Asymmetric silicate dust distribution toward the silicate carbon star BM Geminorum

Ohnaka, K.; Izumiura, H.; Leinert, Ch.; Driebe, T.; Weigelt, G.; Wittkowski, M.

Abstract

Context. Despite their carbon-rich photospheres, silicate carbon stars show 10 mu m silicate emission. They are considered to have circumbinary or circum-companion disks, which serve as a reservoir of oxygen-rich material shed by mass loss in the past. Aims. We present N-band spectro-interferometric observations of the silicate carbon star BM Gem using MIDI at the Very Large Telescope Interferometer ( VLTI). Our aim is to probe the spatial distribution of oxygen-rich dust at high spatial resolution. Methods. Using the UT2-UT3 and UT3-UT4 configurations, BM Gem was observed with VLTI/MIDI at 44 - 62 m baselines. Results. The N-band visibilities observed for BM Gem decrease steeply between 8 and similar to 10 mu m and increase gradually longward of similar to 10 mu m, reflecting the optically thin silicate emission feature emanating from sub-micron-sized amorphous silicate grains. The differential phases obtained at baselines of similar to 44 - 46 m show significant non-zero values (similar to-70 degrees) in the central part of the silicate emission feature between similar to 9 and 11 mu m, revealing a photocenter shift and the asymmetric nature of the silicate emitting region. The observed N-band visibilities and differential phases can be described adequately by a simple geometrical model in which the unresolved star is surrounded by a ring with azimuthal brightness modulation. The best-fit model is characterized by a broad ring (similar to 70 mas across at 10 mu m) with a bright region offset from the unresolved star by similar to 20 mas at a position angle of similar to 280 degrees. This model can be interpreted as a system with a circum-companion disk and is consistent with the spectroscopic signatures of an accretion disk around an unseen companion, which were discovered in the violet spectrum of BM Gem.

Más información

Título según WOS: ID WOS:000259966600018 Not found in local WOS DB
Título de la Revista: ASTRONOMY & ASTROPHYSICS
Volumen: 490
Número: 1
Editorial: EDP SCIENCES S A
Fecha de publicación: 2008
Página de inicio: 173
Página final: 178
DOI:

10.1051/0004-6361:200810229

Notas: ISI