Alpha Pictoris

Alpha Pictoris (α Pic, α Pictoris) is the brightest star in the southern constellation of Pictor. It has an apparent visual magnitude of 3.27,[2] which is bright enough to be viewed from urban areas in the southern hemisphere. This star is close enough for its distance to be measured using parallax shifts, which yields a value of roughly 97 light-years (30 parsecs) from the Sun, with a 5% margin of error.[1] Alpha Pictoris has the distinction of being the south pole star of the planet Mercury.[14]

α Pictoris
Location of α Pictoris (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Pictor
Right ascension  06h 48m 11.45512s[1]
Declination −61° 56′ 29.0008″[1]
Apparent magnitude (V) 3.27[2]
Characteristics
Spectral type A8 Vn kA6[3]
U−B color index +0.13[2]
B−V color index +0.21[2]
Astrometry
Radial velocity (Rv)+20.6[4] km/s
Proper motion (μ) RA: –66.07[1] mas/yr
Dec.: +242.97[1] mas/yr
Parallax (π)33.78 ± 1.78[1] mas
Distance97 ± 5 ly
(30 ± 2 pc)
Absolute magnitude (MV)0.86[5]
Orbit[6]
Period (P)1618+1407
−325 days
Semi-major axis (a)36+15
−2 mas
Eccentricity (e)0.39+0.35
−0.17
Inclination (i)118±3°
Longitude of the node (Ω)24±5°
Periastron epoch (T)953+707
−640
Argument of periastron (ω)
(secondary)		92+22
−44°
Details
Mass2.04[5] M☉
Radius1.6[7] R☉
Luminosity13[8] L☉
Surface gravity (log g)3.48[9] cgs
Temperature7530[9] K
Metallicity [Fe/H]–0.11[3] dex
Rotational velocity (v sin i)206[10] km/s
Age660[11][12] Myr
Other designations
CD-61°1478, Gl 248, HD 50241, HIP 32607, HR 2550, LTT 2656, SAO 249647.[13]
Database references
SIMBADdata

Properties

With an estimated age of 660 million years,[11][12] this is a relatively young Lambda Boötis star.[15] The stellar classification of A8 Vn kA6[3] shows this peculiarity, with the kA6 notation indicating weaker than normal calcium K-lines in the spectrum. The 'n' following the main sequence luminosity class of V indicates the absorption lines in the spectrum are broad and nebulous. This is caused by the rapid spin of the star, which has a high projected rotational velocity of 206 km/s.[10] Spectroscopy shows narrow, time-varying absorption features being caused by circumstellar gas moving toward the star. This is not the result of interstellar matter, but a shell of gas along the orbital plane. Alpha Pictoris is categorized as a rapidly rotating shell star that may have recently ejected mass from its outer atmosphere.[9][16]

Alpha Pictoris is larger than the Sun, with twice[5] the mass and a 60% greater radius.[7] It is radiating 13[8] times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 7530 K.[9] At this heat, the star glows with the white hue of an A-type star.[17] The space velocity components of this star in the galactic coordinate system are U = -22, V = -20 and W = -9 km/s.[18]

Data from the Hipparcos mission indicate this may be an unresolved binary system with a companion orbiting at a semimajor axis of around 1 AU, or the same distance that the Earth orbits from the Sun.[15] Alpha Pictoris is an X-ray source, which is unusual for an A-type star since stellar models don't predict them to have magnetic dynamos. This emission may instead be originating from the companion.[9][19]

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References
  1. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
  2. Johnson, H. L.; Iriarte, B.; Mitchell, R. I.; Wisniewskj, W. Z. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4: 99–110. Bibcode:1966CoLPL...4...99J.
  3. Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Northern Sample I", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637
  4. Wilson, R. E. (1953). "General Catalogue of Stellar Radial". Carnegie Institute Washington D.C. Publication. Washington D.C.: Carnegie Institution Publication 601. Bibcode:1953GCRV..C......0W.
  5. Pizzolato, N.; Maggio, A.; Sciortino, S. (September 2000), "Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases", Astronomy and Astrophysics, 361: 614–628, Bibcode:2000A&A...361..614P
  6. Goldin, A.; Makarov, V. V. (September 2006), "Unconstrained Astrometric Orbits for Hipparcos Stars with Stochastic Solutions", The Astrophysical Journal Supplement Series, 166 (1): 341–350, arXiv:astro-ph/0606293, Bibcode:2006ApJS..166..341G, doi:10.1086/505939
  7. Pasinetti Fracassini, L. E.; Pastori, L.; Covino, S.; Pozzi, A. (February 2001). "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics". Astronomy and Astrophysics. 367 (2): 521–524. arXiv:astro-ph/0012289. Bibcode:2001A&A...367..521P. doi:10.1051/0004-6361:20000451.
  8. Malagnini, M. L.; Morossi, C. (November 1990), "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars", Astronomy and Astrophysics Supplement Series, 85 (3): 1015–1019, Bibcode:1990A&AS...85.1015M
  9. Hempel, M.; Schmitt, J. H. M. M. (2003). "High resolution spectroscopy of circumstellar material around A stars". Astronomy and Astrophysics. 408 (3): 971–979. Bibcode:2003A&A...408..971H. doi:10.1051/0004-6361:20030946.
  10. Royer, F.; Zorec, J.; Gómez, A. E. (February 2007). "Rotational velocities of A-type stars. III. Velocity distributions". Astronomy and Astrophysics. 463 (2): 671–682. arXiv:astro-ph/0610785. Bibcode:2007A&A...463..671R. doi:10.1051/0004-6361:20065224.
  11. Su, K. Y. L.; et al. (December 2006). "Debris Disk Evolution around A Stars". The Astrophysical Journal. 653 (1): 675–689. arXiv:astro-ph/0608563. Bibcode:2006ApJ...653..675S. doi:10.1086/508649.
  12. Song, Inseok; Caillault, J.-P.; Barrado y Navascués, David; Stauffer, John R. (January 2001). "Ages of A-Type Vega-like Stars from uvbyβ Photometry". The Astrophysical Journal. 546 (1): 352–357. arXiv:astro-ph/0010102. Bibcode:2001ApJ...546..352S. doi:10.1086/318269.
  13. "LTT 2656". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2009-09-10.
  14. Moore, Patrick (2007), Moore on Mercury: the planet and the missions, Springer, p. 121, ISBN 978-1846282577
  15. Goldin, A.; Makarov, V. V. (November 2007). "Astrometric Orbits for Hipparcos Stochastic Binaries". The Astrophysical Journal Supplement Series. 173 (1): 137–142. arXiv:0706.0361. Bibcode:2007ApJS..173..137G. doi:10.1086/520513.
  16. Roberge, Aki; Weinberger, Alycia J. (March 2008). "Debris Disks around Nearby Stars with Circumstellar Gas". The Astrophysical Journal. 676 (1): 509–517. arXiv:0711.4561. Bibcode:2008ApJ...676..509R. doi:10.1086/527314.
  17. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on February 22, 2012, retrieved 2012-01-16
  18. Gliese, W. (1969). "Catalogue of Nearby Stars". Veröffentlichungen des Astronomischen Rechen-Instituts Heidelberg. 22: 1. Bibcode:1969VeARI..22....1G.
  19. Schröder, C.; Schmitt, J. H. M. M. (November 2007). "X-ray emission from A-type stars". Astronomy and Astrophysics. 475 (2): 677–684. Bibcode:2007A&A...475..677S. doi:10.1051/0004-6361:20077429.
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