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Planetary nebulae hosting accreting white dwarfs: A possible solution for the mysterious cut-off of Planetary Nebula Luminosity Function?
Abstract
Many 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 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 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, [O iii]-bright PNe, which are characterised 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 [O 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.
... The basic structure of a PN is of a hot, effective temperature of eff > ∼ 3 × 10 4 K, central star that is the remnant of an asymptotic giant branch (AGB) stellar progenitor or of a red giant (RG) star, and an expanding nebula that was the envelope of the AGB or RG progenitor of the PN (e.g., Kwok 1983;Tweedy & Kwitter 1994;Soker 2006;Schönberner et al. 2007;Cox et al. 2012;Guerrero & De Marco 2013;Kwitter & Henry 2022). Most PNe come from AGB stars, with only a small fraction from RG stars (e.g., Hillwig et al. 2017;Jones et al. 2020Jones et al. , 2022Jones et al. , 2023. The central star evolves to become a white dwarf (WD). ...
... We here use the term WD to indicate also central stars that are not yet WDs but evolving to become WDs. Some WDs might accrete mass from their non-degenerate companions (Hamann et al. 2003;Guerrero et al. 2019;Jones et al. 2019), a process that might explain some puzzles, like the luminosity function of PNe (Ciardullo 2016;Davis et al. 2018;Souropanis et al. 2023). Merger of a WD companion with the core might even set a type Ia supernova explosion during the PN phase (e.g., Tsebrenko & Soker 2013Cikota et al. 2017;Chiotellis et al. 2020Chiotellis et al. , 2021. ...
... This evolution leads to a post-RG PN with a central NS-WD binary system. Post RG planetary nebulae are rare compared with post-AGB planetary nebulae (e.g., Hillwig et al. 2017;Jones et al. 2020Jones et al. , 2022Jones et al. , 2023. These are formed by binary interaction (e.g., Hall et al. 2013). ...
We present a possible evolutionary pathway to form planetary nebulae (PNe) with close neutron star (NS)-white dwarf (WD) binary central stars. By employing the binary population synthesis technique we find that the evolution involves two common envelope evolution (CEE) phases and a core collapse supernova explosion between them that forms the NS. Later the lower mass star engulfs the NS as it becomes a red giant, a process that leads to the second CEE phase and to the ejection of the envelope. This leaves a hot horizontal branch star that evolves to become a helium WD and an expanding nebula. Both the WD and the NS power the nebula. The NS in addition might power a pulsar wind nebula inside the expanding PN. From our simulations we find that the Galactic formation rate of NS-WD PNe is 1.8 × 10−5 yr−1 while the Galactic formation rate of all PNe is 0.42 yr−1. There is a possibility that one of the observed Galactic PNe might be a NS-WD PN, and a few NS-WD PNe might exist in the Galaxy. The central binary systems might be sources for future gravitational wave detectors like LISA, and possibly of electromagnetic telescopes.
... . The basic structure of a PN is of a hot, effective temperature of eff > ∼ 3 × 10 4 K, central star that is the remnant of an asymptotic giant branch (AGB) stellar progenitor or of a red giant (RG) star, and an expanding nebula that was the envelope of the AGB or RG progenitor of the PN (e.g., Kwok 1983;Tweedy & Kwitter 1994;Soker 2006;Schönberner et al. 2007;Cox et al. 2012;Guerrero & De Marco 2013;Kwitter & Henry 2022). Most PNe come from AGB stars, with only a small fraction from RG stars (e.g., Hillwig et al. 2017;Jones et al. 2020Jones et al. , 2022Jones et al. , 2023. The central star evolves to become a white dwarf (WD). ...
... We here use the term WD to indicate also central stars that are not yet WDs but evolving to become WDs. Some WDs might accrete mass from their non-degenerate companions (Hamann et al. 2003;Guerrero et al. 2019;Jones et al. 2019), a process that might explain some puzzles, like the luminosity function of PNe (Ciardullo 2016;Davis et al. 2018;Souropanis et al. 2023). Merger of a WD companion with the core might even set a type Ia supernova explosion during the PN phase (e.g., Tsebrenko & Soker 2013Cikota et al. 2017;Chiotellis et al. 2020Chiotellis et al. , 2021. ...
... This evolution leads to a post-RG PN with a central NS-WD binary system. Post RG planetary nebulae are rare compared with post-AGB planetary nebulae (e.g., Hillwig et al. 2017;Jones et al. 2020Jones et al. , 2022Jones et al. , 2023. These are formed by binary interaction (e.g., Hall et al. 2013). ...
We present a possible evolutionary pathway to form planetary nebulae (PNe) with close neutron star (NS)-white dwarf (WD) binary central stars. By employing a comprehensive binary population synthesis technique we find that the evolution involves two common envelope evolution (CEE) phases and a core collapse supernova explosion between them that forms the NS. Later the lower mass star engulfs the NS as it becomes a red giant, a process that leads to the second CEE phase and to the ejection of the envelope. This leaves a hot horizontal branch star that evolves to become a helium WD and an expanding nebula. Both the WD and the NS power the nebula. The NS in addition might power a pulsar wind nebula inside the expanding PN. From our simulations we find that the Galactic formation rate of NS-WD PNe is $1.8 \times 10^{-5} {\rm yr}^{-1}$ while the Galactic formation rate of all PNe is $0.42 {\rm yr}^{-1}$. There is a possibility that one of the observed Galactic PNe might be a NS-WD PN, and a few NS-WD PNe might exist in the Galaxy. The central binary systems might be sources for future gravitational wave detectors like LISA, and possibly of electromagnetic telescopes.
... There is no consensus regarding the physical origin of the rough constancy of the bright-end cutoff to the PNLF (e.g., Ciardullo 2012; Davis et al. 2018;Gesicki et al. 2018;Valenzuela et al. 2019;Kwitter & Henry 2022;Souropanis et al. 2023). Ciardullo (2012) outlined a number of theoretical reasons that work against a consistent cutoff luminosity; most notably, early-type galaxies do not host massive stars like starforming late-type galaxies. ...
The [O iii ] 5007 Å line is typically the brightest line in planetary nebula (PN) spectra. Observations show that the brightest [O iii ] 5007 Å PN in a galaxy—the planetary nebula luminosity function (PNLF) bright-end cutoff—is surprisingly independent of galaxy type. To understand the origin of this puzzling uniformity, we simulate PNe with a range of cloud and star parameters using the photoionization code CLOUDY. We find that the peak [O iii ] 5007 Å luminosity depends weakly on both the central stellar effective temperature at high temperature and on the total PN ejecta mass; however, the peak [O iii ] 5007 Å luminosity depends strongly on the central stellar luminosity and the PN dust-to-gas mass ratio. We explain these scalings physically. They imply that a higher dust-to-gas mass ratio at higher central stellar luminosity can help explain a constant bright-end cutoff in the PNLF across galaxy types. This prediction is testable with a survey of galactic PNe. The surviving remnants of double white dwarf (WD) mergers should also produce photoionized nebulae analogous to PNe. These may be preferentially present at the high luminosity end of the [O iii ] PLNF and could explain the existence of PNe in early-type galaxies that are more luminous in [O iii ] than expected from single-star evolutionary models. The presence of WD mergers in both young and old stellar populations could contribute to the uniformity of the [O iii ] PNLF across galaxy types; such nebulae would lack the hydrogen lines otherwise characteristic of PNe.
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. Gaia G BP − G RP 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.
Context. Super-soft X-ray sources were established as a heterogeneous class of objects from observations of the Large Magellanic Cloud (LMC).
Aims. We have searched for new sources of this class in the X-ray images obtained from the XMM-Newton survey of the LMC and additional archival observations.
Methods. We first selected candidates by visual inspection of the image and screened out the artefacts that can mimic super-soft X-ray sources as well as the bright foreground stars that create optical loading in the detectors. We obtained four new super-soft X-ray sources for which we performed detailed X-ray timing and spectral analyses and searched for possible optical counterparts to identify their nature. We also looked at archival ROSAT and Swift observations to investigate the long-term behaviour of the sources.
Results. XMMU J050452.0−683909 is identified as the central star of the planetary nebula SMP LMC 21 in the LMC. We suggest XMMU J051854.8−695601 and XMMU J050815.1−691832 as new soft intermediate polars based on the nature of their X-ray spectrum. Their estimated absorption-corrected luminosities and the blackbody radii indicate that they are located in our Galaxy, rather than the LMC. We discovered coherent pulsations of 497 s from XMMU J044626.6-692011, which indicates a magnetic cataclysmic variable nature of the source. The location of XMMU J044626.6−692011 in the LMC or our Galaxy is less clear. It could either be a white dwarf in the LMC with nuclear burning on its surface near the Eddington limit or another soft intermediate polar in our Galaxy.
Conclusions. The discovery of new super-soft X-ray sources makes a significant contribution to the known population in our Galaxy. An observed higher density of sources in the direction of the Magellanic Clouds can likely be explained by the relatively low Galactic column density in their direction as well as a large number of existing observations sensitive at low X-ray energies.
One of the key methods for determining the unknown nature of Type Ia supernovae (SNe Ia) is the search for traces of interaction between the SN ejecta and the circumstellar structures at the resulting supernova remnants (SNRs Ia). So far, the observables that we receive from well-studied SNRs Ia cannot be explained self-consistently by any model presented in the literature. In this study, we suggest that the circumstellar medium (CSM) being observed to surround several SNRs Ia was mainly shaped by planetary nebulae (PNe) that originated from one or both progenitor stars. Performing two-dimensional hydrodynamic simulations, we show that the ambient medium shaped by PNe can account for several properties of the CSM that have been found to surround SNe Ia and their remnants. Finally, we model Kepler’s SNR considering that the SN explosion occurred inside a bipolar PN. Our simulations show good agreement with the observed morphological and kinematic properties of Kepler’s SNR. In particular, our model reproduces the current expansion parameter of Kepler’s SNR, the partial interaction of the remnant with a dense CSM at its northern region and finally the existence of two opposite protrusions (‘ears’) at the equatorial plane of the SNR.
Context. We have compiled a catalogue of central stars of planetary nebulae (CSPN) with reliable distances and positions obtained from Gaia Data Release 2 (DR2) astrometry. Distances derived from parallaxes allow us to analyse the galactic distribution and estimate other parameters such as sizes, kinematical ages, bolometric magnitudes, and luminosities.
Aims. Our objective is to analyse the information regarding distances together with other available literature data about photometric properties, nebular kinematics, and stellar effective temperatures to throw new light on this rapid and rather unknown evolutionary phase. We seek to understand how Gaia distances compare with other indirect methods commonly used and, in particular, with those derived from non-local thermodynamic equilibrium (non-LTE) models; how many planetary nebulae (PNe) populate the Galaxy; and how are they spatially distributed. We also aim to comprehend their intrinsic luminosities, range of physical sizes of the nebulae; how to derive the values for their kinematical ages; and whether those ages are compatible with those derived from evolutionary models.
Methods. We considered all PNe listed in catalogues from different authors and in Hong Kong/AAO/Strasbourg/H α (HASH) database. By X-matching their positions with Gaia DR2 astrometry we were able to identify 1571 objects in Gaia second archive, for which we assumed distances calculated upon a Bayesian statistical approach. From those objects, we selected a sample of PNe with good quality parallax measurements and distance derivations, we which refer to as our Golden Astrometry PNe sample (GAPN), and obtained literature values of their apparent sizes, radial and expansion velocities, visual magnitudes, interstellar reddening, and effective temperatures.
Results. We found that the distances derived from DR2 parallaxes compare well with previous astrometric derivations of the United States Naval Observatory and Hubble Space Telescope, but that distances inferred from non-LTE model fitting are overestimated and need to be carefully reviewed. From literature apparent sizes, we calculated the physical radii for a subsample of nebulae that we used to derive the so-called kinematical ages, taking into account literature expansion velocities. Luminosities calculated with DR2 distances were combined with literature central stars Teff values in a Hertzsprung–Russell (HR) diagram to infer information on the evolutionary status of the nebulae. We compared their positions with updated evolutionary tracks finding a rather consistent picture. Stars with the smallest associated nebular radii are located in the flat luminosity region of the HR diagram, while those with the largest radii correspond to objects in a later stage, getting dimmer on their way to become a white dwarf. Finally, we commented on the completeness of our catalogue and calculated an approximate value for the total number of PNe in the Galaxy.
We present a new census of Galactic and extragalactic symbiotic stars (SySts). This compilation contains 323 known and 87 candidate SySts. Of the confirmed SySts, 257 are Galactic and 66 extragalactic. The spectral energy distributions (SEDs) of 348 sources have been constructed using 2MASS and AllWISE data. Regarding the Galactic SySts, 74% are S-types, 13% D and 3.5% D$^{\prime}$. S-types show an SED peak between 0.8 and 1.7 $\mu$m, whereas D-type show a peak at longer wavelengths between 2 and 4 $\mu$m. D$^{\prime}$-type, on the other hand, display a nearly flat profile. Gaia distances and effective temperatures are also presented. According to their Gaia distances, S-type are found to be members of both thin and thick Galactic disk populations, while S+IR- and D-types are mainly thin disk sources. Gaia temperatures show a reasonable agreement with the temperatures derived from SEDs within their uncertainties. A new census of the OVI $\lambda$6830 Raman-scattered line in SySts is also presented. From a sample of 298 SySts with available optical spectra, 55% are found to emit the line. No significant preference is found among the different types. The report of the OVI $\lambda$6830 Raman-scattered line in non-SySts is also discussed as well as the correlation between the Raman-scattered OVI line and X-ray emission. We conclude that the presence of the OVI Raman-scattered line still provides a strong criterion for identifying a source as a SySt.
It has recently been noted that there seems to be a strong correlation between planetary nebulae with close binary central stars, and highly enhanced recombination line abundances. We present new deep spectra of seven objects known to have close binary central stars, and find that the heavy element abundances derived from recombination lines exceed those from collisionally excited lines by factors of 5-95, placing several of these nebulae among the most extreme known abundance discrepancies. This study nearly doubles the number of nebulae known to have a binary central star and an extreme abundance discrepancy. A statistical analysis of all nebulae with measured recombination line abundances reveals no link between central star surface chemistry and nebular abundance discrepancy, but a clear link between binarity and the abundance discrepancy, as well as an anti-correlation between abundance discrepancies and nebular electron densities: all nebulae with a binary central star with a period of less than 1.15 days have an abundance discrepancy factor exceeding 10, and an electron density less than $\sim$1000 cm$^{-3}$; those with longer period binaries have abundance discrepancy factors less than 10 and much higher electron densities. We find that [O~{\sc ii}] density diagnostic lines can be strongly enhanced by recombination excitation, while [S~{\sc ii}] lines are not. These findings give weight to the idea that extreme abundance discrepancies are caused by a nova-like eruption from the central star system, occurring soon after the common-envelope phase, which ejects material depleted in hydrogen, and enhanced in CNONe but not in third-row elements.
Planetary Nebulae (PN) emit enormous amount of energy in several emission lines. Measuring the line-flux for PNe in a given stellar population, the Planetary Nebula Luminosity Function (PNLF) can be compiled. Surveys of PNe revealed that the faint-end of the PNLF can be approximated by a simple exponential dependency expected for an expanding spherical shell. However at the bright-end there exists a steep cut-off which was unexpected and remains unexplained. Interestingly, the cut-off value appears to be nearly the same for different stellar populations as young spiral galaxies and old elliptical galaxies and, despite the lack of understanding, became an extragalactic distance estimator. Here we show that the recently computed post-AGB evolutionary tracks are capable to explain the decades old mystery. All new models with ages between 1 and 7 Gyr (progenitor masses between 2.0 and 1.1 of solar mass) evolve fast enough to ionize the PN, and at similar post-AGB luminosity which allows the [O III] 500.7nm line to reach nearly the same magnitude. The new models predict that the Sun at the end of its life will form a rather faint PN.
The lines-of-sight to highly reddened SNe Ia show peculiar continuum polarization curves, growing toward blue wavelengths and peaking at $\lambda_{max} \lesssim 0.4 \mu m$, like no other sight line to any normal Galactic star. We examined continuum polarization measurements of a sample of asymptotic giant branch (AGB) and post-AGB stars from the literature, finding that some PPNe have polarization curves similar to those observed along SNe Ia sight lines. Those polarization curves are produced by scattering on circumstellar dust. We discuss the similarity and the possibility that at least some SNe Ia might explode during the post-AGB phase of their binary companion. Furthermore, we speculate that the peculiar SNe Ia polarization curves might provide observational support to the core-degenerate progenitor model.
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.
Accreting white dwarfs (WDs) with non-degenerate companions are expected to emit in soft X-rays and the UV, if accreted H-rich
material burns stably. They are an important component of the unresolved emission of elliptical galaxies, and their combined
ionizing luminosity may significantly influence the optical line emission from warm interstellar medium (ISM). In an earlier
paper, we modelled populations of accreting WDs, first generating WD with main-sequence, Hertzsprung gap and red giant companions
with the population synthesis code bse, and then following their evolution with a grid of evolutionary tracks computed with mesa. Now we use these results to estimate the soft X-ray (0.3–0.7 keV), H- and He ii-ionizing luminosities of nuclear burning WDs and the number of supersoft X-ray sources for galaxies with different star formation
histories. For the starburst case, these quantities peak at ∼1 Gyr and decline by ∼1–3 orders of magnitude by the age of 10 Gyr.
For stellar ages of ∼10 Gyr, predictions of our model are consistent with soft X-ray luminosities observed by Chandra in nearby elliptical galaxies and He ii
4686 Å/H β line ratio measured in stacked Sloan Digital Sky Survey spectra of retired galaxies, the latter characterizing
the strength and hardness of the UV radiation field. However, the soft X-ray luminosity and He ii 4686 Å/H β ratio are significantly overpredicted for stellar ages of ≲4–8 Gyr. We discuss various possibilities to resolve
this discrepancy and tentatively conclude that it may be resolved by a modification of the typically used criteria of dynamically
unstable mass-loss for giant stars.
Six planetary nebulae (PN) are known in the Kepler space telescope field of view, three of which are newly identified. Of the five central stars of PN with useful Kepler data, one, J193110888+4324577, is the first short-period, post-common envelope binary exhibiting relativistic beaming effects.
A second, the central star of the newly identified PN Pa 5, has a rare O(He) spectral type and a periodic variability consistent
with an evolved companion, where the orbital axis is almost aligned with the line of sight. The third PN, NGC 6826, has a
fast rotating central star, something that can only be achieved in a merger. Fourth, the central star of the newly identified
PN Kn 61, has a PG1159 spectral type and a mysterious semi-periodic light variability which we conjecture to be related to
the interplay of binarity with a stellar wind. Finally, the central star of the circular PN A61 does not appear to have a
photometric variability above 2 mmag. With the possible exception of the variability of Kn 61, all other variability behaviour,
would not easily have been detected from the ground. We conclude, based on very low numbers, that there may be many more close
binary or close binary products to be discovered with ultra-high-precision photometry. With a larger number of high-precision
photometric observations, we will be able to determine how much higher than the currently known 15 per cent, the short-period
binary fraction for central stars of PN is likely to be.
The discrepancy between abundances computed using optical recombination lines
(ORLs) and collisionally excited lines (CELs) is a major unresolved problem in
nebular astrophysics. We show here that the largest abundance discrepancies are
reached in planetary nebulae with close binary central stars. This is
illustrated by deep spectroscopy of three nebulae with a post common-envelope
(CE) binary star. Abell 46 and Ou5 have O++/H+ abundance discrepancy factors
larger than 50, and as high as 300 in the inner regions of Abell 46. Abell 63
has a smaller discrepancy factor around 10, but still above the typical values
in ionized nebulae. Our spectroscopic analysis supports previous conclusions
that, in addition to "standard" hot (Te~10000 K) gas, a colder (Te~1000 K)
ionized component that is highly enriched in heavy elements also exists. These
nebulae have low ionized masses, between 0.001 and 0.1 solar masses depending
on the adopted electron densities and temperatures. Since the much more massive
red-giant envelope is expected to be entirely ejected in the CE phase, the
currently observed nebulae would be produced much later, in post-CE mass loss
episodes when the envelope has already dispersed. These observations add
constraints to the abundance discrepancy problem. Possible explanations are
revised. Some are naturally linked to binarity, such as for instance
high-metallicity nova ejecta, but it is difficult at this stage to depict an
evolutionary scenario consistent with all the observed properties. The
hypothesis that these nebulae are the result of tidal destruction, accretion
and ejection of Jupiter-like planets is also introduced.
We present X-ray spectral analysis of 20 point-like X-ray sources detected in
Chandra Planetary Nebula Survey (ChanPlaNS) observations of 59 planetary
nebulae (PNe) in the solar neighborhood. Most of these 20 detections are
associated with luminous central stars within relatively young, compact
nebulae. The vast majority of these point-like X-ray-emitting sources at PN
cores display relatively "hard" ($\geq0.5$~keV) X-ray emission components that
are unlikely to be due to photospheric emission from the hot central stars
(CSPN). Instead, we demonstrate that these sources are well modeled by
optically-thin thermal plasmas. From the plasma properties, we identify two
classes of CSPN X-ray emission: (1) high-temperature plasmas with X-ray
luminosities, $L_{\rm X}$, that appear uncorrelated with the CSPN bolometric
luminosity, $L_{\rm bol}$; and (2) lower-temperature plasmas with $L_{\rm
X}/L_{\rm bol}\sim10^{-7}$. We suggest these two classes correspond to the
physical processes of magnetically active binary companions and self-shocking
stellar winds, respectively. In many cases this conclusion is supported by
corroborative multiwavelength evidence for the wind and binary properties of
the PN central stars. By thus honing in on the origins of X-ray emission from
PN central stars, we enhance the ability of CSPN X-ray sources to constrain
models of PN shaping that invoke wind interactions and binarity.
We present results from the most recent set of observations obtained as part
of the Chandra X-ray observatory Planetary Nebula Survey (ChanPlaNS), the first
comprehensive X-ray survey of planetary nebulae (PNe) in the solar neighborhood
(i.e., within ~1.5 kpc of the Sun). The survey is designed to place constraints
on the frequency of appearance and range of X-ray spectral characteristics of
X-ray-emitting PN central stars and the evolutionary timescales of
wind-shock-heated bubbles within PNe. ChanPlaNS began with a combined Cycle 12
and archive Chandra survey of 35 PNe. ChanPlaNS continued via a Chandra Cycle
14 Large Program which targeted all (24) remaining known compact (R_neb <~ 0.4
pc), young PNe that lie within ~1.5 kpc. Results from these Cycle 14
observations include first-time X-ray detections of hot bubbles within NGC
1501, 3918, 6153, and 6369, and point sources in HbDs 1, NGC 6337, and Sp 1.
The addition of the Cycle 14 results brings the overall ChanPlaNS diffuse X-ray
detection rate to ~27% and the point source detection rate to ~36%. It has
become clearer that diffuse X-ray emission is associated with young (<~5x10^3
yr), and likewise compact (R_neb<~0.15 pc), PNe with closed structures and high
central electron densities (n_e>~1000 cm^-3), and rarely associated with PNe
that show H_2 emission and/or pronounced butterfly structures. Hb 5 is one such
exception of a PN with a butterfly structure that hosts diffuse X-ray emission.
Additionally, of the five new diffuse X-ray detections, two host [WR]-type
CSPNe, NGC 1501 and NGC 6369, supporting the hypothesis that PNe with central
stars of [WR]-type are likely to display diffuse X-ray emission.
We present narrow-band [O III]λ5007 and Hα images, as well
as long-slit high-resolution echelle spectra of the planetary nebula NGC
6058. Our data reveal that NGC 6058 is a multipolar planetary nebula of
˜45 arcsec in extent that is formed by four bipolar outflows
oriented at different position angles. Assuming homologous expansion for
all the structures, and a distance of 3.5 kpc, we obtain polar
velocities of ˜68 km s-1 for three of them. The
estimated kinematical ages suggest that the three oldest outflows were
ejected at intervals of ˜1100 and ˜400 yr, during which the
ejection axis changed its orientation by ˜60° and
˜40°, respectively. Although an inner ring-like structure is
suggested by the direct images, the kinematics shows that no equatorial
ring or toroid exists in the nebula. On the contrary, the long-slit
spectra reveal that the ring-like structure corresponds to a fourth
outflow that is oriented almost perpendicular to the other three. This
fourth outflow is the youngest one and appears to be interacting with
the other three, creating a protruding zone that sweeps material in a
region almost perpendicular to the major axes of the oldest outflows.
This structure also presents two bright arcuate regions along the
direction of the older outflows, and on opposite sides of the central
star. From our model, we suggest that NGC 6058 could be at an
intermediate evolutionary stage between starfish planetary nebulae and
multipolar planetary nebula with apparent equatorial lobes.
Models of planetary-nebula (PN) formation involving stellar-mass-loss processes are reviewed. Mass loss in the red giant (RG) progenitors of
The nebula Menzel 3 (Mz 3) has arguably the most complex bipolar morphology, consisting of three nested pairs of bipolar lobes and an equatorial ellipse. Its three pairs of bipolar lobes share the same axis of symmetry but have very different opening angles and morphologies: the innermost pair of bipolar lobes shows closed-lobe morphology, whereas the other two have open lobes with cylindrical and conical shapes, respectively. We have carried out high-dispersion spectroscopic observations of Mz 3 and detected distinct kinematic properties among the different morphological components. The expansion characteristics of the two outer pairs of lobes suggest that they originated in an explosive event, whereas the innermost pair of lobes resulted from the interaction of a fast wind with the surrounding material. The equatorial ellipse is associated with a fast equatorial outflow, which is unique among bipolar nebulae. The dynamical ages of the different structures in Mz 3 suggest episodic bipolar ejections, and the distinct morphologies and kinematics among these different structures reveal fundamental changes in the system between these episodic ejections.
Nova V458 Vul erupted on 2007 August 8 and reached a visual magnitude of 8.1 a few days later. Hα images obtained 6 weeks before the outburst as part of the IPHAS Galactic plane survey reveal an 18th magnitude progenitor surrounded by an extended nebula. Subsequent images and spectroscopy of the nebula reveal an inner nebular knot increasing rapidly in brightness due to flash ionization by the nova event. We derive a distance of 13 kpc based on light travel time considerations, which is supported by two other distance estimation methods. The nebula has an ionized mass of 0.2 M☉ and a low expansion velocity: this rules it out as ejecta from a previous nova eruption, and is consistent with it being a ~14,000 year old planetary nebula, probably the product of a prior common envelope (CE) phase of evolution of the binary system. The large derived distance means that the mass of the erupting WD component of the binary is high. We identify two possible evolutionary scenarios, in at least one of which the system is massive enough to produce a Type Ia supernova upon merging.
Far-Ultraviolet Spectroscopic Explorer spectra were obtained of the supersoft X-ray binary RX J0019.8+2156 (QR And) during 16 consecutive spacecraft orbits, covering the binary orbit (P = 15.85 hr) with about 0.2 phase overlap. The spectrum is dominated by strong H2 absorption (column density ~1020 g cm-2), which appears at the velocity different from other interstellar absorption lines and may be partially circumbinary. This absorption makes study of spectral features from the binary system difficult. The only well-detected emission lines are He II λ1085 and O VI λ1032 (the other line of the O VI doublet, at 1037 Å, is largely obscured by strong H2 absorption). The O VI shows a P Cygni profile that varies in velocity and strength with binary phase. We compare this with similar changes seen in Balmer line profiles. We extract the far-ultraviolet (FUV) light curve and compare it with the optical light curve. There is an eclipse in both wavelength regions, but the FUV minimum lasts much longer, well beyond the visible light egress. The FUV results are discussed in connection with the binary model and mass flows within the system.
M 2-9, the Butterfly nebula, is an outstanding representative of extreme
aspherical flows. It presents unique features such as a pair of high-velocity
dusty polar blobs and a mirror-symmetric rotating pattern in the inner lobes.
Imaging monitoring of the evolution of the nebula in the past decade is
presented. We determine the proper motions of the dusty blobs, which infer a
new distance estimate of 1.3+-0.2 kpc, a total nebular size of 0.8 pc, a speed
of 147 km/s, and a kinematical age of 2500 yr. The corkscrew geometry of the
inner rotating pattern is quantified. Different recombination timescales for
different ions explain the observed surface brightness distribution. According
to the images taken after 1999, the pattern rotates with a period of 92+-4 yr.
On the other hand, the analysis of images taken between 1952 and 1977 measures
a faster angular velocity. If the phenomenon were related to orbital motion,
this would correspond to a modest orbital eccentricity (e=0.10+-0.05), and a
slightly shorter period (86+-5 yr). New features have appeared after 2005 on
the west side of the lobes and at the base of the pattern. The geometry and
travelling times of the rotating pattern support our previous proposal that the
phenomenon is produced by a collimated spray of high velocity particles (jet)
from the central source, which excites the walls of the inner cavity of M 2-9,
rather than by a ionizing photon beam. The speed of such a jet would be
remarkable: between 11000 and 16000 km/s. The rotating-jet scenario may explain
the formation and excitation of most of the features observed in the inner
nebula, with no need for additional mechanisms, winds, or ionization sources.
All properties point to a symbiotic-like interacting binary as the central
source of M 2-9.
During an X-ray survey of the Small Magellanic Cloud, carried out with the XMM-Newton satellite, we detected significant soft X-ray emission from the central star of the high-excitation planetary nebula SMP SMC 22. Its very soft spectrum is well fit with a non local thermodynamical equilibrium model atmosphere composed of H, He, C, N, and O, with abundances equal to those inferred from studies of its nebular lines. The derived effective temperature of 1.5x10^5 K is in good agreement with that found from the optical/UV data. The unabsorbed flux in the 0.1-0.5 keV range is about 3x10^{-11} erg cm^-2 s^-1, corresponding to a luminosity of 1.2x10^37 erg/s at the distance of 60 kpc. We also searched for X-ray emission from a large number of SMC planetary nebulae, confirming the previous detection of SMP SMC 25 with a luminosity of (0.2-6)x10^35 erg/s (0.1-1 keV). For the remaining objects that were not detected, we derived flux upper limits corresponding to luminosity values from several tens to hundreds times smaller than that of SMP SMC 22. The exceptionally high X-ray luminosity of SMP SMC 22 is probably due to the high mass of its central star, quickly evolving toward the white dwarf's cooling branch, and to a small intrinsic absorption in the nebula itself. Comment: Accepted for publication on Astronomy and Astrophysics
Aims. We report the discovery of three faint, super-soft X-ray sources in LMC fields observed with XMM-Newton.Methods. We analyse the three new sources together with RX J0537.7-7034 and RX J0507.1-6743, both known since ROSAT.Results. We identify XMMU J050803.1-684017 with the LMC planetary nebula LHA 120-N 102 = LMC SMP 29. The EPIC-pn spectrum of XMMU J050803.1-684017 can be fitted with a blackbody spectrum with an effective temperature of ~(26–51) eV and a bolometric luminosity of (0.1-30)$\times$10$^{36}$ erg s$^{-1}$, depending on the assumed absorption. The source is consistent with the nucleus of a planetary nebula. The EPIC-pn spectrum of XMMU J052530.5-671501 is characterized by a blackbody temperature of ~(38–120) eV, a best-fit bolometric luminosity of ~3$\times$10$^{37}$ erg s$^{-1}$ and absorbing LMC column of $\sim8^{+2}_{-8}$$\times$10$^{21}$ cm$^{-2}$. This most likely highly-absorbed super-soft source resembles the LMC super-soft source CAL 87. The EPIC-pn spectrum of XMMU J052215.0-701658 yields a blackbody temperature of ~(24–83) eV, but there are only about 40 source counts and the spectral parameters of the source are not well constrained. We observe RX J0537.7-7034 with EPIC-pn to be about a factor of 15 fainter compared to the ROSAT observation 11 years earlier. RX J0507.1-6743 is observed as an absorbed super-soft source by XMM-Newton and the improved X-ray position coincides with a MACHO star which is consistent with a symbiotic star.
Binarity has been hypothesised to play an important, if not ubiquitous, role in the formation of planetary nebulae (PNe). Yet there remains a severe paucity of known binary central stars required to test the binary hypothesis and to place strong constraints on the physics of the common-envelope (CE) phase of binary stellar evolution. Large photometric surveys offer an unrivalled opportunity to efficiently discover many binary central stars. We have combined photometry from the OGLE microlensing survey with the largest sample of PNe towards the Galactic Bulge to systematically search for new binaries. A total of 21 periodic binaries were found thereby more than doubling the known sample. The orbital period distribution was found to be best described by CE population synthesis models when no correlation between primary and secondary masses is assumed for the initial mass ratio distribution. A comparison with post-CE white dwarf binaries indicates both distributions are representative of the true post-CE period distribution with most binaries exhibiting periods less than one day. An estimated close binary fraction of 12--21% is derived and is the first robust and independent validation of the prevailing 10--15% fraction estimated by Bond (2000). This suggests that binarity is not a precondition for the formation of PNe and that close binaries do not play a dominant role in the shaping of nebular morphologies. Systematic effects and biases of the survey are discussed with implications for future photometric surveys.
The structure and kinematics of the bipolar nebula Mz 3 have been investigated by means of HST, CTIO and ESO images and spectra. At least four distinct outflows have been identified which, from the inside to the outside, are the following: a pair of bright bipolar lobes, two opposite highly collimated column-shaped outflows, a conical system of radial structure, and a very dim, previously unnoticed, low-latitude and flattened (ring-like) radial outflow. A simple Hubble-law describes the velocity field of the ballisticaly expanding lobes, columns and rays, suggesting that their shaping has being done at very early stages of evolution, in a sort of eruptive events with increasing degree of collimation and expansion ages ranging from ~600 for the inner structures to ~1600 years (per kpc to the nebula) for the largest ones. Comment: 12 pages, 14 figures, accepted by A&A. Full resolution version available at http://www.iac.es/proyect/pn_iac/
Steadily accreting white dwarfs (WDs) are efficient sources of ionization and thus are able to create extended ionized nebulae in their vicinity. These nebulae represent ideal tools for the detection of accreting WDs, given that in most cases the source itself is faint. In this work, we combine radiation transfer simulations with known H- and He-accreting WD models, providing for the first time the ionization state and the emission-line spectra of the formed nebulae as a function of the WD mass, the accretion rate and the chemical composition of the accreted material. We find that the nebular optical line fluxes and radial extent vary strongly with the WD’s accretion properties, peaking in systems with WD masses of 0.8–1.2 $\rm M_{\odot }$. Projecting our results on so-called BPT diagnostic diagrams, we show that accreting WD nebulae possess characteristics distinct from those of H ii-like regions, while they have line ratios similar to those in galactic low-ionization emission-line regions. Finally, we compare our results with the relevant constraints imposed by the lack of ionized nebulae in the vicinity of supersoft X-ray sources (SSSs) and Type Ia supernova remnants – sources that are related to steadily accreting WDs. The large discrepancies uncovered by our comparison rule out any steadily accreting WD as a potential progenitor of the studied remnants and additionally require the ambient medium around the SSSs to be less dense than 0.2 $\rm cm^{-3}$. We discuss possible alternatives that could bridge the incompatibility between the theoretical expectations and relevant observations.
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 percent for all the observed PNe, or 23.5 percent 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.
A characteristic feature that is frequently found in nearby supernova remnants (SNRs) is the existence of two antisymmetric, local protrusions that are projected as two ‘ears’ in the morphology of the nebula. In this paper, we present a novel scenario for the ‘ear’ formation process, according to which the two lobes are formed through the interaction of the SNR with a bipolar circumstellar medium (CSM) that was surrounding the explosion’s centre. We conduct two-dimensional hydrodynamic simulations and we show that the SNR shock breakout from the bipolar CSM triggers the inflation of two opposite protrusions at the equator of the remnant, which retain their size and shape from several hundreds up to a few thousand years of the SNR evolution. We run a set of models by varying the supernova (SN) and CSM properties and we demonstrate that the extracted results reveal good agreement with the observables, regarding the sizes, lifespan, morphology and kinematics of the ‘ears’. We discuss the plausibility of our model in nature and we suggest that the most likely progenitors of the ‘ear-carrying’ SNRs are the luminous blue variables or the red/yellow supergiants for the SNRs resulting from core collapse SN events, and the symbiotic binaries or the planetary nebulae for the SNRs formed by Type Ia SNe. Finally, we compare our model with other ‘ear’ formation models found in the literature and we show that there are distinctive differences among them, concerning the orientation of the ‘ears’ and the phase in which the ‘ear’ formation process occurs.
The central star of NGC 2392 shows the hardest X-ray emission among central stars of planetary nebulae (CSPNe). The recent discovery of a spectroscopic companion with an orbital period of 1.9 days could provide an explanation for its hard X-ray emission, as well as for the collimation of its fast outflow. Here, we analyze the available Chandra and XMM-Newton X-ray observations to determine accurately the spectral and temporal variation properties of the CSPN of NGC 2392. The X-ray emission can be described by an absorbed thermal plasma model with temperature MK and X-ray luminosity (8.7 ± 1.0) × 10 ³⁰ erg s ⁻¹ . No long-term variability is detected in the X-ray emission level, but the Chandra light curve is suggestive of short-term variations with a period ∼0.26 days. The possible origins of this X-ray emission are discussed. X-ray emission from the coronal activity of a companion or shocks in the stellar wind can be ruled out. Accretion of material from an unseen main-sequence companion onto the CSPN or from the CSPN wind onto a white dwarf companion are the most plausible origins for its hard X-ray emission, although the mismatch between the rotational period of the CSPN and the modulation timescale of the X-ray emission seems to preclude the former possibility.
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 ofM3-1 an important test case with which to constrain the formation processes of cataclysmic variables, novae, and perhaps even supernovae type Ia.
We measure the Balmer decrements of 23 of the brightest planetary nebulae (PNe) in the inner bulge (r ≲ 3′) of M31 and deredden the bright end of the region's [O iii] λ5007 PN luminosity function. We show that the most luminous PNe produce ≳1200 L o of power in their [O iii] λ5007 line, implying central star luminosities of at least ∼11,000 L o. Even with the most recent accelerated-evolution post-AGB models, such luminosities require central star masses in excess of 0.66 M o and main-sequence progenitors of at least ∼2.5 M o. Since M31's bulge has very few intermediate-age stars, we conclude that conventional single-star evolution cannot be responsible for these extremely luminous objects. We also present the circumstellar extinctions for the region's bright PNe and demonstrate that the distribution is similar to that found for PNe in the Large Magellanic Cloud, with a median value of A 5007 = 0.71. Finally, we compare our results to extinction measurements made for PNe in the E6 elliptical NGC 4697 and the interacting lenticular NGC 5128. We show that such extinctions are not unusual and that the existence of very high-mass PN central stars is a general feature of old stellar populations. Our results suggest that single-star population synthesis models significantly underestimate the maximum luminosities and total integrated light of AGB stars. © 2018. The American Astronomical Society. All rights reserved.
SMP LMC 88 is one of the planetary nebulae (PN) in the Large Magellanic Cloud. We identify in its spectrum Raman scattered O VI lines at 6825 and 7083A. This unambiguously classifies the central object of the nebula as a symbiotic star (SySt). We identified the cold component to be a K-type giant, making this the first D'-type (yellow) SySt discovered outside the Galaxy. The photometric variability in SMP LMC 88 resembles the the orbital variability of Galactic D'-type SySt with its low amplitude and sinusoidal lightcurve shape. The SySt classification is also supported by the He I diagnostic diagram.
Planetary nebulae are traditionally considered to represent the final evolutionary stage of all intermediate-mass stars ($\sim$0.7-8Msol). Recent evidence seems to contradict this picture. In particular, since the launch of the Hubble Space Telescope it has become clear that planetary nebulae display a wide range of striking morphologies which cannot be understood in a single star scenario, instead pointing towards a binary evolution in a majority of systems. Here, we summarise our current understanding of the importance of binarity in the formation and shaping of planetary nebulae, as well as the surprises that recent observational studies have revealed with respect to our understanding of binary evolution in general. These advances have critical implications, including for the understanding of mass transfer processes in binary stars - particularly the all-important but ever-so poorly understood `common envelope phase' - as well as the formation of cosmologically important type Ia supernovae.
We investigate the possible progenitors of the planetary nebulae (PNs) which populate the top 0.5 mag of the [O III] 5007 planetary nebula luminosity function (PNLF). We show that the absolute luminosity of the PNLF cutoff demands that the central stars of these most luminous planetaries be greater than 0.6 Msun, and that such high-mass PN cores must exist in every galaxy. We also use the bolometric-luminosity specific PN number density to show that in early-type galaxies, [O III]-bright planetaries are relatively rare, with only about 10% of stars evolving to these bright magnitudes. We demonstrate that the combination of these two facts implies that either all early-type systems contain a small, smoothly distributed component of young (< 1 Gyr old) stars, or another mechanism exists for creating high-core mass planetaries. We argue that binary-star evolution is this second mechanism, and demonstrate that blue stragglers have the appropriate core properties and number density to explain the observations. We discuss the implications of this alternative mode of stellar evolution, and speculate on how coalesced binaries might affect the use of PNs for measuring a galaxy's star-formation history and chemical evolution.
The Post Asymptotic Giant Branch (AGB) phase is arguably one of the least
understood phases of the evolution of low- and intermediate- mass stars. The
two grids of models presently available are based on outdated micro- and
macro-physics and do not agree with each other. We study the timescales of
post-AGB and CSPNe in the context of our present understanding of the micro-
and macro-physics of stars. We want to assess whether new post-AGB models,
based on the latter improvements in TP-AGB modeling, can help to understand the
discrepancies between observation and theory and within theory itself. We
compute a grid of post-AGB full evolutionary sequences that include all
previous evolutionary stages from the Zero Age Main Sequence to the White Dwarf
phase. Models are computed for initial masses between 0.8 and 4 $M_\odot$ and
for a wide range of initial metallicities ($Z_0=$0.02, 0.01, 0.001, 0.0001),
this allow us to provide post-AGB timescales and properties for H-burning
post-AGB objects with masses in the relevant range for the formation of
planetary nebulae ($\sim$ 0.5 - 0.8, $M_\odot$).
We find post-AGB timescales that are at least $\sim 3$ to $\sim 10$ times
shorter than those of old post-AGB stellar evolution models. This is true for
the whole mass and metallicity range. The new models are also $\sim$ 0.1 - 0.3
dex brighter than the previous models with similar remnant masses. Post-AGB
timescales show only a mild dependence on metallicity. The shorter post-AGB
timescales derived in the present work are in agreement with recent
semiempirical determinations of the post-AGB timescales from the CSPNe in the
Galactic Bulge. Due to the very different post-AGB crossing times,
initial-final mass relation and luminosities of the present models, they will
have a significant impact in the predictions for the formation of planetary
nebulae and the planetary nebulae luminosity function.
The behaviour of carbon-oxygen (CO) white dwarfs (WDs) subject to direct helium accretion is extensively studied. We aim to
analyse the thermal response of an accreting WD to mass deposition at different timescales. The analysis has been performed
for initial WD masses and accretion rates in the range 0.60–1.02 M⊙ and 10−9–10−5 M⊙ yr−1, respectively. Thermal regimes in the parameter space MWD–$\dot{M}_{\rm He}$ leading to formation of red-giant-like structures, steady burning of He, and mild, strong and dynamical flashes have been
identified and the transition between these regimes has been studied in detail. In particular, the physical properties of
WDs experiencing the He-flash accretion regime have been investigated to determine the mass retention efficiency as a function
of the accretor total mass and accretion rate. We also discuss to what extent the building up of a He-rich layer via H burning
could be described according to the behaviour of models accreting He-rich matter directly. Polynomial fits to the obtained
results are provided for use in binary population synthesis computations. Several applications for close binary systems with
He-rich donors and CO WD accretors are considered and the relevance of the results for interpreting He novae is discussed.
Using three independent directions we estimate that the fraction of type Ia
supernovae (SNe Ia) exploding inside planetary nebulae (PNe), termed SNIPs, is
at least ~20%. Our three directions are as follows. (i) Taking the variable
sodium absorption lines in some SN Ia to originate in a massive circumstellar
matter (CSM), as has been claimed recently, we use the results of Sternberg et
al. (2014) to imply that > 20% of SN Ia occur inside a PN (or a PN descendant),
hence classify them as SNIPs. (ii) We next use results that show that whenever
there are hydrogen lines in SN Ia the hydrogen mass in the CSM is large > 1
M_Sun, hence the explosion is a SNIP. We make the simplest assumption that the
probability for explosion is constant in time for up to about 10^5 years after
the merger of the core with the white dwarf (WD) in the frame of the
core-degenerate scenario. This results with at least few x10% of SNe Ia that
may have a SNIP origin. (iii) We examine the X-ray morphologies of 13
well-resolved close-by SN remnants (SNRs) Ia, showing that 15%-25% of all SNRs
Ia possess opposite ear-like features, which we take as evidence of SNIP
origin. Our results, together with several other recent results, lead us to
conclude that the two scenarios most contributing to SNe Ia are the core
degenerate and the double degenerate scenarios. Together these two account for
>95% of all SNe Ia.
The chemical compositions of 41 planetary nebulae are established on the
basis of an analysis of image tube scanner measurements, supplemented by
IUE data. An attempt is made to calculate a theoretical model that gives
satisfactory values of the observed intensities, as well as a number of
excitation-sensitive ratios, in order to obtain ionization correction
factors applicable to the ionic concentrations that will lead to total
abundance values. The quality of individual nebular analyses varies,
depending on the completeness and accuracy of the observational data and
the complexity of the nebular structure. Quality estimates are assigned
for each element in each nebula, and an overall reliability index is
given to each object. It is concluded that the confidence with which one
can speak of the chemical composition of a nebula varies significantly.
We have computed new stellar evolution models that include the effects of rotation and magnetic torques under different hypotheses. The goal is to test whether a single star can sustain the rotational velocities needed in the envelope for magnetohydrodynamical(MHD) simulations to shape bipolar planetary nebulae (PNe) when high mass-loss rates take place. Stellar evolution models with main sequence masses of 2.5 and 5 M
☉ and initial rotational velocities of 250 km s–1 have been followed through the PNe formation phase. We find that stellar cores have to be spun down using magnetic torques in order to reproduce the rotation rates observed for white dwarfs. During the asymptotic giant branch phase and beyond, the magnetic braking of the core has a practically null effect on increasing the rotational velocity of the envelope since the stellar angular momentum is efficiently removed by the wind. We have also tested the best possible case scenarios in rather non-physical contexts to give enough angular momentum to the envelope. We find that we cannot get the envelope of a single star to rotate at the speeds needed for MHD simulations to form bipolar PNe. We conclude that single stellar rotators are unlikely to be the progenitors of bipolar PNe under the current MHD model paradigm.
We examine the properties of white dwarfs (WDs) accreting hydrogen-rich
matter in and near the stable burning regime of accretion rates as modeled by
time-dependent calculations done with Modules for Experiments in Stellar
Astrophysics (MESA). We report the stability boundary for WDs of masses between
0.51 solar masses and 1.34 solar masses as found via time-dependent
calculations. We also examine recurrent novae that are accreting at rates close
to, but below, the stable burning limit and report their recurrence times and
ignition masses. Our dense grid in accretion rates finds the expected minimum
possible recurrence times as a function of the WD mass. This enables inferences
to be made about the minimum WD mass possible to reach a specific recurrence
time. We compare our computational models of post-outburst novae to the stably
burning WDs and explicitly calculate the duration and effective temperature
(Teff) of the post-novae WD in the supersoft phase. We agree with the measured
turnoff time - Teff relation in M31 by Henze and collaborators, infer WD masses
in the 1.0-1.3 solar masses range, and predict ejection masses consistent with
those observed. We close by commenting on the importance of the hot helium
layer generated by stable or unstable hydrogen burning for the short- and
long-term evolution of accreting white dwarfs.
We report the discovery of a planetary nebula centered on the poorly studied
symbiotic binary star DT Ser. In a few other symbiotic stars spatially resolved
nebulae have been discovered: however, only one of them might be a genuine
planetary nebula, while the others are likely to originate in complex mass
ejections episodes from the interacting binary central stars, possibly related
to nova-like outbursts. The rim of the planetary nebula around DT Ser is
severely distorted toward a brighter star, 5 arcsec away. In infrared WISE
data, this star shows the presence of a detached cold dust shell such as those
observed in post-AGB stars. The apparent association of the symbiotic star and
its planetary nebula with the nearby possible post-AGB object is discussed. We
also discuss the sparse and conflicting literature data that could support an
observed variability of the surface brightness of the planetary nebula. The
puzzling and intriguing characteristics displayed by DT Ser are surely worth
further and more detailed investigations.
We present a population synthesis calculation to derive the total number of planetary nebulae (PNs) in the Galaxy that descend from single stars and stars in binary systems. Using the most recent literature results on Galactic and stellar formation and stellar evolution, we predict the total number of Galactic PNs with radii < 0.9 pc to be (4.6 +/- 1.3); 10(4). We do not claim this to be the complete population, since there can be visible PNs with radii larger than this limit. However, by taking this limit, we make our predicted population inherently comparable to the observationally based value of Peimbert and Jacoby (8000 +/- 2000 objects). Our prediction is discrepant with the observations at the 2.9 sigma level, a disagreement that we argue is meaningful in view of our specific treatment of the uncertainty. We conclude that it is likely that only a subset of the stars thought to be capable of making a visible PN actually do. In the second paper in this series, an argument will be presented that the bulk of the Galactic PN population might be better explained if only binaries produce PNs. The predicted local PN formation rate density from single stars and binaries is (1.1 +/- 0.5); 10(-12) PNs yr(-1) pc(-3), lower than recent estimates (2.1 x 10(-12) PNs yr(-1) pc(-3)), which are based on local PN counts and the PN distance scale, but more in line with the white dwarf (WD) birthrate densities [(1.0 +/- 0.25) x 10(-12) WDs yr(-1) pc(-3)]. The predicted PN birthrate density will be revised down if we assume that only binaries make PNs, implying that the PN distance scale has to be revised to larger values.
We present intermediate resolution long-slit spectra and narrowband Hα, [N II], and [O III] images of PM 1-242, PM 318, and PM 1-333, three IRAS sources classified as possible planetary nebulae. The spectra show that the three objects are true planetary nebulae and allow us to study their physical properties; the images provide a detailed view of their morphology. PM 1-242 is a medium- to high-excitation (e.g., He IIλ4686/Hβ ~ 0.4; [N II]λ6584/Hα ~ 0.3) planetary nebula with an elliptical shape containing [N II] enhanced point-symmetric arcs. An electron temperature [T
e([S III])] of ~ 10250 K and an electron density [N
e([S II])] of ~ 2300 cm–3 are derived for PM 1-242. Abundance calculations suggest a large helium abundance (He/H ~ 0.29) in PM 1-242. PM 1-318 is a high-excitation (He IIλ4686/Hβ ~ 1) planetary nebula with a ring-like inner shell containing two enhanced opposite regions, surrounded by a fainter round attached shell brighter in the light of [O III]. PM 1-333 is an extended planetary nebula with a high-excitation (He IIλ4686/Hβ
up to ~ 0.9) patchy circular main body containing two low-excitation knotty arcs. A low N
e([S II]) of ~ 450 cm–3 and T
e([O III]) of ~
15000 K are derived for this nebula. Abundance calculations suggest that PM 1-333 is a type I planetary nebula. The lack of a sharp shell morphology, low electron density, and high excitation strongly suggest that PM 1-333 is an evolved planetary nebula. PM 1-333 also shows two low-ionization polar structures whose morphology and emission properties are reminiscent of collimated outflows. We compare PM 1-333 with other evolved planetary nebulae with collimated outflows and find that outflows among evolved planetary nebulae exhibit a large variety of properties, in accordance with these observed in younger planetary nebula.
Using 3D numerical hydrodynamical simulations, we show that jets launched prior to Type Ia supernova (SN Ia) explosion in
the core-degenerate (CD) scenario can account for the appearance of two opposite lobes (‘Ears’) along the symmetry axis of
the SN remnant (SNR). In the double-degenerate (DD) and CD scenarios the merger of the two degenerate compact objects is very
likely to lead to the formation of an accretion disc, that might launch two opposite jets. In the CD scenario, these jets
interact with the envelope ejected during the preceding common envelope phase. If explosion occurs shortly after the merger
process, the exploding gas and the jets will collide with the ejected nebula, leading to SNR with axisymmetric components
including ‘Ears’. We also explore the possibility that the jets are launched by the companion white dwarf prior to its merger
with the core. This last process is similar to the one where jets are launched in some pre-planetary nebulae. The SNR ‘Ears’
in this case are formed by a spherical SN Ia explosion inside an elliptical planetary nebula-like object. We compare our numerical
results with two SNRs – Kepler and G299.2−2.9.
An extensive grid of optically thick model PN is computed in order to
determine the extent to which the emission-line fluxes used in the
planetary nebular distance scale are affected by the stellar effective
temperature and the nebular and stellar metallicity. It is concluded
that the nebular flux in the H-beta line is closely related to the
luminosity of the central star, but that the more commonly used flux in
the forbidden O III line at 5007 A can also be calibrated to give a
reliable estimate of this quantity. A simple method is presented for
determining the stellar effective temperature and the luminosity, and
the nebular metallicity using only the Balmer lines and the lines of
forbidden O III in the optical. As an absolute calibration of the
planetary nebular distance scale, the excitation, extinction, and
metallicity-corrected cutoff in the luminosity function are derived for
the planetary nebulae in both the SMC and LMC, and the true distance
modulus to the LMC is derived by a new hydrogen-reignition clump-fitting
technique based on self-consistent helium-burning evolutionary models
for the central stars.
The identification of 53 faint planetary nebulae (PN) in the Magellanic
Clouds has allowed the determination of the planetary nebula luminosity
function, which provides a guideline for extrapolation of insufficiently
deep surveys of more distant galaxies to estimate the total number of PN
in those galaxies. A review of the luminosity specific number of PN in
10 local group galaxies suggests that this parameter provides adequate
consistency for estimating the total number of PN in our Galaxy, which
is found to be 10,000 plus or minus 4000.
Classical novae are a subset of the cataclysmic variable (CV) class of objects which undergo outbursts with peak luminosities ˜5×l037–5×l038 erg s–1 every 104–105 years. Around 10–5–10–4
M
⊙ of material is ejected at velocities typically 1,000 km s–1 at outburst. The central system is a semi-detached binary containing a white dwarf and (usually) a late-type, main-sequence companion. The companion fills its Roche lobe, and loses material, via an accretion disk, onto the surface of the white dwarf. Orbital periods are normally found to be in the range 3–10 h with CV orbits generally of low eccentricity (see ref. 1 for a review). As part of a continuing programme of observations of the old nova GK Persei, we examined Infrared Astronomical Satellite (IRAS) images in the region of the nova, and discovered extended emission in the far infrared. These observations are interpreted in terms of an ancient planetary nebula ejected from the central binary system. If this interpretation is correct, then several unique phenomena associated with GK Per may be explained. In addition, GK Per would then provide valuable clues to the evolutionary status of classical novae, and the later stages of planetary nebula formation.
A comprehensive review of the contemporary status of the problem of planetary nebulae is presented. The characteristics of their galactic distribution, their evolution and their cosmogony are emphasised. Though the review is based on all available information on the planetary nebulae and their nuclei, the literature cited in detail covers those papers published in the years 1982–1987.
High-resolution, spatially-resolved profiles of Hα. He II λ6560 and [O III] λ5007 and deep narrow-band CCD images in the Hα and [O III] λ5007 emission lines have been obtained of the planetary nebula (PN) NGC 4361. In addition, VLA-DnC λ3.6-cm continuum observations are presented. This material allows one to explore in unprecedented detail the morphology and kinematics of this PN. The morphology of this object is complex given the highly filamentary structure of the envelope, which is confirmed to possess a low mass. The halo has a high expansion velocity that yields incompatible kinematic and evolutionary ages, unless previous acceleration of the nebular expansion is considered. However, the most remarkable result from the present observations is the detection of a bipolar outflow in NGC 4361, which is unexpected in a PN with a Population II low-mass-core progenitor. It is shown that shocks resulting from the interaction of the bipolar outflow with the outer shell are able to provide an additional heating source in this nebula.
The central star of the planetary nebula N 66 (alias WS 35, SMP 83 and HV 5967) in the Large Magellanic Cloud enhanced its brightness dramatically in 1993 and 1994. Within the subsequent four years it returned to the previous level. Its spectrum resembles that of a Wolf-Rayet star of the nitrogen sequence (WN4.5). We monitored the object intensively from ground and with the Hubble Space Telescope. Now we present the complete set of spectroscopic observations from the different epochs before, during and after the brightness outburst of N 66. The stellar spectra from the different epochs are analyzed in detail by means of most advanced non-LTE models for expanding stellar atmospheres. The main results are: the luminosity, $\log L/L_\odot = 4.6$, before and after the outburst is exceptionally high for a central star of a planetary nebula. During the outburst in 1994, it even climbed up to $\log L/L_\odot = 5.4$ for about one year. The effective temperature of about 112 kK remained roughly constant, i.e. the luminosity mainly increased because of a larger effective stellar radius. The mass loss rate increased from $10^{-5.7} ~M_{\odot}\,{\rm yr^{-1}}$ in the quiet state to $10^{-5.0}~ M_{\odot}\,{\rm yr^{-1}}$ during the outburst. The chemical composition of the stellar atmosphere is that of incompletely CNO-processed matter: it is dominated by helium with a rest of hydrogen, nitrogen being slightly enhanced and carbon strongly depleted. We extensively discuss possible scenarios for the nature and evolutionary origin of N 66, which should explain the exceptional stellar parameters, the atmospheric composition, the outburst mechanism, and the existence of the bipolar nebula which was ejected only a few thousand years ago and contains about 0.6 solar masses of hydrogen-rich matter. If being a single star, N 66 might be (i) a low-mass star after the Asymptotic Giant Branch, as usually adopted for central stars of planetary nebulae, (ii) a massive, i.e. non-degenerate star, or (iii) a merger produced from two white dwarfs. Although there are no direct indications for binarity, we alternatively discuss whether N 66 might be (iv) a massive star which lost its hydrogen envelope in a recent common-envelope phase with a less massive companion, or (v) a white dwarf accreting mass from a companion with a high rate. None of the scenarios is free of any contradiction to at least one of the observational facts. However, the binary scenarios pose less severe problems. If N 66 is a white dwarf accreting matter in a close-binary system, its present accretion rate would bring it to the Chandrasekhar limit within a few hundred thousand years. Thus N 66 might be a candidate for a future type Ia supernova explosion in our cosmic neighborhood.
The [O III] 5007 planetary nebula luminosity function (PNLF) occupies an important place on the extragalactic distance ladder: it is the only standard candle that can be applied to all the large galaxies of the Local Supercluster. We review the method's precision, and use it to show that the distance scale defined by Cepheids and the Surface Brightness Fluctuation method is likely too large by ~ 7%. We also discuss some of the physics underlying the phenomenon, and present clues as why the technique is so resilient.