Letter to the Editor

VINCI-VLTI measurements of HR 4049: The physical size of the circumbinary envelope^*

¹ Università degli Studi di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
² INAF-Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monteporzio Catone, Italy e-mail: antoniucci@mporzio.astro.it
³ ESO-European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany

Received: 22 June 2004
Accepted: 30 October 2004

Abstract

We present the first detection of the envelope which surrounds the post-AGB binary source HR 4049. VINCI-VLTI K-band interferometric observations of this source imply the existence of a large structure with a Gaussian angular FWHM  mas or uniform disk diameter of  mas. With the Hipparcos parallax of  mas these values correspond to a physical size of  AU and  AU, respectively. Our measurements, covering an azimuth range of ~60°  for the sky-projected baseline, provide information on the geometry of the emitting region and show that there is only a slight variation of the measured angular values along the different directions sampled. Thus, our results are consistent with a spherical geometry of the envelope. However, we cannot completely rule out the existence of an asymmetric envelope (like the circumbinary disk envisaged by some recent models) because of the limited spatial frequency and azimuth range covered by the observations.