10 research outputs found
A new model for heating of Solar North Polar Coronal Hole
This paper presents a new model of North Polar Coronal Hole (NPCH) to study
dissipation/propagation of MHD waves. We investigate the effects of the
isotropic viscosity and heat conduction on the propagation characteristics of
the MHD waves in NPCH. We first model NPCH by considering the differences in
radial as well as in the direction perpendicular to the line of sight
(\textit{los}) in temperature, particle number density and non-thermal
velocities between plumes and interplume lanes for the specific case of
\ion{O}{VI} ions. This model includes parallel and perpendicular (to the
magnetic field) heat conduction and viscous dissipation. Next, we derive the
dispersion relations for the MHD waves in the case of absence and presence of
parallel heat conduction. In the case of absence of parallel heat conduction,
we find that MHD wave dissipation strongly depends on the viscosity for
modified acoustic and Alfven waves. The energy flux density of acoustic waves
varies between and while the energy
flux density of Alfven waves turned out to be between . But, solutions of the magnetoacustic waves show that
the parallel heat conduction introduce anomalous dispersion to the NPCH plasma
wherein the group velocity of waves exceeds the speed of light in vacuum. Our
results suggests all these waves may provide significant source for the
observed preferential accelerating and heating of \ion{O}{VI} ions, in turn
coronal plasma heating and an extra accelerating agent for fast solar wind in
NPCH.Comment: 17 pages, 11 figures, Submitted to MNRA
Observations of Faint Eclipsing Cataclysmic Variables
We present time-resolved photometry of six faint (V>17mag) cataclysmic
variables (CVs); one of them is V849 Oph and the others are identified from the
Sloan Digital Sky Survey (SDSS J0920+0042, SDSS J1327+6528, SDSS J1227+5139,
SDSS J1607.02+3623, SDSS J1457+5148). The optical CCD photometric observations
of these objects were performed at the T\"UB\.ITAK National Observatory
(Turkey) between February 2006 and March 2009. We aimed to detect short time
scale orbital variability arisen from hot-spot modulation, flickering
structures which occur from rapid fluctuations of material transferring from
red star to white dwarf and orbital period changes for selected short-period
(P<4h) CVs at quiescence. Results obtained from eclipse timings and light
curves morphology related to white dwarf stars, accretion disks and hot-spots
are discussed for each system. Analysis of the short time coverage of data,
obtained for SDSS J1227+5139 indicates a cyclical period change arisen from
magnetic activity on the secondary star. Photometric period of SDSS J1607+3623
is derived firstly in this study, while for the other five systems light
elements are corrected using the previous and new photometric observations. The
nature of SDSS J1457+5148 is not precisely revealed that its light curve shows
any periodicity that could be related to the orbital period
Photometric observations and orbital period variations of HS 0705 + 6700 and NY Vir
We present photometric observations of two post-common-envelope stars, NY Vir (=PG 1336-018) and HS 0705 + 6700. The V band CCD observation of NY Vir was performed by a 40 cm telescope at Ege University Observatory and the R band observations of HS 0705 + 6700 were performed by 100 cm telescope at TÜBTAK National Observatory. The new light curves were analyzed by the WD code and the physical parameters of stars were determined. We obtained new mid-eclipse timings for HS 0705 + 6700 and combined them with those previously published data. The analysis of the O-C residuals yields a period of about 8.06 ± 0.28 yr and an amplitude of 98.5 s for the system HS 0705 + 6700, which is attributed to the third star physically bounded to the evolved eclipsing pair. A mass function of 1.2 × 10-4 M? for the third star is obtained. The existence of a third star is also confirmed by the light curve analysis, indicating light contribution of about 0.043 at phase 0.25 in R-bandpass of the eclipsing pair. Using mass-luminosity relationship of the low mass stars we estimate a mass of 0.12 M? with an orbital inclination of about 20°. The O-C residuals obtained for the system NY Vir were represented by a downward parabola which indicates orbital period decrease in the system. Using the coefficient of quadratic term we calculate a rate of orbital period decrease of about dP/dt = -4.09 × 10-8days yr-1. The period decrease we have measured in NY Vir may be explained by angular momentum loss from the binary system. © 2011 Elsevier B.V. All rights reserved.2006/FEN/004The authors thank Ege University observatory for allowing us telescope times. We also thank TÜBİTAK for a partial support using T100 telescope with project number 10CT100-98. This study forms part of the Ph.D. thesis of CMÇ and was supported by the Ege University Research Project (2006/FEN/004). The authors are grateful to Prof. Dr. Ö.L. Deg^irmenci for helping the period variation analysis ( Deg^irmenci, 2011 ). -