Photospheric and chromospheric active regions on three single-lined RS CVn binaries

Biazzo, K.; Frasca, A.; Catalano, S.; Marilli, E.

doi:10.1051/0004-6361:20053213

Cited by 26 publications

(36 citation statements)

References 31 publications

(39 reference statements)

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“…This level of variation is one order of magnitude above the observed dispersion seen in the Hipparcos data. The same is true for a wide range of temperature differences of typical star spots ranging from ∆T = 200 − 1200 K (e.g., Biazzo et al 2006;O'Neal 2006). Nevertheless, hypothetic surface structure phenomena might mimic the presence of an exoplanet.…”

Section: Photometrymentioning

confidence: 55%

Precise radial velocities of giant stars

Ortiz

Reffert

Trifonov

et al. 2016

A&A

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Context. For over 12 yr, we have carried out a precise radial velocity (RV) survey of a sample of 373 G-and K-giant stars using the Hamilton Échelle Spectrograph at the Lick Observatory. There are, among others, a number of multiple planetary systems in our sample as well as several planetary candidates in stellar binaries. Aims. We aim at detecting and characterizing substellar and stellar companions to the giant star HD 59686 A (HR 2877, HIP 36616). Methods. We obtained high-precision RV measurements of the star HD 59686 A. By fitting a Keplerian model to the periodic changes in the RVs, we can assess the nature of companions in the system. To distinguish between RV variations that are due to non-radial pulsation or stellar spots, we used infrared RVs taken with the CRIRES spectrograph at the Very Large Telescope. Additionally, to characterize the system in more detail, we obtained high-resolution images with LMIRCam at the Large Binocular Telescope. Results. We report the probable discovery of a giant planet with a mass of m p sin i = 6.92 +0.18 −0.24 M Jup orbiting at a p = 1.0860 +0.0006 −0.0007 au from the giant star HD 59686 A. In addition to the planetary signal, we discovered an eccentric (e B = 0.729 +0.004 −0.003 ) binary companion with a mass of m B sin i = 0.5296 +0.0011 −0.0008 M orbiting at a close separation from the giant primary with a semi-major axis of a B = 13.56 +0.18 −0.14 au. Conclusions. The existence of the planet HD 59686 Ab in a tight eccentric binary system severely challenges standard giant planet formation theories and requires substantial improvements to such theories in tight binaries. Otherwise, alternative planet formation scenarios such as second-generation planets or dynamical interactions in an early phase of the system's lifetime need to be seriously considered to better understand the origin of this enigmatic planet.

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Section: Photometrymentioning

confidence: 55%

Precise radial velocities of giant stars

Ortiz

Reffert

Trifonov

et al. 2016

A&A

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“…No rotational modulation of EW Hα emerges over the data scatter. This result may be surprising, because rotational modulation of the Hα emission frequently has been detected in several highly-and mildly-active stars (see, e.g., Frasca et al 2000Frasca et al , 2008bAlekseev & Kozlova 2002, 2003Biazzo et al 2006Biazzo et al , 2007b. However, in some cases, no clear rotational modulation of chromospheric diagnostics has been detected despite the contemporaneous wave-like behaviour in the photometry (see, e.g., Catalano et al 2000).…”

Section: Hα Linementioning

confidence: 98%

“…The B − V color shows a scattered modulation with an amplitude of only 0. m 025, which is at a low level of detectability (∼2σ). To evaluate the significance of the B − V variation, we performed a χ 2 test by fitting a periodic function (Fourier polynomial), following the scheme proposed by Biazzo et al (2006). Notwithstanding the low amplitude, the B − V modulation turns out to be significant.…”

Section: Photospheric Activity 471 Light Curvementioning

confidence: 99%

The young active star SAO 51891 (V383 Lacertae)

Biazzo

Frasca

Marilli

et al. 2009

A&A

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Aims. The aim of this work is to investigate the surface inhomogeneities of a young, late-type star, SAO 51891, at different atmospheric levels, from the photosphere to the upper chromosphere, analyzing contemporaneous optical high-resolution spectra and broad-band photometry. Methods. The full spectral range of FOCES@CAHA (R 40 000) is used to perform the spectral classification and to determine the rotational and radial velocities. The lithium abundance is measured to obtain an age estimate. The BVRIJHK s photometric bands are used to construct the spectral energy distribution (SED). The variations in the observed BV fluxes and effective temperature are used to infer the presence of photospheric spots and observe their behavior over time. The chromospheric activity is studied applying the spectral subtraction technique to Hα, Ca ii H & K, H , and Ca ii IRT lines.Results. We find SAO 51891 to be a young K0-1V star with a lithium abundance close to the Pleiades upper envelope, confirming its youth (∼100 Myr), which is also inferred from its kinematical membership of the Local Association. No infrared excess is detected from analysis of its SED, limiting the amount of remaining circumstellar dust. We detect a rotational modulation of the luminosity, effective temperature, Ca ii H & K, H , and Ca ii IRT total fluxes. A simple spot model with two main active regions, about 240 K cooler than the surrounding photosphere, fits the observed light and temperature curves very well. The small-amplitude radial velocity variations are also well reproduced by our spot model. The anti-correlation of light curves and chromospheric diagnostics indicates chromospheric plages spatially associated with the spots. The largest modulation amplitude is observed for the H flux suggesting that this line is very sensitive to the presence of chromospheric plages. Conclusions. SAO 51891 is a young active star, lacking significant amounts of circumstellar dust or any evidence of low mass companions, and displays the typical phenomena produced by magnetic activity. The spots are larger and warmer than those in less active main-sequence stars. If some debris is still present around the star, it will only be detectable by future far-infrared and sub-mm observations (e.g., Herschel or ALMA). The RV variation produced by the starspots has an amplitude comparable with those induced by Jupiter-mass planets orbiting close to the host star. SAO 51891 is another good example of an active star in which the detection of planets may be hampered by the high activity level.

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“…Indeed, the relative position and size of ARs at different atmospheric levels can provide information on the magnetic field topology. In the past ten years, rotational modulation due to surface inhomogeneities at photospheric and chromospheric levels has been revealed in several RS CVn binaries (Frasca et al 1998;Catalano et al 2000;Biazzo et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Spots, plages, and flares onλAndromedae and II Pegasi

Frasca¹,

Biazzo²,

Taș

et al. 2007

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155

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Aims. We present the results of a contemporaneous photometric and spectroscopic monitoring of two RS CVn binaries, namely λ And and II Peg. The aim of this work is to investigate the behavior of surface inhomogeneities in the atmospheres of the active components of these systems that have nearly the same temperatures but different gravities. Methods. The light curves and the modulation of the surface temperature, as recovered from line-depth ratios (LDRs), were used to map the photospheric spots, while the Hα emission was used as an indicator of chromospheric inhomogeneities. The spot temperatures and sizes were derived from a spot model applied to the contemporaneous light and temperature curves. Results. We find larger and cooler spots on II Peg (T sp 3600 K) than on λ And (T sp 3900 K); this could be the result of both the difference in gravity and the higher activity level of the former. Moreover, we find a clear anti-correlation between the Hα emission and the photospheric diagnostics (temperature and light curves). We have detected a modulation in the intensity of the He i D 3 line with the star rotation, suggesting surface features also in the upper chromosphere of these stars. A rough reconstruction of the 3D structure of their atmospheres was also performed by applying a spot/plage model to the light and temperature curves and to the Hα flux modulation. In addition, a strong flare affecting the Hα, the He i D 3 , and the cores of Na i D 1,2 lines has been observed on II Peg.Conclusions. The spot/plage configuration has been reconstructed in the visible component of λ And and II Peg, which have nearly the same temperature but very different gravities and rotation periods. A close spatial association of photospheric and chromospheric active regions, at the time of our observations, was found in both stars. Larger and cooler spots were found on II Peg, the system with the active component of higher gravity and a higher activity level. The area ratio of plages to spots seems to decrease when the spots get bigger. Moreover, with both this and literature data, a correlation between the temperature difference ∆T = T ph − T sp and the surface gravity is also suggested.

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Photospheric and chromospheric active regions on three single-lined RS CVn binaries

Cited by 26 publications

References 31 publications

Precise radial velocities of giant stars

Precise radial velocities of giant stars

The young active star SAO 51891 (V383 Lacertae)

Spots, plages, and flares onλAndromedae and II Pegasi

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