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Odd Carbon Abundance Around Beta Pictoris

Beta Pictoris, an A5 dwarf star some 63 light years from the Earth, is well known to exoplanet hunters, some of whom have been studying its circumstellar dust disk since its discovery by the Infrared Astronomical Satellite (IRAS). That disk was first detected way back in 1983, and is thought to be perhaps 1100 AU wide and much more massive than the disk from which our own Solar System formed. The disk and possible planetary formation going on there has always been tantalizingly like our own system’s, but now we get a surprise.

For as a new paper in Nature suggests, this young system (between eight and twenty million years old) contains much more carbon gas than expected. This work comes courtesy of the Far Ultraviolet Spectroscopic Explorer satellite (FUSE), along with Hubble’s imaging spectrograph. The presence of carbon may solve at least one Beta Pictoris mystery: why didn’t the star’s radiation reduce the gas orbiting it? A hidden mass of hydrogen had been suspected as blocking the outflow, but the authors believe that ionized carbon is the cause.

From the paper:

“Neither oxygen nor carbon feels strong radiation pressure in the β Pic disk, since the star is relatively faint in the far-UV where the strong absorption lines of these species lie. By contrast, metals such as Na and Fe feel extremely strong radiation pressure and could be blown out of the system, producing apparent C and O overabundances relative to these elements…”

But the larger questions remain: what put the carbon into this system, and why is it overabundant relative to other elements, like oxygen, that also feel weak radiation pressure? The answer will demand new work, and the authors suggest the B9 primary star of the binary system Sigma Herculis might be a place to start, since circumstellar dust is being blown away from this UV-bright star in ways that offer interesting parallels as well as differences from Beta Pictoris. But until then, two intriguing ideas emerge from the current work:

  • Planets may already be forming within the Beta Pictoris disk. Since the comets and asteroids around Beta Pictoris might contain large amounts of graphite and methane, carbon-rich materials, any planets that are evolving here will have a similar composition and probably methane-rich atmospheres.
  • The Beta Pictoris asteroids and comets might be just like those of the early Solar System, suggesting that our young system might have had far more organic material available to it than today’s studies of asteroids and comets suggest. “We might be observing processes that occurred early in our solar system’s development,” said Nature co-author Alycia Weinberger (Carnegie Institution).
  • The paper is Roberge, Feldman, Weinberger et al., “Stabilization of the disk around Beta Pictoris by extremely carbon-rich gas,” in Nature 441 (8 June 2006), pp. 724-726 and also available here.

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    • ljk April 8, 2011, 12:52

      The new carbon symbiotic star IPHAS J205836.43+503307.2

      Authors: R.L.M. Corradi, L. Sabin, U. Munari, G. Cetrulo, A. Englaro, R. Angeloni, R. Greimel, A. Mampaso

      (Submitted on 7 Apr 2011)

      Abstract: We are performing a search for symbiotic stars using IPHAS, the INT Halpha survey of the northern Galactic plane, and follow-up observations. Candidate symbiotic stars are selected on the basis of their IPHAS and near-IR colours, and spectroscopy and photometry are obtained to determine their nature.

      We present here observations of the symbiotic star candidate IPHAS J205836.43+503307.2. The optical spectrum shows the combination of a number of emission lines, among which are the high-excitation species of [OIII], HeII, [Ca V], and [Fe VII], and a red continuum with the features of a star at the cool end of the carbon star sequence. The nebular component is spatially resolved: the analysis of the spatial profile of the [NII]6583 line in the spectrum indicates a linear size of ~2.5 arcsec along the east-west direction. Its velocity structure suggests an aspherical morphology.

      The near-infrared excess of the source, which was especially strong in 1999, indicated that a thick circumstellar dust shell was also present in the system. The carbon star has brightened in the last decade by two to four magnitudes at red and near-infrared wavelengths. Photometric monitoring during a period of 60 days from November 2010 to January 2011 reveals a slow luminosity decrease of 0.2 magnitudes.

      From the observed spectrophotometric properties and variability, we conclude that the source is a new Galactic symbiotic star of the D-type, of the rare kind that contains a carbon star, likely a carbon Mira. Only two other systems of this type are known in the Galaxy.

      Comments: 6 pages, 4 figures

      Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

      Journal reference: Astronomy & Astrophysics, 2011, Volume 529, A56

      DOI: 10.1051/0004-6361/201016406

      Cite as: arXiv:1104.1299v1 [astro-ph.SR]

      Submission history

      From: Romano L. M. Corradi [view email]

      [v1] Thu, 7 Apr 2011 10:58:28 GMT (62kb)