arXiv subjects

Nicholas Chornay

Publications and source records attributed to Nicholas Chornay.

5 recordsLinked to original sources

arXiv2026

Candidates for the most [$O_{III}$] $\lambda5007$-luminous planetary nebula in the Milky Way. I. Integrated light properties of NGC 6572, NGC 6884, and M 1-71

The bright-end cutoff of the planetary nebula luminosity function (PNLF) serves as an extragalactic standard candle. However, the physical properties of planetary nebulae (PNe) at the PNLF cutoff have been studied only in nearby galaxies, where the PNe appear mostly as point sources. Galactic PNLF is further poorly constrained, primarily due to uncertainties in Galactic PN distances. Following a recent Galactic PNLF survey based on Gaia distances, we aim to characterise PN candidates at the Galactic PNLF cutoff. We observed three PN candidates at the Galactic PNLF cutoff using the Potsdam Multi-Aperture Spectrophotometer (PMAS). We determined their chemical abundances and constructed photoionisation models to derive the central star luminosity (L) and effective temperature (Teff). We constrained the central star masses and most likely distances consistent with the prediction of stellar evolution models. Using these distances, we determined the absolute magnitude M5007. PNe of our sample are located within the top 1 mag of the Galactic PNLF (-4.20 < M5007 <-3.60), with similar nebular properties and a narrow progenitor mass range (1.30-1.75 Msolar). The measured extinction is mostly dominated by the foreground Galactic extinction. The trend between the circum-nebular extinction and central star mass of our PNe is in agreement with those derived in the Large Magellanic Cloud (LMC) and M31. All PNe in our sample exhibit weak-emission line star (wels) features in their spectra, but we confirmed that some of these lines originate from the nebula. The PNe are similar in terms of their nebular properties and evolutionary stage. Their characteristics are also consistent with the most [OIII]5007-luminous PNe in the LMC and M31. We demonstrate the importance of circum-nebular extinction and the initial-final mass relation (IFMR) to understand the universality of PNLF as a standard candle.

astro-ph.GA↗

arXiv2026

Two hot pre-white dwarfs inside the red-giant-branch planetary nebula Pa 13 -- Double core evolution or common envelope-induced rejuvenation?

Close binary central stars of PNe offer a unique window for investigating the conditions immediately following the ejection of a common envelope (CE). Double eclipsing and double-lined double systems are particularly valuable as they provide minimally model-dependent constraints on fundamental binary parameters. We report that the nucleus of Pa13 (P=0.3988d) belongs to this rare class of systems and present a comprehensive analysis of its double-degenerate binary. We performed a two-component NLTE spectral analysis based on phase-resolved X-Shooter spectroscopy, multi-band light-curve modeling, SED fitting, as well as a kinematic analysis. Both stars are found to be hot pre-white dwarfs, with Star1 being cooler but larger (Teff=50kK, R=0.40Rsol) than Star2 (Teff=75kK, R=0.16Rsol). The weakness of spectral lines of Star2 made both the atmospheric and RV analyses challenging, and we uncovered a strong sensitivity of the assumed surface ratio to its derived RV curve. Yet, the RV curve and Kiel mass of Star1 (M1=0.41+/-0.02Msol) could be determined precisely, allowing for a dynamical mass determination of Star2 (M2=0.39+/-0.04Msol). We uncovered that Pa13 exhibits a small but significant orbital eccentricity (e=0.02+/-0.01), making it only the second post-CE binary nucleus with a measured eccentricity. We conclude that Pa13 provides hitherto the strongest evidence that PNe can be observed around post-RGB stars. Immediately after the CE-ejection, Star1 likely still filled its Roche lobe, suggesting that Pa13 is a more evolved, detached descendant of over-contact double-degenerate systems such as Hen2-428. Since the mass ratio of Pa13 is close to unity the system may have formed through double-core CE evolution. Alternatively, there must exist an efficient CE-induced rejuvenation mechanism capable of reheating the cool white dwarf in the binary, as already indicated by Hen2-428. (abbreviated)

astro-ph.SR↗

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.

astro-ph.SR↗

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.

astro-ph.SR↗

arXiv2023

The messy death of a multiple star system and the resulting planetary nebula as observed by JWST

Planetary nebulae (PNe), the ejected envelopes of red giant stars, provide us with a history of the last, mass-losing phases of 90 percent of stars initially more massive than the Sun. Here, we analyse James Webb Space Telescope (JWST) Early Release Observation (ERO) images of the PN NGC3132. A structured, extended H2 halo surrounding an ionised central bubble is imprinted with spiral structures, likely shaped by a low-mass companion orbiting the central star at 40-60 AU. The images also reveal a mid-IR excess at the central star interpreted as a dusty disk, indicative of an interaction with another, closer companion. Including the previously known, A-type visual companion, the progenitor of the NGC3132 PN must have been at least a stellar quartet. The JWST images allow us to generate a model of the illumination, ionisation and hydrodynamics of the molecular halo, demonstrating the power of JWST to investigate complex stellar outflows. Further, new measurements of the A-type visual companion allow us to derive the value for the mass of the progenitor of a central star to date with excellent precision: 2.86+/-0.06 Mo. These results serve as path finders for future JWST observations of PNe providing unique insight into fundamental astrophysical processes including colliding winds, and binary star interactions, with implications for supernovae and gravitational wave systems.

astro-ph.SR↗