Spot activity on HD 89546 (FG UMa) from long‐term photometry     

O. zdarcan  S. Evren  G.W. Henry 《Astronomische Nachrichten》2012,333(2):138-152

We present the analysis of 20 years of time‐series BV photometry of the SB1 RS CVn binary HD 89546. The system's yearly mean V brightness, the B – V color index, the photometric period, and the light curve amplitude all show clear cyclic variability with an ≈9‐year time scale. We also find some evidence for brightness variability on a time scale longer than the 20‐year time span of our observations, perhaps indicating a longer cycle analogous to the solar Gleissberg cycle. We estimate the unspotted V magnitude of HD 89546 to be 7.^m154, which is ≈0.^m2 brighter than the observed maximum brightness. Spot modelling of the system shows that spot temperature variations affect the observed B – V color as well as the V brightness. Two active longitudes are observed, centered around 180° and 360° longitude on the G9 III primary, each covering a longitude range of 120°. Furthermore, two inactive longitude zones are seen spanning only 60° between the two active longitudes. The longitudinal distribution of the spots exhibits no strong cyclic variability but does show rapid jumps of 120° that look like the flip‐flop phenomenon. We estimate the differential rotation coefficient of the star as k = 0.086 by considering the range of observed photometric period variations and assumed latitudinal spot variations over 45° (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

The statistical analyses of flares detected in B band photometry of UV Ceti type stars     

H.A. Dal  S. Evren 《New Astronomy》2012,17(4):399-410

In this study, we present the unpublished flare data collected from 222 flares detected in the B band observations of five stars and the results derived by statistical analysis and modeling of these data. Six basic properties have been found with a statistical analysis method applied to all models and analyses for the flares detected in the B band observation of UV Ceti type stars. We have also compared the U and B bands with the analysis results. This comparison allowed us to evaluate the methods used in the analyses. The analyses provided the following results. (1) The flares were separated into two types, fast and slow flares. (2) The mean values of the equivalent durations of the slow and the fast flares differ by a factor of 16.2 ± 3.7. (3) Regardless of the total flare duration, the maximum flare energy can reach a different Plateau level for each star. (4) The Plateau values of EV Lac and EQ Peg are higher than the others. (5) The minimum values of the total flare duration increase toward the later spectral types. This value is called the Half-Life value in models. (6) Both the maximum flare rise times and the total flare duration obtained from the observed flares decrease toward the later spectral types.  相似文献   

Comparative Evaluation for Characterization of Produced Water Generated from Oil,Gas, and Oil–Gas Production Fields     

Hale Ozgun  Mustafa Evren Ersahin  Selime Erdem  Burcu Atay  Sema Sayili  Esra Eren  Pelin Hoshan  Doga Atay  Mahmut Altinbas  Cumali Kinaci  Ismail Koyuncu 《洁净——土壤、空气、水》2013,41(12):1175-1182

A reliable wastewater characterization is a prerequisite for the selection of an acceptable treatment strategy for produced water which exhibits significant differences due to the varied kinds of wells, seasonal changes, and formation types. A complete characterization of produced water generated from oil, gas, and oil–gas fields in Turkey was performed based on seasonal and locational variations. The results showed that the produced water generated from oil field wells was highly polluted and wastewater volume was higher in comparison to gas and oil–gas field wells. Besides, the characterization of produced water was varying in a wide range based on seasonal and locational variations. Useful relationships were observed between chloride, sodium, bromide, and total dissolved solids concentrations. The results can be used in the design, operation, and optimization of wastewater treatment systems of petroleum and oil industries for future studies.  相似文献   

Beachrock as evidence of sea-level lowstand during the classical period,Parion antique city,Marmara Sea,Turkey     

Ahmet Evren Erginal 《Geodinamica Acta》2013,26(1-2):96-103

Results obtained from beachrock lying on the north coast of the antique city of Parion in Çanakkale province, NW Turkey, are presented based on field data, petrographic analyses, cement fabrics, and radiocarbon dating. Extending to 20?m offshore at a depth of ?2?m, the studied 50-cm thick beachrock is poorly sorted lithic sandstone. Both exposed and submerged parts are characterized by sequentially precipitated marine phreatic and vadose cements composed of micrite encrustations with micro-organism borings, pseudopeloidal aggregates of high-Mg calcites with scalenohedral habits and meniscus bridges. Radiocarbon ages point to a deposition during the classical period when the sea level was below (between ?1 and ?1.5?m) that of the present. The beachrock witnesses a granule- and pebble-dominated wide beach prior to cementation, suggesting that Parion’s fortification walls were behind the coastline during this lowstand and raises questions concerning the existence of a harbor north of the city.  相似文献   

Investigation of the nature of slip surface using geochemical analyses and 2-D electrical resistivity tomography: a case study from Lapseki area, NW Turkey     

Ahmet Evren Erginal  Beyhan Öztürk  Yunus Levent Ekinci  Alper Demirci 《Environmental Geology》2009,58(6):1167-1175

The nature and subsurface structure of the slip surface of a landslide was studied on the basis of geochemical analyses and 2-D electrical resistivity tomography (ERT) survey. Head scarp and lateral slip surfaces of the landslide marked by clear slickensided shear planes were composed of the average amounts of clayey silt (32.5%) and sand (67.5%). Energy dispersive X-ray spectroscopy (EDX) data revealed the enrichment of Si (23.24%), Fe (12.2%), Al (9.51%) and C (8.34%) in the elemental composition of the disturbed slip surface. From X-ray diffractometry (XRD) data, six main clay types were determined, such as Volkonskoite, Halloysite, Ferrosilite, Saponite, Illite and Nontronite. The ERT survey displayed that the landslide developed as a reactivation on the upper part of an old landslide body.  相似文献   

B,V photometry of the active RS CVn system II Peg     

S. Evren 《Astrophysics and Space Science》1988,143(1):123-136

In this work,B andV photometry of the RS CVn-type binary II Peg is presented. The light curves obtained in 1983 and 1984 display two unequal maxima. The light curves of the system have different amplitudes. The amplitude seems to vary with three different periods. 10, 6, and 4 years of periods may be attributed to those variations.  相似文献   

VZ CVn: a close binary system with γ Doradus-like variations     

C. &#;banolu  G. Ta&#;  E. Sipahi  S. Evren 《Monthly notices of the Royal Astronomical Society》2007,376(2):573-579

We present new photometric two-colour observations of the double-lined close binary star VZ CVn. Combining two data sets obtained in 1971–72 and in 2006, the physical parameters of both components were derived. After removing the light variations due to the eclipses and proximity effects, a periodic variation in the more massive component with a dominant period of 1.068 76 d could be detected in the first photometric data set. In accordance with its position on the Hertzsprung–Russell diagram and both its pulsation period and pulsation constant of 0.62 d, the primary component of VZ CVn should be an excellent γ Doradus candidate. The less massive secondary component seems to have smaller radius with respect to its mass. Both components appear to have lower luminosities with respect to their masses; hence, their radiative properties seem to be different. The evolutionary status of the components is also discussed.  相似文献   

Short-term amplitude variation of FM COM (=HR 4684)     

M. Pararó  J. Pena  R. Peniche  C. Ibanoglu  Z. Tunca  S. Evren 《Astrophysics and Space Science》1993,210(1-2):185-187

Using unpublished data obtained in 1982 at Mexico and Turkey combined with Hungarian observations the process of amplitude variation of the frequency at 18.5 c/d is shown. The time scale of the amplitude increase is less than 100 days.  相似文献   

One of the first members of RS CVn‐type systems: MM Herculis     

G. Ta  S. Evren 《Astronomische Nachrichten》2013,334(3):251-263

We present the long‐term multi‐colour photometry of MM Her which is one of the first members of the RS CVn‐type of eclipsing binary systems. We took advantage of its photometry‐spanning 33 years to evaluate its long‐term variation, which is caused by the evolution of the activity structures located on the surface of the cooler component. In this study we found that the long‐term variation in the brightness, colour, and amplitude of seasonal light curves over the years could be represented by two periods: one of which is of around 22.5 years, and is similar to all in this regard, but the other is a period value of about 9.5 years for the brightness variation, and of about 7.5 years for the variation in colour and amplitude. The analysis of the spot minimum phases gives a migration period of approximately 7.8 years. We also presented a new light curve analysis solution, and improved its light elements in this study. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

BV photometry of quadrupole system ET Bootis     

O. Özdarcan  S. Evren 《New Astronomy》2012,17(7):610-615

In this study, we present the first Johnson BV photometry of the eclipsing binary star ET Bootis, which is member of a physically connected visual pair. Analysis of times of light minima enables us to calculate accurate ephemeris of the system via O–C analysis and observed an increase in period which we believe is a result of the light-time effect in the outer visual orbit. Secondly, we determined the total brightness and color of the system in light maxima and minima. Photometric solution of the system indicates that the contribution of the visual pair to the total light is about 40% in Johnson V band. Furthermore, photometric analysis shows that the primary star in the eclipsing binary has F8 spectral type while it confirms the G5 spectral type for the visual pair. Masses of the components in eclipsing binary are M₁ = 1.109 ± 0.014 M_⊙ and M₂ = 1.153 ± 0.011 M_⊙. Absolute radii of the components are R₁ = 1.444 ± 0.007 R_⊙ and R₂ = 1.153 ± 0.007 R_⊙. Physical properties of the components leads 176 ± 7 pc distance for the system and suggests an age of 6.5 billion years.  相似文献