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Papers by Letizia Stanghellini

Planetary Nebulae Beyond the Milky Way

The recent HST optical images, and the optical and ultraviolet spectra, of Magellanic Cloud plane... more The recent HST optical images, and the optical and ultraviolet spectra, of Magellanic Cloud planetary nebulae (PNe), together with the large database that has been collected in the past decade, allows unprecedented insight into the evolution of PNe and their central stars. In this paper we present a selection of recent results: The analysis of PN morphology, both in the optical and ultraviolet emission lines; the relation between nebular morphology and the chemistry produced by stellar evolution; the direct determination of the transition time from observations; and the study of the nature and evolutionary stage of the components of the planetary nebula luminosity function.

Hst Proposal, Jun 29, 2004

Magellanic Cloud Planetary Nebulae (PNs) offer insight of both the population and evolution of lo... more Magellanic Cloud Planetary Nebulae (PNs) offer insight of both the population and evolution of low-and intermediate-mass stars, in environments that are free of the distance bias and the differential reddening that hinder the observations of the Galactic sample. The study of LMC and SMC PNs also offers the direct comparison of stellar populations with different metallicity. We present a selection of the results from our recent HST surveys, including (1) the morphological analysis of Magellanic PNs, and the statistics of the morphological samples in the LMC and the SMC; (2) the surface brightness versus radius relationship; and (3) the analysis and modeling of the [O III]/Hβ PN luminosity functions in the LMC and the SMC.

Asymmetrical Planetary Nebulae, 1995

Hst Proposal, Jul 1, 2000

Astrophysics and Space Science Library, 2000

Planetary Nebulae (PNe) have been used satisfactory to test the effects of stellar evolution on t... more Planetary Nebulae (PNe) have been used satisfactory to test the effects of stellar evolution on the Galactic chemical environment. Moreover, a link exists between nebular morphology and stellar populations and evolution. We present the latest results on Galactic PN morphology, and an extension to a distance unbiased and homogeneous sample of Large Magellanic Cloud PNe. We show that PNe and their morphology may be successfully used as probes of stellar evolution and populations.

The Local Group as an Astrophysical Laboratory

Nebulae (PNs) in the Magellanic Clouds offer the unique opportunity to study both the population ... more Nebulae (PNs) in the Magellanic Clouds offer the unique opportunity to study both the population and evolution of low-and intermediate-mass stars, in an environment that is free of the distance scale bias and the differential reddening that hinder the observations of the Galactic sample. The study of LMC and SMC PNs also offers the direct comparison of stellar populations with different metallicity. The relative proximity of the Magellanic Clouds allows detailed spectroscopic analysis of the PNs therein, while the Hubble Space Telescope (HST) is necessary to obtain their spatially-resolved images. In this paper we discuss the history and evolution of this relatively recent branch of stellar astrophysics by reviewing the pioneering studies, and the most recent ground-and space-based achievements. In particular, we present the results from our recent HST surveys, including the metallicity dependence of PN identification (and, ultimately, the metallicity dependence of PN counts in galaxies); the morphological analysis of Magellanic PNs, and the correlations between morphology and other nebular properties; the relations between morphology and progenitor mass and age; and the direct analysis of Magellanic central stars and their importance to stellar evolution. Our morphological results are broadly consistent with the predictions of stellar evolution if the progenitors of asymmetric PNs have on average larger masses than the progenitors of symmetric PNs, without any assumption or relation to binarity of the stellar progenitors.

The asymptotic giant branch (AGB) phase of stellar evolution is common to most stars of low and i... more The asymptotic giant branch (AGB) phase of stellar evolution is common to most stars of low and intermediate mass. Most of the carbon and nitrogen in the Universe is produced by AGB stars. The final fate of the AGB envelopes are represented by planetary nebulae (PN). By studying PN abundances and compare them with the yields of stellar evolution is

Proceedings of the International Astronomical Union, 2011

We have used the SuperCOSMOS Hα Survey to look for faint outer structures such as halos, ansae an... more We have used the SuperCOSMOS Hα Survey to look for faint outer structures such as halos, ansae and jets around known planetary nebulae across 4000 square degrees of the southern Milky Way. Our search will contribute to a more accurate census of these features in the Galactic PN population. Candidate common-envelope PNe have also been identified on the basis of their microstructures. We also intend to determine more reliable distances for these PNe, which should allow a much better statistical basis for the post-AGB total mass budget. Our survey offers fresh scope to address this important issue.

The correlations between planetary nebula (PN) morphology and the nature of their progenitors are... more The correlations between planetary nebula (PN) morphology and the nature of their progenitors are explored by examining homogeneous PN samples in the Galaxy and the Magellanic Clouds. We selected PNe with reliable abundances from spectral analysis, and whose morphology is known, and compared the abundances of the element at variance with stellar evolution with the final yields of Asymptotic Giant Branch (AGB) stellar models. We found that most asymmetric PNe derive from the evolution of massive AGB stars both in the Galactic disk and the Magellanic Clouds.

The Astrophysical Journal, 1997

The discrepancy between the observed abundances of 3 He in the interstellar medium and those pred... more The discrepancy between the observed abundances of 3 He in the interstellar medium and those predicted by stellar and galactic chemical evolution remains largely unexplained. In this paper, we attempt to shed some light on this unsolved problem by presenting a quantitative comparison of the 3 He abundances recently measured in six planetary nebulae (IC 289, NGC 3242, NGC 6543, NGC 6720, NGC 7009, NGC 7662) with the corresponding predictions of stellar evolution theory. The determination of the mass of the planetary nebulae progenitors allows us to dismiss, to a good degree of confidence, the hypothesis that the abundance of 3 He in the envelope of all low-mass stars (M ∼ < 2.5 M) is strongly reduced with respect to the standard theoretical values by some mixing mechanism acting in the latest phases of stellar evolution. The abundance versus mass correlation, allowance made for the limitation of the sample, is in fact found to be fully consistent with the classical prediction of stellar evolution. We examine the implications of this result on the galactic evolution of 3 He with the help of a series of models with standard and non-standard (i.e. 3 He depleted) nucleosynthesis prescriptions in varying percentages of low-mass stars. The results are found to be consistent with the abundances determined in the pre-solar material and in the local interstellar medium only if the vast majority of low-mass stars (more than 70-80 %) follows non-standard prescriptions. This implies that either the sample of planetary nebulae under exam is highly biased and therefore not representative of the whole population of low-mass stars, or the solution to the 3 He problem lies elsewhere.

The Astrophysical Journal, 1991

Stability analyses are performed for nonradial g(+)-mode pulsations of postasymptotic AGB stellar... more Stability analyses are performed for nonradial g(+)-mode pulsations of postasymptotic AGB stellar models to determine the location of their pulsational instability strips in the Hertzsprung-Russell diagram. Stellar models are analyzed that are assumed to have undergone a major mass loss event either near the tip of the AGB or shortly thereafter and, therefore, consist of a 50-percent carbon 50-percent oxygen

Arxiv preprint astro-ph/0610206, 2006

Planetary nebulae (PN) represent the evolutionary fate of the asymptotic giant branch (AGB) stell... more Planetary nebulae (PN) represent the evolutionary fate of the asymptotic giant branch (AGB) stellar envelopes, thus are ideally suited to study the chemical impact of AGB stars. Stellar evolution predict elemental enrichment through the AGB evolution, and convective dredge-up episodes allow the products of stellar evolution to reach the stellar outer layers. Planetary nebulae are probes of these processes, and are also probes of the environment at the time of formation of their progenitors, through the elements not affected by AGB evolution. Ultimately PN may be used to test AGB stars as actors and probes. Planetary nebulae are easily identified and detected in the galaxy, the Magellanic Clouds, and beyond, thus they are probes of AGB evolution an stellar populations in different environments as well.

Monthly Notices of the Royal Astronomical Society, 2005

The ultraviolet (UV) spectra of 16 blazars (z 1) from the archives of the Hubble Space Telescope ... more The ultraviolet (UV) spectra of 16 blazars (z 1) from the archives of the Hubble Space Telescope Faint Object Spectrograph have been analysed in order to study in a systematic way the properties of their broad UV emission lines. We find that the luminosities of the most prominent and intense lines, Lyα and C IV λ1549, are similar to those of normal radio-loud quasars at comparable redshifts. However, the equivalent widths of blazar lines are significantly smaller than those of radio-loud quasars. Therefore, while the intrinsic broad-line region luminosity of blazars appears to be indistinguishable from that of radio-loud quasars, their continuum must be comparatively higher, most probably due to relativistic beaming. We have combined the UV luminosities of the debeamed continuum with the emitting gas velocity to derive estimates of the masses of the central supermassive black holes. The size of the broad-line region was computed in two ways: (1) via an empirical relationship between UV continuum luminosity and broad-line region size, and (2) through the external photon density required by blazar models to reproduce the inverse Compton components observed at γ-rays. The second method yields significantly different results from the first method, suggesting that it provides only a very rough estimate or a lower limit on the size of the broad-line region. We find that the average mass of the central black holes in blazars is ∼2.8 × 10 8 M , with a large dispersion, comparable to those computed for other radio-loud active galactic nuclei.