TY - JOUR
T1 - Mid-infrared interferometry of dust around massive evolved stars
AU - Rajagopal, Jayadev
AU - Menut, Jean Luc
AU - Wallace, D.
AU - Danchi, W. C.
AU - Chesneau, O.
AU - Lopez, B.
AU - Monnier, J. D.
AU - Ireland, M.
AU - Tuthill, P. G.
PY - 2007/12/20
Y1 - 2007/12/20
N2 - We report long-baseline interferometric measurements of circumstellar dust around massive evolved stars with the MIDI instrument on the Very Large Telescope Interferometer and provide spectrally dispersed visibilities in the 8 -13 μm wavelength band. We also present diffraction-limited observations at 10.7 μm on the Keck Telescope with baselines up to 8.7 m, which explore larger scale structure. We have resolved the dust shells around the late-type WC stars WR 106 and WR 95 and the enigmatic NaSt 1 (formerly WR 122), suspected to have recently evolved from a luminous blue variable (LBV) stage. For AG Car, the prototypical LBV in our sample, we marginally resolve structure close to the star, distinct from the well-studied detached nebula. The dust shells around the two WC stars show fairly constant size in the 8-13 μm MIDI band, with Gaussian half-widths of ∼25 to 40 mas, and the Keck observations reveal an additional extended structure around WR 106. The visibility profiles for NaSt 1 obtained from two MIDI baselines indicate a compact source embedded in an extended structure. The compact dust we detect around NaSt 1 and AG Car favors recent or ongoing dust formation. Using the measured visibilities, we build spherically symmetric radiative transfer models of the WC dust shells, which enable detailed comparison with existing SED-based models. Our results indicate that the inner radii of the shells are within a few tens of AU from the stars. In addition, our models favor grain size distributions with large (∼ 1 μm) dust grains. This proximity of the inner dust to the hot central star emphasizes the difficulty faced by current theories in forming dust in the hostile environment around WR stars. Although we detect no direct evidence for binarity for these objects, dust production in a colliding-wind interface in a binary system is a feasible mechanism in WR systems under these conditions.
AB - We report long-baseline interferometric measurements of circumstellar dust around massive evolved stars with the MIDI instrument on the Very Large Telescope Interferometer and provide spectrally dispersed visibilities in the 8 -13 μm wavelength band. We also present diffraction-limited observations at 10.7 μm on the Keck Telescope with baselines up to 8.7 m, which explore larger scale structure. We have resolved the dust shells around the late-type WC stars WR 106 and WR 95 and the enigmatic NaSt 1 (formerly WR 122), suspected to have recently evolved from a luminous blue variable (LBV) stage. For AG Car, the prototypical LBV in our sample, we marginally resolve structure close to the star, distinct from the well-studied detached nebula. The dust shells around the two WC stars show fairly constant size in the 8-13 μm MIDI band, with Gaussian half-widths of ∼25 to 40 mas, and the Keck observations reveal an additional extended structure around WR 106. The visibility profiles for NaSt 1 obtained from two MIDI baselines indicate a compact source embedded in an extended structure. The compact dust we detect around NaSt 1 and AG Car favors recent or ongoing dust formation. Using the measured visibilities, we build spherically symmetric radiative transfer models of the WC dust shells, which enable detailed comparison with existing SED-based models. Our results indicate that the inner radii of the shells are within a few tens of AU from the stars. In addition, our models favor grain size distributions with large (∼ 1 μm) dust grains. This proximity of the inner dust to the hot central star emphasizes the difficulty faced by current theories in forming dust in the hostile environment around WR stars. Although we detect no direct evidence for binarity for these objects, dust production in a colliding-wind interface in a binary system is a feasible mechanism in WR systems under these conditions.
UR - http://www.scopus.com/inward/record.url?scp=40249111522&partnerID=8YFLogxK
U2 - 10.1086/522515
DO - 10.1086/522515
M3 - Article
AN - SCOPUS:40249111522
VL - 671
SP - 2017
EP - 2027
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
ER -