Doppler imaging of Speedy Mic using the VLT. Fast spot evolution on a young K-dwarf star We study the short-term evolution of starspots on the ultrafast-rotatingstar HD 197890 (“Speedy Mic” = BO Mic, K 0-2 V,Prot=0.380 d) based on two Doppler images taken about 13stellar rotations apart. Each image is based on spectra densely samplinga single stellar rotation. The images were reconstructed by our Dopplerimaging code CLDI (Clean-like Doppler imaging) from line profilesextracted by spectrum deconvolution. Our Doppler images constructed fromtwo independent wavelength ranges agree well on scales down to 10°on the stellar surface. In conjunction with nearly parallel V-bandphotometry our observations reveal a significant evolution of the spotpattern during as little as two stellar rotations. We suggest that sucha fast spot evolution demands care when constructing Doppler images ofhighly active stars based on spectral time series extending over severalstellar rotations. The fast intrinsic spot evolution on BO Mic impedesthe determination of a surface differential rotation; in agreement withearlier results by other authors we determine an upper limit of |α | < 0.004 ± 0.002.
Photometric reductions and the lightcurve of (51) NEMAUSA The light curve of the minor planet (51) Nemausa is derived on the basisof 1779 photoelectric (B and V) observations and a photometric reductionusing a rigorous least squares method. Separate light curves are givenfor the B and V observations, respectively. An absolute B-V magnitudefor (51) Nemusa of 0.787 + or - 0.004 mag was estimated. A detaileddescription of the least squares method is presented.
UBV photometry of E region standard stars of intermediate brightness Photometry data are given for 335 stars in the nine E regions.Observations were made using a photometer and filters on the 47 cmreflector at Cape Town. The stellar dispersions are summarized. Data arepresented in tabular form.
