CW Leonis

CW Leonis or IRC +10216 is a variable 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.[10]

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) 14.5 (var.)[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[4]
Astrometry
Proper motion (μ) RA: 35±1 mas/yr
Dec.: 12±1[5] mas/yr
Parallax (π)10.56 ± 2.02 mas[6]
Distanceapprox. 310 ly
(approx. 90 pc)
Details
Mass0.7 - 0.9[5] M☉
Radius560[7] R☉
Luminosity8,500 (average), 11,850 (maximum)[7] L☉
Temperature2,300[7] (1,915 - 2,105)[8] 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[9]
Database references
SIMBADdata

Properties
A LINEAR (white-light) light curve for CW Leonis, adapted from Palaversa et al. (2013)[11]

CW Leonis is believed to be in a late stage of its life, blowing off its own sooty atmosphere to form a white dwarf. 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.[12] 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☉.[13] The brightness of the star varies by about two magnitudes over its pulsation period, and may have been increasing over a period of years. One study finds an increase in the mean brightness of about a magnitude between 2004 and 2014.[14] Many studies of this star are done at infrared wavelengths because of its very red colour; published visual magnitudes are uncommon and often dramatically different. The Guide Star Catalog from 2006 gives an apparent visual magnitude]] of 19.23.[15] The ASAS-SN variable star catalog based on observations from 2014 to 2018 reports a mean magnitude of 17.56 and an amplitude of 0.68 magnitudes.[16] An even later study gives a mean magnitude of 14.5 and an amplitude of 2.0 magnitudes.[2]

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.[13] The extended envelope contains at least 1.4 solar masses of material.[17] 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.[18]

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,[19] but water is now thought to form naturally in the atmospheres of all carbon stars.[20]

Distance
CW Leonis glows from deep within a thick shroud of dust in this image from the NASA/ESA Hubble Space Telescope.

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.[17] 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.[12]

Companion

Several papers have suggested that CW Leonis has a close binary companion.[14] 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.[6]

See also

References
  1. Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E.; Fowler, John W.; Gizis, John E.; Howard, Elizabeth V.; Huchra, John P.; Jarrett, Thomas H.; Kopan, Eugene L.; Kirkpatrick, J. Davy; Light, Robert M.; Marsh, Kenneth A.; McCallon, Howard L.; Schneider, Stephen E.; Stiening, Rae; Sykes, Matthew J.; Weinberg, Martin D.; Wheaton, William A.; Wheelock, Sherry L.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues. 2246: II/246. Bibcode:2003yCat.2246....0C.
  2. Gigoyan, K. S.; Kostandyan, G. R.; Gigoyan, K. K.; Sarkissian, A.; Meftah, M.; Russeil, D.; Zamkotsian, F.; Rahmatullaeva, F. D.; Paronyan, G. (2021). "Investigations of the Periodic Variables in the Catalina and Linear Databases". Astrophysics. 64 (1): 20. Bibcode:2021Ap.....64...20G. doi:10.1007/s10511-021-09664-5. S2CID 254251265.
  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. 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.
  5. 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. S2CID 96460867.
  6. 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. S2CID 119070871.
  7. Schmidt, M. R.; He, J. H.; Szczerba, R.; Bujarrabal, V.; Alcolea, J.; Cernicharo, J.; Decin, L.; Justtanont, K.; Teyssier, D.; Menten, K. M.; Neufeld, D. A.; Olofsson, H.; Planesas, P.; Marston, A. P.; Sobolev, A. M.; De Koter, A.; Schöier, F. L. (2016). "Herschel/HIFI observations of the circumstellar ammonia lines in IRC+10216". Astronomy & Astrophysics. 592: A131. arXiv:1606.01878. Bibcode:2016A&A...592A.131S. doi:10.1051/0004-6361/201527290. PMC 5217166. PMID 28065983.
  8. 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.
  9. "V* CW Leo -- Variable Star of Mira Cet type". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2011-05-09.
  10. 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.
  11. Palaversa, Lovro; Ivezić, Željko; Eyer, Laurent; Ruždjak, Domagoj; Sudar, Davor; Galin, Mario; Kroflin, Andrea; Mesarić, Martina; Munk, Petra; Vrbanec, Dijana; Božić, Hrvoje; Loebman, Sarah; Sesar, Branimir; Rimoldini, Lorenzo; Hunt-Walker, Nicholas; VanderPlas, Jacob; Westman, David; Stuart, J. Scott; Becker, Andrew C.; Srdoč, Gregor; Wozniak, Przemyslaw; Oluseyi, Hakeem (October 2013). "Exploring the Variable Sky with LINEAR. III. Classification of Periodic Light Curves". The Astronomical Journal. 146 (4): 101. arXiv:1308.0357. Bibcode:2013AJ....146..101P. doi:10.1088/0004-6256/146/4/101. hdl:1721.1/92739. S2CID 31317836.
  12. 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. S2CID 14279789.
  13. 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. S2CID 56163906.
  14. Kim, Hyosun; Lee, Ho-Gyu; Mauron, Nicolas; Chu, You-Hua (2015). "HST Images Reveal Dramatic Changes in the Core of IRC+10216". The Astrophysical Journal. 804 (1): L10. arXiv:1412.0083. Bibcode:2015ApJ...804L..10K. doi:10.1088/2041-8205/804/1/L10. S2CID 118558287.
  15. Lasker, Barry M.; et al. (August 2008). "The Second-Generation Guide Star Catalog: Description and Properties". The Astronomical Journal. 136 (2): 735–766. arXiv:0807.2522. Bibcode:2008AJ....136..735L. doi:10.1088/0004-6256/136/2/735. S2CID 17641056.
  16. Jayasinghe, T.; Kochanek, C. S.; Stanek, K. Z.; Shappee, B. J.; Holoien, T. W. -S.; Thompson, Todd A.; Prieto, J. L.; Dong, Subo; Pawlak, M.; Shields, J. V.; Pojmanski, G.; Otero, S.; Britt, C. A.; Will, D. (2018). "The ASAS-SN catalogue of variable stars I: The Serendipitous Survey". Monthly Notices of the Royal Astronomical Society. 477 (3): 3145. arXiv:1803.01001. Bibcode:2018MNRAS.477.3145J. doi:10.1093/mnras/sty838.
  17. 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. S2CID 118705396.
  18. 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. S2CID 16389370.
  19. 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. S2CID 16682238.
  20. 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. S2CID 62787287.
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