HD 190228 is a star with an orbiting substellar companion in the northern constellation of Vulpecula. Its apparent magnitude is 7.30[2] – too faint to be seen with the naked eye – and the absolute magnitude is 3.34.[2] Based on parallax measurements, it is located at a distance of 205 light-years (63 parsecs) from the Sun.[1] The system is drifting closer with a radial velocity of −50 km/s.[5]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Vulpecula |
| Right ascension | 20h 03m 00.77266s[1] |
| Declination | +28° 18′ 24.6871″[1] |
| Apparent magnitude (V) | 7.30[2] |
| Characteristics | |
| Evolutionary stage | subgiant[3] |
| Spectral type | G5 IV[4] |
| B−V color index | 0.793±0.006[2] |
| Astrometry | |
| Radial velocity (Rv) | −50.110±0.0032[5] km/s |
| Proper motion (μ) | RA: 104.273 mas/yr[1] Dec.: −69.961 mas/yr[1] |
| Parallax (π) | 15.8973 ± 0.0159 mas[1] |
| Distance | 205.2 ± 0.2 ly (62.90 ± 0.06 pc) |
| Absolute magnitude (MV) | 3.36[2] |
| Details[6] | |
| Mass | 1.18±0.05 M☉ |
| Radius | 2.38±0.13 R☉ |
| Luminosity | 4.57+1.39 −0.77 L☉ |
| Surface gravity (log g) | 3.92±0.02 cgs |
| Temperature | 5,311±13 K |
| Metallicity [Fe/H] | –0.24±0.06 dex |
| Rotational velocity (v sin i) | 1.43±0.51 km/s |
| Age | 5.07±0.78 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
| ARICNS | data |
The spectrum of HD 190228 presents as a subgiant star with a stellar classification of G5 IV,[4] indicating it has exhausted the supply of hydrogen at its core and is evolving off the main sequence. The star is older than the Sun with an age over 5 billion years with a projected rotational velocity of 1.4 km/s. A metal-poor star, it has 18% more mass than the Sun and has grown to 2.4 times the Sun's girth. The star is radiating roughly 4.6 times the luminosity of the Sun from its photosphere at an effective temperature of 5,311 K.[6]
Planetary system
editIn 2000, it was announced that a giant exoplanet was orbiting the star with a minimum mass of 5 Jupiter masses, designated HD 190228 b.[8][9] The planetary nature of the object was questioned because of the low metal content of the star: giant planets are more likely to be found around high-metallicity stars, so it was argued that the object was more likely to be a brown dwarf.[3] A 2011 study using astrometric measurements from Hipparcos found that, with 95% confidence, HD 190228 b is in fact a brown dwarf of 49.4±14.8 Jupiter masses in a nearly face-on orbit.[10]
However, later studies in 2022 and 2023 using both Hipparcos and Gaia astrometry found much lower true masses, close to the minimum mass. While the former study notes that their inclination measurement is poorly constrained, and that further study should better constrain the mass, the latter says that the low-mass solution is preferred given the relatively large uncertainty in the Hipparcos data.[11][12] Thus, as of 2023[update] it seems likely that HD 190228 b is an exoplanet. It takes 3.1 years to orbit the star, and its orbit is elliptical with an eccentricity of 0.55.
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (years) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 6.1+1.2 −1.0 MJ |
2.293±0.031 | 3.1391+0.0053 −0.005 |
0.547+0.01 −0.011 |
48+16 −10 or 132+10 −16° |
— |
References
edit- ^ a b c d e 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.
- ^ a b c d e 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.
- ^ a b Chen, Y. Q.; Zhao, G. (2001). "The companion of HD 190228: Planet or brown dwarf?". Astronomy and Astrophysics. 374 (1): L1–L4. Bibcode:2001A&A...374L...1C. doi:10.1051/0004-6361:20010790.
- ^ a b White, Russel J.; et al. (June 2007). "High-Dispersion Optical Spectra of Nearby Stars Younger Than the Sun". The Astronomical Journal. 133 (6): 2524–2536. arXiv:0706.0542. Bibcode:2007AJ....133.2524W. doi:10.1086/514336. S2CID 122854.
- ^ a b Soubiran, C.; et al. (2018). "Gaia Data Release 2. The catalogue of radial velocity standard stars". Astronomy and Astrophysics. 616: A7. arXiv:1804.09370. Bibcode:2018A&A...616A...7S. doi:10.1051/0004-6361/201832795. S2CID 52952408.
- ^ a b Jofré, E.; et al. (2015). "Stellar parameters and chemical abundances of 223 evolved stars with and without planets". Astronomy & Astrophysics. 574: A50. arXiv:1410.6422. Bibcode:2015A&A...574A..50J. doi:10.1051/0004-6361/201424474. S2CID 53666931.
- ^ "HD 190228". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2022-01-25.
- ^ "European Southern Observatory: Six Extrasolar Planets Discovered". SpaceRef Interactive Inc. 7 August 2000. Retrieved 15 August 2009.
- ^ Perrier, C.; et al. (2003). "The ELODIE survey for northern extra-solar planets. I. Six new extra-solar planet candidates". Astronomy and Astrophysics. 410 (3): 1039–1049. arXiv:astro-ph/0308281. Bibcode:2003A&A...410.1039P. doi:10.1051/0004-6361:20031340. S2CID 6946291.
- ^ Sahlmann, J.; et al. (2011). "The companion of HD 190228: Planet or brown dwarf?". Astronomy and Astrophysics. 525. A95. arXiv:1009.5991. Bibcode:2011A&A...525A..95S. doi:10.1051/0004-6361/201015427. S2CID 119276951.
- ^ Feng, Fabo; 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.
- ^ a b Xiao, Guang-Yao; et al. (May 2023). "The Masses of a Sample of Radial-Velocity Exoplanets with Astrometric Measurements". Research in Astronomy and Astrophysics. 23 (5): 055022. arXiv:2303.12409. Bibcode:2023RAA....23e5022X. doi:10.1088/1674-4527/accb7e. S2CID 257663647.