Astronomy: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 is actually a binary star system, whose components complete an orbit every three years and seven months.[6] It 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]
Properties
With an estimated age of 660 million years,[11][12] the primary component 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 A is larger than the Sun, with a 60% greater mass[6] and a 355% greater radius.[7] It is radiating 40 times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 7,550 K.[8] At this heat, the star glows with the white hue of an A-type star.[17] It is also one of the brightest known Delta Scuti variables.[18] The space velocity components of this star in the galactic coordinate system are U = -22, V = -20 and W = -9 km/s.[19]
Data from the Hipparcos mission uncovered the presence of a binary companion[15] with a companion orbiting at a semimajor axis of around 3.25 AU, or three times the distance from Earth to the Sun.[6] 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][20]
Notes
- ↑ Calculated using a3 = (M1 + M2)
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where a is the semi-major axis in astronomical units, M1 and M2 are the primary and secondary's mass respectively, in M☉, and P is the period in years.
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V.
- ↑ 2.0 2.1 2.2 2.3 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.
- ↑ 3.0 3.1 3.2 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. doi:10.1086/504637. Bibcode: 2006AJ....132..161G.
- ↑ 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.
- ↑ 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.
- ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 Dholakia, Shishir; Murphy, Simon J; Huang, Chelsea X; Venner, Alexander; Wright, Duncan (2024-11-13). "A catalogue of binary stars from phase modulation in the first four years of TESS mission photometry". Monthly Notices of the Royal Astronomical Society 536 (3): 2313–2323. doi:10.1093/mnras/stae2551. ISSN 0035-8711.
- ↑ 7.0 7.1 McDonald, I.; Zijlstra, A. A.; Watson, R. A. (2017-10-01). "Fundamental parameters and infrared excesses of Tycho-Gaia stars". Monthly Notices of the Royal Astronomical Society 471: 770–791. doi:10.1093/mnras/stx1433. ISSN 0035-8711. Bibcode: 2017MNRAS.471..770M. Alpha Pictoris' database entry at VizieR.
- ↑ 8.0 8.1 8.2 Zorec, J.; Royer, F. (January 2012). "Rotational velocities of A-type stars. IV. Evolution of rotational velocities". Astronomy & Astrophysics 537: A120. doi:10.1051/0004-6361/201117691. Bibcode: 2012A&A...537A.120Z. Alpha Pictoris' database entry at VizieR.
- ↑ 9.0 9.1 9.2 Hempel, M.; Schmitt, J. H. M. M. (2003). "High resolution spectroscopy of circumstellar material around A stars". Astronomy and Astrophysics 408 (3): 971–979. doi:10.1051/0004-6361:20030946. Bibcode: 2003A&A...408..971H.
- ↑ 10.0 10.1 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. doi:10.1051/0004-6361:20065224. Bibcode: 2007A&A...463..671R.
- ↑ 11.0 11.1 Su, K. Y. L. (December 2006). "Debris Disk Evolution around A Stars". The Astrophysical Journal 653 (1): 675–689. doi:10.1086/508649. Bibcode: 2006ApJ...653..675S.
- ↑ 12.0 12.1 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. doi:10.1086/318269. Bibcode: 2001ApJ...546..352S.
- ↑ "LTT 2656". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=LTT+2656.
- ↑ Moore, Patrick (2007). Moore on Mercury: the planet and the missions. Springer. p. 121. ISBN 978-1846282577. https://books.google.com/books?id=2_n4T_k7lIIC&pg=PT121.
- ↑ 15.0 15.1 Goldin, A.; Makarov, V. V. (November 2007). "Astrometric Orbits for Hipparcos Stochastic Binaries". The Astrophysical Journal Supplement Series 173 (1): 137–142. doi:10.1086/520513. Bibcode: 2007ApJS..173..137G.
- ↑ Roberge, Aki; Weinberger, Alycia J. (March 2008). "Debris Disks around Nearby Stars with Circumstellar Gas". The Astrophysical Journal 676 (1): 509–517. doi:10.1086/527314. Bibcode: 2008ApJ...676..509R.
- ↑ "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. https://web.archive.org/web/20120222183238/http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html. Retrieved 2012-01-16.
- ↑ Antoci, V et al. (11 December 2019). "The first view of δ Scuti and γ Doradus stars with the TESS mission". Monthly Notices of the Royal Astronomical Society 490 (3): 4040–4059. doi:10.1093/mnras/stz2787. Bibcode: 2019MNRAS.490.4040A.
- ↑ Gliese, W. (1969). "Catalogue of Nearby Stars". Veröffentlichungen des Astronomischen Rechen-Instituts Heidelberg 22: 1. Bibcode: 1969VeARI..22....1G.
- ↑ Schröder, C.; Schmitt, J. H. M. M. (November 2007). "X-ray emission from A-type stars". Astronomy and Astrophysics 475 (2): 677–684. doi:10.1051/0004-6361:20077429. Bibcode: 2007A&A...475..677S.
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