Transitions in magnetic behavior at the substellar boundary

التفاصيل البيبلوغرافية
العنوان: Transitions in magnetic behavior at the substellar boundary
المؤلفون: Magaudda, E., Stelzer, B., Osten, R. A., Pineda, J. S., Raetz, St., McKay, M.
المصدر: A&A 687, A95 (2024)
سنة النشر: 2024
المجموعة: Astrophysics
مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
الوصف: We aim at advancing our understanding of magnetic activity and the underlying dynamo mechanism at the end of the main-sequence. To this end, we collected simultaneous X-ray and radio observations for a sample of M7-L0 dwarfs using XMM-Newton jointly with the JVLA and the ATCA. We also included data from the all-sky surveys of eROSITA on board the Russian Spektrum-Roentgen-Gamma mission (SRG) and rotation periods from TESS together with an archival compilation of X-ray and radio data for UCDs from the literature. We limit the sample to objects with rotation period <1d, focusing on the study of a transition in magnetic behavior suggested by a drastic change in the radio detection rate at vsini \approx 38 km/s. We compiled the most up-to-date radio/X-ray luminosity relation for 26 UCDs with rotation periods lower than 1d, finding that rapid rotators lie the furthest away from the G\"udel-Benz relation previously studied for earlier-type stars. Radio bursts are mainly experienced by very fast UCDs, while X-ray flares are seen along the whole range of rotation. We examined the L_{\rm x}/L_{\rm bol} vs P_{\rm rot} relation, finding no evident relation between the X-ray emission and rotation, reinforcing previous speculations on a bimodal dynamo across late-type dwarfs. One radio-detected object has a rotation period consistent with the range of auroral bursting sources; while it displays moderately circularly polarized emission. A radio flare from this object is interpreted as gyrosynchrotron emission, and it displays X-ray and optical flares. We also found a slowly rotating apparent auroral emitter, that is also one of the X-ray brightest radio-detected UCDs. We speculate that this UCD is experiencing a transition of its magnetic behavior since it produces signatures expected from higher mass M dwarfs along with emerging evidence of auroral emission.
Comment: A&A submitted
نوع الوثيقة: Working Paper
DOI: 10.1051/0004-6361/202449403
URL الوصول: http://arxiv.org/abs/2401.17292
رقم الأكسشن: edsarx.2401.17292
قاعدة البيانات: arXiv
الوصف
DOI:10.1051/0004-6361/202449403