The long-period Galactic Cepheid RS Puppis

Abstract

Context. The bright southern Cepheid RS Pup is surrounded by a circumstellar nebula reflecting the light from the central star. The propagation of the light variations from the Cepheid inside the dusty nebula creates spectacular light echoes that can be observed up to large distances from the star itself. This phenomenon is currently unique in this class of stars. Aims. For this relatively distant star, the trigonometric parallax available from Hipparcos has a low accuracy. A careful observation of the light echoes has the potential to provide a very accurate, geometric distance to RS Pup. Methods. We obtained a series of CCD images of RS Pup with the NTT/EMMI instrument covering the variation period of the star (P = 41.4 d), allowing us to track the progression of the light wavefronts over the nebular features surrounding the star. We measured precisely the phase lag of the photometric variation in several regions of the circumstellar nebula. Results. From our phase lag measurements, we derive a geometric distance of 1992 ± 28 pc to RS Pup. This distance is affected by a total uncertainty of 1.4%, and corresponds to a parallax of π = 0.502 ± 0.007 mas and a distance modulus of µ = 11.50 ± 0.03. Conclusions. The geometric distance we derive is by far the most accurate to a Cepheid, and among the most accurate to any star. RS Pup appears both as somewhat neglected and particularly promising to investigate the mass-loss history of Cepheids. Thanks to its highly accurate distance, it is also bound to become an important luminosity fiducial for the long period part of the period-luminosity diagram.

The circumstellar envelopes of the Cepheids $\mathsf{\ell}$ Carinae and RS Puppis

“…Before these observations, only one Cepheid was known with certainty to be surrounded by a circumstellar envelope (CSE), RS Pup. This large nebula (≈2 ) scatters the light from the central star, and hosts one of the most striking examples of light echoes known to date (Kervella et al 2008). Another Cepheid, SU Cas, is close to a nebula, but the physical association is uncertain.…”

“…3 shows the circumstellar nebula of RS Pup in the V band, from observations with the NTT/EMMI instrument by Kervella et al (2008). In this wavelength range, we observe the scattered light from the central star.…”

“…15. While we discuss here the overall properties of the observed circumstellar emission, we postpone the presentation of a detailed model of the Cepheid CSEs to a future publication, that will incorporate the present results and the scattered light observations of RS Pup's nebula obtained by Kervella et al (2008).…”

“…In the following, we will phase the observations using reference epochs T 0 (expressed in Modified Julian Date) and periods of T 0 = 52289.916 and P = 35.5513 days for Car (Szabados 1989), T 0 = 54090.836 and P = 41.4389 days for RS Pup (Kervella et al 2008). …”

“Astrophysique sur Mesure”, E-learning in Astronomy and Astrophysics

“…Previous projects have shown that maintenance is very costly when authors use HTML Kervella et al 2008); Right: understanding a scheme or an image (optical scheme of the HARPS spectrometer dedicated to very high precision radial velocity measurement, Pepe et al 2003). to create courses : the mix of content and presentation markup makes separate changes in either of these areas much harder. The use of CSS can help alleviate these problems with the definition of classes for document parts, but XML goes much further.…”