The optical photometric variability of Herbig Ae/Be stars from TESS

TL;DR

This work presents a comprehensive time-domain photometric study of 188 HAeBe stars using TESS Full Frame Images, delivering 452 light curves and a uniform analysis of variability across sectors 1–45. By classifying light curves into nine morphologies and computing Q and M metrics along with characteristic timescales, the study maps variability patterns onto stellar and circumstellar properties, including inner-disk radii $R_{ m in}$ and accretion rates. The results reveal that ~95% of HAeBes are variable on timescales from minutes to ~months, with stochastic variability dominating and a minority showing quasi-periodic or periodic behavior; a notable paucity of dippers at higher masses suggests larger inner-disk radii and longer occultation timescales. A key finding is a potential mass-dependent transition near $M \\sim$ $6$–$7$ $M_ extodot$, where variability amplitudes and types shift, indicating changes in accretion dynamics or inner-disk structure. Overall, the paper demonstrates that HAeBe time-domain behavior shares core similarities with lower-mass YSOs for $M < \,7$ $M_ extodot$ while highlighting clear mass-related differences linked to inner disk geometry and accretion processes, with implications for magnetic activity and disk evolution in intermediate-mass PMS stars.

Abstract

We have carried out a photometric time domain study of 188 intermediate-mass young stars observed in Full Frame Image mode with the TESS satellite over the first 3.3 years of its mission. The majority of these targets are classified as Herbig Ae/Be stars (HAeBes). All were monitored at optical wavelengths for at least one 27-day TESS sector, with many having multiple sectors of data. From a custom aperture photometry pipeline, we produced light curves and analyzed the variability therein, as a function of stellar and circumstellar properties. Based on visual and statistical analysis, we find that ~95% of HAeBes are variable on timescales of 10 minutes to 1 month, with the most common light curve morphology being stochastic. Approximately 15% of the set display quasi-periodic variability. In comparison to sets of low-mass T Tauri stars monitored with optical space telescopes, the Herbig Ae/Be stars display a much lower incidence of ``dipper" behaviors (quasi-periodic or aperiodic fading events), as well as periodic modulations. As posited by previous work, we conclude that magnetic starspots are rare on HAeBes, and that the inner circumstellar dust rims of these objects lie at substantially larger radii than for low-mass young stars. Beyond these differences, the accretion dynamics of young stars less than ~7$M_\odot$ appear to be largely consistent based on their time domain properties from data streams of up to three months' duration. We do, however, find tentative evidence for a change in variability amplitude above this mass boundary, particularly for quasi-periodic behavior.

Figures (57)

• Figure 1: Spectral type distribution for the photometric sample employed in this work (Herbig Ae/Be stars), as well as those from previous works on lower mass stars ("CTTS"). Spectral types are labeled at the zero subtype (i.e., "A" is A0), and adopted from 2021AA...650A.182G. If a range of spectral types is given, we take the subtype at the middle. As seen in the histogram, late B and early A stars comprise the most common types here, while earlier samples were dominated by late K and M types.
• Figure 2: Representative examples of light curve morphology types from our Herbig Ae/Be sample observed by TESS. We omit eclipsing binaries and non-variable objects.
• Figure 3: Q-M diagram for the portion of the Herbig Ae/Be star sample with more certain variable types, as shown by the color coding. Point size represents a scaling of variability amplitude to the one third power. Data for objects with more than one sector of data appear as multiple points in this plot. The pile-up of points at $Q=1$ illustrates the sequence of objects with no discernible period.
• Figure 4: Top: Amplitudes for the sample of Herbig Ae/Be stars presented in this work, as a function of timescale. Points are color-coded by variability type and correspond to data from individual sectors; as such, some stars appear multiple times. Bottom: We show the sample quantities, but for the low-mass T Tauri stars from 2018AJ....156...71C and 2022AJ....163..212C.
• Figure 5: Light curves for two stars with pronounced changes in variability morphology and amplitude over a couple years. While relatively rare, these cases highlight the possibility that HAeBe variability drivers may shift dramatically on relatively short astronomical timescales.