Alpha Circini

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α Circini
Diagram showing star positions and boundaries of the Circinus constellation and its surroundings
Cercle rouge 100%.svg

Location of α Circini (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Circinus
Right ascension 14h 42m 30.41958s[1]
Declination −64° 58′ 30.4934″[1]
Apparent magnitude (V) 3.19[2]
Characteristics
Spectral type A7 Vp SrCrEu[3]
U−B color index +0.12[2]
B−V color index +0.24[2]
Astrometry
Radial velocity (Rv) +7.2[4] km/s
Proper motion (μ) RA: −192.53[1] mas/yr
Dec.: −233.51[1] mas/yr
Parallax (π) 60.35 ± 0.14[1] mas
Distance 54.0 ± 0.1 ly
(16.57 ± 0.04 pc)
Details
Mass 1.5–1.7[5] M
Radius 1.967 ± 0.066[6] R
Luminosity 10.51 ± 0.60[5] L
Surface gravity (log g) 4.1[5] cgs
Temperature 7,500[5] K
Metallicity [Fe/H] 0.13[7] dex
Rotation 4.4790 ± 0.0001 days[8]
Rotational velocity (v sin i) 13.0 ± 1.5[8] km/s
Age ~12 million[9] years
Other designations
17. G Circini,[citation needed] HD 128898, HIP 71908, HR 5463, SAO 252853.[10]
Database references
SIMBAD data

Alpha Circini (α Cir, α Circini) is a variable star in the faint, southern, circumpolar constellation of Circinus. At an apparent visual magnitude of 3.19,[2] it is the brightest star in the constellation and can be readily seen with the naked eye from the southern hemisphere. Parallax measurements of this star yield an estimated distance of 54.0 light-years (16.6 parsecs) from the Earth.[1]

This star belongs to a class of variables known as rapidly oscillating Ap stars. It oscillates with multiple, non-radial pulsation cycles and a dominant cycle of 6.8 minutes.[8] The spectrum shows peculiar features caused by chemical stratification of the outer atmosphere. It displays a moderate deficiency of carbon, nitrogen and oxygen, while there is an overabundance of chromium (Cr).[5] The stellar classification of A7 Vp SrCrEu[3] indicates that this is a main sequence star with enhanced levels of strontium (Sr), chromium, and europium (Eu) in its atmosphere (compared to a typical star like the Sun).[11]

The mass of Alpha Circini is about 150% to 170% the mass of the Sun[5] and it has double the Sun's radius,[6] while the luminosity is more than 10 times that of the Sun. The effective temperature of the outer envelope is about 7,500 K, giving it the white hue typical of A-type stars.[5][12] It is rotating with a period of 4.5 days and the pole is inclined by about 37 ± 4° to the line of sight from the Earth.[8]

Based upon its location and motion through space, Alpha Circini is a candidate member of a stellar kinematic group known as the Beta Pictoris moving group. This group shares a common origin and has an estimated age of about 12 million years. At the birth of this group, Alpha Circini was estimated to be located at a distance of about 91 ly (28 pc) from the center of the assemblage.[9]

References[edit]

  1. ^ a b c d e f 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. ^ a b c d 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 
  3. ^ a b 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. ^ Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick, Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E 
  5. ^ a b c d e f g Kochukhov, O.; Shulyak, D.; Ryabchikova, T. (June 2009), "A self-consistent empirical model atmosphere, abundance and stratification analysis of the benchmark roAp star α Circini", Astronomy and Astrophysics 499 (3): 851–863, arXiv:0903.3512, Bibcode:2009A&A...499..851K, doi:10.1051/0004-6361/200911653 
  6. ^ a b Bruntt, H. et al. (June 2008), "The fundamental parameters of the roAp star α Circini", Monthly Notices of the Royal Astronomical Society 386 (4): 2039–2046, arXiv:0803.1518, Bibcode:2008MNRAS.386.2039B, doi:10.1111/j.1365-2966.2008.13167.x 
  7. ^ North, P.; Berthet, S.; Lanz, T. (January 1994), "The nature of the F STR lambda 4077 stars. 3: Spectroscopy of the barium dwarfs and other CP stars", Astronomy and Astrophysics 281 (3): 775–796, Bibcode:1994A&A...281..775N 
  8. ^ a b c d Bruntt, H. et al. (June 2009), "Asteroseismic analysis of the roAp star α Circini: 84d of high-precision photometry from the WIRE satellite", Monthly Notices of the Royal Astronomical Society 396 (2): 1189–1201, arXiv:0903.3967, Bibcode:2009MNRAS.396.1189B, doi:10.1111/j.1365-2966.2009.14804.x 
  9. ^ a b Nakajima, Tadashi; Morino, Jun-Ichi; Fukagawa, Misato (September 2010), "Potential Members of Stellar Kinematical Groups within 20 pc of the Sun", The Astronomical Journal 140 (3): 713–722, Bibcode:2010AJ....140..713N, doi:10.1088/0004-6256/140/3/713 
  10. ^ "V* alf Cir -- Variable Star of alpha2 CVn type", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2012-01-04 
  11. ^ Kaler, James B., "ALPHA CIR (Alpha Circini)", Stars (University of Illinois), retrieved 2012-01-04 
  12. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16