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HD 63433

HD 63433

A light curve for V377 Geminorum, plotted from TESS data,[1] with the 6.46 day rotation period shown in red,
Observation data
Epoch J2000      Equinox J2000
Constellation Gemini[a]
Right ascension 07h 49m 55.05s[2]
Declination 27° 21′ 47.45″[2]
Apparent magnitude (V) 6.92[3]
Characteristics
Evolutionary stage Main sequence[4]
Spectral type G5V[4]
Variable type BY Draconis[5][6]
Astrometry
Radial velocity (Rv)−16.07±0.13[3] km/s
Proper motion (μ) RA: −10.0268±0.0846 mas/yr[3]
Dec.: −11.3143±0.0487 mas/yr[3]
Parallax (π)44.6848 mas[7]
Distance73.035±0.073 ly
(22.4035±0.0225 pc)[3]
Absolute magnitude (MV)5.19[8]
Details[9]
Mass0.99±0.03 M☉
Radius0.912±0.034 R☉
Luminosity0.753±0.026 L☉
Surface gravity (log g)4.52±0.05[4] cgs
Temperature5640±74 K
Metallicity [Fe/H]0.03±0.05[4] dex
Rotation6.45±0.05 d
Rotational velocity (v sin i)7.3±0.3 km/s
Age414±23 Myr
Other designations
V377 Gem, BD+27°1490, HD 63433, HIP 38228, SAO 79729, PPM 98012, TOI-1726, TYC 1933-747-1, GSC 01933-00747, 2MASS J07495506+2721473[7]
Database references
SIMBADdata

HD 63433 (TOI-1726, V377 Geminorum) is a G-type main sequence star located 73 light-years from Earth in the zodiacal constellation Gemini,[9][a] visually close to the star Pollux.[7] It has nearly the same radius and mass of the Sun, hence being classified as a Sun-like star.[9] However, it is much younger than the Sun, less than one tenth as old with an age of about 400 million years.[9][b] With an apparent magnitude of 6.9, it is not visible to the naked eye, but can be seen with a small telescope[11] or binoculars.[12] Based on its kinematic, rotational and lithium abundance properties, it is part of the Ursa Major Moving Group.[9] There are three exoplanets orbiting it, one is classified as an Earth-sized planet, while the two others are mini-Neptunes.[4]

Characteristics

HD 63433 is a G-type main sequence star with a radius of 0.912 R☉, a mass of 0.99 M☉, an effective temperature of 5640 K and a spectral type G5V.[9] Its properties are quite similar to those of the Sun, which has a spectral type G2V and a temperature of 5772 K.[13] Therefore, it is classified as a solar analog.[9] HD 63433, however, is much younger than the Sun, having an age of 414 million years,[9] just 9% of the solar age of 4.6 billion years.[10] It has a surface gravity of 33.8 g[c] and a rotational period of 6.45 days,[9] which is 3.8 times faster than the Sun.

With an apparent magnitude of 6.92m,[3] it is below the limit for naked-eye visibility, generally defined as 6.5m,[14] which would mean that this star is not visible to the naked eye, but easily visible using a small telescope[11] or binoculars.[15][12] Despite being faint, HD 63433 is actually the third-brightest star with transiting exoplanets confirmed by the Transiting Exoplanet Survey Satellite, with only Pi Mensae (5.65m)[16] and HR 858 (6.38m)[17] being brighter.[9][18]

According to stellar kinematics, lithium abundance and stellar rotation, HD 63433 is part of the Ursa Major moving group.[9] It was initially identified as a possible member of this group by Gaidos (1998)[19] and included as a possible member in later analyses, until HD 63433's membership in this moving group was finally confirmed by Mann et al. in 2020.[9] As it is part of this moving group, its age is estimated at 414 ± 23 million years, the same as the group.[9]

It is located in the northern hemisphere, about 73 light-years from the Earth, in the constellation of Gemini.[11] It is visually close to Pollux, the brightest star in the constellation.[7] HD 63433 is predicted to approach within 7.33 light-years of the Sun in 1.33 million years.[20] That will make it one of the nearest stars to the Sun. Its closest neighbor is the orange dwarf HD 63991, located at a distance of 2.7 light years.[11]

Nearest stars to HD 63433[11]
Name Distance

(light-years)

HD 63991 2.7
LSPM J0801+2342 6.1
HD 68017 9
BD+31 1781 9.1
G 90-52 9.2

Variability

HD 63433 belongs to the class of BY Draconis variables,[5][6] stars have variations in their luminosity due to their rotation together with sunspots and other chromospheric activities. The brightness of the star varies by 0.05 magnitudes over a period of 6.46 days.[6]

It was found to be variable by Gaidos et al. in 2000.[21] The star was given the variable-star designation V377 Geminorum in 2006.[22]

Planetary system

The star HD 63433 is orbited by 3 exoplanets, all discovered by the transit method.

The first ones to be discovered, HD 63433 b and HD 63433 c, are mini-Neptunes[23] that were discovered in by Mann et al. in 2020 using the Transiting Exoplanet Survey Satellite.[24] In 2024, an additional planet was discovered, after an analysis of a transit signal detected by TESS. Named HD 63433 d, it is an Earth-sized planet.[25]

According to theoretical models, the compositions of the mini-Neptunes HD 63433 b and c are mostly silicate and water, with no iron dominance, surrounded by a gaseous envelope which, in the case of planet c, makes up around 2% of the planet.[23]

The planetary system of HD 63433 is quite young, at around 400 million years old, it is only 9.13% as old as the Solar System.[4][25][d] HD 63433 d is also the smallest planet that is less than 500 million years old.

Temperature
comparisons 		HD 63433 b[23] HD 63433 c[23] HD 63433 d[4]
Global equilibrium temperature 769 – 967 K
496 – 694 °C
925 – 1281 °F 		540 – 679 K
267 – 406 °C
513 – 763 °F 		1040 K
767 °C
1413 °F
The HD 63433 planetary system[4][23]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
d — 0.0503±0.0027 4.21 0.16+0.36
−0.12 		88.73±1° 1.073+0.046
−0.044 R🜨
b <21.76 M🜨 0.0719+0.0044
−0.0031 		7.11 0.24+0.27
−0.18 		— 2.14+0.087
−0.069 R🜨
c 15.54±3.86 M🜨 0.1458±0.015 20.55 0.161+0.014
−0.013 		— 2.692+0.108
−0.088 R🜨

HD 63433 b

The middle planet, HD 63433 b, is a mini-Neptune planet that was discovered together with HD 63433 c.[4] HD 63433 b is 2.14 times larger than Earth,[23] but is about 45% smaller than Neptune.[e] The planet has an upper mass limit of 21.7 M🜨,[23] which is 21% greater than the mass of Neptune (17.15 M🜨 [26]). These values calculate an upper density limit of 13 g/cm3,[23] 2 times greater than that of Earth,[f] and similar to that of the chemical element Mercury. HD 63433 b orbits its parent star at a distance of 0.0719 astronomical units (10,760,000 km) – about 5 times closer than Mercury is to the Sun – and completes one revolution every 7 days and 3 hours. The relative proximity of its star makes it hot, with an equilibrium temperature between 769 and 967 Kelvin (496 and 694 °C).[23][g]

HD 63433 b was probably a mini-Neptune that later lost its atmosphere.[28] Some factors, such as the fact that no absorption of Ly-α was detected during its transit, and its mass-loss timescale being shorter than the age of the planetary system, indicate that it has already lost its primordial atmosphere, and could be a rocky planetary core.[28] However, if HD 63433 b were a rocky core, it would need to be unusually massive and, therefore, a water-rich composition in addition to an atmosphere with a high mean molecular weight could explain both the radius and the non-detection of the Ly-α.[28]

Artist's impression of known planets in the HD 63433 system and size comparison with Earth

HD 63433 c

Main article: HD 63433 c

The outermost planet, HD 63433 c, is a mini-Neptune planet discovered together with HD 63433 b.[9] It is 2.7 times larger than Earth,[23] but 30% smaller than the Solar System's ice giants, Neptune and Uranus. Being 15.5 times more massive than the Earth,[23] it is more massive than Uranus (14.54 M🜨), but still less massive than Neptune (17.15 M🜨). The density of HD 63433 c calculated at 4.6 g/cm3, slightly lower than that of Earth,[23] but greater than the densities of all gas giants in the Solar System.

Orbiting its star at a distance of 0.145 astronomical units (21,700,000 km) in an orbital period of 20 days,[23] it is the outermost planet in its planetary system, but still close to its star, making it a warm planet, with a planetary equilibrium temperature estimated between 267 and 406 °C.[23][h]

Due to the high radiation received from its star, the atmosphere of HD 63433 c, made up of hydrogen, is slowly being stripped away and escaping from the planet, like a hot air balloon.[29] The hot gas escapes into the space at a velocity of 50 km/s, forming a gas cocoon 12 times larger than the planet itself.[29] As its atmosphere evaporates, HD 63433 c will slowly become a super-Earth planet.[29]

HD 63433 d

Main article: HD 63433 d

HD 63433 d was the last planet to be discovered in the system, 4 years after planets b and c.[4] With a diameter of ~13,690 km, it is very similar to Earth in size, being only 7% larger, but its mass is currently unknown.[4] It is the innermost planet orbiting HD 63433, having a semi-major axis (mean distance from its star) of 0.0503 astronomical units (7,520,000 km) and an orbital period of just 4 days.[4] The extreme proximity to its star makes it extremely hot, having a daytime temperature estimated at 1,260 °C (2,300 °F),[4][i] hot enough to melt all the minerals present on its surface,[30] as well as being tidally locked, meaning that one half of the planet is always facing towards its star, while the other is always facing away from it.[31][25] The planet also possibly lacks a substantial atmosphere.[4][25][30]

It is believed that the dayside of the planet, always facing its star due to tidal locking, is fully composed of lava due to the high surface temperature,[32][25] in addition to possibly having volcanic activity.[33][34] Meanwhile, the nightside of the planet, which never faces its star, may be the opposite, resembling Pluto with glaciers of frozen nitrogen.[35]

HD 63433 d was discovered in 2024, through an analysis of a transit observation made by the Transiting Exoplanet Survey Satellite (TESS).[25] As two other planets had already been discovered in the system, the transit signals of these objects were removed, thus revealing an additional transit signal that reappeared every 4.2 days.[25][36][4] Further investigation allowed researchers to confirm that this signal was from another orbiting exoplanet, now called HD 63433 d.[25] The discovery was announced on January 10, 2024, in The Astronomical Journal.[31][35]

Scientific importance

The HD 63433 planetary system plays an important role in understanding the evolution of planetary systems in the first billion years after formation.[9][4] As HD 63433 is relatively bright (6.9m) and close (73 ly away), its planets b and c can have their atmospheres characterized by the Hubble Space Telescope and James Webb Space Telescope.[28] This star is also a favorable target for studies of atmospheric mass loss in exoplanets, as it is a young and active star with close-in mini-Neptune planets, in addition to having a negative radial velocity (−16.07 km/s).[28]

See also

Notes and references

  1. ^ a b Obtained with a right ascension of 07h 49m 55.06s and a declination of 27° 21′ 47.5″[7] on this website
  2. ^ The age of the Sun is around 4.6 billion years.[10]
  3. ^ From a logarithm of 4.52, later divided by 980.665.
  4. ^ The age of the Solar System is 4.532 billion years.
  5. ^ Neptune is 3.883 times larger than Earth.[26]
  6. ^ The density of Earth is 5.513 g/cm3.[27]
  7. ^ Assuming albedos of 0.6 and 0 respectively.
  8. ^ Assuming albedos of 0.6 and 0 respectively.
  9. ^ Assuming an albedo of 0, similar to the measured albedo of TRAPPIST-1b.
  1. ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 19 March 2023.
  2. ^ a b 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.
  3. ^ a b c d e "HD 63433 | NASA Exoplanet Archive". exoplanetarchive.ipac.caltech.edu. Retrieved 2024-01-13.
  4. ^ a b c d e f g h i j k l m n o p Capistrant, Benjamin K.; Soares-Furtado, Melinda; Vanderburg, Andrew; Jankowski, Alyssa; Mann, Andrew W.; Ross, Gabrielle; Srdoc, Gregor; Hinkel, Natalie R.; Becker, Juliette (2024-01-09), "TESS Hunt for Young and Maturing Exoplanets (THYME) XI: An Earth-sized Planet Orbiting a Nearby, Solar-like Host in the 400Myr Ursa Major Moving Group", The Astronomical Journal, 167 (2): 54, arXiv:2401.04785, Bibcode:2024AJ....167...54C, doi:10.3847/1538-3881/ad1039
  5. ^ a b Notsu, Yuta; Honda, Satoshi; Maehara, Hiroyuki; Notsu, Shota; Namekata, Kosuke; Nogami, Daisaku; Shibata, Kazunari (2017-02-01). "Spectroscopic observations of active solar-analog stars having high X-ray luminosity, as a proxy of superflare stars". Publications of the Astronomical Society of Japan. 69 (1): 12. arXiv:1611.03659. doi:10.1093/pasj/psw116. ISSN 0004-6264.
  6. ^ a b c "VSX : Detail for V0377 Gem". www.aavso.org. Retrieved 2024-01-21.
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  12. ^ a b Macrobert, Alan (28 July 2006). "Binoculars: Halfway to a Telescope". Sky & Telescope. American Astronomical Society. Retrieved 11 May 2024.
  13. ^ "Sun Fact Sheet". nssdc.gsfc.nasa.gov. Retrieved 2024-01-11.
  14. ^ Curtis, Heber Doust (1903-01-01). "On the limits of unaided vision". Lick Observatory Bulletin. 38: 67–69. Bibcode:1903LicOB...2...67C. doi:10.5479/ADS/bib/1903LicOB.2.67C. ISSN 0075-9317. S2CID 124815809.
  15. ^ Siegel-Itzkovich, Judy (January 14, 2024). "Earth-sized exoplanet discovered in 'our solar backyard' by international team". The Jerusalem Post. Archived from the original on January 20, 2024. Retrieved January 20, 2024.
  16. ^ Johnson, H. L.; Mitchell, R. I.; Iriarte, B.; Wisniewski, W. Z. (1966-01-01). "UBVRIJKL Photometry of the Bright Stars". Communications of the Lunar and Planetary Laboratory. 4: 99–110. Bibcode:1966CoLPL...4...99J.
  17. ^ Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000-03-01). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27 – L30. Bibcode:2000A&A...355L..27H. ISSN 0004-6361.
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  20. ^ Bailer-Jones, C.A.L.; et al. (2018), "New stellar encounters discovered in the second Gaia data release", Astronomy & Astrophysics, 616: A37, arXiv:1805.07581, Bibcode:2018A&A...616A..37B, doi:10.1051/0004-6361/201833456, S2CID 56269929.
  21. ^ Gaidos, E. J.; Henry, G. W.; Henry, S. M. (August 2000). "Spectroscopy and Photometry of Nearby Young Solar Analogs". The Astronomical Journal. 120 (2): 1006–1013. Bibcode:2000AJ....120.1006G. doi:10.1086/301488. Retrieved 11 May 2024.
  22. ^ Kazarovets, E. V.; Samus, N. N.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (August 2006). "The 78th Name-List of Variable Stars" (PDF). Information Bulletin on Variable Stars. 5721: 1. Bibcode:2006IBVS.5721....1K. Retrieved 11 May 2024.
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  26. ^ a b "Neptune Fact Sheet". nssdc.gsfc.nasa.gov. Retrieved January 24, 2024.
  27. ^ "Facts About Earth - NASA Science". science.nasa.gov. Retrieved 2023-12-04.
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  29. ^ a b c "Puffy Planets Lose Atmospheres, Become Super-Earths". hubblesite.org. February 3, 2022. Retrieved January 19, 2024.
  30. ^ a b Thomson, Jess (January 12, 2024). "Hellish World With 2,294 F 'Lava Hemisphere' Discovered by NASA". Newsweek. Retrieved January 23, 2024.
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  32. ^ Gough, Evan (January 12, 2024). "Half of this Exoplanet is Covered in Lava". Universe Today.
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