Upsilon Tauri

Not to be confused with Y Tauri.

Upsilon Tauri (υ Tauri) is a solitary,^[11] white-hued star in the zodiac constellation of Taurus, and is a member of the Hyades star cluster.^[8] It is faintly visible to the naked eye with an apparent visual magnitude of +4.3. Based upon an annual parallax shift of 21.21 mas seen from Earth, it is around 154 light years from the Sun.

υ Tauri

Location of υ Tauri (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Taurus
Right ascension	04h 26m 18.46368s[1]
Declination	+22° 48′ 48.8885″[1]
Apparent magnitude (V)	4.28 – 4.31[2]
Characteristics
Spectral type	A8 Vn[3]
U−B color index	+0.14[4]
B−V color index	+0.25[4]
Variable type	δ Scuti[2]
Astrometry
Radial velocity (Rv)	32.2±1.1[5] km/s
Proper motion (μ)	RA: +108.81[1] mas/yr Dec.: −46.80[1] mas/yr
Parallax (π)	21.21±0.25 mas[1]
Distance	154 ± 2 ly (47.1 ± 0.6 pc)
Absolute magnitude (MV)	+0.91[6]
Details
Mass	1.55[7] M☉
Radius	1.803[8] R☉
Luminosity	32.5[9] L☉
Surface gravity (log g)	3.50[7] cgs
Temperature	7,398±252[7] K
Rotation	0.415 d[8]
Rotational velocity (v sin i)	243[3] km/s
Age	827[7] Myr
Other designations
υ Tau, υ1 Tau, 69 Tauri, BD+22 696, FK5 2326, HD 28024, HIP 20711, HR 1392, SAO 76608[10]
Database references
SIMBAD	data

Properties

A light curve for Upsilon Tauri, plotted from TESS data^[12]

This is an A-type main sequence star with a stellar classification of A8 Vn.^[3] It is classified as a Delta Scuti type variable star and its brightness varies from magnitude +4.28 to +4.31 with a period of 3.56 hours.^[2] At an estimated age of 827 million years,^[7] it is spinning rapidly with a rotation period of just 0.415 days.^[8] This is giving the star an oblate shape with an equatorial bulge that is 9% larger than the polar radius.^[13]

Occasionally this star system shares the Bayer designation υ Tauri with 72 Tauri, which is separated from it by 0.29° in the sky.^[14]

Naming

With φ, κ¹, κ² and χ, it composed the Arabic were the Arabs' Al Kalbain, the Two Dogs.^[15] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Kalbain were the title for five stars : φ as Alkalbain I, χ as Alkalbain II, κ¹ as Alkalbain III, κ² as Alkalbain IV and this star (υ) as Alkalbain V.^[16]