arXiv subjects

Peter Goodhew

Publications and source records attributed to Peter Goodhew.

8 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.

astro-ph.SR↗

arXiv2026

K 1-6 is a photoionised ISM nebula shaped by a fast-moving hot white dwarf in a triple system

K 1-6 has long been classified as a planetary nebula (PN) hosting a binary central star, yet it has remained poorly studied due to its faintness. The central star exhibits pronounced photometric variability whose origin has so far been unclear. We aim to present a comprehensive characterisation of the K 1-6 system, including the physical properties of its stellar components and the nature of the surrounding nebulosity. We conducted a multi-wavelength analysis combining optical and UV spectroscopy obtained with the Gran Telescopio Canarias, the Telescopio Nazionale Galileo, the Nordic Optical Telescope, and the Hubble Space Telescope. We also present long-term multi-band ground- and space-based photometry, including high-cadence data from the Transiting Exoplanet Survey Satellite, narrow-band imaging, and the latest astrometric constraints from Gaia. Our results show that the nebula is not a remnant PN, but instead consists of interstellar medium photoionised by a hot white dwarf, which is relatively evolved. It has a cooling age of 1-2 Myr, implying that any original PN has long since dissipated. We further find that the central object is a hierarchical triple system, comprising an inner binary with an orbital period likely of the order of thousands of days and a distant tertiary companion on a timescale of tens of thousands of years. The optically dominant cool component of the inner binary is an inflated K-type star displaying extreme magnetic activity, including large-amplitude variability and flaring. Its properties resemble those of BY Dra-type binaries and Abell 35-type systems, and are difficult to reconcile with single-star evolution, pointing instead to a history of binary interaction.

astro-ph.SR↗

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.

astro-ph.SR↗

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.

astro-ph.SR↗

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.

astro-ph.SR↗

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.

astro-ph.SR↗

arXiv2023

The unusual planetary nebula nucleus in the Galactic open cluster M37 and six further hot white dwarf candidates

Planetary nebulae in Galactic open star clusters are rare objects; only three are known to date. They are of particular interest because their distance can be determined with high accuracy, allowing one to characterize the physical properties of the planetary nebula and its ionizing central star with high confidence. Here we present the first quantitative spectroscopic analysis of a central star in an open cluster, namely the faint nucleus of IPHASX J055226.2$+$323724 in M37. This cluster contains 14 confirmed white dwarf members, which were previously used to study the initial-to-final-mass relation of white dwarfs, and six additional white dwarf candidates. We performed an atmosphere modeling of spectra taken with the 10m Gran Telescopio Canarias. The central star is a hot hydrogen-deficient white dwarf with an effective temperature of 90,000 K and spectral type PG1159 (helium- and carbon-rich). We know it is about to transform into a helium-rich DO white dwarf because the relatively low atmospheric carbon abundance indicates ongoing gravitational settling of heavy elements. The star belongs to a group of hot white dwarfs that exhibit ultrahigh-excitation spectral lines possibly emerging from shock-heated material in a magnetosphere. We find a relatively high stellar mass of $M= 0.85^{+0.13}_{-0.14}$ M$_\odot$. This young white dwarf is important for the semi-empirical initial-final mass relation because any uncertainty related to white-dwarf cooling theory is insignificant with respect to the pre-white-dwarf timescale. Its post-asymptotic-giant-branch age of $170,000-480,000$ yr suggests that the extended planetary nebula is extraordinarily old. We also performed a spectroscopic analysis of the six other white dwarf candidates of M37, confirming one as a cluster member.

astro-ph.SR↗

arXiv2022

WHTZ 1: A high excitation Planetary Nebula not a gaseous cocoon from runaway star HD 185806

We present evidence that the nebular cocoon and bow-shock emission nebula putatively and recently reported as deriving from the 9th magnitude "runaway" star HD 185806 is the previously discovered but obscure planetary nebula WHTZ 1 (Ra 7). It has a Gaia DR3 G~16 blue ionizing star at its geometric centre. We present imagery, spectroscopy, other data and arguments to support that this emission source is a high excitation Planetary Nebula not a stellar wind bow shock.

astro-ph.SR↗