Sidus Ludovicianum

Sidus Ludovicianum, also known as HD 116798,^[6] is an 8th-magnitude star in the asterism of the Big Dipper in the constellation Ursa Major, halfway between Mizar and Alcor. A line-of-sight companion with Mizar and Alcor (with a spectral type similar to the latter), it is roughly four times more distant. It has the spectral type A8/F0 III.^[4] That spectral class suggests it is a giant star, but evolutionary models place it on the main sequence.^[1]

Sidus Ludovicianum

Location of Sidus Ludovicianum (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Ursa Major
Right ascension	13h 24m 51.8521s[1]
Declination	+54° 53′ 50.841″[1]
Apparent magnitude (V)	+7.58[2]
Characteristics
Evolutionary stage	main sequence[1]
Spectral type	A5-F0[3][4]
Astrometry
Radial velocity (Rv)	−3.42±0.35[1] km/s
Proper motion (μ)	RA: −20.171 mas/yr[1] Dec.: −5.330 mas/yr[1]
Parallax (π)	10.9650±0.0281 mas[1]
Distance	297.5 ± 0.8 ly (91.2 ± 0.2 pc)
Details
Mass	1.5[1] M☉
Radius	1.6[1] R☉
Luminosity	6.2[1] L☉
Surface gravity (log g)	4.13[1] cgs
Temperature	7,223[1] K
Age	961[1] Myr
Other designations
Sidus Ludovicianum, BD+55°1602, GC 18150, HD 116798, SAO 28748, TYC 3850-257-1, 2MASS J13245185+5453509[5][6]
Database references
SIMBAD	data

Sidus Ludovicianum between the brighter Mizar and Alcor (north is towards the right)

The star was observed on 2 December 1722 by Johann Georg Liebknecht, who mistook it for a planet and named it after Louis V, Landgrave of Hesse-Darmstadt. In different sources the name may be written as "Sidus Ludovicianum",^[7] "Sidus Ludoviciana",^[6] or "Stella Ludoviciana". Unknown to Liebknecht, it had been previously observed by Benedetto Castelli in 1616.^[8]: 257

The star is six times more luminous than the Sun, 1.6 times its radius, and has a surface temperature of 7,200 K.^[1] Spectral classification based on a spectrum taken for radial velocity measurement tentatively determined a spectral and luminosity class of A8/F0III,^[4] which would indicate that it has exhausted its core hydrogen and started to evolve away from the main sequence, however giant stars of this type should be at least ten times more luminous than measured for Sidus Ludovicianum.^[1] It shows evidence of Gamma Doradus pulsations, and is a likely member of a young stellar association known as Group-X.^[9]