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

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 -3exception of a major increase in emitted flux in a broad wavelength region centered near 3 µm in 2002. In contrast, HD 31648 has exhibited sporadic changes in the entire 3-13 µm region throughout this span of time. In both stars the changes in the 1-5 µm 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.

Relating jet structure to photometric variability: the Herbig Ae star HD 163296

“…A.2), 2001-2 (N obs = 3), and 2011-12 (N obs = 4). The first two epochs were also reported by Sitko et al (2008). The 2002 event marked a 30% increase in flux in the L-band.…”

“…Part of these data are also presented in Sitko et al (2008). Some of the L and M band data were extracted from spectra obtained with The Aerospace Corporation's Broad-band Array Spectrograph System (BASS), which covers the 3-13 µm wavelength region.…”

“…Some of the L and M band data were extracted from spectra obtained with The Aerospace Corporation's Broad-band Array Spectrograph System (BASS), which covers the 3-13 µm wavelength region. BASS is described more fully in Sitko et al (2008). Additional JHKLM photometric data were obtained using the SpeX spectrograph (Rayner et al 2003).…”

“…Also, the emission profile is smooth, i.e., does not originate in a sharply contrasted inner disk rim. HD 163296 also shows significant variations in its NIR brightness on timescales of years (Sitko et al 2008).…”

Strong near-infrared emission in the sub-AU disk of the Herbig Ae star HD 163296: evidence of refractory dust?

“…Weak X-ray emission (L x /L ∼ 5 × 10 −6 ) was detected on large scales and attributed to the jet (Günther & Schmitt 2009). In the NIR, the SED time variability was interpreted to be due to changes in the inner disk structure, on timescales similar to the generation of the HH objects (Sitko et al 2008).…”