NO Aurigae

NO Aurigae is a pulsating variable star in the constellation Auriga. It is an unusually-luminous asymptotic giant branch star about 3,500 light years away. It is a 6th magnitude star faintly visible to the naked eye under very good observing conditions.

NO Aurigae

Location of NO Aurigae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Auriga
Right ascension	05h 40m 42.050s[1]
Declination	+31° 55′ 14.20″[1]
Apparent magnitude (V)	6.21[2] (6.06 - 6.44[3])
Characteristics
Evolutionary stage	Asymptotic giant branch[4]
Spectral type	M2S Iab[3]
U−B color index	+2.22[5]
B−V color index	+2.09[5]
R−I color index	+1.41[5]
Variable type	LC[3]
Astrometry
Radial velocity (Rv)	7.21±0.45[6] km/s
Proper motion (μ)	RA: 0.061±0.093[1] mas/yr Dec.: −2.959±0.051[1] mas/yr
Parallax (π)	0.9189±0.0930 mas[1]
Distance	approx. 3,500 ly (approx. 1,100 pc)
Absolute magnitude (MV)	−5.88[2]
Details
Mass	4.93±1.18[7] M☉
Radius	439 ± 61[8] R☉
Luminosity	30,900[8] L☉
Surface gravity (log g)	−0.037[9] cgs
Temperature	3,651±31[8] K
Other designations
BD+31°1049, HD 37536, HIP 26718, HR 1939, SAO 58322
Database references
SIMBAD	data

Variability

A light curve for NO Aurigae plotted from Hipparcos data^[10]

In 1969, Olin Jeuck Eggen announced that the star, then called HR 1939, is a variable star.^[11] It was given its variable star designation in 1972.^[12] NO Aurigae is listed in the General Catalogue of Variable Stars as a slow irregular variable, indicating that no regularity could be found in the brightness variations. Other studies have suggested possible periods of 102.1, 173, and 226 days, and would classify it as a semiregular variable star.^[13] The maximum visual magnitude range is 6.05–6.50.^[13]

Properties

Most studies of NO Aurigae treat it as a red supergiant member of the Auriga OB1 stellar association at about 1.4 kpc.^[14][15] On this basis it would have a luminosity around 67,000 L_☉ and a radius around 630 R_☉.^[2][14]

NO Aurigae is an MS star, intermediate between spectral type M and S. These are typically Asymptotic Giant Branch stars which can appear with supergiant spectra due to their large size and low mass.^[4] Possible detection of Technetium in the spectrum is a symptom of the third dredge-up which occurs only in late AGB stars.^[15]