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Post Info TOPIC: RS Puppis
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Title: The long-period Galactic Cepheid RS Puppis - II. 3D structure and mass of the nebula from VLT/FORS polarimetry
Authors: P. Kervella, A. Mérand, L. Szabados, W. B. Sparks, R. J. Havlen, H. E. Bond, E. Pompei, P. Fouqué, D. Bersier, M. Cracraft

The long-period Cepheid RS Pup is surrounded by a large dusty nebula reflecting the light from the central star. Due to the changing luminosity of the central source, light echoes propagate into the nebula. This remarkable phenomenon was the subject of Paper I. The origin and physical properties of the nebula are however uncertain: it may have been created through mass loss from the star itself, or it could be the remnant of a pre-existing interstellar cloud. Our goal is to determine the 3D structure of the nebula, and estimate its mass. Knowing the geometrical shape of the nebula will also allow us to retrieve the distance of RS Pup in an unambiguous manner using a model of its light echoes (in a forthcoming work). The scattering angle of the Cepheid light in the circumstellar nebula can be recovered from its degree of linear polarization. We thus observed the nebula surrounding RS Pup using the polarimetric imaging mode of the VLT/FORS instrument, and obtained a map of the degree and position angle of linear polarisation. From our FORS observations, we derive a 3D map of the distribution of the dust, whose overall geometry is an irregular and thin layer. The nebula does not present a well-defined symmetry. Using a simple model, we derive a total dust mass of M(dust) = 2.9 ±0.9 solar masses for the dust within 1.8 arcmin of the Cepheid. This translates into a total mass of M(gas+dust) = 290 ±120 solar masses, assuming a dust-to-gas ratio of 1.0 ±0.3 %. The high mass of the dusty nebula excludes that it was created by mass-loss from the star. However, the thinness nebula is an indication that the Cepheid participated to its shaping, e.g. through its radiation pressure or stellar wind. RS Pup therefore appears as a regular long-period Cepheid located in an exceptionally dense interstellar environment.

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Blobrana


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RS PUP Light Echoes



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Blobrana


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Taking advantage of the presence of light echoes, a team of astronomers have used an ESO telescope to measure, at the 1% precision level, the distance of a Cepheid - a class of variable stars that constitutes one of the first steps in the cosmic distance ladder.
The team of astronomers studied RS Pup, a bright Cepheid star located towards the constellation of Puppis ('the Stern') and easily visible with binoculars. RS Pup varies in brightness by almost a factor of five every 41.4 days. It is 10 times more massive than the Sun, 200 times larger, and on average 15 000 times more luminous.

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Blobrana


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A team of astronomers have used an ESO (European Southern Observatory) telescope to measure the distance to a star, using the help of light echoes.
The star, known as a Cepheid, belongs to a class of variable stars that constitute one of the first steps in the distance scale of the Universe.

"Our measurements with ESO's New Technology Telescope at La Silla allow us to obtain the most accurate distance to a Cepheid" - Pierre Kervella, lead-author of the paper reporting the result.

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Spectral type:    F8Iab
Period: 41.4 days
Distance: 6500 light years, plus or minus 90 light years.

Position(2000): RA 08 13 04.2160, Dec:  -34 34 42.697

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