Alpha Arae
 α Arae in the constellation Ara. |
|
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) |
|
|---|---|
| Constellation | Ara |
| Right ascension | 17h 31m 50.4933s[1] |
| Declination | −49° 52′ 34.121″[1] |
| Apparent magnitude (V) | 2.76 to 2.90[2] |
| Characteristics | |
| Spectral type | B3Ve[3] |
| U−B color index | −0.69[2] |
| B−V color index | −0.17[2] |
| R−I color index | −0.24[2] |
| Variable type | BE[4] |
| Astrometry | |
| Radial velocity (Rv) | 0[1] km/s |
| Proper motion (μ) | RA: −31.27[1] mas/yr Dec.: −67.15[1] mas/yr |
| Parallax (π) | 13.46 ± 0.95[1] mas |
| Distance | 240 ± 20 ly (74 ± 5 pc) |
| Absolute magnitude (MV) | −1.5[note 1] |
| Details | |
| Mass | 6.8[3] M☉ |
| Radius | 4.4[3] R☉ |
| Luminosity (bolometric) | 5,800[3] L☉ |
| Temperature | 19,000[3] K |
| Rotation | 12 h[note 2][3] |
| Rotational velocity (v sin i) | 375[3] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
Alpha Arae (α Arae, α Ara) is the second brightest star in the constellation Ara.
With β and σ Ara it forms the Chinese asterism Choo （pinyin: chǔ, 杵）, "pestle" in traditional Chinese astronomy. It was the second star of Choo （杵二）, but R. H. Allen used the name Choo for this star only.[6] Patrick Moore lists Choo as a proper name for this star in his star catalogue of the constellation Ara.[7] This name is also spelt Tchou.[citation needed] There is another Choo in the constellation Pegasus.
In Chinese, 杵 (Chǔ), meaning Pestle, refers to an asterism consisting of α Arae, σ Arae and β Arae.[8] Consequently, α Arae itself is known as 杵二 (Chǔ èr, English: the Second Star of Pestle.)[9]
It is a variable Be star approximately 240 light-years from the Earth, with an apparent visual magnitude which varies between 2.76m and 2.90m.[1][2]
Like other Be stars, Alpha Arae rotates quickly, rapidly enough in fact to be surrounded by a equatorial disk of material ejected from the star.[10] In 2003 and 2005, Alpha Arae was observed by infrared interferometry, using the MIDI and AMBER instruments at the VLT Interferometer. The results, published in 2005 and 2007, appear to show that Alpha Arae has an equatorial rotational speed of about 470 km/s, that it is surrounded by a dense equatorial disk of material in Keplerian (rather than uniform) rotation, and that it is losing mass by a polar stellar wind with a terminal velocity of approximately 1,000 km/s. There is also some evidence that Alpha Arae is orbited by a companion at 0.7 AU.[3][11]
[edit] Visual companion
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) |
|
|---|---|
| Constellation | Ara |
| Right ascension | 17h 31m 51.3s[12] |
| Declination | −49° 53′ 24″[12] |
| Apparent magnitude (V) | 11.0[12] |
| Characteristics | |
| Spectral type | K0V[2] |
| Position (relative to A) | |
| Epoch of observation | 2000 |
| Angular distance | 49.7″ [5] |
| Position angle | 168° [5] |
| Other designations | |
| Database references | |
| SIMBAD | data |
The Be star described above has a visual companion star, CCDM J17318-4953B, located approximately 50 arcseconds away, with an apparent visual magnitude of about 11.[5] The two stars appear close to each other by coincidence and are not physically close in space.[2]
[edit] Notes
[edit] References
- ^ a b c d e f g h V* alf Ara -- Eruptive variable Star, database entry, SIMBAD. Accessed on line November 26, 2008.
- ^ a b c d e f g HR 6510, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line November 26, 2008.
- ^ a b c d e f g h First direct detection of a Keplerian rotating disk around the Be star α Arae using AMBER/VLTI, A. Meilland et al., Astronomy and Astrophysics 464, #1 (March 2007), pp. 59–71, doi:10.1051/0004-6361:20064848, Bibcode: 2007A&A...464...59M. See Tables 1 and 4 for parameters of the star, circumstellar disk, and polar winds.
- ^ alf Ara, database entry, The combined table of GCVS Vols I-III and NL 67-78 with improved coordinates, General Catalogue of Variable Stars, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line November 26, 2008.
- ^ a b c d e Entry 17318-4953, The Washington Double Star Catalog, United States Naval Observatory. Accessed on line November 26, 2008.
- ^ a b Allen, R. H., (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc.. p. 63. ISBN 0486210790.[1]
- ^ Moore, P., (1983). The Guinness Book of Astronomy Facts and Feats (Second ed.). Middlesex: Guinness Superlatives Ltd. p. 187. ISBN 0851122944.
- ^ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 9789867332257.
- ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
- ^ To Be or Not to Be: Is It All About Spinning?: VLTI Discerns How Matter Behaves in Disc Around a Be Star, ESO press release 35/06, September 20, 2006. Accessed on line December 12, 2008.
- ^ First VLTI/MIDI observations of a Be star: Alpha Arae, O. Chesneau et al., Astronomy and Astrophysics 435, #1 (May 2005), pp. 275–287, doi:10.1051/0004-6361:20041954, Bibcode: 2005A&A...435..275C.
- ^ a b c d CD-49 11511B -- Star in double system, database entry, SIMBAD. Accessed on line November 26, 2008.
[edit] See also
[edit] External links
- HR 6510, entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50.
- Image of Alpha Arae from Aladin.
