|Right Ascension|| 18 : 47 : 28.9 (h:m:s)
|Declination|| -05 : 42 : 18 (deg:m:s)
|Distance|| 2.5 (kly)
|Visual brightness|| 4.45 .. 8.20 (mag)
|Period|| 140.05 (days)
|Spectra type|| K0Ibpv
This variable star has been discovered by Edward Pigott in 1795 (Pigott & Englefield, 1797). It is a yellow giant variable star of the RV Tauri type, and varies semi-regularly between 5th and 8th magnitude.
Various observers have determined primary periods between 140 and 146 days. Normally, the star's brightness varies between mag 4.8 and mag 6.0, but every fourth or fifth minimum drps to mag 8.0 or fainter. Superimposed over the primary period is at least one other period. According to Burnham, this star was in vestigated by McLaughlin who found that the star's spectrum is normally about G2, and it oscillates similar to a Cepheid variable, besides that the radial velocity of its oscillation is much more irregular. In particular, near the deep minimum reddens to about M3, and shows titanium-oxide bands, which are typical for red-giant spectra. During the consequent rise, hydrogen emission lines appear in the spectrum, which gradually turn to absorption lines as the star reaches its maximum. Spectral studies indicate that the various layers of the star ar expanding and contracting at different rates, and that the star is really huge in linear dimension: at least about 100 times the diameter of our sun. Absolute magnitude was estimated at -4.5 to -5.0, and its mass about 20-30 times that of our sun. This results in a distance estimate of 2,500 to 3,000 light-years.
Other spectral classifications have been G0e Ia near its maximum, K0p Ib near the minimum, in the Moscow General Catalogue of Variable Stars of 1970, and G8 to M3 by J.S. Glasby (1969).
The star shows a proper motion of about 0.06 arc seconds per year, and is receding from us at about 26.5 miles per second (42.4 km/s).
R Scuti is situated near the northern edge of a rich Milky Way star cloud, the Scutum Cloud. It lies just about 1deg south of Beta Scuti, and about 1deg NW of bright open star cluster M11.