Searching for Magnetospheres around Herbig Ae/Be Stars

Mikhail Pogodin,Olesya Kozlova,Natalia Drake,Nina Beskrovnaya,Ilya Alekseev,Sergei Pavlovskiy,Swetlana Hubrig,Silva Järvinen,Markus Schöller

doi:10.3390/universe7120489

Mikhail Pogodin, Olesya Kozlova + Show 7 more

Open Access

https://doi.org/10.3390/universe7120489

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Abstract

We describe four different approaches for the detection of magnetospheric accretion among Herbig Ae/Be stars with accretion disks. Studies of several unique objects have been carried out. One of the objects is the Herbig Ae star HD 101412 with a comparatively strong magnetic field. The second is the early-type Herbig B6e star HD 259431. The existence of a magnetosphere in these objects was not recognized earlier. In both cases, a periodicity in the variation of some line parameters, originating near the region of the disk/star interaction, has been found. The third object is the young binary system HD 104237, hosting a Herbig Ae star and a T Tauri star. Based on the discovery of periodic variations of equivalent widths of atmospheric lines in the spectrum of the primary, we have concluded that the surface of the star is spotted. Comparing our result with an earlier one, we argue that these spots can be connected with the infall of material from the disk onto the stellar surface through a magnetosphere. The fourth example is the Herbig Ae/Be star HD 37806. Signatures of magnetospheric accretion in this object have been identified using a different method. They were inferred from the short-term variability of the He i λ5876 line profile forming in the region of the disk/star interaction.

Highlights

Herbig Ae/Be stars (HAeBes) are widely recognized as pre-main sequence (PMS)objects with pronounced emission line features and a far-infrared (FIR) excess indicative of cool dust in their accretion disks [1,2,3]
Assuming that the observational signs of a magnetosphere can be revealed if RA/R > 1.5 and adopting a mean value of the mass accretion rate Mfor HAeBes equal to 5 × 10−7 M /yr [16], and the solar value for the ratio M/R, we can estimate a lower limit of B > 500 G for R = 2.5 R (Herbig Ae stars) and B > 200 G for R = 6 R (Herbig Be stars)
We consider several diagnostical methods for the magnetospheric accretion in Herbig Ae/Be stars, which are surrounded by accretion disks

Summary

Introduction

Objects with pronounced emission line features and a far-infrared (FIR) excess indicative of cool dust in their accretion disks [1,2,3]. This work presents a review of several of our investigations, in which other methods to study magnetic fields in the Herbig Ae/Be stars were proposed It is based on a search for any signs of magnetospheric accretion from a disk onto a star. Assuming that the observational signs of a magnetosphere can be revealed if RA/R > 1.5 and adopting a mean value of the mass accretion rate Mfor HAeBes equal to 5 × 10−7 M /yr [16], and the solar value for the ratio M/R, we can estimate a lower limit of B > 500 G for R = 2.5 R (Herbig Ae stars) and B > 200 G for R = 6 R (Herbig Be stars) These values of B appear quite reasonable for the HAeBes. Provided the magnetic axis of the star is not coincident with the axis of stellar rotation (i.e., a magnetic oblique rotator), the geometrical configuration inside the magnetosphere. We present four examples of a successful detection of magnetospheres around Herbig Ae/Be stars

The Magnetic Herbig Ae Star HD 101412

The Young Magnetized Binary System HD 104237

Findings

Conclusions