Starspot photometry with robotic telescopes.
$UBV(RI)_{\rm C}$ and <i>by</i> light curves of 47 active stars in 
1996/97

Strassmeier, K. G.; Serkowitsch, E.; Granzer, T.

doi:10.1051/aas:1999116

Cited by 54 publications

(55 citation statements)

References 43 publications

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“…An IUE search for rotational modulation of ultraviolet emission-line fluxes produced negative results as well (Simon 1986). Even our long-term APT observations did not lead to a conclusive period (Strassmeier et al 1999) although signals at 6.96 days and 2.31 days were present in the U-band APT data but were formally below the limit of significance, i.e. had an amplitude signal-to-noise ratio of below 4:1 according to the criteria by Breger et al (1993).…”

Section: Introductionmentioning

confidence: 65%

“…The T1 UBV and T7 VI C data are a continuation of the 1996/97 data already described and analyzed in Strassmeier et al (1997aStrassmeier et al ( ,1999 and were taken on a single-reading-per-night basis with T1 from fall 1997 until spring 2003 and with T7 until 1998. Table 1 summarizes the exact time ranges of all new observations in this paper.…”

Section: Apt Strömgren and Johnson Photometry From 1997-2003mentioning

confidence: 99%

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

Strassmeier¹,

Granzer²,

Kopf³

et al. 2010

A&A

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Context. The single rapidly-rotating G0 giant 31 Comae has been a puzzle because of the absence of photometric variability despite its strong chromospheric and coronal emissions. As a Hertzsprung-gap giant, it is expected to be at the stage of rearranging its moment of inertia, hence likely also its dynamo action, which could possibly be linked with its missing photospheric activity. Aims. Our aim is to detect photospheric activity, obtain the rotation period, and use it for a first Doppler image of the star's surface. Its morphology could be related to the evolutionary status. Methods. We carried out high-precision, white-light photometry with the MOST satellite, ground-based Strömgren photometry with automated telescopes, and high-resolution optical echelle spectroscopy with the new STELLA robotic facility. Results. The MOST data reveal, for the first time, light variations with a full amplitude of 5 mmag and an average photometric period of 6.80 ± 0.06 days. Radial-velocity variations with a full amplitude of 270 m s −1 and a period of 6.76 ± 0.02 days were detected from our STELLA spectra, which we also interpret as due to stellar rotation. The two-year constancy of the average radial velocity of +0.10 ± 0.33 km s −1 confirms the star's single status, as well as the membership in the cluster Melotte 111. A spectrum synthesis gives T eff = 5660 ± 42 K, log g = 3.51 ± 0.09, and [Fe/H] = −0.15 ± 0.03, which together with the revised Hipparcos distance, suggests a mass of 2.6 ± 0.1 M and an age of ≈540 Myr. The surface lithium abundance is measured to be nearly primordial. A detection of a strong He i absorption line indicates nonradiative heating processes in the atmosphere. Our Doppler images show a large, asymmetric polar spot, cooler than T eff by ≈1600 K, and several small low-to-mid latitude features that are warmer by ≈300-400 K and are possibly of chromospheric origin. We computed the convective turnover time for 31 Com as a function of depth and found on average τ C ≈ 5 days. Conclusions. 31 Com appears to be just at the onset of rapid magnetic braking and Li dilution because its age almost exactly coincides with the predicted onset of envelope convection. That we recover a big polar starspot despite the Rossby number being larger than unity, and thus no efficient (envelope) dynamo is expected, leads us to conclude that 31 Com still harbors a fossil predominantly poloidal magnetic field. However, the increasing convective envelope may have just started an interface dynamo that now is the source of the warm surface features and the corresponding UV and X-ray emission.

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Section: Introductionmentioning

confidence: 65%

Section: Apt Strömgren and Johnson Photometry From 1997-2003mentioning

confidence: 99%

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

Strassmeier¹,

Granzer²,

Kopf³

et al. 2010

A&A

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“…(But note that no such cycle is seen in the data from Radick et al 1998. ) This undulation is superimposed upon a secular decline discernable in the robotic telescope data from Strassmeier et al (1997Strassmeier et al ( , 1999 and . Such a trend hints at considerable variability on a much longer time scale.…”

Section: Introductionmentioning

confidence: 92%

“…B T light-curves: a) EK Dra, b) EK Dra (full line) and six fiducial stars. From 1994 onwards EK Dra has been monitored by APTs (Strassmeier et al 1997;Strassmeier et al 1999, and yet unpublished measurements). These photo-electrically measured brightnesses, not averaged, are shown too.…”

Section: Constancy Of Fiducial Starsmentioning

confidence: 99%

EK Draconis: Long-term photometry on Sonneberg Sky-Patrol plates

Fröhlich

Tschäpe

Rüdiger

et al. 2002

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Abstract. We performed long-term photometry of the young solar analog EK Draconis (HD 129333) using 1030 blue-sensitive Sky-Patrol plates taken at Sonneberg Observatory from 1958 onwards. A secular dimming of 0.0057 ± 0.0008 mag/y beginning around 1975 was found. Hence, the recent trend first observed with Automatic Photoelectric Telescopes (APTs) is confirmed and traced back to the mid-seventies.

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“…This effect indicates the presence of the chromospherically active regions (plages) which concentrate at the most spotted regions. Fekel et al (1986a); 2) Eggen (1984); 3) Strassmeier & Hall (1988); 4) Jetsu (1993); 5) Cutispoto (1991); 6) Cutispoto (1993); 7) Cutispoto (1996); 8) Strassmeier et al (1993); 9) Cutispoto (1998a); 10) Cutispoto (1998b); 11) Strassmeier et al (1997); 12) Cutispoto et al (2001); 13) Alekseev & Gershberg (1996a); 14) ; 15) Alekseev (1999); 16) ; 17) Strassmeier et al (1999).…”

Section: The Starspots -Active Regions Connectionmentioning

confidence: 99%

Starspots and active regions on the emission red dwarf star $LQ~Hydrae$

Alekseev

Козлова

2002

A&A

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Abstract. The quasi-simultaneous electrophotometric, polarimetric and spectroscopic observations of the single active spotted star LQ Hya are presented. The photometric variability of the star can be described completely by a zonal starspots model. Spotted regions occupy up to 23% of the total stellar surface. The temperature difference between the unspotted photosphere and starspots is about 800 K. Starspots are localized at the low and middle latitudes. We find for the first time broad-band linear polarization of the stellar light and its rotational modulation connected to the local magnetic region on the stellar surface. We suspect that there is a spacial connection between plages, magnetic regions and the mostly spotted stellar longitudes.

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Starspot photometry with robotic telescopes. $UBV(RI)_{\rm C}$ and by light curves of 47 active stars in 1996/97

Cited by 54 publications

References 43 publications

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

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

EK Draconis: Long-term photometry on Sonneberg Sky-Patrol plates

Starspots and active regions on the emission red dwarf star $LQ~Hydrae$

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