HD 97658

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HD 97658
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Leo
Right ascension 11h 14m 33s
Declination +25° 42′ 37″
Apparent magnitude (V) 6.27 ± 0.10[1]
Characteristics
Spectral type K1V
B−V color index 0.843 ± 0.022[1]
Astrometry
Proper motion (μ) RA: -106.48 mas/yr
Dec.: +48.82 mas/yr
Parallax (π) 47.36 ± 0.75 mas
Distance 69 ± 1 ly
(21.1 ± 0.3 pc)
Details
Mass 0.75 ± 0.02[1] M
Radius 0.70 ± 0.02[1] R
Luminosity 0.30 ± 0.02[1] L
Surface gravity (log g) 4.52 ± 0.06[1] cgs
Temperature 5119 ± 44[1] K
Metallicity [Fe/H] -0.30 ± 0.03[1] dex
Rotation 38.5 ± 1.0[1]
Rotational velocity (v sin i) 0.92 ± 0.05[1] km/s
Age 6.1 ± 0.7[1] Gyr
Other designations
Database references
SIMBAD data

HD 97658 is a star 69 light years away in the constellation of Leo. The star is slightly too dim to be seen with the naked eye, though almost any additional equipment will allow it to be seen. The star itself is a metal-poor early K-dwarf that is somewhat older than the sun.

Planetary system[edit]

On November 1, 2010, a super-earth was announced orbiting the star along with Gliese 785 b as part of the NASA-UC Eta-Earth program. The planet orbits in just under 9.5 days and was originally thought to have a minimum mass of 8.2 ± 1.2 M.[2] Spurred by the possibility of transits, additional data was acquired for less than a year which found a lower mass for the star and hence reduced the minimum mass of the planet to 6.4 ± 0.7 M, and improved certainty on the time of possible transit. Transits of the planet were apparently detected and announced on September 12, 2011; this would make HD 97658 the second-to-brightest star with a transiting planet after 55 Cancri and indicating a low-density planet like Gliese 1214 b.[1] However, the occurrence of transits was quietly retracted on April 11, 2012,[3] and three days later it was announced that observations by the MOST space telescope could not confirm transits.[4] Transits of radii larger than 1.87 R were ruled out.

Further transit measurements were taken in April 2012 and were confirmed with transit readings made in the following year, March and April 2013. It was determined that HD 97658 b had a diameter 2.34 times that of Earth.[5] Using a radial velocity mass of 7.86 M and the radius measured from the transits taken in 2012 and 2013 and in early 2014, the density of the planet was calculated as 3.44 g cm−3.[5] It is likely therefore that the super-Earth exoplanet HD 97658 b has a large rocky core covered with a thick layer of volatiles, either a deep ocean of water or a thick atmosphere possibly made up of a mixture of helium and hydrogen.[5] The gravity on this exoplanet's surface is about 1.6 times greater than that of Earth's.[5][6]

The HD 97658 planetary system[5][6]
Companion
(in order from star)
Mass Semimajor axis
(AU)
Orbital period
(days)
Eccentricity Inclination Radius
b 7.55 +0.83
−0.79
 M
0.0796 ± 0.0012 9.4909 +0.0016
−0.0015
0.064 +0.061
−0.044
89.45 +0.37
−0.43
°
2.247 +0.098
−0.095
 R

References[edit]

  1. ^ a b c d e f g h i j k l Henry, Gregory W.; et al. (2011). "Detection of a Transiting Low-Density Super-Earth (version 1)". arXiv:1109.2549v1. 
  2. ^ Howard, Andrew W.; et al. (2010). "The NASA-UC Eta-Earth Program. III. A Super-Earth Orbiting HD 97658 and a Neptune-mass Planet Orbiting Gl 785". arXiv:1011.0414. Bibcode:2011ApJ...730...10H. doi:10.1088/0004-637X/730/1/10. 
  3. ^ Henry, Gregory W.; et al. (2011). "Detection of a Transiting Low-Density Super-Earth (version 2)". arXiv:1109.2549v2. 
  4. ^ Dragomir, Diana; et al. (2012). "Non-detection of transits of the super-Earth HD 97658b with MOST photometry". arXiv:1204.3135. Bibcode:2012ApJ...759L..41D. doi:10.1088/2041-8205/759/2/L41. 
  5. ^ a b c d e Dragomir, Diana; et al. (May 2013). "A warm, likely volatile-rich super-Earth: HD 97658b transits, but not quite when expected". arXiv:1305.7260. Bibcode:2013ApJ...772L...2D. doi:10.1088/2041-8205/772/1/L2. 
  6. ^ a b Transit confirmation and improved stellar and planet parameters for the super-Earth HD 97658 b and its host star V. Van Grootel, M. Gillon, D. Valencia, N. Madhusudhan, D. Dragomir, A.R. Howe, A.S. Burrows, B.-O. Demory, D. Deming, D. Ehrenreich, C. Lovis, M. Mayor, F. Pepe, D. Queloz, R. Scuflaire, S. Seager, D. Segransan, S. Udry