LTT 1445 A,BC

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 51.39367s[1]
Declination −16° 35′ 36.0312″[1]
Apparent magnitude (V) 11.22±0.02[2]
LTT 1445 BC
Right ascension 03h 01m 51.04s[2]
Declination −16° 35′ 31.1″[2]
Apparent magnitude (V) 11.37±0.03[2]
Characteristics
Spectral type M2.5+M3.0+M[3][2]
Astrometry
LTT 1445 A
Radial velocity (Rv)−5.74±0.33[1] km/s
Proper motion (μ) RA: −369.972 mas/yr[1]
Dec.: −267.931 mas/yr[1]
Parallax (π)145.6922 ± 0.0244 mas[1]
Distance22.387 ± 0.004 ly
(6.864 ± 0.001 pc)
Orbit[2]
PrimaryLTT 1445 B
CompanionLTT 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
A
Mass0.257±0.014 M☉[4] M☉
Radius0.271+0.019
−0.010 R☉[4] R☉
Luminosity (bolometric)0.00805±0.00035[2] L☉
Surface gravity (log g)4.967+0.061
−0.075[2] cgs
Temperature3,337±150[2] K
Metallicity [Fe/H]−0.34±0.08[2] dex
B
Mass0.215±0.014[2] M☉
Radius0.236±0.027[2] R☉
C
Mass0.161±0.014[2] M☉
Radius0.197±0.027[2] R☉
Rotation1.4 d[4]
Other designations
BD−17 588, HIP 14101, WDS J03019-1633A,BC, IRAS 02595-1647, 2MASS J03015142-1635356, 2MASS J03015107-1635306, TIC 98796344, TOI-455, GJ 3192, GJ 3193
Database references
SIMBADA,BC

LTT 1445 is a triple M-dwarf system 22.4 light-years (6.9 parsecs) distant[1] 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 October 2022 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 transiting planets suggests that the entire system is co-planar, with orbits in one plane.[2]

The TESS light curve showed stellar flares and rotational modulation due to starspots, likely on either the B or C component.[2][6]

Planetary system

LTT 1445 Ab

LTT 1445 Ab is an exoplanet located approximately 22 light years away from Earth. Astrophysicists of the Harvard Center for Astrophysics discovered it in June 2019 with data from the Transiting Exoplanet Survey Satellite.[7][2] The team obtained follow-up observations, including HARPS radial velocity measurements to constrain the mass of the planet.

LTT 1445 Ab takes 5 days to orbit its star, which in turn orbits two sibling stars, making a total of three stars in the system.[7][8][2]

In July 2021, the mass of the planet was measured as 2.87±0.25 Earth masses, confirming an Earth-like composition.[9]

In 2022, a planetary transmission spectrum showed no evidence for an atmosphere, although an atmosphere with high altitude hazes cannot be ruled out yet.[10] LTT 1445 Ab likely has a rocky composition, and because it orbits close to the M-dwarf, it has an equilibrium temperature of 431±23 K (158 °C; 316 °F).[4]

LTT 1445 Ac

A second planet, LTT 1445 Ac, was also found in 2021 on a 3.12 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. 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.[9] The planet's existence was independently confirmed in 2022.[5]

In 2023, observations with the Hubble Space Telescope allowed a more precise determination of the planet's size, supporting a rocky composition for both planets. Its equilibrium temperature is 516±28 K (243 °C; 469 °F).[4]

LTT 1445 Ad

A third planetary candidate on a 24.3-day orbit, LTT 1445 Ad, was found in 2022. This is a possibly rocky super-Earth orbiting within the habitable zone.[5]

The LTT 1445 A planetary system[5][4]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
c 1.37±0.19 M🜨 0.02659+0.00047
−0.00049 		3.1238994 <0.223[9] 87.46+0.13
−0.21° 		1.07+0.10
−0.07 R🜨
b 2.73+0.25
−0.23 M🜨 		0.03810+0.00067
−0.00070 		5.3587635 <0.110[9] 89.53+0.33
−0.40° 		1.34+0.11
−0.06 R🜨
d ≥2.72±0.75 M🜨 0.09±0.02 24.30+0.03
−0.08 		— — —

See also

References

  1. ^ a b c d e f 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.
  2. ^ a b c d e f g h i j k l m n o p q r s Winters, Jennifer G.; et al. (October 2019). "Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M-dwarf System at 6.9 pc". The Astronomical Journal. 158 (4): 152. arXiv:1906.10147. Bibcode:2019AJ....158..152W. doi:10.3847/1538-3881/ab364d. hdl:2144/39814. ISSN 0004-6256. S2CID 195584444.
  3. ^ Henry, Todd J.; Jao, Wei-Chun; Winters, Jennifer G.; Dieterich, Sergio B.; Finch, Charlie T.; Ianna, Philip A.; Riedel, Adric R.; Silverstein, Michele L.; Subasavage, John P.; Vrijmoet, Eliot Halley (June 2018). "The Solar Neighborhood XLIV: RECONS Discoveries within 10 parsecs". The Astronomical Journal. 155 (6): 265. arXiv:1804.07377. Bibcode:2018AJ....155..265H. doi:10.3847/1538-3881/aac262. ISSN 0004-6256. S2CID 53983430.
  4. ^ a b c d e f Pass, Emily K.; Winters, Jennifer G.; et al. (July 2023). "HST/WFC3 Light Curve Supports a Terrestrial Composition for the Closest Exoplanet to Transit an M Dwarf". The Astronomical Journal. 166 (4): 171. arXiv:2307.02970. Bibcode:2023AJ....166..171P. doi:10.3847/1538-3881/acf561.
  5. ^ a b c d Lavie, B.; et al. (2023). "Planetary system around LTT 1445A unveiled by ESPRESSO:Multiple planets in a triple M-dwarf system". Astronomy and Astrophysics. 673: A69. arXiv:2210.09713. Bibcode:2023A&A...673A..69L. doi:10.1051/0004-6361/202143007. S2CID 252967989.
  6. ^ Howard, Ward S.; et al. (August 2019). "EvryFlare. I. Long-term Evryscope Monitoring of Flares from the Cool Stars across Half the Southern Sky". Astrophysical Journal. 881 (1): 9. arXiv:1904.10421. Bibcode:2019ApJ...881....9H. doi:10.3847/1538-4357/ab2767. ISSN 0004-637X. S2CID 128361715.
  7. ^ a b Brennan, Pat. "Discovery Alert: Rocky Planet Swelters Under Three Red Suns". Exoplanet Exploration: Planets Beyond our Solar System. Archived from the original on 2023-05-23. Retrieved 2020-02-13.
  8. ^ Bartels, Meghan (26 July 2019). "This Newfound Alien Planet Has 3 Suns". Space.com. Archived from the original on 13 February 2021. Retrieved 24 February 2021.
  9. ^ a b c d Winters, Jennifer G.; et al. (30 July 2021). "A Second Planet Transiting LTT~1445A and a Determination of the Masses of Both Worlds". The Astronomical Journal. 163 (4): 168. arXiv:2107.14737. Bibcode:2022AJ....163..168W. doi:10.3847/1538-3881/ac50a9. S2CID 236635391.
  10. ^ Diamond-Lowe, Hannah; Mendonca, Joao M.; Charbonneau, David; Buchhave, Lars A. (2023). "Ground-based Optical Transmission Spectroscopy of the Nearby Terrestrial Exoplanet LTT 1445Ab". The Astronomical Journal. 165 (4): 169. arXiv:2210.11809. Bibcode:2023AJ....165..169D. doi:10.3847/1538-3881/acbf39.
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