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تسجيل مستخدم جديدStability of an active longitude of the giant PZ Mon
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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.
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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.
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.
Two sets of multiple-color ($B, V, R_c, I_c$) light curves of PZ UMa were observed in dependently with the 2.4 meter telescope at the Thai National Observatory and the 1 meter telescope at Yunnan Observatories. The light curves were analyzed with the
Wilson-Devinney program and the two sets of light curves produced consistent results, which show that PZ UMa is a W-subtype contact binary with an extreme mass ratio ($M_{1}/M_{2} = 0.18)$. The basic physical parameters of PZ UMa were determined to be $M_{2} = 0.77(2)M_odot$, $M_{1} = 0.14(1)M_odot$, $R_{2} = 0.92(1)R_odot$, $R_{1} = 0.43(1)R_odot$, $L_{2} = 0.46(2)L_odot$ and $L_{1} = 0.15(3)L_odot$. The orbital period analysis of PZ UMa revealed a 13.22 year periodicity, which implies that there may be a tertiary component orbiting around the binary system. The mass and orbital radius of the tertiary component were calculated to be $M_{3} = 0.88 M_odot$ and $a_{3} = 3.67 AU$, if the orbit was coplanar with the central binary system. It is interesting that the minimum mass of the tertiary was calculated to be $M_{3min} = 0.84 M_odot$, which means the tertiary component is even larger than the primary star and the secondary one of PZ UMa. PZ UMa is a late-type contact binary with stellar activity. The OConnell effect appeared on its light curves when it was observed on April 2016. However, the OConnell effect reversed when the target was observed again on December 2016. The changes of the OConnell effect in such a short time-scale strongly support the occurrence of rapidly changing magnetic activity on this W UMa binary.
This paper describes a multiwavelengh optical study of chromospheres in two X-ray/EUV selected active binary stars with strong H_alpha emission, V789 Mon (2RE J0725-002) and GZ Leo (2RE J1101+223). The goal of the study is to determine radial velocit
ies and fundamental stellar parameters in chromospherically active binary systems in order to include them in the activity-rotation and activity-age relations. We carried out high resolution echelle spectroscopic observations and applied spectral subtraction technique in order to measure emission excesses due to chromosphere. The detailed study of activity indicators allowed us to characterize the presence of different chromospheric features in these systems and enabled to include them in a larger activity-rotation survey. We computed radial velocities of the systems using cross correlation with the radial velocity standards. The double-line spectral binarity was confirmed and the orbital solutions improved for both systems. In addition, other stellar parameters such as: spectral types, projected rotational velocities (vsini), and the equivalent width of the lithium LiI 6707.8 AA absorption line were determined.
Despite frequent references in modern reviews to a seventeenth-century Venetian longitude prize, only a single, circumstantial reference to the alleged prize is known from contemporary sources. Edward Harrisons scathing assessment of the conditions g
overning the award of an alleged Venetian longitude prize simultaneously disparages the rewards offered by the Dutch States General. However, the latter had long run its course by 1696, the year of the citation, thus rendering Harrisons reference unreliable. Whereas other longitude awards offered by the leading European maritime nations attracted applicants from far and wide, often accompanied by extensive, self-published pamphlets, the alleged Venetian prize does not seem to have been subject to similar hype. The alleged existence of seventeenth-century Venetian award is particularly curious, because the citys fortune was clearly in decline, and longitude determination on the open seas does not appear to have been a priority; the citys mariners already had access to excellent portolan charts. It is therefore recommended that authors refrain from referring to a potentially phantom Venetian longitude prize in the same context as the major sixteenth- to eighteenth-century European awards offered by the dominant sea-faring nations.
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