Planetary Nebula Luminosity Function Research Articles

Toward Precision Cosmology with Improved Planetary Nebula Luminosity Function Distances Using VLT-MUSE. II. A Test Sample from Archival Data

Thanks to the MUSE integral field spectrograph on board the Very Large Telescope (VLT), extragalactic distance measurements with the [O iii] λ5007 planetary nebula luminosity function (PNLF) are now possible out to ∼40 Mpc. Here we analyze the VLT/MUSE data for 20 galaxies from the ESO public archive to identify the systems’ planetary nebulae (PNe) and determine their PNLF distances. Three of the galaxies do not contain enough PNe for a robust measure of the PNLF, and the results for one other system are compromised of the galaxy’s internal extinction. However, we obtain robust PNLF distances for the remaining 16 galaxies, two of which are isolated and beyond 30 Mpc in a relatively unperturbed Hubble flow. From these data, we derive a Hubble constant of 74.2 ± 7.2 (stat) ±3.7 (sys) km s−1 Mpc−1, a value that is very similar to that found from other quality indicators (e.g., Cepheids, the tip of the red giant branch, and surface brightness fluctuations). At present, the uncertainty is dominated by the small number of suitable galaxies in the ESO archive and their less-than-ideal observing conditions and calibrations. Based on our experience with these systems, we identify the observational requirements necessary for the PNLF to yield a competitive value for H 0 that is independent of the Type Ia supernova distance scale.

The Origin of the Consistent Planetary Nebula Luminosity Function Bright-end Cutoff

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.

The Effect of Superpositions on the Planetary Nebula Luminosity Function

Planetary nebula (PN) surveys in systems beyond ∼10 Mpc often find high-excitation, point-like sources with [O iii] λ5007 fluxes greater than the apparent bright-end cutoff of the planetary nebula luminosity function (PNLF). Here we identify PN superpositions as one likely cause for the phenomenon and describe the proper procedures for deriving PNLF distances when object blends are a possibility. We apply our technique to two objects: a model Virgo-distance elliptical galaxy observed through a narrowband interference filter, and the Fornax lenticular galaxy NGC 1380 surveyed with the MUSE integral-field unit spectrograph. Our analyses show that even when the most likely distance to a galaxy is unaffected by the possible presence of PN superpositions, the resultant value will still be biased toward too small a distance due to the asymmetrical nature of the error bars. We discuss the future of the PNLF in an era where current ground-based instrumentation can push the technique to distances beyond ∼35 Mpc.

MUSE crowded field 3D spectroscopy in NGC 300

Aims. We perform a deep survey of planetary nebulae (PNe) in the spiral galaxy NGC 300 to construct its planetary nebula luminosity function (PNLF). We aim to derive the distance using the PNLF and to probe the characteristics of the most luminous PNe. Methods. We analysed 44 fields observed with MUSE at the VLT, covering a total area of ∼11 kpc2. We find [O III]λ5007 sources using the differential emission line filter (DELF) technique. We identified PNe through spectral classification with the aid of the BPT diagram. The PNLF distance was derived using the maximum likelihood estimation technique. For the more luminous PNe, we also measured their extinction using the Balmer decrement. We estimated the luminosity and effective temperature of the central stars of the luminous PNe based on estimates of the excitation class and the assumption of optically thick nebulae. Results. We identify 107 PNe and derive a most-likely distance modulus $ (m-M)_0 = 26.48^{+0.11}_{-0.26} $ ($ d = 1.98^{+0.10}_{-0.23} $ Mpc). We find that the PNe at the PNLF cutoff exhibit relatively low extinction, with some high-extinction cases caused by local dust lanes. We present the lower limit luminosities and effective temperatures of the central stars for some of the brighter PNe. We also identify a few Type I PNe that come from a young population with progenitor masses > 2.5 M⊙ but do not populate the PNLF cutoff. Conclusions. The spatial resolution and spectral information of MUSE allow precise PN classification and photometry. These capabilities also enable us to resolve possible contamination by diffuse gas and dust, improving the accuracy of the PNLF distance to NGC 300.

Planetary nebulae hosting accreting white dwarfs: a possible solution for the mysterious cut-off of planetary nebula luminosity function?

ABSTRACTMany 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 planetary nebula (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 white dwarf (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, [${\rm O\, \small {\rm III}}$]-bright PNe, which are characterized 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 [${\rm O\, \small {\rm III}}$] 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 Planetary Nebula Luminosity Function in the Era of Precision Cosmology

One of the great surprises of the late 1980s was the discovery that the [O III] λ5007 planetary nebula luminosity function (PNLF) could be used as a precision extragalactic standard candle. Despite the lack of any robust theory for the phenomenon, the technique passed a myriad of internal and external tests, and became an extremely reliable tool for obtaining distances to large galaxies within ∼20 Mpc. But in more recent years, the use of the technique has declined, due in part to the changing landscape of cosmology. Here we review the history of the PNLF, the experiments that confirmed its utility, and the reasons why interest in the method faded at the turn of the millennium. We also describe how and why the PNLF is making a comeback, and present some of the method’s recent results. Finally, we discuss how the PNLF must be analyzed in the era of precision cosmology, and detail the issues that must be overcome in order to address the current tension between local measures of the Hubble constant and values derived from the microwave background. If these issues can be understood, then the PNLF can provide a useful cross-check on distance measurements out to ∼40 Mpc.

Planetary nebula luminosity function distances for 19 galaxies observed by PHANGS–MUSE

ABSTRACT We provide new planetary nebula luminosity function (pnlf) distances to 19 nearby spiral galaxies that were observed with VLT/MUSE by the PHANGS collaboration. Emission line ratios are used to separate planetary nebulae (pne) from other bright $[\mathrm{O}\, {\small III}]$ emitting sources like compact supernovae remnants (snrs) or H ii regions. While many studies have used narrowband imaging for this purpose, the detailed spectral line information provided by integral field unit (ifu) spectroscopy grants a more robust way of categorizing different $[\mathrm{O}\, {\small III}]$ emitters. We investigate the effects of snr contamination on the pnlf and find that we would fail to classify all objects correctly, when limited to the same data narrowband imaging provides. However, the few misclassified objects usually do not fall on the bright end of the luminosity function, and only in three cases does the distance change by more than 1σ. We find generally good agreement with literature values from other methods. Using metallicity constraints that have also been derived from the same ifu data, we revisit the pnlf zero-point calibration. Over a range of 8.34 < 12 + log (O/H) < 8.59, our sample is consistent with a constant zero-point and yields a value of $M^{*} = -4.542^{+0.103}_{-0.059}\, \mathrm{mag}$, within 1σ of other literature values. MUSE pushes the limits of pnlf studies and makes galaxies beyond ${20}{\, \mathrm{Mpc}}$ accessible for this kind of analysis. This approach to the pnlf shows great promise for leveraging existing archival ifu data on nearby galaxies.

On the most luminous planetary nebulae of M 31

Context. The planetary nebula luminosity function (PNLF) is a standard candle that comprises a key rung on the extragalactic distance ladder. The method is based on the empirical evidence that the luminosity function of planetary nebulae (PNe) in the [O III] λ5007 nebular emission line reaches a maximum value that is approximately invariant with population age, metallicity, or host galaxy type. However, the presence of bright PNe in old stellar populations is not easily explained by single-star evolutionary models. Aims. To gain information about the progenitors of PNe at the tip of the PNLF, we obtained the deepest existing spectra of a sample of PNe in the galaxy M 31 to determine their physico-chemical properties and infer the post-asymptotic giant branch (AGB) masses of their central stars (CSs). Precise chemical abundances allow us to confront the theoretical yields for 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. Methods. Using the OSIRIS instrument at the 10.4 m Gran Telescopio Canarias (GTC), optical spectra of nine bright M 31 PNe were obtained: four of them at the tip of the PNLF, and the other five some 0.5 mag fainter. A control sample of 21 PNe with previous GTC spectra from the literature is also included. We analyze their physical properties and chemical abundances (He, N, O, Ar, Ne, and S), searching for relevant differences between bright PNe and the control samples. The CS masses are estimated with Cloudy modeling using the most recent evolutionary tracks. Results. The studied PNe show a remarkable uniformity in all their nebular properties, and the brightest PNe show relatively large electron densities. Stellar characteristics also span a narrow range: ⟨L*/L⊙⟩ = 4300 ± 310, ⟨Teff⟩ = 122 000 ± 10 600 K for the CSs of the four brightest PNe, and ⟨L*/L⊙⟩ = 3300 ± 370, ⟨Teff⟩ = 135 000 ± 26 000 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 Mi = 1.5 M⊙. Conclusions. These figures provide robust observational constraints for the stellar progenitors that produce the PNLF cutoff in a star-forming galaxy such as M 31, 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 nucleosynthesis models for stars of these masses.

The Fornax3D project: Planetary nebulae catalogue and independent distance measurements to Fornax cluster galaxies

Extragalactic planetary nebulae (PNe) offer a way to determine the distance to their host galaxies thanks to the nearly universal shape of the planetary nebulae luminosity function (PNLF). Accurate PNe distance measurements rely on obtaining well-sampled PNLFs and the number of observed PNe scales with the encompassed stellar mass. This means either disposing of wide-field observations or focusing on the bright central regions of galaxies. In this work we take this second approach and conduct a census of the PNe population in the central regions of galaxies in the Fornax cluster, using VLT/MUSE data for the early-type galaxies observed over the course of the Fornax3D survey. Using such integral-field spectroscopic observations to carefully separate the nebular emission from the stellar continuum, we isolated [O III] 5007 Å sources of interest, filtered out unresolved impostor sources or kinematic outliers, and present a catalogue of 1350 unique PNe sources across 21 early-type galaxies, which includes their positions, [O III] 5007 Å line magnitudes, and line-of-sight velocities. Using the PNe catalogued within each galaxy, we present independently derived distance estimates based on the fit to the entire observed PNLF observed while carefully accounting for the PNe detection incompleteness. With these individual measurements, we arrive at an average distance to the Fornax cluster itself of 19.86 ± 0.32 Mpc (μPNLF = 31.49 ± 0.04 mag). Our PNLF distance measurements agree well with previous distances based on surface brightness fluctuations, finding no significant systematic offsets between the two methods as otherwise reported in previous studies.

The Fornax 3D project: PNe populations and stellar metallicity in edge-on galaxies

Context. Extragalactic planetary nebulae (PNe) are useful distance indicators and are often used to trace the dark-matter content in external galaxies. At the same time, PNe can also be used as probes of their host galaxy stellar populations and to help understand the later stages of stellar evolution. Previous works have indicated that a specific number of PNe per stellar luminosity can vary across different galaxies and as a function of stellar-population properties, for instance increasing with decreasing stellar metallicity. Aims. In this study we further explore the importance of stellar metallicity in driving the properties of the PNe population in early-type galaxies, using three edge-on galaxies in the Fornax cluster offering a clear view into their predominantly metal-rich and metal-poor regions near the equatorial plane or both below and above it, respectively. Methods. Using very large telescope-multi unit spectroscopic explorer (VLT-MUSE) integral-field observations and dedicated PNe detection procedures, we constructed the PNe luminosity function and computed the luminosity-specific number of PNe α in both in- and off-plane regions of our edge-on systems. Results. Comparing these α values with metallicity measurements also based on the same MUSE data, we find no evidence for an increase in the specific abundance of PNe when transitioning between metal-rich and metal-poor regions. Conclusions. Our analysis highlights the importance of ensuring spatial consistency to avoid misleading results when investigating the link between PNe and their parent stellar populations, and suggest that in passively evolving systems variations in the specific number of PNe may pertain to rather extreme metallicity regimes found either in the innermost or outermost regions of galaxies.

Toward Precision Cosmology with Improved PNLF Distances Using VLT-MUSEI. Methodology and Tests

Abstract The [O iii] λ5007 planetary nebula luminosity function (PNLF) is an established distance indicator that has been used for more than 30 yr to measure the distances of galaxies out to ∼15 Mpc. With the advent of the Multi-Unit Spectroscopic Explorer on the Very Large Telescope (MUSE) as an efficient wide-field integral-field spectrograph, the PNLF method is due for a renaissance, as the spatial and spectral information contained in the instrument’s data cubes provides many advantages over classical narrowband imaging. Here we use archival MUSE data to explore the potential of a novel differential emission-line filter (DELF) technique to produce spectrophotometry that is more accurate and more sensitive than other methods. We show that DELF analyses are superior to classical techniques in high surface brightness regions of galaxies, and we validate the method both through simulations and via the analysis of data from two early-type galaxies (NGC 1380 and NGC 474) and one late-type spiral (NGC 628). We demonstrate that with adaptive optics support or under excellent seeing conditions, the technique is capable of producing precision (≲0.05 mag) [O iii] photometry out to distances of 40 Mpc while providing discrimination between planetary nebulae and other emission-line objects such as H ii regions, supernova remnants, and background galaxies. These capabilities enable us to use MUSE to measure precise PNLF distances beyond the reach of Cepheids and the tip of the red giant branch method and become an additional tool for constraining the local value of the Hubble constant.

The survey of planetary nebulae in Andromeda (M 31)

Context.The Andromeda (M 31) galaxy displays several substructures in its inner halo. Different simulations associate their origin with either a single relatively massive merger, or with a larger number of distinct, less massive accretions.Aims.The origin of these substructures as remnants of accreted satellites or perturbations of the pre-existing disc would be encoded in the properties of their stellar populations (SPs). The metallicity and star formation history of these distinct populations leave traces on their deep [O III] 5007 Å planetary nebulae luminosity function (PNLF). By characterizing the morphology of the PNLFs, we constrain their origin.Methods.From our 54 sq. deg. deep narrow-band [O III] survey of M 31, we identify planetary nebulae in six major inner-halo substructures: the Giant Stream, North East Shelf, G1 Clump, Northern Clump, Western Shelf, and Stream D. We obtain their PNLFs and those in two disc annuli, with galactocentric radii ofRGC= 10–20 kpc andRGC= 20–30 kpc. We measure PNLF parameters from cumulative fits and statistically compare the PNLFs in each substructure and disc annulus. We link these deep PNLF parameters and those for the Large Magellanic Cloud (LMC) to published metallicities and resolved stellar population-age measurements for their parent SPs.Results.The absolute magnitudes (M*) of the PNLF bright cut-off for these sub-populations span a significant magnitude range, despite being located at the same distance and having a similar line-of-sight extinction. TheM*values of the Giant Stream, W Shelf, and Stream D PNLFs are fainter than those predicted by PN evolution models by 0.6, 0.8, and 1.5 mag, respectively, assuming the measured metallicity of the parent stellar populations. The faint-end slope of the PNLF increases linearly with decreasing fraction of stellar mass younger than 5 Gyr across the M 31 regions and the LMC. From their PNLFs, the Giant Stream and NE Shelf are consistent with being stellar debris from an infalling satellite, while the G1 Clump appears to be linked with the pre-merger disc with an additional contribution from younger stars.Conclusions.The SPs of the substructures are consistent with those predicted by simulations of a single fairly massive merger event that took place 2–3 Gyr ago in M31. Stream D has an unrelated, distinct origin. Furthermore, this study provides independent evidence that the faint-end of the PNLF is preferentially populated by planetary nebulae evolved from older stars.

The halo of M 105 and its group environment as traced by planetary nebula populations

Context. M 105 (NGC 3379) is an early-type galaxy in the Leo I group. The Leo I group is the nearest group that contains all main galaxy types and can thus be used as a benchmark to study the properties of the intra-group light (IGL) in low-mass groups. Aims. We present a photometric survey of planetary nebulae (PNe) in the extended halo of the galaxy to characterise its PN populations and investigate the presence of an extended PN population associated with the intra-group light. Methods. We use PNe as discrete stellar tracers of the diffuse light around M 105. These PNe were identified on the basis of their bright [O III]5007 Å emission and the absence of a broad-band continuum using automated detection techniques. We compare the PN number density profile with the galaxy surface-brightness profile decomposed into metallicity components using published photometry of the Hubble Space Telescope in two halo fields. Results. We identify 226 PNe candidates within a limiting magnitude of m5007, lim = 28.1 from our Subaru-SuprimeCam imaging, covering 67.6 kpc (23 effective radii) along the major axis of M 105 and the halos of NGC 3384 and NGC 3398. We find an excess of PNe at large radii compared to the stellar surface brightness profile from broad-band surveys. This excess is related to a variation in the luminosity-specific PN number α with radius. The α-parameter value of the extended halo is more than seven times higher than that of the inner halo. We also measure an increase in the slope of the PN luminosity function at fainter magnitudes with radius. Conclusions. We infer that the radial variation of the PN population properties is due to a diffuse population of metal-poor stars ([M/H] < −1.0) following an exponential profile, in addition to the M 105 halo. The spatial coincidence between the number density profile of these metal-poor stars and the increase in the α-parameter value with radius establishes the missing link between metallicity and the post-asymptotic giant branch phases of stellar evolution. We estimate that the total bolometric luminosity associated with the exponential IGL population is 2.04 × 109 L⊙ as a lower limit. The lower limit on the IGL fraction is thus 3.8%. This work sets the stage for kinematic studies of the IGL in low-mass groups.

A study of extragalactic planetary nebulae populations based on spectroscopy. I. Data compilation and first findings

ABSTRACT We compile published spectroscopic data and [O iii] magnitudes of almost 500 extragalactic planetary nebulae (PNe) in 13 galaxies of various masses and morphological types. This is the first paper of a series that aims to analyse the PN populations and their progenitors in these galaxies. Although the samples are not complete or homogeneous, we obtain some first findings through the comparison of a few intensity line ratios and nebular parameters. We find that the ionized masses and the luminosities in H β, LH β, of around 30 objects previously identified as PNe indicate that they are most likely compact H ii regions. We find an anticorrelation between the electron densities and the ionized masses in M 31, M 33, and NGC 300 that suggests that most of the PNe observed in these galaxies are probably ionization bounded. This trend is absent in LMC and SMC suggesting that many of their PNe are density bounded. The He ii λ4686/H β values found in many PNe in LMC and some in M 33 and SMC are higher than in the other galaxies. Photoionization models predict that these high values can only be reached in density bounded PNe. We also find that the brightest PNe in the sample are not necessarily the youngest since there is no correlation between electron densities and the H β luminosities. The strong correlation found between LH β and $L_{[\rm {O}\, \small {III}] }$ implies that the so far not understood cut-off of the planetary nebula luminosity function (PNLF) based on [O iii] magnitudes can be investigated using LH β, a parameter much easier to study.

Clustering of Local Group Distances: Publication Bias or Correlated Measurements? VII. A Distance Framework out to 100 Mpc

Abstract We consider the body of published distance moduli to the Fornax and Coma galaxy clusters, with specific emphasis on the period since 1990. We have carefully homogenized our final catalogs of distance moduli onto the distance scale established in the previous papers in this series. We assessed systematic differences associated with the use of specific tracers and consequently discarded results based on application of the Tully–Fisher relation and of globular cluster and planetary nebula luminosity functions. We recommend “best” weighted relative distance moduli for the Fornax and Coma clusters with respect to the Virgo cluster benchmark of mag and mag. The set of weighted mean distance moduli (distances) we derived as most representative of the clusters’ distances is m − M 0 F o r n a x = 31.41 ± 0.15 m a g ( D = 19.1 − 1.2 + 1.4 M p c ) a n d = 31.21 ± 0.28 m a g ( D = 17.5 − 2.2 + 2.4 M p c ) , m − M 0 C o m a = 34.99 ± 0.38 m a g ( D = 99.5 − 15.9 + 19.0 M p c ) a n d = 34.78 ± 0.27 m a g ( D = 90.4 − 10.6 + 11.9 M p c ) , where the first distance modulus for each cluster is the result of our analysis of the direct, absolute distance moduli, while the second modulus is based on distance moduli relative to the Virgo cluster. While the absolute and relative distance moduli for both clusters are mutually consistent within the uncertainties, the relative distance moduli yield shorter absolute distances by ∼1σ. It is unclear what may have caused this small difference for both clusters; lingering uncertainties in the underlying absolute distance scale appear to have given rise to a systematic uncertainty of the order of 0.20 mag.

Revised Simulations of the Planetary Nebulae Luminosity Function

Abstract We describe a revised procedure for the numerical simulation of planetary nebulae luminosity functions (PNLFs), improving on previous work. The procedure is now based on new H-burning post-asymptotic giant branch (AGB) evolutionary tracks. For a given stellar mass, the new central stars are more luminous and evolve faster. We have slightly changed the distribution of the [O iii] 5007 intensities relative to those of and the generation of absorbing factors, while still basing their numerical modeling on empirical information extracted from studies of galactic planetary nebulae (PNs) and their central stars. We argue that the assumption of PNs being completely optically thick to H-ionizing photons leads to conflicts with observations and show that to account for optically thin PNs is necessary. We then use the new simulations to estimate a maximum final mass, clarifying its meaning, and discuss the effect of internal dust extinction as a possible way of explaining the persistent discrepancy between PNLFs and surface brightness fluctuation distances. By adjusting the range of minimum to maximum final mass, it is also possible to explain the observed variety of PNLF shapes at intermediate magnitudes. The new PN formation rates are calculated to be slightly lower than suggested by previous simulations based on older post-AGB evolutionary tracks.

The survey of planetary nebulae in Andromeda (M 31)

Context.The Andromeda (M 31) galaxy subtends nearly 100 square degrees on the sky. Any study of its halo must therefore account for the severe contamination from the Milky Way halo stars whose surface density displays a steep gradient across the entire M 31 field of view.Aims.Our goal is to identify a population of stars firmly associated with the M 31 galaxy. Planetary nebulae (PNe) are one such population that are excellent tracers of light, chemistry, and motion in galaxies. We present a 16 square degree survey of the disc and inner halo of M 31 with the MegaCam wide-field imager at the CFHT to identify PNe, and characterise the luminosity-specific PN number and PN luminosity function (PNLF) in M 31.Methods.PNe were identified via automated detection techniques based on their bright [O III] 5007 Å emission and absence of a continuum. Subsamples of the faint PNe were independently confirmed by matching with resolvedHubbleSpace Telescope sources from the PanchromaticHubbleAndromeda Treasury and spectroscopic follow-up observations with HectoSpec at the MMT.Results.The current survey reaches two magnitudes fainter than the previous most sensitive survey. We thus identify 4289 PNe, of which only 1099 were previously known. By comparing the PN number density with the surface brightness profile of M 31 out to ∼30 kpc along the minor axis, we find that the stellar population in the inner halo has a luminosity-specific PN number value that is seven times higher than that of the disc. We measure the luminosity function of the PN population and find a bright cut-off and a slope consistent with previous determinations. Interestingly, it shows a significant rise at the faint end, present in all radial bins covered by the survey. This rise in the M 31 PNLF is much steeper than that observed for the Magellanic clouds and Milky Way bulge.Conclusions.The significant radial variation of the PN specific frequency value indicates that the stellar population at deprojected minor-axis radii larger than ∼10 kpc is different from that in the disc of M 31. The rise at the faint end of the PNLF is a property of the late phases of the stellar population. M 31 shows two major episodes of star formation and the rise at the faint end of the PNLF is possibly associated with the older stellar population. It may also be a result of varying opacity of the PNe.

The True Luminosities of Planetary Nebulae in M31's Bulge: Massive Central Stars from an Old Stellar Population

Abstract 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 ⊙ of power in their [O iii] λ5007 line, implying central star luminosities of at least ∼11,000 L ⊙. Even with the most recent accelerated-evolution post-AGB models, such luminosities require central star masses in excess of 0.66 M ⊙ and main-sequence progenitors of at least ∼2.5 M ⊙. 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.

Jsolated Stars of Low Metallicity

We study the effects of a reduced mass-loss rate on the evolution of low metallicity Jsolated stars, following our earlier classification for angular momentum (J) isolated stars. By using the stellar evolution code MESA we study the evolution with different mass-loss rate efficiencies for stars with low metallicities of Z = 0 . 001 and Z = 0 . 004 , and compare with the evolution with solar metallicity, Z = 0 . 02 . We further study the possibility for late asymptomatic giant branch (AGB)—planet interaction and its possible effects on the properties of the planetary nebula (PN). We find for all metallicities that only with a reduced mass-loss rate an interaction with a low mass companion might take place during the AGB phase of the star. The interaction will most likely shape an elliptical PN. The maximum post-AGB luminosities obtained, both for solar metallicity and low metallicities, reach high values corresponding to the enigmatic finding of the PN luminosity function.

Newly discovered Planetary Nebulae population in Andromeda (M31): PN Luminosity function and implications for the late stages of stellar evolution

AbstractStars with masses between ∼0.7 and 8 M⊙ end their lives as Planetary Nebulae (PNe). With the MegaCam at CFHT, we have carried out a survey of the central 16 sq. degrees of Andromeda (M31) reaching the outer disk and halo, using a narrow-band [OIII]5007 and a broad-band g filter. This survey extends previous PN samples both in uniform area coverage and depth. We identify ∼4000 PNe in M31, of which ∼3000 are new discoveries. We detect PNe down to ∼6 mag below the bright cut-off of the PN luminosity function (PNLF), ∼2 mag deeper than in previous works. We detect a steep rise in the number of PNe at ∼4.5 mag fainter than the bright cut-off. It persists as we go radially outwards and is steeper than that seen in the Magellanic clouds. We explore possible reasons for this rise, which give insights into the stellar population of M31.