R Crateris

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R Crateris
RCrtLightCurve.png
A visual band light curve for R Crateris, plotted from ASAS data. [1]
Observation data
Epoch J2000       Equinox J2000
Constellation Crater
Right ascension 11h 00m 33.85257s [2]
Declination −18° 19 29.5827 [2]
Apparent magnitude  (V)8.1 - 9.5 [3]
Characteristics
Evolutionary stage AGB [4]
Spectral type M7/8III [5]
Variable type SRb [6]
Astrometry
Radial velocity (Rv)20.94±1.50 [2]  km/s
Proper motion (μ)RA: −29.373±0.180 [2]   mas/yr
Dec.: −2.499±0.172 [2]   mas/yr
Parallax (π)4.7027 ± 0.1528  mas [2]
Distance 690 ± 20  ly
(213 ± 7  pc)
Details
Mass 1.91 [7]   M
Radius 633 [8]   R
Luminosity 8,151 [8]   L
Surface gravity (log g)−0.86 [8]   cgs
Temperature 3,295 [9]   K
Other designations
HD  95384, HIP  53809, SAO  156389, IRC  −20222, RAFGL 1450 [10]
Database references
SIMBAD data

R Crateris is a star about 700 light years from the Earth in the constellation Crater. It is a semiregular variable star, ranging in brightness from magnitude 8.1 to 9.5 over a period of about 160 days. [3] It is not visible to the naked-eye, but can be seen with a small telescope, or binoculars. [11] R Crateris is a double star; the variable star and its magnitude 9.9 F8V companion are separated by 65.4 arcseconds. [12]

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. [13]

R Crateris is an oxygen-rich asymptotic giant branch star, losing mass at a rate of 8×10−7  solar 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. [14]

Near-infrared radiation from R Crateris was detected in the first Two-Micron Sky Survey, published in 1969. [15] 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. [16] 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. [17] The total mass of the shell, including both dust and gas, is estimated to be about (6.4±2)×10−2 solar masses. [18] Infrared imaging of the innermost (sub-arcsecond) portion of the dust shell shows a bipolar structure. [4] [19]

In the early 1970s, maser emission from OH and H2O was detected in R Cratoris' circumstellar shell. [20] SiO maser emission was detected in 1985. [21] Thermal (non-maser) emission from CO was detected in 1986. [22]

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. [23]

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References

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