LTT 1445

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LTT 1445 A,BC
LTT 1445 HST ACS F330W.png
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]
Distance 22.387 ± 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
Mass 0.257±0.014 M [4]   M
Radius 0.271+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
Temperature 3,337±150 [2]   K
Metallicity [Fe/H]−0.34±0.08 [2]   dex
B
Mass 0.215±0.014 [2]   M
Radius 0.236±0.027 [2]   R
C
Mass 0.161±0.014 [2]   M
Radius 0.197±0.027 [2]   R
Rotation 1.4  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
SIMBAD A,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 b c. [5]

Contents

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
c1.37±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🜨
b2.73+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±0.0224.30+0.03
−0.08

See also

Related Research Articles

<span class="mw-page-title-main">HD 219134</span> Star in the constellation Cassiopeia

HD 219134 is a main-sequence star in the constellation of Cassiopeia. It is smaller and less luminous than the Sun, with a spectral class of K3V, which makes it an orange-hued star. HD 219134 is relatively close to our system, with an estimated distance of 21.34 light years. This star is close to the limit of apparent magnitude that can still be seen by the unaided eye. The limit is considered to be magnitude 6 for most observers. This star has a magnitude 9.4 optical companion at an angular separation of 106.6 arcseconds.

HD 147506, also known as HAT-P-2 and formally named Hunor, is a magnitude 8.7 F8 dwarf star that is somewhat larger and hotter than the Sun. The star is approximately 419 light-years from Earth and is positioned near the keystone of Hercules. It is estimated to be 2 to 3 billion years old, towards the end of its main sequence life. There is one known transiting exoplanet, and a second planet not observed to transit.

Pi Mensae, also known as HD 39091, is a yellow dwarf star in the constellation of Mensa. This star has a high proper motion. The apparent magnitude is 5.67, which can be visible to the naked eye in exceptionally dark, clear skies. It is nearly 60 light-years away. The star is slightly larger than the Sun in terms of mass, size, luminosity, temperature and metallicity, and is about 730 million years younger. It hosts three known planets.

Kepler-80, also known as KOI-500, is a red dwarf star of the spectral type M0V. This stellar classification places Kepler-80 among the very common, cool, class M stars that are still within their main evolutionary stage, known as the main sequence. Kepler-80, like other red dwarf stars, is smaller than the Sun, and it has both radius, mass, temperatures, and luminosity lower than that of our own star. Kepler-80 is found approximately 1,223 light years from the Solar System, in the stellar constellation Cygnus, also known as the Swan.

K2-3, also known as EPIC 201367065, is a red dwarf star with three known planets. It is on the borderline of being a late orange dwarf/K-type star, but because of its temperature, it is classified as a red dwarf.

GJ 9827 is a star in the constellation of Pisces. It is a K-type main-sequence star with an apparent magnitude of 10.250. It is 97 light-years away, based on parallax.

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K2-28 is a metal rich M4-type main sequence star. One confirmed transiting exoplanet is known to orbit this star. There is another star 5.2 arcseconds to the north–east of K2-28 however this star has a different proper motion and is therefore physically unrelated and probably a background star.

Kepler-51 is a Sun-like star that is about 500 million years old. It is orbited by three super-puff planets—Kepler-51b, c, and d—which have the lowest known densities of any known exoplanet. The planets are similar in radius to gas giants like Jupiter, but have unusually small masses for their size, only a few times greater than Earth’s.

HD 197037 is a binary star system. Its primary or visible star, HD 197037 A, is a F-type main-sequence star. Its surface temperature is 6150±34 K. HD 197037 A is depleted in heavy elements compared to the Sun, with a metallicity Fe/H index of −0.16±0.03, but is younger at an age of 3.408±0.924 billion years.

HD 175289 is a binary star system. Its primary star, also known as Kepler-410A, is a F-type subgiant star, orbited by the orange dwarf star Kepler-410B on a wide orbit. The companion star was discovered in 2012.

TOI-270, also known as L 231-32, is a red dwarf star 73.3 light-years away in the constellation Pictor. It has about 39% the mass and 38% the radius of the Sun, and a temperature of about 3,506 K. TOI-270 hosts a system of three known exoplanets.

References

  1. 1 2 3 4 5 6 7 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. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 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. 1 2 3 4 5 6 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. 1 2 3 4 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. 1 2 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. 1 2 3 4 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 .