An analysis of optical and infrared spectra of the peculiar carbon-rich giant TU Gem
|1Polinovsky, GO, 1Yakovina, LA, 1Pavlenko, YV |
1Main Astronomical Observatory of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
|Kinemat. fiz. nebesnyh tel (Online) 2014, 30(4):38-57|
|Start Page: Physics of Stars and Interstellar Medium|
TU Gem has been known as a peculiar carbon giant of galactic halo, but its belonging to the type of CH stars is still debated. We estimated the TU Gem atmospheric parameters through the simulation of the star’s spectrum and comparison of the simulation result with observations for two broad spectral ranges, namely, λ=400—720 nm and λ= 900 — 2440 nm. For the analysis we used the low-dispersion optical spectrum of TU Gem by Barnbaum et al. (1996) (R ~ 600) and the infrared spectrum by Tanaka et al. (2007) (R ~ 2600). The atmospheric models were calculated by the program SAM12 (Pavlenko, 2003). Because of the estimate ambiguity for metallicity ([Fe/H]) from our spectral data, only effective temperature of TU Gem, which weakly depends on the metallicity, is determined with confidence, namely, Tef = 3000 ± 100 K. The values of C/O, [C/Fe] and [N/Fe] were estimated for the ranges of –2.0 ≤ [Fe/H] ≤ 0.0 with the step Δ[Fe/H] = 0.5. Our evaluation [C/Fe] =0.63—0.67 at the value [Fe/H] = –1 is higher than the estimate [C/Fe] =0.21 at [Fe/H] = –1.1 by Kipper et al. (1996), and the abundance evaluations [N/Fe] =+1.0 at called metallicities coincide. This brings TU Gem closer to CH stars, but for more accurate conclusions a detailed analysis of the chemical composition of the TU Gem atmosphere is required.
|Keywords: atmosphere, CH stars, TU Gem|
1.E. A. Gurtovenko and R. I. Kostyk, “The system of solar oscillator strengths,” Preprint MAO-98-3E (Main Astronomical Observatory, National Academy of Sciences of Ukraine, Kyiv, 1998).
2.T. A. Kipper and M. A. Kipper, “Chemical composition of the carbon halo star V Ari,” Pis’ma Astron. Zh. 16, 1113–1117 (1990).
3.L. S. Lyubimkov, The Chemical Composition of Stars: Analysis Method and Results (NPF Astroprint, Odessa, 1995) [in Russian].
4.I. Eglitis, “Spectrophotometric studies of carbon stars,” Nauchn. Inf. 67, 54–62 (1989).
5.C. Barnbaum, “A high-resolution spectral atlas of carbon stars,” Astrophys. J., Suppl. Ser. 90, 317–432 (1994).
6.C. Barnbaum and K. H. Hinkle, “Infrared and optical velocities of carbon stars,” Astron. J. 110, 805–822 (1995).
7.C. Barnbaum, R. P. S. Stone, and P. C. Keenan, “A moderate-resolution spectral atlas of carbon stars: R, J, N, CH, and barium stars,” Astrophys. J., Suppl. Ser. 105, 419–473 (1996). http://archive.is/tFI87
8.J. H. Baumert, “Eight-color photometry of carbon stars,” PhD Thesis (Ohio State Univ., Columbus, 1972).
9.J. Bergeat and L. Chevallier, “The mass loss of C-rich giants,” Astron. Astrophys. 429, 235–246 (2005).
10.J. Bergeat, A. Knapic, and B. Rutily, “The effective temperatures of carbon-rich stars,” Astron. Astrophys. 369, 178–209 (2001).
11.P. F. Bernath, J. H. Black, and J. W. Brault, “The spectrum of magnesium hydride,” Astrophys. J. 298, 375–381 (1985).
12.J. A. Cardelli, G. C. Clayton, and J. S. Mathis, “The relationship between infrared, optical, and ultraviolet extinction,” Astrophys. J. 345, 245–256 (1989).
13.S. A. Clough, M. W. Shephard, E. J. Mlawer, et al., “Atmospheric radiative transfer modeling: a summary of the AER codes,” J. Quant. Spectrosc. Radiat. Transfer 91, 233–244 (2005).
14.C. Fabricius, E. Hog, V. V. Makarov, et al., “The Tycho double star catalogue,” Astron. Astrophys. 384, 180–189 (2002).
15.D. Goorvitch, “Infrared CO line list for the X 1Σ+ state,” Astrophys. J., Suppl. Ser. 95, 535–552 (1994).
16.C. E. Gow, “Spectrophotometry of cool carbon stars,” Publ. Astron. Soc. Pac. 89, 510–518 (1977).
17.D. F. Gray, The Observation and Analysis of Stellar Photospheres (Cambrige Univ. Press, New York, 2005).
18.U. G. Jorgensen and M. Larsson, “Molecular opacities of astrophysical interest: the A 2Π-X 2Σ+ system of CN,” Astron. Astrophys. 238, 424–434 (1990).
19.T. Kipper, “Chemical composition of a halo carbon star TT CVn,” Balt. Astron. 1, 181–189 (1992).
20.T. Kipper and U. G. Jorgensen, “Chemical composition of the metal-poor carbon star HD 187216,” Astron. Astrophys. 290, 148–158 (1994).
21.T. Kipper, U. G. Jorgensen, V. G. Klochkova, and V. E. Panchuk, “Chemical composition of metal-poor carbon stars in the halo,” Astron. Astrophys. 306, 489–500 (1996).
22.F. Kupka, N. Piskunov, T. A. Ryabchikova, et al., “VALD-2: progress of the Vienna Atomic Line Data Base,” Astron. Astrophys., Suppl. Ser. 138, 119–133 (1999).
23.R. L. Kurucz, CD-ROMs nos. 1–23. http://kurucz.harvard.edu/cdroms.html
24.D. L. Lambert, B. Gustafsson, K. Eriksson, and K. H. Hinkle, “The chemical composition of carbon stars. I. Carbon, nitrogen, and oxygen in 30 cool carbon stars in the Galactic disk,” Astrophys. J., Suppl. Ser. 62, 373–425 (1986).
25.D. L. Lambert, “Stellar photospheres and molecules — A view from the bridge,” Lect. Notes Phys. 428, 1–28 (1994).
26.J. J. Nassau and V. M. Blanco, “Carbon stars in two northern Milky Way zones,” Astrophys. J. 125, 195–209 (1957).
27.K. Ohnaka and T. Tsuji, “Quantitative analysis of carbon isotopic ratios in carbon stars. I. 62 N-type and 15 Sctype carbon stars,” Astron. Astrophys. 310, 933–951 (1996).
28.H. Olofsson, K. Eriksson, B. Gustafsson, and U. Carlstrom, “A study of circumstellar envelopes around bright carbon stars. I. Structure, kinematics and mass-loss rate,” Astrophys. J., Suppl. Ser. 87, 267–304 (1993).
29.Ya. V. Pavlenko, “Model atmospheres of red giants,” Astron. Rep. 47, 59–67 (2003).
30.Ya. V. Pavlenko and L. A. Yakovina, “Model atmospheres of carbon giants with high carbon abundance,” Kinematics Phys. Celestial Bodies 25, 302–308 (2009).
31.Ya. V. Pavlenko and H. R. A. Jones, “Carbon monoxide bands in M dwarfs,” Astron. Astrophys. 396, 967–975 (2002).
32.B. F. Peery, Jr., “Distances and luminosities of irregular variables of type N,” Astrophys. J. 199, 135–144 (1975).
33.F. Querci, M. Querci, and V. G. Kunde, “Opacity probability distribution functions for electronic systems of CN and C2 molecules including their stellar isotopic forms,” Astron. Astrophys. 15, 256–274 (1971).
34.F. Querci, M. Querci, and T. Tsuji, “Model atmospheres for C type stars,” Astron. Astrophys. 31, 265–282 (1974).
35.A. Richichi and T. Chandrasekhar, “Near-infrared observations of the carbon stars TU Geminorum and SS Virginis at milliarcsecond resolution,” Astron. Astrophys. 451, 1041–1044 (2006).
36.E. F. Schlafly and D. P. Finkbeiner, “Measuring reddening with Sloan Digital Sky Survey stellar spectra and recalibrating SFD,” Astrophys. J. 737, 103 (2011).
37.D. J. Schlegel, D. P. Finkbeiner, and M. Davis, “Maps of dust infrared emission for use in estimation of reddening and cosmic microwave background radiation foregrounds,” Astrophys. J. 500, 525–553 (1998).
38.V. I. Shenavrin, O. G. Taranova, and A. E. Nadzhip, “Search for and study of hot circumstellar dust envelopes,” Astron. Rep. 55, 31–81 (2011).
39.G. H. Smith, “The chemical inhomogenerity of globular clusters,” Publ. Astron. Soc. Pac. 99, 67–90 (1987).
40.M. Tanaka, A. Letip, Y. Nishimaki, et al., “Near-infrared spectra of 29 carbon stars: simple estimates of effective temperature,” Publ. Astron. Soc. Jpn. 59, 939–953 (2007).
41.T. Tsuji, “Molecular abundances in stellar atmospheres. II,” Astron. Astrophys. 23, 411–431 (1973).
42.T. Tsuji, “Intrinsic properties of carbon stars. I. Effective temperature scale of N-type carbon stars,” J. Astrophys. Astron. 2, 95–113 (1981).
43.A. Ulla, P. Thejll, T. Kipper, and U. G. Jorgensen, “Infrared observations of peculiar carbon stars,” Astron. Astrophys. 319, 244–249 (1997).
44.R. S. Urdahl, Y. Bao, and W. M. Jackson, “An experimental determination of the heat of formation of C2 and the C-H bond dissociation energy in C2H,” Chem. Phys. Lett. 178, 425–428 (1991).
45.A. D. Vanture, “The CH stars. II. Carbon, nitrogen and oxygen abundances,” Astron. J. 104, 1986–1996 (1992).
46.A. D. Vanture, “The CH stars. III. Heavy element abundances,” Astron. J. 104, 1997–2004 (1992).
47.Y. Yamashita, “A study of carbon star spectra based on the C-classification,” Publ. Dom. Astrophys. Obs. 13, 67–101 (1967).
48.M. Yuasa and W. Unno, “Distance determination of mass-losing stars,” Publ. Astron. Soc. Jpn. 51, 197–209 (1999).