away since that time. Kapteyn's Star is distinctive in a number of regards: it has a high radial velocity, orbits the Milky Way retrograde, and is the nearest-known halo star to the Sun. It is a member of a moving group of stars that share a common trajectory through space, named the Kapteyn moving group. Based upon their element abundances, these stars may once have been members of Omega Centauri, a globular cluster that is thought to be the remnant of a dwarf galaxy that merged with the Milky Way. During this process, the stars in the group, including Kapteyn's Star, may have been stripped away as tidal debris.

Kapteyn's Star is between one quarter and one third the size and mass of the Sun and has a much cooler effective temperature at about {{val|fmt=commas|3500|ul=K}}, with some disagreement in the exact measurements between different observers. The stellar classification is sdM1, which indicates that it is a subdwarf with a luminosity lower than that of a main-sequence star at the same spectral type of M1. The abundance of elements other than hydrogen and helium, what astronomers term the metallicity, is about 14% of the abundance in the Sun. It is a variable star of the BY Draconis type with the identifier VZ Pictoris. This means that the luminosity of the star changes because of magnetic activity in the chromosphere coupled with rotation moving the resulting star spots into and out of the line of sight with respect to the Earth.

The star has a mass of {{Solar mass|0.27}}, a radius of {{Solar radius|0.29}} and has about 1.2% of the Sun's luminosity. It has a surface temperature of {{val|3550|fmt=commas|ul=K}} and is roughly 11 billion years old. In comparison, the Sun is about 4.6 billion years old and has a surface temperature of {{val|fmt=commas|5,778|u=K}}. Stars like Kapteyn's Star have the ability to live up to 100–200 billion years, ten to twenty times longer than the Sun will live.

Search for planets

In 2014, Kapteyn's Star was announced to host two planets, Kapteyn b and Kapteyn c, based on Doppler spectroscopy observations by the HARPS spectrometer which is housed at the European Southern Observatory's La Silla Observatory in Chile, at the Keck Observatory in Hawaii, and at the PFS Observatory, also in Chile. Kapteyn b was described as the oldest-known potentially habitable planet, estimated to be 11 billion years old, while Kapteyn c was described as beyond the host star's habitable zone.[http://www.solstation.com/stars/kapteyns.htm Kapteyn's Star] at SolStations.com. {{Anchor|In fiction}}The announcement of the planetary system was accompanied by a science-fiction short-story, "Sad Kapteyn", written by writer Alastair Reynolds.

However, subsequent research by Robertson et al. (2015) found that the orbital period of Kapteyn b is an integer fraction (1/3) of their estimated stellar rotation period, and thus the planetary signal is most likely an artifact of stellar activity. The authors did not rule out the existence of Kapteyn c, calling for further observation. This refutation was questioned by the team that published the exoplanet discovery paper. Guinan et al. (2016) (as well as earlier authors) found a lower value for the stellar rotation, which lent support to the original planetary finding.

In 2021, a new analysis found no evidence for either planet, and found that the observed radial velocity signals are in fact artifacts of the star's rotation and activity, after the rotational period of the star was refined, with a rotational period very similar to that of candidate c. There is currently no evidence for planets orbiting Kapteyn's Star.

{{gallery|mode=packed|height=184|align=center

|File:Kapteyn2.jpg|Jacobus Cornelius Kapteyn, the Dutch astronomer who discovered Kapteyn's Star

|File:VZPicLightCurve.png|A visual band light curve for VZ Pictoris The red curve shows the sine function that best fits the data.

|File:Kapteyn's Star Comparison.jpg|Comparison with Sun, Jupiter and Earth

}}

References

{{reflist|refs=

{{citation | title=Close encounters of the stellar kind | last1=Bailer-Jones | first1=C. A. L. | journal=Astronomy & Astrophysics | volume=575 | id=A35 | pages=13 | date=March 2015 | doi=10.1051/0004-6361/201425221 | bibcode=2015A&A...575A..35B | postscript=. | arxiv = 1412.3648 | s2cid=59039482 }}

{{citation | postscript=. | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=NAME+Kapteyn%27s+star | title=V* VZ Pic -- Variable Star | work=SIMBAD | publisher=Centre de Données astronomiques de Strasbourg | access-date=2009-10-14 | archive-url=https://web.archive.org/web/20160303232553/http://simbad.u-strasbg.fr/simbad/sim-id?Ident=NAME+Kapteyn's+star | archive-date=2016-03-03 | url-status=live }}.

{{citation | postscript=. | last=Kapteyn | first=J. C. | author-link=Jacobus Kapteyn | title=Stern mit grösster bislang bekannter Eigenbewegung | year=1898 | journal=Astronomische Nachrichten | volume=145 | issue=9–10 | pages=159–160 | doi=10.1002/asna.18981450906 | bibcode=1897AN....145..159K | url=https://zenodo.org/record/1424761 }}.

{{citation | postscript=. | first=E. E. | last=Barnard | author-link=Edward Emerson Barnard | year=1916 | title=A small star with large proper motion | journal=Astronomical Journal | volume=29 | issue=695 | page=181 | bibcode = 1916AJ.....29..181B | doi = 10.1086/104156 }}.

{{citation | postscript=. | url=http://www.sai.msu.su/groups/cluster/gcvs/cgi-bin/search.cgi?search=VZ+pic | title=VZ Pic | work=General Catalogue of Variable Stars, Sternberg Astronomical Institute, Moscow, Russia | access-date=2009-10-14 | archive-url=https://web.archive.org/web/20110927235117/http://www.sai.msu.su/groups/cluster/gcvs/cgi-bin/search.cgi?search=VZ+pic | archive-date=2011-09-27 | url-status=live }}

{{citation | postscript=. | display-authors=1 | first1=E. | last1=Kotoneva | first2=K. | last2=Innanen | first3=P. C. | last3=Dawson | first4=P. R. | last4=Wood | first5=M. M. | last5=De Robertis | title=A study of Kapteyn's star | year=2005 | journal=Astronomy & Astrophysics | volume=438 | pages=957–962 | doi=10.1051/0004-6361:20042287 | bibcode=2005A&A...438..957K | issue=3 | doi-access=free }}.

{{citation | postscript=. | url=https://www.newscientist.com/article/mg20427334.100-backward-star-aint-from-round-here.html | title=Backward star ain't from round here | journal=New Scientist | date=November 4, 2009 | access-date=September 2, 2017 | archive-url=https://web.archive.org/web/20150525093255/http://www.newscientist.com/article/mg20427334.100-backward-star-aint-from-round-here.html | archive-date=May 25, 2015 | url-status=live }}

{{citation | postscript=. | doi=10.1111/j.1365-2966.2004.07671.x | title=Chemical abundance analysis of Kapteyn's Star | last1=Woolf | first1=V. M. | last2=Wallerstein | first2=G. | author2-link=George Wallerstein | journal=Monthly Notices of the Royal Astronomical Society | volume=350 | issue=2 | pages=575–579 | year=2004 | bibcode=2004MNRAS.350..575W | s2cid=15907478 | doi-access=free }}.

{{citation | postscript=. | contribution=Kapteyn's Star | pages=108–109 | title=The Hundred Greatest Stars | first=James B. | last=Kaler | publisher=Copernicus Books | year=2002 }}.

{{citation | postscript=. | last=Eggen | first=O. J. | author-link=Olin J. Eggen | title=The Ross 451 Group of Halo Stars | journal=Astronomical Journal | volume=112 | page=2661 |date=December 1996 | bibcode=1996AJ....112.2661E |doi = 10.1086/118210 }}

{{citation | postscript=. | last1=Wylie-de Boer | first1=Elizabeth | last2=Freeman | first2=Ken | last3=Williams | first3=Mary | title=Evidence of Tidal Debris from ω Cen in the Kapteyn Group | journal=The Astronomical Journal | volume=139 | issue=2 | pages=636–645 |date=February 2010 | doi=10.1088/0004-6256/139/2/636 | bibcode=2010AJ....139..636W |arxiv = 0910.3735 | s2cid=119217292 }}

{{citation | postscript=. | display-authors=1 | last1=Koen | first1=C. | last2=Kilkenny | first2=D. | last3=van Wyk | first3=F. | last4=Marang | first4=F. | title=UBV(RI)_C JHK observations of Hipparcos-selected nearby stars | journal=Monthly Notices of the Royal Astronomical Society | volume=403 | issue=4 | pages=1949–1968 |date=April 2010 | doi=10.1111/j.1365-2966.2009.16182.x | bibcode=2010MNRAS.403.1949K | doi-access=free }}

{{citation | postscript=. | last1=Woolf | first1=Vincent M. | last2=Wallerstein | first2=George | title=Metallicity measurements using atomic lines in M and K dwarf stars | journal=Monthly Notices of the Royal Astronomical Society | volume=356 | issue=3 | pages=963–968 |date=January 2005 | doi=10.1111/j.1365-2966.2004.08515.x | doi-access=free | bibcode=2005MNRAS.356..963W |arxiv = astro-ph/0410452 | s2cid=15664454 }}

The abundance is given by taking the metallicity to the power of 10. From Woolf and Wallerstein (2005), [M/H] ≈ –0.86 dex. Thus:

: 10^−0.86 = 0.138

{{citation | postscript=.

| title=Mass-radius relation of low and very low-mass stars revisited with the VLTI

| journal=Astronomy and Astrophysics | volume=505 | issue=1

| date=October 2009 | pages=205–215

| doi=10.1051/0004-6361/200911976

| bibcode=2009A&A...505..205D |arxiv = 0906.0602

|last1=Demory |first1=Brice-Olivier

|last2=Ségransan |first2=Damien

|last3=Forveille |first3=Thierry

|last4=Queloz |first4=Didier

|last5=Beuzit |first5=Jean-Luc

|last6=Delfosse |first6=Xavier

|last7=Di Folco |first7=Emmanuel

|last8=Kervella |first8=Pierre

|last9=Le Bouquin |first9=Jean-Baptiste

|last10=Perrier |first10=Christian

|last11=Benisty |first11=Myriam

|last12=Duvert |first12=Gilles

|last13=Hofmann |first13=Karl-Heinz

|last14=Lopez |first14=Bruno

|last15=Petrov |first15=Romain

|s2cid=14786643

}}

{{citation | postscript=.

| title=Two planets around Kapteyn's star : a cold and a temperate super-Earth orbiting the nearest halo red-dwarf

| first3=Mikko | last3=Tuomi | first4=Mathias | last4=Zechmeister

| journal=Monthly Notices of the Royal Astronomical Society: Letters

| volume=443 |pages=L89–L93 | year=2014

| arxiv=1406.0818 | bibcode = 2014MNRAS.443L..89A

| doi = 10.1093/mnrasl/slu076 | doi-access=free

| s2cid=67807856

}}

{{citation | postscript=.

| title=Sad Kapteyn | date=Jun 4, 2014

| work=Science fiction story released with the announcement of planetary system

| url=http://ph.qmul.ac.uk/sad-kapteyn

| access-date=2014-06-04

| archive-url=https://web.archive.org/web/20140606234251/http://ph.qmul.ac.uk/sad-kapteyn

| archive-date=June 6, 2014 | url-status=live }}

{{citation | postscript=.

| title=Dictionary of Nomenclature of Celestial Objects

| url=http://cds.u-strasbg.fr/cgi-bin/Dic-Simbad?CPD

| archive-url=https://web.archive.org/web/20150925144116/http://cds.u-strasbg.fr/cgi-bin/Dic-Simbad?CPD

| date=2015-09-25 | archive-date=2015-09-25

| work=SIMBAD | publisher=Centre de Données astronomiques de Strasbourg }}

{{citation | postscript=.

| title=On the Discovery of a Certain Proper Motion

| last=Gill | first=D.

| journal=The Observatory

| date=1899 | pages=99–101 }}

{{citation | postscript=.

| bibcode=1884RNAO....7...96.

| title=Resultados del Observatorio Nacional Argentino

| date=1884

| volume=7 | page=98 }}

{{citation | postscript=.

| url=http://www.sci-news.com/astronomy/science-kapteyn-b-c-two-exoplanets-kapteyns-star-01965.html

| title=Kapteyn b and c: Two Exoplanets Found Orbiting Kapteyn's Star

| publisher=Sci-News | access-date=23 July 2014

| archive-url=https://web.archive.org/web/20140803022339/http://www.sci-news.com/astronomy/science-kapteyn-b-c-two-exoplanets-kapteyns-star-01965.html

| archive-date=3 August 2014 | url-status=live }}

{{citation

| title=Stellar activity mimics a habitable-zone planet around Kapteyn's star

| last1=Robertson | first1=Paul | last2=Roy | first2=Arpita

| author3-link=Suvrath Mahadevan | last3=Mahadevan | first3=Suvrath

| journal=The Astrophysical Journal Letters

| doi=10.1088/2041-8205/805/2/L22 | bibcode=2015ApJ...805L..22R

| arxiv=1505.02778 | s2cid=117871083 | postscript=. }}

{{citation

| title=Living with a Red Dwarf: Rotation and X-Ray and Ultraviolet Properties of the Halo Population Kapteyn's Star

| journal=The Astrophysical Journal

| doi=10.3847/0004-637X/821/2/81 | bibcode= 2016ApJ...821...81G

| arxiv=1602.01912 | s2cid=119283541 | postscript=. | doi-access=free }}

{{citation | postscript=.

| title=A Gaussian Process Regression Reveals No Evidence for Planets Orbiting Kapteyn's Star

| last1=Bortle | first1=Anna | last2=Fausey | first2=Hallie

| last3=Ji | first3=Jinbiao | last4=Dodson-Robinson | first4=Sarah

| last5=Ramirez Delgado | first5=Victor | last6=Gizis | first6=John

| display-authors=1 | journal=The Astronomical Journal

| volume=161 | issue=5 | year=2021 | pages=230

| arxiv=2103.02709 | doi=10.3847/1538-3881/abec89

| bibcode=2021AJ....161..230B | s2cid=232110395 | doi-access=free }}

{{citation | postscript=.

| last=Wall | first=Mike

| title=Found! Oldest Known Alien Planet That Might Support Life

| url=http://www.space.com/26115-oldest-habitable-alien-planet-kapteyn-b.html

| date=3 June 2014 | work=Space.com

| access-date=10 January 2015 }}

{{citation | postscript=.

| title=Red Dwarfs and the End of the Main Sequence

| last1=Adams | first1=Fred C.

| last2=Laughlin | first2=Gregory | last3=Graves | first3=Genevieve J. M.

| work=Gravitational Collapse: From Massive Stars to Planets

| date=2004

| volume=22

| pages=46–49

| publisher=Revista Mexicana de Astronomía y Astrofísica

| bibcode=2004RMxAC..22...46A

}}

{{citation | postscript=.

| title=No Evidence for Activity Correlations in the Radial Velocities of Kapteyn's Star

| last1=Anglada-Escudé | first1=G. | last2=Tuomi | first2=M.

| last3=Arriagada | first3=P. | last4=Zechmeister | first4=M.

| last5=Jenkins | first5=J. S. | last6=Ofir | first6=A.

| url=http://stacks.iop.org/0004-637X/830/i=2/a=74

| journal=The Astrophysical Journal|language=en

| volume=830 | issue=2 | pages=74 | date=2016

| doi=10.3847/0004-637X/830/2/74 | issn=0004-637X

| bibcode=2016ApJ...830...74A | arxiv=1506.09072

| hdl=2299/17695 | s2cid=14348277 | doi-access=free }}

{{citation | postscript=.

| last=Cain|first=Fraser|date=September 15, 2008

| title=Temperature of the Sun

| url=http://www.universetoday.com/18092/temperature-of-the-sun/

| url-status=dead | access-date=19 February 2011

| publisher=Universe Today

| archive-date=29 August 2010

| archive-url=https://web.archive.org/web/20100829025937/http://www.universetoday.com/18092/temperature-of-the-sun/}}

{{citation | postscript=.

| last=Cain | first=Fraser

| date=16 September 2008

| title=How Old is the Sun?

| publisher=Universe Today

| url=http://www.universetoday.com/18237/how-old-is-the-sun/|url-status=dead

| access-date=19 February 2011 | archive-date=18 August 2010

| archive-url=https://web.archive.org/web/20100818191941/http://www.universetoday.com/18237/how-old-is-the-sun/}}

{{citation | postscript=.

| first=David | last=Dickinson

| url=http://www.universetoday.com/112363/discovered-two-new-planets-for-kapteyns-star/

| title=Discovered: Two New Planets for Kapteyn's Star

| work=Universe Today

| date=June 4, 2014 }}

}}

External links

[http://www.solstation.com/stars/kapteyns.htm SolStation.com: Kapteyn's Star]
[http://ph.qmul.ac.uk/news/ancient-worlds-around-kapteyns-star Press release on planetary system]

Category:M-type main-sequence stars

Category:M-type subdwarfs

Category:BY Draconis variables

Category:Local Bubble

Category:Hypothetical planetary systems

Category:Discoveries by Robert T. A. Innes