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

Fröhlich, H.‐E.; Tschäpe, R.; Rüdiger, G.; Strassmeier, K. G.

doi:10.1051/0004-6361:20020860

Cited by 19 publications

(23 citation statements)

References 27 publications

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“…The results by Fröhlich et al (2002) and Järvinen et al (2005) indicated that the magnitude of EK Dra was decreasing for at least the past 45 years. This implies that a part of the surface is continuously covered with spots.…”

Section: Comparison With Long-term Photometrymentioning

confidence: 94%

“…The 21 years of photometric observations show a decreasing trend in the brightness. The older measurements from Sonneberg Sky-Patrol plates (Fröhlich et al 2002) show that EK Dra was even brighter in the past. Therefore, for determining the unspotted V magnitude, the maximum V magnitude of each individual subset (from Järvinen et al 2005) was plotted against the amplitude of the subset.…”

Section: Mass Age and Lithium Abundancementioning

confidence: 99%

“…Combined with the Sonneberg Sky-Patrol plate results (Fröhlich et al 2002), their analysis revealed that the total spot area varies on a time scale longer than 45 years with a periodic variation of about 10.5 years. Also, spots were found to group around two active longitudes separated on average by 180…”

Section: Introductionmentioning

confidence: 99%

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EK Draconis

Järvinen

Berdyugina

Korhonen

et al. 2007

A&A

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Context. As a young solar analogue, EK Draconis provides an opportunity to study the magnetic activity of the infant Sun. Aims. We present three new surface temperature maps of EK Draconis and compare them with previous results obtained from longterm photometry. Furthermore, we determined a set of stellar parameters and compared the determined values with the corresponding solar values. Methods. Atmospheric parameters were determined by comparing observed and synthetic spectra calculated with stellar atmosphere models. Surface temperature maps were obtained using the Occamian approach inversion technique. The differential rotation of EK Dra was estimated using two different methods. Results. A detailed model atmosphere analysis of high resolution spectra of EK Dra has yielded a self-consistent set of atmospheric parameters: T eff = 5750 K, log g = 4.5, [M/H] = 0.0, ξ t = 1.6 km s −1 . The evolutionary models imply that the star is slightly more massive than the Sun and has an age between 30−50 Myr, which agrees with the determined lithium abundance of log N(Li) = 3.02.Moreover, the atmospheric parameters, as well as the wings of the Ca ii 8662 Å, indicate that the photosphere of EK Dra is very similar to the one of the present Sun, while their chromospheres differ. There also seems to be a correlation between magnetic features seen in the photosphere and chromosphere. The temperature images reveal spots of only 500 K cooler than the quiet photosphere. The mean spot latitude varies with time. The obtained differential rotation is very small, but the sign of it supports solar type differential rotation on EK Dra.

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Section: Comparison With Long-term Photometrymentioning

confidence: 94%

Section: Mass Age and Lithium Abundancementioning

confidence: 99%

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EK Draconis

Järvinen

Berdyugina

Korhonen

et al. 2007

A&A

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“…The equivalent width of Li I is about 0.2 Å, and therefore it must be relatively young. Fröhlich et al (2002, and references therein) discuss the age and activity connection.…”

Section: Introductionmentioning

confidence: 99%

The young active binary star EK Draconis

König

Guenther

Woitas

et al. 2005

A&A

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Abstract. EK Dra (HD 129333) is a young, active, nearby star that is orbited by a low mass companion. By combining new speckle observations with old and new radial velocity measurements we find that the orbit is highly eccentric with e = 0.82 ± 0.03, and we derive the true masses of both components. The masses are 0.9 ± 0.1 M and 0.5 ± 0.1 M , for the primary and secondary, respectively. From high resolution spectra we derive a new T eff of 5700 ± 70 K and a log g of 4.37 ± 0.10, which is different to previous estimates. However, the new spectroscopic distance differs by only 5.8% to the distance derived by parallax measurement by the Hipparcos satellite and thus the stellar parameters are presumably more realistic than older determinations. We derive a somewhat higher value for the metallicity of [Fe/H] = −0.16 ± 0.07. EK Dra turns out to be one of the few nearby young stars that will evolve similarly to the Sun. The precise radial velocity measurements taken in the course of this program also allow us to shed more light on the activity of this star. In 2001 and 2002 we find radial velocity variation with a period of 2.767 ± 0.005 days which we interpret as the rotation period. This signal vanishes in 2003. However the signal can be recovered if only the spectra in which the photospheric lines are asymmetric are used. On the other hand, we do not find a close correlation between the asymmetry of photospheric lines and the radial velocity.

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“…As examples we mention that Phillips & Hartmann (1978) determined first time long-term starspot activity of BY Dra and CC Eri from Harvard plates from half a century between 1900-1950, and Fröhlich et al (2002 used the Sonneberg plate collection for studying the long-term behaviour of the solar-type single active star EK Dra and the K-giant primary of the close binary HK Lac, respectively. Vogt et al (2004) found several new variables on the Sonneberg plate collection of 34 years, most of them are early type stars from late B to A, showing slow long-term changes on the timescale of a few thousand days.…”

Section: Introductionmentioning

confidence: 99%

Long‐term photometry of three active red giants in close binary systems: V2253 Oph, IT Com and IS Vir

Oláh¹,

Moór²,

Strassmeier³

et al. 2013

Astron Nachr

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We present and analyze long-term optical photometric measurements of the three active stars V2253 Oph, IT Com and IS Vir. All three systems are single-lined spectroscopic binaries with an early K giant as primary component but in different stages of orbital-rotational synchronization. Our photometry is supplemented by 2MASS and WISE near-IR and mid-IR magnitudes and then used to obtain more accurate effective temperatures and extinctions. For V2253 Oph and IT Com, we found their spectral energy distributions consistent with pure photospheric emission. For IS Vir, we detect a marginal mid-IR excess which hints towards a dust disk. The orbital and rotational planes of IT Com appear to be coplanar, contrary to previous findings in the literature. We apply a multiple frequency analysis technique to determine photometric periods, and possibly changes of periods, ranging from days to decades. New rotational periods of 21.55±0.03 d, 65.1±0.3 d, and 23.50±0.04 d were determined for V2253 Oph, IT Com, and IS Vir, respectively. Splitting of these periods led to tentative detections of differential surface rotations of δP/P ≈ 0.02 for V2253 Oph and 0.07 for IT Com. Using a time-frequency technique based on short-term Fourier transforms we present evidence of cyclic light variations of length ≈ 10 yr for V2253 Oph and 5-6 yr for IS Vir. A single flip-flop event has been observed for IT Com of duration 2-3 yr. Its exchange of the dominant active longitude had happened close to a time of periastron passage, suggesting some response of the magnetic activity from the orbital dynamics. The 21.55-d rotational modulation of V2253 Oph showed phase coherence also with the orbital period, which is 15 times longer than the rotational period, thus also indicating a tidal feedback with the stellar magnetic activity.

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

Cited by 19 publications

References 27 publications

EK Draconis

EK Draconis

The young active binary star EK Draconis

Long‐term photometry of three active red giants in close binary systems: V2253 Oph, IT Com and IS Vir

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