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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.
| The zero point of the Cepheid period-luminosity relation in the 1.05 micron wave band
New observations of the Cepheids in the galactic clusters and externalgalaxies LMC, NGC 6822, NGC 300, and Sex A in the 1.05-micron wave band(IV) are presented. The slope of the P-L(IV) relation derived from theCepheids in the LMC agree with that in the SMC and that obtained forGalactic Cepheids. The zero point of the relation has been determinedfrom the distances to the galactic Cepheid clusters obtained throughZAMS fitting and referenced to the Pleiades modulus of 5.57. Thebolometric P-L relations derived individually using the data in V, J, Kwave bands are found to have the same slope and the zero point asobserved in the IV wave band. The comparison of the bolometric P-Lrelation with that obtained theoretically by Becker, Iben, and Tuggleshows agreement in the value of the slope. But the theoreticalmagnitudes are brighter by 0.4 mag. The true distance moduli to the LMC,the SMC, NGC 6822, NGC 300, and Sex A have been derived from P-L(IV)data and are found to be as 18.42, 18.83, 23.18, 25.72, and 25.27,respectively.
| UBV (RI)c standard stars in the E- and F-regions and in the Magellanic Clouds - a revised catalogue.
Not Available
| 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.
| Photometric standard stars for the UBV and (RI)KC systems.
Not Available
| Fainter Standards for VRI Photometry in the E Regions
Not Available
| Standard magnitudes in the E regions.
Not Available
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Observation and Astrometry data
| Constellation: | Sagittarius |
| Right ascension: | 20h20m22.65s |
| Declination: | -42°54'04.2" |
| Apparent magnitude: | 7.776 |
| Distance: | 381.679 parsecs |
| Proper motion RA: | -24.7 |
| Proper motion Dec: | 11.5 |
| B-T magnitude: | 9.04 |
| V-T magnitude: | 7.881 |
Catalogs and designations:
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