R Scuti

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R Scuti
Observation data
Epoch J2000      Equinox J2000
Constellation Scutum
Right ascension 18h 47m 28.95s[1]
Declination −05° 42′ 18.5″
Apparent magnitude (V) 4.2—8.6[2][3] (naked eye)
Spectral type G0Iae-K2p(M3)Ibe[2][3]
Variable type RV Tau[2][1]
Radial velocity (Rv) 44.0[1] km/s
Parallax (π) 2.32 ± 0.82[1] mas
Distance approx. 1,400 ly
(approx. 400 pc)
Absolute magnitude (MV) -2.6 (@431pc)[4]
-3.8(?) (@750pc)[5]
Radius 87.4[4] R
Luminosity 1000[4]
9400 ± 7100[6] L
Temperature 4500[6]—5190[4] K
Other designations
HD 173819, HIP 92202, 2MASS J18472894-0542185, SAO 142620[1]

R Scuti (R Sct) is a star in the constellation of Scutum. It is a yellow supergiant and is a pulsating variable known as a RV Tauri variable.

It was discovered in 1795 by Edward Pigott at a time when only a few variable stars were known to exist.[7] R Sct is the brightest of the RV Tau-type stars[8] and the American Association of Variable Star Observers (AAVSO) contains over 110,000 observations of this star.[7] At its brightest it is visible to the naked eye, and at its dimmest can be located with good binoculars.[7] In the sky it is about 1 degree northwest of the Wild Duck Cluster (Messier 11).[7]


Hipparcos gives a parallax of 2.32 milli-arcseconds for R Sct,[1] giving it an estimated distance of 431 parsecs (1,410 light-years).[4] But a period–luminosity relation similar to what is used for Cepheid variables suggests that R Sct is at a distance of 750 parsecs (2,400 light-years) with a luminosity of around 9400 Suns.[6] But this would make R Sct twice as luminous as the next most luminous RV Tau-type star in the study.[6] The author of the period–luminosity study doubts the high luminosity and resulting distance, and it has been argued (Matsuura2002) that R Sct is a thermal-pulsing AGB star, observed in a helium-burning phase instead of a post-AGB star.[6] In either case the luminosity is far below the Ia-Ib spectral type would indicate (30,000-100,000 L would be more typical), and R Scuti is clearly in an unusual evolutionary state.

AAVSO light curve of RV Tau R Sct from 1 Jan 2009 to 24 Nov 2010. Up is brighter and down is fainter. Day numbers are Julian day.

See also[edit]


  1. ^ a b c d e f "R Scuti". SIMBAD Astronomical Database. Retrieved 2010-11-24. 
  2. ^ a b c "GCVS Query=R Sct". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. Retrieved 2010-11-24. 
  3. ^ a b "R Sct". AAVSO: Variable Star Plotter (VSP). Retrieved 2010-11-24. 
  4. ^ a b c d e "Spectral analysis for the RV Tau star R Sct". NOAO Education & Public Outreach. Retrieved 2010-11-24. 
  5. ^ absmag "M" = vmag "5.5" + absmag of G2V main sequence star "5" - 5 log (distance)
    M=5.5+5-5(log 750)=-3.8
  6. ^ a b c d e Ruyter, S; Winckel; Dominik; Waters; Dejonghe (2005). "Strong dust processing in circumstellar discs around 6 RV Tauri stars. Are dusty RV Tauri stars all binaries?". Astronomy and Astrophysics 435 (1): 161–166. arXiv:astro-ph/0503290v1. Bibcode:2005A&A...435..161D. doi:10.1051/0004-6361:20041989. 
  7. ^ a b c d "R Scuti : A Favorite Among Its Class". AAVSO. Retrieved 2010-11-24. 
  8. ^ "GCVS Type=RV". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. Retrieved 2010-11-24. 

External links[edit]