The Last Gasps of VY Canis Majoris: Aperture Synthesis and Adaptive Optics Imagery

Abstract

We present new observations of the red supergiant VY CMa at 1.25, 1.65, 2.26, 3.08, and 4.8 km. Two complementary observational techniques were utilized : nonredundant aperture masking on the 10 m Keck I telescope, yielding images of the innermost regions at unprecedented resolution, and adaptive optics imaging on the ESO 3.6 m telescope at La Silla, attaining an extremely high (D105) peak-to-noise dynamic range over a wide Ðeld. For the Ðrst time the inner dust shell has been resolved in the nearinfrared to reveal a one-sided extension of circumstellar emission within (D15 of the star. The 0A .1 R * ) line-of-sight optical depths of the circumstellar dust shell at 1.65, 2.26, and 3.08 km have been estimated to be 1.86^0.42, 0.85^0.20, and 0.44^0.11, respectively. These new results allow the bolometric luminosity of VY CMa to be estimated independent of the dust shell geometry, yielding A L * B 2 ] 105 L _ . variety of dust condensations, including a large scattering plume and a bow-shaped dust feature, were observed in the faint, extended nebula up to 4A from the central source. While the origin of the nebulous plume remains uncertain, a geometrical model is developed assuming the plume is produced by radially driven dust grains forming at a rotating Ñow insertion point with a rotational period between 1200 and 4200 yr, which is perhaps the stellar rotational period or the orbital period of an unseen companion.

Near‐ and Mid‐Infrared Subarcsecond Structure of the Dusty Symbiotic Star R Aquarii

“…The full two-dimensional Fourier coverage out to 10 m baselines a †orded by the masking experiment has proved highly successful at recovering asymmetric circumstellar structures in other systems (e.g., Monnier et al 1999 ;Tuthill, Monnier, & Danchi 1999a). However, in the case of R Aqr, the optical depth to the star is relatively low in the near-IR (q \ 0.01 at 2.2 km), so that the star greatly outshines the contribution from the dust shell.…”

Mid‐Infrared Interferometry on Spectral Lines. II. Continuum (Dust) Emission around IRC +10216 and VY Canis Majoris

“…Many properties of VY CMa were recently reviewed in Monnier et al (1999b), which included new near-IR imagery of its complicated circumstellar environment.…”

Infrared interferometry of circumstellar envelopes

“…Very nice results have recently been reported Weigelt et al 1998;Osterbart et al 1998;Irrgang et al 1998;Weigelt et al 1999). P. Tuthill leads the other group, which uses aperture masking techniques on the Keck-I telescope with maximum baselines of 11 m. Results can be found in this volume ) and in other publications Monnier et al 1999).…”

“…In addition, the variation of inner radii indicated an episodic emission time-scale of 20-50 years. The lSI has monitored a number of AGB stars for a 10-year period now, discovering complex shell geometries and time variation around multiple sources (Greenhill et al 1995;Bester et al 1996;Monnier et al 1997;Hale et al 1997;Lopez et al 1997). High spatial resolution observations with AI~A~10 5 presently underway should reveal the location of NH 3 and SiH 4 molecules, and help explain their anomalously high observed abundances around AGB stars (e.g., Betz, McLaren & Spears 1979;Goldhaber 1988).…”

“…Other techniques exist with the same goal in mind, but the limited space afforded to this review necessarily restricts the scope to exclude lunar occultation (e.g., Ragland, Chandrasekhar & Ashok 1997;Kaufl et al 1998) and adaptive optics works (e.g., Cruzalebes et al 1998;Monnier et al 1999). This review will also ignore the rapidly increasing interferometric successes at observing the stellar surfaces themselves (Dyck et al 1996;Wilson, Dhillon & Haniff 1997;Burns et al 1998;Van Belle et al 1998;Young et al 1999), but rather will concentrate on the circumstellar envelopes of late-type stars.…”