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Cool spots on the surface of the active giant PZ Mon

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 نشر من قبل Yury Pakhomov V
 تاريخ النشر 2019
  مجال البحث فيزياء
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Based on the multiband (BVRIJHKL) photometric observations of the active red giant PZ Mon performed for the first time in the winter season of 2017-2018, we have determined the main characteristics of the spotted stellar surface in a parametric three-spot model. The unspotted surface temperature is Teff=4730 K, the temperature of the cool spots is Tspot=3500 K, their relative area is about 41%, and the temperature of the warm spots is Twarm=4500 K with a maximum relative area up to 20%. The distribution of spots over the stellar surface has been modeled. The warm spots have been found to be distributed at various longitudes in the hemisphere on the side of the secondary component and are most likely a result of its influence.



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Based on our photometric observations in 2015-2016 and archival photometric data for the active red giant PZ Mon, we have found the main characteristics of the stellar surface: the unspotted surface temperature Teff=4730K, the spot temperature Tspot= 3500K, and the relative spot area from 30 to 40%. The best agreement with the observations has been achieved in our three-spot model including a cool polar spot with a temperature of about 3500K as well as large and small warm spots with a temperature of about 4500K. The stable polar spot is responsible for the long-period brightness variations. Its presence is confirmed by an analysis of the TiO 7054$~AA$ molecular band. The small-amplitude 34-day variability is attributable to the warm spots located on the side of the secondary component, which determine the relatively stable active longitude.
Analysis of photometric data of the active giant PZ Mon is presented. Using ASAS-3 project data and new more accurate photometry we establish that during 15 years of PZ Mon CCD observations the light curve remains stable, and consequently a longitude of the active spotted area is stable. The small deviations may be explained by differential rotation or inhomogeneous distribution of spots on the active hemisphere of PZ Mon. The stability of the active longitude and its location on the PZ Mon surface indicates on the secondary component as reason of stellar activity.
124 - Heidi Korhonen 2013
The existence of starspots on late-type giant stars in close binary systems, that exhibit rapid rotation due to tidal locking, has been known for more than five decades. Photometric monitoring spanning decades has allowed studying the long-term magne tic activity in these stars revealing complicated activity cycles. The development of observing and analysis techniques that has occurred during the past two decades has also enabled us to study the detailed starspot and magnetic field configurations on these active giants. In the recent years magnetic fields have also been detected on slowly rotating giants and supergiant stars. In this paper I review what is known of the surface magnetism in the cool giant and supergiant stars.
We present new ages and abundance measurements for the pre-main sequence star PZ Tel. PZ Tel was recently found to host a young and low-mass companion. Using FEROS spectra we have measured atomic abundances (e.g. Fe and Li) and chromospheric activity for PZ Tel and used these to obtain metallicity and age estimates for the companion. We find PZ Tel to be a rapidly rotating (vsini=73pm5km/s), ~solar metallicity star (logN(Fe)=-4.37 dex or [Fe/H]=0.05 dex) with a measured mean logRHK of -4.12. We measure a NLTE lithium abundance of logN(Li)=3.1pm0.1dex, which from depletion models gives rise to an age of 7+4-2 Myrs for the system. The measured chromospheric activity returns an age of 26pm2Myrs, as does fitting pre-main sequence evolutionary tracks (Tau_evol=22pm3Myrs), both of which are in disagreement with the lithium age. We speculate on reasons for this difference and introduce new models for lithium depletion that incorporates both rotation and magnetic field affects. We also synthesize solar, metal-poor and metal-rich substellar evolutionary models to better determine the bulk properties of PZ Tel B, showing that PZ Tel B is probably more massive than previous estimates, meaning the companion is not a giant exoplanet. We show how PZ Tel B compares to other currently known age and metallicity benchmark systems and try to empirically test the effects of dust opacity as a function of metallicity on the near infrared colours of brown dwarfs. Current models suggest that in the near infrared observations are more sensitive to low-mass companions orbiting more metal-rich stars. We also look for trends between infrared photometry and metallicity amongst a growing population of substellar benchmark objects, and identify the need for more data in mass-age-metallicity parameter space. [Abridged]
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