arXiv subjects

Romano L. M. Corradi

Publications and source records attributed to Romano L. M. Corradi.

At least 19 recordsLinked to original sources

arXiv2026

Appraising the Necklace: A post-common-envelope carbon dwarf inside an apparently carbon-poor planetary nebula

Context: The Necklace nebula is a bipolar, post-common-envelope planetary nebula, the central star of which has been shown to have a dwarf carbon star companion. Aims: We aim to understand the origins of the Necklace and its dwarf carbon central star. Methods: We study the carbon abundance of the nebula through far ultraviolet spectroscopy obtained with the Hubble Space Telescope. Furthermore, through simultaneous modelling of multiband light and velocity curves, we attempt to constrain the parameters of the central star system. Results: Puzzlingly, we find that the region of the inner nebula observed with the Hubble Space Telescope is seemingly not carbon-rich, at odds with the dwarf carbon star nature of the companion of the central star. The initial mass of the nebular progenitor was likely very close to the limit to become carbon-rich, perhaps experiencing a very late thermal pulse. The dwarf carbon star companion is found to be significantly inflated with respect to that expected for an isolated main sequence star of the same mass. Conclusions: The properties of the central binary are consistent with the progenitor having become carbon-rich and its companion having accreted a significant amount of that carbon-enriched material. However, it is unclear how this evolutionary hypothesis can be reconciled with the inner nebula potentially being carbon poor.

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arXiv2023

Analysis of Integral Field Spectroscopy observations of the planetary nebula Hen 2-108 and its central star

The study of planetary nebulae provides important constraints for many aspects of stellar and Galactic evolution. Hen 2-108 is a poorly known planetary nebula with a slight elliptical morphology and a peculiar central star (CS), which has defied classification. In this work, we present the first detailed integral field spectroscopic study of the planetary nebula Hen 2-108 and its CS. We provide spatially resolved flux maps for important emission lines, as well as diagnostic maps of extinction and electronic density and temperature. Physical conditions and chemical abundances were also calculated from the integrated spectrum. The analysis was also performed with the code satellite which uses a distinct strategy to evaluate physical and chemical properties. Both satellite and traditional procedure give consistent results, showing some variation in physical and chemical properties. We detect and measure a number of faint heavy element recombination lines from which we find a significant abundance discrepancy factor for O/H, and possibly for N/H. Pseudo 3D photoionization models were used to assist in the interpretation with results supporting the low-ionisation nature of this nebula, indicating a CS with Teff = 40 kK and a shell structure. The spectrum of the CS has been analysed with a detailed model for expanding atmospheres to infer stellar parameters, finding that it is a [Of/WN8] type with T* = 41.5 kK, making it a new addition to a small set (~20) of rare objects.

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arXiv2023

On the computation of interstellar extinction in photoionized nebulae

Ueta & Otsuka (2021) proposed a method, named as the "Proper Plasma Analysis Practice", to analyze spectroscopic data of ionized nebulae. The method is based on a coherent and simultaneous determination of the reddening correction and physical conditions in the nebulae. The same authors (Ueta & Otsuka 2022, UO22) reanalyzed the results of Galera-Rosillo et al. (2022, GR22) on nine of the brightest planetary nebulae in M31. They claim that, if standard values of the physical conditions are used to compute the extinction instead of their proposed method, extinction correction is underestimated by more than 50% and hence, ionic and elemental abundance determinations, especially the N/O ratio, are incorrect. Several tests were performed to assess the accuracy of the results of GR22, when determining: i) the extinction coefficient, ii) the electron temperature and density, and iii) the ionic abundances. In the latter case, N+ /H+ ionic abundance was recalculated using both H_alpha and H_beta as the reference H I emissivity. The analysis shows that the errors introduced by adopting standard values of the plasma conditions by GR22 are small, within their quoted uncertainties. On the other hand, the interstellar extinction in UO22 is found to be overestimated for five of the nine nebulae considered. This propagates into their analysis of the properties of the nebulae and their progenitors. The python notebook used to generate all the results presented in this paper are of public access on a Github repository. The results from GR22 are proven valid and the conclusions of the paper hold firmly. Although the PPAP is, in principle, a recommended practice, we insist that it is equally important to critically assess which H I lines are to be included in the determination of the interstellar extinction coefficient, and to assert that physical results are obtained for the undereddened line ratios.

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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.

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arXiv2021

MUSE spectroscopy of planetary nebulae with high abundance discrepancies

We present MUSE deep integral-field unit spectroscopy of three planetary nebulae(PNe) with high abundance discrepancy factors (ADF > 20): NGC 6778, M 1-42 and Hf 2-2. We have constructed flux maps for more than 40 emission lines, and use them to build extinction, electron temperature (T$_e$), electron density (n$_e$), and ionic abundances maps of a number of ionic species. The effects of the contribution of recombination to the auroral [N II] and [O II] lines on T$_e$ and the abundance maps of low-ionization species are evaluated using recombination diagnostics. As a result, low T$_e$ values and a downward gradient of T$_e$ are found toward the inner zones of each PN. Spatially, this nearly coincides with the increase of abundances of heavy elements measured using recombination lines in the inner regions of PNe, and strongly supports the presence of two distinct gas phases: a cold and metal-rich and a warm one with "normal" metal content. We have simultaneously constructed, for the first time, the ADF maps of O$^+$ and O$^{2+}$ and found that they centrally peak for all three PNe under study. We show that the main issue when trying to compute realistic abundances from either ORLs or CELs is to estimate the relative contribution of each gas component to the H I emission, and we present a method to evaluate it. It is also found that, for the studied high-ADF PNe, the amount of oxygen in the cold and warm regions is of the same order.

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arXiv2021

On the most luminous planetary nebulae of M31

To study the progenitors of PNe at the tip of the Planetary Nebula Luminosity Function (PNLF), we obtained the deepest existing spectra of a sample of PNe in the galaxy M31. Precise chemical abundances allow us to confront the theoretical yields for Asymptotic Giant Branch (AGB) stellar masses and metallicities expected at the bright end of the PNLF. Central star masses of the sampled PNe provide direct information on the controversial origin of the universal cutoff of the PNLF. Using the 10.4m Gran Telescopio Canarias (GTC) optical spectra of nine bright M31 PNe were obtained: four of them at the tip of the PNLF, and the other five some 0.5 magnitudes fainter. A control sample of 21 PNe with previous GTC spectra from literature is also included. Their physical properties and chemical abundances (He, N, O, Ar, Ne and S) are analysed. The central star masses are estimated with Cloudy modelling using the most recent evolutionary tracks. The studied PNe show a remarkable uniformity in all their nebular properties, the brightest PNe showing relatively large electron densities. Stellar characteristics also span a narrow range: ${ = 4300 \pm 310, = 122000 \pm 10600 K}$ for the central stars of the four brightest PNe, and ${ = 3300 \pm 370, < Teff> = 135000 \pm 26000 K}$ for those in the control set. This groups all the brightest PNe at the location of maximum temperature in the post-AGB tracks for stars with initial masses ${M = 1.5 M_{\odot}}$. These figures provide robust observational constraints about the stellar progenitors producing the PNLF cutoff in a star-forming galaxy such as M31, where a large range of initial masses is in principle available. Inconsistency is found, however, in the computed N/O abundance ratios of five nebulae, which are 1.5 to 3 times larger than predicted by the existing models for stars of these masses.

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arXiv2020

The post-common-envelope binary central star of the planetary nebula ETHOS 1

We present a detailed study of the binary central star of the planetary nebula ETHOS 1 (PN G068.1+11.0). Simultaneous modelling of light and radial velocity curves reveals the binary to comprise a hot and massive pre-white-dwarf with an M-type main-sequence companion. A good fit to the observations was found with a companion that follows expected mass-temperature-radius relationships for low-mass stars, indicating that despite being highly irradiated it is consistent with not being significantly hotter or larger than a typical star of the same mass. Previous modelling indicated that ETHOS 1 may comprise the first case where the orbital plane of the central binary does not lie perpendicular to the nebular symmetry axis, at odds with the expectation that the common envelope is ejected in the orbital plane. We find no evidence for such a discrepancy, deriving a binary inclination in agreement with that of the nebula as determined by spatio-kinematic modelling. This makes ETHOS 1 the ninth post-common-envelope planetary nebula in which the binary orbital and nebular symmetry axes have been shown to be aligned, with as yet no known counter-examples. The probability of finding such a correlation by chance is now less than 0.00002%.

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arXiv2020

The post-common-envelope binary central star of the planetary nebula PN G283.7-05.1: A possible post-red-giant-branch planetary nebula central star

We present the discovery and characterisation of the post-common-envelope central star system in the planetary nebula PN G283.7$-$05.1. Deep images taken as part of the POPIPlaN survey indicate that the nebula may possess a bipolar morphology similar to other post-common-envelope planetary nebulae. Simultaneous light and radial velocity curve modelling reveals the newly discovered binary system to comprise a highly-irradiated, M-type main-sequence star in a 5.9 hour orbit with a hot pre-white-dwarf. The nebular progenitor is found to have a particularly low mass of around 0.4 M$_\odot$, making PN G283.7$-$05.1 one of only a handful of candidate planetary nebulae to be the product of a common-envelope event while still on the red giant branch. Beyond its low mass, the model temperature, surface gravity and luminosity are all found to be consistent with the observed stellar and nebular spectra through comparison with model atmospheres and photoionisation modelling. However, the high temperature (T$_\mathrm{eff}\sim$95kK) and high luminosity of the central star of the nebula are not consistent with post-RGB evolutionary tracks.

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arXiv2019

On the triple-star origin of the planetary nebula Sh 2-71

Recent studies have indicated that triple star systems may play a role in the formation of an appreciable number of planetary nebulae, however only one triple central star is known to date (and that system is likely too wide to have had much influence on the evolution of its component stars). Here, we consider the possibility that Sh 2-71 was formed by a triple system which has since broken apart. We present the discovery of two regions of emission, seemingly aligned with the proposed tertiary orbit (i.e. in line with the axis formed by the two candidate central star systems previously considered in the literature). We also perform a few simple tests of the plausibility of the triple hypothesis based on the observed properties (coordinates, radial velocities, distances and proper motions) of the stars observed close to the projected centre of the nebula, adding further support through numerical integrations of binary orbits responding to mass loss. Although a number of open questions remain, we conclude that Sh 2-71 is currently one of the best candidates for planetary nebula formation influenced by triple-star interactions.

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arXiv2018

Co-spatial UV-optical HST/STIS Spectra of Six Planetary Nebulae: Nebular and Stellar Properties

This paper represents the conclusion of a project that had two main goals: (1) to investigate to what extent planetary nebulae (PNe) are chemically homogeneous; and (2) to provide physical constraints on the central star properties of each PN. We accomplished the first goal by using HST/STIS spectra to measure the abundances of seven elements in numerous spatial regions within each of six PN (IC 2165, IC 3568, NGC 2440, NGC 5315, NGC 5882, and NGC 7662). The second goal was achieved by computing a photoionization model of each nebula, using our observed emission line strengths as constraints. The major finding of our study is that the nebular abundances of He, C, N, O, Ne, S, and Ar are consistent with a chemically homogeneous picture for each PN. Additionally, we found through experimenting with three different density profiles (constant, Gaussian, and Gaussian with a power-law) that the determination of the central star's temperature and luminosity is only slightly sensitive to the profile choice. Lastly, post-AGB evolutionary model predictions of temperature and luminosity available in the literature were plotted along with the values inferred from the photoionization model analysis to yield initial and final mass estimates of each central star.

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arXiv2018

The short orbital period binary star at the heart of the planetary nebula M 3-1

We present the discovery of a 3h5m orbital-period binary star at the heart of the planetary nebula M 3-1 - the shortest period photometrically-variable central star known and second only to V458 Vul, in general. Combined modelling of light and radial velocity curves reveals both components to be close to Roche-lobe-filling, strongly indicating that the central star will rapidly evolve to become a cataclysmic variable, perhaps experiencing a similar evolution to V458 Vul resulting in a nova eruption before the planetary nebula has fully dissipated. While the short orbital period and near Roche-lobe filling natures of both components make the central binary of M 3-1 an important test case with which to constrain the formation processes of cataclysmic variables, novae and perhaps even supernovae type Ia.

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arXiv2017

The planetary nebula IC 4776 and its post-common-envelope binary central star

We present a detailed analysis of IC 4776, a planetary nebula displaying a morphology believed to be typical of central star binarity. The nebula is shown to comprise a compact hourglass-shaped central region and a pair of precessing jet-like structures. Time-resolved spectroscopy of its central star reveals periodic radial velocity variability consistent with a binary system. While the data are insufficient to accurately determine the parameters of the binary, the most likely solutions indicate that the secondary is probably a low-mass main sequence star. An empirical analysis of the chemical abundances in IC 4776 indicates that the common-envelope phase may have cut short the AGB evolution of the progenitor. Abundances calculated from recombination lines are found to be discrepant by a factor of approximately two relative to those calculated using collisionally excited lines, suggesting a possible correlation between low abundance discrepancy factors and intermediate-period post-common-envelope central stars and/or Wolf-Rayet central stars. The detection of a radial velocity variability associated with binarity in the central star of IC 4776 may be indicative of a significant population of (intermediate-period) post-common-envelope binary central stars which would be undetected by classic photometric monitoring techniques.

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arXiv2016

Analysis of Co-spatial UV-optical STIS Spectra of Planetary Nebula NGC 3242

This project sought to consider two important aspects of the planetary nebula NGC 3242 using new long-slit HST/STIS spectra. First, we investigated whether this object is chemically homogeneous by dividing the slit into different regions spatially and calculating the abundances of each region. The major result is that the elements of He, C, O, and Ne are chemically homogeneous within uncertainties across the regions probed, implying that the stellar outflow was well-mixed. Second, we constrained the stellar properties using photoionization models computed by CLOUDY and tested the effects of three different density profiles on these parameters. The three profiles tested were a constant density profile, a Gaussian density profile, and a Gaussian with a power law density profile. The temperature and luminosity were not affected significantly by the choice of density structure. The values for the stellar temperature and luminosity from our best fit model are 89.7$^{+7.3}_{-4.7}$kK and log(L/Lsol)=3.36$^{+0.28}_{-0.22}$, respectively. Comparing to evolutionary models on an HR diagram, this corresponds to an initial and final mass of 0.95$^{+0.35}_{-0.09}$ Msol and 0.56$^{+0.01}_{-0.01}$ Msol, respectively.

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arXiv2016

Imaging the elusive H-poor gas in the high ADF planetary nebula NGC 6778

We present the first direct image of the high-metallicity gas component in a planetary nebula (NGC 6778), taken with the OSIRIS Blue Tunable Filter centered on the O II 4649+50 angstroms optical recombination lines (ORLs) at the 10.4m Gran Telescopio Canarias. We show that the emission of these faint O II ORLs is concentrated in the central parts of the planetary nebula and is not spatially coincident either with emission coming from the bright [O III] 5007 angstroms collisionally excited line (CEL) or the bright H alpha recombination line. From monochromatic emission line maps taken with VIMOS at the 8.2m Very Large Telescope, we find that the spatial distribution of the emission from the auroral [O III] 4363 line resembles that of the O II ORLs but differs from nebular [O III] 5007 CEL distribution, implying a temperature gradient inside the planetary nebula. The centrally peaked distribution of the O II emission and the differences with the [O III] and H I emission profiles are consistent with the presence of an H-poor gas whose origin may be linked to the binarity of the central star. However, determination of the spatial distribution of the ORLs and CELs in other PNe, and a comparison of their dynamics is needed to further constrain the geometry and ejection mechanism of the metal-rich (H-poor) component and hence, understand the origin of the abundance discrepancy problem in PNe.

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arXiv2015

Discovery of an eclipsing dwarf nova in the ancient nova shell Te 11

We report on the discovery of an eclipsing dwarf nova (DN) inside the peculiar, bilobed nebula Te 11. Modelling of high-speed photometry of the eclipse finds the accreting white dwarf to have a mass 1.18 M$_\odot$ and temperature 13 kK. The donor spectral type of M2.5 results in a distance of 330 pc, colocated with Barnard's loop at the edge of the Orion-Eridanus superbubble. The perplexing morphology and observed bow shock of the slowly-expanding nebula may be explained by strong interactions with the dense interstellar medium in this region. We match the DN to the historic nova of 483 CE in Orion and postulate that the nebula is the remnant of this eruption. This connection supports the millennia time scale of the post-nova transition from high to low mass-transfer rates. Te 11 constitutes an important benchmark system for CV and nova studies as the only eclipsing binary out of just three DNe with nova shells.

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arXiv2015

NGC 6778: Strengthening the link between extreme abundance discrepancy factors and central star binarity in planetary nebulae

We present new optical spectra of the nearby, bright, planetary nebula NGC 6778. The nebula has been known to emit strong recombination lines for more than 40 years but this is the first detailed study of its abundances. Heavy element abundances derived from recombination lines are found to exceed those from collisionally excited lines by a factor of ~20 in an integrated spectrum of the nebula, which is among the largest known abundance discrepancy factors. Spatial analysis of the spectra shows that the abundance discrepancy factor is strongly, centrally peaked, reaching ~40 close to the central star. The central star of NGC 6778 is known to be a short period binary, further strengthening the link between high nebular abundance discrepancy factors and central star binarity.

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arXiv2015

The post-common envelope central stars of the planetary nebulae Henize 2-155 and Henize 2-161

We present a study of Hen 2-155 and Hen 2-161, two planetary nebulae which bear striking morphological similarities to other planetary nebulae known to host close-binary central stars. Both central stars are revealed to be photometric variables while spectroscopic observations confirm that Hen 2-155 is host to a double-eclipsing, post-common-envelope system with an orbital period of 3h33m making it one of the shortest period binary central stars known. The observations of Hen 2-161 are found to be consistent with a post-common-envelope binary of period ~1 day. A detailed model of central star of Hen 2-155, is produced, showing the nebular progenitor to be a hot, post-AGB remnant of approximately 0.62 Msol, consistent with the age of the nebula, and the secondary star to be an M dwarf whose radius is almost twice the expected ZAMS radius for its mass. In spite of the small numbers, all main-sequence companions, of planetary nebulae central stars, to have had their masses and radii constrained by both photometric and spectroscopic observations have also been found to display this "inflation". The cause of the "inflation" is uncertain but is probably related to rapid accretion, immediately before the recent common-envelope phase, to which the star has not yet thermally adjusted. The chemical composition of both nebulae is also analysed, showing both to display elevated abundance discrepancy factors. This strengthens the link between elevated abundance discrepancy factors and close binarity in the nebular progenitor.

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arXiv2015

Co-spatial Long-slit UV/Optical Spectra of Ten Galactic Planetary Nebulae with HST/STIS I. Description of the Observations, Global Emission-line Measurements, and CNO Abundances

We present observations and initial analysis from an HST/STIS program to obtain the first co-spatial, UV-optical spectra of ten Galactic planetary nebulae (PNe). Our primary objective was to measure the critical emission lines of carbon and nitrogen with unprecedented S/N and spatial resolution over UV-optical range, with the ultimate goal of quantifying the production of these elements in low- and intermediate-mass stars. Our sample was selected from PNe with a near-solar metallicity, but spanning a broad range in N/O. This study, the first of a series, concentrates on the observations and emission-line measurements obtained by integrating along the entire spatial extent of the slit. We derived ionic and total elemental abundances for the seven PNe with the strongest UV line detections (IC~2165, IC~3568, NGC~2440, NGC~3242, NGC~5315, NGC~5882, and NGC~7662). We compare these new results with other recent studies of the nebulae, and discuss the relative merits of deriving the total elemental abundances of C, N, and O using ionization correction factors (ICFs) versus summed abundances. For the seven PNe with the best UV line detections, we conclude that summed abundances from direct diagnostics of ions with measurable UV lines gives the most accurate values for the total elemental abundances of C and N. In some cases where significant discrepancies exist between our abundances and those from other studies, we show that the differences can often be attributed to their use of fluxes that are not co-spatial. Finally, we examined C/O and N/O versus O/H and He/H in well-observed Galactic, LMC, and SMC PNe, and found that highly accurate abundances are essential for properly inferring elemental yields from their progenitor stars.

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