HD 21693
| Observation data EpochJ2000.0EquinoxJ2000.0 | |
|---|---|
| Constellation | Reticulum |
| Right ascension | 03h27m12.482s[1] |
| Declination | −58° 19′ 25.25″[1] |
| Apparent magnitude(V) | 7.94[2] |
| Characteristics | |
| Spectral type | G9IV-V[3] |
| B−Vcolor index | 0.775[2] |
| Astrometry | |
| Radial velocity(Rv) | 39.64±0.12[1]km/s |
| Proper motion(μ) | RA:248.88[1]mas/yr Dec.:94.75[1]mas/yr |
| Parallax(π) | 30.0199 ± 0.0339mas[1] |
| Distance | 108.6 ± 0.1ly (33.31 ± 0.04pc) |
| Absolute magnitude(MV) | 5.39[4] |
| Details | |
| Mass | 0.896±0.033[5]M☉ |
| Radius | 0.93[1]R☉ |
| Luminosity | 0.66[1]L☉ |
| Surface gravity(logg) | 4.37±0.04[6]cgs |
| Temperature | 5,430±26[6]K |
| Metallicity[Fe/H] | 0.00±0.02[6]dex |
| Rotation | 35.2±4.0days[7] |
| Rotational velocity(vsini) | 1.6[7]km/s |
| Age | 6.8±4.4[5]Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
HD 21693is astarin theconstellationReticulum.It has anapparent visual magnitudeof 7.94,[2]therefore it is not visible to thenaked eye.From itsparallaxmeasured by theGaiaspacecraft, it is located at a distance of 108.6light-years(33.3parsecs) from Earth.[1]
This is a G-type star with aspectral typeof G9IV-V, with features intermediate betweenmain sequenceandsubgiant.In 2011, the discovery of two Neptune-massexoplanetsaround HD 21693 was announced.
Star
[edit]This star is classified with aspectral typeof G9IV-V,[3]indicating it is a slightly evolved star that is between themain sequenceand thesubgiantbranch. Stellar evolution models suggest that it is right at the end of the main sequence, on the hook before the subgiantturnoff,[1]with a mass of 0.90M☉and an age of around 7 billion years, although with a high uncertainty of plus or minus 4 billion years.[5]From its Gaia-measured distance and brightness, it is calculated to have a radius of 0.93R☉and a luminosity of 0.66L☉.[1]Itseffective temperatureis 5,430Kand itsmetallicity,the proportion of elements heavier than helium, and approximately equal to that of the Sun.[6]
HD 21693 exhibits a stellar activity cycle with a period of 10 years, similar to thesolar cycle,evidenced by long-term variations in various spectral activity indicators. ItslogR′HKchromospheric activity indexvaries between −5.02 and −4.83 during the cycle, an amplitude that is similar to that of the Sun's magnetic cycle. This index also shows a weaker variation with a period of 33.5 days, which may correspond to the star'srotationperiod. The activity cycle also affects theradial velocityof the star, which had to be taken into account when creating the orbital solution of the planets in the system.[7]
HD 21693 has no knowncompanion stars.One observation by the NACO instrument at theVery Large Telescopefailed to detect other stars in the system, with a detection limit of 0.09M☉at 0.5arcseconds(16.7 AU).[8]
Planetary system
[edit]In 2011 the discovery of twoexoplanetsorbiting HD 21693 was announced, detected by theradial velocity methodusing observations taken by theHARPSspectrograph, at theLa Silla Observatory.[9]The detailed analysis of the discovery was only published in 2019. The HARPS instrument made 210 measurements of the star's radial velocity between 2003 and 2015, revealing two period signals caused by the gravitational influence of orbiting planets, plus a 10-year signal caused by the star's activity cycle. The planetary signals have no equivalent in the star's spectral activity indicators, which confirms their planetary nature. The radial velocityresiduals,after removing all periodic signals, still show higher variability than expected, which can be caused by stronggranulationon the star's surface.[7]
The inner planet, HD 21693 b, has aminimum massof8.2M🜨and is the transition regime betweensuper-EarthsandNeptune-mass planets. Since the radial velocity method used in its discovery cannot determine theinclinationof its orbit, the planet's true mass cannot be determined, although the true mass is usually close to the minimum value. This planet orbits the star at a distance of 0.15AUwith aperiodof 22.7 days.[7]
The outer planet, HD 21693 c, has a minimum mass of17.4M🜨,similar to the mass of Neptune. It is located at a distance of 0.26 AU from the star and has an orbital period of 53.7 days. The planets in the system have a period ratio of 2.37, which is close to a 5:2 commensurability. In one possible formation scenario, they experienced convergentmigrationshortly after their formation, which trapped them in a 5:2resonance,but this resonance was lost shortly after the dissipation of theprotoplanetary disk.[7]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | ≥8.23+1.08 −1.05M🜨 |
0.1455+0.0058 −0.0063 |
22.6786+0.0085 −0.0087 |
0.12+0.09 −0.08 |
— | — |
| c | ≥17.37+1.77 −1.79M🜨 |
0.2586+0.0103 −0.0113 |
53.7357+0.0312 −0.0309 |
0.07+0.06 −0.05 |
— | — |
See also
[edit]- Stars with planets discovered in the same paper:[7]HD 20003,HD 20781,HD 31527,HD 45184,HD 51608,HD 134060,HD 136352
References
[edit]- ^abcdefghijkVallenari, A.; et al. (Gaia collaboration) (2023)."GaiaData 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.S2CID244398875. Gaia DR3 record for this sourceatVizieR.
- ^abcd"HD 21693".SIMBAD.Centre de données astronomiques de Strasbourg.Retrieved2023-02-01.
- ^abGray, R. O.; Corbally, C. J.; Garrison, R. F.; McFadden, M. T.; Bubar, E. J.; McGahee, C. E.; O'Donoghue, A. A.; Knox, E. R. (2006), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample",The Astronomical Journal,132(1): 161–170,arXiv:astro-ph/0603770,Bibcode:2006AJ....132..161G,doi:10.1086/504637,S2CID250741593
- ^Luck, R. Earle (March 2018), "Abundances in the Local Region. III. Southern F, G, and K Dwarfs",The Astronomical Journal,155(3): 31,Bibcode:2018AJ....155..111L,doi:10.3847/1538-3881/aaa9b5,S2CID125765376,111
- ^abcDelgado Mena, E.; Moya, A.; Adibekyan, V.; Tsantaki, M.; González Hernández, J. I.; Israelian, G.; Davies, G. R.; Chaplin, W. J.; Sousa, S. G.; Ferreira, A. C. S.; Santos, N. C. (2019), "Abundance to age ratios in the HARPS-GTO sample with Gaia DR2. Chemical clocks for a range of [Fe/H]",Astronomy and Astrophysics,624:624,arXiv:1902.02127,Bibcode:2019A&A...624A..78D,doi:10.1051/0004-6361/201834783,S2CID90259810
- ^abcdSousa, S. G.; Santos, N. C.; Mayor, M.; Udry, S.; Casagrande, L.; Israelian, G.; Pepe, F.; Queloz, D.; Monteiro, M. J. P. F. G. (2008), "Spectroscopic parameters for 451 stars in the HARPS GTO planet search program. Stellar [Fe/H] and the frequency of exo-Neptunes",Astronomy and Astrophysics,487(1): 373,arXiv:0805.4826,Bibcode:2008A&A...487..373S,doi:10.1051/0004-6361:200809698,S2CID18173201
- ^abcdefghUdry, S.; Dumusque, X.; Lovis, C.; Ségransan, D.; Diaz, R. F.; Benz, W.; Bouchy, F.; Coffinet, A.; Lo Curto, G.; Mayor, M.; Mordasini, C.; Motalebi, F.; Pepe, F.; Queloz, D.; Santos, N. C.; Wyttenbach, A.; Alonso, R.; Collier Cameron, A.; Deleuil, M.; Figueira, P.; Gillon, M.; Moutou, C.; Pollacco, D.; Pompei, E. (2019), "The HARPS search for southern extra-solar planets. XLIV. Eight HARPS multi-planet systems hosting 20 super-Earth and Neptune-mass companions",Astronomy and Astrophysics,622,Bibcode:2019A&A...622A..37U,doi:10.1051/0004-6361/201731173,hdl:11336/150873
- ^Dietrich, J.; Ginski, C. (2018), "Archival VLT/NaCo multiplicity investigation of exoplanet host stars",Astronomy and Astrophysics,620:A102,arXiv:1811.09666,Bibcode:2018A&A...620A.102D,doi:10.1051/0004-6361/201731341,S2CID119294338
- ^Mayor, M.; Marmier, M.; Lovis, C.; Udry, S.; Ségransan, D.; Pepe, F.; Benz, W.; Bertaux, J. -L.; Bouchy, F.; Dumusque, X.; Lo Curto, G.; Mordasini, C.; Queloz, D.; Santos, N. C. (2011),The HARPS search for southern extra-solar planets XXXIV. Occurrence, mass distribution and orbital properties of super-Earths and Neptune-mass planets,arXiv:1109.2497
