The Catania Automatic Photoelectric Telescope on Mt. Etna: asystematic study of magnetically active stars

Rodonò, M.; Cutispoto, G.; Lanza, A. F.; Messina, S.

doi:10.1002/1521-3994(200112)322:5/6<333::aid-asna333>3.0.co;2-6

Cited by 18 publications

(17 citation statements)

References 16 publications

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“…As soon as the current photometric monitorings (e.g. Rodonò et al 2002;Messina & Guinan 2002) make available the more numerous and longer-term photometric data sets for F-, K-and M-type stars, we will be in the position to check the validity of our assumption. However, at present we cannot say if the dependence of the efficiency of the coronal heating mechanism on the spectral type is effective or if it depends on the prevailing type (uniform or asymmetric) of distribution of spotted regions in the photosphere, which may as well be spectral-type dependent.…”

Section: Discussionmentioning

confidence: 99%

Dependence of coronal X-ray emission on spot-induced brightness variations in cool main sequence stars

Messina

Pizzolato²,

Guinan³

et al. 2003

A&A

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Abstract.The maximum amplitude (A max ) of spot-induced brightness variations from long-term V-band photometry and the ratio L X /L bol between X-ray and bolometric luminosities are suitable indicators of the level of magnetic activity in the photosphere and in the corona of late-type stars, respectively. By using these activity indicators we investigate the dependence of coronal X-ray emission on the level of photospheric starspot activity in a homogeneous sample of low mass main sequence field and cluster stars of different ages (IC 2602, IC 4665, IC 2391, α Persei, Pleiades and Hyades). First, the activity-rotation connection at the photospheric level is re-analysed, as well as its dependence on spectral type and age. The upper envelope of A max increases monotonically with decreasing rotational period (P) and Rossby number (R 0 ) showing a break around 1.1 d that separates two rotation regimes where the starspot activity shows different behaviours. The A max -P and A max -R 0 relations are fitted with linear, exponential and power laws to look for the function which best represents the trend of the data. The highest values of A max are found among K-type stars and at the ages of α Persei and Pleiades. We also analyse the activity-rotation connection at the coronal level as well as its dependence on spectral type. The level of X-ray emission increases with increasing rotation rate up to a saturation level. The rotational period at which saturation occurs is colour-dependent and increases with advancing spectral type. Also the L X /L bol -P and L X /L bol -R 0 relations are fitted with linear, exponential and power laws to look for the best fitting function. Among the fastest rotating stars (P ≤ 0.3 d) there is evidence of super-saturation. Also the highest values of L X /L bol are found among K-type stars. Finally, the photospheric-coronal activity connection is investigated by using for the first time the largest ever sample of light curve amplitudes as indicators of the magnetic filling factor. The activity parameters L X /L bol and A max are found to be correlated with each other, thus confirming the dependence of coronal activity on photospheric magnetic fields. More precisely, the L X /L bol -A max distribution shows the presence of an upper envelope, which is constant at the L X /L bol −3.0 saturation level, and of a lower envelope. The best fit to the lower envelope is given by a power law with steepness decreasing from F-G to M spectral types. However, it is considered a tentative result, since the fit reduced chi-squares are large. Such spectral-type dependence may be related to a colour dependence of A max on the total starspot filling factor, as well as to the coronal emission being possibly more sensitive to starspot activity variations in F-and G-type than in M-type stars. The L X /L bol -A max mean values for each cluster in our sample decrease monotonically with increasing age, showing that the levels of photospheric and coronal activity evolve in time according to a single power law till the S...

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Section: Discussionmentioning

confidence: 99%

Dependence of coronal X-ray emission on spot-induced brightness variations in cool main sequence stars

Messina

Pizzolato²,

Guinan³

et al. 2003

A&A

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“…The photometric precision of the V-band data of the Phoenix-25 APT is about 0.01 mag, whereas that of the Catania APT-80 is about 0.005 mag. The instrumental equipments and observational strategies of our APTs are described by Rodonò et al (2000) and Rodonò et al (2001).…”

Section: The Photometric Data Setmentioning

confidence: 99%

Long-term starspot evolution, activity cycle, and orbital period variation of V711 Tauri (HR 1099)

Lanza

Piluso

Rodonò

et al. 2006

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The long-term optical photometry of V711 Tau (HR 1099) from 1975 to 2001 is analysed with different techniques to provide information on the activity of this widely studied RS CVn-type binary. Pooled variance analysis gives a characteristic timescale of evolution for the photospheric pattern of starspots of the order of 100-200 days, while periodogram analysis of seasonal photometric data reveals that the rotational modulation period is 2.837 ± 0.094 d, without significant changes during the 26 analysed years. Considering subsets of the entire data sequence along which the rotational modulation of the optical flux stays stable, a set of 66 light curves is obtained. They are modelled by means of inversion techniques based on Maximum Entropy and Tikhonov regularizations to derive the distributions in longitude and the total amount of the spotted area on the more luminous K1 IV component that dominates the optical variability of the system. An extensive comparison with published Doppler Imaging maps shows the advantages and drawbacks of inversion techniques based solely on optical photometry. The large-scale structure of the longitudinal distribution of the spotted area is correctly reproduced, although individual starspots revealed by Doppler Imaging cannot be detected because of the limited spatial resolution of the photometric imaging. On the other hand, the variation of the total spotted area is best reconstructed from optical photometry and shows an activity cycle with a period of 19.5 ± 2.0 yr, upon which a short-term modulation might be superposed having variable amplitude and phase and a mean duration of approximately 3-5 years. The distributions of the spotted area versus longitude show the presence of one dominant preferential longitude from 1975 to 1989; afterwards, two preferential longitudes with comparable spotted areas are detected. Their migration rates with respect to the orbital reference frame are variable versus time, possibly as a consequence of a variable drift rate of the respective non-axisymmetric dynamo modes. The variation of the orbital period of the system appears to be correlated with the magnetic activity of the K1 IV component. Specifically, the decrease of the orbital period that occurred around 1990 coincides with a re-configuration of the stellar magnetic field, as indicated by the simultaneous variation of its different proxies. In combination with previous studies, these results allow us to discriminate among different theoretical models proposed to explain the connection between magnetic activity and orbital dynamics.Key words. stars: activity -stars: starspots -stars: magnetic fields -stars: late-type -stars: binaries: spectroscopicstars: individual: V711 Tauri -stars: individual: HR 1099 IntroductionV711 Tauri (HR1099, HD 22468) is one of the most extensively studied members of the RS CVn class of magnetically active close binaries. It is a detached, non-eclipsing SB2 system, consisting of a K1 subgiant star, filling about 80% of its Roche lobe, and a G5 dwarf star on...

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“…We also performed a new search for starspot cycles. In fact, we considered the most recent photometry presented by Berdyugina et al (2002 and references therein) and that collected by the APT80 telescope of Catania Astrophysical Observatory (Rodonò et al 2001;Messina et al 2002), which were not yet taken into account in previous starspot cycle studies. Three starspot cycles were found: P cyc1 = 3.2 ± 0.1 yr, P cyc2 = 6.2 ± 0.3 yr, P cyc3 = 11.4 ± 0.4 yr.…”

Section: Periodogramsmentioning

confidence: 99%

Magnetic activity of six young solar analogues II. Surface Differential Rotation from long-term photometry

Messina

Guinan²

2003

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127

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Abstract. The present paper is the second of a series dedicated to the study of the magnetic activity in a selected sample of young solar analogues. The sample includes five single G0-G5V stars with ages between 130 Myr and 700 Myr: EK Dra, π 1 UMa, HN Peg, k 1 Cet and BE Cet. In this study we also include the Pleiades-age ( 130 Myr) K0V star DX Leo. Our analysis is based on high precision photometric observations carried out as part of The Sun in Time project, aimed at a multiwavelength study of stars with solar-like global properties, but with different ages and thus at different stages of evolution. In the first paper of this series we presented the photometric observations and determined the existence of starspot cycles and their correlation with the global stellar properties. In the present paper we investigate the surface differential rotation (SDR). The periodogram analysis of the photometric data time series has allowed us to determine the rotational periods and to derive the following results: i) all the selected stars show variations of the rotational period. Such variations are definitely periodic and in phase with the starspot cycle for BE Cet and DX Leo. They are likely periodic and in phase also for π 1 UMa, EK Dra and HN Peg, but still need confirmation. By analogy with the solar butterfly diagram, the rotational period variations are interpretable in terms of surface differential rotation, that is, they are attributable to the existence of active latitude belts migrating during the activity cycle on a differentially rotating star; ii) BE Cet, π 1 UMa and EK Dra show a solar-like pattern of SDR, that is the rotational period steadily decreases along the activity cycle, jumping back to higher values at the beginning of the next cycle; on the contrary, DX Leo, k 1 Cet and HN Peg show an antisolar pattern; iii) the amplitude of the rotational period variations shows a power law dependence on the rotational period similar to that found in previous studies. Contrary to theoretical predictions, the cycle length is not correlated to the Dynamo number, it is indeed positively correlated to the SDR amplitude. More precisely, stars tend to concentrate along three different branches with the cycle length increasing with increasing ∆Ω/Ω. Moreover, we found that the SDR amplitude changes from cycle to cycle, which is reminiscent of a wave of excess rotation propagating in latitude; iiii) the apparently different solar and antisolar behaviours are probably due to different inclinations of the stellar rotation axis under which the star is seen. The long-term photometry of the young single star LQ Hya, although not included in the initial project, is also used in the present analysis to enlarge the investigated sample. We determined for LQ Hya three different starspot cycles and an antisolar pattern of SDR.

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The Catania Automatic Photoelectric Telescope on Mt. Etna: asystematic study of magnetically active stars

Cited by 18 publications

References 16 publications

Dependence of coronal X-ray emission on spot-induced brightness variations in cool main sequence stars

Dependence of coronal X-ray emission on spot-induced brightness variations in cool main sequence stars

Long-term starspot evolution, activity cycle, and orbital period variation of V711 Tauri (HR 1099)

Magnetic activity of six young solar analogues II. Surface Differential Rotation from long-term photometry

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