Eddy currents due to magnetic flux perpendicular to the sheets of a lamination iron core are represented on a number of 2D slice models, which are embedded in a 3D model of the entire device using a ...multi-scale technique. The choice of a different spatial resolution enables to attain an advantageous convergence of the discretization error for the eddy-current power losses, compared to a standard modelling technique using an anisotropic surrogate material.
Variability of eclipse timing: the case of V471 Tauri Kundra, Emil; Hambálek, Ľubomír; Vanaverbeke, Siegfried ...
Monthly notices of the Royal Astronomical Society,
11/2022, Letnik:
517, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
The post-common envelope binary V471 Tauri has been an object of interest for decades. V471 Tau shows various phenomena due to its evolutionary state and unique properties, e.g. its magnetic ...accretion and eclipse timing variation (ETV). Previous authors explained the ETVs by different sometimes contradictory theories. In this paper, we present and analyse the variability of the eclipse timing of this star. We observed V471 Tauri over the last 10 yr and covered the second cycle of its period variation. Based on our analysis of the presented data, we assess the possible existence of a brown dwarf in this system and derive its orbital parameters. We compare the results of our dynamical modelling to the solution predicted by Applegate-mechanism theories, which have been developed in recent studies. We found that the observed ETV cannot be explained only by the presence of additional components to the binary.
ABSTRACT
We present spot properties on 32 periodic young stellar objects in IC 5070. Long term, ∼5 yr, light curves in the V, R, and I-bands are obtained through the HOYS (Hunting Outbursting Young ...Stars) citizen science project. These are dissected into 6 months long slices, with 3 months oversampling, to measure 234 sets of amplitudes in all filters. We fit 180 of these with reliable spot solutions. Two thirds of spot solutions are cold spots, the lowest is 2150 K below the stellar temperature. One third are warm spots that are above the stellar temperature by less than ∼2000 K. Cold and warm spots have maximum surface coverage values of 40 per cent, although only 16 per cent of warm spots are above 20 per cent surface coverage as opposed to 60 per cent of the cold spots. Warm spots are most likely caused by a combination of plages and low-density accretion columns, most common on objects without inner disc excess emission in K − W2. Five small hot spot solutions have <3 per cent coverage and are 3000–5000 K above the stellar temperature. These are attributed to accretion, and four of them occur on the same object. The majority of our objects are likely to be accreting. However, we observe very few accretion hot spots as either the accretion is not stable on our time-scale or the photometry is dominated by other features. We do not identify cyclical spot behaviour on the targets. We additionally identify and discuss a number of objects that have interesting amplitudes, phase changes, or spot properties.
ABSTRACT
This paper is one in a series reporting results from small telescope observations of variable young stars. Here, we study the repeating outbursts of three likely Be stars based on long-term ...optical, near-infrared, and mid-infrared photometry for all three objects, along with follow-up spectra for two of the three. The sources are characterized as rare, truly regularly outbursting Be stars. We interpret the photometric data within a framework for modelling light-curve morphology, and find that the models correctly predict the burst shapes, including their larger amplitudes and later peaks towards longer wavelengths. We are thus able to infer the start and end times of mass loading into the circumstellar discs of these stars. The disc sizes are typically 3 – 6 times the areas of the central star. The disc temperatures are ∼40 per cent, and the disc luminosities are ∼10 per cent of those of the central Be star, respectively. The available spectroscopy is consistent with inside-out evolution of the disc. Higher excitation lines have larger velocity widths in their double-horned shaped emission profiles. Our observations and analysis support the decretion disc model for outbursting Be stars.
An attempt is made here to revisit structure formation in a proto-stellar cloud during the early phase of evolution. A molecular cloud subject to a set of various initial conditions in terms of ...initial temperature and amplitude of azimuthal density perturbation is investigated numerically. Special emphasis is on the analysis of ring- and spiral-type instabilities that have shown dependence on certain initial conditions chosen for a rotating solar mass cloud of molecular hydrogen. Generally, a star-forming hydrogen gas is considered to be initially at 10 K. We have found that a possible oscillation around this typical value can affect the fate of a collapsing cloud in terms of its evolving structural properties leading to proto-star formation. We explored the initial temperature range of the cloud between 8 K to 12 K and compared the physical properties of each within the first phase of proto-star formation. We suggest that the spiral structures are more likely to form in strongly perturbed molecular cores that initiate their phase of collapse from temperatures below 10 K, whereas cores with initial temperatures above 10 K develop, instead of a spiral structure, a ring-type structure which subsequently experiences fragmentation. A transition from a spiral to ring instability can be observed at a typical initial temperature of 10 K.
K2 observations of the weak-lined T Tauri binary V928 Tau A and B show the detection of a single, asymmetric eclipse, which may be due to a previously unknown substellar companion eclipsing one ...component of the binary with an orbital period >66 days. Over an interval of about 9 hr, one component of the binary dims by around 60%, returning to its normal brightness about 5 hr later. From modeling of the eclipse shape, we find evidence that the eclipsing companion may be surrounded by a disk or a vast ring system. The modeled disk has a radius of 0.9923 0.0005 R*, with an inclination of 56 78 0 03, a tilt of 41 22 0 05, an impact parameter of −0.2506 0.0002 R*, and an opacity of 1.00. The occulting disk must also move at a transverse velocity of 6.637 0.002 R* day−1, which, depending on whether it orbits V928 Tau A or B, corresponds to approximately 73.53 or 69.26 km s−1. A search in ground-based archival data reveals additional dimming events, some of which suggest periodicity, but no unambiguous period associated with the eclipse observed by K2. We present a new epoch of astrometry that is used to further refine the orbit of the binary, presenting a new lower bound of 67 yr, and constraints on the possible orbital periods of the eclipsing companion. The binary is also separated by 18″ (∼2250 au) from the lower-mass CFHT-BD-Tau 7, which is likely associated with V928 Tau A and B. We also present new high-dispersion optical spectroscopy that we use to characterize the unresolved stellar binary.
ABSTRACT
Studying rotational variability of young stars is enabling us to investigate a multitude of properties of young star-disc systems. We utilize high cadence, multiwavelength optical time ...series data from the Hunting Outbursting Young Stars citizen science project to identify periodic variables in the Pelican Nebula (IC 5070). A double blind study using nine different period-finding algorithms was conducted and a sample of 59 periodic variables was identified. We find that a combination of four period finding algorithms can achieve a completeness of 85 per cent and a contamination of 30 per cent in identifying periods in inhomogeneous data sets. The best performing methods are periodograms that rely on fitting a sine curve. Utilizing Gaia EDR3 data, we have identified an unbiased sample of 40 periodic young stellar objects (YSOs), without using any colour or magnitude selections. With a 98.9 per cent probability, we can exclude a homogeneous YSO period distribution. Instead, we find a bi-modal distribution with peaks at 3 and 8 d. The sample has a disc fraction of 50 per cent, and its statistical properties are in agreement with other similarly aged YSOs populations. In particular, we confirm that the presence of the disc is linked to predominantly slow rotation and find a probability of 4.8 × 10−3 that the observed relation between period and presence of a disc has occurred by chance. In our sample of periodic variables, we also find pulsating giants, an eclipsing binary, and potential YSOs in the foreground of IC 5070.
•A spectrum and multicolour photometric observations are presented for NSV 1907.•NSV 1907 was identified as a deeply eclipsing, nova-like cataclysmic variable.•We find Porb=0.2761069 days and ...establish the presence of a secondary minimum.•We propose NSV 1907 as a new moderately bright long-period SW Sextantis star.•We find a possible 4.2 day period (the nodal precession period of the disc?).
NSV 1907, formerly listed as an irregular variable in variability catalogues, was classified as an Algol-type eclipsing binary in the Catalina Surveys Periodic Variable Star Catalogue. We have identified NSV 1907 as an ultraviolet (UV) bright source using measurements from the GALEX space telescope and detected obvious out-of-eclipse variability in archival photometric data from the Catalina Sky Survey, which instigated a closer examination of the object. A spectrum and extensive multicolour photometric observations were acquired, from which we deduce that NSV 1907 is a deeply eclipsing, nova-like cataclysmic variable. Apart from the orbital variations (deep eclipses with a period of P ≈ 6.63 hours), changes in mean brightness and irregular short-term variability (flickering) were observed. The presence of a secondary minimum at phase φ ≈ 0.5 was established, which indicates a significant contribution of the companion star to the optical flux of the system. We find possible evidence for sinusoidal variations with a period of P ≈ 4.2 d, which we interpret as the nodal precession period of the accretion disc. No outbursts or VY Scl-like drops in brightness were detected either by the CSS or during our photometric monitoring. Because of its spectral characteristics and the observed variability pattern, we propose NSV 1907 as a new moderately bright long-period SW Sextantis star. Further photometric and spectroscopic observations are encouraged.
PDF
