X-Ray Determination of the Variable Rate of Mass Accretion onto TW Hydrae

Diagnostics of electron temperature (Te), electron density (ne), and hydrogen column density (NH) from the Chandra High Energy Transmission Grating spectrum of He-like Ne ix in TW Hydrae (TW Hya), in conjunction with a classical accretion model, allow us to infer the accretion rate onto the star dir...

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Authors: Brickhouse, N. S.; Cranmer, S. R.; Dupree, A. K.; Günther, H. M.; Luna, Gerardo Juan Manuel; Wolk, S. J.
Format: Article
Status:Published version
Publication date:2012
Country:Argentina
Institution:Consejo Nacional de Investigaciones Científicas y Técnicas
Repository:CONICET Digital (CONICET)
Language:English
OAI Identifier:oai:ri.conicet.gov.ar:11336/19528
Online Access:http://hdl.handle.net/11336/19528
Access Level:Open access
Keyword:accretion, accretion disks
stars: formation
stars: individual (TW Hydrae)
techniques: spectroscopic
https://purl.org/becyt/ford/1.3
https://purl.org/becyt/ford/1
Summary:Diagnostics of electron temperature (Te), electron density (ne), and hydrogen column density (NH) from the Chandra High Energy Transmission Grating spectrum of He-like Ne ix in TW Hydrae (TW Hya), in conjunction with a classical accretion model, allow us to infer the accretion rate onto the star directly from measurements of the accreting material. The new method introduces the use of the absorption of Ne ix lines as a measure of the column density of the intervening, accreting material. On average, the derived mass accretion rate for TW Hya is 1.5 × 10−9 M yr−1, for a stellar magnetic field strength of 600 G and a filling factor of 3.5%. Three individual Chandra exposures show statistically significant differences in the Ne ix line ratios, indicating changes in NH, Te, and ne by factors of 0.28, 1.6, and 1.3, respectively. In exposures separated by 2.7 days, the observations reported here suggest a five-fold reduction in the accretion rate. This powerful new technique promises to substantially improve our understanding of the accretion process in young stars.

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