R Sculptoris

R Sculptoris is a variable star system in the southern constellation of Sculptor.^[11][12] Parallax measurements provide a distance estimate of approximately 1,435 ± 98 light-years from the Sun.^[1] An independent estimate based on measurements of an ejected shell surrounding the star yield a distance of 1,180 ± 140 light-years.^[6] The star is drifting closer with a radial velocity of −5.4 km/s.^[5]

R Sculptoris

Location of R Sculptoris (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Sculptor
Right ascension	01h 26m 58.09462s[1]
Declination	−32° 32′ 35.4377″[1]
Apparent magnitude (V)	+5.72[2]
Characteristics
Spectral type	C6,5ea(Np)[3]
U−B color index	+7.67[2]
B−V color index	+3.87[2]
Variable type	SRb[4]
Astrometry
Radial velocity (Rv)	−5.40[5] km/s
Proper motion (μ)	RA: −9.784[1] mas/yr Dec.: −30.900[1] mas/yr
Parallax (π)	2.2724±0.1471 mas[1]
Distance	1,180±140 ly (361±44 pc)[6]
Absolute magnitude (MV)	−0.45[7]
Details
Mass	1.3±0.7 [8] M☉
Radius	411±43[9] R☉
Luminosity	8,000±1,000[9] L☉
Surface gravity (log g)	−0.5±0.1[9] cgs
Temperature	2640±80 [8] K
Metallicity [Fe/H]	0.0[3] dex
Other designations
R Scl, CD−33°525, HD 8879, HIP 6759, HR 423, SAO 193122, WDS J01270-3233A, AAVSO 0122-33[10]
Database references
SIMBAD	data

Benjamin Apthorp Gould discovered that the star's brightness varies, in 1872. It was listed with its variable star designation, R Sculptoris, in Annie Jump Cannon's 1907 work Second Catalog of Variable Stars.^[13] Although the General Catalogue of Variable Stars lists its maximum brightness as magnitude 9.1,^[14] far too faint to be seen with the naked eye, both AAVSO and ASAS data shows that R Sculptoris is occasionally brighter than 6th magnitude, and faintly visible to the naked eye under excellent observing conditions.^[15][16]

A visual band light curve for R Sculptoris, plotted from ASAS data^[17]

This is an aging giant star on the asymptotic giant branch with a stellar classification of C6,5ea(Np),^[3] which indicates a carbon-rich atmosphere. It is a semi-regular pulsating star of the SRb^[4] type that is nearing the end of its fusing lifespan. A sine curve fitted to the last ten pulsation cycles prior to 2017 give a pulsation period of 376 days with an amplitude of 0.75 magnitude. The star is shedding its outer atmosphere, and it is surrounded by a thin shell of dust and gas that was created during the most recent thermal pulse around 2,000 years ago.^[6]

Observations have revealed a spiral structure in the material around the star.^[18] The spiral is suspected to be caused by an unseen companion star.^[11] The spiral windings are consistent with an orbital period of ~350 years.^[18]

Gallery

• 
  This image captures approximately 20x20 milliarcseconds.^[19]
• 
  Spiral spotted by ALMA around the star (data visualisation).
• 
  R Sculptoris and its hidden companion, taken by Hubble Space Telescope