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

TL;DR

This study analyzes over 25 years of infrared data for two Herbig Ae stars, revealing significant variability in their disks that impacts models of their structure and evolution.

Contribution

It provides long-term infrared observations of HD 31648 and HD 163296, highlighting disk variability and its implications for understanding Herbig Ae stars.

Findings

HD 163296 showed a major flux increase near 3 microns in 2002.

HD 31648 exhibited sporadic flux changes across 3-13 microns.

Disk regions near dust sublimation vary over time, affecting grain size and crystallinity.

Abstract

Infrared photometry and spectroscopy covering a time span of a quarter century are presented for HD 31648 (MWC 480) and HD 163296 (MWC 275). Both are isolated Herbig Ae stars that exhibit signs of active accretion, including driving bipolar flows with embedded Herbig-Haro (HH) objects. HD 163296 was found to be relatively quiescent photometrically in its inner disk region, with the exception of a major increase in emitted flux in a broad wavelength region centered near 3 microns in 2002. In contrast, HD 31648 has exhibited sporadic changes in the entire 3-13 micron region throughout this span of time. In both stars the changes in the 1-5 micron flux indicate structural changes in the region of the disk near the dust sublimation zone, possibly causing its distance from the star to vary with time. Repeated thermal cycling through this region will result in the preferential survival of large grains, and an increase in the degree of crystallinity. The variability observed in these objects has important consequences for the interpretation of other types of observations. For example, source variability will compromise models based on interferometry measurements unless the interferometry observations are accompanied by nearly-simultaneous photometric data.