Diagnosing Mass Flows Around Herbig Ae/Be Stars Using the He I 10830 Line

TL;DR

This study investigates the He I 10830 line profiles in Herbig Ae/Be stars, revealing differences from classical T Tauri stars in accretion and outflow mechanisms, suggesting smaller magnetospheres and alternative accretion processes.

Contribution

It provides the first detailed comparison of He I 10830 profiles between Herbig Ae/Be stars and T Tauri stars, highlighting differences in accretion and wind signatures and proposing smaller magnetospheres in Herbig stars.

Findings

Herbig Be stars do not show typical disk wind signatures.

Herbig Ae stars generally exhibit magnetospheric accretion evidence.

Smaller magnetospheres in Herbig stars lead to different accretion and outflow characteristics.

Abstract

We examine He I 10830 profile morphologies for a sample of 56 Herbig Ae/Be stars (HAEBES). We find significant differences between HAEBES and CTTSs in the statistics of both blue-shifted absorption (i.e. mass outflows) and red-shifted absorption features (i.e. mass infall or accretion). Our results suggest that, in general, Herbig Be (HBe) stars do not accrete material from their inner disks in the same manner as CTTSs, which are believed to accrete material via magnetospheric accretion, while Herbig Ae (HAe) stars generally show evidence for magnetospheric accretion. We find no evidence in our sample of narrow blue--shifted absorption features which are typical indicators of inner disk winds and are common in He I 10830 profiles of CTTSs. The lack of inner disk wind signatures in HAEBES, combined with the paucity of detected magnetic fields on these objects, suggests that accretion through large magnetospheres which truncate the disk several stellar radii above the surface is not as common for HAe and late-type HBe stars as it is for CTTSs. Instead, evidence is found for smaller magnetospheres in the maximum red-shifted absorption velocities in our HAEBE sample. These velocities are, on average, a smaller fraction of the system escape velocity than is found for CTTSs, suggesting accretion is taking place closer to the star. Smaller magnetospheres, and evidence for boundary layer accretion in HBe stars, may explain the less common occurrence of red--shifted absorption in HAEBES. Evidence is found that smaller magnetospheres may be less efficient at driving outflows compared to CTTS magnetospheres.