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HD 219828 is a star with two exoplanetary companions in the constellation of Pegasus. With an apparent visual magnitude of 8.04, it is an eighth magnitude star that is too dim to be readily visible to the naked eye. The star is located at a distance of approximately 237 light years from the Sun based on parallax measurements, but is drifting closer with a radial velocity of −24 km/s.

The stellar classification of this star is G0IV, matching a subgiant star that is ending the hydrogen fusion in its core. It is a metal-rich star that has slightly evolved off the main sequence. HD 219828 is older than two billion years with a low level of chromospheric activity and is spinning with a projected rotational velocity of 2.9 km/s. It has 1.23 times the mass of the Sun with radius estimates ranging from 1.47 to 1.69 the Sun's girth. The star is radiating three times the luminosity of the Sun from its slightly enlarged photosphere at an effective temperature of 5,891 K.

Planetary system

In 2007, a Neptune-mass planet was found orbiting the star by Melo. According to the author, assuming an Earth-like rocky composition, the planet could have a radius 2.2 times that of Earth. This could be demonstrated if a transit were observed, though, as authors state, it would be a difficult task. At this point, it was suggested that a best fit orbital solution hints the presence of an additional planetary companion (so far unconfirmed) with 70% of Jupiter's mass, likely orbital separation of 0.68 Astronomical units and eccentric orbit (e=0.3). However, in 2016, refined analysis of the radial velocity data confirmed the presence of an outer planet (or possibly a brown dwarf) larger and more eccentric than was originally believed. With a high eccentricity and a high mass ratio between the two planets, the system is quite unique. The planet c is a potential target for Gaia astrometry or atmospheric characterization using direct imaging or high-resolution spectroscopy, and in 2022 its inclination and true mass were measured using Gaia astrometry.

See also

• HD 159868
• List of extrasolar planets

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. ^ Santos, N. C.; et al. (2016). "An extreme planetary system around HD219828. One long-period super Jupiter to a hot-neptune host star". Astronomy & Astrophysics. 592: A13. arXiv:1605.06942. Bibcode:2016A&A...592A..13S. doi:10.1051/0004-6361/201628374. S2CID 96428891.
3. "HD 219828". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-12-19.
4. Valencia, Diana; et al. (2006). "Internal structure of massive terrestrial planets". Icarus (Submitted manuscript). 181 (2): 545–554. arXiv:astro-ph/0511150. Bibcode:2006Icar..181..545V. doi:10.1016/j.icarus.2005.11.021. S2CID 118946944.
5. Melo, C.; et al. (2007). "A new Neptune-mass planet orbiting HD 219828". Astronomy and Astrophysics. 467 (2): 721–727. arXiv:astro-ph/0702459. Bibcode:2007A&A...467..721M. doi:10.1051/0004-6361:20066845. S2CID 13524822.
6. ^ Feng, Fabo; Butler, R. Paul; et al. (August 2022). "3D Selection of 167 Substellar Companions to Nearby Stars". The Astrophysical Journal Supplement Series. 262 (21): 21. arXiv:2208.12720. Bibcode:2022ApJS..262...21F. doi:10.3847/1538-4365/ac7e57. S2CID 251864022.

External links

• "HD 219828". Extrasolar Planets Encyclopaedia. Archived from the original on July 2, 2007.

v t e Constellation of Pegasus
Pegasus in Chinese astronomy List of stars in Pegasus
Stars	Bayer α (Markab) β (Scheat) γ (Algenib) δ (Alpheratz) ε (Enif) ζ (Homam) η (Matar) θ (Biham) ι κ λ μ (Sadalbari) ν ξ ο π π ρ σ τ (Salm) υ (Alkarab) φ χ ψ Flamsteed 1 2 3 4 5 7 9 11 12 13 14 15 16 17 18 19 20 21 23 25 28 30 31 32 33 34 35 36 37 38 39 40 41 45 51 (Helvetios) 52 55 56 57 58 59 60 61 63 64 65 66 67 69 70 71 72 73 74 75 76 77 78 79 80 82 83 85 86 87 23 Psc 34 Vul Variable R S U W Z RU RV RZ SV TW TY AG AQ AT AU AV AW BB BH BK BO BP BX BY DH DI DY EE EF EQ EZ GT GX HN HO HP HR HX II IK IM IP KT KU LL LO LS MS MT NV NZ OY PT V342 V343 V354 V363 V372 V376 V391 HR 19 49 8116 8219 8221 8231 8250 8257 8258 8274 8292 8325 8341 8348 8358 8359 8364 8372 8391 8397 8412 8415 8435 8441 8455 8456 8458 8460 8461 8466 8475 8482 8491 8503 8514 8543 8555 8564 8587 8604 8605 8608 8631 8638 8642 8737 8784 8788 8792 8824 8831 8833 8838 8839 8873 8922 8942 8953 8970 9039 9055 9078 9109 HD 434 204603 205011 205422 205603 206689 206793 208897 209709 210890 211076 213025 215549 215733 219196 219828 220288 220773 221170 221493 225292 Other BD+14 4559 (Solaris) BD +17 4708 BD +28 4211 GD 246 Gl 829 Gl 880 HAT-P-8 NGC 8 NGC 18 NGC 30 PG 2131+066 PG 2303+243 PSR B2127+11C PSR B2303+30 Q2343-BX418 WASP-10 WASP-21 (Tangra) WASP-52 (Anadolu) WASP-59 WASP-60 (Morava) X2127+119 3C 454.3
Exoplanets 51 Pegasi b (Dimidium) WASP-10b BD+14 4559 b (Pirx) TOI-5678 b HD 209458 b HR 8799 b c d e
Star clusters	Other Balbinot 1 Messier 15
Nebulae	Other Pease 1
Galaxies	NGC 1 2 9 14 15 16 22 23 26 41 42 52 7033 7034 7042 7043 7053 7056 7066 7068 7074 7085 7190 7217 7236 7237 7303 7312 7315 7317 7318 7319 7320 7320c 7331 7332 7427 7448 7454 7457 7466 7469 7479 7610 7619 7625 7673 7674 7678 7720 7726 7735 7741 7742 NGC 7752 NGC 7753 7767 7769 7773 7800 7814 Other BX442 CTA-102 Einstein Cross Huchra's lens IC 5145 IC 5337 Markarian 335 Pegasus Dwarf Irregular Galaxy Pegasus Dwarf Spheroidal Galaxy Q2343-BX418
Galaxy clusters Abell 2390 NGC 7331 Group Stephan's Quintet
Astronomical events SN 1990U SN 2008ha SN 2013fs
Category

• G-type subgiants
• Planetary systems with two confirmed planets
• Pegasus (constellation)
• Durchmusterung objects
• Henry Draper Catalogue objects
• Hipparcos objects