Astronomy:HD 97658

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Short description: Star in the constellation Leo
HD 97658
Observation data
Equinox J2000.0]] (ICRS)
Constellation Leo[1]
Right ascension  11h 14m 33.1613s[2]
Declination +25° 42′ 37.392″[2]
Apparent magnitude (V) 7.762±0.012[3]
Characteristics
Evolutionary stage Main sequence[4]
Spectral type K1V[5]
B−V color index 0.843±0.022[3]
Variable type Planetary transit variable
Astrometry
Radial velocity (Rv)−1.579±0.0011[6] km/s
Proper motion (μ) RA: −107.534±0.091[2] mas/yr
Dec.: 48.662±0.090[2] mas/yr
Parallax (π)46.412 ± 0.022[7] mas
Distance70.27 ± 0.03 ly
(21.55 ± 0.01 pc)
Absolute magnitude (MV)6.14[8]
Details
Mass0.773+0.015−0.018[7] M☉
Radius0.728±0.008[7] R☉
Luminosity (bolometric)0.351±0.007[7] L☉
Surface gravity (log g)4.52 ± 0.06[3] cgs
Temperature5212±43[7] K
Metallicity [Fe/H]−0.30±0.03[3] dex
Rotation38.5±1.0[3]
Rotational velocity (v sin i)0.92±0.05[3] km/s
Age3.9+2.6−2.03[7] Gyr
Other designations
BD+26° 2184, GJ 3651, HD 97658, HIP 54906, SAO 81730, GSC 01981-01168, 2MASS J11143316+2542374[9]
Database references
SIMBADdata

HD 97658 is a star with an exoplanetary companion in the equatorial constellation of Leo. The star is too dim to be seen with the naked eye, having an apparent visual magnitude of 7.76.[3] It is located at a distance of 70 light years based on parallax, but is slowly drifting closer with a radial velocity of −1.6 km/s.[6]

This is an ordinary K-type main-sequence star with a stellar classification of K1V.[5] The star has 77% of the mass and 73% of the radius of the Sun.[7] Estimates of the star's age ranges from four to six billion years.[7] It is spinning with a rotation period of around 39 days[3] and shows a magnetic activity cycle of 9.6 years, which is slightly shorter than the solar cycle. The chromospheric activity is lower than average for stars of this class.[10]

HD 97658 is radiating 35% of the luminosity of the Sun from its photosphere at an effective temperature of 5,212 K.[7] The star has a low metallicity – the atmospheric abundance of elements with a higher atomic number than helium, which explains why it lies 0.46 magnitudes below average for main sequence stars of its type.[4]

Planetary system

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🜨.[4] 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.[3] However, the occurrence of transits was quietly retracted on April 11, 2012,[11] and three days later it was announced that observations by the MOST space telescope could not confirm transits.[12] 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.[13] 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.[13] 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.[13] The gravity on this exoplanet's surface is about 1.6 times greater than that of Earth's.[13][14] The planetary transmission spectrum of HD 97658 b taken in 2020 have revealed presence of clouds up to millibar pressure. Although no conclusion can be made on atmosphere composition, best model fitting is obtained with hydrogen-helium envelope with carbon monoxide and methane admixture.[10] No helium was detected at HD 97658 b in 2020 though.[15]

The HD 97658 planetary system[13][14][10]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b 7.81 +0.55−0.44 M⊕ 0.0796 ± 0.0012 9.49073 ±0.00015 0.03 +0.034−0.021 89.6 ±0.1° 2.247 +0.098−0.095 R⊕

See also

References

  1. ↑ Roman, Nancy G. (1987). "Identification of a Constellation From a Position". Publications of the Astronomical Society of the Pacific 99 (617): 695–699. doi:10.1086/132034. Bibcode: 1987PASP...99..695R.  Vizier query form
  2. ↑ 2.0 2.1 2.2 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Henry, Gregory W.; et al. (2011). "Detection of a Transiting Low-Density Super-Earth". arXiv:1109.2549v1 [astro-ph.SR].
  4. ↑ 4.0 4.1 4.2 Howard, Andrew W. et al. (2011). "The NASA-UC Eta-Earth Program. III. A Super-Earth Orbiting HD 97658 and a Neptune-mass Planet Orbiting Gl 785". The Astrophysical Journal 730 (1): 10. doi:10.1088/0004-637X/730/1/10. Bibcode: 2011ApJ...730...10H. 
  5. ↑ 5.0 5.1 Koen, C. et al. (April 21, 2010). "UBV(RI)CJHK observations of Hipparcos-selected nearby stars". Monthly Notices of the Royal Astronomical Society 403 (4): 1949–1968. doi:10.1111/j.1365-2966.2009.16182.x. Bibcode: 2010MNRAS.403.1949K. 
  6. ↑ 6.0 6.1 Soubiran, C. et al. (2018). "Gaia Data Release 2. The catalogue of radial velocity standard stars". Astronomy and Astrophysics 616: A7. doi:10.1051/0004-6361/201832795. Bibcode: 2018A&A...616A...7S. 
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Ellis, Tyler G. et al. (2021). "Directly Determined Properties of HD 97658 from Interferometric Observations". The Astronomical Journal 162 (3): 118. doi:10.3847/1538-3881/ac141a. Bibcode: 2021AJ....162..118E. 
  8. ↑ Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode: 2012AstL...38..331A. 
  9. ↑ "HD 97658". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+97658. 
  10. ↑ 10.0 10.1 10.2 Guo, Xueying et al. (2020). "Updated Parameters and a New Transmission Spectrum of HD 97658b". The Astronomical Journal 159 (5): 239. doi:10.3847/1538-3881/ab8815. Bibcode: 2020AJ....159..239G. 
  11. ↑ Henry, Gregory W.; et al. (2011). "Detection of a Transiting Low-Density Super-Earth". arXiv:1109.2549v2 [astro-ph.SR].
  12. ↑ Dragomir, Diana et al. (2012). "Non-detection of transits of the super-Earth HD 97658b with MOST photometry". The Astrophysical Journal 759 (2): L41. doi:10.1088/2041-8205/759/2/L41. Bibcode: 2012ApJ...759L..41D. http://library2.smu.ca/xmlui/handle/01/25345. 
  13. ↑ 13.0 13.1 13.2 13.3 13.4 Dragomir, Diana et al. (May 2013). "MOST Detects Transits of HD 97658b, a Warm, Likely Volatile-rich Super-Earth". The Astrophysical Journal 772 (1): L2. doi:10.1088/2041-8205/772/1/L2. Bibcode: 2013ApJ...772L...2D. 
  14. ↑ 14.0 14.1 Van Grootel, V. et al. (1 May 2014). "Transit confirmation and improved stellar and planet parameters for the super-Earth HD 97658 b and its host star". The Astrophysical Journal 786 (1): 2. doi:10.1088/0004-637X/786/1/2. Bibcode: 2014ApJ...786....2V. 
  15. ↑ Kasper, David et al. (2020). "Non-detection of Helium in the Upper Atmospheres of Three Sub-Neptune Exoplanets". The Astronomical Journal 160 (6): 258. doi:10.3847/1538-3881/abbee6. Bibcode: 2020AJ....160..258K. 

Coordinates: Sky map 11h 14m 33.1613s, +25° 42′ 37.392″



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