HD 3167

HD 3167 is a single,[4] orange-hued star in the zodiac constellation of Pisces that hosts a system with three exoplanets.[8][9] The star is too faint to be seen with the naked eye, having an apparent visual magnitude of 8.97.[2] The distance to HD 3167 can be determined from its annual parallax shift of 21.1363 mas as measured by the Gaia space observatory,[1] yielding a range of 154 light years. It has a relatively high proper motion, traversing the celestial sphere at the rate of 0.204″ per year.[10] Since it was first photographed during the Palomar observatory sky survey in 1953, it had moved over 12.5″ by 2017.[5] The star is moving away from the Earth with an average heliocentric radial velocity of +19.5 km/s.[4]

HD 3167
Observation data
Epoch J2000      Equinox J2000
Constellation Pisces
Right ascension 00h 34m 57.524s[1]
Declination +04° 22′ 53.28″[1]
Apparent magnitude (V) 8.97[2]
Characteristics
Evolutionary stage Main sequence
Spectral type K0 V[3]
B−V color index 0.827±0.021
Variable type Constant[2]
Astrometry
Radial velocity (Rv)+19.5±0.1[4] km/s
Proper motion (μ) RA: +107.569 mas/yr[1]
Dec.: −173.334 mas/yr[1]
Parallax (π)21.1363 ± 0.0187 mas[1]
Distance154.3 ± 0.1 ly
(47.31 ± 0.04 pc)
Absolute magnitude (MV)5.67[2]
Details[5][6]
Mass0.837+0.053
−0.043 M☉
Radius0.880+0.012
−0.013 R☉
Luminosity0.56[2] L☉
Surface gravity (log g)4.47±0.05 cgs
Temperature5,261±60 K
Metallicity [Fe/H]0.04±0.05 dex
Rotational velocity (v sin i)1.7±1.1 km/s
Age7.8±4.3 Gyr
Other designations
K2-96, BD+03° 68, HD 3167, HIP 2736, LTT 10198, EPIC 220383386, 2MASS J00345752+0422531[7]
Database references
SIMBADdata

This is an ordinary K-type main-sequence star with a stellar classification of K0 V[3] and no significant variability.[2] The star has 86% of the mass of the Sun and 86% of the Sun's radius.[5] It is a chromospherically inactive[4] star and is radiating 56%[2] of the Sun's luminosity from its photosphere at an effective temperature of 5,261 K. The spin of the star displays a relatively low projected rotational velocity of around 1.7 km/s. It has a near solar metallicity – a term astronomers use for the proportion of elements other than hydrogen and helium in a stellar atmosphere.[5]

In October 2021, astronomers reported that the orbits of the detected exoplanets hosted by the star are oddly unusual: two planets (HD 3167 c; HD 3167 d) revolve around the star on polar orbits, i.e. orbits that pass over the poles of the star, whereas the third planet (HD 3167 b) orbits around the equator of the star instead.[11][12]

Planetary system

In 2016, data collected during the extended K2 mission of the Kepler space telescope was used to identify two transiting exoplanet candidates orbiting this star, designated HD 3167 b and HD 3167 c. This made it one of the closest and brightest such multi-transiting stars known at the time. The lack of chromospheric activity makes it ideal for the precise radial velocity (RV) measurements needed to estimate the masses of its planets.[4] Follow-up RV observations showed additional perturbation signals beyond the two planets already identified.[13] This led to the discovery in 2017 of a third, non-transiting planet, designated HD 3167 d.[5]

The close-orbiting body HD 3167 b has a mass of 5.02 M🜨 and radius 1.70 R🜨. It most likely has had its atmosphere stripped away by the host star, leaving a rocky planet with about 15% iron by mass. HD 3167 b is orbiting HD 3167 with a period of 23.03 hours, an orbital inclination of 83.4°, and an assumed orbital eccentricity of zero – a circular orbit. The semimajor axis of its orbit is 0.01815 AU, or just four times the star's radius.[5]

The second planet, HD 3167 c, has an orbital period of 29.8454 days and an eccentricity of less than 0.267. The semimajor axis is 0.1795 AU. It has 9.80 M🜨 and 3.01 R🜨, giving it a low bulk density of 1.97+0.94
−0.59 g/cm3.[5] This suggests either a mini-Neptune[13] with a gaseous envelope consisting mainly of hydrogen and helium, or a planet consisting of mostly water. In 2020, transmission spectroscopy measurements of its atmosphere strongly favored a model with a high (>700 × Solar) metallicity atmosphere, due to discovered molecular absorption bands which cannot be attributed to hydrogen or helium.[14] The incident flux from the host star is around 16 times the amount the Earth receives from the Sun, and it is less susceptible to atmospheric stripping than HD 3167 b.

The orbital inclination of HD 3167 d is inclined at least 1.3° away from the orbital planes of the other two exoplanets. Its orbit is expected to remain stable for periods longer than 100 million years only if this inclination is less than 40°. It has an orbital period of 8.509±0.045 d, placing it in between the other two orbits, and shows a minimum mass of 6.90 M🜨. The true mass is most likely less than Neptune.[5]

A fourth planet, HD 3167 e, was discovered in 2022 by the radial-velocity method.[15]

The HD 3167 planetary system[6]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 4.97+0.24
−0.23 M🜨		 0.01796+0.00037
−0.00031		 0.959641±0.000011 0 (fixed) 83.4+4.6
−7.7°		 1.67+0.17
−0.10 R🜨
d ≥4.33±0.45 M🜨 0.0763±0.0015 8.4112±0.0052 <0.12 — —
c 11.13+0.78
−0.74 M🜨		 0.1776+0.0037
−0.0031		 29.8454±0.0012 <0.060 89.3+0.5
−1.0°		 3.00+0.45
−0.21 R🜨
e ≥8.41±1.02 M🜨 0.3885±0.0079 96.63±0.29 <0.15 — —

References
  1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  3. Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, 5, Bibcode:1999MSS...C05....0H.
  4. Vanderburg, Andrew; et al. (September 2016), "Two Small Planets Transiting HD 3167", The Astrophysical Journal Letters, 829 (1): 6, arXiv:1607.05248, Bibcode:2016ApJ...829L...9V, doi:10.3847/2041-8205/829/1/L9, S2CID 41001644, L9.
  5. Christiansen, Jessie L.; Vanderburg, Andrew; et al. (September 2017), "Three's Company: An Additional Non-transiting Super-Earth in the Bright HD 3167 System, and Masses for All Three Planets", The Astronomical Journal, 154 (3): 17, arXiv:1706.01892, Bibcode:2017AJ....154..122C, doi:10.3847/1538-3881/aa832d, S2CID 54196245, 122.
  6. Bonomo, A. S.; Dumusque, X.; et al. (April 2023). "Cold Jupiters and improved masses in 38 Kepler and K2 small-planet systems from 3661 high-precision HARPS-N radial velocities. No excess of cold Jupiters in small-planet systems". Astronomy & Astrophysics. arXiv:2304.05773.
  7. "HD 3167". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved October 6, 2018.
  8. Anderson, Natali (June 11, 2017), "HD 3167d: New Super-Earth Discovered around Nearby Star", Science News, Sci-News.com, retrieved October 7, 2018.
  9. Nowakowski, Tomasz (July 20, 2016), "Two super-Earth-sized planets discovered orbiting a nearby star", Phys.org, Science X Network, retrieved October 7, 2018.
  10. Lépine, Sébastien; Shara, Michael M. (March 2005), "A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)", The Astronomical Journal, 129 (3): 1483–1522, arXiv:astro-ph/0412070, Bibcode:2005AJ....129.1483L, doi:10.1086/427854, S2CID 2603568.
  11. O'Callaghan, Jonathan (6 November 2021), "Star System With Right-Angled Planets Surprises Astronomers - Two planets orbit the poles while another revolves around the star's equator, suggesting a mysterious, undetected force", The New York Times, retrieved 7 November 2021.
  12. Bourrier, V.; et al. (27 October 2021), "The Rossiter–McLaughlin effect revolutions: an ultra-short period planet and a warm mini-Neptune on perpendicular orbits", Astronomy & Astrophysics, 654 (A152): A152, Bibcode:2021A&A...654A.152B, doi:10.1051/0004-6361/202141527.{{citation}}: CS1 maint: multiple names: authors list (link)
  13. Gandolfi, Davide; et al. (September 2017), "The transiting multi-planet system HD3167: a 5.7 M🜨 Super-Earth and a 8.3 M🜨 mini-Neptune", The Astronomical Journal, 154 (3): 15, arXiv:1706.02532, Bibcode:2017AJ....154..123G, doi:10.3847/1538-3881/aa832a, S2CID 43466609, 123.
  14. Mikal-Evans, Thomas; et al. (2020), "Transmission Spectroscopy for the Warm Sub-Neptune HD 3167c: Evidence for Molecular Absorption and a Possible High-metallicity Atmosphere", The Astronomical Journal, 161: 18, arXiv:2011.03470, Bibcode:2021AJ....161...18M, doi:10.3847/1538-3881/abc874, S2CID 226278240.
  15. Bourrier, V.; et al. (2022), "A CHEOPS-enhanced view of the HD 3167 system", Astronomy & Astrophysics, 668: A31, arXiv:2209.06937, doi:10.1051/0004-6361/202243778, S2CID 251861892
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