Stellar X‐ray accretion signatures. Issue 2 (8th March 2017)

• Record Type: Journal Article
• Authors: Schneider, P. C.; Günther, H. M.; Robrade, J.
• Is Part Of: Astronomische Nachrichten. Volume 338:Issue 2/3(2017)
• Page Start: 201
• Page End: 206
• Publication Date: 2017-03-08
• Subjects: stars: formation -- stars: premain sequence -- T Tauri stars -- accretion, accretion disks -- X‐rays: stars; Astronomy -- Periodicals; 520.5
• DOI: 10.1002/asna.201713331
• Languages: English
• ISSNs: 0004-6337

Abstract

Abstract : Accretion is observed in a wide range of objects with partially overlapping properties. In this paper, we focus on accretion in young stars. Material impacting the stellar surface is shock‐heated to temperatures of a few 10 6 K (MK), which is ideally suited for observations in the X‐ray regime. Indeed, young, accreting stars show a surplus of cool plasma, thought to be somehow related to accretion, the so‐called soft excess. High‐resolution grating spectroscopy with instruments like the Reflection Grating Spectrometer (RGS) on board XMM‐Newton allows us to infer the properties of this cool plasma. We present results from our recent 250‐ks XMM‐Newton/Chandra program targeting the prototypical T Tau system and compare them with other accreting systems, focusing on potentially different accretion modes. We find a strong cool excess in T Tau but line ratios indicative of low densities. Thus, the cool excess in T Tau, and likely in other accreting stars, is not caused directly by postshock emission from accretion spots, which are expected in magnetic stars like T Tau. Rather, the coolest plasma might be linked to other processes in accreting stars, such as an interaction of the corona with postshock plasma.