CW Leonis orIRC +10216 is avariablecarbon star that is embedded in a thick dust envelope. It was first discovered in 1969 by a group of astronomers led byEric Becklin, based upon infrared observations made with the 62-inchCaltech Infrared Telescope atMount 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 theSolar System.[10]
ALINEAR (white-light)light curve for CW Leonis, adapted from Palaversaet al. (2013)[11]
CW Leonis is believed to be in a late stage of its life, blowing off its own sooty atmosphere to form awhite dwarf. Based upon isotope ratios ofmagnesium, the initial mass of this star has been constrained to lie between 3–5solar 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] Itsbolometric 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 atinfrared wavelengths because of its very red colour; published visual magnitudes are uncommon and often dramatically different. TheGuide Star Catalog from 2006 gives an apparent visual magnitude of 19.23.[15] TheASAS-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) × 10−5solar masses per year.[13] Theextended envelope contains at least 1.4solar masses of material.[17] Speckle observations from 1999 show a complex structure to thisdust envelope, including partial arcs and unfinished shells. This clumpiness may be caused by a magnetic cycle in the star that is comparable to thesolar cycle in the Sun and results in periodic increases in mass loss.[18]
Variouschemical elements and about 50molecules have been detected in the outflows from CW Leonis, among othersnitrogen,oxygen andwater,silicon, andiron. One theory was that the star was once surrounded by comets that melted once the star started expanding,[19] but water is now thought to form naturally in the atmospheres of all carbon stars.[20]
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 theastrosphere 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 surroundinginterstellar medium.[17] It is moving with aspace velocity of [U, V, W] = [21.6 ± 3.9,12.6 ± 3.5,1.8 ± 3.3] km s−1.[12]
Several papers have suggested that CW Leonis has a closebinary companion.[14]ALMA andastrometric 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 closestcarbon star to the Earth.[6]
^abcdefCutri, 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.
^abGigoyan, 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.S2CID254251265.
^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.
^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.S2CID62787287.
