R Trianguli

R Trianguli (abbreviated as R Tri) is a short-period oxygen-rich^[4] Mira variable in Triangulum with a period of 266.9 days,^[2] discovered by T. H. E. C. Espin in 1890.^[7] When it is near its maximum brightness, it is faintly visible to the naked eye under excellent observing conditions.

R Trianguli

Location of R Trianguli (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Triangulum
Right ascension	02h 37m 02.340s[1]
Declination	+34° 15′ 51.34″[1]
Apparent magnitude (V)	5.4–12.6[2]
Characteristics
Spectral type	M3.5-8IIIe[2]
Apparent magnitude (B)	8.524±0.018
Apparent magnitude (G)	6.699±0.055
Apparent magnitude (R)	8.24
Apparent magnitude (J)	2.23±0.27
Apparent magnitude (H)	1.36±0.22
Apparent magnitude (K)	1.05±0.21
Variable type	Mira[2]
Astrometry
Radial velocity (Rv)	67.52±0.88[1] km/s
Proper motion (μ)	RA: +34.272 mas/yr[1] Dec.: −10.683 mas/yr[1]
Parallax (π)	2.4334±0.2487 mas[1]
Distance	approx. 1,300 ly (approx. 410 pc)
Details
Mass	1.71[3] M☉
Radius	196±41[4] R☉
Luminosity	1,784[5] L☉
Surface gravity (log g)	−0.09[1] cgs
Temperature	3184±120[4] K
Other designations
R Tri, HR 758, HD 16210, HIP 12193, 2MASS J02370234+3415513, Gaia DR2 134874621777526400, Gaia DR3 134874621778128896[6]
Database references
SIMBAD	data

The star is losing about 1.1×10⁻⁷ M_☉/yr, close to average for a short-period Mira variable.^[8] While most short-period Mira variables reside in the Galactic halo, R Trianguli is a member of the thick disk, and its proper motion is fairly high for its distance.^[4] Its angular diameter in the K band was measured in 2002 to be, on average, 5.22±0.30 mas, with a shape suggesting that there is an optically thin disk structure surrounding the star.^[4]

A visual band light curve for R Trianguli, plotted from AAVSO data^[9]