arXiv subjects

Brent Miszalski

Publications and source records attributed to Brent Miszalski.

At least 37 records · Page 2Linked to original sources

arXiv2018

SALT HRS discovery of the binary nucleus of the Etched Hourglass Nebula MyCn 18

The shaping of various morphological features of planetary nebulae (PNe) is increasingly linked to the role of binary central stars. Identifying a binary within a PN offers a powerful tool with which to directly investigate the formation mechanisms behind these features. The Etched Hourglass Nebula, MyCn 18, is the archetype for several binary-linked morphological features, yet it has no identified binary nucleus. It has the fastest jets seen in a PN of 630 km s$^{-1}$, a central star position offset from the nebula centre, and a bipolar nebula with a very narrow waist. Here we report on the Southern African Large Telescope (SALT) High Resolution Spectrograph (HRS) detection of radial velocity variability in the nucleus of MyCn 18 with an orbital period of $18.15\pm0.04$ days and a semi-amplitude of $11.0\pm0.3$ km s$^{-1}$. Adopting an orbital inclination of $38\pm5$ deg and a primary mass of $0.6\pm0.1$ $M_\odot$ yields a secondary mass of $0.19\pm0.05$ $M_\odot$ corresponding to an M5V companion. The detached nature of the binary rules out a classical nova (CN) as the origin of the jets or the offset central star as hypothesised in the literature. Furthermore, scenarios that produce the offset central star during the AGB and that form narrow waist bipolar nebulae result in orbital separations 80--800 times larger than observed in MyCn 18. The inner hourglass and jets may have formed from part of the common envelope ejecta that remained bound to the binary system in a circumbinary disk, whereas the offset central star position may best be explained by proper motion. Detailed simulations of MyCn 18 are encouraged that are compatible with the binary nucleus to further investigate its complex formation history.

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arXiv2018

A D'-type symbiotic binary in the planetary nebula SMP LMC 88

SMP LMC 88 is one of the planetary nebulae (PN) in the Large Magellanic Cloud. We identify in its spectrum Raman scattered O VI lines at 6825 and 7083A. This unambiguously classifies the central object of the nebula as a symbiotic star (SySt). We identified the cold component to be a K-type giant, making this the first D'-type (yellow) SySt discovered outside the Galaxy. The photometric variability in SMP LMC 88 resembles the the orbital variability of Galactic D'-type SySt with its low amplitude and sinusoidal lightcurve shape. The SySt classification is also supported by the He I diagnostic diagram.

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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

The variability of the BRITE-est Wolf-Rayet binary, $γ^2$ Velorum I. Photometric and spectroscopic evidence for colliding winds

We report on the first multi-color precision light curve of the bright Wolf-Rayet binary $γ^2$ Velorum, obtained over six months with the nanosatellites in the BRITE- Constellation fleet. In parallel, we obtained 488 high-resolution optical spectra of the system. In this first report on the datasets, we revise the spectroscopic orbit and report on the bulk properties of the colliding winds. We find a dependence of both the light curve and excess emission properties that scales with the inverse of the binary separation. When analyzing the spectroscopic properties in combination with the photometry, we find that the phase dependence is caused only by excess emission in the lines, and not from a changing continuum. We also detect a narrow, high-velocity absorption component from the He I $λ$5876 transition, which appears twice in the orbit. We calculate smoothed-particle hydrodynamical simulations of the colliding winds and can accurately associate the absorption from He I to the leading and trailing arms of the wind shock cone passing tangentially through our line of sight. The simulations also explain the general strength and kinematics of the emission excess observed in wind lines such as C III $λ$5696 of the system. These results represent the first in a series of investigations into the winds and properties of $γ^2$ Velorum through multi-technique and multi-wavelength observational campaigns.

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arXiv2016

Active phases and flickering of a symbiotic recurrent nova T CrB

T CrB is a symbiotic recurrent nova known to exhibit active phases, characterised by apparent increases in the hot component temperature and the appearance of flickering, i.e. changes in the observed flux on the time-scale of minutes. Historical UV observations have ruled out orbital variability as an explanation for flickering and instead suggest flickering is caused by variable mass transfer. We have analysed optical and X-ray observations to investigate the nature of the flickering as well as the active phases in T CrB. The spectroscopic and photometric observations confirm that the active phases follow two periods of ~1000d and ~5000d. Flickering in the X-rays is detected and follows an amplitude-flux relationship similar to that observed in the optical. The flickering is most prominent at harder X-ray energies, suggesting that it originates in the boundary layer between the accretion disc and the white dwarf. The X-ray radiation from the boundary layer is then reprocessed by a thick accretion disc or a nebula into UV radiation. A more detailed understanding of flickering would benefit from long-term simultaneous X-ray and optical monitoring of the phenomena in symbiotic recurrent novae and related systems such as Z And type symbiotic stars.

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arXiv2015

Discovery of an eclipsing dwarf nova in the ancient nova shell Te 11

We report on the discovery of an eclipsing dwarf nova (DN) inside the peculiar, bilobed nebula Te 11. Modelling of high-speed photometry of the eclipse finds the accreting white dwarf to have a mass 1.18 M$_\odot$ and temperature 13 kK. The donor spectral type of M2.5 results in a distance of 330 pc, colocated with Barnard's loop at the edge of the Orion-Eridanus superbubble. The perplexing morphology and observed bow shock of the slowly-expanding nebula may be explained by strong interactions with the dense interstellar medium in this region. We match the DN to the historic nova of 483 CE in Orion and postulate that the nebula is the remnant of this eruption. This connection supports the millennia time scale of the post-nova transition from high to low mass-transfer rates. Te 11 constitutes an important benchmark system for CV and nova studies as the only eclipsing binary out of just three DNe with nova shells.

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arXiv2015

An X-Shooter view of the symbiotic star [JD2002] 11

We aimed to verify the nature and derive the basic parameters of the symbiotic star candidate [JD2002] 11. For this purpose, we obtained and analysed an X-Shooter spectrum of [JD2002] 11. We also used optical and infrared photometry available for the object. Emission-line diagnostic ratios are characteristic of a dusty type symbiotic star and reveal a two-component nebula (low- and high-density). The spectral energy distribution is well fitted with a two-component blackbody spectrum with the respective temperatures of 1150 K and 600 K. The total luminosity of $\rm 3000\,L_{\odot}$ is consistent with the expected luminosity of a typical Mira star, embedded in an optically thick dust shell. We conclude that [JD2002] 11 is the ninth symbiotic star in total and only the second dusty type symbiotic star discovered in the Small Magellanic Cloud.

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arXiv2015

The role of binarity in Wolf-Rayet central stars of planetary nebulae

Over a hundred planetary nebulae (PNe) are known to have H-deficient central stars that mimic the spectroscopic appearance of massive Wolf-Rayet stars. The formation of these low-mass Wolf-Rayet stars, denoted [WR] stars, remains poorly understood. While several binary formation scenarios have been proposed, there are too few [WR] binaries known to determine their feasibility. Out of nearly 50 post-common-envelope (post-CE) binary central stars known, only PN G222.8$-$04.2 ([WC7], $P=1.26$ d) and NGC 5189 ([WO1], $P=4.05$ d) have a [WR] component. The available data suggests that post-CE central stars with [WR] components lack main sequence companions and have a wider orbital separation than typical post-CE binaries. There is also some indirect evidence for wide binaries that could potentially lead to the discovery of more [WR] binaries.

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arXiv2015

Post-common-envelope Wolf-Rayet central stars of planetary nebulae

Nearly 50 post-common-envelope (post-CE) close binary central stars of planetary nebulae (CSPNe) are now known. Most contain either main sequence or white dwarf (WD) companions that orbit the WD primary in around 0.1-1.0 days. Only PN~G222.8-04.2 and NGC~5189 have post-CE CSPNe with a Wolf-Rayet star primary (denoted [WR]), the low-mass analogues of massive Wolf-Rayet stars. It is not well understood how H-deficient [WR] CSPNe form, even though they are relatively common, appearing in over 100 PNe. The discovery and characterisation of post-CE [WR] CSPNe is essential to determine whether proposed binary formation scenarios are feasible to explain this enigmatic class of stars. The existence of post-CE [WR] binaries alone suggests binary mergers are not necessarily a pathway to form [WR] stars. Here we give an overview of the initial results of a radial velocity monitoring programme of [WR] CSPNe to search for new binaries. We discuss the motivation for the survey and the associated strong selection effects. The mass functions determined for PN~G222.8-04.2 and NGC~5189, together with literature photometric variability data of other [WR] CSPNe, suggest that of the post-CE [WR] CSPNe yet to be found, most will have WD or subdwarf O/B-type companions in wider orbits than typical post-CE CSPNe (several days or months c.f. less than a day).

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arXiv2015

The post-common envelope central stars of the planetary nebulae Henize 2-155 and Henize 2-161

We present a study of Hen 2-155 and Hen 2-161, two planetary nebulae which bear striking morphological similarities to other planetary nebulae known to host close-binary central stars. Both central stars are revealed to be photometric variables while spectroscopic observations confirm that Hen 2-155 is host to a double-eclipsing, post-common-envelope system with an orbital period of 3h33m making it one of the shortest period binary central stars known. The observations of Hen 2-161 are found to be consistent with a post-common-envelope binary of period ~1 day. A detailed model of central star of Hen 2-155, is produced, showing the nebular progenitor to be a hot, post-AGB remnant of approximately 0.62 Msol, consistent with the age of the nebula, and the secondary star to be an M dwarf whose radius is almost twice the expected ZAMS radius for its mass. In spite of the small numbers, all main-sequence companions, of planetary nebulae central stars, to have had their masses and radii constrained by both photometric and spectroscopic observations have also been found to display this "inflation". The cause of the "inflation" is uncertain but is probably related to rapid accretion, immediately before the recent common-envelope phase, to which the star has not yet thermally adjusted. The chemical composition of both nebulae is also analysed, showing both to display elevated abundance discrepancy factors. This strengthens the link between elevated abundance discrepancy factors and close binarity in the nebular progenitor.

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arXiv2015

LMC S63: a historical reappraisal of the outburst behaviour of a deeply eclipsing Magellanic symbiotic star

We present an analysis of multi-epoch low-resolution spectrophotometry, complemented by the light curves provided by massive photometric surveys spanning over 100 years, of the symbiotic binary LMC S63. We showed that it is an eclipsing binary with the orbital period of 1050d. We also found evidence of outbursts in history of the white dwarf. If it was a Z-And type outburst, as is most likely, it would be a second such outburst recorded in the Magellanic Cloud symbiotic system. We confirmed that the red giant is enhanced in carbon, and estimated C/O~1.2 by fitting a model atmosphere to the SALT spectrum. We also found bi-periodic pulsations of the red giant, and demonstrated that it is similar to other carbon variables with confirmed bi-periodicity.

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arXiv2015

A radial velocity survey for post-common-envelope Wolf-Rayet central stars of planetary nebulae: First results and discovery of the close binary nucleus of NGC 5189

The formation of Wolf-Rayet central stars of planetary nebulae ([WR] CSPNe) whose spectroscopic appearance mimics massive WR stars remains poorly understood. Least understood is the nature and frequency of binary companions to [WR] CSPNe that may explain their H-deficiency. We have conducted a systematic radial velocity (RV) study of 6 [WR] CSPNe to search for post-common-envelope (post-CE) [WR] binaries. We used a cross-correlation method to construct the RV time-series as successfully done for massive close binary WR stars. No significant RV variability was detected for the late-[WC] type nuclei of Hen 2-113, Hen 3-1333, PMR 2 and Hen 2-99. Significant, large-amplitude variability was found in the [WC4] nucleus of NGC 5315. In the [WO1] nucleus of NGC 5189 we discovered significant periodic variability that reveals a close binary with $P_\mathrm{orb}=4.04\pm0.1$ d. We measured a semi-amplitude of $62.3\pm1.3$ km s$^{-1}$ that gives a companion mass of $m_2\ge0.5$ $M_\odot$ or $m_2=0.84$ $M_\odot$ (assuming $i=45^\circ$). The most plausible companion type is a massive WD as found in Fleming 1. The spectacular nebular morphology of NGC 5189 fits the pattern of recently discovered post-CE PNe extremely well with its dominant low-ionisation structures (e.g. as in NGC 6326) and collimated outflows (e.g. as in Fleming 1). The anomalously long 4.04 d orbital period is either a once-off (e.g. NGC 2346) or it may indicate there is a sizeable population of [WR] binaries with massive WD companions in relatively wide orbits, perhaps influenced by interactions with the strong [WR] wind.

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arXiv2014

OGLE-SMC-LPV-00861 (LIN 9): the first proven Z And outburst in a Magellanic symbiotic star

We report on the discovery of a new Small Magellanic Cloud (SMC) symbiotic star, OGLE-SMC-LPV-00861, previously catalogued as H$α$ emission line source LIN 9. The OGLE light curve shows multiple-maxima outburst behaviour over $\sim$1200 d with a maximum outburst of $ΔV=1.5$ mag. An optical spectrum of LIN 9 taken with the Southern African Large Telescope (SALT) at quiescence reveals a K5 red giant with emission lines confirming its symbiotic star nature, demonstrating the potential use of ongoing large time-domain surveys to identify strong symbiotic star candidates. It is the first Magellanic symbiotic star proven to show poorly understood Z And outbursts. At outburst the estimated hot component luminosity is $L\sim3165$ $L_\odot$, compared to $L\sim225$ $L_\odot$ at quiescence. Further observations are needed, especially at outburst, to better understand this unique Z And-like system at a known distance, and to provide essential input to physical models of the Z And phenomenon.

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arXiv2014

Identification of new Galactic symbiotic stars with SALT. I. Initial discoveries and other emission line objects

We introduce the first results from an ongoing, systematic survey for new symbiotic stars selected from the AAO/UKST SuperCOSMOS H$α$ Survey (SHS). The survey aims to identify and characterise the fainter population of symbiotic stars underrepresented in extant catalogues. The accreting white dwarfs (WDs) in symbiotic stars, fuelled by their red giant donors with high mass loss rate winds, make them promising candidates for type Ia supernovae. Several candidates were observed spectroscopically with the Southern African Large Telescope (SALT). A total of 12 bona-fide and 3 possible symbiotic stars were identified. The most remarkable example is a rare carbon-rich symbiotic star that displays coronal [Fe X] $λ$6375 emission, suggesting it may be a supersoft X-ray source with a massive WD. Several other emission line objects with near-infrared colours similar to symbiotic stars are listed in an appendix, including 6 B[e] stars, 4 planetary nebulae (PNe), 2 possible Be stars, one [WC9] Wolf-Rayet (WR) central star of a PN and one WC9 WR star. These initial discoveries will help shape and refine the candidate selection criteria that we expect will uncover several more symbiotic stars as the survey progresses.

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arXiv2014

The Morpho-kinematics of Planetary Nebulae with Binary Central Stars

It is now clear that a binary formation pathway is responsible for a significant fraction of planetary nebulae, and this increased sample of known binaries means that we are now in a position to begin to constrain their influence on the formation and evolution of their host nebulae. Here, we will review current understanding of how binarity influences the resulting nebulae, based on observations and modelling of both the central binary systems and the planetary nebulae themselves. We will also highlight the most important test-cases which have proved the most interesting in studying the evolution of binaries into and through the planetary nebula phase.

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arXiv2014

The post-common-envelope, binary central star of the planetary nebula Hen 2-11

We present a detailed photometric study of the central star system of the planetary nebula Hen 2-11, selected for study because of its low-ionisation filaments and bipolar morphology - traits which have been strongly linked with central star binarity. Photometric monitoring with NTT-EFOSC2 reveals a highly irradiated, double-eclipsing, post-common-envelope system with a period of 0.609 d. Modelling of the lightcurve indicates that the nebular progenitor is extremely hot, while the secondary in the system is probably a K-type main sequence star. The chemical composition of the nebula is analysed, showing Hen 2-11 to be a medium-excitation non-Type I nebula. A simple photoionisation model is constructed determining abundance ratios of C/O and N/O which would be consistent with the common-envelope cutting short the AGB evolution of the nebular progenitor. The detection of a post-common-envelope binary system at the heart of Hen 2-11 further strengthens the link between binary progeny and the formation of axisymmetric planetary nebulae with patterns of low-ionisation filaments, clearly demonstrating their use as morphological indicators of central star binarity.

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arXiv2013

A remarkable sample of new symbiotic stars towards the Galactic Bulge

Symbiotic stars are the longest orbital period interacting binaries, where nova-like outbursts are generated by the accretion of a high mass loss rate red giant wind onto a white dwarf companion. Long-term photometric monitoring surveys such as OGLE and MACHO are ideal platforms to identify nova-like events in symbiotic stars, however there are only a handful of known systems within the small footprint of these surveys. We introduce a systematic Halpha emission line object survey for new symbiotic stars covering 35 deg^2 towards the Galactic Bulge that combines deep 2dF/AAOmega spectroscopy with OGLE and MACHO photometry. This powerful combination has uncovered nearly two dozen new symbiotic stars, more than a dozen probable symbiotic stars, and several other unusual Halpha emission line stars. While we don't find any nova-like activity, the lightcurves do exhibit semi-regular and Mira pulsations, orbital variations and slower changes due to dust. Here we introduce a few of the new symbiotics, including H1-45, only the fourth known carbon symbiotic Mira. This remarkable discovery may be the first luminous carbon star belonging to the Galactic Bulge, according to its period-luminosity relation distance of 6.2+-1.4 kpc, potentially shedding new light on the puzzling lack of luminous carbon stars in the Bulge. We also present two old novae captured in the nebular phase, complementing other surveys to better characterise the old nova population.

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arXiv2013

Symbiotic stars and other Halpha emission line stars towards the Galactic Bulge

Symbiotic stars are interacting binaries with the longest orbital periods and their multi-component structure makes them rich astrophysical laboratories. The accretion of a high mass loss rate red giant wind on to a white dwarf (WD) makes them promising Type Ia supernovae (SNe Ia) progenitors. Systematic surveys for new Galactic symbiotic stars are critical to identify new promising SNe Ia progenitors (e.g. RS Oph) and to better estimate the total population size to compare against SNe Ia rates. Central to the latter objective is building a complete census of symbiotic stars towards the Galactic Bulge. Here we report on the results of a systematic survey of Halpha emission line stars covering 35 deg^2. It is distinguished by the combination of deep optical spectroscopy and long-term lightcurves that improve the certainty of our classifications. A total of 20 bona-fide symbiotic stars are found (13 S-types, 6 D-types and 1 D'-type), 35% of which show the symbiotic specific Raman-scattered OVI emission bands, as well as 15 possible symbiotic stars that require further study (6 S-types and 9 D-types). Lightcurves show a diverse range of variability including stellar pulsations (semi-regular and Mira), orbital variations and slow changes due to dust. Orbital periods are determined for 5 S-types and pulsation periods for 3 D-types. The most significant D-type found is H1-45 and its carbon Mira with a pulsation period of 408.6 days, corresponding to a distance of ~6.2+-1.4 kpc and M_K=-8.06+-0.12 mag. If H1-45 belongs to the Galactic Bulge, then it would be the first bona-fide luminous Galactic Bulge carbon star. The lack of luminous carbon stars in the Bulge is a longstanding unsolved problem. A possible explanation for H1-45 may be that the carbon enhancement was accreted from the progenitor of the WD companion. A wide variety of unusual emission line stars were also identified. (abridged)

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