LTT 1445

LTT 1445 is a triple M-dwarf system about 22 light-years distant[4] in the constellation Eridanus. The primary LTT 1445 A hosts one exoplanet that transits the star every five days. As of August 2019 it is the second closest transiting exoplanet system discovered, with the closest being HD 219134 bc.[4]

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 51.39s[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)145.5466 ± 0.0800[3] mas
Distance22.41 ± 0.01 ly
(6.871 ± 0.004 pc)
Orbit[1]
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
MassA: 0.256 ± 0.014[1] M☉
B: 0.215 ± 0.014[1] M☉
C: 0.161 ± 0.014[1] M☉
RadiusA: 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
TemperatureA: 3337 ± 150[1] K
Metallicity [Fe/H]A: -0.34 ± 0.08[1] dex
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

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 is suggesting a 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][5]

Planetary system

LTT 1445Ab was discovered in June 2019[6] with data from the Transiting Exoplanet Survey Satellite by astrophysicists of the Harvard Center for Astrophysics.[4] 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]

The LTT 1445Ab planetary system[1]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b <8.4 M⊕ 0.03807+0.00068
−0.00071		 5.35882+0.00030
−0.00031		 0.19+0.35
−0.14		 89.40+0.41
−0.46°		 1.38+0.13
−0.12 R⊕

See also

References
  1. Winters, Jennifer G.; Medina, Amber A.; Irwin, Jonathan M.; Charbonneau, David; Astudillo-Defru, Nicola; Horch, Elliott P.; Eastman, Jason D.; Halley Vrijmoet, Eliot; Henry, Todd J.; Diamond-Lowe, Hannah; Winston, Elaine (October 2019). "Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M-dwarf System at 6.9 pc". AJ. 158 (4): 152. Bibcode:2019AJ....158..152W. doi:10.3847/1538-3881/ab364d. hdl:2144/39814. ISSN 0004-6256. S2CID 195584444.
  2. 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". AJ. 155 (6): 265. arXiv:1804.07377. Bibcode:2018AJ....155..265H. doi:10.3847/1538-3881/aac262. ISSN 0004-6256. S2CID 53983430.
  3. Gaia Collaboration (2018-08-01). "Gaia Data Release 2 - Summary of the contents and survey properties". Astronomy & Astrophysics. 616: A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. ISSN 0004-6361. S2CID 49211658.
  4. Brennan, Pat. "Discovery Alert: Rocky Planet Swelters Under Three Red Suns". Exoplanet Exploration: Planets Beyond our Solar System. Retrieved 2020-02-13.
  5. Howard, Ward S.; Corbett, Hank; Law, Nicholas M.; Ratzloff, Jeffrey K.; Glazier, Amy; Fors, Octavi; del Ser, Daniel; Haislip, Joshua (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.
  6. THREE RED SUNS IN THE SKY: A TRANSITING, TERRESTRIAL PLANET IN A TRIPLE M DWARF SYSTEM AT 6.9 PARSECS, 2019, arXiv:1906.10147
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