Pregalactic-primordial low-mass stars

Kızıloğlu, Nilgün Gülşan
Eryurt, Dilhan Ezer
The Main-Sequence positions as well as the evolutionary behavior of Population III stars up to an evolution age of 2×1010 yr, taking this time as the age of the Universe, have been investigated in the mass range 0.2 and 0.8M ⊙. While Population III stars with masses greater than 0.3M ⊙ develop a radiative core during the approach to the Main Sequence, stars with masses smaller than 0.3M ⊙ reach the Main Sequence as a wholly convective stars. Population III stars with masses greater than 0.5M ⊙ show a brightening of at most 2.2 in bolometric magnitude when the evolution is terminated as compared to the value which corresponds to zero-age Main Sequence. The positions of stars with masses smaller than 0.5M ⊙ remain almost the same in the H-R diagram. If Population III stars have formed over a range of redshifts, 6<Z<1500, the original starlight of low-mass Population III stars could now be the part of infrared and/or microwave background spectrum between 7 and 1400 μm.
Astrophysics and Space Science


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...
Pre-Main-Sequence evolution of rotating low-mass stars
Kızıloğlu, Nilgün (Springer Science and Business Media LLC, 1989-4)
The evolutionary behaviour of rotating low-mass stars in the mass range 0.2 and 0.9M ⊙ has been investigated during the pre-Main-Sequence phase. The angular momentum is conserved locally in radiative regions and totally in convective regions, according to a predetermined angular velocity distribution depending on the structure of the star. As the stars contract toward the zero-age Main Sequence, they spin up under the assumption that the angular momentum is conserved during the evolution of the stars. When ...
Instability of radial oscillations of Wolf-Rayet star models
Kırbıyık, Halil (Springer Science and Business Media LLC, 1987)
By taking some evolutionary models of an initially 60M ⊙-star, their radial vibrational stabilities have been investigated. These models, evolving with mass loss, are in the advanced stages of their evolution, and burn He in their cores. Calculations have been performed for the first and second harmonics as well as for the fundamental mode; and some of these models were found to be vibrationally unstable in the fundamental mode.
Asteroseismic investigation of 44 Tau, a slowly rotating delta Scuti star
Kirbiyik, H; Civelek, R; Kiziloglu, N (Springer Science and Business Media LLC, 2003-01-01)
Evolutionary model calculations of 44 Tau, a delta-Scuti star, have been carried out. The star in question is a slow rotator (vsini = 6.8 kms(-1)). However small it may be, the effect of rotation on the oscillation properties of the star was thought to be worth of studying. Models were evolved with uniform rotation. Radial and non-radial adiabatic oscillation frequencies were calculated. In determining oscillation frequencies rotation has been treated as a perturbation. First order effect has been considere...
Age determination of the open cluster NGC 2287 (M41)
Küçük, İbrahim; Eryurtezer, Dilan (Springer Science and Business Media LLC, 1988)
We have estimated the age of the open cluster NGC 2287 (M41) by taking into account the rotation of the member stars. TheUBV photoelectric measurement values were taken from Eggen (1974). Besides the Main-Sequence stars this cluster has seven red giants, all of them above the turn-off point. Having obtained the theoretical Hertzsprung-Russell diagram from observed colour-magnitude diagram, we have discussed two methods, given in the literature, to estimate the age of the cluster under consideration. The f...
Citation Formats
N. G. Kızıloğlu and D. E. Eryurt, “Pregalactic-primordial low-mass stars,” Astrophysics and Space Science, pp. 83–90, 1987, Accessed: 00, 2020. [Online]. Available: