Matthias M. Weber

Calibrating the Cepheid period-luminosity relation from the infrared surface brightness technique I. The p-factor, the Milky Way relations, and a universal K-band relation

Aims. We determine period-luminosity relations for Milky Way Cepheids in the optical and near-IR bands. These relations can be used directly as reference for extra-galactic distance determination to Cepheid populations with solar metallicity, and they form the basis for a direct comparison with relations obtained in exactly the same manner for stars in the Magellanic Clouds, presented in an accompanying paper. In that paper we show that the metallicity effect is very small and consistent with a null effect, particularly in the near-IR bands, and we combine here all 111 Cepheids from the Milky Way, the LMC and SMC to form a best relation. Methods. We employ the near-IR surface brightness (IRSB) method to determine direct distances to the individual Cepheids after we have recalibrated the projection factor using the recent parallax measurements to ten Galactic Cepheids and the constraint that Cepheid distances to the LMC should be independent of pulsation period. Results. We confirm our earlier finding that the projection factor for converting radial velocity to pulsational velocity depends quite steeply on pulsation period, p = 1.550− 0.186 log(P) in disagrement with recent theoretical predictions. We find PL relations based on 70 Milky Way fundamental mode Cepheids of MK = −3.33(±0.09)(log(P) − 1.0) − 5.66(±0.03), WVI = −3.26(±0.11)(log(P) − 1.0) − 5.96(±0.04). Combining the 70 Cepheids presented here with the results for 41 Magellanic Cloud Cepheids which are presented in an accompanying paper, we find MK = −3.30(±0.06)(log(P) − 1.0) − 5.65(±0.02), WVI = −3.32(±0.08)(log(P) − 1.0) − 5.92(±0.03). Conclusions. We delineate the Cepheid PL relation using 111 Cepheids with direct distances from the IRSB analysis. The relations are by construction in agreement with the recent HST parallax distances to Cepheids and slopes are in excellent agreement with the slopes of apparent magnitudes versus period observed in the LMC.

Doppler imaging of stellar surface structure - XXII. Time-series mapping of the young rapid rotator LQ Hydrae

We reconstruct a time series of 28 surface temperature maps (Doppler-images) of the spotted single K2-dwarf LQxa0Hya from 35 consecutive stellar rotations in Nov.–Dec. 1996. Two more maps are obtained from data in late April and early May 2000. All maps show spot activity preferably at low latitudes between -20°u2000and +50°, with a concentration in a band centered at around +30°, and with only occasional evidence for a higher-latitude spot extension. No trace of a polar spot is found at any of the above epochs. Most of this morphology can be reproduced by our flux-tube emergence model, except for the equatorial activity where the strong Coriolis force due to the rapid rotation always deflects flux tubes to higher latitudes. We also present the detection of weak differential surface rotation from a number of cross-correlation maps of the time-series images in late 1996. A solar-type differential rotation law, i.e. the equator rotating faster than the poles, with

The Blazhko behaviour of RR Geminorum I CCD photometric results in 2004

DeltaOmega=+0.022

Doppler imaging of stellar surface structure XXIII. the ellipsoidal K giant binary ζ Andromedae

xa0rad/day (lap time of ≈ 280 days) is in agreement with the data. Using the available photoelectric observations from 21 years we refine the rotation period to

Rotation and magnetic activity of the Hertzsprung-gap giant 31 Comae

1.60066pm0.00013

Spectroscopic orbit of Capella (Weber+, 2011)

days and find a remarkable phase coherence over the course of 21 years, supporting the recent finding of active longitudes by Berdyugina etxa0al. Furthermore, our photometry shows a complex multi-cyclic long-term brightness variability with three periods of

Milky Way Cepheids radial velocities (Storm+, 2011)

13.8pm2.8

31 Com radial velocities (Strassmeier+, 2010)

xa0years, its harmonic

STELLA Robotic Observatory for Stellar Activity Research

6.9pm0.8

Evolution of stellar active regions: differential rotation of five K giants

and