HR 4072

HR 4072 is a binary star^[9] system in the northern circumpolar constellation of Ursa Major. It has the variable star designation ET Ursae Majoris, abbreviated ET UMa,^[5] while HR 4072 is the system's designation from the Bright Star Catalogue. It has a white hue and is faintly visible to the naked eye with an apparent visual magnitude that fluctuates around 4.94.^[3] The system is located at a distance of approximately 339 light years from the Sun based on parallax measurements.^[2] The radial velocity measurement is poorly constrained, but it appears to be drifting closer to the Sun at the rate of around −3 km/s.^[3]

HR 4072

A light curve for ET Ursae Majoris, plotted from TESS data[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Ursa Major
Right ascension	10h 24m 07.84801s[2]
Declination	+65° 33′ 59.1239″[2]
Apparent magnitude (V)	4.94[3]
Characteristics
Spectral type	A1:VpSiSrHg[4]
B−V color index	−0.052±0.012[3]
Variable type	α2 CVn[5]
Astrometry
Radial velocity (Rv)	−2.24±0.03[6] km/s
Proper motion (μ)	RA: −9.427[2] mas/yr Dec.: −20.994[2] mas/yr
Parallax (π)	9.61±0.20 mas[2]
Distance	339 ± 7 ly (104 ± 2 pc)
Absolute magnitude (MV)	−0.15[3]
Orbit[6]
Period (P)	11.579113±0.000010 d
Semi-major axis (a)	1.634±0.001 mas
Eccentricity (e)	0.2943±0.0009
Longitude of the node (Ω)	133.49±0.13°
Periastron epoch (T)	2,457,756.168±0.005 JD
Argument of periastron (ω) (primary)	176.50±0.20°
Semi-amplitude (K1) (primary)	38.17±0.04 km/s
Semi-amplitude (K2) (secondary)	62.11±0.09 km/s
Details[6]
A
Mass	2.779±0.153 M☉
Radius	3.16±0.11 R☉
Luminosity	101±8 L☉
Surface gravity (log g)	3.88±0.05 cgs
Temperature	10,260±100 K
Metallicity	${\displaystyle {\begin{smallmatrix}\left[{\ce {M}}/{\ce {H}}\right]\end{smallmatrix}}}$ = +0.11±0.04
Metallicity [Fe/H]	+0.39[7] dex
Rotational velocity (v sin i)	≤4.2 km/s
B
Mass	1.708±0.094 M☉
Radius	1.73±0.06 R☉
Luminosity	9.7±1.0 L☉
Surface gravity (log g)	4.22±0.05 cgs
Temperature	7,860±140 K
Metallicity	${\displaystyle {\begin{smallmatrix}\left[{\ce {M}}/{\ce {H}}\right]\end{smallmatrix}}}$ = −0.05±0.07
Rotational velocity (v sin i)	5.1±2.1 km/s
Other designations
ET UMa, BD+66 664, GJ 9327, HD 89822, HIP 50933, HR 4072, SAO 15163, PPM 17427, PLX 2433, TYC 4150-1302-1, IRAS 10205+6549, 2MASS J10240782+6533590[8]
Database references
SIMBAD	data

This is a double-lined spectroscopic binary^[7] star system with an orbital period of 11.58 days and an eccentricity of 0.29.^[6] The orbit for this star was first determined by R. H. Baker in 1912, then later revised.^[10][6]

The primary, designated component A, is an Ap type chemically-peculiar star^[11][12][13] with a stellar classification of A1:VpSiSrHg,^[4] although it has also been considered to be a mercury-manganese star.^[14] The suffix notation indicates abundance anomalies of silicon, strontium, and mercury in the spectrum. It is an α² Canum Venaticorum variable with an amplitude of 0.05 magnitude in the B (blue) band.^[5] The star is rotating slowly with a projected rotational velocity of 4.5 km/s.^[7] It is three times larger than the Sun, radiating about 100 solar luminosities from its photosphere at an effective temperature of 10,260 K.^[6]

The secondary component has been reported to have characteristics of an Am star.^[12] It is a F-type star with 1.73 times the size of the Sun and 1.71 times its mass. Its luminosity is about 10 times that of the Sun, or one-tenth of that of the primary, and it has an effective temperature of 7,900 K.^[6]