LTT 3780

LTT 3780

Observation data Epoch J2000      Equinox J2000
Constellation	Hydra
Right ascension	10^h 18^m 35.137^s[1]
Declination	−11° 43′ 00.24″[1]
Apparent magnitude (V)	13.07±0.015[2]
Characteristics
Spectral type	M3.5 V + M5.0 V[3]
Apparent magnitude (B)	14.678
Apparent magnitude (G)	11.8465±0.0005[2]
Apparent magnitude (J)	9.007±0.030[2]
Astrometry
Proper motion (μ)	RA: −341.537 mas/yr[1] Dec.: −247.747 mas/yr[1]
Parallax (π)	45.3972 ± 0.0301 mas[1]
Distance	71.85 ± 0.05 ly (22.03 ± 0.01 pc)
Absolute magnitude (MV)	11.36±0.02[2]
Position (relative to LTT 3780)[3]
Component	LP 729-55
Epoch of observation	J2015.5
Angular distance	15.81±0.150″
Position angle	96.9±0.2°
Projected separation	348±3 AU
Details
LTT 3780
Mass	0.401±0.012[2] M☉
Radius	0.374±0.011[2] R☉
Luminosity	0.167±0.003[3] L☉
Surface gravity (log g)	4.896±0.029[2] cgs
Temperature	3,331±157[2] K
Metallicity [Fe/H]	0.09±0.16 dex[3] 0.28^+0.11 −0.13[2] dex
Rotation	104±15[2]
Rotational velocity (v sin i)	< 1.3[2] km/s
Age	3.10+6.20 −0.98[4] Gyr
LP 729-55
Mass	0.136±0.004[2] M☉
Radius	0.173±0.005[2] R☉
Other designations
G 162-44, LP 729-54, LTT 3780, NLTT 23974, 2MASS J10183516-1142599[5]
Database references
SIMBAD	data

LTT 3780, also known as TOI-732 or LP 729-54, is the brighter component of a wide visual binary star system in the constellation Hydra. This star is host to a pair of orbiting exoplanets. Based on parallax measurements, it is located at a distance of 72 light years from the Sun. LTT 3780 has an apparent visual magnitude of 13.07,^[2] requiring a telescope to view.

The spectrum of LTT 3780 presents as a small M-type main-sequence star, a red dwarf, with a stellar classification of M3.5 V. It is spinning very slowly, with a rotation period of 104 days.^[2] The abundance of iron, an indicator of the star's metallicity, appears higher than in the Sun.^[3] The star is inactive, showing a negligible level of magnetic activity in its chromosphere.^[2] It has about 40% of the mass and 37% of the radius of the Sun. The star is radiating just 17% of the Sun's luminosity from its photosphere at an effective temperature of 3,331.^[2]

Collectively designated LDS 3977, the two stars in this system share a common proper motion and have an angular separation of 15.8″, which corresponds to a (physical) projected separation of 348 AU.^[3] At this separation, the orbital period would be ~9,100 years.^[2] The fainter member is a red dwarf with a class of M5.0 V.^[3] It has 14% of the mass of the Sun and 17% of the Sun's radius.^[2]

Planetary system

In 2020, an analysis carried out by a team of astronomers led by astronomer Ryan Cloutier of the TESS project confirmed the existence of two planets on mildly eccentric orbits, the inner being a super-Earth and the outer a small gas planet about half the mass of Uranus.

LTT 3780 c

Astronomers utilizing the Gemini South 8.1-meter telescope performed an atmospheric survey of LTT 3780 c through high-resolution transmission spectroscopy. From observations during a single transit, they detected tentative signs of methane in the atmosphere but found no traces of ammonia, even though it is highly detectable in a cloud-free, hydrogen-rich atmosphere.^[6]

Size comparison of the two known planets of LTT 3780 (artistic concept) with Earth

The LTT 3780 planetary system^[2]^[3]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	2.34+0.24 −0.23 M🜨	0.01203+0.00054 −0.00053	0.77±0.001	0.064+0.075 −0.046	85.9°	1.35±0.06 R🜨
c	6.29+0.63 −0.61 M🜨	0.0762±0.0034	12.252131+0.000072 −0.000064	0.115+0.07 −0.065	89.08°	2.42±0.1 R🜨

See also

• List of extrasolar planets
• List of multiplanetary systems

References

1. 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. Cloutier, Ryan; et al. (2020). "A pair of TESS planets spanning the radius valley around the nearby mid-M dwarf LTT 3780". The Astronomical Journal. 160 (1): 3. arXiv:2003.01136. Bibcode:2020AJ....160....3C. doi:10.3847/1538-3881/ab91c2. S2CID 211817805.
3. Nowak, G.; et al. (2020). "The CARMENES search for exoplanets around M dwarfs. Two planets on the opposite sides of the radius gap transiting the nearby M dwarf LP 729-54". Astronomy & Astrophysics. A173: 642. arXiv:2003.01140. Bibcode:2020A&A...642A.173N. doi:10.1051/0004-6361/202037867. S2CID 211818198.
4. Bonfanti, A.; et al. (2024). "Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley". Astronomy & Astrophysics. 682 A66. arXiv:2311.12577. Bibcode:2024A&A...682A..66B. doi:10.1051/0004-6361/202348180.
5. "LTT 3780". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-03-06.
6. Cabot, Samuel H. C.; et al. (2024-05-01). "High-resolution Spectroscopic Reconnaissance of a Temperate Sub-Neptune". The Astrophysical Journal Letters. 966 (1) L10. arXiv:2403.18891. Bibcode:2024ApJ...966L..10C. doi:10.3847/2041-8213/ad3828.