My arae

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Star
Cervantes
My Arae
Schematic representation (color) of the star μ Arae and one of its planets
Schematic representation (color) of the star μ Arae and one of its planets
AladinLite
Observation
dates equinox :  J2000.0 , epoch : J2000.0
Constellation altar
Right ascension 17 h 44 m 8.7 s
declination -51 ° 50 ′ 2.6 ″
Apparent brightness 5.12 likes
Typing
Known exoplanets 4th
B − V color index +0.70 
U − B color index +0.24 
R − I index +0.34 
Spectral class G3 IV-V
Astrometry
Radial velocity (−9.42 ± 0.01) km / s
parallax (64.08 ± 0.12)  mas
distance (50.87 ± 0.09)  ly
(15.61 ± 0.03)  pc
Visual absolute brightness M vis +4.2 mag
Proper movement 
Rec. Share: (−15.31 ± 0.17)  mas / a
Dec. portion: (−190.92 ± 0.15)  mas / a
Physical Properties
Dimensions (1.10 ± 0.02)  M ☉
radius (1.36 ± 0.06)  R ☉
Luminosity

(1.90 ± 0.10)  L ☉

Effective temperature (5820 ± 50)  K.
Metallicity [Fe / H] (0.32 ± 0.02)
Rotation time approx. 27 d
Age (6.34 ± 0.80) bill.  A
Other names
and catalog entries
Bayer name μ Arae
Cordoba Survey CD −51 ° 11094
Bright Star Catalog HR 6585 [1]
Henry Draper Catalog HD 160691 [2]
Gliese catalog FY 691 [3]
Hipparcos catalog HIP 86796 [4]
SAO catalog SAO 244981 [5]
Tycho catalog TYC 8355-436-1 [6]
2MASS catalog 2MASS J17440870-5150027 [7]
Other names Cervantes, NLTT 45314, FK5  262
annotation
  1. ↑ estimated from apparent brightness and distance

My Arae ( μ Arae , also: Cervantes ) is a yellow-orange-colored, sun-like star with an apparent brightness of 5.1 mag in the northeast corner of the constellation Altar ( Ara ), where it can also be seen with the naked eye under good conditions. It is classified in the spectral class G and in the luminosity class V - IV . The star is about 50  light years from our sun. Its diameter is about 1.4 times and its mass about 1.1 times that of the sun ; this corresponds to approx. 360,000 earth masses. From the difference in brightness between μ Arae and the Sun, it can be assumed that the star is already more developed and also older than the 4.6 billion years of the Sun. In addition, it is very rich in metals .

Planetary system

In August 2006, four planets were known in the My Arae system. Three of them have a high mass and are probably so-called gas giants. The innermost planet is comparable in mass to Uranus and is either terrestrial in nature or a small gas planet .

Discovery story

In 2001 the discovery of the first planet - My Arae b (also: Quijote ) - was announced by a team of American and Australian researchers. The planet moves in a highly eccentric orbit and orbits its star once in 743 days. It was discovered by means of a measurement of the radial velocity of My arae (measurement of the Doppler shift of the spectral lines of the star ).

Further observations led to the discovery of a second object, My Arae c (also: Dulcinea ), which was made public in 2004. At that time it was assumed that it was a planet with a strongly eccentric orbit that would take 8.2 years to complete one orbit.

In the same year, the small inner planet My Arae d (also: Rocinante ) followed, with a mass comparable to that of Uranus and an orbital period of only 9 days. He thus formed the first example of a now called Hot Neptune . Its surface temperature is likely to be around 900 K. The discovery was made possible by high-precision measurements of the radial velocity My Araes with the spectrograph of the High Accuracy Radial velocity Planet Searcher (HARPS) in the La Silla Observatory of the European Southern Observatory .

In 2006, two independent teams led by researchers Krzysztof Gozdziewski and Francesco Pepe came to the conclusion that there must be a fourth planet that orbits the parent star in an almost circular orbit once every 311 days. This new model of the My Arae system is also based on other parameters for the previously discovered planets, whose orbits are now much less eccentric. With the discovery of My Arae e (also: Sancho ) the system rose to become the second known exosolar planetary system with four planets. The other was 55 Cancri , but a fifth planet has since been discovered there.

Structure of the system

The My Arae system consists of an inner uranium-sized planet with an orbital period of 9 days and three other massive companions - probably gas giants - on wide, almost circular orbits. These circular orbits are in contrast to the highly eccentric orbits usually observed in long-period exoplanets. The innermost planet could be a so-called chthonic planet - a previously hypothetical class of planets that arises when a gas planet loses its shell under the influence of the solar wind and only the rock core remains. An alternative theory states that the planet has already formed as a terrestrial planet in the innermost regions of the My-Arae system, so it is a "super-earth".

The inner gas giants e and b are almost in a 1: 2 ratio of orbital resonance and therefore strongly influence each other. However, this cannot always have been the case, as simulations show that such a system becomes unstable after 78 million years. However, since the planetary system of My Arae is much older, this orbital relationship cannot have existed from the beginning. So there are still a few questions to be answered.

The search for protoplanetary disks did not yield any results. If My Arae has a debris disk that can be compared to our Kuiper belt , it is too diffuse to be seen from Earth.

My arae planet
Planet
(according to the distance from the central star) 		Discovery year Minimum dimensions
(in M J ) 		Cycle time
(in days) 		Major semi-axis
(in AU) 		eccentricity
c ( Dulcinea ) 2004 0.03321 9.6386 ± 0.0015 0.09094 0.172 ± 0.040
d ( Rocinante ) 2004 0.5219 310.55 ± 0.83 0.9210 0.067 ± 0.012
b ( Quixote ) 2000 1.676 643.25 ± 0.90 1.497 0.128 ± 0.017
e ( Sancho ) 2006 1,814 4205.8 ± 758.9 5.235 0.099 ± 0.063

Life?

From the companions of My Araes, the gas planet b moves within the habitable zone around its star - the zone that allows water in its liquid form. The strong gravity of the gas giant should make the formation of earth-like planets impossible here; But that does not mean that the large moons around My Arae b could not have a life-friendly climate. Here, however, the question remains whether the mass of the moons would be large enough to maintain a dense atmosphere - another indispensable requirement for the existence of liquid water. In addition, the dose of ultraviolet radiation received by My Arae b is too low to support the formation of biomolecules. Planet e receives a dose of ultraviolet radiation comparable to Earth, but is too hot to have moons with a surface covered by water.

Web links

Commons : My Arae  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d mu. Era. In: SIMBAD . Center de Données astronomiques de Strasbourg , accessed on 23 August 2020 .
  2. ^ Hipparcos catalog (ESA 1997)
  3. ↑ a b c Bright Star Catalog
  4. ↑ HD 160691 from Raghavan et al .: A survey of stellar families: multiplicity of solar-type stars. 2010
  5. ↑ a b c d e f M. Soriano, S. Vauclair: New seismic analysis of the exoplanet-host star Mu Arae . In: Astronomy & Astrophysics . 513, 2009, p. A49. arxiv : 0903.5475 . bibcode : 2010A & A ... 513A..49S . doi : 10.1051 / 0004-6361 / 200911862 .
  6. ↑ Mu Arae. Jim Kaler, accessed August 23, 2020 .
  7. ↑ Naming Stars. IAU , accessed on August 23, 2020 .
  8. ^ Pepe et al .: The HARPS search for southern extra-solar planets. VIII. Μ Arae, a system with four planets . In: Astronomy & Astrophysics . 462, No. 2, 2007, pp. 769-776. arxiv : astro-ph / 0608396 . bibcode : 2007A & A ... 462..769P . doi : 10.1051 / 0004-6361: 20066194 .
  9. ↑ Naming of exoplanets. IAU , accessed on August 23, 2020 .