Mid-infrared sizes of circumstellar disks around Herbig Ae/Be stars measured with MIDI on the VLTI^*

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: leinert@mpia-hd.mpg.de
² Sterrenkundig Instituut “Anton Pannekoek”, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
³ Instituut voor Sterrenkunde, Celestijnenlaan 200B, 3001 Leuven, Belgium
⁴ Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France
⁵ Sterrewacht Leiden, Niels-Bohr-Weg 2, 2300 RA Leiden, The Netherlands
⁶ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁷ Laboratoire d'Études Spatiales et d'Instrumentation en Astrophysique, Observatoire de Meudon, 5 place Jules Janssen, 92190 Meudon, France
⁸ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA
⁹ Max-Planck-Institut für Astrophysik, Karl-Scharzschild-Straße 1, 85741 Garching, Germany
¹⁰ ASTRON, Oude Hoogeveesnsedijk 4, PO Box 2, 7990 AA Dwingeloo, The Netherlands
¹¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
¹² Observatoire de la Côte d'Azur, Boulevard de l'Observatoire, BP 4229, 06304 Nice Cedex 4, France
¹³ Kapteyn Institute, Landleven 12, Postbus 800, 9700 AV Groningen, The Netherlands
¹⁴ Harvard-Smithonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
¹⁵ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹⁶ Kiepenheuer-Institut für Sonnenforschung, Schöneckstr.6, 79104 Freiburg, Germany

Received: 1 February 2004
Accepted: 9 April 2004

Abstract

We present the first long baseline mid-infrared interferometric observations of the circumstellar disks surrounding Herbig Ae/Be stars. The observations were obtained using the mid-infrared interferometric instrument MIDI at the European Southern Observatory (ESO) Very Large Telescope Interferometer VLTI on Cerro Paranal. The 102 m baseline given by the telescopes UT1 and UT3 was employed, which provides a maximum full spatial resolution of 20 milli-arcsec (mas) at a wavelength of 10 μm. The interferometric signal was spectrally dispersed at a resolution of 30, giving spectrally resolved visibility information from 8 μm to 13.5 μm. We observed seven nearby Herbig Ae/Be stars and resolved all objects. The warm dust disk of HD 100546 could even be resolved in single-telescope imaging. Characteristic dimensions of the emitting regions at 10 μm are found to be from 1 AU to 10 AU. The 10 μm sizes of our sample stars correlate with the slope of the 10–25 μm infrared spectrum in the sense that the reddest objects are the largest ones. Such a correlation would be consistent with a different geometry in terms of flaring or flat (self-shadowed) disks for sources with strong or moderate mid-infrared excess, respectively. We compare the observed spectrally resolved visibilities with predictions based on existing models of passive centrally irradiated hydrostatic disks made to fit the SEDs of the observed stars. We find broad qualitative agreement of the spectral shape of visibilities corresponding to these models with our observations. Quantitatively, there are discrepancies that show the need for a next step in modelling of circumstellar disks, satisfying both the spatial constraints such as are now available from the MIDI observations and the flux constraints from the SEDs in a consistent way.