Vibrational stability of pre-main sequence stars

Burhan, Mehmet
In this study, vibrational properties and stability of delta-Scuti like pulsating pre-main sequence stars have been investigated. Studies were held in the mass range 2-4 Mo and limited to radial linear adiabatic pulsations. Numerical computations were performed by the oscillation program written by Kırbıyık & Al-Murad (1993). The models were selected to be at the latest phases of the pre-main sequence evolution where the luminosity starts to increase. We have limited our calculations upto the end of the radiative inner regions, since at the surface of the star, our adiabatic perturbation computation does not perfectly fit to the relatively thin non-adiabatic convective envelope of the star. The results of the stability analysis showed that the PMS models undergo an instability whose time period is a function of mass. Instability Strip of pulsating PMS stars was re-drawn with comparison to M. Marconi & F.Palla (1998). The effect of gravitational contraction on stability was also investigated.


X-ray observations of accretion powered pulsars
İnam, Sıtkı Çağdaş; Baykal, Altan; Department of Physics (2004)
In this thesis, X-ray observations of four accretion powered pulsars are presented. Using RXTE observations of 4U 1907+09, we found three new pulse periods of the source. We found that the source spun-down almost at a constant rate of Þ
Frequency-resolved spectroscopy of XB1323-619 using XMM-Newton data: detection of a reflection region in the disc
Balman, Şölen (Oxford University Press (OUP), 2010-09-21)
We present the frequency-resolved energy spectra (FRS) of the low-mass X-ray binary dipper XB1323-619 during persistent emission in four different frequency bands using an archival XMM-Newton observation. FRS method helps to probe the inner zones of an accretion disc. XB1323-619 is an Atoll source and a type-I burster. We find that the FRS is well described by a single blackbody component with kT in a range 1.0-1.4 keV responsible for the source variability in the frequency ranges of 0.002-0.04 and 0.07-0.3...
The effect of rotation, up to second order, on the oscillation frequencies of some delta-scuti stars
Doğan, Gülnur; Kırbıyık, Halil; Department of Physics (2007)
In this work, the effect of rotation on the oscillation frequencies of some radially and nonradially oscillating Delta-Scuti stars have been explored. Rotation has been considered as a perturbation and treated up to the second order. Series of evolutionary models have been calculated for the oscillating stars in question and compared with the observational parameters. Three stars are considered: V350 Peg with no rotation, CC And with a rotational velocity Vsini=20 km/s, and BS Tuc with Vsini=130 km/s. We fi...
RXTE and Chandra observations of galactic microquasars GRO J1655-40 and GRS 1915+105
Bülbül, Gül Esra; Baykal, Altan; Department of Physics (2006)
In this thesis, RXTE timing analysis of Galactic Microquasars GRO J1655-40 and GRS 1915+105, the Chandra and RXTE joint spectral analysis of GRS 1915+105 are presented. We have investigated quasi periodic oscillations (QPOs) in the black hole binaries GRO J1655-40 and GRS 1915+105 observed in 99 and 122 observations made by the Proportional Counter Array (PCA) on board Rossi X-Ray Timing Explorer (RXTE) in both low energy band (2-12 keV) and high energy band (13-27 keV), respectively. Four different X-ray s...
Radial and nonradial oscillations of 44 Tauri
Civelek, R; Kiziloglu, N; Kirbiyik, H (American Astronomical Society, 2001-10-01)
Evolutionary stellar models of 44 Tauri, a multiperiodic delta Scuti star, have been developed theoretically and compared with earlier observational reports. The models depict 44 Tau at the hydrogen-shell-burning stage, when it is in radiative equilibrium with a very thin surface convective layer. Using the models, we performed calculations to obtain radial and nonradial adiabatic oscillation frequencies, and the equations were treated linearly. The results showed that the radial fundamental (6.899 cycles d...
Citation Formats
M. Burhan, “Vibrational stability of pre-main sequence stars,” M.S. - Master of Science, Middle East Technical University, 2004.