V Cyg

Caution!! Although I am happy to share my research notes below with all visitors to my webpages, these pages are mainly designed for my own use and subject to change without warning. I do not guarantee the correctness of all contents as well.

V Cyg -- a carbon rich Mira star (== IRAS 20396+4757, IRC +50338, AFGL 2632, SAO 49940) ( SIMBAD entry )

Period = 421.27 day, V-band maximum @ JD2440680 +-0.03 (Mira type variable, see Barnes & Barnes, 1971IBVS..513....1B)
Spectral type = N
Distance1 = 183 ~ 520 pc (with parallax = 3.69+-1.77 mas in Simbad)
Distance2 = 430 +-60 pc (with P-Lbol and P-MK relation, see Bieging & Wilson, 2001AJ....122..979B)
Proper motion = -6.43 -12.62 mas/yr (from Simbda)
Luminosity = 6200 Lsun (from P-Lbol relation, see Bieging & Wilson, 2001AJ....122..979B)
Mass =
Mass loss rate = 1.2 x 10^-6 Msun/yr (from CO 2-1 line modeling for dist = 370pc, see Schoier & Olofsson, 2000A&A...359..586S)
Vexp = 11.8 +-0.6 km/s (from CO 2-1 line, see Knapp et al., 1998ApJS..117..209K)
Vlsr = 14.0 +-0.5 km/s (from CO 2-1 line, see Knapp et al., 1998ApJS..117..209K)
R* =

• (from Bujarrabal & Alcolea, 1991A&A...251..536B)
  Facts: They mapped CO and SiO lines toward 10 evolved stars, including V Cyg. They found that the CSE is nearly circular in almost all stars except V Cyg (elongated). The maxima of the CO and 13CO maps is offset to the south of the stellar position.
  Opinions:  no.
  (figs: the CO and SiO spectra of V Cyg. Note: (1) the center is offset to the south of the origin (the stellar position); (2) the small narrow feature around -2 km/s could be interstellar cloud emission.)
  
• (from Lazaro et al., 1994MNRAS.269..365L)
  Facts: They observed NIR spectra of 15 bright and cool C-stars, including V Cyg.
  Opinions:  no.
  (figs: the NIR spectrum of V Cyg)
  
• (from Bieging et al., 2000ApJ...543..897B)
  Facts: They used HHT to observe SiO and HCN line toward 30 AGB stars of M,S,C types.The two molecules are detected in almost all stars, regardless of their types. V Cyg is included in this sample.
  Opinions: They conclude that
       (1) the HCN line ratios suggest that it is produced by non-LTE chemistry (e.g., shock chemistry) in M stars;
       (2) HCN/SiO line ratio with similar excitation energies clearly separate C-stars from M or S stars, and the ratio increases with mass loss rate of M and S stars.
  (figs: the spectra of V Cyg: left -- SiO 5-4; left middel -- SiO 8-7; middel right -- HCN 3-2 (the small feature could be maser; right -- HCN 4-3 (the small feature could be maser))
  
• (from Bieging, 2001ApJ...549L.125B)
  Facts: They find evidence of HCN (01^{1c}0) J=3-2,4-3 millimeter maser line in 5 carbon stars (HHT observations): R Scl, V384 Per, R Lep, Y CVn, and V Cyg. Variability is also recognized for R Scl.
  Opinions: They conclude that (1) more than HCN masers may present in more than half of C stars; (2) the masers occur in inner CSE around the star.
  (fig: HCN lines of V Cyg.)
  
• (from Schoier & Olofsson, 2000A&A...359..586S)
  Facts: They observed 13CO 2-1 of 20 cool carbon stars, including V Cyg.
  Opinions: They determined quantities by radiative transfer calculation: for V Cyg, 12CO/13CO = 20, Tau(CO 2-1) = 1.1, Mlr = 1.2x10^-6 Msun/yr, T* = 1500K, L* = 6200 Lsun, for a distance of 370 pc.
• (from Bieging & Wilson, 2001AJ....122..979B)
  Facts: They used OVRO to map V Cyg with a high resolution of 1.2". They combined the interferometry data with an IRAM 30m single dish map to produce high fidelity channel maps. A clumpy and non-circular expanding envelope is found. The radial distribution of CO 2-1 brightness temperature follows Tb(r) = 21.2 exp(r/3.14") K quite well. A strong narrow peak is found around 22 km/s in the line profile towards the map center, which is difficult to interpret. There is interstellar cloud which shows up as a narrow peak near -2 km/s in the integrated CO spectrum. They constructed a model to interpret the CO map:
      (1) [CO/H2] = (9x10^-4) exp(-(r/r_ph)^2), (r_ph is the CO photodissociation radius given by the model of Mamon et al., 1988)
      (2) Tk(r) = Tk0 * (r/r0)^p, p = -0.8 when r < r_b and p is a free parameter when r > r_b; and r_b is also a free parameter; r0 is a free parameter. (emperically assumed)
      (3) Mass loss rate is constant with time and is a free parameter in model fitting. (later, it is assumed to be decreasing with time: better fit)
      (4) Vexp = 11.3 km/s is constant.
      (5) Vlsr = +13.8 km/s.
  The free parameters are: r_ph, r0, p, r_b, Mlr.
  Opinions: (1) the outer CO envelope of V Cyg is not very opticallly thick, thus CO levels are not completely thermalized, so that the observed line intensity by single dishes is not very sensitive to the gas temperature, but sensitive to the gas density (opacity). With thisin mind, they find that the mass loss rate of V Cyg must be decreasing with time to achieve a better fit of both IRAM 30m spectrum (14" beam) and the OVRO map center spectrum (1.2" beam). Their good fit model has the free parameters as:
         r_ph = 1.2x10^17 cm,
         Tk0 = 23K,
         r_b = 6x10^15 cm,
         p = 0 for r>r_b,
         Mlr = 6x10^-7 Msun/yr (for r < r_b) and 1.6x10^-6 Msun/yr (for r > r_b).
  (2) In their model, they find that the CO levels are thermalized up to R = 10^16 cm, byond which Tex < Tk.
  (figs: left -- CO2-1 channel maps; left middle -- CO 2-1 integrated map; middle right -- annularly averaged CO intensity ~ r relation; right -- CO 2-1 line profile at the center pixel (upper) and integrated over the whole map.)
  
• (from Menzies et al., 2006MNRAS.369..783M)
  Facts: They measured optical radial velocity for 38 C-type Mira stars. They give the results for V Cyg: P = 417 days, distance = 440 pc.