Theta Eridani

Theta Eridani, Latinized from θ Eridani, is a binary system in the constellation of Eridanus with a combined apparent magnitude of 2.88. Its two components are designated θ1 Eridani, formally named Acamar /ˈækəmɑːr/ (the traditional name of the system), and θ2 Eridani. The system's distance from the Sun based on parallax measurements is approximately 165 light-years.

Theta Eridani
Location of θ Eridani (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Eridanus
θ1 Eri
Right ascension 02h 58m 15.6764s
Declination −40° 18′ 16.839″
Apparent magnitude (V) 3.18
θ2 Eri
Right ascension 02h 58m 16.4037s
Declination −40° 18′ 16.906″
Apparent magnitude (V) 4.11
Characteristics
θ1 Eri
Spectral type A3IV-V
U−B color index +0.14
B−V color index +0.128±0.012
θ2 Eri
Spectral type A1V
B−V color index +0.08
Variable type suspected
Astrometry
θ1 Eri
Radial velocity (Rv)+11.9±2.6 km/s
Proper motion (μ) RA: −57.132 mas/yr
Dec.: +23.058 mas/yr
Parallax (π)19.9047 ± 0.2062 mas
Distance164 ± 2 ly
(50.2 ± 0.5 pc)
θ2 Eri
Proper motion (μ) RA: −50.502 mas/yr
Dec.: +16.613 mas/yr
Parallax (π)19.5270 ± 0.1372 mas
Distance167 ± 1 ly
(51.2 ± 0.4 pc)
Absolute magnitude (MV)−0.59 (combined)
Details
θ1 Eri
Mass2.6 M☉
Radius4.85 R☉
Luminosity145 L☉
Temperature8,200 K
Rotational velocity (v sin i)65.1 km/s
θ2 Eri
Mass1.95 M☉
Radius2.7 R☉
Luminosity37 L☉
Surface gravity (log g)3.83 cgs
Temperature8,293 K
Metallicity [Fe/H]−0.197 dex
Rotational velocity (v sin i)102.5 km/s
Other designations
Theta Eri, θ Eri, CD−40° 771, HIP 13847, SAO 216113, CCDM J02583-4018, WDS 02583-4018
θ1 Eri: Acamar, HD 18622, HR 897
θ2 Eri: HD 18623, HR 898
Database references
SIMBADθ1 Eri
θ2 Eri
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