Theta1 Microscopii

For other stars with the name θ Microscopii, see Theta Microscopii.

θ¹ Microscopii, Latinized as Theta¹ Microscopii, is a suspected binary star^[10] system in the southern constellation of Microscopium. It is visible to the naked eye was a faint, white-hued point of light with an apparent visual magnitude of 4.82.^[2] The distance to this system is approximately 179 light years based on parallax.^[1]

A light curve for Theta¹ Microscopii, plotted from TESS data^[11]

Theta1 Microscopii

Location of θ1 Microscopii (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Microscopium
Right ascension	21h 20m 45.62633s[1]
Declination	−40° 48′ 34.3607″[1]
Apparent magnitude (V)	4.82[2]
Characteristics
Spectral type	A7VpSrCrEu[3]
U−B color index	-0.07[2]
B−V color index	+0.02[2]
Variable type	α2 CVn[4]
Astrometry
Radial velocity (Rv)	+2.30[5] km/s
Proper motion (μ)	RA: +75.480[1] mas/yr Dec.: +8.657[1] mas/yr
Parallax (π)	18.2678±0.5314 mas[1]
Distance	179 ± 5 ly (55 ± 2 pc)
Absolute magnitude (MV)	1.03[6]
Details[7]
Mass	2.32+0.18 −0.26 M☉
Radius	2.35±0.34 R☉
Luminosity	36.3+8.4 −6.8 L☉
Surface gravity (log g)	4.06±0.12 cgs
Temperature	9,240±480 K
Metallicity [Fe/H]	0.00[8] dex
Rotational velocity (v sin i)	43.7±1.7 km/s
Age	437±209 Myr
Other designations
θ1 Mic, CD−41°14475, FK5 802, GC 29854, HD 203006, HIP 105382, HR 8151, SAO 230644, WDS J21208-4049[9]
Database references
SIMBAD	data

The primary is an α² CVn variable with a period of 2.125 days and a magnitude ranging from 4.77 to 4.87,^[4] as well as an Ap star, a chemically peculiar star with strong metallic lines in its spectrum.^[3][6] It is an A-type main-sequence star with a stellar classification of A7VpSrCrEu,^[3] where the suffix notation indicates abundance anomalies of strontium, chromium, and europium. The star is 437 million years old with 2.3 times the mass of the Sun and 2.4 times the Sun's radius. It is radiating 36 times the luminosity of the Sun from its photosphere at an effective temperature of 9,240 K.^[7]

Its companion is a magnitude 7.42 star at an angular separation of 0.10″ from the primary along a position angle of 46°, as of 2018.^[12]