Spectroscopic signatures of magnetospheric accretion in Herbig Ae/Be stars - I. The case of HD?101412

摘要

Context. Models of magnetically-driven accretion and outflows reproduce many observational properties of T?Tauri stars. This concept is not well established for the more massive Herbig Ae/Be stars. Aims. We intend to examine the magnetospheric accretion in Herbig Ae/Be stars and search for rotational modulation using spectroscopic signatures, in this first paper concentrating on the well-studied Herbig Ae star HD?101412. Methods. We used near-infrared spectroscopic observations of the magnetic Herbig Ae star HD?101412 to test the magnetospheric character of its accretion disk/star interaction. We reduced and analyzed 30 spectra of HD?101412, acquired with the CRIRES and X-shooter spectrographs installed at the VLT (ESO, Chile). The spectroscopic analysis was based on the He? i λ 10?830 and Pa γ lines, formed in the accretion region. Results. We found that the temporal behavior of these diagnostic lines in the near-infrared spectra of HD?101412 can be explained by rotational modulation of line profiles generated by accreting gas with a period hbox{$P = 20d53pm 1d68$} . The discovery of this period, about half of the magnetic rotation period hbox{$P_{m m} = 42d076$} previously determined from measurements of the mean longitudinal magnetic field, indicates that the accreted matter falls onto the star in regions close to the magnetic poles intersecting the line-of-sight two times during the rotation cycle. We intend to apply this method to a larger sample of Herbig Ae/Be stars.