Dust around First‐Ascent Red Giants

Abstract

We examine models for the physical conditions in the dust envelopes around the closest and most conspicuous examples of luminosity class III red giants with infrared excesses such as d And.(1) It has been previously suggested that the dust is sporadically ejected from the stars, but for most such stars, this model seems unlikely. (2) Another possibility is that in some cases we might be witnessing emission from interstellar dust that happens to be near the star, a "" cirrus hot spot. ÏÏ Since 70% of the red giants with infrared excesses lie within 100 pc of the Galactic plane where this phenomenon must sometimes occur, many of the excesses might be explained by this e †ect. However, a difficulty with this model for at least a few bright sources is that if the clouds have a uniform density, we expect sizes at 60 km that are about a factor of 10 larger than found for the best studied examples. It seems likely that some class III giants do possess circumstellar dust. (3) The inferred mass of dust around some class III red giants is larger than 1026 g, more matter than would be expected when a Vega-type star evolves o † the main sequence. Because the dust is inferred to be more than 100 AU from the star, we hypothesize that the large inferred dust masses is the result of the disintegration of comets. This model can be tested by using the Space Infrared Telescope Facility to measure the 60 km sizes.

Spectroscopic survey of post-AGB star candidates

“…Being a giant with infrared emission (GL97), GLMP 9 deserves further investigation. Several authors have tried to explain why stars with luminosity class III have infrared emission and as such several possibilities have been proposed (Zuckerman et al 1995;Jura 1999). …”

Post-main-sequence evolution of A star debris discs

“…Infrared excess observed around giant stars (e.g. Jura 1999), and the helix nebula (Su et al 2007), on the other hand, has been interpreted as a disc similar to debris discs on the MS (although alternative interpretations do exist; see e.g. Kim, Zuckerman & Silverstone 2001).…”

Search for Lithium-Rich Stars Among G-K Giants with IR-excess

“…On the first hand there are a few G-K giant stars which are known to have IR excess, which is not the case of the majority of the giants. The origin of the dust responsible for the IR excess could be: sporadic mass-loss events from these stars (Zuckerman et al 1995) during a possibly short-lived phase of evolution, a Vega-like disk heated by the star evolving into a giant (Judge et al 1987;Plets et al 1997), a hot spot produced by a nearby diffuse cloud (cirrus) locally heated by the star (Jura 1999). …”