English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The nearest accreting T Tauri star, TW Hya was observed with spectroscopicand photometric measurements simultaneous with a long se gmented exposure usingthe CHANDRA satellite. Contemporaneous optical photometry from WASP-S indicatesa 4.74 day period was present during this time. Absence of a similarperiodicity in the H-alpha flux and the total X-ray flux points to a differentsource of photometric variations. The H-alpha emission line appearsintrinsically broad and symmetric, and both the profile and its variabilitysuggest an origin in the post-shock cooling region. An accretion event,signaled by soft X-rays, is traced spectroscopically for the first time throughthe optical emission line profiles. After the accretion event, downflowingturbulent material observed in the H-alpha and H-beta lines is followed by He I(5876A) broadening. Optical veiling increases with a delay of about 2 hoursafter the X-ray accretion event. The response of the stellar coronal emissionto an increase in the veiling follows about 2.4 hours later, giving directevidence that the stellar corona is heated in part by accretion. Subsequently,the stellar wind becomes re-established. We suggest a model that incorporatesthis sequential series of events: an accretion shock, a cooling downflow in asupersonically turbulent region, followed by photospheric and later, coronalheating. This model naturally explains the presence of broad optical andultraviolet lines, and affects the mass accretion rates determined fromemission line profiles.

TW Hya: Spectral Variability, X-Rays, and Accretion Diagnostics