* Astronomy

Blobrana · L

RE: HD 44179

Blobrana · L

Title: The nature of the Na I D-lines in the Red Rectangle
Authors: Joshua D. Thomas, Adolf N. Witt, Jason P. Aufdenberg, Jon E. Bjorkman, Julie A. Dahlstrom, Steven R. Federman, Lew M. Hobbs, Uma P. Vijh, Donald G. York

In this paper we examine the profiles of the complex Na I D-lines in the Red Rectangle. The spectra were acquired with the ARCES echelle spectrograph R = 38,000 on the 3.5-m telescope at the Apache Point Observatory. Additional spectra taken with STIS were acquired from the Hubble Legacy Archive (HLA) and were used to independently confirm the spatial origin of the spectral features. The profile of a single D-line consists of double-peaked emission, red-shifted absorption and blue-shifted absorption. We find that the double-peaked emission originates from the bipolar outflow, the red-shifted absorption feature is due to the photospheric line, and the blue-shifted absorption arises from the bipolar outflow as seen against the photosphere of the luminous post-AGB component in HD 44179. In order to better understand the Na I D-line profile, we examined the periodically variable asymmetric photospheric absorption lines. The asymmetric lines are interpreted as a signature of slow self-accretion following enhanced mass-loss around periastron. An empirical model was constructed to remove the photospheric component from the Na I D-line profile in order to study the nebular emission and absorption of sodium along the line-of-sight to the primary. This paper also discusses the different origins of the single-peaked emission, the double-peaked emission and the blue-shifted and red-shifted absorption components.

Read more (546kb, PDF)

Blobrana · L

Space dust annoys astronomers just as much as the household variety when it interferes with their observations of distant stars. And yet space dust also poses one of the great mysteries of astronomy.

"We not only do not know what the stuff is, but we do not know where it is made or how it gets into space" - Donald York, the Horace B. Horton Professor in Astronomy and Astrophysics at the University of Chicago.

But now York, the University of Toledo's Adolf Witt and their collaborators have observed a double-star system that displays all the characteristics that astronomers suspect are associated with dust production. The Astrophysical Journal will publish a paper reporting their discovery in March.
The double star system, designated HD 44179, sits within what astronomers call the Red Rectangle, an interstellar cloud of gas and dust (nebula) located approximately 2,300 light years from Earth.
One of the double stars is of a type that astronomers regard as a likely source of dust. These stars, unlike the sun, have already burned all the hydrogen in their cores. Labelled post-AGB (post-asymptotic giant branch) stars, these objects collapsed after burning their initial hydrogen, until they could generate enough heat to burn a new fuel, helium.

Read more

Position(2000): RA 06 19 58.2160, Dec -10 38 14.691