Volume 572, December 2014
|Number of page(s)||13|
|Section||Stellar structure and evolution|
|Published online||03 December 2014|
We tested the dependency of the measured vsini on the spot coverage of IL Hya. For this, we have assumed different spot distributions with both polar caps and equatorial belts simultaneously. The corresponding line profiles with a given vsini were calculated using the forward version of our Doppler imaging code TempMapForward (Rice & Strassmeier 2000). Finally, we measured the FWHM of the lines to derive vsini. The stellar parameters of IL Hya used were those given in Sect. 3.3 and in Weber & Strassmeier (1998), and were kept constant over the whole course of the test, only the polar and equatorial spot-coverage was gradually changed. These tests were carried out for polar caps of different areas with fixed equatorial belts, and vice versa. We note, that these spot configurations are symmetric and do not result in rotational modulation. We also note, that microturbulence affects EWs and therefore the measured FWHMs, but this also did not change during the tests.
The results clearly indicate that a shrinking polar cap with a fixed equatorial belt results in significantly lower vsini, while a shrinking belt with a fixed cap produces constant, or slightly higher vsini. The shrinking huge polar cap yields slightly higher vsini at first, and then significantly lower vsini later on.
Dependency test of measured v sin i on spot coverage. Shrinking polar caps from 30° radius by 5° steps with a constant equatorial belt between −30° and + 30° and −25° and + 25° latitudes are represented by diamonds and stars, respectively; the effect of a huge shrinking polar cap from 45° radius by 5° steps with a thin equatorial belt between −10° and + 10°, and without equatorial belt, are represented by plusses (vertical structures from the right to the left). The starting v sin i of 26.5 is represented by a dashed line, around it is seen the effect of an equatorial belt without a polar cap marked with stars; crosses, squares and triangles denote shrinking equatorial belts from −30° and + 30° with 5° steps and with constant radii of polar caps of 15°,20° and 25°, respectively (horizontal structures upwards). Below: two representative starting configurations are given to visualize the spots.
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© ESO, 2014
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