HD 15337

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HD 15337
Fornax IAU.svg
Red circle.svg
Location of HD 15337 (circled)
Observation data
Epoch J2000.0 [1]        Equinox J2000.0 [1]
Constellation Fornax
Right ascension 02h 27m 28.37813s
Declination −27° 38′ 06.7368″
Apparent magnitude  (V)9.09 [2]
Characteristics
Spectral type K1V [3]
B−V color index 0.86 [4]
J−H color index 0.338 [4]
J−K color index 0.509 [4]
Astrometry
Radial velocity (Rv)−3.882 [5] km/s
Proper motion (μ)RA: -73.581 [1] mas/yr
Dec.: −211.935 [1] mas/yr
Parallax (π)22.2922±0.016  mas [1]
Distance 146.3 ± 0.1  ly
(44.86 ± 0.03  pc)
Absolute magnitude  (MV)5.56+0.05
−0.06 [a]
Orbit [6]
Period (P)760+550
−280 yr
Semi-major axis (a)88+38
−23  AU
Eccentricity (e)0.746+0.082
−0.100
Inclination (i)116±13°
Details [7]
A
Mass 0.905±0.045 [6]   M☉
Radius 0.855±0.008  R☉
Luminosity 0.472+0.023
−0.024 [8]   L☉
Surface gravity (log g)4.37±0.08  cgs
Temperature 5131±74  K
Metallicity [Fe/H]0.03±0.04  dex
Rotation 36.55 d
Age 9.6+3.8
−3.9  Gyr
B
Mass 0.262+0.019
−0.018 [6]   M☉
Other designations
CD−28°784, CPD−28°228, Gaia DR3 5068777809824976256, HD 15337, HIP 11433, SAO 167802, PPM 245027, TOI-402, TIC 120896927, TYC 6435-434-1, 2MASS J02272838-2738064 [4]
Database references
SIMBAD data

HD 15337 (TOI-402) is a binary star in the southern constellation of Fornax. It has an apparent magnitude of 9.09, making it too faint to be observed by the naked eye from Earth, but readily visible using a small telescope. [9] It is located 146 light-years (45 parsecs) distant based on stellar parallax, and is currently heading towards the Solar System with a radial velocity of −3.9 km/s.

Contents

Characteristics

This is a relatively wide system with an orbital period that is thought to be 760 years. The semi-major axis is 88 AU, but the eccentricity of the orbit is high, at 0.75. [6]

The primary is about 15% smaller than the Sun in both mass and radius and radiates slightly less than half the Sun's luminosity from its photosphere. It has a spectral type of K1V and an effective temperature of 5,131 K (4,858 °C; 8,776 °F), giving the star an orange hue. It is 9.6+3.8
−3.9 billion years old, making it much older than the Solar System. The star has a solar-like metallicity and displays similar amounts of stellar activity to the Sun, [8] though when the star was only 150 million years old, it may have emitted between 3.7 and 127 times the high-energy luminosity of the Sun in the present day. [3]

The secondary has just 26% of the mass of the Sun. [6]

Planetary system

In May 2019, a pair of exoplanets were discovered to revolve around the primary star through transit observations by the TESS space telescope, namely HD 15337 b and c. [3] The two planets are far closer to their host star than Mercury is to the Sun (0.3871 AU [10] ), which heats them up to equilibrium temperatures of 1,001 K (728 °C; 1,342 °F) and 642 K (369 °C; 696 °F), [3] respectively, both of which are hot enough to melt lead (m.p.327  °C [11] ).

The inner planet, HD 15337 b, has a radius of 1.770 R🜨 and a mass of 6.519 M🜨. This places its density at 6.458  g/cm3 , [7] meaning it is denser than Earth (5.513  g/cm3 [12] ) and very likely to be a rocky super-Earth. [3] The outer planet, c, is only slightly more massive than b at 6.792 M🜨, but possesses a radius over 40% larger, which makes it much less dense at 2.303  g/cm3 , [7] suggesting a mini-Neptune-like composition with a thick (>0.01 M🜨 [7] ) gaseous envelope probably consisting of hydrogen and helium. [8] This striking difference in the structure of the two planets in spite of their similar masses implies that the two planets are on opposite sides of the small planet radius gap, making the HD 15337 system a prime target for research in planetary formation and evolution. [3] [8]

In 2024, the planetary parameters of both planets were precisely gauged through photometric observations by CHEOPS and radial velocity measurements by HARPS. As a result, the uncertainties of HD 15337 b's mass and radius were each reduced to less than 2% and 7%, which put the planet among the most accurately characterized terrestrial exoplanets at the time. Additionally, the radius of HD 15337 c was constrained to within a 3% margin of error. [7]

The HD 15337 A planetary system [7]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b6.519  M🜨 0.05245 [8] 4.75598040.05889.30° 1.770  R🜨
c6.792  M🜨 0.1235 [8] 17.1805460.09688.41° 2.526  R🜨

See also

Notes

  1. ↑ Calculated from star's luminosity.

References

  1. 1 2 3 4 5 Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics . 649: A1. arXiv: 2012.01533 . Bibcode:2021A&A...649A...1G. doi: 10.1051/0004-6361/202039657 . S2CID   227254300. (Erratum:  doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  2. ↑ Høg, E.; et al. (February 2000). "The Tycho-2 Catalogue of the 2.5 Million Brightest Stars". Astronomy and Astrophysics. 355 (1): L27 –L30. Bibcode:2000A&A...355L..27H.
  3. 1 2 3 4 5 6 Gandolfi, Davide; et al. (6 May 2019). "The Transiting Multi-planet System HD15337: Two Nearly Equal-mass Planets Straddling the Radius Gap". The Astrophysical Journal Letters. 876 (2). American Astronomical Society: L24. arXiv: 1903.05623 . Bibcode:2019ApJ...876L..24G. doi: 10.3847/2041-8213/ab17d9 . ISSN   2041-8205.
  4. 1 2 3 4 "HD 15337". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 9 October 2024.
  5. ↑ Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics . 616. A1. arXiv: 1804.09365 . Bibcode: 2018A&A...616A...1G . doi: 10.1051/0004-6361/201833051 . Gaia DR2 record for this source at VizieR.
  6. 1 2 3 4 5 An, Qier; Brandt, Timothy D.; Brandt, G. Mirek; Venner, Alexander (11 August 2025). "Orbits and Masses for 156 Companions from Combined Astrometry and Radial Velocities, and A Validation of Gaia Non-Single Star Solutions". The Astrophysical Journal Supplement Series . arXiv: 2508.08374 .
  7. 1 2 3 4 5 6 Rosário, N. M.; et al. (2024). "Precise characterisation of HD 15337 with CHEOPS: A laboratory for planet formation and evolution". Astronomy & Astrophysics. 686. EDP Sciences: A282. arXiv: 2403.16621 . Bibcode:2024A&A...686A.282R. doi: 10.1051/0004-6361/202347759 . ISSN   0004-6361.
  8. 1 2 3 4 5 6 Dumusque, Xavier; et al. (28 June 2019). "Hot, rocky and warm, puffy super-Earths orbiting TOI-402 (HD 15337)". Astronomy & Astrophysics. 627. EDP Sciences: A43. arXiv: 1903.05419 . Bibcode:2019A&A...627A..43D. doi: 10.1051/0004-6361/201935457 . ISSN   0004-6361.
  9. ↑ Sherrod, P. Clay; Koed, Thomas L. (2003). A Complete Manual of Amateur Astronomy: Tools and Techniques for Astronomical Observations. Astronomy Series. Courier Dover Publications. p. 9. ISBN   0-486-42820-6.
  10. ↑ Williams, David R. (25 November 2020). "Mercury Fact Sheet". NASA. Archived from the original on 3 April 2019. Retrieved 19 April 2021.
  11. ↑ Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. p. 12-219. ISBN   978-0-8493-0484-2.
  12. ↑ Williams, David R. (16 March 2017). "Earth Fact Sheet". NASA/Goddard Space Flight Center. Archived from the original on 8 May 2013. Retrieved 26 July 2018.
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