Phi Sagittarii
 Location of φ Sagittarii (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 45m 39.38610s[1] |
| Declination | –26° 59′ 26.7944″[1] |
| Apparent magnitude (V) | 3.17[2] |
| Characteristics | |
| Spectral type | B8.5 III[3] to B7 IV[4] |
| U−B color index | –0.36[5] |
| B−V color index | –0.11[5] |
| Astrometry | |
| Radial velocity (Rv) | +21.5[2] km/s |
| Proper motion (μ) | RA: +50.61[1] mas/yr Dec.: +1.22[1] mas/yr |
| Parallax (π) | 13.63 ± 0.19[1] mas |
| Distance | 239 ± 3 ly (73 ± 1 pc) |
| Details | |
| Mass | 4–4.2[6] M☉ |
| Radius | 4.8[6] R☉ |
| Luminosity | 475[6] L☉ |
| Temperature | 14,990[4] K |
| Rotational velocity (v sin i) | 35[7] km/s |
| Age | 1.65 × 108[6] years |
| Other designations | |
Phi Sagittarii (φ Sgr, φ Sagittarii) is a star in the southern constellation of Sagittarius. It is a member of the teapot asterism marking the junction of lid and handle.[9] In ancient Chinese astronomy, it is the 3rd star of 6 stars in the Dipper or 'South Dipper' mansion of the Black Tortoise of the North.[citation needed] With an apparent visual magnitude of 3.17,[2] it is the ninth brightest star in the constellation and is readily visible to the naked eye. Parallax measurements place it at a distance of roughly 239 light-years (73 pc) from the Earth.[1]
The stellar classification of this star has been rated at B8.5 III[3] and B7 IV,[4] with a luminosity class of III indicating it is a giant star, while a class of IV suggests it is still a subgiant star. Both represent stages in the evolution of a star after it has exhausted the hydrogen at its core. This energy is being radiated from the star's outer envelope at an effective temperature of 14,990 K,[4] which produces the blue-white hue typical of B-type stars.[10]
In the past, this star catalogued as a spectroscopic binary and a companion was apparently detected through lunar occultation.[11] However, it is most likely a solitary star[12][6] and any nearby stars are merely optical companions.
[edit] References
- ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, Bibcode 2007A&A...474..653V, doi:10.1051/0004-6361:20078357
- ^ a b c Wielen, R. et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions, Astronomisches Rechen-Institut Heidelberg, Bibcode 1999VeARI..35....1W
- ^ a b Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, 3, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode 1982MSS...C03....0H
- ^ a b c d Zorec, J. et al. (July 2009), "Fundamental parameters of B supergiants from the BCD system. I. Calibration of the (λ_1, D) parameters into Teff", Astronomy and Astrophysics 501 (1): 297–320, Bibcode 2009A&A...501..297Z, doi:10.1051/0004-6361/200811147
- ^ a b Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99), Bibcode 1966CoLPL...4...99J
- ^ a b c d e Kaler, James B., "PHI SGR (Phi Sagittarii)", Stars (University of Illinois), http://stars.astro.illinois.edu/sow/phisgr.html, retrieved 2012-01-15
- ^ Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal 573 (1): 359–365, Bibcode 2002ApJ...573..359A, doi:10.1086/340590
- ^ "phi Sgr -- Star", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Phi+Sagittarii, retrieved 2012-01-15
- ^ Mollise, Rod (2006), The urban astronomer's guide: a walking tour of the cosmos for city sky watchers, Patrick Moore's practical astronomy series, Springer, p. 148, ISBN 1846282160, http://books.google.com/books?id=Z0mvZk0s_TMC&pg=PA148
- ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16
- ^ Finsen, W. S. (April 1951), "The duplicity of phi Sgr", Astronomical Journal 56: 56, Bibcode 1951AJ.....56Q..56F, doi:10.1086/106589
- ^ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society 389 (2): 869–879, Bibcode 2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x
