Central Stars Of Planetary Nebulae Research Articles

Binary central stars of planetary nebulae in the Large Magellanic Cloud

Context. Close binary central stars of planetary nebulae (PNe) must have formed through a common envelope evolution during the giant phase experienced by one of the stars. Transfer of the angular momentum from the binary system to the envelope leads to the shortening of the binary separations from the radius of red giant to the radius of the order of few tenths of AU. Thus, close binary central stars of planetary nebulae are laboratories to study the common envelope phase of evolution. The close binary fraction in the Galaxy has been measured in various sky surveys, but the close binary fraction is not yet well constrained for the Magellanic Clouds, and our results may help the study of common envelope evolution in low-metallicity environments. Aims. This paper presents a continuation of our study of variability in the Magellanic Cloud planetary nebulae on the basis of data from the OGLE survey. Previously, we had analysed the OGLE data in the Small Magellanic Cloud. Here, the study is extended to the Large Magellanic Cloud (LMC). In this paper we search for close binary central stars with the aim to constrain the binary fraction and period distribution in the LMC. Methods. We identified 290 counterparts of PNe in the LMC in the I-band images from the OGLE-III and OGLE-IV surveys. However, the light curves of ten objects were not accessible in the OGLE database, and thus we analysed the time series photometry of 280 PNe. Results. In total, 32 variables were found, but 5 of them turned out to be foreground objects. Another 18 objects show irregular or regular variability that is not attributable to the binarity of their central stars. Their status and the nature of their variability will be verified in the follow-up paper. Nine binary central stars of PNe with periods between 0.24 and 23.6 days were discovered. The obtained fraction for the LMC PNe is 3.3-1.6+2.6% without correcting for incompleteness. This number is significantly lower than the 12–21% derived in the analogous search in the Galactic bulge. We discuss this difference, taking into account observational biases. The lower binary fraction suggests a lower efficiency of the common envelope phase in producing close binaries in the LMC compared to the Galaxy.

The origin of the planetary nebula M 1–16

We investigated the origin of the Planetary Nebula (PN) M 1–16 using narrow-band optical imaging, and high- and low-resolution optical spectra to perform a detailed morpho-kinematic and chemical studies. M 1–16 is revealed to be a multipolar PN that predominantly emits in [O III] in the inner part of the nebula and [N II] in the lobes. A novel spectral unsharp masking technique was applied to the position-velocity (PV) maps to reveal a set of multiple structures at the centre of M 1–16 spanning radial velocities from −40 km s−1 to 20 km s−1, with respect to the systemic velocity. The morpho-kinematic model indicates that the deprojected velocity of the lobe outflows are ≥100 km s−1, and particularly the larger lobes and knots have a deprojected velocity of ≃350 km s−1; the inner ellipsoidal component has a deprojected velocity of ≃29 km s−1. A kinematical age of ~8700 yr has been obtained from the model assuming a homologous velocity expansion law and a distance of 6.2 ± 1.9 kpc. The chemical analysis indicates that M 1–16 is a Type I PN with a central star of PN (CSPN) mass in the range of ≃0.618 – 0.713 M⊙ and an initial mass for the progenitor star between 2.0 and 3.0 M⊙ (depending on metallicity). An Teff ≃ 140 000 K and log(L/L⊙) = 2.3 was estimated using the 3MdB photoionisation models to reproduce the ionisation. stage of the PN. All of these results have led us to suggest that M 1–16 is an evolved PN, contrary to the scenario of proto-PN suggested in previous studies. We propose that the mechanism responsible for the morphology of M 1–16 is related to the binary (or multiple star) evolution scenario.

The Variability and Radial Velocity of Planetary Nebula Central Stars

The extremely accurate estimates of stellar variability and radial velocity in the Gaia Data Release 3 (Gaia DR3) have enabled us to examine the close binarity and radial velocity (RV) of central stars (CSs) of planetary nebulae (PNe). This study is twofold: (1) searching for new close binary CS candidates to better understand how binarity affects the formation and evolution of PNe; and (2) extending the sample size of known RVs of PNe in order to understand their kinematics and the dynamics of the Milky Way. As a target sample, we used all true, possible, and likely PNe available in the literature. Then, we looked for their matched Gaia DR3 sources that provide measurements of variability and RV. As a result, we detected the first large collection of trustworthy photometric variability of 26 symbiotic stars and 82 CSs. In this CS group, there are 24 sources already classified as true close binary CSs in the literature. Hence, we discovered 58 new close binary CS candidates. This close binary (CB) sample represents more than half of what is currently available in the literature. In addition, we identified the radial velocities for 51 PNe. To our knowledge, 24 of these were measured for the first time. The RV measurements predicted by Gaia, based on the Doppler shift of the CS absorption lines, and those derived from nebular emission lines, show satisfactory agreement except for a few extremely high-velocity PNe.

Planetary nebulae hosting accreting white dwarfs: a possible solution for the mysterious cut-off of planetary nebula luminosity function?

ABSTRACTMany binary companions to the central stars of planetary nebulae (PNe) are found to be inflated, perhaps indicating that accretion onto the central star might occur during the planetary nebula (PN) phase. The discovery of a handful of nova eruptions and supersoft X-ray sources inside PNe supports this hypothesis. In this paper, we investigate the impact that hosting a steadily accreting white dwarf (WD) would have on the properties and evolution of a PN. By pairing the published accreting nuclear-burning WD models with radiation transfer simulations, we extract the time evolution of the emission line spectra and ionization properties of a PN that surrounds a 0.6$\, \rm M_{\odot }$ steadily nuclear-burning WD as a function of the mass accretion rate. We find that accreting WDs are able to form very extended, high excitation, [${\rm O\, \small {\rm III}}$]-bright PNe, which are characterized by high nebular electron temperatures. Their properties remain almost invariant with time and their visibility time can be much longer compared to PNe powered by single WDs. We discuss the implications of our findings in explaining specific characteristics observed in PNe. Finally, we examine how accreting WDs affect the planetary nebula luminosity function (PNLF) by covering WD masses in the range of 0.5–0.8$\, \rm M_{\odot }$ and for various accretion rates within the steady accretion regime. We find that for all but the lowest accretion rates, the [${\rm O\, \small {\rm III}}$] luminosities are almost constant and clustered very close to the PNLF cut-off value. Our results suggest that mass-accreting WDs in interacting binaries might play a role in understanding the invariant cut-off of the PNLF.

A New Study on a Type Iax Stellar Remnant and its Probable Association with SN 1181

We report observations and modeling of the stellar remnant and presumed double-degenerate merger of Type Iax supernova Pa 30, which is the probable remnant of SN 1181 AD. It is the only known bound stellar SN remnant and the only star with Wolf–Rayet features that is neither a planetary nebula central star nor a massive Population I progenitor. We model the unique emission-line spectrum with broad, strong O vi and O viii lines as a fast stellar wind and shocked, hot gas. Non-LTE wind modeling indicates a mass-loss rate of ∼10−6 M ⊙ yr−1 and a terminal velocity of ∼15,000 km s−1, consistent with earlier results. O viii lines indicate shocked gas temperatures of T ≃ 4 MK. We derive a magnetic field upper limit of B < 2.5 MG, below earlier suggestions. The luminosity indicates a remnant mass of 1.0–1.65 M ⊙ with ejecta mass 0.15 ± 0.05 M ⊙. Archival photometry suggests the stellar remnant has dimmed by ∼0.5 mag over 100 yr. A low Ne/O < 0.15 argues against an O-Ne white dwarf in the merger. A cold dust shell is only the second detection of dust in an SN Iax and the first of cold dust. Our ejecta mass and kinetic energy estimates of the remnant are consistent with Type Iax extragalactic sources.

Editorial: Planetary nebulae as tools for astrophysics

Planetary nebulae (PNe) represent the ejected outer layers of an evolved low-to-intermediate mass 11star, and consist of ionized, neutral, and molecular components, along with dust. In total, the nebular 12 material contains the stellar envelope that was ejected during the AGB phase or through binary 13 interactions with a companion. The PN central star is formed by the former core of the AGB or RGB 14 progenitor of the PNe, which is now contracting towards the white dwarf phase. The PN central star 15 is a post-AGB object which has evolved crossing the HR diagram, and has an effective temperature 16 of 28,000 K up to more than 250,000 K. It emits a large fraction of its light as UV photons that ionize 17 the envelope. PNe are mainly studied through imaging, photometry and low-and high-resolution 18 spectroscopy techniques which allow determination of the physical conditions and chemical 19 abundances in the nebula. Through this kind of analysis it is possible to study the physical processes 20 in ionized plasmas, the evolution and characteristics of the central star, along with the mechanisms of 21 ejection of the nebula and the evolution of the interstellar medium (ISM) -in external galaxies as 22 well as in the Milky Way -which will be enriched with elements produced in the stellar 23 nucleosynthesis and brought to the stellar surface via several dredge-up episodes. Further, an accurate 24 census of PNe provides an important constraint on a galaxy's star formation history.

A Survey for C ii Emission-line Stars in the Large Magellanic Cloud. II. Final Results and the Origin of C ii Emission in [WC] Spectra

We present the final results of an imaging and spectroscopic search for stars in the Large Magellanic Cloud (LMC) with C ii λλ7231, 7236 emission lines. The goal is to identify and study [WC11] stars, the coolest of the low-mass Wolf–Rayet sequence, and a subset of central stars of planetary nebulae where the C ii lines are known to be especially prominent. A recent serendipitous discovery of an LMC [WC11] raised the possibility that these objects, although difficult to identify, might in fact be more common than previously believed. Several new members of this rare class have been found in this survey. It now seems clear, however, that a significant number of these stars are not hiding among the general [WC] population. We point out that the C ii doublet intensity ratio observed in our spectra proves to neatly divide the objects into two distinct groups, with the C ii emission likely originating from either the stellar wind or a surrounding nebula. The physics of the C ii emission mechanism correctly explains this bifurcation. Spectral subtypes are suggested for most of the objects. The numerous spectroscopic clues now available for these objects should facilitate future detailed modeling.

Morphologies and Central Stars of Planetary Nebulae in the Galactic bulge from VLT, HST and Pan-STARRS imaging

ABSTRACT This is the first in a series of papers that present sets of different results for 136 compact, known planetary nebulae within a 10 × 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 Hubble Space Telescope 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 per cent) 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 Gaia. This is based on both Very Large Telescope (VLT) and deep archival Pan-STARRS broad-band imagery. Some 11 putative central stars previously reported, based on Gaia positions, are also not the true central star. In other cases, the 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. 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 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.

New Close Binary Central Stars of Planetary Nebulae from Gaia DR3 Epoch Photometry

Close binary interactions perform a key role in the formation and shaping of planetary nebulae (PNe). However only a small fraction of Galactic PNe are known to host close binary systems. Many such systems are detectable through photometric variability. We searched recently published epoch photometry data from Gaia DR3 for planetary nebula central stars with periodic photometric variability indicative of binarity, uncovering four previously unknown close binaries.

A census of post-AGB stars in Gaia DR3: evidence for a substantial population of Galactic post-RGB stars

ABSTRACT This paper presents the first census of Galactic post-asymptotic giant branch (post-AGB) stars in the Hertzsprung–Russell (HR) diagram. We combined Gaia DR3 parallax-based distances with extinction corrected integrated fluxes and derived luminosities for a sample of 185 stars that had been proposed to be post-AGB stars in the literature. The luminosities allow us to create an HR diagram containing the largest number of post-AGB candidate objects to date. A significant fraction of the objects fall outside the typical luminosity range as covered by theoretical evolutionary post-AGB tracks as well as observed for planetary nebula central stars. These include massive evolved supergiants and lower luminosity objects. Here, we highlight the fact that one-third of the post-AGB candidates are underluminous and we identify these with the recently recognized class of post-red giant branch objects thought to be the result of binary evolution.

A New Statistical Distance Scale for Planetary Nebulae, Based on Gaia EDR3

The present work aims to build a new statistical distance scale for planetary nebulae (PNe) based on a rigorous calibration sample. The distances of the calibration sample are derived from the trigonometric parallax method using the recent measurements of Gaia Early Data Release 3 (Gaia EDR3). The new distance scale is created by applying the well-known linear relationship between the radio surface brightness temperature and the nebular radius. The calibration sample is made up of 96 PNe of accurately computed distances with uncertainties less than 20%. Earlier ground- and space-based trigonometric parallaxes of PNe display inconsistency with those of Gaia, particularly the Hipparcos results. In addition, these measurements have appreciably lower precision than those of Gaia. When compared to the trigonometric technique, the expansion and kinematic methods exhibited more consistency than the spectroscopic, extinction, gravity, and photoionization methods. Furthermore, contrary to earlier results in the literature, the extinction and gravity methods, on average, underestimate and slightly overestimate the PN distances respectively. As a byproduct of extracting the Gaia parallaxes, we detect the radial velocity and variability for 14 and 3 PN central stars (CSs), respectively. To our knowledge, the variability of Hen 2-447 CS has been determined for the first time.

Hot white dwarf candidates from the IGAPS-GALEX cross-match

ABSTRACT White dwarf (WD) stars are often associated with the central stars of planetary nebulae (CSPNe) on their way to the cooling track. A large number of WD star candidates have been identified; thanks to optical large-scale surveys such as Gaia DR2 and EDR3. However, hot-WD/CSPNe stars are quite elusive in optical bands due to their high temperatures and low-optical luminosities. The Galaxy Evolution Explorer (GALEX) matched with the INT Galactic Plane Survey (IGAPS) allowed us to identify hot-WD candidates by combining the GALEX far-UV (FUV)and near-UV (NUV)with optical photometric bands (g, r, i, and Hα). After accounting for source confusion and filtering bad photometric data, a total of 236 485 sources were found in the GALEX and IGAPS footprint (GaPHAS). A preliminary selection of hot stellar sources was made using the GALEX colour cut on FUV−NUV&amp;gt; −0.53, yielding 74 hot-WD candidates. We analysed their spectral energy distribution (SED) by developing a fitting program for single- and two-body SED using an MCMC algorithm; 41 are probably binary systems (a binary fraction of ∼55 per cent was estimated). Additionally, we classified the WD star candidates using different infrared (IR) colours available for our sample, obtaining similar results as in the SED analysis for the single and binary systems. This supports the strength of the fitting method and the advantages of the combination of GALEX UV with optical photometry. Ground-based time-series photometry and spectra are required in order to confirm the nature of the WD star candidates.

On the Detectability of Post-common-envelope Binary Central Stars of Planetary Nebulae

Abstract Common envelope evolution is widely accepted as the principal shaping agent in the formation of aspherical planetary nebulae. However, only some 20% of planetary nebulae are found to host post-common-envelope binary central stars. To probe the detectability of post-common-envelope binary central stars, and their potential to evade detection, we simulate the light curves of an array of these systems varying their stellar and orbital parameters. We find that while binaries with late-type companions and/or long orbital periods will likely go undetected, they are unlikely to represent a large fraction of the overall post-common-envelope central star population.

Two evolved close binary stars: GALEX J015054.4+310745 and the central star of the planetary nebula Hen 2-84

ABSTRACT As part of a survey to find close binary systems among central stars of planetary nebula, we present two newly discovered binary systems. GALEX J015054.4+310745 is identified as the central star of the possible planetary nebula Fr 2-22. We find it to be a single-lined spectroscopic binary with an orbital period of 0.2554435(10) d. We support the previous identification of GALEX J015054.4+310745 as an sdB star and provide physical parameters for the star from spectral modelling. We identify its undetected companion as a likely He white dwarf. Based on this information, we find it unlikely that Fr 2-22 is a true planetary nebula. In addition, the central star of the true planetary nebula Hen 2-84 is found to be a photometric variable, likely due to the irradiation of a cool companion. The system has an orbital period of 0.485645(30) d. We discuss limits on binary parameters based on the available light-curve data. Hen 2-84 is a strongly shaped bipolar planetary nebula, which we now add to the growing list of axially or point-symmetric planetary nebulae with a close binary central star.

The post-common-envelope binary central star of the planetary nebula Ou 5: a doubly eclipsing post-red-giant-branch system

ABSTRACT We present a detailed study of the stellar and orbital parameters of the post-common envelope binary central star of the planetary nebula Ou 5. Low-resolution spectra obtained during the primary eclipse – to our knowledge the first isolated spectra of the companion to a post-common-envelope planetary nebula central star – were compared to catalogue spectra, indicating that the companion star is a late K- or early M-type dwarf. Simultaneous modelling of multiband photometry and time-resolved radial velocity measurements was then used to independently determine the parameters of both stars as well as the orbital period and inclination. The modelling indicates that the companion star is low mass (∼0.25 M⊙) and has a radius significantly larger than would be expected for its mass. Furthermore, the effective temperature and surface gravity of nebular progenitor, as derived by the modelling, do not lie on single-star post-AGB evolutionary tracks, instead being more consistent with a post-RGB evolution. However, an accurate determination of the component masses is challenging. This is principally due to the uncertainty on the locus of the spectral lines generated by the irradiation of the companion’s atmosphere by the hot primary (used to derive companion star’s radial velocities), as well as the lack of radial velocities of the primary.

Planetary nebulae in Gaia EDR3: Central star identification, properties, and binarity

Context. The Gaia Early Data Release 3 (EDR3), published in December 2020, features improved photometry and astrometry compared to that published in the previous DR2 file and includes a substantially larger number of sources, of the order of 2000 million, making it a paradigm of big data astronomy. Many of the central stars of planetary nebulae (CSPNe) are inherently faint and difficult to identify within the field of the nebula itself. Gaia measurements may be relevant not only in identifying the ionising source of each nebula, but also in the study their physical and evolutionary properties. Aims. We demonstrate how Gaia data mining can effectively help to solve the issue of central star misidentification, a problem that has plagued the field since its origin. As we did for DR2, our objective is to present a catalogue of CSPNe with astrometric and photometric information in EDR3. From that catalogue, we selected a sample of stars with high-quality astrometric parameters, on which we carried out a more accurate analysis of CSPNe properties. Methods.GaiaGBP − GRP colours allow us to select the sources with sufficient temperatures to ionise the nebula. In order to estimate the real colour of a source, it is important to take into account interstellar extinction and, in the case of compact nebulae, nebular extinction when available. In addition, distances derived from EDR3 parallaxes (combined with consistent literature values) can be used to obtain nebular intrinsic properties from those observed. With this information, CSPNe can be plotted in an Hertzsprung-Russell diagram. From information on the spectral classification of the CS (from the literature) and evolutionary models for post-AGB stars, their evolutionary state can then be analysed. Furthermore, EDR3 high-quality astrometric data enable us to search for objects comoving with CSs in the field of each nebula by detecting sources with parallaxes and proper motions similar to those of the CS. Results. We present a catalogue of 2035 PNe with their corresponding CS identification from among Gaia EDR3 sources. We obtain the distances for those with known parallaxes in EDR3 (1725 PNe). In addition, for a sub-sample (405 PNe) with the most accurate distances, we obtain different nebular properties such as their Galactic distribution, radius, kinematic age, and morphology. Furthermore, for a set of 74 CSPNe, we present the evolutionary state (mass and age) derived from their luminosities and effective temperatures from evolutionary models. Finally, we highlight the detection of several wide binary CSPNe through an analysis of the EDR3 astrometric parameters, and we contribute to shedding some light on the relevance of close binarity in CSPNe.

Physical and Chemical Properties of Wolf–Rayet Planetary Nebulae

Abstract Wolf–Rayet ([WR]) and weak-emission-line (wels) central stars of planetary nebulae (PNs) have hydrogen-deficient atmospheres, whose origins are not well understood. In the present study, we have conducted plasma diagnostics and abundance analyses of 18 Galactic PNs surrounding [WR] and wels nuclei, using collisionally excited lines (CELs) and optical recombination lines (ORLs) measured with the Wide Field Spectrograph on the Australian National University 2.3 m telescope at the Siding Spring Observatory complemented with optical archival data. Our plasma diagnostics imply that the electron densities and temperatures derived from CELs are correlated with the intrinsic nebular Hβ surface brightness and excitation class, respectively. Self-consistent plasma diagnostics of heavy-element ORLs of N2+ and O2+ suggest that a small fraction of cool (≲7000 K), dense (∼104–105 cm−3) materials may be present in some objects, though with large uncertainties. Our abundance analyses indicate that the abundance discrepancy factors (ADFs ≡ ORLs/CELs) of O2+ are correlated with the dichotomies between forbidden-line and He i temperatures. Our results likely point to the presence of a tiny fraction of cool, oxygen-rich dense clumps within diffuse warm ionized nebulae. Moreover, our elemental abundances derived from CELs are mostly consistent with asymptotic giant branch models in the range of initial masses from 1.5 to 5 M ⊙. Further studies are necessary to understand better the origins of abundance discrepancies in PNs around [WR] and wels stars.

One star, two star, red star, blue star: an updated planetary nebula central star distance catalogue from Gaia EDR3

Context. Planetary nebulae (PNe) are a brief but important phase of stellar evolution. The study of Galactic PNe has historically been hampered by uncertain distances, but the parallaxes of PN central stars (CSPNe) measured by Gaia are improving the situation. Aims. Gaia’s Early Data Release 3 (EDR3) offers higher astrometric precision and greater completeness compared to previous releases. Taking advantage of these improvements requires that the CSPNe in the catalogue be accurately identified. Methods. We applied our automated technique based on the likelihood ratio method to cross-match known PNe with sources in Gaia EDR3, using an empirically derived position and colour distribution to score candidate matches. Results. We present a catalogue of over 2000 sources in Gaia EDR3 that our method has identified as likely CSPNe or compact nebula detections. We show how the more precise parallaxes of these sources compare to previous PN statistical distances and introduce an approach to combining them to produce tighter distance constraints. We also discuss Gaia’s handling of close companions and bright nebulae. Conclusions. Gaia is unlocking new avenues for the study of PNe. The catalogue presented here will remain valid for the upcoming Gaia Data Release 3 (DR3) and thus provide a valuable resource for years to come.

Binary central stars of planetary nebulae identified with Kepler/K2

ABSTRACT We present the identification of 34 likely binary central stars (CSs) of planetary nebulae (PNe) from Kepler/K2 data, seven of which show eclipses. Of these, 29 are new discoveries. Two additional CSs with more complicated variability are also presented. We examined the light curves of all ‘possible’, ‘likely’, and ‘true’ PNe in every Kepler/K2 campaign (0 through 19) to identify CS variability that may indicate a binary CS. For Campaigns 0, 2, 7, 15, and 16, we find 6 likely or confirmed variables among 21 PNe. Our primary effort, though, was focused on Campaign 11 which targeted a Galactic bulge field containing approximately 183 PNe, in which we identified 30 candidate variable CSs. The periods of these variables range from 2.3 h to 30 d, and based on our analysis, most are likely to be close binary star systems. We present periods and preliminary classifications (eclipsing, double degenerate, or irradiated systems) for the likely binaries based on light-curve shape. From our total sample of 204 target PNe, with a correction for incompleteness due to magnitude limits, we calculate a binary fraction of PN central stars to be 20.7 per cent for all the observed PNe, or 23.5 per cent if we limit our sample only to ‘true’ PNe. However, these fractions are almost certainly lower limits due to the large angular size of the Kepler pixels, which leads to reduced sensitivity in detecting variability, primarily as a result of dilution and noise from the nebula and neighbouring stars. We discuss the binary population of CSs based on these results as part of the total known sample of close binary CSs.

Towards a more complete sample of binary central stars of planetary nebulae with Gaia

Context. Many if not most planetary nebulae (PNe) are now thought to be the outcome of binary evolutionary scenarios. However, only a few percent of the PNe in the Milky Way are known to host binary systems. The high-precision repeated observing and long time baseline of Gaia make it well suited for detecting new close binaries through photometric variability. Aims. We aim to find new close binary central stars of PNe (CSPNe) using data from the Gaia mission, building towards a statistically significant sample of post-common envelope, close binary CSPNe. Methods. As the vast majority of Gaia sources do not have published epoch photometry, we used the uncertainty in the mean photometry as a proxy for determining the variability of our CSPN sample in the second Gaia data release. We derived a quantity that expresses the significance of the variability, and considered what is necessary to build a clean sample of genuine variable sources. Results. Our selection recovers a large fraction of the known close binary CSPN population, while other CSPNe lying in the same region of the parameter space represent a promising set of targets for ground-based confirmatory follow-up observations. Gaia epoch photometry for four of the newly identified variable sources confirms that the variability is genuine and consistent with binarity.