Abstract
Four ultraluminous infrared galaxies (ULIRGs) observed with JWST/NIRcam in the Cosmos Evolution Early Release Science program offer an unbiased preview of the
z
∼ 2 ULIRG population. The ...objects were originally selected at 24
μ
m and have strong polycyclic aromatic hydrocarbon emission features observed with Spitzer/Infrared Spectrometer. The four objects have similar stellar masses of ∼10
11
M
⊙
but otherwise are quite diverse. One is an isolated disk galaxy, but it has an active nucleus as shown by X-ray observations and by a bright point-source nucleus. Two others are merging pairs with mass ratios of 6–7:1. One has active nuclei in both components, while the other has only one active nucleus: the one in the less-massive neighbor, not the ULIRG. The fourth object is clumpy and irregular and is probably a merger, but there is no sign of an active nucleus. The intrinsic spectral energy distributions for the four active galactic nuclei in these systems are typical of type-2 QSOs. This study is consistent with the idea that even if internal processes can produce large luminosities at
z
∼ 2, galaxy merging may still be necessary for the most luminous objects. The diversity of these four initial examples suggests that large samples will be needed to understand the
z
∼ 2 ULIRG population.
In this paper, the high-precision light curves of the Kepler target KIC 5950759 are analyzed. The Fourier analysis of the long cadence (LC) light curve reveals three independent frequencies. Two of ...them are main pulsation modes: F0 = 14.221373(21) d−1 and F1 = 18.337249(44) d−1. The third independent frequency, fm = 0.3193 d−1, is found in LC data with a signal-to-noise ratio of 6.2. A weak modulation of fm to F0 and F1 modes (triplet structures centered on F0 and F1) are detected both in long and short cadence data. This is the first detection of the modulation effect in a double-mode high-amplitude δ Scuti (HADS) star. The most possible cause of the modulation effect in the light curves is amplitude modulation with the star's rotation frequency of 0.3193 d−1. The preliminary analysis suggests that KIC 5950759 is in the bottom of the HADS instability strip and likely situated in the main sequence. Spectroscopic observations are necessary to verify the true nature of the modulation terms.
Context . Over the last few years, δ Scuti stars have been at the center of the attention of the asteroseismology community thanks to the derivation of seismic indices connected to stellar ...parameters. The statistical analysis of the wealth of data offered by a large space survey such as the Transiting Exoplanet Survey Satellite (TESS), the identification of new δ Scuti stars, and the correlation between asteroseismic indices and stellar parameters in the resulting sample are therefore of utmost interest. Aims . The goal of our study is to analyze the statistical properties of stellar parameters and characterize the asteroseismic indices of δ Scuti stars observed in TESS cycle 4. Methods . We used TESS 2 min cadence photometric data and the corresponding Fourier transform to identify δ Scuti stars. The asteroseismic indices for these stars were determined using an empirical relation and a 2D autocorrelation method. Results . We discovered 765 δ Scuti stars from the data obtained by the TESS mission, from Sectors 40–55, corresponding to cycle 4 and observed with a 2 min cadence. Of these stars, 179 δ Scuti stars have low-resolution spectral parameters from LAMOST. We first analyzed the relation between pulsation and stellar parameters from TESS observations and the distribution of δ Scuti stars with two different stellar parameters, TESS Input Catalog (TIC) and Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), within the classical instability strip. Most of the stars lie within the instability strip and follow the period-luminosity relation of δ Scuti stars. Additionally, the majority of the stars exhibit pulsation properties consistent with those expected for δ Scuti stars, including periods falling within the typical range, amplitudes at the millimagnitude level, and fundamental parameters such as spectral type, effective temperature, log g, and luminosity that match the characteristics of δ Scuti stars. This confirms the reliability of the δ Scuti stars we have identified. We subsequently obtained the large frequency separation (∆ ν ), v max , and ν (Amax) for 179 δ Scuti stars with LAMOST parameters by using an empirical relation and a 2D autocorrelation method, and obtained the relations between these asteroseismic indices. These stars will provide significant support for a deeper study of the internal structure and evolution of stars.
ABSTRACT
Using the short-cadence data (1-min interval) of the Kepler space telescope, we conducted a statistical analysis for the characteristic time of stellar flares on Sun-like stars (SLS). Akin ...to solar flares, stellar flares show rise and decay light-curve profiles, which reflect the two distinct phases (rise phase and decay phase) of the flare process. We derived characteristic times of the two phases for stellar flares of SLS, resulting in a median rise time of about 5.9 min and a median decay time of 22.6 min. It is found that both the rise time and the decay time of the stellar flares follow a lognormal distribution. The peak positions of the lognormal distributions for flare rise time and decay time are 3.5 min and 14.8 min, respectively. These time values for stellar flares are similar to the time-scale of solar flares, which supports the idea that stellar flares and solar flares have the same physical mechanism. The statistical results obtained in this work for SLS can be a benchmark of flare characteristic times when comparing with other types of stars.
Abstract
We describe a complete, flux-density-limited sample of galaxies at redshift 0.8 <
z
< 1.3 selected at 16
μ
m. At the selection wavelength near 8
μ
m rest, the observed emission comes from ...both dust heated by intense star formation and active galactic nuclei (AGNs). Fitting the spectral energy distributions (SEDs) of the sample galaxies to local-galaxy templates reveals that more than half the galaxies have SEDs dominated by star formation. About one-sixth of the galaxy SEDs are dominated by an AGN, and nearly all of the rest of the SEDs are composite. Comparison with X-ray and far-infrared observations shows that combinations of luminosities at rest-frame 4.5 and 8
μ
m give good measures of both AGN luminosity and star formation rate. The sample galaxies mostly follow the established star-forming main sequence for
z
= 1 galaxies, but of the galaxies more than 0.5 dex above that main sequence, more than half have AGN-type SEDs. Similarly, the most luminous AGNs tend to have higher star formation rates than the main-sequence value. Galaxies with stellar masses >10
11
M
⊙
are unlikely to host an AGN. About 1% of the sample galaxies show an SED with dust emission typical of neither star formation nor an AGN.
We report on the detection of sporadic, strong single pulses coexisting with a periodic weak emission in the duration of weak mode of PSR B0826-34. The intensities and durations of these pulses are ...comparable with those of the subpulses in the strong mode, and these pulses are distributed within the phase ranges of the main-pulse and interpulse of the strong-mode average profile. These results suggest that there is very possibly sporadic, very short timescale turn-on of strong-mode emission during the weak-mode state of the pulsar. The emission features of the bursts of strong pulses of PSR B0826-34 during its weak-mode state are similar to those of the rotating radio transients (RRATs). PSR B0826-34 is the second known pulsar, which oscillates between pulsar-like and RRAT-like modes.
ABSTRACT
An increasing number of white dwarf stars shows atmospheric chemical composition polluted by heavy elements accreted from debris disc material. The existence of such debris discs strongly ...suggests the presence of one or more planet(s) whose gravitational interaction with rocky planetesimals is responsible for their disruption by tidal effect. The ZZ Ceti pulsator and polluted DAZ white dwarf GD 133 are good candidates for searching such a potential planet. We started in 2011 a photometric follow-up of its pulsations. As a result of this work in progress, we used the data gathered from 2011 to 2015 to make an asteroseismological analysis of GD 133, providing the star parameters from the best-fitting model with M/M⊙ = 0.630 ± 0.002, Teff = 12 400 ± 70 K, log(MHe/M) = −2.00 ± 0.02, log(MH/M) = −4.50 ± 0.02, and determining a rotation period of ≈7 d.
Abstract
We report on radiation properties of extreme nulling pulsar J1502−5653 by analysing the data acquired from the Parkes 64-m telescope at 1374 MHz. The radio emission from this pulsar exhibits ...sequences of several tens to several hundred consecutive burst pulses, separated by null pulses, and the appearance of the emission seems quasi-periodic. The null fraction from the data is estimated to be 93.6 per cent. No emission is detected in the integrated profile of all null pulses. Systematic modulations of pulse intensity and phase are found at the beginning of burst pulse sequences just after null. The intensity usually rises to a maximum for the first few pulses, then declines exponentially afterwards, and becomes stable after a few tens of pulse periods. The peak phase appears at later longitudes for the first pulse, then drifts to earlier longitudes rapidly, and then systematic drifting gradually vanishes, while the intensity becomes stable. In this pulsar, the intensity variation and phase modulation of pulses are correlated in a short duration after the emission starts following a null. Observed properties of the pulsar are compared with other nulling pulsars published previously, and the possible explanation for phase modulation is discussed.
We report on the short timescale intensity fluctuations of PSR B1133+16 and PSR B1237+25 due to scintillation at 1.54 GHz. The structure functions of intensity fluctuations are constructed and the ...linear fittings are applied to the structure regime in log–log plots to get the slope values. The slope of the SFs for PSR B1237+25 are less than that of PSR B1133+16, and both of them are much less than 2. For PSR B1133+16, the slope values agree very well with a Kolmogorov spectrum predicted value 5/3, whereas PSR B1237+25 not. We investigate the dynamic spectrum and obtain its auto-correlation function (ACF). Scintillation parameters are obtained by fitting to the autocorrelation function of the dynamic spectrum. The observed diffractive interstellar scintillation (DISS) timescales agree well with the observations and are consistent with some expected values, but the observed de-correlation frequency bandwidths are much less than predicted ones. The expected refractive interstellar scintillation (RISS) timescales are also estimated by using our derived diffractive scintillation parameters. They are consistent with the timescales of slow pulse intensity fluctuations. We proposed that the short timescale of pulse intensity variations caused by the DISS are modulated by the slow variations due to the effects of RISS.
We present high-quality observations of PSR B0826-34 at 1374 MHz. The emission from this pulsar exhibits strong bursts of pulses followed by long periods of ‘null’ pulses. When it is strong, the ...radiation extends throughout the whole pulse period. We show for the first time that there is weak emission during the ‘null’ phases, which should therefore be considered to be a different mode rather than being null. During this weak mode, the profile is similar to that observed in the strong mode at low radio frequency. Using a phase-tracking method, the pattern of drifting subpulses during the strong mode is seen to be coherent across the whole profile. The drift rate is variable and includes positive and negative values. 13 subpulse bands have been directly observed, covering the whole longitude range. The subpulses and their spacings (P2) are wider in one half of the profile than those in the other half. This difference, and the variation of observed P2 within the two regions, can be accounted for if the magnetic pole is inclined to the rotation axis by about 0 5. These two regions appear to represent radiation from outer and inner cones. The intensity modulation of subpulses in all longitude ranges is related to the magnitude of the drift rate.
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