arXiv subjects

Konstanze Zwintz

Publications and source records attributed to Konstanze Zwintz.

At least 37 records · Page 2Linked to original sources

arXiv2019

Bright Southern Variable Stars in the bRing Survey

Besides monitoring the bright star $β$ Pic during the near transit event for its giant exoplanet, the $β$ Pictoris b Ring (bRing) observatories at Siding Springs Observatory, Australia and Sutherland, South Africa have monitored the brightnesses of bright stars ($V$ $\simeq$ 4--8 mag) centered on the south celestial pole ($δ$ $\leq$ -30$^{\circ}$) for approximately two years. Here we present a comprehensive study of the bRing time series photometry for bright southern stars monitored between 2017 June and 2019 January. Of the 16762 stars monitored by bRing, 353 of them were found to be variable. Of the variable stars, 80% had previously known variability and 20% were new variables. Each of the new variables was classified, including 3 new eclipsing binaries (HD 77669, HD 142049, HD 155781), 26 $δ$ Scutis, 4 slowly pulsating B stars, and others. This survey also reclassified four stars based on their period of pulsation, light curve, spectral classification, and color-magnitude information. The survey data were searched for new examples of transiting circumsecondary disk systems, but no candidates were found.

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arXiv2019

Photometry of Beta Lyrae in 2018 by the BRITE satellites

Observations of Beta Lyr in four months of 2018 by three BRITE Constellation satellites (the red-filter BTr and BHr, and the blue-filter BLb) permitted a first, limited look into the light-curve variability in two spectral bands. The variations were found to be well correlated outside the innermost primary minima with the blue variations appearing to have smaller amplitudes than the red; this reduction may reflect their presumed origin in the cooler, outer parts of the accretion disk. This result must be confirmed with more extensive material as the current conclusions are based on observations spanning slightly less than three orbital cycles of the binary. The assumption of an instrumental problem and the applied corrections made to explain the unexpectedly large amplitude of the red-filter light-curve observed with the BTr satellite in 2016 are fully confirmed by the 2018 results.

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arXiv2019

Transiting exocomets detected in broadband light by TESS in the $β$ Pictoris system

We search for signs of falling evaporating bodies (FEBs, also known as exocomets) in photometric time series obtained for $β$ Pictoris after fitting and removing its $δ$ Scuti type pulsation frequencies. Using photometric data obtained by the TESS satellite we determine the pulsational properties of the exoplanet host star $β$ Pictoris through frequency analysis. We then prewhiten the 54 identified $δ$ Scuti p-modes and investigate the residual photometric time series for the presence of FEBs. We identify three distinct dipping events in the light curve of $β$ Pictoris over a 105-day period. These dips have depths from 0.5 to 2 millimagnitudes and durations of up to 2 days for the largest dip. These dips are asymmetric in nature and are consistent with a model of an evaporating comet with an extended tail crossing the disk of the star. We present the first broadband detections of exocomets crossing the disk of $β$ Pictoris, consistent with the predictions made 20 years earlier by Lecavelier Des Etangs et al. (1999). No periodic transits are seen in this time series. These observations confirm the spectroscopic detection of exocomets in Calcium H and K lines that have been seen in high resolution spectroscopy.

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arXiv2019

Astro2020 Science White Paper: gravity-wave asteroseismology of intermediate- and high-mass stars

The evolution of a star is driven by the physical processes in its interior making the theory of stellar structure and evolution the most crucial ingredient for not only stellar evolution studies, but any field of astronomy which relies on the yields along stellar evolution. High-precision time-series photometric data assembled by recent space missions revealed that current models of stellar structure and evolution show major shortcomings already in the two earliest nuclear burning phases, impacting all subsequent phases prior to the formation of the end-of-life remnant. This white paper focuses specifically on the transport of chemical elements and of angular momentum in the stellar structure and evolution models of stars born with convective core, as revealed by their gravity-mode oscillations.

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arXiv2019

Seismic modelling of early B-type pulsators observed by BRITE: I. $θ$ Ophiuchi

We analyse time-series observations from the BRITE-Constellation of the well known $β$ Cephei type star $θ$ Ophiuchi. Seven previously known frequencies were confirmed and nineteen new frequency peaks were detected. In particular, high-order g modes, typical for the SPB (Slowly Pulsating B-type star) pulsators, are uncovered. These low-frequency modes are also obtained from the 7-year SMEI light curve. If g modes are associated with the primary component of $θ$ Oph, then our discovery allows, as in the case of other hybrid pulsators, to infer more comprehensive information on the internal structure. To this aim we perform in-depth seismic studies involving simultaneous fitting of mode frequencies, reproducing mode instability and adjusting the relative amplitude of the bolometric flux variations. To explain the mode instability in the observed frequency range a significant increase of the mean opacity in the vicinity of the $Z$-bump is needed. Moreover, constraints on mass, overshooting from the convective core and rotation are derived. If the low-frequency modes come from the speckle B5 companion then taking into account the effects of rotation is enough to explain the pulsational mode instability.

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arXiv2019

Stellar Astrophysics and Exoplanet Science with the Maunakea Spectroscopic Explorer (MSE)

The Maunakea Spectroscopic Explorer (MSE) is a planned 11.25-m aperture facility with a 1.5 square degree field of view that will be fully dedicated to multi-object spectroscopy. A rebirth of the 3.6m Canada-France-Hawaii Telescope on Maunakea, MSE will use 4332 fibers operating at three different resolving powers (R ~ 2500, 6000, 40000) across a wavelength range of 0.36-1.8mum, with dynamical fiber positioning that allows fibers to match the exposure times of individual objects. MSE will enable spectroscopic surveys with unprecedented scale and sensitivity by collecting millions of spectra per year down to limiting magnitudes of g ~ 20-24 mag, with a nominal velocity precision of ~100 m/s in high-resolution mode. This white paper describes science cases for stellar astrophysics and exoplanet science using MSE, including the discovery and atmospheric characterization of exoplanets and substellar objects, stellar physics with star clusters, asteroseismology of solar-like oscillators and opacity-driven pulsators, studies of stellar rotation, activity, and multiplicity, as well as the chemical characterization of AGB and extremely metal-poor stars.

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arXiv2018

Discovery of δ Scuti Pulsations in the Young Hybrid Debris Disk Star HD 156623

The bRing robotic observatory network was built to search for circumplanetary material within the transiting Hill sphere of the exoplanet $β$ Pic b across its bright host star $β$ Pic. During the bRing survey of $β$ Pic, it simultaneously monitored the brightnesses of thousands of bright stars in the southern sky ($V$ $\simeq$ 4-8, $δ$ $\lesssim$ -30$^{\circ}$). In this work, we announce the discovery of $δ$ Scuti pulsations in the A-type star HD 156623 using bRing data. HD 156623 is notable as it is a well-studied young star with a dusty and gas-rich debris disk, previously detected using ALMA. We present the observational results on the pulsation periods and amplitudes for HD 156623, discuss its evolutionary status, and provide further constraints on its nature and age. We find strong evidence of frequency regularity and grouping. We do not find evidence of frequency, amplitude, or phase modulation for any of the frequencies over the course of the observations. We show that HD 156623 is consistent with other hot and high frequency pre-MS and early ZAMS $δ$ Scutis as predicted by theoretical models and corresponding evolutionary tracks, although we observe that HD 156623 lies hotter than the theoretical blue edge of the classical instability strip. This, coupled with our characterization and Sco-Cen membership analyses, suggest that the star is most likely an outlying ZAMS member of the $\sim$16 Myr Upper Centaurus-Lupus subgroup of the Sco-Cen association.

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arXiv2018

A BRITE view on the massive O-type supergiant V973 Scorpii: Hints towards internal gravity waves or subsurface convection zones

Stochastically-triggered photospheric light variations reaching $\sim$$40$ mmag peak-to-valley amplitudes have been detected in the O8Iaf supergiant V973 Scorpii as the outcome of two months of high-precision time-resolved photometric observations with the BRIght Target Explorer (BRITE) nanosatellites. The amplitude spectrum of the time series photometry exhibits a pronounced broad bump in the low-frequency regime ($\lesssim$$0.9$ d$^{-1}$) where several prominent frequencies are detected. A time-frequency analysis of the observations reveals typical mode lifetimes of the order of $5-10$ days. The overall features of the observed brightness amplitude spectrum of V973 Sco match well with those extrapolated from two-dimensional hydrodynamical simulations of convectively-driven internal gravity waves randomly excited from deep in the convective cores of massive stars. An alternative or additional possible source of excitation from a subsurface convection zone needs to be explored in future theoretical investigations.

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arXiv2018

Light-curve instabilities of Beta Lyrae observed by the BRITE satellites

Photometric instabilities of $β$ Lyr were observed in 2016 by two red-filter BRITE satellites over more than 10 revolutions of the binary, with $\sim$100-minute sampling. Analysis of the time series shows that flares or fading events take place typically 3 to 5 times per binary orbit. The amplitudes of the disturbances (relative to the mean light curve, in units of the maximum out-of-eclipse light-flux, f.u.) are characterized by a Gaussian distribution with $σ=0.0130\pm0.0004$ f.u. Most of the disturbances appear to be random, with a tendency to remain for one or a few orbital revolutions, sometimes changing from brightening to fading or the reverse. Phases just preceding the center of the deeper eclipse showed the most scatter while phases around secondary eclipse were the quietest. This implies that the invisible companion is the most likely source of the instabilities. Wavelet transform analysis showed domination of the variability scales at phase intervals $0.05-0.3$ (0.65--4 d), with the shorter (longer) scales dominating in numbers (variability power) in this range. The series can be well described as a stochastic Gaussian process with the signal at short timescales showing a slightly stronger correlation than red noise. The signal de-correlation timescale $τ=(0.068\pm0.018)$ in phase or $(0.88\pm0.23)$~d appears to follow the same dependence on the accretor mass as that observed for AGN and QSO masses 5--9 orders of magnitude larger than the $β$~Lyr torus-hidden component.

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arXiv2018

BRITE-Constellation reveals evidence for pulsations in the enigmatic binary $η$ Carinae

$η$ Car is a massive, eccentric binary with a rich observational history. We obtained the first high-cadence, high-precision light curves with the BRITE-Constellation nanosatellites over 6 months in 2016 and 6 months in 2017. The light curve is contaminated by several sources including the Homunculus nebula and neighboring stars, including the eclipsing binary CPD$-$59$^\circ$2628. However, we found two coherent oscillations in the light curve. These may represent pulsations that are not yet understood but we postulate that they are related to tidally excited oscillations of $η$ Car's primary star, and would be similar to those detected in lower-mass eccentric binaries. In particular, one frequency was previously detected by van Genderen et al. and Sterken et al. through the time period of 1974 to 1995 through timing measurements of photometric maxima. Thus, this frequency seems to have been detected for nearly four decades, indicating that it has been stable in frequency over this time span. These pulsations could help provide the first direct constraints on the fundamental parameters of the primary star if confirmed and refined with future observations.

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arXiv2017

The exoplanet host star beta Pictoris seen by BRITE-Constellation

BRITE-Constellation has observed the exoplanet host star $β$ Pictoris for 225 days from November 2016 to June 2017. These data allow for an accurate description of the pulsational properties and an asteroseismic interpretation. They were also observed as part of an international observing campaign which aims to detect the transit of $β$ Pictoris b's Hill sphere and study the circumstellar disk around $β$ Pictoris itself.

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arXiv2017

BRITE-Constellation high-precision time-dependent photometry of the early-O-type supergiant $ζ$ Puppis unveils the photospheric drivers of its small- and large-scale wind structures

From $5.5$ months of dual-band optical photometric monitoring at the $1$ mmag level, BRITE-Constellation has revealed two simultaneous types of variability in the O4I(n)fp star $ζ$ Puppis: one single periodic non-sinusoidal component superimposed on a stochastic component. The monoperiodic component is the $1.78$ d signal previously detected by Coriolis/SMEI, but this time along with a prominent first harmonic. The shape of this signal changes over time, a behaviour that is incompatible with stellar oscillations but consistent with rotational modulation arising from evolving bright surface inhomogeneities. By means of a constrained non-linear light curve inversion algorithm we mapped the locations of the bright surface spots and traced their evolution. Our simultaneous ground-based multi-site spectroscopic monitoring of the star unveiled cyclical modulation of its He II $\lambda4686$ wind emission line with the $1.78$-day rotation period, showing signatures of Corotating Interaction Regions (CIRs) that turn out to be driven by the bright photospheric spots observed by BRITE. Traces of wind clumps are also observed in the He II $\lambda4686$ line and are correlated with the amplitudes of the stochastic component of the light variations probed by BRITE at the photosphere, suggesting that the BRITE observations additionally unveiled the photospheric drivers of wind clumps in $ζ$ Pup and that the clumping phenomenon starts at the very base of the wind. The origins of both the bright surface inhomogeneities and the stochastic light variations remain unknown, but a subsurface convective zone might play an important role in the generation of these two types of photospheric variability.

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arXiv2017

Constraining the near-core rotation of the gamma Doradus star 43 Cygni using BRITE-Constellation data

Photometric time series of the $γ$ Dor star 43 Cyg obtained with the BRITE-Constellation nano-satellites allow us to study its pulsational properties in detail and to constrain its interior structure. We aim to find a g-mode period spacing pattern that allows us to determine the near-core rotation rate of 43 Cyg and redetermine the star's fundamental atmospheric parameters and chemical composition. We conducted a frequency analysis using the 156-days long data set obtained with the BRITE-Toronto satellite and employed a suite of MESA/GYRE models to derive the mode identification, asymptotic period spacing and near-core rotation rate. We also used high-resolution, high signal-to-noise ratio spectroscopic data obtained at the 1.2m Mercator telescope with the HERMES spectrograph to redetermine the fundamental atmospheric parameters and chemical composition of 43 Cyg using the software Spectroscopy Made Easy (SME). We detected 43 intrinsic pulsation frequencies and identified 18 of them to be part of a period spacing pattern consisting of prograde dipole modes with an asymptotic period spacing $ΔΠ_{l=1}$ of $2970^{+700}_{-570} \rm s$. The near-core rotation rate was determined to be $f_{\rm rot} = 0.56^{+0.12}_{-0.14}\,\rm d^{-1}$. The atmosphere of 43 Cyg shows solar chemical composition at an effective temperature of 7150 $\pm$ 150 K, a log g of 4.2 $\pm$ 0.6 dex and a projected rotational velocity, $v {\rm sin}i$, of 44 $\pm$ 4 kms$^{-1}$. The morphology of the observed period spacing patterns shows indications of the presence of a significant chemical gradient in the stellar interior.

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arXiv2017

BRITE-Constellation: Data processing and photometry

The BRITE mission is a pioneering space project aimed at the long-term photometric monitoring of the brightest stars in the sky by means of a constellation of nano-satellites. Its main advantage is high photometric accuracy and time coverage inaccessible from the ground. The main aim of this paper is the presentation of procedures used to obtain high-precision photometry from a series of images acquired by the BRITE satellites in two modes of observing, stare and chopping. We developed two pipelines corresponding to the two modes of observing. The assessment of the performance of both pipelines is presented. It is based on two comparisons, which use data from six runs of the UniBRITE satellite: (i) comparison of photometry obtained by both pipelines on the same data, which were partly affected by charge transfer inefficiency (CTI), (ii) comparison of real scatter with theoretical expectations. It is shown that for CTI-affected observations, the chopping pipeline provides much better photometry than the other pipeline. For other observations, the results are comparable only for data obtained shortly after switching to chopping mode. Starting from about 2.5 years in orbit, the chopping mode of observing provides significantly better photometry for UniBRITE data than the stare mode. This paper shows that high-precision space photometry with low-cost nano-satellites is achievable. The proposed meth- ods, used to obtain photometry from images affected by high impulsive noise, can be applied to data from other space missions or even to data acquired from ground-based observations.

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arXiv2016

A BRITE view on delta Scuti and gamma Doradus stars

BRITE-Constellation has obtained data for a few delta Scuti and gamma Doradus type stars. A short overview of the pulsational content found in five stars - beta Cassiopeiae, epsilon Cephei, M Velorum, beta Pictoris and QW Puppis - is given and the potential of BRITE-Constellation observations of delta Scuti and gamma Doradus pulsators is discussed.

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arXiv2016

43 Cygni observed with BRITE-Constellation

The gamma Doradus star 43 Cygni was observed by BRITE-Toronto for 156 days in 2015. From this data set we identified 37 pulsation frequencies which show a regular period spacing pattern that will be subject of a more detailed asteroseismic analysis.

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arXiv2016

The potential of space observations for pulsating pre-main sequence stars

The first asteroseismic studies of pre-main sequence (pre-MS) pulsators have been conducted based on data from the space telescopes MOST and CoRoT with typical time bases of less than 40 days. With these data, a relation between the pulsational properties of pre-MS delta Scuti stars and their relative evolutionary phase on their way from the birthline to the zero-age main sequence was revealed. But it is evident from comparison with the more evolved pulsators in their main sequence or post-main sequence stages observed by the main Kepler mission, that many more questions could be addressed with significantly longer time bases and ultra-high precision. Here, I will discuss the observational status of pre-MS asteroseismology and the potential of future space observations for this research field.

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arXiv2014

Tracing early stellar evolution with asteroseismology: pre-main sequence stars in NGC 2264

Asteroseismology has been proven to be a successful tool to unravel details of the internal structure for different types of stars in various stages of their main sequence and post-main sequence evolution. Recently, we found a relation between the detected pulsation properties in a sample of 34 pre-main sequence (pre-MS) delta Scuti stars and the relative phase in their pre-MS evolution. With this we are able to demonstrate that asteroseismology is similarly powerful if applied to stars in the earliest stages of evolution before the onset of hydrogen core burning.

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