# 47 Ursae Majoris

Observation data Characteristics Epoch J2000.0      Equinox J2000.0 The red dot shows the location of 47 Ursae Majoris in Ursa Major. Constellation Ursa Major Right ascension 10h 59m 27.97s[1] Declination +40° 25′ 48.9″[1] Apparent magnitude (V) +5.03 Spectral type G1V U−B color index 0.13 B−V color index 0.61 Radial velocity (Rv) +12.6 km/s Proper motion (μ) RA: –317.01 ± 0.22[1] mas/yr Dec.: 54.64 ± 0.20[1] mas/yr Parallax (π) 71.11 ± 0.25[1] mas Distance 45.9 ± 0.2 ly (14.06 ± 0.05 pc) Absolute magnitude (MV) 4.41[2] Mass 1.08[3] M☉ Radius 1.172 ± 0.111 [4] R☉ Luminosity 1.48[note 1] L☉ Surface gravity (log g) 4.377[3] cgs Temperature 5887 ± 3.8 [5] K Metallicity 110% solar[3] Rotational velocity (v sin i) 2.80[3] km/s Age 6.03 × 109[6] years BD+41°2147, FK5 1282, GC 15087, GCTP 2556.00, Gliese 407, HD 95128, HIP 53721, HR 4277, LTT 12934, SAO 43557 SIMBAD data Exoplanet Archive data ARICNS data Extrasolar Planets Encyclopaedia data

47 Ursae Majoris (often abbreviated 47 UMa) is a solar analog, yellow dwarf star approximately 46 light-years[1] away from Earth in the constellation of Ursa Major. As of 2011, it has been confirmed that three Jupiter-like extrasolar planets orbit the star. Because of this, 47 Ursae Majoris was listed as one of top 100 target stars for NASA's former Terrestrial Planet Finder mission.[7]

## Distance and visibility

47 Ursae Majoris is located fairly close to the Solar System: according to astrometric measurements made by the Hipparcos astrometry satellite, the star exhibits a parallax of 71.11 milliarcseconds, corresponding to a distance of 45.913 light-years.[1] With an apparent magnitude of +5.03, it is visible to the naked eye under good conditions.

## Stellar components

47 Ursae Majoris has a similar mass to that of our Sun. It is slightly more metal-rich than the Sun, having around 110% of the solar abundance of iron. With a spectral type of G1V, it is also slightly hotter than the Sun, at around 5,882 K.[3] 47 Ursae Majoris has an absolute magnitude of +4.29, implying it has a visual luminosity around 60% greater than the Sun.

Like the Sun, 47 Ursae Majoris is on the main sequence, converting hydrogen to helium in its core by nuclear fusion. Based on its chromospheric activity, the star may be around 6,000 million years old, though evolutionary models suggest an older age of around 8,700 million years.[6] Other studies have yielded estimates of 4,400 and 7,000 million years for the star.[8]

## Planetary system

In 1996 an extrasolar planet was announced in orbit around 47 Ursae Majoris by Geoffrey Marcy and R. Paul Butler. The discovery was made by observing the change in the star's radial velocity as the planet's gravity pulled it around. The measurements were made by observing the Doppler shift of the star's spectrum.[9] The planet, designated 47 Ursae Majoris b, was the first long-period extrasolar planet discovered. Unlike the majority of known long-period extrasolar planets, 47 Ursae Majoris b has a low-eccentricity orbit. The planet is at least 2.53 times the mass of Jupiter 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 of Mars and Jupiter.[10]

Orbits of the planets in the 47 Ursae Majoris system. The orbit of 47UMa d is currently quite uncertain; both it and that of 47 UMa c may be circular.

In 2001, preliminary astrometric measurements made by the Hipparcos probe suggest the orbit of 47 Ursae Majoris b is inclined at an angle of 63.1° to the plane of the sky. If these measurements are confirmed, this implies the planet's true mass is around 2.9 times that of Jupiter.[11] However, subsequent analysis suggests that the Hipparcos measurements are not precise enough to accurately determine the orbits of substellar companions, and the inclination and true mass remain unknown.[12]

A second planet, designated 47 Ursae Majoris c, was announced in 2002 by Debra Fischer, Geoffrey Marcy, and R. Paul Butler. The discovery was made using the same radial velocity method used to detect the first planet. 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 and Saturn in the Solar System, with the orbital ratio (close to 5:2), and mass ratio roughly similar.[13]

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".[14] Analysis of a longer dataset spanning over 6,900 days suggests that while a second planet in the system is likely, periods near 2,500 days have a high false alarm probability, and the best fit model gives an orbital period of 7,586 days at a distance of 7.73 AU from the star. Nevertheless, the parameters of the second planet are still highly uncertain.[15] 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 Fischer et al. paper is cited as a reference in spite of the fact that it gives different parameters,[13][16] though this solution has been adopted by the Extrasolar Planets Encyclopaedia.[17]

In 2010, the discovery of a third planet, designated 47 Ursae Majoris d, was made by using the Bayesian Kepler Periodogram. Using this model of this planetary system found out 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. This 1.64 MJ planet has an orbital period of 14,002 days or 38.33 years and a semimajor axis of 11.6 AU with a moderate eccentricity of 0.16.[10] It would be the longest-period planet discovered by radial velocity method, although longer-period planets only priorly been discovered by direct imaging and pulsar timing.

Simulations suggest that the inner part of the habitable zone of 47 Ursae Majoris could host a terrestrial planet in a stable orbit, though the outer regions of the habitable zone would be disrupted by the gravitational influence of the planet 47 Ursae Majoris b.[18] 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 during accretion.[19] This may mean any terrestrial planets orbiting in the habitable zone of 47 Ursae Majoris are likely to be small and dry. As of 2008, there have been two METI messages sent to 47 Ursae Majoris. Both were transmitted from Eurasia's largest radar — 70-meter (230-foot) Eupatoria Planetary Radar. The first message, the Teen 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.[20]

The 47 Ursae Majoris planetary system[10]
Companion
(in order from star)
Mass Semimajor axis
(AU)
Orbital period
(days)
b >2.53+0.07
−0.06
MJ
2.10 ± 0.02 1078 ± 2 0.032 ± 0.014
c >0.540+0.066
−0.073
MJ
3.6 ± 0.1 2391+100
−70
0.098+0.047
−0.096
d >1.64+0.29
−0.48
MJ
11.6+2.1
−2.9
14002+4018
−5095
0.16+0.09
−0.16

## Notes

1. ^ From $\begin{smallmatrix}L=4 \pi R^2 \sigma T_{\rm eff}^4 \end{smallmatrix}$, where $\begin{smallmatrix}L \end{smallmatrix}$ is the luminosity, $\begin{smallmatrix}R \end{smallmatrix}$ is the radius, $\begin{smallmatrix}T_{\rm eff}\end{smallmatrix}$ is the effective surface temperature and $\begin{smallmatrix}\sigma \end{smallmatrix}$ is the Stefan–Boltzmann constant

## References

1. F. van Leeuwen (2007). "HIP 53721". Hipparcos, the New Reduction. Retrieved 2009-12-08.
2. ^ Elgarøy, Øystein; Engvold, Oddbjørn; Lund, Niels (March 1999), "The Wilson-Bappu effect of the MgII K line - dependence on stellar temperature, activity and metallicity", Astronomy and Astrophysics 343: 222–228, Bibcode:1999A&A...343..222E
3. "Stars Table". Catalog of Nearby Exoplanets. Archived from the original on 17 October 2008. Retrieved 2008-10-04.
4. ^ G. T. van Belle, K. von Braun (2009). "Directly Determined Linear Radii and Effective Temperatures of Exoplanet Host Stars". Astrophysical Journal 694 (2): 1085–1098. arXiv:0901.1206. Bibcode:2009ApJ...694.1085V. doi:10.1088/0004-637X/694/2/1085.
5. ^ V. V. Kovtyukh; Soubiran, C. et al. (2003). "High precision effective temperatures for 181 F-K dwarfs from line-depth ratios". Astronomy and Astrophysics 411 (3): 559–564. arXiv:astro-ph/0308429. Bibcode:2003A&A...411..559K. doi:10.1051/0004-6361:20031378.
6. ^ a b C. Saffe; Gómez, M. et al. (2005). "On the Ages of Exoplanet Host Stars". Astronomy and Astrophysics 443 (2): 609–626. arXiv:astro-ph/0510092. Bibcode:2005A&A...443..609S. doi:10.1051/0004-6361:20053452.
7. ^ "#72 HIP 53721". TPF-C Top 100. Archived from the original on 19 August 2006. Retrieved 22 July 2006.
8. ^ E. E. Mamajek, L. A. Hillenbrand (2008). "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics". Astrophysical Journal 687 (2): 1264–1293. arXiv:0807.1686. Bibcode:2008ApJ...687.1264M. doi:10.1086/591785.
9. ^ R. P. Butler; Marcy, Geoffrey W. (1996). "A Planet Orbiting 47 Ursae Majoris". Astrophysical Journal Letters 464 (2): L153–L156. Bibcode:1996ApJ...464L.153B. doi:10.1086/310102.
10. ^ a b c P. C. Gregory, D. A. Fischer (2010). "A Bayesian periodogram finds evidence for three planets in 47 Ursae Majoris". Monthly Notices of the Royal Astronomical Society 403 (2): 731–747. arXiv:1003.5549. Bibcode:2010MNRAS.403..731G. doi:10.1111/j.1365-2966.2009.16233.x.
11. ^ I. Han, D. C. Black, G. Gatewood (2001). "Preliminary Astrometric Masses for Proposed Extrasolar Planetary Companions". Astrophysical Journal Letters 548 (1): L57–L60. Bibcode:2001ApJ...548L..57H. doi:10.1086/318927.
12. ^ D. Pourbaix, F. Arenou (2001). "Screening the Hipparcos-based astrometric orbits of sub-stellar objects". Astronomy and Astrophysics 372 (3): 935–944. arXiv:astro-ph/0104412. Bibcode:2001A&A...372..935P. doi:10.1051/0004-6361:20010597.
13. ^ a b D. A. Fischer; Marcy, Geoffrey W. et al. (2002). "A Second Planet Orbiting 47 Ursae Majoris". Astrophysical Journal 564 (2): 1028–1034. Bibcode:2002ApJ...564.1028F. doi:10.1086/324336.
14. ^ D. Naef; Mayor, M. et al. (2004). "The ELODIE survey for northern extra-solar planets. III. Three planetary candidates detected with ELODIE". Astronomy and Astrophysics 414: 351–359. arXiv:astro-ph/0310261. Bibcode:2004A&A...414..351N. doi:10.1051/0004-6361:20034091.
15. ^ R. A. Wittenmyer, M. Endl, W. D.Cochran (2007). "Long-Period Objects in the Extrasolar Planetary Systems 47 Ursae Majoris and 14 Herculis". Astrophysical Journal 654 (1): 625–632. arXiv:astro-ph/0609117. Bibcode:2007ApJ...654..625W. doi:10.1086/509110.
16. ^ "Planets Table". Catalog of Nearby Exoplanets. Archived from the original on 21 September 2008. Retrieved 2008-10-04.
17. ^ Jean Schneider (2011). "Notes for Planet 47 Uma c". Extrasolar Planets Encyclopaedia. Retrieved 3 October 2011.
18. ^ B. Jones; Underwood, David R. et al. (2005). "Prospects for Habitable "Earths" in Known Exoplanetary Systems". Astrophysical Journal 622 (2): 1091–1101. arXiv:astro-ph/0503178. Bibcode:2005ApJ...622.1091J. doi:10.1086/428108.
19. ^ S. Raymond (2006). "The Search for other Earths: limits on the giant planet orbits that allow habitable terrestrial planets to form". Astrophysical Journal Letters 643 (2): L131–134. arXiv:astro-ph/0605136. Bibcode:2006ApJ...643L.131R. doi:10.1086/505596.
20. ^ А. Л. Зайцев (7 June 2004). "Передача и поиски разумных сигналов во Вселенной". Пленарный доклад на Всероссийской астрономической конференции ВАК-2004 "Горизонты Вселенной", Москва, МГУ. (Russian)