S Crateris
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Crater |
| Right ascension | 11h 52m 45.098s[1] |
| Declination | −07° 35′ 48.08″[1] |
| Apparent magnitude (V) | 8.64 - 9.51[2] |
| Characteristics | |
| Evolutionary stage | AGB[1] |
| Spectral type | M6e–M7e[3] |
| B−V color index | 1.078[4] |
| Variable type | SRb[3] |
| Astrometry | |
| Radial velocity (Rv) | 43.55[1] km/s |
| Proper motion (μ) | RA: −3.52[1] mas/yr Dec.: −5.08[1] mas/yr |
| Parallax (π) | 2.33±0.13 mas[5] |
| Distance | 430[5] pc |
| Details | |
| Radius | 260[5] R☉ |
| Luminosity | 5970[5] L☉ |
| Temperature | 3097[5] K |
| Other designations | |
| HD 103154, HIP 57917, SAO 138457, AFGL 4830S, IRAS 11501−0719, IRC −10259, 2MASS J11524508−0735482[1] | |
| Database references | |
| SIMBAD | data |
S Crateris (also designated S Crt) is a semiregular variable star of subtype SRb[3][1] located in the Crater constellation. It is an asymptotic giant branch (AGB) star[1] with a spectral type of M6e-M7e.[3] The star was discovered to vary in brightness by Williamina Fleming in 1906.[3]
Observation
S Crateris is situated at right ascension 11h 52m 45.098s, declination −07° 35′ 48.08″ (J2000.0).[1] Its apparent magnitude in the V band varies between approximately 8.64 and 9.51, giving an amplitude of about 0.87 mag.[3] In the infrared, the star is considerably brighter: the 2MASS catalog lists magnitudes of J = 2.055, H = 1.127, and K = 0.786.[1][3]
Variability
S Crateris is classified as a semiregular variable of type SRb in both the General Catalogue of Variable Stars[5] and the AAVSO Variable Star Index.[3] Its pulsation period is 155 days.[3][5] The optical light curve in the V band exhibits a variation of approximately 0.8 magnitudes.[5] The reference epoch is HJD 2452284.2 (9 January 2002).[3]
Distance
The distance to S Crateris has been the subject of several independent measurements that yielded notably inconsistent results prior to modern VLBI observations. Early estimates based on the period-luminosity relation of Mira variables placed the star at distances of 285 and 420 pc.[5] The original Hipparcos Catalogue measured a parallax of 2.04±1.31 mas, corresponding to a distance of approximately 490 pc, but with a large uncertainty.[5] The revised Hipparcos reduction by van Leeuwen (2007) yielded a parallax of 1.26±0.92 mas,[4] corresponding to a distance of roughly 794 pc.
Proper motion
The absolute proper motion of S Crateris, derived from VERA observations after subtracting the internal motion of the reference maser spot, is (μα, μδ) = (−3.17±0.22, −5.41±0.22 mas/yr.[5] This is consistent with the value reported in the revised Hipparcos catalog of (−3.37±1.00, −4.68±0.75) mas/yr.[4][5] The SIMBAD database lists proper motion values of −3.520 and −5.084 mas/yr from the Gaia-based catalog.[1] The heliocentric radial velocity is 43.55 km/s.[1]
Water masers and circumstellar outflow
S Crateris hosts a water maser source at 22 GHz.[5] The stellar systemic LSR velocity is 37.85 km s−1.[5]
VERA observations conducted from October 2005 to May 2007 detected internal motions of 26 individual maser spots, with a typical transverse speed of 5.56 km s−1.[5] Analysis of the three-dimensional velocity field revealed a bipolar outflow with its major axis oriented along the northeast–southwest direction, at a position angle of approximately 255°.[5] The outflow axis is inclined at approximately 43° to the plane of the sky, with the southwestern lobe directed away from the observer.[5] The projected maser distribution radius of 14.2 ± 3.5 mas corresponds to a linear radius of 8.96 AU at the adopted distance of 430 pc.[5]
The maser flux at 34.7 km s−1 underwent a radio flare beginning in February 2006, reaching a peak of 371 Jy on 31 March 2006, before declining to approximately 60 Jy by July 2006.[5]
References
- 1 2 3 4 5 6 7 8 9 10 11 12 13 "V* S Crt". SIMBAD Astronomical Database. Retrieved 6 April 2026.
- ↑ Pojmanski, G. (2002). "The All Sky Automated Survey. Catalog of Variable Stars. I. 0 h - 6 hQuarter of the Southern Hemisphere". Acta Astronomica. 52: 397. arXiv:astro-ph/0210283. Bibcode:2002AcA....52..397P.
- 1 2 3 4 5 6 7 8 9 10 "S Crt". AAVSO Variable Star Index. Retrieved 6 April 2026.
- 1 2 3 "HIP 57917 – Hipparcos, the New Reduction". VizieR / van Leeuwen, F. (2007).
- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Nakagawa, Akiharu; Tsushima, Miyuki; Ando, Kazuma; Bushimata, Takeshi; Choi, Yoon Kyung; et al. (2008). "VLBI Astrometry of AGB Variables with VERA - A Semiregular Variable S Crateris". Publications of the Astronomical Society of Japan. 60 (5): 1013–1021. arXiv:0808.1151. Bibcode:2008PASJ...60.1013N. doi:10.1093/pasj/60.5.1013.
