Strong latitudinal shear in the shallow convection zone of a rapidly rotating A-star

• Published in: Astronomy and astrophysics (Berlin) 2005-01, Vol.430 (1), p.L17-L20
• Main Authors: Reiners, A., Hünsch, M., Hempel, M., Schmitt, J. H. M. M.
• Format: Article
• Language: English
• Subjects: clusters: individual: IC 4665; line: profiles; stars: individual: IC 4665 V 102/P35; stars: rotation
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:200400120

We have derived the mean broadening profile of the star V 102 in the region of the open cluster IC 4665 from high resolution spectroscopy. At a projected equatorial rotation velocity of $v\,\sin{i} = (105 \pm 12)$ km s-1 we find strong deviation from classical rotation. We discuss several scenarios, the most plausible being strong differential rotation in latitudinal direction. For this scenario we find a difference in angular velocity of $\Delta\Omega = 3.6 \pm 0.8$ rad d-1 ($\Delta\Omega/\Omega = 0.42 \pm 0.09)$. From the Hα line we derive a spectral type of A9 and support photometric measurements classifying IC 4665 V 102 as a non-member of IC 4665. At such early spectral type this is the strongest case of differential rotation observed so far. Together with three similar stars, IC 4665 V 102 seems to form a new class of objects that exhibit extreme latitudinal shear in a very shallow convective envelope.