Spitzer infrared spectrograph spectroscopy of the 10Myr old EF Cha debris disk: Evidence for phyllosilicate-rich dust in the terrestrial zone

Thayne Currie, Carey M. Lisse, Aurora Sicilia-Aguilar, George H. Rieke, Kate Y L Su

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We describe Spitzer Infrared Spectrograph spectroscopic observations of the ∼10Myr old star, EF Cha. Compositional modeling of the spectra from 5 μm to 35 μm confirms that it is surrounded by a luminous debris disk with LD /L ∼ 10-3, containing dust with temperatures between 225 K and 430 K, characteristic of the terrestrial zone. The EF Cha spectrum shows evidence for many solid-state features, unlike most cold, low-luminosity debris disks but like some other 10-20Myr old luminous, warm debris disks (e.g., HD 113766A). The EF Cha debris disk is unusually rich in a species or combination of species whose emissivities resemble that of finely powdered, laboratory-measured phyllosilicate species (talc, saponite, and smectite), which are likely produced by aqueous alteration of primordial anhydrous rocky materials. The dust and, by inference, the parent bodies of the debris also contain abundant amorphous silicates and metal sulfides, and possibly water ice. The dust's total olivine to the pyroxene ratio of ∼2 also provides evidence of aqueous alteration. The large mass volume of grains with sizes comparable to or below the radiation blow-out limit implies that planetesimals may be colliding at a rate high enough to yield the emitting dust but not so high as to devolatize the planetesimals via impact processing. Because phyllosilicates are produced by the interactions between anhydrous rock and warm, reactive water, EF Cha's disk is a likely signpost for water delivery to the terrestrial zone of a young planetary system.

Original languageEnglish (US)
Article number115
JournalAstrophysical Journal
Issue number2
Publication statusPublished - Jun 10 2011



  • astrochemistry
  • infrared: stars
  • planets and satellites: formation
  • protoplanetary disks
  • stars: individual (EF Cha)
  • techniques: spectroscopic

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

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