Friedrich August Theodor Winnecke discovered that the star is variable in 1861. In 1907 it appeared with its variable star designation, R Crateris, in Annie Jump Cannon'sSecond Catalog of Variable Stars.[13] Although the period for large brightness changes in R Crateris is listed as ~160 days, in 1982 Silvia Livi and Thaisa Bergmann reported small (~0.1 magnitude) variations on timescales of less than one hour. The rapid variations seem to be more regular when the star is near maximum brightness.[14]
R Crateris is an oxygen-rich asymptotic giant branch star, losing mass at a rate of 8×10−7solar masses per year via a stellar wind.[4] At large distances from the star, the wind is expanding into space at 11.7±0.3 km/sec.[15]
Near-infrared radiation from R Crateris was detected in the first Two-Micron Sky Survey, published in 1969.[16] It was detected in the far-infrared by the IRAS satellite, and that emission was resolved by IRAS, showing that the star is surrounded by a large circumstellar shell containing dust.[17] High resolution far-infrared images of R Crateris taken by the Herschel Space Observatory show that the emitting region of the shell, roughly 280 arcseconds (0.94 light year) across, consists primarily of two non-concentric arcs well separated from the star itself. The arcs are probably bowshocks formed as the dusty stellar wind collides with the interstellar medium.[18] The total mass of the shell, including both dust and gas, is estimated to be about (6.4±2)×10−2 solar masses.[19] Infrared imaging of the innermost (sub-arcsecond) portion of the dust shell shows a bipolar structure.[4][20]
In the early 1970s, maser emission from OH and H2O was detected in R Cratoris' circumstellar shell.[21] SiO maser emission was detected in 1985.[22] Thermal (non-maser) emission from CO was detected in 1986.[23]
With the high angular resolution provided by Very Long Baseline Interferometry, the H2O maser emission is seen to arise from small (milli-arcsecond) blobs, whose proper motions through the inner region of the circumstellar shell can be measured. These observations give additional evidence that R Cratoris has developed a bipolar stellar wind.[24]
^Houk, N.; Smith-Moore, M. (1988). Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Volume 4, Declinations -26°.0 to -12°.0. University of Michigan, Ann Arbor, MI. Bibcode:1988mcts.book.....H. ISBN0835703312.
