LTT 1445
 Hubble ACS/HRC image showing all three stars. Upper left is LTT 1445 A and in the lower right part of the image is the LTT 1445 BC pair. | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Eridanus |
| LTT 1445 A | |
| Right ascension | 03h 01m 51.39s[1] |
| Declination | −16° 35′ 36.1″[1] |
| Apparent magnitude (V) | 11.22 ± 0.02[1] |
| LTT 1445 BC | |
| Right ascension | 03h 01m 51.04s[1] |
| Declination | –16° 35′ 31.1″[1] |
| Apparent magnitude (V) | 11.37±0.03[1] |
| Characteristics | |
| Spectral type | M2.5+M3.0+M[2][1] |
| Astrometry | |
| LTT 1445 A | |
| Proper motion (μ) | RA: -369.196 ± 0.140[3] mas/yr Dec.: -268.510 ± 0.147[3] mas/yr |
| Parallax (π) | 145.6922 ± 0.0244[4] mas |
| Distance | 22.387 ± 0.004 ly (6.864 ± 0.001 pc) |
| Orbit[1] | |
| Primary | LTT 1445 B |
| Companion | LTT 1445 C |
| Period (P) | 36.2 ± 5.3 yr |
| Semi-major axis (a) | 1.159 ± 0.076″ |
| Eccentricity (e) | 0.50 ± 0.11 |
| Inclination (i) | 89.64 ± 0.13° |
| Longitude of the node (Ω) | 137.63 ± 0.19° |
| Periastron epoch (T) | 2019.2 ± 1.7 |
| Argument of periastron (ω) (secondary) | 209 ± 13° |
| Details | |
| Mass | A: 0.256 ± 0.014[1] M☉ B: 0.215 ± 0.014[1] M☉ C: 0.161 ± 0.014[1] M☉ |
| Radius | A: 0.276+0.024 −0.019[1] R☉ B: 0.236 ± 0.027[1] R☉ C: 0.197 ± 0.027[1] R☉ |
| Luminosity (bolometric) | A: 0.00805 ± 0.00035[1] L☉ |
| Surface gravity (log g) | A: 4.967+0.061 −0.075[1] cgs |
| Temperature | A: 3337 ± 150[1] K |
| Metallicity [Fe/H] | A: -0.34 ± 0.08[1] dex |
| Other designations | |
| Database references | |
| SIMBAD | A,BC |
LTT 1445 is a triple M-dwarf system about 22 light-years distant[5] in the constellation Eridanus. The primary LTT 1445 A hosts two exoplanets- one discovered in 2019 that transits the star every 5.36 days, and another found in 2021 that transits the star every 3.12 days, close to a 12:7 resonance. As of August 2019 it is the second closest transiting exoplanet system discovered, with the closest being HD 219134 bc.[5]
Stellar system[]
All three stars in the system are M-dwarfs, with masses between 0.16 M☉ and 0.26 M☉. LTT 1445 A and LTT 1445 BC are separated by about 34 astronomical units and orbit each other with a period of about 250 years. The BC pair orbit each other about every 36 years in an eccentric orbit (e= ~0.5). The alignment of the three stars and the edge-on orbit of the BC pair suggests co-planarity of the system. The existence of a transiting planet LTT 1445Ab suggests that the entire system is co-planar, with orbits in one plane.[1]
The TESS light curve showed stellar flares and rotational modulation due to starspots, likely on either the B or C component.[1][6]
Planetary system[]
LTT 1445Ab was discovered in June 2019[7] with data from the Transiting Exoplanet Survey Satellite by astrophysicists of the Harvard Center for Astrophysics.[5] The team obtained follow-up observations, including HARPS radial velocity measurements to constrain the mass of the planet. The planet orbits only one host star in a stable orbit. The planet likely has a rocky composition and because it orbits close to the M-dwarf, it has an equilibrium temperature of 433+28
−27 Kelvin (160 °C; 320 °F).[1]
In July 2021, the mass of the planet was measured as 2.87±0.25 Earth masses, confirming an earthlike composition.[8] A second planet, LTT 1445Ac, was also found on a 3.1 day orbital period, with a mass of 1.54+0.20
−0.19 Earth masses. Although it transits the star too, its smaller size made it difficult to detect before the radial velocity measurements, and still makes it difficult to estimate its exact size.[8] The planets orbit near a 12:7 orbital resonance with one another - Ac orbiting 11.988 times for every 7 orbits Ab makes - oscillating one full orbit away from a 'perfect' resonance every 104 years.
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| 1.54+0.20 −0.19 M |