Theta Tauri

Theta Tauri (θ Tauri, abbreviated Theta Tau, θ Tau) is a wide double star in the constellation of Taurus and a member of the Hyades open cluster.

θ Tauri

Hyades showing θ Tauri
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Taurus
θ1 Tauri
Right ascension	04h 28m 34.49209s[1]
Declination	+15° 57′ 44.2832″[2]
Apparent magnitude (V)	+3.84
θ2 Tauri
Right ascension	04h 28m 39.74455s[1]
Declination	+15° 52′ 15.1226″[2]
Apparent magnitude (V)	+3.35 - 3.42[3]
Characteristics
θ1 Tauri
Spectral type	G9 III Fe-0.5[4]
θ2 Tauri
Spectral type	A7 III[5]
Variable type	δ Scuti[3]
Astrometry
θ1 Tauri
Parallax (π)	21.4183±0.3731 mas[1]
Distance	152 ± 3 ly (46.7 ± 0.8 pc)
Absolute magnitude (MV)	+0.416[6]
θ2 Tauri
Parallax (π)	20.8354±0.3731 mas[2]
Distance	157 ± 3 ly (48.0 ± 0.9 pc)
Absolute magnitude (MV)	+0.08[7]
Orbit[8]
Primary	A
Companion	B
Period (P)	5,997 days
Eccentricity (e)	0.64
Semi-amplitude (K1) (primary)	8.39 km/s
Orbit[9]
Primary	Aa
Companion	Ab
Period (P)	140.7302 days
Semi-major axis (a)	18.91″
Eccentricity (e)	0.7360
Inclination (i)	47.8°
Semi-amplitude (K1) (primary)	32.95 km/s
Semi-amplitude (K2) (secondary)	43.68 km/s
Details
Aa
Mass	2.86[10] M☉
Radius	4.4[10] R☉
Luminosity	59[9] L☉
Surface gravity (log g)	3.6[10] cgs
Temperature	7,800[10] K
Rotational velocity (v sin i)	68.4[9] km/s
Ab
Mass	2.16[10] M☉
Radius	2.7[10] R☉
Luminosity	21[9] L☉
Temperature	7,800[9] K
Rotational velocity (v sin i)	113[9] km/s
Age	650[9] Myr
θ1 Tauri
Mass	2.67[11] M☉
Radius	9.42±0.22[12] R☉
Luminosity	47.7±2.3[12] L☉
Surface gravity (log g)	3.21[11] cgs
Temperature	4,940±55[12] K
Metallicity [Fe/H]	+0.14[11] dex
Rotational velocity (v sin i)	1.40[11] km/s
Age	510[11] Myr
Other designations
θ Tauri
θ1 Tauri: 77 Tauri, BD+15 631, HD 28307, HIP 20885, HR 1411, SAO 93955
θ2 Tauri: Chamukuy, 78 Tauri, BD+15 632, HD 28319, HIP 20894, HR 1412, SAO 93957
Database references
SIMBAD	θ1 Tauri
	θ2 Tauri

θ Tauri is composed of two 3rd magnitude stars, designated Theta¹ Tauri (Theta Tauri B) and Theta² Tauri (Theta Tauri A). Theta² is brighter, hence the pair are sometimes referred to as Theta Tauri B and A, respectively. They are separated by 5.62 arcminutes (0.094°) on the sky. Based upon parallax measurements, Theta¹ Tauri is located at a distance of 152 ly (47 pc), while Theta² Tauri is at a distance of 157 light-years (48 parsecs). θ Tauri A and B are both spectroscopic binaries; the four components are designated Theta Tauri Aa (formally named Chamukuy /ˈtʃɑːmuːkuːi/), Ab, Ba, and Bb.

Nomenclature

The θ Tauri pair, showing contrasting blue and yellow colors, in the Hyades cluster. In this image, θ¹ Tauri is above in yellow, and θ² Tauri is below in light blue.

θ Tauri (Latinised to Theta Tauri) is the double star's Bayer designation;^{[citation needed]} θ¹ Tauri and θ² Tauri those of its two constituents. The designations of the two constituents as Theta Tauri A and B, and those of the four components - Theta Tauri Aa, Ab, Ba and Bb - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).^[13]

In the mythology of the Maya peoples, Theta Tauri is known as Chamukuy, meaning a small bird in the Yucatec Maya language.^[14] In 2016, the IAU organized a Working Group on Star Names (WGSN)^[15] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.^[16] It approved the name Chamukuy for the component Theta Tauri Aa on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.^[17]

In Chinese, 畢宿 (Bì Xiù), meaning Net, refers to an asterism consisting of Theta² Tauri, Epsilon Tauri (named Ain), Delta³ Tauri, Delta¹ Tauri, Gamma Tauri, Alpha Tauri (Aldebaran), 71 Tauri and Lambda Tauri.^[18] Consequently, the Chinese name for Theta² Tauri itself is 畢宿六 (Bì Xiù liù), "the Sixth Star of Net".^[19]

Properties

A light curve for Theta² Tauri, plotted from TESS data^[20]

Theta Tauri A has a mean apparent magnitude of +3.40. It is classified as a Delta Scuti type variable star and its brightness varies from magnitude +3.35 to +3.42 with a period of 1.82 hours.^[21] Its primary component, Theta Tauri Aa, is a white A-type giant. The secondary, Theta Tauri Ab, is of the 6th magnitude and is 0.005 arcseconds, or at least 2 AU, distant. It completes an orbit once every 141 days.

Theta Tauri B is the dimmer constituent. Its primary component, Theta Tauri Ba, is an orange K-type giant with an apparent magnitude of +3.84. The secondary, Theta Tauri Bb, is of the 7th-magnitude. It has a mass of 1.31 M_☉ and orbits the primary every 16.26 years on a fairly eccentric (at 0.570) orbit.^[22]