Title: Spectral Evidence for an Inner Carbon-Rich Circumstellar Dust Belt in the Young HD36546 A-Star System,
Abstract: Using the NASA/IRTF SpeX & BASS spectrometers we have obtained novel 0.7 - 13
um observations of the newly imaged HD36546 debris disk system. The SpeX
spectrum is most consistent with the photospheric emission expected from an
Lstar ~ 20 Lsun, solar abundance A1.5V star with little/no extinction and
excess emission from circumstellar dust detectable beyond 4.5 um.
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 and BASS spectra with archival WISE/AKARI/IRAS/Herschel photometery, we
find an outer cold dust belt at ~135K and 20 - 40 AU from the primary, likely
coincident with the disk imaged by Subaru (Currie et al. 2017), and a new
second inner belt with temperature ~570K and an unusual, broad SED maximum in
the 6 - 9 um region, tracing dust at 1.1 - 2.2 AU. An SED maximum at 6 - 9 um
has been reported in just two other A-star systems, HD131488 and HD121191, both
of ~10 Myr age (Melis et al. 2013). From Spitzer, we have also identified the
~12 Myr old A7V HD148567 system as having similar 5 - 35 um excess spectral
features (Mittal et al. 2015). 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 um excess. Assuming a common origin for the 4 young
Astar systems' disks, we suggest they are experiencing an early era of
carbon-rich planetesimal processing.