Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Pictor |
Right ascension | 05h 11m 40.58984s [1] |
Declination | −45° 01′ 06.3617″ [1] |
Apparent magnitude (V) | 8.853±0.008 [2] |
Characteristics | |
Spectral type | sdM1 [3] or M1.5V [2] [4] |
U−B color index | +1.21 [5] |
B−V color index | 1.57±0.012 [2] |
Variable type | BY Dra [6] |
Astrometry | |
Radial velocity (Rv) | 245.05±0.13 [1] km/s |
Proper motion (μ) | RA: +6,491.223 mas/yr [1] Dec.: −5,708.614 mas/yr [1] |
Parallax (π) | 254.1986 ± 0.0168 mas [1] |
Distance | 12.8308 ± 0.0008 ly (3.9339 ± 0.0003 pc) |
Absolute magnitude (MV) | 10.89 [3] |
Details [2] | |
Mass | 0.281±0.014 M☉ |
Radius | 0.291±0.025 R☉ |
Luminosity | 0.012 L☉ |
Surface gravity (log g) | 4.96±0.13 cgs |
Temperature | 3,570±80 K |
Metallicity [Fe/H] | −0.86±0.05 dex |
Rotation | 124.71±0.19 d [7] |
Rotational velocity (v sin i) | 9.15 [8] km/s |
Age | 11.5+0.5 −1.5 Gyr |
Other designations | |
Database references | |
SIMBAD | The star |
planet b | |
planet c |
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. [9]
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, [10] 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. [7]
Attention was first drawn to what is now known as Kapteyn's Star by the Dutch astronomer Jacobus Kapteyn in 1898. [11] 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. [12] 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, [13] 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 [14] although equal credit should be accorded to Robert Innes. [15] 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. [14] [16] [17] In 2014, two super-Earth planet candidates in orbit around the star were announced, [10] but later refuted. [7]
Based upon parallax measurements, Kapteyn's Star is 12.83 light-years (3.93 parsecs ) from the Earth. [1] It came within 7.0 ly (2.1 pc) of the Sun about 10,900 years ago and has been moving away since that time. [18] Kapteyn's Star is distinctive in a number of regards: it has a high radial velocity, [14] orbits the Milky Way retrograde, [17] and is the nearest-known halo star to the Sun. [19] It is a member of a moving group of stars that share a common trajectory through space, named the Kapteyn moving group. [20] 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. [17] [21] [22]
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 3500 K, with some disagreement in the exact measurements between different observers. [17] The stellar classification is sdM1, [3] 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. [23] [24] 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. [6]
The star has a mass of 0.27 M☉, a radius of 0.29 R☉ and has about 1.2% of the Sun's luminosity. It has a surface temperature of 3,550 K and is roughly 11 billion years old. [10] In comparison, the Sun is about 4.6 billion years old [25] and has a surface temperature of 5,778 K. [26] 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. [27]
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. [28] Kapteyn b was described as the oldest-known potentially habitable planet, estimated to be 11 billion years old, [10] while Kapteyn c was described as beyond the host star's habitable zone. [29] [30] [10]
Kapteyn b was thought to make a complete orbit around its parent star about every 48.62 days at a distance of 0.17 AU, with an eccentricity of 0.21, meaning its orbit is mildly elliptical. Kapteyn c was thought to orbit with a period of 121.5 days at a distance of 0.31 AU, with an eccentricity of 0.23. Both planets were thought to be super-Earths, with minimum masses of 4.8 and 7.0 ME, respectively. [10]
The purported planets were thought to be close to a 5:2 period commensurability, but resonances could not be confirmed. Dynamical integration of the orbits suggested [10] that the pair of planets are in a dynamical state called apsidal co-rotation, which usually implies that the system is dynamically stable over long time scales. [31] Guinan et al. (2016) suggested that the present day star could potentially support life on Kapteyn b, but that the planet's atmosphere may have been stripped away when the star was young (~0.5 Gyr) and highly active. [2] The announcement of the planetary system was accompanied by a science-fiction short-story, "Sad Kapteyn", written by writer Alastair Reynolds. [32]
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. [33] This refutation was questioned by the team that published the exoplanet discovery paper. [34] Guinan et al. (2016) (as well as earlier authors) found a lower value for the stellar rotation, which lended support to the original planetary finding. [2]
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. [7] There is currently no evidence for planets orbiting Kapteyn's Star.
107 Piscium is a single star in the constellation of Pisces. 107 Piscium is the star's Flamsteed designation. John Flamsteed numbered the stars of Pisces from 1 to 113, publishing his Catalogus Britannicus in 1725. He accidentally numbered 107 Piscium twice, as he also allocated it the designation of 2 Arietis. This star is faintly visible to the naked eye with an apparent visual magnitude that has been measured varying between 5.14 and 5.26. However, that finding of variation was not confirmed by subsequent observations and is most likely spurious data. It is located at a distance of about 24.8 light years away from the Sun. 107 Piscium is drifting closer to the Sun with a radial velocity of −33.6, and is predicted to come as close as 15.4 light-years in around 135,800 years.
54 Piscium is an orange dwarf star approximately 36 light-years away in the constellation of Pisces. In 2003, an extrasolar planet was confirmed to be orbiting the star, and in 2006, a brown dwarf was also discovered orbiting it.
HD 147513 is a star in the southern constellation of Scorpius. It was first catalogued by Italian astronomer Piazzi in his star catalogue as "XVI 55". With an apparent magnitude of 5.38, according to the Bortle scale it is visible to the naked eye from suburban skies. Based upon stellar parallax measurements by the Hipparcos spacecraft, HD 147513 lies some 42 light years from the Sun.
HD 20367 is a star in the constellation of Aries, close to the border with the Perseus constellation. It is a yellow-white hued star that is a challenge to view with the naked eye, having an apparent visual magnitude of 6.40. Based upon parallax measurements, it is located 85 light years from the Sun. It is drifting further away with a radial velocity of +6.5 km/s. Based upon its movement through space, it is a candidate member of the Ursa Major Moving Group of co-moving stars that probably share a common origin.
Gliese 674(GJ 674) is a small red dwarf star with an exoplanetary companion in the southern constellation of Ara. It is too faint to be visible to the naked eye, having an apparent visual magnitude of 9.38 and an absolute magnitude of 11.09. The system is located at a distance of 14.85 light-years from the Sun based on parallax measurements, but is drifting closer with a radial velocity of −2.9 km/s. It is a candidate member of the 200 million year old Castor stream of co-moving stars.
Chi Virginis is a double star in the constellation Virgo. Based upon parallax measurements, it is approximately 315 light-years from Earth. It has an apparent visual magnitude of 4.65, which is bright enough to be seen with the unaided eye under suitable viewing conditions.
94 Ceti is a trinary star system approximately 73 light-years away in the constellation Cetus.
10 Tauri is a single star in the zodiac constellation of Taurus. It can be seen with the naked eye, having an apparent visual magnitude of 4.29. An annual parallax shift of 71.62 mas provides a distance estimate of 45.5 light years. It is moving further from the Sun with a radial velocity of +28 km/s and has a relatively high proper motion.
12 Ophiuchi is a variable star in the constellation Ophiuchus. No companions have yet been detected in orbit around this star, and it remains uncertain whether or not it possesses a dust ring.
HD 11964 is a binary star system located 110 light-years away from the Sun in the equatorial constellation of Cetus. It is visible in binoculars or a telescope but is too faint to be seen with the naked eye, having an apparent visual magnitude of 7.51. The system is drifting closer to the Sun with a radial velocity of −9 km/s. Two extrasolar planets have been confirmed to orbit the primary.
Gliese 412 is a pair of stars that share a common proper motion through space and are thought to form a binary star system. The pair have an angular separation of 31.4″ at a position angle of 126.1°. They are located 15.8 light-years distant from the Sun in the constellation Ursa Major. Both components are relatively dim red dwarf stars.
HD 222582 is a multiple star system in the equatorial constellation of Aquarius. It is invisible to the naked eye with an apparent visual magnitude of 7.7, but can be viewed with binoculars or a small telescope. The system is located at a distance of 137 light years from the Sun based on parallax, and it is drifting further away with a radial velocity of +12 km/s. It is located close enough to the ecliptic that it is subject to lunar occultations.
39 Cygni is a binary star system near the southern border of the northern constellation of Cygnus, approximately 270 light years away from Earth. It is visible to the naked eye as an orange-hued star with an apparent visual magnitude of 4.43. The system is moving closer to the Sun with a heliocentric radial velocity of −15 km/s.
GJ 1062 is a single red dwarf star in the constellation Eridanus, positioned about two degrees to the SSE of Epsilon Eridani. It is also known as LHS 20 and Ross 578. The star is invisible to the naked eye with an apparent visual magnitude of +13.0, requiring a telescope with at least a 25 cm (10 in) aperture to view. It is located at a distance of 52.7 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −85 km/s. The star has a high proper motion, traversing the sky at the rate of 3.033 arcseconds per year.
6 Ceti is a single star in the equatorial constellation of Cetus. It is visible to the naked eye with an apparent magnitude of 4.89. The annual parallax shift as measured from Earth's orbit is 53.34 mas, which yields a distance estimate of 61.1 light years. The star is moving further from the Sun with a constant radial velocity of +16.70 km/s. It is one of the IAU's standard velocity stars.
56 Pegasi is a binary star system in the northern constellation of Pegasus. It is visible to the naked eye with a combined apparent visual magnitude of 4.74. The system is approximately 590 light years away from the Sun based on parallax, but is drifting closer with a radial velocity of −28 km/s. It is listed as a member of the Wolf 630 moving group.
75 Tauri is a single, orange-hued star in the zodiac of constellation Taurus. It is a dim star but visible to the naked eye with an apparent visual magnitude of 4.96. Based upon an annual parallax shift of 17.47 mas as seen from Earth's orbit, it is located around 187 light years away. Due to its position near the ecliptic, it is subject to lunar occultations. The star is moving further from the Sun with a heliocentric radial velocity of +16 km/s.
HD 168009 is a star in the northern constellation of Lyra. It has an apparent visual magnitude of 6.3, placing it just above to below the normal limit of stars visible to the naked eye under good viewing conditions of 6-6.5. An annual parallax shift of 42.93 mas provides a distance estimate of 76 light years. It is moving closer to the Sun with a heliocentric radial velocity of −65 km/s. In about 328,000 years from now, the star will make its closest approach at a distance of around 17 ly (5.1 pc).
Gliese 686 is a star in the constellation of Hercules, with an apparent magnitude +9.577. Although it is close to the Solar System – at 26.6 light-years – it is not the closest known star in its constellation, since Gliese 661 is 20.9 light years away. The closest system to this star is the bright μ Herculis, at 4.5 light years. They are followed by GJ 1230 and Gliese 673, at 7.2 and 7.6 light years respectively.
14 Trianguli, also known as HD 15656, is a spectroscopic binary located in the northern constellation Triangulum. It has an apparent magnitude of 5.14, making it faintly visible to the naked eye in ideal conditions. Gaia DR3 parallax measurements place the system 433 light years away, and it is currently approaching the Solar System with a heliocentric radial velocity of −37 km/s. At its current distance, 14 Tri's brightness is diminished by 0.21 magnitude due to interstellar dust. It has an absolute magnitude of −0.46.