45,769 research outputs found
The temporal changes of the pulsational periods of the pre-white dwarf PG 1159-035
PG 1159-035, a pre-white dwarf with T=140000 K, is the prototype of the
PG1159 spectroscopic class and the DOV pulsating class. Changes in the star
cause variations in its oscillation periods. The measurement of temporal change
in the oscillation periods, dP/dt, allows us to estimate directly rates of
stellar evolutionary changes, such as the cooling rate and the envelope
contraction rate, providing a way to test and refine evolutionary models for
pre-white dwarf pulsating stars.
We measured 27 pulsation modes period changes. The periods varied at rates of
between 1 and 100 ms/yr, and several can be directly measured with a relative
standard uncertainty below 10%. For the 516.0 s mode (the highest in amplitude)
in particular, not only the value of dP/dt can be measured directly with a
relative standard uncertainty of 2%, but the second order period change,
d(dP/dt)/dt, can also be calculated reliably. By using the (O-C) method we
refined the dP/dt and estimated the d(dP/dt)/dt for six other pulsation
periods. As a first application, we calculated the change in the PG 1559-035
rotation period, dP_rot/dt = -2.13*10^{-6} s/s, the envelope contraction rate
dR/dt = -2.2*10^{-13} solar radius/s, and the cooling rante dT/dt =
-1.42*10^{-3} K/s.Comment: 8 pages; 2 figures; 2 tables; appendix with 2 table
Low mass variable stars in the globular cluster NGC 6397
We have conducted a photometric survey of the globular cluster NGC 6397 in a
search for variable stars. We obtained ~11h of time-resolved photometric images
with one ne European Southern Observatory-Very Large Telescope using the FOcal
Reducer and low dispersion Spectrograph imager distributed over two consecutive
nights. We analyzed 8391 light curves of stars brighter than magnitude 23 with
the 465 nm-filter, and we identified 412 variable stars, reaching ~ 4.8 +- 0.2
per cent of variability with timescales between 0.004 and 2d, with amplitudes
variation greater than +- 0.2 mag.Comment: 9 figures, complementary dat
The pulsation modes of the pre-white dwarf PG 1159-035
Context. PG 1159-035, a pre-white dwarf with T_(eff) ≃ 140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star.
Aims. We have three principal aims: to increase the number of detected and identified pulsation modes in PG 1159-035, study trapping of the star's pulsation modes, and to improve or constrain the determination of stellar parameters.
Methods. We used all available WET photometric data from 1983, 1985, 1989, 1993 and 2002 to identify the pulsation periods.
Results. We identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M/M_⊙ = 0.59 ± 0.02 for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at r_c/R_* = 0.83 ± 0.05. From the multiplet splitting, we calculated the rotational period P_(rot) = 1.3920 ± 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for ℓ = 1 modes and less than 50% for ℓ = 2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars
Probing Mass Segregation in NGC 6397
In this study, we present a detailed study of mass segregation in the
globular clister NGC 6397. First, we carry out a photometric analysis of
projected ESO-VLT data (between 1 and 10 arcmin from the cluster centre),
presenting the luminosity function corrected by completeness. The luminosity
function shows a higher density of bright stars near the central region of the
data, with respect to the outer region. We calculate a deprojected model
(covering the whole cluster) estimating a total number of stars of 193000 +-
19000. The shapes of the surface brightness and density-number profiles versus
the radial coordinate r (instead of the projected coordinate R) lead to a
decreasing luminosity for an average star, and thus of mass, up to 1 arcmin,
quantifying the mass segregation. The deprojected model does not show evidence
of mass segregation outside this region
On the equivalence of Lambda(t) and gravitationally induced particle production cosmologies
The correspondence between cosmological models powered by a decaying vacuum
energy density and gravitationally induced particle production is investigated.
Although being physically different in the physics behind them we show that
both classes of cosmologies under certain conditions can exhibit the same
dynamic and thermodynamic behavior. Our method is applied to obtain three
specific models that may be described either as Lambda(t)CDM or gravitationally
induced particle creation cosmologies. In the point of view of particle
production models, the later class of cosmologies can be interpreted as a kind
of one-component unification of the dark sector. By using current type Ia
supernovae data, recent estimates of the cosmic microwave background shift
parameter and baryon acoustic oscillations measurements we also perform a
statistical analysis to test the observational viability within the two
equivalent classes of models and we obtain the best-fit of the free parameters.
By adopting the Akaike information criterion we also determine the rank of the
models considered here. Finally, the particle production cosmologies (and the
associated decaying Lambda(t)-models) are modeled in the framework of field
theory by a phenomenological scalar field model.Comment: 9 pages, 3 figures, new comments and 8 references added. Accepted for
publication in Physics Letters
Efficiency of low versus high airline pressure in stunning cattle with a pneumatically powered penetrating captive bolt gun
The efficiency of stunning cattle was assessed in 443 animals (304 pure Zebu and 139 crossbred cattle), being mainly mature bulls and cows. Cattle were stunned using a Jarvis pneumatically powered penetrating captive bolt gun operating with low (160–175 psi, N = 82) and high (190 psi, N = 363) airline pressure, which was within the manufactures specifications. Signs of brain function and the position of the shots on the heads were recorded after stunning. Velocity of the captive bolt and its physical parameters were calculated. Cattle shot with low pressures showed more rhythmic respiration (27 vs. 8%, P < 0.001), less tongue protrusion (4 vs. 12%, P = 0.03) and less masseter relaxation (22 vs. 48%, P < 0.001). There was an increased frequency of shots in the ideal position when cattle were shot with the low compared to high airline pressures (15.3 vs. 3.1%). Bolt velocity and its physical parameters were significantly (P < 0.01) higher when using high pressure. Airline pressures below 190 psi are inappropriate when shooting adult Zebu beef cattle with pneumatically powered penetrating captive bolt guns
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