LTT 3780

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, 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. The abundance of iron, an indicator of the star's metallicity, appears higher than in the Sun. The star is inactive, showing a negligible level of magnetic activity in its chromosphere. 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.

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

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.