arXiv subjects

Albert Zijlstra

Publications and source records attributed to Albert Zijlstra.

At least 37 records · Page 2Linked to original sources

arXiv2022

Morphologies and Central Stars of Planetary Nebulae in the Galactic bulge from VLT, $\textit{HST}$ and Pan-STARRS imaging

This is the first in a series of papers that present sets of different results for 136 compact, known planetary nebulae within a 10 $\times$ 10 degree region of the Galactic bulge. We use a large, previously unpublished sample of our own extensive ESO 8 m VLT deep imaging and spectroscopic data. This is combined with archival deep $\textit{HST}$ imaging where available to provide a detailed morphological classification and study. The influence of angular resolution and sensitivity when assigning a morphology is discussed. A large fraction (68%) of the sample are shown to be bipolars and the implications for this in the context of planetary nebulae progenitors are explored. Four new planetary nebula central stars are also identified which are not in $\textit{Gaia}$. This is based on both VLT and deep archival Pan-STARRS broad-band imagery. Some 11 putative central stars previously reported, based on $\textit{Gaia}$ positions, are also not the true central star. In other cases the $\textit{Gaia}$ central stars reported in the literature are actually based on the overall centroid position of a very compact planetary nebula rather than the actual central star within it. $\textit{Gaia}$ parallax distances and kinematic ages for PNe in this sample are provided where possible based on fresh angular size measures from the new VLT imagery and $\textit{Gaia}$ distances and literature expansion velocities when available. All these results are discussed within the context of the overall characteristics of the Galactic bulge and its planetary nebula population.

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arXiv2022

The infrared [WC] stars

A number of late [WC] stars have unique infrared properties, not found among the non-[WC] planetary nebulae, and together define a class of IR-[WC] stars. They have unusual IRAS colours, resembling stars in the earliest post-AGB evolution and possibly related to PAH formation. Most or all show a double chemistry, with both a neutral (molecular) oxygen-rich and an inner carbon-rich region. Their dense nebulae indicate recent evolution from the AGB, suggesting a fatal-thermal-pulse (FTP) scenario. Although both the colours and the stellar characteristics predict fast evolution, it is shown that this phase must last for 10^4 yr. The morphologies of the nebulae are discussed. For one object in Sgr, the progenitor mass (1.3 solar masses) is known. The stellar temperatures of the IR-[WC] stars appear much higher in low metallicity systems (LMC, Sgr). This may be indicative of an extended 'pseudo' photosphere. It is proposed that re-accretion of ejected gas may slow down the post-AGB evolution and so extend the life time of the IR-[WC] stars.

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arXiv2022

FAST search for circumstellar atomic hydrogen--I: the young planetary nebula IC 4997

Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in Guizhou, China, we detect the 21cm neutral atomic hydrogen absorption in the young planetary nebula IC 4997. The absorption arises from a shell also associated with Na I D lines. The H I shell has a mass of $1.46\times10^{-2}$ M$_\odot$ and a dynamic age of 990yr. The column density of H I is estimated to be $7.1\times10^{20}$ cm$^{-2}$, which can be well explained in terms of a photodissociation region around the ionized nebula, limited by self shielding of H$_2$. We find that the atomic-to-ionized hydrogen ratio is 0.6, suggesting that H I substantially contributes to overall nebular mass.

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arXiv2021

The remnant and origin of the historical supernova 1181AD

The guest star of AD 1181 is the only historical supernova of the last millennium that is without a definite counterpart. The previously proposed association with supernova remnant 3C58 is in strong doubt because of the inferred age of this remnant. Here we report a new identification of SN 1181 with our codiscovery of the hottest known Wolf Rayet star of the Oxygen sequence (dubbed Parkers star) and its surrounding nebula Pa 30. Our spectroscopy of the nebula shows a fast shock with extreme velocities of approx. 1,100kms. The derived expansion age of the nebula implies an explosive event approx 1,000 years ago which agrees with the 1181 AD event. The on sky location also fits the historical Chinese and Japanese reports of SN 1181 to 3.5degrees. Pa 30 and Parkers star have previously been proposed to be the result of a double-degenerate merger, leading to a rare Type Iax supernova. The likely historical magnitude and the distance suggest the event was subluminous for normal supernova. This agrees with the proposed Type Iax association which would also be the first of its kind in the Galaxy. Taken together, the age, location, event magnitude and duration elevate Pa 30 to prime position as the counterpart of SN 1181. This source is the only Type Iax supernova where detailed studies of the remnant star and nebula are possible. It provides strong observational support for the double degenerate merger scenario for Type Iax supernovae.

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arXiv2021

Radio stars of the SKA

Radio emission from stars can be used, e.g., to study ionized winds or stellar flares. The radio emission is faint and studies have been limited to few objects. The Square Kilometer Array (SKA) will bring a survey ability to the topic of radio stars. In this paper we investigate what the SKA can detect, and what sensitivity will be required for deep surveys of the stellar Milky Way. We focus on the radio emission from OB stars, Be stars, flares from M dwarfs, and Ultra Compact HII regions. The stellar distribution in the Milky Way is simulated using the Besancon model, and various relations are used to predict their radio flux. We find that the full SKA will easily detect all UltraCompact HII regions. At the limit of 10 nJy at 5 GHz, the SKA can detect 1500 Be stars and 50 OB stars per square degree, out to several kpc. It can also detect flares from 4500 M dwarfs per square degree. At 100 nJy the numbers become about 8 times smaller. SKA surveys of the Galactic plane should be designed for high sensitivity. Deep imaging should consider the significant number of faint flares in the field, even outside the plane of the Milky Way.

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arXiv2021

Atomium: The astounding complexity of the near circumstellar environment of the M-type AGB star R Hydrae. I. Morpho-kinematical interpretation of CO and SiO emission

Evolved low- to intermediate-mass stars are known to shed their gaseous envelope into a large, dusty, molecule-rich circumstellar nebula which typically develops a high degree of structural complexity. Most of the large-scale, spatially correlated structures in the nebula are thought to originate from the interaction of the stellar wind with a companion. As part of the Atomium large programme, we observed the M-type asymptotic giant branch (AGB) star R Hydrae with ALMA. The morphology of the inner wind of R Hya, which has a known companion at ~3500 au, was determined from maps of CO and SiO obtained at high angular resolution. A map of the CO emission reveals a multi-layered structure consisting of a large elliptical feature at an angular scale of ~10'' that is oriented along the north-south axis. The wind morphology within the elliptical feature is dominated by two hollow bubbles. The bubbles are on opposite sides of the AGB star and lie along an axis with a position angle of ~115 deg. Both bubbles are offset from the central star, and their appearance in the SiO channel maps indicates that they might be shock waves travelling through the AGB wind. An estimate of the dynamical age of the bubbles yields an age of the order of 100 yr, which is in agreement with the previously proposed elapsed time since the star last underwent a thermal pulse. When the CO and SiO emission is examined on subarcsecond angular scales, there is evidence for an inclined, differentially rotating equatorial density enhancement, strongly suggesting the presence of a second nearby companion. The position angle of the major axis of this disc is ~70 deg in the plane of the sky. We tentatively estimate that a lower limit on the mass of the nearby companion is ~0.65 Msol on the basis of the highest measured speeds in the disc and the location of its inner rim at ~6 au from the AGB star.

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arXiv2020

Atomium: A high-resolution view on the highly asymmetric wind of the AGB star Pi1 Gruis. I. First detection of a new companion and its effect on the inner wind

The nebular circumstellar environments of cool evolved stars are known to harbour a rich morphological complexity of gaseous structures on different length scales. A large part of these density structures are thought to be brought about by the interaction of the stellar wind with a close companion. The S-type asymptotic giant branch star Pi1 Gruis, which has a known companion at ~440 au and is thought to harbour a second, closer-by (<10 au) companion, was observed with the Atacama Large Millimeter/submillimeter Array as part of the ATOMIUM Large programme. In this work, the brightest CO, SiO, and HCN molecular line transitions are analysed. The continuum map shows two maxima, separated by 0.04'' (6 au). The CO data unambiguously reveal that Pi1 Gru's circumstellar environment harbours an inclined, radially outflowing, equatorial density enhancement. It contains a spiral structure at an angle of 38+/-3 deg with the line-of-sight. The HCN emission in the inner wind reveals a clockwise spiral, with a dynamical crossing time of the spiral arms consistent with a companion at a distance of 0.04'' from the asymptotic giant branch star, which is in agreement with the position of the secondary continuum peak. The inner wind dynamics imply a large acceleration region, consistent with a beta-law power of ~6. The CO emission suggests that the spiral is approximately Archimedean within 5'', beyond which this trend breaks down as the succession of the spiral arms becomes less periodic. The SiO emission at scales smaller than 0.5'' exhibits signatures of gas in rotation, which is found to fit the expected behaviour of gas in the wind-companion interaction zone. An investigation of SiO maser emission reveals what could be a stream of gas accelerating from the surface of the AGB star to the companion. Using these dynamics, we have tentatively derived an upper limit on the companion mass to be ~1.1 Msol.

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arXiv2020

Betelgeuse fainter in the sub-millimetre too: an analysis of JCMT and APEX monitoring during the recent optical minimum

Betelgeuse is the nearest Red Supergiant star and it underwent an unusually deep minimum at optical wavelengths during its most recent pulsation cycle. We present submillimetre observations taken by the James Clerk Maxwell Telescope and Atacama Pathfinder Experiment over a time span of 13 years including the optical dimming. We find that Betelgeuse has also dimmed by \sim20\% at these longer wavelengths during this optical minimum. Using radiative-transfer models, we show that this is likely due to changes in the photosphere (luminosity) of the star as opposed to the surrounding dust as was previously suggested in the literature.

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arXiv2019

CO in the C1 globule of the Helix nebula with ALMA

We present and analyse 12CO, 13CO and C18O(2-1) ALMA observations of the C1 globule inside the Helix nebula in order to determine its physical properties. Our findings confirm the molecular nature of the globule with a multi-peak structure. The 12CO line has a high optical depth of about 10. The derived 12C/13C ratio of 10 and 16O/18O ratio of 115 are not in agreement with the expected isotopic ratios of carbon-rich AGB stars. Assuming that the 12CO optical depth has been underestimated, we can find a consistent fit for an initial mass of 2 Msol. We obtain a molecular mass of 2x10-4 Msol for the C1 globule, which is much higher than its mass in the literature. Clumping could play a role in the high molecular mass of the knot. The origin of the tail is discussed. Our findings show that the most probable model appears to be shadowing. The kinematics and molecular morphology of the knot are not consistent with a wind-swept model and the photoevaporation model alone is not enough to explain the nature of the globule. We propose an integrated model where the effects of the photoevaporation, the stream and shadowing models are all considered in the tail shaping process.

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arXiv2019

ALMA reveals the aftermath of a white dwarf--brown dwarf merger in CK Vulpeculae

We present Atacama Large Millimeter-Submillimeter Array (ALMA) observations of CK Vulpeculae which is identified with "Nova Vulpeculae 1670". They trace obscuring dust in the inner regions of the associated nebulosity. The dust forms two cocoons, each extending ~5 arcsec north and south of the presumed location of the central star. Brighter emission is in a more compact east-west structure (2 arcsec by 1 arcsec) where the cocoons intersect. We detect line emission in NH$_2$CHO, CN, four organic molecules and C$^{17}$O. CN lines trace bubbles within the dusty cocoons; CH$_3$OH a north-south S-shaped jet; and other molecules a central cloud with a structure aligned with the innermost dust structure. The major axis of the overall dust and gas bubble structure has a projected inclination of ~24 degrees with respect to a 71 arcsec extended "hourglass" nebulosity, previously seen in H alpha. Three cocoon limbs align with dark lanes in the inner regions of the same H alpha images. The central 2 arcsec by 1 arcsec dust is resolved into a structure consistent with a warped dusty disc. The velocity structure of the jets indicates an origin at the centre of this disc and precession with an unknown period. Deceleration regions at both the northern and southern tips of the jets are roughly coincident with additional diffuse dust emission over regions approximately 2 arcsec across. These structures are consistent with a bipolar outflow expanding into surrounding high density material. We suggest that a white dwarf and brown dwarf merged between 1670 and 1672, with the observed structures and extraordinary isotopic abundances generated as a result.

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arXiv2019

A high-mass Planetary Nebula in a Galactic Open Cluster

Planetary Nebulae are the ionised ejected envelopes surrounding the remnant cores of dying stars. Theory predicts that main-sequence stars with one to about eight times the mass of our sun may eventually form planetary nebulae. Until now no example has been confirmed at the higher mass range. Here we report that planetary nebula BMP J1613-5406 is associated with Galactic star cluster NGC 6067. Stars evolving off the main sequence of this cluster have a mass around five solar masses. Confidence in the planetary nebula-cluster association comes from their tightly consistent radial velocities in a sightline with a steep velocity-distance gradient, common distances, reddening and location of the planetary nebula within the cluster boundary. This is an unprecedented example of a planetary nebular whose progenitor star mass is getting close to the theoretical lower limit of core-collapse supernova formation. It provides evidence supporting theoretical predictions that 5+ solar mass stars can form planetary nebulae. Further study should provide fresh insights into stellar and Galactic chemical evolution.

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arXiv2018

Central Stars of Planetary Nebulae in Galactic Open Clusters: Providing additional data for the White Dwarf Initial-to-Final-Mass Relation

Accurate (<10%) distances of Galactic star clusters allow precise estimation of the physical parameters of any physically associated Planetary Nebula (PN) and also that of its central star (CSPN) and its progenitor. The progenitor's mass can be related to the PN's chemical characteristics and furthermore, provides additional data for the widely used white dwarf (WD) initial-to-final mass relation (IFMR) that is crucial for tracing the development of both carbon and nitrogen in entire galaxies. To date there is only one PN (PHR1315- 6555) confirmed to be physically associated with a Galactic open cluster (ESO 96 -SC04) that has a turn-off mass $\sim$2 M$_{\odot}$. Our deep HST photometry was used for the search of the CSPN of this currently unique PN. In this work, we present our results.

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arXiv2018

Extended Dust Emission from Nearby Evolved Stars

We present JCMT SCUBA-2 $450μ$m and $850μ$m observations of 14 Asymptotic Giant Branch (AGB) stars (9 O--rich, 4 C-rich and 1 S--type) and one Red Supergiant (RSG) in the Solar Neighbourhood. We combine these observations with \emph{Herschel}/PACS observations at $70μ$m and $160μ$m and obtain azimuthally-averaged surface-brightness profiles and their PSF subtracted residuals. The extent of the SCUBA-2 850 $μ$m emission ranges from 0.01 to 0.16 pc with an average of $\sim40\%$ of the total flux being emitted from the extended component. By fitting a modified black-body to the four-point SED at each point along the radial profile we derive the temperature ($T$), spectral index of dust emissivity ($β$) and dust column density ($Σ$) as a function of radius. For all the sources, the density profile deviates significantly from what is expected for a constant mass-loss rate, showing that all the sources have undergone variations in mass-loss during this evolutionary phase. In combination with results from CO line emission, we determined the dust-to-gas mass ratio for all the sources in our sample. We find that, when sources are grouped according to their chemistry, the resulting average dust-to-gas ratios are consistent with the respective canonical values. However we see a range of values with significant scatter which indicate the importance of including spatial information when deriving these numbers.

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arXiv2018

Herschel Planetary Nebula Survey (HerPlaNS): Hydrogen Recombination Laser Lines in Mz 3

The bipolar nebula Menzel 3 (Mz 3) was observed as part of the \textit{Herschel} Planetary Nebula Survey (\textit{HerPlaNS}), which used the PACS and SPIRE instruments aboard the \textit{Herschel Space Observatory} to study a sample of planetary nebulae (PNe). In this paper, one of the series describing \textit{HerPlaNS} results, we report the detection of H I recombination lines (HRLs) in the spectrum of Mz 3. Inspection of the spectrum reveals the presence of 12 HRLs in the 55 to 680 $μ$m range covered by the PACS and SPIRE instruments (H11$α$ to H21$α$ and H14$β$). The presence of HRLs in this range is unusual for PNe and has not been reported in Mz 3 before. Our analysis indicates that the HRLs we observed are enhanced by laser effect occurring in the core of Mz 3. Our arguments for this are: (i) the available Mz 3 optical to submillimetre HRL $α$ line intensity ratios are not well reproduced by the spontaneous emission of optically thin ionized gas, as would be typical for nebular gas in PNe; (ii) the compact core of Mz 3 is responsible for a large fraction of the Herschel HRLs emission; (iii) the line intensity ratios for Mz 3 are very similar to those in the core emission of the well known star MWC 349A, where laser effect is responsible for the enhancement of HRLs in the Herschel wavelength range; (iv) the physical characteristics relevant to cause laser effect in the core of MWC 349A are very similar to those in the core of Mz 3.

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arXiv2017

The binary fraction of planetary nebula central stars: the promise of VPHAS+

The majority of planetary nebulae (PNe) are not spherical, and current single-star models cannot adequately explain all the morphologies we observe. This has led to the Binary Hypothesis, which states that PNe are preferentially formed by binary systems. This hypothesis can be corroborated or disproved by comparing the estimated binary fraction of all PNe central stars (CS) to that of the supposed progenitor population. One way to quantify the rate of CS binarity is to detect near infra-red (IR) excess indicative of a low-mass main sequence companion. In this paper, a sample of known PNe within data release 2 of the ongoing VPHAS+ are investigated. We give details of the method used to calibrate VPHAS+ photometry, and present the expected colours of CS and main sequence stars within the survey. Objects were scrutinized to remove PN mimics from our sample and identify true CS. Within our final sample of 7 CS, 6 had previously either not been identified or confirmed. We detected an $i$ band excess indicative of a low-mass companion star in 3 CS, including one known binary, leading us to to conclude that VPHAS+ provides the precise photometry required for the IR excess method presented here, and will likely improve as the survey completes and the calibration process finalised. Given the promising results from this trial sample, the entire VPHAS+ catalogue should be used to study PNe and extend the IR excess-tested CS sample.

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arXiv2016

Pulsation-triggered mass loss from AGB stars: the 60-day critical period

Low- and intermediate-mass stars eject much of their mass during the late, red giant branch (RGB) phase of evolution. The physics of their strong stellar winds is still poorly understood. In the standard model, stellar pulsations extend the atmosphere, allowing a wind to be driven through radiation pressure on condensing dust particles. Here we investigate the onset of the wind, using nearby RGB stars drawn from the Hipparcos catalogue. We find a sharp onset of dust production when the star first reaches a pulsation period of 60 days. This approximately co-incides with the point where the star transitions to the first overtone pulsation mode. Models of the spectral energy distributions show stellar mass-loss rate suddenly increases at this point, by a factor of ~10 over the existing (chromospherically driven) wind. The dust emission is strongly correlated with both pulsation period and amplitude, indicating stellar pulsation is the main trigger for the strong mass loss, and determines the mass-loss rate. Dust emission does not strongly correlate with stellar luminosity, indicating radiation pressure on dust has little effect on the mass-loss rate. RGB stars do not normally appear to produce dust, whereas dust production by asymptotic giant branch stars appears commonplace, and is probably ubiquitous above the RGB-tip luminosity. We conclude that the strong wind begins with a step change in mass-loss rate, and is triggered by stellar pulsations. A second rapid mass-loss-rate enhancement is suggested when the star transitions to the fundamental pulsation mode, at a period of ~300 days.

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arXiv2015

Identification of a Class of Low-Mass Asymptotic Giant Branch Stars Struggling to Become Carbon Stars in the Magellanic Clouds

We have identified a new class of Asymptotic Giant Branch (AGB) stars in the Small and Large Magellanic Clouds (SMC/LMC) using optical to infrared photometry, light curves, and optical spectroscopy. The strong dust production and long-period pulsations of these stars indicate that they are at the very end of their AGB evolution. Period-mass-radius relations for the fundamental-mode pulsators give median current stellar masses of 1.14 M_sun in the LMC and 0.94 M_sun in the SMC (with dispersions of 0.21 and 0.18 M_sun, respectively), and models suggest initial masses of <1.5 M_sun and <1.25 M_sun, respectively. This new class of stars includes both O-rich and C-rich chemistries, placing the limit where dredge-up allows carbon star production below these masses. A high fraction of the brightest among them should show S star characteristics indicative of atmospheric C/O ~ 1, and many will form O-rich dust prior to their C-rich phase. These stars can be separated from their less-evolved counterparts by their characteristically red J-[8] colors.

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arXiv2015

Planetary nebulae in 2014: A review of research

Planetary nebulae had a double anniversary in 2014, 250 year since their discovery and 150 year since the correct spectroscopic identification. This paper gives an overview of planetary nebula research published in 2014. Topics include surveys, central stars, abundances, morphologies, magnetic fields, stellar population and galactic dynamics. An important continuing controversy is the discrepancy between recombination-line and forbidden-line abundances. A new controversy is the relation between symbiotic stars and [WC] stars. PN of the year is undoubtedly CRL 618, with papers on its binary symbiotic/[WC] nucleus, rapid stellar evolution, expanding jets and magnetic fields.

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