XZ Tauri

XZ Tauri is a binary system approximately 460 light-years away in the constellation Taurus. The system consists of two T Tauri stars orbiting each other about 6 billion kilometers apart (roughly the same distance as Pluto is from the Sun). The system made news in 2000 when a superflare was observed in the system.

XZ Tauri

A visual band light curve for XZ Tauri. The main plot shows the long-term variability, and the inset shows the year 2000 superflare on the north star. Adapted from Dodin et al. (2016)[1] and Coffey et al. (2004).[2]
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Taurus
Right ascension	04h 31m 40.08690s[3]
Declination	+18° 13′ 56.6424″[3]
Apparent magnitude (V)	10.40[4]
Characteristics
Spectral type	M2.0 + M3.5[5]
Astrometry
Proper motion (μ)	RA: 9.1[6] mas/yr Dec.: −17.8[6] mas/yr
Distance	460 ly (140[7] pc)
Orbit[8]
Primary	A[a]
Companion	B
Period (P)	155 yr
Semi-major axis (a)	0.172+0.002 −0.003″
Eccentricity (e)	0.742+0.025 −0.034
Inclination (i)	0.0°
Argument of periastron (ω) (secondary)	−42.2+2.0 −4.7°
Details[5]
A[a]
Mass	0.37 M☉
Radius	1.1 R☉
Luminosity	0.17 L☉
B
Mass	0.29 M☉
Radius	1.7 R☉
Luminosity	0.31 L☉
Temperature	3,550[7] K
Age	4.6[7] Myr
Other designations
XZ Tau, GSC 01269-00171[9]
Database references
SIMBAD	data

A third star, component C, has been observed at a separation of 0.09″, but subsequent observations failed to find it.^[10][8] The T Tauri star HL Tauri, 23″ away, is also sometimes listed as a companion.^[9]

The discovery by Pelageya Fedorovna Shajn, that XZ Tauri is a variable star, was announced in 1928.^[11]

Gallery

• 
  Hubble image of XZ Tauri.^[12]
• 
  An animation of the 2000 superflare in the system.

Notes

1. Sources vary on their definitions of the primary and secondary components. A is defined here as the more massive component, with a lower temperature but higher luminosity. Other sources refer to the components as north and south,^[2] or Aa and Ab.^[9] The southerly star Ab is generally brighter at optical wavelengths and more massive, but is less luminous.