| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Caelum[a] |
| Right ascension | 04h 32m 42.63s[1] |
| Declination | −39° 47′ 12.15″[1] |
| Apparent magnitude (V) | 12.482[1] |
| Characteristics | |
| A | |
| Evolutionary stage | Red dwarf |
| Spectral type | M2V[2] |
| Apparent magnitude (B) | 13.5[1] |
| Apparent magnitude (R) | 11.533[1] |
| Apparent magnitude (G) | 9.02[1] |
| Apparent magnitude (H) | 8.501[1] |
| Apparent magnitude (K) | 8.264[1] |
| B−V color index | 1.018[1] |
| Astrometry | |
| Radial velocity (Rv) | 10.94±0.28[3] km/s |
| Total velocity | 94.6±0.4[2] km/s |
| Proper motion (μ) | RA: 239.41 mas/yr[4] Dec.: -967.77 mas/yr[4] |
| Parallax (π) | 50.34 ± 0.02 mas[3] |
| Distance | 64.79 ± 0.03 ly (19.865 ± 0.008 pc)[3] |
| Details[2] | |
| A | |
| Mass | 0.345±0.014 M☉ |
| Radius | 0.329±0.01 R☉ |
| Luminosity | 0.0145±0.0003 L☉ |
| Temperature | 3490±50 K |
| Metallicity [Fe/H] | −0.36±0.06 dex |
| Rotation | 66±22 d |
| Age | 4.22±0.87[5] or 4–9 Gyr |
| Other designations | |
. | |
| Database references | |
| SIMBAD | data |
LHS 1678 (TOI-696) is an astrometric binary star system, located about 65 light-years from the Earth in the constellation Caelum. It is made up of a red dwarf and a companion star whose nature is still uncertain, but is likely to be a brown dwarf.[2] The red dwarf star is known to host three small, close-in exoplanets.[6] The apparent magnitude of LHS 1678 is 12.5, which is too dim to be seen with the naked eye or a small telescope.[7]
Characteristics edit
LHS 1678 is a binary star, more precisely an astrometric binary. It is made up of a red dwarf star and a likely brown dwarf star.[2] They are sometimes called LHS 1678 A and B, respectively.[4] The projected separation of the system, i.e. the observed separation between both stars, is a maximum of 5 astronomical units (750,000,000 km). The orbit is expected to be highly inclined, and the orbital period is in the order of decades.[2]
The system is located in the southern celestial hemisphere, within the constellation Caelum. The apparent magnitude is 12.5, which is too faint to be seen to the naked eye or even a small telescope.[7] Gaia DR3 provides a parallax of 50.34 mas to LHS 1678, which translates into a distance of 19.86 pc (64.8 ly) to the system.[3] LHS 1678 is moving away from Earth at a velocity of 10.9 km/s.[3] The system has a high proper motion, from 1983 to 2022, it has moved 0.5 arcminutes across the sky.[2]
LHS 1678 A edit
The primary component of the system is a red dwarf star (spectral type M3V, sometimes called LHS 1678 A[4]) which has 0.345 times the mass and 0.329 times the Sun's radius.[2] It has a surface effective temperature of 3,490 K (3,220 °C), which is significantly cooler than the Sun,[b] and is emitting a luminosity equivalent to 1.45% of the solar luminosity.[2] LHS 1678 A is metal-poor compared to the Sun, with an abundance of iron equivalent to 44% of the solar level.[2] Its rotational period is between 42 and 86 days[2][c] (the Sun's rotational period is 24.5 days for reference[8]), and its age is estimated to be 4.22 billion years.[5] It hosts three exoplanets orbiting it which are smaller than Earth.[6]
LHS 1678 A occupes an unusual position in the HR diagram. It is located in a narrow position in the diagram, characterized by a gap in the lower main sequence. This gap, which can be more accurately described as a deficit of stars, is associated with a transition from partially convective interiors to fully convective interiors in red dwarfs.[2]
The star has little variability in its brightness; no signs of starspots or stellar flares have been found after two months of observations. It also shows no signs of magnetic activity.[2]
LHS 1678 B edit
The secondary companion is a probable brown dwarf, sometimes called LHS 1678 B,[4] that has been detected trough long-baseline astrometry from RECONS.[2] Observations from the Very Large Telescope's NaCo adaptive optics rule out any companion with a mass larger than 70 MJ at a projected separation larger than 5 astronomical units. The companion has been not observed directly. It may be intsead a Jovian planet, but the astrometric monitoring data indicates that it is likely a brown dwarf. The possibility of the companion to be a white dwarf is ruled out by the astrometry and radial velocity of the system. It is more likely in or below the hydrogen burning limit, but is nature remains uncertain.[2]
The nearest star to the system is Alpha Caeli, at a distance of 3.3 light-years.[7] Alpha Caeli is also the brightest star in Caelum.
| Name | Distance
(light-years) |
|---|---|
| Alpha Caeli | 3.3 |
| UPM J0448-3539 | 5.9 |
| L 147-6 | 6 |
| CD-34 1770 | 7.5 |
| UPM J0415-4602 | 8 |
Planetary system edit
The red dwarf LHS 1678 hosts three exoplanets, which are smaller than Earth and were discovered by the transit method.[4] The first exoplanets discovered were LHS 1678 b and c, discovered by Silverstein et al. 2022, which also announced the existence of a third possible exoplanet.[2] This planet was later confirmed in 2024, and received the designation LHS 1678 d.[6]
All planets are close to their host star: LHS 1678 b, c and d have orbital periods of about 21 hours, 3.7 and 5 days respectively. LHS 1678 c and d are close to a 4:3 orbital resonance, meaning that for every four orbits completed by LHS 1678 c, LHS 1678 d completes three orbits. Orbital resonances in planetary systems are occasionally linked to transit-timing variations, but no transit-timing variations were detected during a 3-year span.[6]
The masses of the planets have been not measured, but future high-quality radial velocity measurements might measure their masses. Estimates of 0.26+0.14
−0.1 M🜨, 0.81+0.55
−0.29 M🜨 and 0.92+0.66
−0.34 M🜨 for the planets b, c and d were placed using the forecaster procedure, with large margins of error.[6]
| Name | Mass (ME) |
Radius (R🜨) |
Semi-major axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Flux (S🜨) |
|---|---|---|---|---|---|---|---|
| b | 0.26+0.14 −0.1 |
0.685+0.037 −0.035 |
0.01239+0.00056 −0.00057 |
0.86 | 0.033+0.035 −0.023 |
88.53+1.02 −1.14 |
94.3+9.1 −8.1 |
| c | 0.81+0.55 −0.29 |
0.941+0.051 −0.05 |
0.0327±0.0015 | 3.694 | 0.039+0.040 −0.025 |
88.82+0.40 −0.26 |
13.5+1.3 −2.1 |
| d | 0.92+0.66 −0.34 |
0.981+0.07 −0.072 |
0.04+0.0018 −0.0017 |
4.965 | 0.036+0.06 −0.027 |
88.31+0.14 −0.13 |
9.1+0.9 −0.8 |
LHS 1678 b edit
LHS 1678 b is an ultra-short period planet.[2][6][d] It takes just 21 hours to complete an orbit around its star, and is located at a distance of 0.0124 astronomical units from it,[6] which is around 1/81 times the Earth-Sun distance.[e] Due to its close proximity to its star, the planet is bombarded with strong radiation, receiving 94 times more radiation from its star than Earth receives from the Sun.[6] This also causes the surface temperature to be hot, estimated to be over 700 K (427 °C).[2] Because of this, LHS 1678 b likely has little or no atmosphere.[6]
The planet has a radius measured to be 0.685 R🜨 (4,369 km),[6] between the radii of Mars and Venus. Its mass is estimated at 0.26 ME,[6] which an upper limit of 0.35 ME, as measured by radial velocity observations.[2]
Notes edit
- ^ Constellation obtained with a right ascension of 04h 32m 42.63s and a declination of −39° 47′ 12.15″[1] on this website.
- ^ The Sun's effective temperature is 5772 K for reference.
- ^ Provided as 64±22 d in the source, but the uncertain of ±22 implies a value between 42 and 86 days
- ^ Ultra-short period planets are planets with orbital periods lower than one day.
- ^ The semi-major axis of Earth and LHS 1678 d are 1 and 0.01239 astronomical units respectively. The ratio between both values (1/0.01239) is approximately 80.710.
References edit
- ^ a b c d e f g h i j "LHS 1678". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2024-05-16.
- ^ a b c d e f g h i j k l m n o p q r s Silverstein, Michele L.; Schlieder, Joshua E.; Barclay, Thomas; Hord, Benjamin J.; Jao, Wei-Chun; Vrijmoet, Eliot Halley; Henry, Todd J.; Cloutier, Ryan; Kostov, Veselin B.; Kruse, Ethan; Winters, Jennifer G.; Irwin, Jonathan M.; Kane, Stephen R.; Stassun, Keivan G.; Huang, Chelsea (2022-04-01). "The LHS 1678 System: Two Earth-Sized Transiting Planets and an Astrometric Companion Orbiting an M Dwarf Near the Convective Boundary at 20 pc". The Astronomical Journal. 163 (4): 151. doi:10.3847/1538-3881/ac32e3. ISSN 0004-6256.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ 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 "LHS 1678 Overview". NASA Exoplanet Archive. Retrieved May 15, 2024.
- ^ a b Engle, Scott G.; Guinan, Edward F. (2023-09-01). "Living with a Red Dwarf: The Rotation–Age Relationships of M Dwarfs". The Astrophysical Journal Letters. 954 (2): L50. doi:10.3847/2041-8213/acf472. ISSN 2041-8205.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ a b c d e f g h i j k l Silverstein, Michele L.; Barclay, Thomas; Schlieder, Joshua E.; Collins, Karen A.; Schwarz, Richard P.; Hord, Benjamin J.; Rowe, Jason F.; Kruse, Ethan; Astudillo-Defru, Nicola; Bonfils, Xavier; Caldwell, Douglas A.; Charbonneau, David; Cloutier, Ryan; Collins, Kevin I.; Daylan, Tansu (2024-03-01). "Validation of a Third Planet in the LHS 1678 System". The Astronomical Journal. 167 (6): 255. doi:10.3847/1538-3881/ad3040. ISSN 0004-6256.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ a b c "★ LHS 1678". Stellar Catalog. Retrieved 2024-03-09.
- ^ "Solar Project". www.star.bris.ac.uk. Retrieved 2024-05-17.