Site Map
Follow us on Facebook Follow us on Twitter YouTube channel
Centro de Astrofísica da Universidade do Porto

Doppler images from dual-site observations of southern rapidly rotating stars - II. Starspot patterns and differential rotation on Speedy Mic

J. R. Barnes, A. Collier Cameron, D. James, J.-F. Donati

We have secured high spatial and temporal resolution spectra of the rapidly rotating K dwarf Speedy Mic (HD 197890) at two sites and a common epoch of observations. The 0.38-d axial rotation period and the V-band magnitude of 9.33 make it a difficult target for Doppler imaging. In order to obtain high signal-to-noise ratio profiles from 300-s exposures, we apply the technique of least-squares deconvolution to the large number of photospheric absorption lines available in each of our spectra. This allows us to derive high-resolution maximum-entropy-regularized Doppler images of the stellar surface. Using these techniques, we also derive radial velocities and accurate projected equatorial rotation velocities which are consistent to within ~1kms-1. Our surface maps reveal one of the most heavily spotted photospheres seen on a rapid rotator, with starspots occurring at all latitudes. At the time of observations, Speedy Mic had no strong polar spot, but it shows spots concentrated in low- and intermediate-latitude bands. We attempt a differential rotation measurement, but lack of sufficient phase coverage allows determination of only a lower limit of 59d for the time it takes the equatorial regions to lap the polar regions. We also find variations in the heavily filled-in Hα line which can be attributed to prominences passing in front of the stellar disc. Despite the rapid rotation, the appearance of the same features on consecutive nights of observations shows the clouds to be stable on time-scales of at least a day.

Monthly Notices of the Royal Astronomical Society
Volume 324, Page 231
June 2001

>> PDF>> ADS>> DOI

Institute of Astrophysics and Space Sciences

Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.

Proceed on CAUP's website|Go to IA website