Long-term monitoring in IC4665: Fast rotation and weak variability in very low mass objects - Astrophysics > Solar and Stellar AstrophysicsReportar como inadecuado




Long-term monitoring in IC4665: Fast rotation and weak variability in very low mass objects - Astrophysics > Solar and Stellar Astrophysics - Descarga este documento en PDF. Documentación en PDF para descargar gratis. Disponible también para leer online.

Abstract: We present the combined results of three photometric monitoring campaignstargeting very low mass VLM stars and brown dwarfs in the young open clusterIC4665 age ~40 Myr. In all three runs, we observe ~100 cluster members,allowing us for the first time to put limits on the evolution of spots andmagnetic activity in fully convective objects on timescales of a few years. For20 objects covering masses from 0.05 to 0.5 Msol we detect a periodic fluxmodulation, indicating the presence of magnetic spots co-rotating with theobjects. The detection rate of photometric periods ~20% is significantlylower than in solar-mass stars at the same age, which points to a massdependence in the spot properties. With two exceptions, none of the objectsexhibit variability and thus spot activity in more than one season. This iscontrary to what is seen in solar-mass stars and indicates that spotconfigurations capable of producing photometric modulations occur relativelyrarely and are transient in VLM objects. The rotation periods derived in thispaper range from 3 to 30h, arguing for a lack of slow rotators among VLMobjects. The periods fit into a rotational evolution scenario with pre-mainsequence contraction and moderate 40-50% angular momentum losses due to windbraking. By combining our findings with literature results, we identify tworegimes of rotational and magnetic properties, called C- and I-sequence. Mainproperties on the C-sequence are fast rotation, weak wind braking, Halphaemission, and saturated activity levels, while the I-sequence is characterisedby slow rotation, strong wind braking, no Halpha emission, and linearactivity-rotation relationship. Rotation rate and stellar mass are the primaryparameters that determine in which regime an object is found. abridged



Autor: Alexander Scholz SUPA, St. Andrews, Jochen Eisloeffel TLS Tautenburg, Reinhard Mundt MPIA Heidelberg

Fuente: https://arxiv.org/







Documentos relacionados