Other
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21443001g&link_type=abstract
American Astronomical Society, AAS Meeting #214, #430.01; Bulletin of the American Astronomical Society, Vol. 41, p.700
Other
Scientific paper
Although the period-luminosity relation is just 100 years old, Cepheids are still surprising stars in many respects. The recent availability of long-baseline infrared interferometers with hectometric baselines allowed us to measure their angular diameters with sub-percent accuracy. Through a variant of the classical Baade-Wesselink method, such interferometric measurements, complemented by spectroscopy, give us their distance from the comparison of the angular size and radius variation amplitudes. This method, although quasi-geometric, presents some particular difficulties that we will briefly discuss. SIM-Lite will provide high-accuracy parallaxes to 40 nearby Cepheids. When combined with high-resolution spectroscopy and interferometry, this will allow us to calibrate the Baade-Wesselink method, and more specifically the projection factor that is currently limiting its accuracy.
In the course of these interferometric observations, we discovered compact circumstellar envelopes around several nearby Cepheids in the near-infrared. In particular, we discovered in 2006 a compact envelope around the long period Cepheid L Car. Another long-period Cepheid, RS Pup, presents a large ( 2') circumstellar nebula scattering the Cepheid light in the visible. These envelopes are particularly interesting for two reasons: their presence could impact the Cepheid distance scale, and they could imply stellar mass loss. We present a brief comparative view of these two Cepheid envelopes. SIM observations will provide dynamical masses for binary systems containing a Cepheid, an essential input for stellar evolution models and our understanding of mass-loss mechanisms.
Gallenne Alexandre
Kervella Pierre
Mérand Antoine
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