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
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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.
The Kilodegree Extremely Little Telescope (KELT) project has been conducting a photometric survey of transiting planets orbiting bright stars for over 10 years. The KELT images have a pixel scale of ...∼23″ pixel−1-very similar to that of NASA's Transiting Exoplanet Survey Satellite (TESS)-as well as a large point-spread function, and the KELT reduction pipeline uses a weighted photometric aperture with radius 3′. At this angular scale, multiple stars are typically blended in the photometric apertures. In order to identify false positives and confirm transiting exoplanets, we have assembled a follow-up network (KELT-FUN) to conduct imaging with spatial resolution, cadence, and photometric precision higher than the KELT telescopes, as well as spectroscopic observations of the candidate host stars. The KELT-FUN team has followed-up over 1600 planet candidates since 2011, resulting in more than 20 planet discoveries. Excluding ∼450 false alarms of non-astrophysical origin (i.e., instrumental noise or systematics), we present an all-sky catalog of the 1128 bright stars (6 < V < 13) that show transit-like features in the KELT light curves, but which were subsequently determined to be astrophysical false positives (FPs) after photometric and/or spectroscopic follow-up observations. The KELT-FUN team continues to pursue KELT and other planet candidates and will eventually follow up certain classes of TESS candidates. The KELT FP catalog will help minimize the duplication of follow-up observations by current and future transit surveys such as TESS.
RW Aur is a binary system composed of two young, low-mass stars. The primary, RW Aur A, has undergone visual dimming events (ΔV = 2-3 mag) in 2011, 2014-16, and 2017-2018. Visual and IR observations ...indicate a gray absorber that moved into the line of sight. This dimming is also associated with changes in the outflow. In 2017, when the optical brightness was almost 2 mag below the long-term average, we triggered a Chandra observation to measure the absorbing column density NH and to constrain dust properties and the gas-to-dust ratio of the absorber. In 2017, the X-ray spectrum is more absorbed than it was in the optically bright state ( ) and shows significantly more hot plasma than in X-ray observations taken before. Furthermore, a new emission feature at 6.63 0.02 keV (statistic) 0.02 keV (systematic) appeared, indicating an Fe abundance an order of magnitude above solar, in contrast with previous sub-solar Fe abundance measurements. Comparing X-ray absorbing column density NH and optical extinction AV, we find that either the gas-to-dust ratio in the absorber is orders of magnitude higher than in the ISM, or the absorber has undergone significant dust evolution. Given the high column density coupled with changes in the X-ray spectral shape, this absorber is probably located in the inner disk. We speculate that a breakup of planetesimals or a terrestrial planet could supply large grains, causing gray absorption; some of these grains would be accreted and enrich the stellar corona with iron, which could explain the inferred high abundance.
ABSTRACT
The Hunting Outbursting Young Stars (HOYS) project performs long-term, optical, multifilter, high cadence monitoring of 25 nearby young clusters and star-forming regions. Utilizing Gaia DR3 ...data, we have identified about 17 000 potential young stellar members in 45 coherent astrometric groups in these fields. Twenty one of them are clear young groups or clusters of stars within 1 kpc and they contain 9143 Gaia selected potential members. The cluster distances, proper motions, and membership numbers are determined. We analyse long-term (≈ 7 yr) V-, R-, and I-band light curves from HOYS for 1687 of the potential cluster members. One quarter of the stars are variable in all three optical filters, and two-thirds of these have light curves that are symmetric around the mean. Light curves affected by obscuration from circumstellar materials are more common than those affected by accretion bursts, by a factor of 2–4. The variability fraction in the clusters ranges from 10 per cent to almost 100 per cent, and correlates positively with the fraction of stars with detectable inner discs, indicating that a lot of variability is driven by the disc. About one in six variables shows detectable periodicity, mostly caused by magnetic spots. Two-thirds of the periodic variables with disc excess emission are slow rotators, and amongst the stars without disc excess two-thirds are fast rotators – in agreement with rotation being slowed down by the presence of a disc.
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.
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.
Extinction and the Dimming of KIC 8462852 Meng, Huan Y. A.; Rieke, George; Dubois, Franky ...
Astrophysical journal/The Astrophysical journal,
10/2017, Letnik:
847, Številka:
2
Journal Article
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To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star over a wide wavelength range from the UV to the mid-infrared from 2015 October through 2016 ...December, using Swift, Spitzer and AstroLAB IRIS. The star faded in a manner similar to the long-term fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period reported is 22.1 9.7 mmag yr−1 in the Swift wavebands, with amounts of 21.0 4.5 mmag in the ground-based B measurements, 14.0 4.5 mmag in V, and 13.0 4.5 in R, and a rate of 5.0 1.2 mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at 3 by three different observatories operating from the UV to the IR. The presence of long-term secular dimming means that previous spectral energy distribution models of the star based on photometric measurements taken years apart may not be accurate. We find that stellar models with K and best fit the Swift data from UV to optical. These models also show no excess in the near-simultaneous Spitzer photometry at 3.6 and 4.5 m, although a longer wavelength excess from a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of the fading favors a relatively neutral color (i.e., , but not flat across all the bands) compared with the extinction law for the general interstellar medium ( ), suggesting that the dimming arises from circumstellar material.
ABSTRACT
The HOYS citizen science project conducts long-term, multifilter, high-cadence monitoring of large YSO samples with a wide variety of professional and amateur telescopes. We present the ...analysis of the light curve of V1490 Cyg in the Pelican Nebula. We show that colour terms in the diverse photometric data can be calibrated out to achieve a median photometric accuracy of 0.02 mag in broad-band filters, allowing detailed investigations into a variety of variability amplitudes over time-scales from hours to several years. Using Gaia DR2, we estimate the distance to the Pelican Nebula to be 870 $^{+70}_{-55}$ pc. V1490 Cyg is a quasi-periodic dipper with a period of 31.447 ± 0.011 d. The obscuring dust has homogeneous properties, and grains larger than those typical in the ISM. Larger variability on short time-scales is observed in U and Rc−H α, with U amplitudes reaching 3 mag on time-scales of hours, indicating that the source is accreting. The H α equivalent width and NIR/MIR colours place V1490 Cyg between CTTS/WTTS and transition disc objects. The material responsible for the dipping is located in a warped inner disc, about 0.15 au from the star. This mass reservoir can be filled and emptied on time-scales shorter than the period at a rate of up to 10−10 M⊙ yr−1, consistent with low levels of accretion in other T Tauri stars. Most likely, the warp at this separation from the star is induced by a protoplanet in the inner accretion disc. However, we cannot fully rule out the possibility of an AA Tau-like warp, or occultations by the Hill sphere around a forming planet.
Abstract
Continuing the project described by Kato et al. (2009, PASJ, 61, S395), we collected times of superhump maxima for 127 SU UMa-type dwarf novae observed mainly during the 2016–2017 season and ...characterized these objects. We provide updated statistics of the relation between the orbital period and the variation of superhumps, the relation between period variations and the rebrightening type in WZ Sge-type objects. We obtained the period minimum of 0.05290(2) d and confirmed the presence of the period gap above the orbital period ∼0.09 d. We note that four objects (NY Her, 1RXS J161659.5+620014, CRTS J033349.8−282244, and SDSS J153015.04+094946.3) have supercycles shorter than 100 d but show infrequent normal outbursts. We consider that these objects are similar to V503 Cyg, whose normal outbursts are likely suppressed by a disk tilt. These four objects are excellent candidates to search for negative superhumps. DDE 48 appears to be a member of ER UMa-type dwarf novae. We identified a new eclipsing SU UMa-type object, MASTER OT J220559.40−341434.9. We observed 21 WZ Sge-type dwarf novae during this interval and report 18 of them in this paper. Among them, ASASSN-16js is a good candidate for a period bouncer. ASASSN-16ia showed a precursor outburst for the first time in a WZ Sge-type superoutburst. ASASSN-16kg, CRTS J000130.5+050624, and SDSS J113551.09+532246.2 are located in the period gap. We have newly obtained 15 orbital periods, including periods from early superhumps.
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