| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cancer |
| Right ascension | 09h 10m 38.79702s[2] |
| Declination | +30° 57′ 47.2911″[2] |
| Apparent magnitude (V) | 5.4 - 7.3[3] |
| Characteristics | |
| Spectral type | M6S[4] |
| Variable type | SRb[3] |
| Astrometry | |
| Proper motion (μ) | RA: −10.723±0.423[2]mas/yr Dec.: −33.822±0.360[2]mas/yr |
| Parallax (π) | 6.6490±0.4946 mas[2] |
| Distance | 490 ± 40 ly (150 ± 10 pc) |
| Absolute magnitude (MV) | 5.4 - 7.3[3] |
| Details | |
| Radius | 225[5] R☉ |
| Luminosity | 4950[6] L☉ |
| Temperature | 3200[6] K |
| Other designations | |
| HD 78712,HR 3639,HIP 45058,SAO 61306[7] | |
| Database references | |
| SIMBAD | data |
RS Cancri, also known asHR 3639 andHD 78712, is a star about 490light years from the Earth in the constellationCancer. It is asemiregular variable star, ranging in brightness frommagnitude 5.4 to 7.3 over a period of about 229 days. During the time intervals when it is brighter than magnitude 6, it may be faintly visible to thenaked eye of an observer far fromcity lights.
The variability of RS Cancri was discovered byEdward Pickering based upon 15 observations made in 1892 and 1898. S. Seliwanow derived a period of 129.5 days for the star, in 1923.[8] In 2005, Saul Adelman and John Dennis found that the star showed two periods well determined by their data,121.8±0.9 and248±7 days, as well as a poorly-determined third period of about 500 days.[9]
RS Cancri is anS-type star,[4] on theasymptotic giant branch.[10] Its spectrum showstechnetium, implying the star has undegone the thirddredge-up.[11] RS Cancri has astellar wind, and is losing mass at a rate of1.7 × 10−7solar masses per year.[5]
RS Cancri has acircumstellar shell. It is a good target for studies of such a shell, because its rather highgalactic latitude (+42 degrees) means that it is cleanly separated from the interstellar dust and gas seen along most lines of sight through thegalactic plane. Dust within the shell produces far-infrared continuum emission that wasresolved byIRAS.[12] Both atomic and molecular gas within the shell are also measurably extended, and have been mapped.[5]
The extensive molecular envelope surrounding RS Cancri was first detected in 1977, by Kwok-Yung (Fred) Lo and Kenneth Bechis, who used the36 footradio telescope onKitt Peak to detect the J=1-0line ofcarbon monoxide (CO).[13] Years later, when observations of spectral lines could be made with more sensitive equipment, it was noticed that the shapes of the spectral lines suggested that RS Cancri has two distinct stellar wind components, expanding into space at different speeds.[14]Interferometric observations have shown that the two winds consist of a ~2 km/sec wind arising from an equatorial disk within the envelope, and an ~8 km/sec bipolar wind.[15] In subsequent decades, additional molecules such as SiO, SO, SO2, H2O HCN and PN have been detected.[6]
{{cite journal}}: CS1 maint: multiple names: authors list (link)