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]

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, S2CID 18759600
  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, S2CID 119476992
  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, S2CID 15673734
  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. S2CID 425754.
  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. S2CID 18475298.
  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. S2CID 14116473.
  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. S2CID 18154947.
  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. S2CID 119586069.
  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. S2CID 18407657.
  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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