Luminosities and mass-loss rates of carbon stars in the Magellanic Clouds

Dust radiative transfer models are presented for 60 carbon stars in the Magellanic Clouds (MCs) for which 5‐35 µm Spitzer infrared spectrograph (IRS) spectra and quasi-simultaneous ground-based JHKL photometry are available. From the modelling, the luminosity and massloss rate are derived (under the assumption of a fixed expansion velocity and dust-to-gas ratio), and the ratio of silicon carbide (SiC) to amorphous carbon (AMC) dust is also derived. This ratio is smaller than observed in Galactic carbon stars, as has been noted before. Light curves for 36 objects can be retrieved from the massive compact halo object (MACHO) and optical gravitational lensing experiment (OGLE) data bases, and periods can be derived for all but two of these. Including data from the literature, periods are available for 53 stars. There is significant scatter in a diagram where the mass-loss rates are plotted against luminosity, and this is partly due to the fact that the luminosities are derived from single-epoch data. The mass-loss rates for the MC objects roughly scatter around the mean relation for Galactic C-stars. The situation is better defined when the mass-loss rate is plotted against pulsation period. For a given period, most of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) stars have mass-loss rates that are in agreement with that observed in Galactic carbon stars (under the assumption that these objects have an expansion velocity and dust-to-gas ratio typical of the mean observed in Galactic carbon Miras). For some SMC sources only, the IRS spectrum at longer wavelengths falls clearly below the model flux predicted by a constant mass-loss rate. An alternative model with a substantial increase of the mass-loss rate to its present-day value over a time-scale of a few tens of years is able to explain the spectral energy distribution (SED) and IRS spectra of these sources. However, the probability to have two such cases in a sample of 60 is small, and makes this not a likely explanation (and testable by re-observing these objects near the end of the lifetime of Spitzer). Alternative explanations are (ad hoc) changes to the dust emissivity at longer wavelengths, and/or deviations from spherical symmetry.

[1]  W. L. Ngai.  MSc Thesis , 2015 .

[2]  A. Frank,et al.  A Spitzer Space Telescope Infrared Spectrograph Spectral Atlas of Luminous 8 μm Sources in the Large Magellanic Cloud , 2006 .

[3]  Air Force Research Laboratory,et al.  A Spitzer IRS Spectral Atlas of Luminous 8 micron Sources in the Large Magellanic Cloud , 2006, astro-ph/0606756.

[4]  L.B.F.M. Waters,et al.  Spitzer observations of acetylene bands in carbon-rich AGB stars in the Large Magellanic Cloud , 2006 .

[5]  M. Egan,et al.  Mid-Infrared Spectroscopy of Carbon Stars in the Small Magellanic Cloud , 2006, astro-ph/0603607.

[6]  M. Feast,et al.  Near‐infrared photometry of carbon stars★ , 2006, astro-ph/0603504.

[7]  P. J. Huggins,et al.  Imaging the circumstellar envelopes of AGB stars , 2006 .

[8]  J. Blommaert,et al.  A Spitzer mid-infrared spectral survey of mass-losing carbon stars in the Large Magellanic Cloud , 2006, astro-ph/0602531.

[9]  M. Groenewegen.  The mid- and far-infrared colours of AGB and post-AGB stars , 2005, astro-ph/0511475.

[10]  I. Yamamura,et al.  Very Large Telescope three micron spectra of dust-enshrouded red giants in the Large Magellanic Cloud , 2005, astro-ph/0510510.

[11]  M. Groenewegen.  Eclipsing binaries in the Galactic bulge: candidates for distance estimates , 2005, astro-ph/0505109.

[12]  A. Zijlstra,et al.  An Empirical formula for the mass-loss rates of dust-enshrouded red supergiants and oxygen-rich asymptotic giant branch stars , 2005, astro-ph/0504379.

[13]  M. Cioni,et al.  Pulsation properties of C stars in the Small Magellanic Cloud , 2005, astro-ph/0503561.

[14]  I. Yamamura,et al.  Three-micron spectra of AGB stars and supergiants in nearby galaxies , 2005, astro-ph/0501247.

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

[16]  M. Sauvage,et al.  ISOCAM Observations of Globular Clusters in the Magellanic Clouds: The Data , 2004 .

[17]  E. Wright,et al.  The Spitzer Space Telescope Mission , 2004, astro-ph/0406223.

[18]  J. R. Houck,et al.  The Infrared Spectrograph (IRS) on the Spitzer Space Telescope , 2004, astro-ph/0406167.

[19]  M. Groenewegen.  Long Period Variables in the Magellanic Clouds: OGLE +2 MASS + DENIS , , 2004, astro-ph/0404561.

[20]  Steven D. Kawaler,et al.  Long Secondary Periods in Pulsating Asymptotic Giant Branch Stars: An Investigation of Their Origin , 2004 .

[21]  J. Bouwman,et al.  MgS in detached shells around carbon stars ⋆ Mining the mass-loss history , 2003, astro-ph/0309777.

[22]  P. Wood,et al.  On the Origin of Long Secondary Periods in Semiregular Variables , 2003 .

[23]  M. Feast,et al.  Obscured asymptotic giant branch variables in the Large Magellanic Cloud and the period–luminosity relation , 2003, astro-ph/0302246.

[24]  M.-R.L. CioniH.J. Habing,et al.  AGB stars in the Magellanic Clouds I: The C/M ratio , 2003, astro-ph/0302051.

[25]  M. Cioni,et al.  AGB stars in the Magellanic Clouds , 2003 .

[26]  P. Marigo.  Asymptotic Giant Branch evolution at varying surface C/O ratio: effects of changes in molecular opacities , 2002, astro-ph/0203036.

[27]  Stephan D. Price,et al.  MSX, 2MASS, and the Large Magellanic Cloud: A Combined Near- and Mid-Infrared View , 2001, astro-ph/0107220.

[28]  U. Jørgensen,et al.  Spectra of carbon-rich asymptotic giant branch stars between 0.5 and 2.5 $\mu$m: Theory meets observation , 2001 .

[29]  J. Loon.  Circumstellar masers in the Magellanic Clouds , 2001, 1210.0983.

[30]  T. Tanabé,et al.  The variability of Magellanic cluster infrared stars , 2000 .

[31]  C. Surace,et al.  The Universe as Seen by ISO , 1999 .

[32]  A. Zijlstra,et al.  Obscured AGB stars in the Magellanic clouds. I. IRAS Candidates , 1997 .

[33]  M. Groenewegen,et al.  Dust Shells Around Carbon Mira Variables , 1997 .

[34]  C. Loup,et al.  Obscured AGB stars in the Magellanic Clouds , 1997 .

[35]  M. Groenewegen,et al.  A revised period-luminosity relation for carbon Miras , 1996 .

[36]  M. J. Lehner,et al.  The MACHO Project LMC Microlensing Results from the First Two Years and the Nature of the Galactic Dark Halo , 1996 .

[37]  Amsterdam,et al.  Obscured asymptotic giant branch stars in the Magellanic clouds. III New IRAS counterparts , 1996, astro-ph/9709119.

[38]  P. Shaver.  Science with Large Millimetre Arrays , 1996 .

[39]  P. Mcgregor.  THE MSSSO NEAR-INFRARED PHOTOMETRIC SYSTEM , 1994 .

[40]  M. Downing,et al.  CASPIR: A cryogenic array spectrometer imager for the MSSSO 2.3 m telescope , 1994 .

[41]  J. Whiteoak,et al.  OH/IR Stars in the Magellanic Clouds , 1992 .

[42]  N. Reid.  Cocoon stars in the Large Magellanic Cloud , 1991 .

[43]  Peter G. Martin,et al.  Shape and clustering effects on the optical properties of amorphous carbon , 1991 .

[44]  P. Wood,et al.  Long-period variables in the Large Magellanic Cloud. II. Infrared photometry, spectral classification, AGB evolution, and spatial distribution , 1990 .

[45]  M. Feast,et al.  A period–luminosity–colour relation for Mira variables , 1989 .

[46]  M. Feast,et al.  Dust shell objects in the SMC , 1989 .

[47]  Ian S. McLean,et al.  Infrared Astronomy with Arrays , 1987 .

[48]  I. Glass,et al.  A survey for red varibles in the LMC – II , 1985 .

[49]  S. H. Moseley,et al.  Laboratory infrared spectra of predicted condensates in carbon-rich stars , 1985 .

[50]  S. H. Moseley,et al.  MgS grain component in circumstellar shells , 1985 .

[51]  M. Bessell,et al.  Long-period variables in the Magellanic Clouds: Supergiants, AGB stars, supernova precursors, planetary nebula precursors, and enrichment of the interstellar medium , 1983 .

[52]  R. Stellingwerf.  Period determination using phase dispersion minimization , 1978 .