CW Leonis

IRC +10216 or CW Leonis is a well-studied carbon star that is embedded in a thick dust envelope. It was first discovered in 1969 by a group of astronomers led by Eric Becklin, based upon infrared observations made with the 62 inches (1.6 m) Caltech Infrared Telescope at Mount Wilson Observatory. Its energy is emitted mostly at infrared wavelengths. At a wavelength of 5 μm, it was found to have the highest flux of any object outside the Solar System.[9]

CW Leonis

CW Leonis in ultraviolet showing the bowshock
Observation data
Epoch J2000      Equinox J2000
Constellation Leo
Right ascension  09h 47m 57.406s[1]
Declination +13° 16′ 43.56″[1]
Apparent magnitude (V) 10.96 - 14.80[2]
Characteristics
Spectral type C9,5e[3]
Apparent magnitude (R) 10.96[1]
Apparent magnitude (J) 7.34[1]
Apparent magnitude (H) 4.04[1]
Apparent magnitude (K) 1.19[1]
Variable type Mira[2]
Astrometry
Proper motion (μ) RA: 35 ± 1 mas/yr
Dec.: 12 ± 1[4] mas/yr
Parallax (π)10.56 ± 2.02[5] mas
Distance130[6] pc
Details
Mass0.7 - 0.9[4] M☉
Radius560[6] R☉
Luminosity8,500 (average), 11,850 (maximum)[6] L☉
Temperature2,300[6] (1,915 - 2,105)[7] K
Other designations
CW Leo, Peanut Nebula, IRC+10216, IRAS 09452+1330, PK 221+45 1, Zel 0945+135, RAFGL 1381, 2MASS J09475740+1316435, SCM 50[8]
Database references
SIMBADdata

Properties

CW Leonis is believed to be in a late stage of its life, blowing off its own sooty atmosphere to form a white dwarf in a distant future. Based upon isotope ratios of magnesium, the initial mass of this star has been constrained to lie between 3–5 solar masses. The mass of the star's core, and the final mass of the star once it becomes a white dwarf, is about 0.7–0.9 solar masses.[10] Its bolometric luminosity varies over the course of a 649-day pulsation cycle, ranging from a minimum of about 6,250 times the Sun's luminosity up to a peak of around 15,800 times. The overall output of the star is best represented by a luminosity of 11,300 L☉.[11]

The carbon-rich gaseous envelope surrounding this star is at least 69,000 years old and the star is losing about (1–4) × 10−5 solar masses per year.[11] The extended envelope contains at least 1.4 solar masses of material.[12] Speckle observations from 1999 show a complex structure to this dust envelope, including partial arcs and unfinished shells. This clumpiness may be caused by a magnetic cycle in the star that is comparable to the solar cycle in the Sun and results in periodic increases in mass loss.[13]

Various chemical elements and about 50 molecules have been detected in the outflows from CW Leonis, among others nitrogen, oxygen and water, silicon and iron. One theory was that the star was once surrounded by comets which melted once the star started expanding,[14] but water is now thought to form naturally in the atmospheres of all carbon stars.[15]

Distance

If the distance to this star is assumed to be at the lower end of the estimate range, 120 pc, then the astrosphere surrounding the star spans a radius of about 84,000 AU. The star and its surrounding envelope are advancing at a velocity of more than 91 km/s through the surrounding interstellar medium.[12] It is moving with a space velocity of [U, V, W] = [21.6 ± 3.9, 12.6 ± 3.5, 1.8 ± 3.3] km s−1.[10]

Companion

Several papers have suggested that CW Leonis has a close binary companion. ALMA and astrometric measurements may show orbital motion. The astrometric measurements, combined with a model including the companion, provide a parallax measurement showing that CW Leonis is the closest carbon star to the Earth.[5]

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See also

References
  1. Cutri, R. M.; et al. (2003). "2MASS All-Sky Catalog of Point Sources". VizieR On-line Data Catalog: II/246. Originally Published in: 2003yCat.2246....0C. 2246. Bibcode:2003yCat.2246....0C.
  2. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  3. Cohen, M. (1979). "Circumstellar envelopes and the evolution of carbon stars". Monthly Notices of the Royal Astronomical Society. 186 (4): 837–852. Bibcode:1979MNRAS.186..837C. doi:10.1093/mnras/186.4.837.
  4. Matthews, L. D.; Gérard, E.; Le Bertre, T. (2015). "Discovery of a shell of neutral atomic hydrogen surrounding the carbon star IRC+10216". Monthly Notices of the Royal Astronomical Society. 449 (1): 220–233. arXiv:1502.02050. Bibcode:2015MNRAS.449..220M. doi:10.1093/mnras/stv263.
  5. Sozzetti, A.; Smart, R. L.; Drimmel, R.; Giacobbe, P.; Lattanzi, M. G. (2017). "Evidence for orbital motion of CW Leonis from ground-based astrometry". Monthly Notices of the Royal Astronomical Society: Letters. 471 (1): L1–L5. arXiv:1706.04391. Bibcode:2017MNRAS.471L...1S. doi:10.1093/mnrasl/slx082.
  6. A bot will complete this citation soon. Click here to jump the queue arXiv:1606.01878.
  7. Bergeat, J.; Knapik, A.; Rutily, B. (2001). "The effective temperatures of carbon-rich stars". Astronomy and Astrophysics. 369: 178–209. Bibcode:2001A&A...369..178B. doi:10.1051/0004-6361:20010106.
  8. "V* CW Leo -- Variable Star of Mira Cet type". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2011-05-09.
  9. Becklin, E. E.; et al. (December 1969). "The Unusual Infrared Object IRC+10216" (PDF). Astrophysical Journal. 158: L133. Bibcode:1969ApJ...158L.133B. doi:10.1086/180450.
  10. Ladjal, D.; et al. (July 2010). "Herschel PACS and SPIRE imaging of CW Leonis". Astronomy and Astrophysics. 518: L141. arXiv:1005.1433. Bibcode:2010A&A...518L.141L. doi:10.1051/0004-6361/201014658.
  11. De Beck, E.; et al. (January 10, 2012), "On the physical structure of IRC+10216", Astronomy & Astrophysics, 539: A108, arXiv:1201.1850, Bibcode:2012A&A...539A.108D, doi:10.1051/0004-6361/201117635
  12. Sahai, Raghvendra; Chronopoulos, Christopher K. (March 2010). "The Astrosphere of the Asymptotic Giant Branch Star IRC+10216". The Astrophysical Journal Letters. 711 (2): L53–L56. arXiv:1001.4997. Bibcode:2010ApJ...711L..53S. doi:10.1088/2041-8205/711/2/L53.
  13. Dinh-V-Trung, Jeremy; Lim (May 2008), "Molecular Shells in IRC+10216: Evidence for Nonisotropic and Episodic Mass-Loss Enhancement", The Astrophysical Journal, 678 (1): 303–308, arXiv:0712.1714, Bibcode:2008ApJ...678..303D, doi:10.1086/527669
  14. Ford, K. E. Saavik; Neufeld, David A.; Goldsmith, Paul F.; Melnick, Gary J. (2003). "Detection of OH toward the Extreme Carbon Star IRC +10216". The Astrophysical Journal. 589 (1): 430–438. arXiv:astro-ph/0302103. Bibcode:2003ApJ...589..430F. doi:10.1086/374552.
  15. Lombaert, R.; Decin, L.; Royer, P.; De Koter, A.; Cox, N. L. J.; González-Alfonso, E.; Neufeld, D.; De Ridder, J.; Agúndez, M.; Blommaert, J. A. D. L.; Khouri, T.; Groenewegen, M. A. T.; Kerschbaum, F.; Cernicharo, J.; Vandenbussche, B.; Waelkens, C. (2016). "Constraints on the H2O formation mechanism in the wind of carbon-rich AGB stars". Astronomy & Astrophysics. 588: A124. arXiv:1601.07017. Bibcode:2016A&A...588A.124L. doi:10.1051/0004-6361/201527049.
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