Iota1 Librae

Iota¹ Librae is a quadruple^[4] star system in the constellation Libra. Its name is a Bayer designation that is Latinized from ι¹ Librae, and abbreviated Iota¹ Lib or ι¹ Lib. Its apparent magnitude is 4.54. It is located 379 light years from earth.^[7]

Iota¹ Librae

Map of the constellation of Libra.
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Libra
Right ascension	15h 12m 13.29025s[1]
Declination	−19° 47′ 30.1592″[1]
Apparent magnitude (V)	+4.54[2] (5.1 + 5.6 + 10.4 + 10.9)[3]
Characteristics
Evolutionary stage	Blue subgiant
Spectral type	B9IVpSi + B9[4] + G5IV[3]
U−B color index	−0.38[2]
B−V color index	−0.08[2]
Variable type	Alpha2 Canum Venaticorum
Astrometry
Radial velocity (Rv)	−11.6[2] km/s
Proper motion (μ)	RA: −35.40[1] mas/yr Dec.: −32.79[1] mas/yr
Parallax (π)	8.59±0.25 mas[1]
Distance	380 ± 10 ly (116 ± 3 pc)
Absolute magnitude (MV)	−0.79[5]
Position (relative to A)[3]
Component	BC
Angular distance	57.8″
Position angle	111°
Orbit[6]
Primary	Aa
Companion	Ab
Period (P)	8163.16 d
Semi-major axis (a)	0.129[3]″
Eccentricity (e)	0.35
Inclination (i)	154.20[3]°
Periastron epoch (T)	2433155 JD
Argument of periastron (ω) (secondary)	7.6°
Semi-amplitude (K1) (primary)	3.4 km/s
Position (relative to B)[3]
Component	C
Angular distance	2.058″
Position angle	111°
Details[3]
Aa
Mass	3.61 M☉
Ab
Mass	3.12 M☉
B
Mass	0.98 M☉
C
Mass	0.91 M☉
Other designations
ι1 Lib, 24 Librae, BD−19°4047, HD 134759, HIP 74392, HR 5652, SAO 159090, WDS J15122-1948A[2]
Database references
SIMBAD	data

Visibility

Due to its southern location, although the star can be seen from most regions of the earth, observers in the southern hemisphere are more advantaged. Near Antarctica, it appears circumpolar, while it always remains invisible only in the vicinity of the Arctic Circle. Its magnitude of 4.5 means that naked eye visibility is dependent on a sky sufficiently free from the effects of light pollution.

The best time for observation in the evening sky falls in the months between May and September; from both hemispheres of the period of visibility remains approximately the same, thanks to the position of the star not far from the celestial equator.

Physical

A light curve for Iota¹ Librae plotted from STEREO data, adapted from Wraight et al. (2012)^[8]

Iota¹ Librae is a four star system.^[4] The inner pair, designated components Aa and Ab, form a spectroscopic binary with an orbital period of 22.35 years and an eccentricity of 0.35.^[6] The brighter member has a stellar classification of B9 IVp Si,^[4] indicating it is a B-type subgiant star with an overabundance of silicon in the photosphere. It is a variable star of the Alpha2 Canum Venaticorum type with a magnitude that varies from 4.53 to 4.56, while its spectrum likewise shows variability.^[9] The secondary component is of class B9.^[4] The two stars are very close together (0.129 arcsec away), respectively of magnitude 5.10 and 5.60.^[3]

The two other stars are the components C and D; separated by 57.8" from AB and 2.058" from each other. The combined spectrum is G5IV, and each star has masses of 0.98 and 0.91 solar masses, and magnitudes 10.40 and 10.90, respectively.^[3]

Due to its position on the ecliptic, it is sometimes obscured by the Moon or planets. A lunar occultation took place April 4, 2012.^[10]