Kelu-1
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Hydra |
| Right ascension | 13h 05m 40.196s |
| Declination | −25° 41′ 05.99″ |
| Characteristics | |
| Spectral type | L2: / L4: |
| Apparent magnitude (J) | 13.83 ± 0.08 / 14.65 ± 0.12 |
| Apparent magnitude (H) | 12.92 ± 0.03 / 13.44 ± 0.04 |
| Apparent magnitude (KS) | 12.32 ± 0.02 / 12.72 ± 0.03 |
| Apparent magnitude (L') | 11.42 ± 0.15 / 11.66 ± 0.15 |
| Astrometry | |
| Proper motion (μ) |
RA: −299.2 ± 1.2 mas/yr Dec.: −4.1 ± 1.4 mas/yr |
| Parallax (π) | 53.6 ± 2.0mas |
| Distance | 61 ± 2 ly (18.7 ± 0.7 pc) |
| Orbit | |
| Primary | A |
| Companion | B |
| Period (P) | 38+8 −6 yr |
| Semi-major axis (a) | 0.339+0.129 −0.066" (6.4+2.4 −1.3 AU) |
| Eccentricity (e) | 0.82+0.1 −0.1 |
| Inclination (i) | 84.9+1.0 −2.0° |
| Longitude of the node (Ω) | 39.4+2.0 −2.0° |
| Periastron epoch (T) | 2452079+200 −400 (Jun 18, 2001) |
|
Argument of periastron (ω) (secondary) |
57.8+15.0 −20.0° |
| Details | |
| Kelu-1 A | |
| Mass | 0.060 ± 0.01 M☉ |
| Luminosity (bolometric) | 1.35–1.74 · 10−4 L☉ |
| Temperature | ≈ 2020 K |
| Age | 0.3–0.5 Gyr |
| Kelu-1 B | |
| Mass | 0.055 ± 0.01 M☉ |
| Luminosity (bolometric) | 0.91–1.12 · 10−4 L☉ |
| Temperature | ≈ 1840 K |
| Age | 0.3–0.5 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | The system |
| A | |
| B | |
Coordinates: 
13h 05m 40.196s, −25° 41′ 05.99″
Kelu-1 is a system of two brown dwarfs of spectral types L2 and L4 located in constellation Hydra at approximately 61 light-years from Earth. It is among the first free-floating later-than-M-type brown dwarfs discovered, and sometimes considered as prototype of L-type brown dwarfs.
In 1987 María Teresa Ruiz decided to start The Calán-ESO proper-motion survey using red plates taken (starting from the 1970s) with the 1-m ESO Schmidt Camera at La Silla Observatory, Chile. The survey was not specially designed for search for brown dwarfs, but in the main for search for another type of celestial bodies—white dwarfs. Pairs of plates, separated by long span of time, were compared with blink comparator to detect objects with high proper motion. Objects with high proper motion, which were found, were selected for follow-up spectroscopy using the 3.6-m telescope, equipped with EFOSC1, at the same observatory.
In March 1997 was carried out spectroscopy with the 3.6-m telescope of the next object, discovered from the pair of plates, separated by 14 years (1979—1993) (at the limit of sensitivity: its apparent magnitude in R band was about 19.5), through its large proper motion, and its spectrum was found very red, very peculiar and very odd-looking. The object's spectrum and its extremely low luminosity led to conclusion that this probably is a brown dwarf. Ruiz et al. named this brown dwarf Kelu-1: «kelu» means «red» in the Mapuche language (the origin of the second part of the name—the number «1»—is unexplained in the article).
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