7,082 research outputs found
Utilizing the Updated Gamma-Ray Bursts and Type Ia Supernovae to Constrain the Cardassian Expansion Model and Dark Energy
We update gamma-ray burst (GRB) luminosity relations among certain spectral
and light-curve features with 139 GRBs. The distance modulus of 82 GRBs at
can be calibrated with the sample at by using the cubic
spline interpolation method from the Union2.1 Type Ia supernovae (SNe Ia) set.
We investigate the joint constraints on the Cardassian expansion model and dark
energy with 580 Union2.1 SNe Ia sample () and 82 calibrated GRBs data
(). In CDM, we find that adding 82 high-\emph{z} GRBs to
580 SNe Ia significantly improves the constrain on
plane. In the Cardassian expansion model, the
best fit is and
, which is consistent with the CDM cosmology in the
confidence region. We also discuss two dark energy models in which
the equation of state is parametrized as and
, respectively. Based on our analysis, we see that our
Universe at higher redshift up to is consistent with the concordance
model within confidence level.Comment: 17 pages, 6 figures, 2 tables; accepted for publication in Advances
in Astronomy, special issue on Gamma-Ray Burst in Swift and Fermi Era. arXiv
admin note: text overlap with arXiv:0802.4262, arXiv:0706.0938 by other
author
Color Behavior Of BL Lacertae Object OJ 287 During Optical Outburst
This paper aims to study the color behavior of the BL Lac object OJ 287
during optical outburst. According to the revisit of the data from the OJ-94
monitoring project and the analysis the data obtained with the 60/90 cm Schmidt
Telescope of NAOC, we found a bluer-when-brighter chromatism in this object.
The amplitude of variation tends to decrease with the decrease of frequency.
These results are consistent with the shock-in-jet model. We made some
simulations and confirmed that both amplitude difference and time delay between
variations at different wavelengths can result in the phenomenon of
bluer-when-brighter. Our observations confirmed that OJ 287 underwent a
double-peaked outburst after about 12 years from 1996, which provides further
evidence for the binary black hole model in this object.Comment: 25 pages, 13 figure
Determination of fundamental properties of an M31 globular cluster from main-sequence photometry
M31 globular cluster B379 is the first extragalactic cluster, the age of
which was determined by main-sequence photometry. In this method, the age of a
cluster is obtained by fitting its CMD with stellar evolutionary models.
However, different stellar evolutionary models use different parameters of
stellar evolution, such as range of stellar masses, different opacities and
equations of state, and different recipes, and so on. So, it is interesting to
check whether different stellar evolutionary models can give consistent results
for the same cluster. Brown et al. (2004a) constrained the age of B379 by
comparing its CMD with isochrones of the 2006 VandenBerg models. Using SSP
models of BC03 and its multi-photometry, Ma et al. (2007) independently
determined the age of B379, which is in good agreement with the determination
of Brown et al. (2004a). The BC03 models are calculated based on the Padova
evolutionary tracks. It is necessary to check whether the age of B379 which,
being determined based on the Padova evolutionary tracks, is in agreement with
the determination of Brown et al. (2004a). So, in this paper, we re-determine
its age using isochrones of the Padova stellar evolutionary models. In
addition, the metal abundance, the distance modulus, and the reddening value
for B379 are also determined in this paper. The results obtained in this paper
are consistent with the previous determinations, which including the age
obtained by Brown et al. (2004a). So, this paper confirms the consistence of
the age scale of B379 between the Padova isochrones and the 2006 VandenBerg
isochrones, i.e. the results' comparison between Brown et al. (2004a) and Ma et
al. (2007) is meaningful. The results obtained in this paper are: the
metallicity [M/H]=-0.325, the age Gyr, the reddening value
E(B-V)=0.08, and the distance modulus .Comment: Accepted for Publication in PASP, 7 pages, 1 figure and 1 tabl
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