| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Ursa Major[1] |
| Right ascension | 10h 59m 27.9728s[2] |
| Declination | +40° 25′ 48.921″[2] |
| Apparent magnitude (V) | +5.03[1] |
| Characteristics | |
| Spectral type | G1V[1] |
| B−Vcolor index | 0.624[1] |
| Astrometry | |
| Radial velocity (Rv) | 11.24(12)[2] km/s |
| Proper motion (μ) | RA: −316.850(97)mas/yr[2] Dec.: 55.180(118)mas/yr[2] |
| Parallax (π) | 72.0070±0.0974 mas[2] |
| Distance | 45.30 ± 0.06 ly (13.89 ± 0.02 pc) |
| Absolute magnitude (MV) | 4.29[1] |
| Details | |
| Mass | 1.02±0.06[3] M☉ |
| Radius | 1.23±0.02[3] R☉ |
| Luminosity | 1.62+0.07 −0.08[3] L☉ |
| Surface gravity (log g) | 4.30±0.02[4] cgs |
| Temperature | 5,880±10[4] K |
| Metallicity | +0.02±0.01[4] |
| Rotation | 24.8±0.8[5] days |
| Rotational velocity (v sin i) | 1.8[6] km/s |
| Age | 8.1+2.4 −3.1[3] Gyr |
| Other designations | |
| Chalawan,47 UMa,BD+41°2147,FK5 1282,GC 15087,GJ 407,HD 95128,HIP 53721,HR 4277,SAO 43557,LTT 12934,PLX 2556.00[7] | |
| Database references | |
| SIMBAD | The star |
| planet b | |
| planet c | |
| planet d | |
| Exoplanet Archive | data |
| ARICNS | data |
47 Ursae Majoris (abbreviated47 UMa), formally namedChalawan/ˈtʃɑːləwən/,[8][9] is ayellow dwarf star approximately 45.3light-years[2] from Earth in theconstellation ofUrsa Major. As of 2011[update], threeextrasolar planets (designated47 Ursae Majoris b,c andd; the first two later named Taphao Thong and Taphao Kaew) are known to orbit the star.
The star is located fairly close to theSolar System: according toastrometric measurements made by theGaia space observatory, it exhibits aparallax of 72.0070milliarcseconds, corresponding to a distance of 45.30 light-years.[2] With anapparent magnitude of +5.03, it is visible to thenaked eye and itsabsolute magnitude of +4.29 implies a visualluminosity around 60% greater than the Sun. Asolar analog, with aspectral type of G1V, it has a similarmass to that of theSun but is slightly hotter at around 5,880K.[3] and slightly moremetal-rich with around 105% of the solarabundance ofiron.[3]
Like the Sun, 47 Ursae Majoris is on themain sequence, convertinghydrogen tohelium in its core bynuclear fusion. Based on itschromospheric activity, the star may be around six billion years old, thoughevolutionary models suggest an older age of around 8.7 billion years.[10] Other studies have yielded estimates of 4.4 and 7 billion years for the star.[11] The low level ofmagnetic activity makes it aMaunder Minimum candidate star.[12]
47 Ursae Majoris is theFlamsteed designation. On their discoveries the planets were successively designated 47 Ursae Majoris b, c and d.
In July 2014 theInternational Astronomical Union launchedNameExoWorlds, a process for giving proper names to certain exoplanets and their host stars.[13] The process involved public nomination and voting for the new names.[14] In December 2015, the IAU announced the winning names were Chalawan for this star and Taphao Thong and Taphao Kaew for two of the planets (b and c, respectively).[15]The winning names were submitted by the Thai Astronomical Society,Thailand. Chalawan (Thai:ชาละวัน[t͡ɕʰāːlāwān]) is amythological crocodile king from the Thai folktaleKrai Thong and Taphao Thong and Taphao Kaew are two sisters associated with the tale.[16] ('Chalawan' is also the name given to anextinctgenus of crocodilian. It contains a single species,Chalawan thailandicus.[17]
In 2016, the IAU organized aWorking Group on Star Names (WGSN)[18] to catalog and standardize proper names for stars. In its first bulletin of July 2016,[19] the WGSN explicitly recognized the names of exoplanets and their host stars approved by the Executive Committee Working Group Public Naming of Planets and Planetary Satellites, including the names of stars adopted during the 2015 NameExoWorlds campaign. This star is now so entered in the IAU Catalog of Star Names.[8]
In 1996 anexoplanet (47 UMa b) was announced in orbit around 47 Ursae Majoris byGeoffrey Marcy andR. Paul Butler. The discovery was made by observing theDoppler shift of the star'sspectrum corresponding to changes in the star'sradial velocity as the planet'sgravity pulled it around.[20] The planet was the firstlong-period extrasolar planet discovered. Unlike the majority of known such planets, it has alow-eccentricity orbit. The planet is at least 2.53 times the mass ofJupiter and takes 1,078 days, or 2.95 years, to orbit its star. If it were to be located in the Solar System, it would lie between the orbits ofMars and Jupiter.[21]
In 2001, preliminary astrometric measurements made by theHipparcos probe suggested the orbit of 47 UMa b isinclined at an angle of 63.1° to the plane of the sky, implying the planet'strue mass is around 2.9 times that of Jupiter.[22] However, subsequent analysis suggested the Hipparcos measurements were not precise enough to accurately determine the orbits of substellar companions, and the inclination and true mass remain unknown.[23]
A second planet (47 UMa c) was announced in 2002 byDebra Fischer, Geoffrey Marcy and R. Paul Butler. The discovery was made using the sameradial velocity method. According to Fischer et al., the planet takes around 2,391 days, or 6.55 years, to complete an orbit. This configuration is similar to the configuration of Jupiter andSaturn in the Solar System, with the orbital ratio (close to 5:2) and mass ratio roughly similar.[24] Subsequent measurements failed to confirm the existence of the second planet, and it was noted that the dataset used to determine its existence left the planet's parameters "almost unconstrained".[25] Analysis of a longer dataset spanning over 6,900 days suggested that while a second planet in the system is likely, periods near 2,500 days have a high false-alarm probability,[why?] and the best fit model gave an orbital period of 7,586 days at a distance of 7.73AU from the star. Nevertheless, the parameters of the second planet were still highly uncertain.[26] On the other hand, the Catalog of Nearby Exoplanets gives a period of 2,190 days, which would put the planets close to a 2:1 ratio of orbital periods, though the reference for these parameters is uncertain: the original Fischeret al. paper is cited as a reference in spite of the fact that it gives different parameters,[24][27] though this solution has been adopted by theExtrasolar Planets Encyclopaedia.[28]
In 2010, the discovery of a third planet (47 UMa d) was made by using theBayesian Kepler Periodogram. Using this model of this planetary system it was determined that it is 100,000 times more likely to have three planets than two planets. This discovery was announced by Debra Fischer and P. C. Gregory. This1.64 MJ planet has an orbital period of 14,002 days, or 38.33 years, and a semi-major axis of 11.6 AU with a moderate eccentricity of 0.16.[21] It would be the longest-period planet discovered by the radial velocity method at the time, although longer-period planets had previously been discovered bydirect imaging andpulsar timing. Further studies in the 2020s have updated and refined the orbits of the three planets.[29]
Simulations suggest that the inner part of thehabitable zone of 47 Ursae Majoris could host aterrestrial planet in a stable orbit, though the outer regions of the habitable zone would be disrupted by the gravitational influence of the planet 47 UMa b.[30] However, the presence of a giant planet within 2.5 AU of the star may have disrupted planet formation in the inner system, and reduced the amount of water delivered to inner planets duringaccretion.[31] This may mean any terrestrial planets orbiting in the habitable zone of 47 Ursae Majoris are likely to be small and dry.
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b (Taphao Thong) | ≥2.395±0.079 MJ | 2.06+0.032 −0.033 | 1,075.61+0.79 −0.67 | 0.0312+0.0071 −0.0073 | — | — |
| c (Taphao Kaew) | ≥0.478+0.031 −0.030 MJ | 3.407+0.054 −0.055 | 2,290±11 | 0.255+0.057 −0.070 | — | — |
| d | ≥1.38+0.16 −0.13 MJ | 12.64+0.49 −0.34 | 16,288+950 −340 | 0.376+0.075 −0.081 | — | — |
As of 2008[update], there have been twoMETI messages sent to 47 Ursae Majoris. Both were transmitted fromEurasia's largestradar—70-metre (230 ft)Eupatoria Planetary Radar. The first message, theTeen Age Message, was sent on September 3, 2001, and it will arrive at 47 Ursae Majoris in July 2047. The second message,Cosmic Call 2, was sent on July 6, 2003, and it will arrive at 47 Ursae Majoris in May 2049.[32]
Because of its planetary system, 47 Ursae Majoris was listed as one of the top 100 target stars forNASA's formerTerrestrial Planet Finder mission,[33] and was also listed as one of 164 target stars for theHabitable Worlds Observatory.[3]
