Resolving the dusty circumstellar environment of the A[e] supergiant HD 62623 with the VLTI/MIDI

摘要

Context. B[e] stars are hot stars surrounded bycircumstellar gas and dust which is responsible for the presence ofemission lines and IR-excess in their spectra. How dust can be formedin this highly illuminated and diluted environment remains an openissue. Aims. HD62623 is one of the very fewA-type supergiants showing the B[e] phenomenon. We studied the geometryof its circumstellar envelope in the mid-infrared using long-baselineinterferometry, which is the only observing technique able to spatiallyresolve objects smaller than a few tens of milliarcseconds. Methods. We obtained nine calibrated visibilitymeasurements between October 2006 and January 2008 using the VLTI/MIDIinstrument in SCI-PHOT mode and PRISM spectral dispersion mode withprojected baselines ranging from13 to 71m and withvarious position angles (PA). We used geometrical models and physicalmodeling with a radiative transfer code to analyze these data. Results. The dusty circumstellar environment ofHD62623 is partially resolved by the VLTI/MIDI, even with theshortest baselines. The environment is flattened ()and can be separated into two components: a compact one whose extensiongrows from 17mas at 8m to 30mas at 9.6m and staysalmost constant up to 13m, and a more extended one that is over-resolvedeven with the shortest baselines. Using the radiative transfer codeMC3D, we managed to model HD62623's circumstellar environmentas a dusty disk with an inner radius of AU,an inclination angle of ,and a mass of .Conclusions. It is the first time that the dustydisk inner rim of a supergiant star exhibiting the B[e] phenomenon issignificantly constrained. The inner gaseous envelope likelycontributes up to20to the total Nband flux and acts like a reprocessing disk.Finally, the hypothesis of a stellar wind deceleration by thecompanion's gravitational effects remains the most probable case sincethe bi-stability mechanism does not seem to be efficient for this star.Key words: techniques: high angularresolution - techniques: interferometric - stars: emission-line, Be -stars: winds, outflows - stars: individual: HD 62623 - circumstellarmatter