Interferometric study on the temporal variability of the brightness distributions of protoplanetary disks

Abstract

Context. Optical and infrared spatially unresolved multi-epoch observations have revealed the variability of pre-main sequence stars and/or their environment. Moreover, structures in orbital motion around the central star, resulting from planet-disk interaction, are predicted to cause temporal variations in the brightness distributions of protoplanetary disks. Through repeated observations of pre-main sequence stars with the Very Large Telescope Interferometer (VLTI) over nearly two decades, the ESO Archive has become a treasure chest containing unprecedented high-resolution multi-epoch near- and mid-infrared observations of the potential planet-forming regions in protoplanetary disks. Aims. We aim to investigate whether the existing multi-epoch observations provide evidence for the variability of the brightness distributions of the innermost few astronomical units of protoplanetary disks and to quantify any variations detected. Methods. We present different approaches to search for evidence of temporal variations based on multi-epoch observations obtained with the VLTI instruments PIONIER, AMBER, and MIDI for 68 pre-main sequence stars. Results. For nine objects in our sample, multi-epoch data obtained using equal baselines are available that allow us to directly detect variations in the visibilities due to temporally variable brightness distributions. Significant variations of the near-infrared visibilities obtained in different epochs with PIONIER and/or AMBER for HD 50138, DX Cha, HD 142527, V856 Sco, HD 163296, and R CrA were found. HD 37806, TW Hya, and CPD-36 6759 show no significant variations. By estimating the impact of a small variation of the baseline on the measured squared visibilities, we are able to compare the data of another 12 pre-main sequence stars. Thereby, we find evidence for temporal variations of the brightness distribution of one additional object, AK Sco. Besides the two binaries DX Cha and AK Sco, HD 50138 and V856 Sco also show signs of variability caused by variations of asymmetric structures in the brightness distribution.

The GRAVITY Young Stellar Object Survey. VI. Mapping the variable inner disk of HD 163296 at sub-au scales

“…In contrast, our findings suggest that there is an intrinsic flux variability associated with changes in the morphology of the source. This is in direct line with the results from Kobus et al (2020) et al (2020). The first work uses archival PIONIER data and parametric models applied to the squared visibilities in order to derive morphological changes in the structure of the source.…”

“…In contrast, it also motivates monitoring campaigns to depict the nature of this asymmetry. Additionally, Kobus et al (2020) suggested symmetric variability at sub-au scales based on the relative changes of the squared visibilities observed in PIONIER and AMBER (λ 0 = 2.2 µm) data. However, these analyses do not include the characterization of the closure phases.…”

The GRAVITY young stellar object survey

“…In contrast, our findings suggest that there is an intrinsic flux variability associated with changes in the morphology of the source. This is in direct line with the results from Kobus et al (2020) who interpret the variability of the squared visibilities for similar baselines at different epochs as changes in the structure of the target. 3.…”

“…Asymmetry: we can appreciate that the loci of the brightest side of the Ring model is changing, which strongly supports A97, page 4 of 30 The presence of an asymmetry and hints in the variability have been previously suggested by several authors in the literature. The two most recent are Kobus et al (2020) and Varga et al (2021). The first work uses archival PIO-NIER data and parametric models applied to the squared visibilities in order to derive morphological changes in the structure of the source.…”

“…In contrast, it also motivates monitoring campaigns to depict the nature of this asymmetry. Additionally, Kobus et al (2020) suggested symmetric variability at sub-au scales based on the relative changes of the squared visibilities observed in PIONIER and AMBER (Astronomical Multi-BEam combineR; λ 0 = 2.2 µm) data. However, these analyses do not include the characterization of the closure phases.…”