Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles - I. Theoretical model – Mass-loss history unravelled in VY CMa

Context. Mass loss plays a dominant role in the evolution of low mass stars while they are on the Asymptotic Giant Branch (AGB). The gas and dust ejected during this phase are a major source in the mass budget of the interstellar medium. Recent studies have pointed towards the importance of variations in the mass-loss history of such objects. Aims. By modelling the full line profile of low excitation CO lines emitted in the circumstellar envelope, we can study the mass-loss history of AGB stars. Methods. We have developed a non-LTE radiative transfer code, which calculates the velocity structure and gas kinetic temperature of the envelope in a self-consistent way. The resulting structure of the envelope provides the input for the molecular line radiative calculations which are evaluated in the comoving frame. The code allows for the implementation of modulations in the mass-loss rate. This code has been benchmarked against other radiative transfer codes and is shown to perform well and efficiently. Results. We illustrate the effects of varying mass-loss rates in case of a superwind phase. The model is applied to the well-studied case of VY CMa. We show that both the observed integrated line strengths as the spectral structure present in the observed line profiles,

[1]  S. Kwok.  Radiation pressure on grains as a mechanism for mass loss in red giants. , 1975 .

[2]  B. Rodgers,et al.  The temperature of the circumstellar envelope of Alpha Orionis , 1991 .

[3]  A. Zijlstra,et al.  Asymptotic giant branch superwind speed at low metallicity , 2004 .

[4]  G. Herbig.  VY CANIS MAJORIS. III. POLARIZATION AND STRUCTURE OF THE NEBULOSITY. , 1972 .

[5]  T. Millar,et al.  Chemical modelling of molecular sources – VI. Carbon-bearing molecules in oxygen-rich circumstellar envelopes , 1988 .

[6]  M. Reid,et al.  The stellar velocity of long-period variables. , 1976 .

[7]  C. McKee,et al.  Far-infrared rotational emission by carbon monoxide , 1982 .

[8]  A. Zijlstra,et al.  The superwind mass-loss rate of the metal-poor carbon star LI-LMC 1813 in the LMC cluster KMHK 1603 , 2003, astro-ph/0302083.

[9]  A. Tielens,et al.  Theoretical studies of the infrared emission from circumstellar dust shells: the infrared characteristics of circumstellar silicates and the mass-loss rate of oxygen-rich late-type giants. , 1989, The Astrophysical journal.

[10]  A. Zijlstra,et al.  The AGB superwind speed at low metallicity , 2004, astro-ph/0410120.

[11]  A. Tielens,et al.  Modeling of the Dust and Gas Outflows from OH 26.5+0.6: The Superwind , 1996 .

[12]  A. Tielens,et al.  Molecular rotational line profiles from oxygen-rich red giant winds , 1994 .

[13]  P. J. Huggins,et al.  The photoproduction of circumstellar OH maser shells , 1982 .

[14]  C. Townes,et al.  Characteristics of dust shells around 13 late-type stars. , 1994 .

[15]  G. Diercksen,et al.  Rate constants for rotational transitions of CO scattered by para-hydrogen , 1985 .

[16]  D. Muhleman,et al.  Very long baseline interferometric observations of the hydroxyl masers in VY Canis Majoris , 1978 .

[17]  H. M. Lee,et al.  Optical properties of interstellar graphite and silicate grains , 1984 .

[18]  J. Castor.  Spectral line formation in Wolf-Rayet envelopes. , 1970 .

[19]  D. Goorvitch,et al.  Calculation of (12)C(16)O and (13)C(16)O X(1)Sigma(+) rovibrational intensities for v less than or equal to 20 and J less than or equal to 150 , 1994 .

[20]  N. Grevesse,et al.  Abundances of the elements: Meteoritic and solar , 1989 .

[21]  S. Green,et al.  Collisional Excitation of H 2O by H 2 Molecules , 1996 .

[22]  A Goldman,et al.  The HITRAN database: 1986 edition. , 1987, Applied optics.

[23]  D. Hollenbach,et al.  Molecule formation and infrared emission in fast interstellar shocks. I Physical processes , 1979 .

[24]  V. Icke,et al.  UvA-DARE ( Digital Academic Repository ) Origin of quasi-periodic shells in dust forming AGB winds , 2022 .

[25]  D. G. Hummer,et al.  Solution of the comoving-frame equation of transfer in spherically symmetric flows. I. Computational method for equivalent-two-level-atom source functions. , 1975 .

[26]  A. D. McLean,et al.  Improved collisional excitation rates for interstellar water. , 1993, The Astrophysical journal. Supplement series.

[27]  M. Morris.  Molecular emission from expanding envelopes around evolved stars. III - Thermal and maser CO emission , 1980 .

[28]  S. Gaposchkin,et al.  Moving Envelopes of Stars , 1960 .

[29]  M. Juvela,et al.  Numerical methods for non-LTE line radiative transfer: Performance and convergence characteristics , 2002, astro-ph/0208503.

[30]  R. Liseau,et al.  The ISO-LWS map of the Serpens cloud core. II. The line spectra , 2002, astro-ph/0202092.

[31]  N. Epchtein,et al.  Mass-loss from dusty, low outflow-velocity AGB stars - I. Wind structure and mass-loss rates , 2003 .

[32]  G. Knapp,et al.  Mass loss from evolved stars. III: Mass loss rates for fifty stars from CO J=1−0 observations , 1985 .

[33]  P. J. Huggins,et al.  Detection of CO emission at 1.3 millimeters from the Betelgeuse circumstellar shell. , 1980 .

[34]  M. Rowan-Robinson,et al.  Radiative transfer in axisymmetric dust clouds , 1990, Monthly Notices of the Royal Astronomical Society.

[35]  P. Bowers,et al.  Circumstellar envelope structure of late-type stars , 1983 .

[36]  N. Scoville,et al.  OH-IR stars. I. Physical properties of circumstellar envelopes , 1976 .

[37]  P. Bowers,et al.  Expanding molecular envelopes around evolved stars. , 1977 .

[38]  Harm Jan Habing,et al.  Asymptotic giant branch stars , 2004 .

[39]  Alexander G. G. M. Tielens,et al.  Photodissociation Regions in the Interstellar Medium of Galaxies , 1999 .

[40]  D. Hollenbach,et al.  The gas-grain interaction in the interstellar medium - Thermal accommodation and trapping , 1983 .

[41]  H. M. Dyck,et al.  Carbon Monoxide Emission from Stars in the IRAS and Revised AFGL Catalogs. I. Mass Loss Driven by Radiation Pressure on Dust Grains , 1986 .

[42]  D. Hollenbach,et al.  Molecule Formation and Infrared Emission in Fast Interstellar Shocks. III. Results for J Shocks in Molecular Clouds , 1989 .

[43]  K. Leuven,et al.  Mass loss and rotational CO emission from Asymptotic Giant Branch stars , 2003, astro-ph/0305207.

[44]  I. Iben,et al.  Asymptotic Giant Branch Evolution and Beyond , 1983 .

[45]  M. Harwit,et al.  The Infrared Continuum Spectrum of VY Canis Majoris , 2001, astro-ph/0109148.

[46]  R. Shah,et al.  Discovery of Multiple Molecular Shells in the Outer Envelope of IRC +10216 , 2004 .

[47]  A. Tielens,et al.  Mass loss from OH/IR stars - Models for the infrared emission of circumstellar dust shells , 1992 .

[48]  C P.,et al.  THE LAST GASPS OF VY CANIS MAJORIS : APERTURE SYNTHESIS AND ADAPTIVE OPTICS IMAGERY , 1999 .

[49]  D. Buhl,et al.  Detection of new stellar sources of vibrationally excited silicon monoxide maser emission at 6.95 millimeters , 1975 .

[50]  H. Olofsson,et al.  Probing the Mass Loss Rate History of Carbon Stars Using CO Line and Dust Continuum Emission , 2002, astro-ph/0206078.

[51]  G. Knapp,et al.  Mass Loss from Evolved Stars. VII. OH Maser Shell Radii and Mass-Loss Rates for OH/IR Stars , 1987 .

[52]  A. Tielens.  Stationary flows in the circumstellar envelopes of M giants , 1983 .

[53]  P. J. Huggins,et al.  Mass loss from evolved stars. I. Observations of 17 stars in the CO(2-1) line. , 1982 .

[54]  G. J. Matthews,et al.  Asymptotic-giant-branch stars , 1992, Nature.

[55]  K. M. Merrill,et al.  Studies of the infrared source CRL 2688 , 1975 .

[56]  K. Nordsieck,et al.  The Size distribution of interstellar grains , 1977 .

[57]  On the origin of the grain-size spectrum of interstellar dust , 1980 .

[58]  J. Holtzman,et al.  Imaging of the Egg Nebula (CRL 2688) with WFPC2/HST: A History of AGB/Post-AGB Giant Branch Mass Loss , 1998 .

[59]  P. Goldsmith,et al.  Molecular cooling and thermal balance of dense interstellar clouds , 1978 .

[60]  M. Lindqvist,et al.  Properties of detached shells around carbon stars Evidence of interacting winds , 2005, astro-ph/0503245.

[61]  P. J. Huggins,et al.  The photodissociation of CO in circumstellar envelopes , 1988 .

[62]  A. Tielens,et al.  THE PHOTOELECTRIC HEATING MECHANISM FOR VERY SMALL GRAPHITIC GRAINS AND POLYCYCLIC AROMATIC HYDROCARBONS , 1994 .

[63]  Robert D. Gehrz,et al.  The Asymmetric Nebula Surrounding the Extreme Red Supergiant Vy Canis Majoris , 2001 .

[64]  A. Tielens,et al.  Photodissociation regions. I - Basic model. II - A model for the Orion photodissociation region , 1985 .

[65]  Bernd Freytag,et al.  Spots on the surface of Betelgeuse -- Results from new 3D stellar convection models , 2002 .

[66]  N. Soker.  A Solar-like Cycle in Asymptotic Giant Branch Stars , 2000, astro-ph/0001281.