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HD 15337

Location of HD 15337 (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Fornax
Right ascension	02 27 28.37813
Declination	−27° 38′ 06.7368″
Apparent magnitude (V)	9.09
Characteristics
Spectral type	K1V
B−V color index	0.86
J−H color index	0.338
J−K color index	0.509
Astrometry
Radial velocity (Rv)	−3.882 km/s
Proper motion (μ)	RA: -73.581 mas/yr Dec.: −211.935 mas/yr
Parallax (π)	22.2922 ± 0.016 mas
Distance	146.3 ± 0.1 ly (44.86 ± 0.03 pc)
Absolute magnitude (MV)	5.56+0.05 −0.06
Details
Mass	0.829±0.038 M☉
Radius	0.855±0.008 R☉
Luminosity	0.472+0.023 −0.024 L☉
Surface gravity (log g)	4.37±0.08 cgs
Temperature	5131±74 K
Metallicity	0.03±0.04 dex
Rotation	36.55 d
Age	9.6+3.8 −3.9 Gyr
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
Database references
SIMBAD	data

HD 15337 (TOI-402) is a star with two orbiting exoplanets 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. 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.

The star 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, 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.

Planetary system

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

The inner planet, HD 15337 b, has a radius of 1.770 R_🜨 and a mass of 6.519 M_E. This places its density at 6.458 g/cm, meaning it is denser than Earth (5.513 g/cm) and very likely to be a rocky super-Earth. The outer planet, c, is only slightly more massive than b at 6.792 M_E, but possesses a radius over 40% larger, which makes it much less dense at 2.303 g/cm, suggesting a mini-Neptune-like composition with a thick (>0.01 M_E) gaseous envelope probably consisting of hydrogen and helium. 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.

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.

See also

• Kepler-93b: another precisely characterized hot super-Earth.

Notes

1. Calculated from star's luminosity.

References

1. ^ 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. ^ 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. ^ "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. ^ 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.
7. ^ 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.
8. 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.
9. Williams, David R. (25 November 2020). "Mercury Fact Sheet". NASA. Archived from the original on 3 April 2019. Retrieved 19 April 2021.
10. Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. p. 12-219. ISBN 978-0-8493-0484-2.
11. 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.

v t e Constellation of Fornax
List of stars in Fornax Fornax in Chinese astronomy Chandra Deep Field South Hubble Legacy Field
Stars	Bayer α (Dalim) β γ γ δ ε ζ η η η ι ι κ λ λ μ ν π ρ σ τ υ φ χ χ χ ψ ω Variable R TZ UZ HR 683 858 HD 15337 20781 20782 20868 (Intan) Other 2MASS J02431371−2453298 HIP 13044 LP 944-20 UDF 2457 WASP-72 (Diya)
Exoplanets HD 16417 b HD 20781 b c d e HD 20782 b HD 20868 b (Baiduri) TOI-849 b
Star clusters NGC 1049
Nebulae NGC 1360
Galaxies	NGC 823 824 922 986 1097 1210 1255 1288 1310 1316 1317 1318 1326 1350 1365 1374 1375 1379 1380 1381 1387 1398 1399 1406 1425 1427 Other Fornax Dwarf HUDF-JD2 GS-NDG-9422 IC 335 IC 1993 JADES-GS-z14-0 JADES-GS-z7-01-QU MRC 0316-257 PGC 13809 UDF 423 UDFj-39546284 UDFy-38135539
Galaxy clusters Fornax Cluster
Astronomical events SN 1992bd SN 1999eu SN 2003B
Category

• K-type main-sequence stars
• Planetary systems with two confirmed planets
• Fornax
• Durchmusterung objects
• Henry Draper Catalogue objects
• Hipparcos objects