Radio frequency interference measurements in Indonesia

We report the first measurements of radio frequency spectrum occupancy performed at sites aimed to host the future radio astronomy observatory in Indonesia. The survey is intended to obtain the radio frequency interference (RFI) environment in a spectral range from low frequency 10 MHz up to 8 GHz. The measurements permit the identification of the spectral occupancy over those selected sites in reference to the allocated radio spectrum in Indonesia. The sites are in close proximity to Australia, the future host of Square Kilometre Array (SKA) at low frequency. Therefore, the survey was deliberately made to approximately adhere the SKA protocol for RFI measurements, but with lower sensitivity. The RFI environment at Bosscha Observatory in Lembang was also measured for comparison. Within the sensitivity limit of the measurement equipment, it is found that a location called Fatumonas in the surrounding of Mount Timau in West Timor has very low level of RFI, with a total spectrum occupancy in this measured frequency range being about 1 %, mostly found at low frequency below 20 MHz. More detailed measurements as well as a strategy for a radio quiet zone must be implemented in the near future.     

A comparison between observed and analytical velocity dispersion profiles of 20 nearby galaxy clusters

We derive analytical expression for the velocity dispersion of galaxy clusters, using the statistical mechanical approach. We compare the observed velocity dispersion profiles for 20 nearby (z≤0.1) galaxy clusters with the analytical ones. It is interesting to find that the analytical results closely match with the observed velocity dispersion profiles only if the presence of the diffuse matter in clusters is taken into consideration. This takes us to introduce a new approach to detect the ratio of diffuse mass, M _diff , within a galaxy cluster. For the present sample, the ratio f=M _diff /M, where M the cluster’s total mass is found to has an average value of 45±12 %. This leads us to the result that nearly 45 % of the cluster mass is impeded outside the galaxies, while around 55 % of the cluster mass is settled in the galaxies.     

Pulsations of the High-Amplitude δ Scuti star YZ Bootis

We present a study on pulsations of the high-amplitudeδScuti star YZ Boo based on photometric observations in Johnson V and R bands with both the Nanshan 1-m telescope of Xinjiang Astronomical Observatory(XAO)and the Xinglong 85-cm telescope of National Astronomical Observatories,Chinese Academy of Sciences(NAOC).Fourier analysis of the light curves reveals the fundamental radial mode and its five harmonics,with the fourth and fifth being newly detected.Thirtynine new times of maximum light are determined from the light curves,and combined with those in the literature,we construct the O-C diagram,derive a new ephemeris and determine a new value for the updated period of 0.104091579(2).In addition,the O-C diagram reveals an increasing rate of period change for YZ Boo.Theoretical models are calculated and constrained with the observationally determined parameters of YZ Boo.The mass and age of YZ Boo are hence derived as M=1.61±0.05 M_⊙ and age=(1.44±0.14)×10~9 yr,respectively.With both the frequency of the fundamental radial mode and the rate of period change,YZ Boo is located at the post main sequence stage.     

The oxygen isotope compositions of olivine in main group (MG) pallasites: New measurements by adopting an improved laser fluorination approach

Oxygen isotope measurements of olivine in main group (MG) pallasites by traditional laser fluorination method are associated with some uncertainties including terrestrial weathering, incomplete olivine reaction, and sample state. We improved our laser fluorination approach by pretreating olivine grains with acid to remove terrestrial weathering products and by modifying the sample holder for an efficient and complete laser reaction. Our experiments on Brahin olivine demonstrate that acid-washing successfully removes the terrestrial weathering with <0.1‰ variation in δ¹⁸O value and, at the same time, improving the ∆¹⁷O value significantly. We also achieved a complete olivine fluorination by employing a custom-designed sample holder with “V”-shaped profile having rounded bottom because incomplete/partial reaction of olivine gives comparatively lighter δ¹⁸O values. Using these new techniques, we present precise triple oxygen isotope data (N = 72) of 25 olivine samples separated from main group pallasites. The data are, on average, ~0.5‰ heavier in δ¹⁸O relative to the values published in the literature for the same samples. Critically, the ∆¹⁷O values of MG pallasites and to some extent their Fo-contents suggest that there are at least two populations of olivine. Based on our improved data set, we propose that MG pallasites potentially have high-∆¹⁷O- and low-∆¹⁷O-bearing subgroups that are statistically distinct. The subgroups present average ∆¹⁷O values of −0.166 ± 0.003 (2SE; N = 16) and −0.220 ± 0.003 (2SE; N = 9), respectively. Furthermore, the high-∆¹⁷O-bearing subgroup samples trend toward lower Fo-contents compared to the other subgroup. Taken together, our data provide evidence that argues against a single parent body origin for MG pallasites.     

Axially Symmetric Bianchi Type-I Bulk-Viscous Cosmological Models with Time-Dependent Λ and q

The present study deals with spatially homogeneous and anisotropic axially symmetric Bianchi type-I cosmological model with time variable cosmological term Λ in the presence of bulk viscous fluid. The Einstein’s field equations are solved explicitly by time varying deceleration parameter q. Consequences of the four cases of phenomenological decay of Λ have been discussed which are consistent with observations. Physical and kinematical parameters of the models are discussed.     

Computation of the structure of a magnetized strange quark star

We have calculated some properties of spin polarized strange quark matter(SQM) in a strong magnetic field at zero temperature using the MIT bag model.We showed that the equation of state of spin polarized SQM is stiffer than that for unpolarized cases.We have also computed the structural properties of a spin polarized strange quark star(SQS) and found that the presence of a magnetic field leads to a more stable SQS when compared to the structural properties of an unpolarized SQS.