Differential interferometric phases at high spectral resolution as a sensitive physical diagnostic of circumstellar disks

TL;DR

This paper introduces a new spectro-interferometric phase effect, CQE-PS, which serves as a sensitive diagnostic for probing the inner regions of gaseous circumstellar disks around Be stars, revealing detailed disk properties.

Contribution

The study identifies and models the central quasi-emission phase signature (CQE-PS), demonstrating its potential to analyze disk density, size, and stellar dimensions at high spectral resolution.

Findings

CQE-PS shape depends on disk density and size

Useful lower limits to stellar size can be derived

Potential to monitor disk evolution and binary interactions

Abstract

Context. The circumstellar disks ejected by many rapidly rotating B stars (so-called Be stars) offer the rare opportunity of studying the structure and dynamics of gaseous disks at high spectral as well as angular resolution. Aims. This paper explores a newly identified effect in spectro-interferometric phase that can be used for probing the inner regions of gaseous edge-on disks on a scale of a few stellar radii. Methods. The origin of this effect (dubbed central quasi-emission phase signature, CQE-PS) lies in the velocity-dependent line absorption of photospheric radiation by the circumstellar disk. At high spectral and marginal interferometric resolution, photocenter displacements between star and isovelocity regions in the Keplerian disk reveal themselves through small interferometric phase shifts. To investigate the diagnostic potential of this effect, a series of models are presented, based on detailed radiative transfer calculations in a viscous decretion disk. Results. Amplitude and detailed shape of the CQE-PS depend sensitively on disk density and size and on the radial distribution of the material with characteristic shapes in differential phase diagrams. In addition, useful lower limits to the angular size of the central stars can be derived even when the system is almost unresolved. Conclusions. The full power of this diagnostic tool can be expected if it can be applied to observations over a full life-cycle of a disk from first ejection through final dispersal, over a full cycle of disk oscillations, or over a full orbital period in a binary system.