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

We investigate the unsaturated horseshoe drag exerted on a low-mass planet byan isothermal gaseous disk. In the globally isothermal case, we use a formal-ism, based on the use of a Bernoulli invariant, that takes into accountpressure effects, and that extends the torque estimate to a region wider thanthe horse- shoe region. We find a result that is strictly identical to thestandard horseshoe drag. This shows that the horseshoe drag accounts for thetorque of the whole corotation region, and not only of the horseshoe region,thereby deserving to be called corotation torque. We find that evanescent waveslaunched downstream of the horseshoe U-turns by the perturbations of vortensityexert a feed-back on the upstream region, that render the horseshoe regionasymmetric. This asymmetry scales with the vortensity gradient and with thedisk's aspect ratio. It does not depend on the planetary mass, and it does nothave any impact on the horseshoe drag. Since the horseshoe drag has a steepdependence on the width of the horseshoe region, we provide an adequatedefinition of the width that needs to be used in horseshoe drag estimates. Wethen consider the case of locally isothermal disks, in which the tempera- tureis constant in time but depends on the distance to the star. The horseshoe dragappears to be different from the case of a globally isothermal disk. Thedifference, which is due to the driving of vortensity in the vicinity of theplanet, is intimately linked to the topology of the flow. We provide adescriptive inter- pretation of these effects, as well as a crude estimate ofthe dependency of the excess on the temperature gradient.

On the horseshoe drag of a low-mass planet. I - Migration in isothermal disks