Spectral Evidence for an Inner Carbon-rich Circumstellar Belt in the Young HD 36546 A-star System

C. M. Lisse, M. L. Sitko, R. W. Russell, M. Marengo, T. Currie, C. Melis, T. Mittal, I. Song

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Using the NASA/IRTF SpeX and BASS spectrometers we have obtained 0.7-13 μm observations of the newly imaged 3-10 Myr old HD 36546 disk system. The SpeX spectrum is most consistent with the photospheric emission expected from an L ∼ 20 L o, solar abundance A1.5V star with little to no extinction, and excess emission from circumstellar dust detectable beyond 4.5 μm. Non-detections of CO emission lines and accretion signatures point to the gas-poor circumstellar environment of a very old transition disk. Combining the SpeX + BASS spectra with archival WISE/AKARI/IRAS/Herschel photometry, we find an outer cold dust belt at ∼135 K and 20-40 au from the primary, likely coincident with the disk imaged by Subaru, and a new second inner belt with a temperature ∼570 K and an unusual, broad SED maximum in the 6-9 μm region, tracing dust at 1.1-2.2 au. An SED maximum at 6-9 μm has been reported in just two other A-star systems, HD 131488 and HD 121191, both of ∼10 Myr age. From Spitzer, we have also identified the ∼12 Myr old A7V HD 148657 system as having similar 5-35 μm excess spectral features. The Spitzer data allows us to rule out water emission and rule in carbonaceous materials - organics, carbonates, SiC - as the source of the 6-9 μm excess. Assuming a common origin for the four young A-star systems' disks, we suggest they are experiencing an early era of carbon-rich planetesimal processing.

Original languageEnglish (US)
Article numberL20
JournalAstrophysical Journal Letters
Issue number2
StatePublished - May 10 2017

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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