Mid-infrared interferometric variability of DG Tau: implications for the inner-disk structure

Abstract

Context. DG Tau is a low-mass pre-main sequence star, whose strongly accreting protoplanetary disk exhibits a so-far enigmatic behavior: its mid-infrared thermal emission is strongly time-variable, even turning the 10 $\mu$m silicate feature from emission to absorption temporarily. Aims. We look for the reason for the spectral variability at high spatial resolution and at multiple epochs. Methods. We study the temporal variability of the mid-infrared interferometric signal, observed with the VLTI/MIDI instrument at six epochs between 2011 and 2014. We fit a geometric disk model to the observed interferometric signal to obtain spatial information about the disk. We also model the mid-infrared spectra by template fitting to characterize the profile and time dependence of the silicate emission. We use physically motivated radiative transfer modeling to interpret the mid-infrared interferometric spectra. Results. The inner disk (r<1-3 au) spectra exhibit a 10 $\mu$m absorption feature related to amorphous silicate grains. The outer disk (r>1-3 au) spectra show a crystalline silicate feature in emission, similar to the spectra of comet Hale-Bopp. The striking difference between the inner and outer disk spectral feature is highly unusual among T Tauri stars. The mid-infrared variability is dominated by the outer disk. The strength of the silicate feature changed by more than a factor of two. Between 2011 and 2014 the half-light radius of the mid-infrared-emitting region decreased from 1.15 to 0.7 au. Conclusions. For the origin of the absorption we discuss four possible explanations: a cold obscuring envelope, an accretion heated inner disk, a temperature inversion on the disk surface and a misaligned inner geometry. The silicate emission in the outer disk can be explained by dusty material high above the disk plane, whose mass can change with time, possibly due to turbulence in the disk.

arXiv comment16 pages, 13 figures

References in corpus (49)

• The Sloan Digital Sky Survey: Technical Summary
• The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
• The Mass Dependence Between Protoplanetary Disks and their Stellar Hosts
• The AKARI/IRC Mid-Infrared All-Sky Survey
• Observational Constraints on the Formation and Evolution of Binary Stars
• The absence of crystalline silicates in the diffuse interstellar medium
• An Optical Spectroscopic Study of T Tauri Stars. I. Photospheric Properties
• The SCUBA Legacy Catalogue: Continuum Objects Detected by SCUBA
• On the Evolutionary Status of Class I Stars and Herbig-Haro Energy Sources in Taurus-Auriga
• Modeling optical properties of cosmic dust grains using a distribution of hollow spheres
• The T Tauri Phase Down to Nearly Planetary Masses: Echelle Spectra of 82 Very Low Mass Stars and Brown Dwarfs
• Mapping the Shores of the Brown Dwarf Desert II: Multiple Star Formation in Taurus-Auriga
• The Taurus Spitzer Survey: New Candidate Taurus Members Selected Using Sensitive Mid-Infrared Photometry
• Shadows cast by a warp in the HD 142527 protoplanetary disk
• The Structure and Emission of the Accretion Shock in T Tauri Stars II: the Ultraviolet Continuum Emission
• Results of the ROTOR-program. I. The long-term photometric variability of classical T Tauri stars
• Annealing of Silicate Dust by Nebular Shocks at 10 AU
• Episodic formation of cometary material in the outburst of a solar-like young star
• PPM-Extended (PPMX) - a catalogue of positions and proper motions
• Investigating planet formation in circumstellar disks: CARMA observations of RY Tau and DG Tau
• Disk Evolution in the three Nearby Star-Forming Regions of Taurus, Chamaeleon, and Ophiuchus
• TASS Mark IV Photometric Survey of the Northern Sky
• A Near-Infrared Spectroscopic Survey of Class I Protostars
• Primordial Circumstellar Disks in Binary Systems: Evidence for Reduced Lifetimes
• Measuring Protoplanetary Disk Accretion with H I Pf-beta
• A Survey for New Members of Taurus with the Spitzer Space Telescope
• The First U.S. Naval Observatory Robotic Astrometric Telescope Catalog (URAT1)
• Evidence for grain growth in T Tauri disks
• Dust Transport in Protostellar Disks Through Turbulence and Settling
• Dust Processing and Grain Growth in Protoplanetary Disks in the Taurus-Auriga Star-Forming Region
• High spatial resolution mid-infrared observations of the low-mass young star TW Hya
• Discovery of a bipolar X-ray jet from the T Tauri star DG Tau
• Star Formation in Space and Time: Taurus-Auriga
• The structure of disks around intermediate-mass young stars from mid-infrared interferometry. Evidence for a population of group II disks with gaps
• Variability of Disk Emission in Pre-Main Sequence and Related Stars. I. HD 31648 and HD 163296 - Isolated Herbig Ae Stars Driving Herbig-Haro Flows
• Optical imaging polarimetry of the LkCa 15 protoplanetary disk with SPHERE ZIMPOL
• Near-infrared absorption properties of oxygen-rich stardust analogues: The influence of coloring metal ions
• The 2008 outburst of EX Lup - silicate crystals in motion
• The T Tauri star RY Tau as a case study of the inner regions of circumstellar dust disks
• The composition and size distribution of the dust in the coma of comet Hale-Bopp
• Spatially Extended Brackett Gamma Emission in the Environments of Young Stars
• The Gould Belt Very Large Array Survey IV: The Taurus-Auriga complex
• Mid-Infrared Spectral Variability Atlas of Young Stellar Objects
• Physical properties of the jet from DG Tauri on sub-arcsecond scales with HST/STIS
• Variations of the 10 um Silicate Features in the Actively Accreting T Tauri Stars: DG Tau and XZ Tau
• Temperature inversion on the surface of externally heated optically thick multigrain dust clouds
• Constraints to the magnetospheric properties of T Tauri stars. I. The C II], Fe II] and Si II] ultraviolet features
• The [Ne III] Jet of DG Tau and its Ionization Scenarios
• Confronting Standard Models of Proto--Planetary Disks With New Mid--Infrared Sizes from the Keck Interferometer

Cited by in corpus (10)

• Are Inner Disc Misalignments Common? ALMA Reveals an Isotropic Outer Disc Inclination Distribution for Young Dipper Stars
• The IGRINS YSO Survey I. Stellar parameters of pre-main sequence stars in Taurus-Auriga
• VLTI/MIDI atlas of disks around low- and intermediate-mass young stellar objects
• Planetesimals Around Stars with TESS (PAST): I. Transient Dimming of a Binary Solar Analog at the End of the Planet Accretion Era
• Interpreting molecular hydrogen and atomic oxygen line emission of T Tauri disks with photoevaporative disk-wind models
• Planetesimals Around Stars with TESS (PAST): II. An M Dwarf "Dipper" Star with a Long-Lived Disk in the TESS Continuous Viewing Zone
• Grain growth in newly discovered young eruptive stars
• A gap at 1 au in the disk of DI Cha A revealed by infrared interferometry
• MINDS survey of silicates in T Tauri disks: Correlation between dust and gas
• The MATISSE view of the inner region of the RY Tau protoplanetary disk