61 research outputs found

    Pulsations in main sequence OBAF-type stars

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    CONTEXT: The third Gaia data release provides photometric time series covering 34 months for about 10 million stars. For many of those stars, a characterisation in Fourier space and their variability classification are also provided. This paper focuses on intermediate- to high-mass (IHM) main sequence pulsators (M ≥  1.3 M⊙) of spectral types O, B, A, or F, known as β Cep, slowly pulsating B (SPB), δ Sct, and γ Dor stars. These stars are often multi-periodic and display low amplitudes, making them challenging targets to analyse with sparse time series. AIMS: We investigate the extent to which the sparse Gaia DR3 data can be used to detect OBAF-type pulsators and discriminate them from other types of variables. We aim to probe the empirical instability strips and compare them with theoretical predictions. The most populated variability class is that of the δ Sct variables. For these stars, we aim to confirm their empirical period-luminosity (PL) relation, and verify the relation between their oscillation amplitude and rotation. METHODS: All datasets used in this analysis are part of the Gaia DR3 data release. The photometric time series were used to perform a Fourier analysis, while the global astrophysical parameters necessary for the empirical instability strips were taken from the Gaia DR3 gspphot tables, and the v sin i data were taken from the Gaia DR3 esphs tables. The δ Sct PL relation was derived using the same photometric parallax method as the one recently used to establish the PL relation for classical Cepheids using Gaia data. RESULTS: We show that for nearby OBAF-type pulsators, the Gaia DR3 data are precise and accurate enough to pinpoint them in the Hertzsprung-Russell (HR) diagram. We find empirical instability strips covering broader regions than theoretically predicted. In particular, our study reveals the presence of fast rotating gravity-mode pulsators outside the strips, as well as the co-existence of rotationally modulated variables inside the strips as reported before in the literature. We derive an extensive period–luminosity relation for δ Sct stars and provide evidence that the relation features different regimes depending on the oscillation period. We demonstrate how stellar rotation attenuates the amplitude of the dominant oscillation mode of δ Sct stars. CONCLUSIONS: The Gaia DR3 time-series photometry already allows for the detection of the dominant (non-)radial oscillation mode in about 100 000 intermediate- and high-mass dwarfs across the entire sky. This detection capability will increase as the time series becomes longer, allowing the additional delivery of frequencies and amplitudes of secondary pulsation modes

    We are legitimate, what about our rights?: The moratorium on logging and the legitimate logging companies contractual rights

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    The study examined whether the moratorium on logging deprives the legitimate players of the logging industry of their contractual rights. Using the non-impairment clause of contracts, involvement of national interest and exercise of police power as sub-issues, the study concludes that there is no deprivation of contractual rights in the issuance of the moratorium on logging. It is highly recommended that there ne uniformity in implementing Executive Order no. 23, urge the DENR to hasten the review of all forest agreements/contracts, and provide alternative sources of livelihood to laid off workers

    Dual-band and single CPW port and planar-slot antenna

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    Band-pass Distributed Power Amplifier in Monolithic Technology for the LTE Band

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    The design and simulated performance of a bandpass MMIC distributed power amplifier to cover the LTE uplink are described. Small- and large-signal simulations have been carried out to evaluate the amplifier's behaviour. Results suggest that the designed amplifier might cover the LTE specifications. The simulated amplifier performance obtained through electromagnetic simulation is encouraging for a future physical implementation. © 2012 IEEE
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