arXiv subjects

Howard E. Bond

Publications and source records attributed to Howard E. Bond.

At least 19 recordsLinked to original sources

arXiv2026

Ionized Nebulae Around Two New Symbiotic Stars: GR Cygni and [D75] 141

In the course of selecting targets for a spectroscopic survey of faint planetary-nebula nuclei, we encountered two anomalous cases of late-type variable stars surrounded by nebulosities discovered by amateur astronomers. We obtained follow-up deep narrow-band images of the two nebulae: StDr Objet 14 (diameter 1.5 arcmin) and StDr 4 (diameter 2.5 arcmin). StDr Objet 14 is found to be a low-excitation nebula, bright only in Ha+[N II], and showing a unique double-ring "bull's-eye" morphology. StDr 4 exhibits a bow-shock structure, bright in Halpha and [S II], embedded in an extended emission nebula. Both central stars, respectively GR Cygni and [D75] 141, are found to be pulsating semiregular variable stars. Our spectroscopic observations show GR Cyg to be a cool carbon star of type C9,2, with emission lines of the Balmer series, [O II] and [O III], [Ne III], [S II], and Fe II. A synthetic narrow-band image of GR Cyg shows that the source of its strong [O II] 3727 A emission line is a knot displaced from the star by about 1.6 arcsec, indicative of a recent collimated ejection event. [D75] 141 is a M6 III red giant, with weak Balmer-series emission. Both stars show a blue excess, and GR Cyg was detected in the near-UV by the GALEX spacecraft. These data establish both stars as new symbiotic binaries, containing a late-type red giant and a hot companion accreting from its stellar wind. We speculate that the double rings surrounding GR Cyg were ejected during helium-shell thermal pulses (or conceivably from recurring nova outbursts), while the nebula around [D75] 141 may be the result of a collision of the symbiotic star's ejecta with an interstellar cloud. Our accidental discoveries of these two binaries because they are surrounded by faint nebulae supports the view that there is a significant population of "missing" symbiotic stars yet to be discovered.

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arXiv2026

SPIRITS 19q: Dust Production by a Subsolar-metallicity Carbon-rich Wolf-Rayet Star in NGC 2403

We present JWST/NIRSpec IFU observations of SPIRITS 19q, the highly dust-producing carbon-rich (WC) binary candidate located in a subsolar-metallicity region of the nearby spiral galaxy NGC 2403. The observations, taken in April of 2024, confirm the association of a dusty outburst observed in 2019 by the Spitzer Space Telescope with an early-type WC star. Using models from the Potsdam Wolf-Rayet (PoWR) LMC model grid we find that the WC star of SPIRITS 19q likely has an especially high mass-loss rate ($\gtrsim$ 10$^{-4}$ $M_{\odot}$ yr$^{-1}$). From the flux peak of the IR transient as measured by Spitzer/IRAC as well as constraints on dust composition and size from the JWST spectrum, we estimate a total dust mass formed in the outburst of 6.6 $\pm$ 0.4 $\times$ 10$^{-6}$ $M_{\odot}$. Assuming a minimum orbital period of 12 years, this corresponds to a period-averaged dust production rate of $\lesssim$ 5.5 $\times$ 10$^{-7}$ $M_{\odot}$ yr$^{-1}$. These observations suggest that even a single WC system can contribute to the dust budget at subsolar metallicities, and that such systems are an important source of carbonaceous dust grains in the early universe.

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arXiv2026

Spectroscopic survey of faint planetary-nebula nuclei. VII. Thirty new hydrogen-deficient central stars

Our ongoing spectroscopic survey of faint planetary-nebula nuclei (PNNi) has revealed 30 new hydrogen-deficient central stars. The majority of them (21) belong to the PG1159 spectral class (having He-C-O-dominated atmospheres). They increase the number of known PN central stars of this type from 25 to 46. Our spectral analysis finds that their effective temperatures are high (T$_{\rm eff}$ = 110,000 - 180,000 K), locating them in the GW Vir pulsational instability strip. Future photometric observations should therefore substantially increase the number of known PNN pulsators (currently, it is nine). We found six new members of the O(He) spectral type (with He-dominated atmospheres; T$_{\rm eff}$ = 120,000 - 150,000 K), tripling the number of known PNNi of this class. Finally, we identified three hot helium-rich white dwarfs with traces of carbon and/or nitrogen (spectral type DOZ; T$_{\rm eff}$ = 70,000 - 100,000 K). They are the first objects of this spectral class found to be associated with a planetary nebula.

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arXiv2026

Spectroscopic Survey of Faint Planetary-Nebula Nuclei. VIII. The Dwarf Barium Central Star of Kohoutek 1-9

In the course of our ongoing survey of faint planetary-nebula nuclei (PNNi), we obtained optical spectroscopy of the central star of the little-studied PN Kohoutek~1-9 (K 1-9). Its spectrum is found to be that of a G-type dwarf with strong absorption features of carbon molecules and s-process elements such as Sr and Ba--a dwarf barium star. K 1-9 thus joins a very small group of PNe with barium-star nuclei. Their likely progenitors are wide binaries in which the primary star reached the thermally pulsing asymptotic-giant-branch (AGB) phase, dredged up C and s-process elements from its interior, and transferred enriched material to the companion through a dense stellar wind. The remnant core is now a hot, optically inconspicuous (pre-)white dwarf, responsible for ionizing the AGB ejecta, and leaving the optical spectrum dominated by the cool barium star. We present deep narrow-band images of K 1-9, obtained by accumulating long exposure times using amateur telescopes. The PN shows a thin-ring morphology, remarkably similar to the "wedding-ring" shapes seen around other members of this class of binary PNNi. The thin ring probably represents material preferentially ejected into the orbital plane of the binary; we note that the PNN is slightly off-center within the ring, as has been predicted theoretically. We suggest several follow-up studies, including precision photometry to search for periodic variations due to starspots on the rotating barium star, and high-resolution spectroscopy to determine atmospheric parameters of the star, chemical abundances, and its rotation velocity.

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arXiv2025

A Bow-Shock Nebula Around the Z Camelopardalis-type Cataclysmic Variable FY Vulpeculae

We present deep images of the faint nebulosity StDr 90, which we have discovered surrounds the cataclysmic variable (CV) star FY Vulpeculae. Archival photometric and spectroscopic observations, and a new optical spectrum, confirm that FY Vul belongs to the Z Camelopardalis subclass of CVs. Our imagery, obtained by accumulating long exposures with amateur telescopes equipped with CMOS cameras, shows a prominent bow shock in the light of [O III] 5007 A, collisionally excited in front of the star as it passes through a relatively dense region in the surrounding interstellar medium (ISM). FY Vul also lies near the edge of an extended faint Halpha-emitting nebula, which we interpret as a "recombination wake," i.e., a Stromgren zone recombining after being photoionized by the star's ultraviolet radiation. FY Vul joins five other CVs known to be associated with optical bow shocks and off-center nebulae. All of them are characterized by luminous accretion disks, which drive fast winds into the ISM that produce the bow shocks.

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arXiv2025

Serendipitous Discovery of a Faint Planetary Nebula in the Massive Young LMC Cluster NGC 1866

During an integral-field spectroscopic study of stars in the massive young open cluster NGC 1866 in the Large Magellanic Cloud, we serendipitously discovered a faint planetary nebula (PN). We designate it "Ka LMC 1," and find that its location near the cluster center, along with the agreement of its radial velocity with that of the cluster, imply a high probability of membership in NGC 1866. The 200 Myr age of the cluster indicates that the PN's progenitor star had an initial mass of about 3.9 Msun. The integrated spectrum of Ka LMC 1 shows strong emission lines of [N II], consistent with it being a "Type I" nitrogen-rich PN. The nebula exhibits a classical ring morphology, with a diameter of ~6", corresponding to an advanced expansion age of about 18,000 yr. Archival images of NGC 1866 obtained with the Hubble Space Telescope reveal a faint blue central star. Comparison of the star's luminosity with predictions from one set of theoretical post-asymptotic-giant-branch evolutionary tracks for single stars implies an age roughly consistent with the dynamical age of the PN, but the agreement with alternative modern tracks is much poorer. Analysis of the emission-line spectrum suggests considerable dust extinction within the nebula; however the central star possibly suffers little reddening because we may be viewing it nearly pole-on in a bipolar PN. Our accidental discovery was made using data that are not ideal for study of Ka LMC 1; we suggest several avenues of future targeted studies that would provide valuable and nearly unique new information for constraining models of late stellar evolution.

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arXiv2025

Variability of Central Stars of Planetary Nebulae with the Zwicky Transient Facility. II. Long-Timescale Variables including Wide Binary and Late Thermal Pulse Candidates

In this second paper on our variability survey of central stars of planetary nebulae (CSPNe) using ZTF, we report 11 long-timescale variables with variability timescales ranging from months to years. We also present preliminary analyses based on spectroscopic and/or photometric follow-up observations for six of them. Among them is NGC 6833, which shows a $980$ day periodic variability with strange characteristics: `triangle-shaped' brightening in $r$, $i$, and WISE bands but almost coincidental shallow dips in the $g$-band. The most plausible explanation is a wide binary with the photometric period being the orbital period. Long-period near-sinusoidal variability was detected in two other systems, NGC 6905 and Kn 26, with periods of $700$ days and $230$ days, respectively, making them additional wide-binary candidates. The latter also shows a short period at $1.18$ hours. We then present CTSS 2 and K 3-5, which show brightening and significant reddening over the whole ZTF baseline. A stellar model fit to the optical spectrum of CTSS 2 reveals it to be one of the youngest post-AGB CSPNe known. Both show high-density emission-line cores. We propose these to be late-thermal-pulse candidates, currently evolving towards the AGB phase. We then present recent HST/COS ultraviolet spectroscopy of the known wide-binary candidate LoTr 1, showing that the hot star is a spectroscopic twin of the extremely hot white dwarf in UCAC2 46706450. Similar to this object, LoTr 1 also has a fast-rotating wide subgiant companion. We suggest that the long photometric period of 11 years is the binary orbital period. Finally, we briefly discuss the ZTF light curves of the remaining variables, namely Tan 2, K 3-20, WHTZ 3, Kn J1857+3931, and IPHAS J1927+0814. With these examples, we present the effectiveness of the von Neumann statistics and Pearson Skew-based metric space in searching for long-timescale variables.

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arXiv2025

Discovery of Faint Nebulosity Around a Z Camelopardalis-type Cataclysmic Variable in Antlia: Nova Shell or Ancient Planetary Nebula?

We report our discovery of a faint nebula surrounding a previously little-studied 15th-mag variable star, ASASSN-19ds, in the southern-hemisphere constellation Antlia. Spectra verify that the star is a cataclysmic variable (CV). Using new and archival photometry, we confirm that ASASSN-19ds is an eclipsing binary with an orbital period of 0.139 days (3.34 hr). Moreover, its out-of-eclipse brightness shows a "sawtooth" light curve with an amplitude of $\sim$1~mag and an interval between peaks that varies between about three to nearly five weeks. Its mean absolute magnitude in the Gaia system is $M_G=+6.5$. These combined properties lead to a classification of ASASSN-19ds as a Z Camelopardalis-type CV. We obtained deep narrow-band images of the nebulosity, using modest-sized telescopes and extremely long exposure times. Our imagery reveals a bipolar morphology, with thin arcs at the ends of the major axis, likely indicating an interaction with the interstellar medium. We consider several scenarios for the origin of the nebula, but from the existing information we are unable to distinguish between it being ejecta from an unobserved classical-nova outburst several centuries ago, or an ancient planetary nebula. Future observations should be able to decide between these possibilities. At the star's distance of only $\sim$557 pc, a nova eruption would have been a spectacular naked-eye event.

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arXiv2025

Two More Bow Shocks and Off-Center Halpha Nebulae Associated with Nova-like Cataclysmic Variables

We report discoveries of bow-shock nebulae, seen in Halpha and [O III] 5007, around two cataclysmic variables (CVs): LS Pegasi and ASASSN-V J205457.73+515731.9 (hereafter ASASJ2054). Additionally, both stars lie near the edges of faint extended Halpha-emitting nebulae. The orientations of the bow shocks are consistent with the directions of the objects' proper motions. The properties of LS Peg and ASASJ2054, and of their nebulae, are remarkably similar to those of SY Cancri, which we described in a recent paper; SY Cnc is a CV likewise associated with a bow shock and an off-center Halpha nebula. These objects join V341 Arae and BZ Camelopardalis, CVs that are also accompanied by similar nebulae. All five stars belong to the nova-like variable (NLV) subclass of CVs, characterized by luminous optically thick accretion disks that launch fast winds into the surrounding space. We suggest that the bow shocks and nebulae result from chance encounters of the NLVs with interstellar gas clouds, with the stars leaving in their wakes Stromgren zones that are recombining after being photoionized by the CVs' ultraviolet and X-ray radiation. Our discoveries illustrate the power of small telescopes equipped with modern instrumentation, and used to accumulate extremely long exposure times, for the detection of very low-surface-brightness nebulae.

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arXiv2025

Testing Cluster Membership of Planetary Nebulae with High-Precision Proper Motions. II. HST Observations of PHR J1315-6555 in the Open Cluster AL 1 (ESO 96-SC04)

Planetary nebulae (PNe) shown to be members of star clusters provide information on their properties and evolutionary histories that cannot be determined for PNe in the field, in particular the initial masses of their progenitor stars. Here we investigate the bipolar PN PHR J1315-6555 (hereafter PHR J1315), which lies near the open cluster AL 1 (ESO 96-SC04) on the sky. Previous work has established that the PN and cluster have similar radial velocities and amounts of interstellar reddening, and similar distances estimated using independent methods. We have obtained new images of the PN and cluster using the Hubble Space Telescope (HST). Combined with archival HST frames taken 12 years earlier, they provide high-precision proper motions (PMs) for two candidate central stars of PHR J1315. We find that the PMs of both candidates are consistent with those of cluster members, strongly confirming the PN's membership in AL 1. The candidate lying closer to the center of PHR J1315 has the color and luminosity of an early F-type dwarf, suggesting that it may be the optical primary in a close post-common-envelope binary. We used the HST data to construct a color-magnitude diagram for AL 1, which we corrected for significant foreground differential reddening. Isochrone fitting reveals that the cluster lies at a remarkably large distance of about 13 kpc, and has an age of about 1.0 Gyr. The initial mass of the progenitor of PHR J1315 was about 2.1 Msun. We suggest followup investigations that would provide tighter constraints on the object's evolution.

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arXiv2025

Variability of Central Stars of Planetary Nebulae with the Zwicky Transient Facility. I. Methods, Short-Timescale Variables, Binary Candidates, and the Unusual Nucleus of WeSb 1

Over the past several decades, time-series photometry of CSPNe has yielded significant results including, but not limited to, discoveries of nearly 100 binary systems, insights into pulsations and winds in young white dwarfs, and studies of stars undergoing very late thermal pulses. We have undertaken a systematic study of optical photometric variability of cataloged CSPNe, using the light curves from the Zwicky Transient Facility (ZTF). By applying appropriate variability metrics, we arrive at a list of 94 highly variable CSPN candidates. Based on the timescales of the light-curve activity, we classify the variables broadly into short- and long-timescale variables. In this first paper in this series, we focus on the former, which is the majority class comprising 83 objects. We report periods for six sources for the first time, and recover several known periodic variables. Among the aperiodic sources, most exhibit a jitter around a median flux with a stable amplitude, and a few show outbursts. We draw attention to WeSb 1, which shows a different kind of variability: prominent deep and aperiodic dips, resembling transits from a dust/debris disk. We find strong evidence for a binary nature of WeSb 1 (possibly an F-type subgiant companion). The compactness of the emission lines and inferred high electron densities make WeSb 1 a candidate for either an EGB 6-type planetary nucleus, or a symbiotic system inside an evolved planetary nebula, both of which are rare objects. To demonstrate further promise with ZTF, we report three additional newly identified periodic sources that do not appear in the list of highly variable sources. Finally, we also introduce a two-dimensional metric space defined by the von Neumann statistics and Pearson Skew and demonstrate its effectiveness in identifying unique variables of astrophysical interest, like WeSb 1.

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arXiv2024

Discovery of Two New Eruptions of the Ultrashort Recurrence Time Nova M31N 2017-01e

We report the recent discovery of two new eruptions of the recurrent nova M31N 2017-01e in the Andromeda galaxy. The latest eruption, M31N 2024-08c, reached $R=17.8$ on 2024 August 06.85 UT, $\sim2$ months earlier than predicted. In addition to this recent eruption, a search of archival PTF data has revealed a previously unreported eruption on 2014 June 18.46 UT that reached a peak brightness of $R\sim17.9$ approximately a day later. The addition of these two eruption timings has allowed us to update the mean recurrence time of the nova. We find $\langle T_\mathrm{rec} \rangle = 924.0\pm7.0$ days ($2.53\pm0.02$ yr), which is slightly shorter than our previous determination. Thus, M31N 2017-01e remains the nova with the second shortest recurrence time known, with only M31N 2008-12a being shorter. We also present a low-resolution spectrum of the likely quiescent counterpart of the nova, a $\sim20.5$ mag evolved B star displaying an $\sim14.3$ d photometric modulation.

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arXiv2024

Discovery of a Bow-Shock Nebula around the Z Cam-type Cataclysmic Variable SY Cancri

We report the serendipitous discovery of a bow-shock nebula around the cataclysmic variable (CV) SY Cancri. In addition, SY Cnc lies near the edge of a faint Halpha-emitting nebula with a diameter of about 15'. The orientation of the bow shock is consistent with the direction of SY Cnc's proper motion. Nebulae are extremely rare around CVs, apart from those known to have undergone classical-nova (CN) outbursts; bow shocks and off-center nebulae are even more unusual. Nevertheless, the properties of SY Cnc and its nebulosity are strikingly similar to those of V341 Ara, another CV that is also associated with a bow shock and is likewise off-center with respect to its faint Halpha nebula. Both stars are binaries with optically thick accretion disks, belonging to the classes of Z Cam CVs or nova-like variables. We discuss three scenarios to explain the properties of the nebulae. They may have resulted from chance encounters with interstellar gas clouds, with the stars leaving in their wakes material that is recombining after being photoionized by UV radiation from the CVs. Alternatively, the large nebulae could be ejecta from unobserved CN outbursts in the recent past, which have been decelerated through collisions with the interstellar medium (ISM), while the stars continue to snowplow through the gas. Or the faint Halpha nebulae may be ambient ISM that was shock-ionized by a CN outburst in the past and is now recombining.

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arXiv2024

Spectroscopic survey of faint planetary-nebula nuclei VI. Seventeen hydrogen-rich central stars

We present an analysis of 17 H-rich central stars of planetary nebulae (PNe) observed in our spectroscopic survey of nuclei of faint Galactic PNe carried out at the 10-m Hobby-Eberly Telescope. Our sample includes ten O(H) stars, four DAO white dwarfs (WDs), two DA WDs, and one sdOB star. The spectra were analyzed by means of NLTE model atmospheres, allowing us to derive the effective temperatures, surface gravities, and He abundances of the central stars. Sixteen of them were analyzed for the first time, increasing the number of hot H-rich central stars with parameters obtained through NLTE atmospheric modeling by approximately 20%. We highlight a rare hot DA WD central star, Abell 24, which has a $T_\mathrm{eff}$ likely in excess of 100kK, as well as the unusually high gravity mass of $0.70 \pm 0.05 \mathrm{M}_\odot$ for the sdOB star Pa 3, which is significantly higher than the canonical extreme horizontal-branch star mass of $\approx 0.48\,\mathrm{M}_{\odot}$. By investigating Zwicky Transient Facility light curves, which were available for our 15 northern objects, we found none of them show a periodic photometric variability larger than a few hundredths of a magnitude. This could indicate that our sample mainly represents the hottest phase during the canonical evolution of a single star when transitioning from an asymptotic giant branch star into a WD. We also examined the spectral energy distributions, detecting an infrared excess in six of the objects, which could be due to a late-type companion or to hot ($\approx 10^3$ K) and\or cool ($\approx 100$ K) dust. We confirm previous findings that spectroscopic distances are generally higher than found through Gaia astrometry, a discrepancy that deserves to be investigated systematically.

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arXiv2024

Testing Cluster Membership of Planetary Nebulae with High-Precision Proper Motions. I. HST Observations of JaFu 1 Near the Globular Cluster Palomar 6

If a planetary nebula (PN) is shown to be a member of a star cluster, we obtain important new constraints on the mass and chemical composition of the PN's progenitor star, which cannot be determined for PNe in the field. Cluster membership can be tested by requiring the projected separation between the PN and cluster to be within the tidal radius of the cluster, and the objects to have nearly identical radial velocities (RVs) and interstellar extinctions, and nearly identical proper motions (PMs). In an earlier study, we used PMs to confirm that three PNe, which had already passed the other tests, are highly likely to be members of Galactic globular clusters (GCs). For a fourth object, the PN JaFu 1, which lies in the Galactic bulge near the GC Palomar 6 on the sky and has a similar RV, the available PM measurement gave equivocal results. We have now obtained new high-resolution images of the central star of JaFu 1 with the Hubble Space Telescope (HST) which, combined with archival HST frames taken 14 and 16 years earlier, provide a high-precision PM. Unfortunately, we find that the PM of the central star differs from that of the cluster with high statistical significance, and thus is unlikely to be a member of Palomar 6. Nevertheless, JaFu 1 is of astrophysical interest because its nucleus appears to be a member of the rare class of "EGB 6-type" central stars, which are associated with compact emission-line knots.

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arXiv2024

The Orbit and Dynamical Mass of Polaris: Observations with the CHARA Array

The 30 year orbit of the Cepheid Polaris has been followed with observations by the CHARA Array (Center for High Angular Resolution Astronomy) from 2016 through 2021. An additional measurement has been made with speckle interferometry at the Apache Point Observatory. Detection of the companion is complicated by its comparative faintness--an extreme flux ratio. Angular diameter measurements appear to show some variation with pulsation phase. Astrometric positions of the companion were measured with a custom grid-based model-fitting procedure and confirmed with the CANDID software. These positions were combined with the extensive radial velocities discussed by Torres (2023) to fit an orbit. Because of the imbalance of the sizes of the astrometry and radial velocity datasets, several methods of weighting are discussed. The resulting mass of the Cepheid is 5.13$\pm$ 0.28 $M_\odot$. Because of the comparatively large eccentricity of the orbit (0.63), the mass derived is sensitive to the value found for the eccentricity. The mass combined with the distance shows that the Cepheid is more luminous than predicted for this mass from evolutionary tracks. The identification of surface spots is discussed. This would give credence to the identification of photometric variation with a period of approximately 120 days as a rotation period. Polaris has some unusual properties (rapid period change, a phase jump, variable amplitude, unusual polarization). However, a pulsation scenario involving pulsation mode, orbital periastron passage (Torres 2023), and low pulsation amplitude can explain these characteristics within the framework of pulsation seen in Cepheids.

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arXiv2024

Spectroscopic Survey of Faint Planetary-Nebula Nuclei. V. The EGB 6-Type Central Star of Abell 57

During our spectroscopic survey of central stars of faint planetary nebulae (PNe), we found that the nucleus of Abell 57 exhibits strong nebular emission lines. Using synthetic narrow-band images, we show that the emission arises from an unresolved compact emission knot (CEK) coinciding with the hot (90,000 K) central star. Thus Abell 57 belongs to the rare class of "EGB 6-type" PNe, characterized by dense emission cores. Photometric data show that the nucleus exhibits a near-IR excess, due to a dusty companion body with the luminosity of an M0 dwarf but a temperature of ~1800 K. Emission-line analysis reveals that the CEK is remarkably dense (electron density ~1.6x10**7 cm**-3), and has a radius of only ~4.5 AU. The CEK suffers considerably more reddening than the central star, which itself is more reddened than the surrounding PN. These puzzles may suggest an interaction between the knot and central star; however, Hubble Space Telescope imaging of EGB 6 itself shows that its CEK lies more than ~125 AU from the PN nucleus. We discuss a scenario in which a portion of the AGB wind that created the PN was captured into a dust cloud around a distant stellar companion; this cloud has survived to the present epoch, and has an atmosphere photoionized by radiation from the hot central star. However, in this picture EGB 6-type nuclei should be relatively common, yet they are actually extremely rare; thus they may arise from a different transitory phenomenon. We suggest future observations of Abell 57 that may help unravel its mysteries.

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arXiv2024

Spectroscopic Survey of Faint Planetary-Nebula Nuclei. IV. The Abell 35-Type Central Star of Pa 27

We present optical spectroscopy of the 12th-mag central star of the planetary nebula (PN) Patchick 27 (Pa 27), obtained during a survey of faint PN nuclei (PNNi) with the Low-Resolution Spectrograph (LRS2) of the Hobby-Eberly Telescope. The optical spectrum of Pa 27 is that of a K0 III red giant with rotationally broadened lines. However, the star is detected in the near-ultraviolet (near-UV) with GALEX, showing that a hot binary component is also present. The spectral-energy distribution from the near-UV to the mid-infrared can be fitted with a combination of the K0 III giant and a hot PNN with an effective temperature of about 50,000 K. Photometric observations of Pa 27, both ground-based and from TESS, show a low-amplitude sinusoidal variation with a period of 7.36 days, probably due to starspots on a rotating and magnetically active cool giant. Pa 27 is a new member of the rare class of "Abell 35-type central stars," which are binary PNNi consisting of a spotted late-type star and a hot pre-white dwarf. They are likely the result of a situation where an AGB star ejects its outer layers in a dense wind, part of which is captured by a distant companion, spinning up its rotation by accretion of material and angular momentum. We suggest several useful follow-up observations.

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