arXiv subjects

Letizia Stanghellini

Publications and source records attributed to Letizia Stanghellini.

At least 19 recordsLinked to original sources

arXiv2025

GTC/OSIRIS Deep Spectroscopy of Galactic Compact Planetary Nebulae: PNG048.5+04.2 and PNG068.7+14.8

We report deep long-slit spectroscopy of two Galactic compact planetary nebulae (PNe), PNG048.5+04.2 and PNG068.7+14.8, obtained using the 10.4m Gran Telescopio Canarias (GTC). These spectra cover a broad wavelength range of ~3630-10370 A, enabling detection of numerous emission lines critical for nebular analysis, including [O II] 3727 and [O III] 4363 in the blue and [S III] 6312,9069 in the red. Also detected in the spectrum of PNG068.7+14.8 are broad C III and C IV lines probably due to stellar emission, indicating that the central star of this PN is [WC]-type. These GTC optical-IR spectra were analyzed in details in conjunction with the archival Spitzer/IRS mid-IR spectra, and elemental abundances of the two PNe determined. Photoionization models were established for the two PNe using CLOUDY, based on the ratios of line fluxes measured from the GTC optical-NIR spectra. Our best photoionization modeling, in combination with state-of-the-art post-AGB evolutionary model tracks, shows that both PNe evolved from low-mass progenitors (<2 M_sun) with relatively young ages (<3 Gyr), although their central cores are probably in different evolutionary stages - the central star of PNG068.7+14.8 is still in the process of heating up, while that of PNG048.5+04.2 has already entered the white dwarf cooling track. A comparison with AGB model predictions also constrains the progenitors of both PNe to be of low masses. Moreover, the two PNe are in line with the radial oxygen gradients exhibited by the Galactic PN populations, using the most up-to-date distances.

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arXiv2024

Abundances of planetary nebulae and evolved stars: Iron and sulfur depletion, and carbon and nitrogen enrichment, in low- and intermediate-mass stellar populations in the Milky Way

We explore the elemental abundances in Galactic planetary nebulae (PNe) compared with those of their stellar progenitors (Red Giant Branch and Asymptotic Giant Branch, RGB and AGB, stars), to explore and quantify the expected -- i.e., due to AGB evolution or condensation onto grains -- differences. We gleaned the current literature for the nebular abundances while we used the APOGEE DR~17 survey data for the stellar sample. We examined the elements in common between the nebular and stellar samples, namely, C, N, O, Fe, and S. We confirm that iron in PNe is mostly entrapped in grains, with an average depletion $<$D[Fe/H]$>$=1.741$\pm$0.486 dex, and we disclose a weak correlation between iron depletion and the [O/H] abundance, D[Fe/H]$=(6.6003\pm2.443)\times{\rm [O/H]} +(1.972\pm0.199)$. Sulfur may also be mildly depleted in PNe, with $<$D[S/H]$>=0.179\pm0.291$ dex. We also found an indication of nitrogen enrichment for PNe $<$E[N/H]$>$=0.393$\pm$0.421 dex, with maximum enrichment (0.980$\pm$0.243) occurring for the PNe whose progenitors have gone through the HBB. The carbon enrichment is $<$E[C/H]$>$=0.332$\pm$0.460 dex when measured for the general PN populations. Our results will be relevant for future Galactic and extragalactic studies comparing nebular and stellar samples.

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arXiv2024

Planetary Nebulae of the Large Magellanic Cloud I: A multiwavelength analysis

Planetary nebulae (PNe) have three main components: a central star (CS), ionised gas and dust in the nebula. Each of them contains critical chemical fingerprints of their evolution, serving as tracers of the evolution, nucleosynthesis and dust production that occurred during the preceding asymptotic giant branch (AGB) phase. We aim to build a bridge to link the PN phase to the evolution of their progenitors, trying to better understand the dust production and mass-loss mechanism during the final AGB phase. Here, we present a comprehensive study of nine Large Magellanic Cloud (LMC) spherical or elliptical PNe whose observations from the ultraviolet (UV) through the infrared (IR) are available in the literature. We characterize nebulae and CSs, finding information as the amount of gas that makes up the nebula and the dust that surrounds the CS, necessary to reconstruct the evolutionary history of mass-loss and dust production. We compare the observed energy distribution of the selected PNe to that obtained from photoionization modeling, taking into account the presence of dust. The physical and chemical parameters of the central stars are then compared with the predictions from the evolutionary tracks. We characterized the source, assigning to each CS a progenitor, early-AGB mass. We estimated the mass of the nebula and the dust-to-gas ratio. For 5 objects, we find evidence for the presence of a near-IR bump, which would be connected to the presence of hot dust.

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arXiv2024

GTC Spectroscopic Surveys of Planetary Nebulae in the Milky Way and M31

We report spectroscopic surveys of planetary nebulae (PNe) in the Milky Way and Andromeda (M31), using the 10.4-m Gran Telescopio Canarias (GTC). The spectra are of high quality and cover the whole optical range, mostly from 3650 \r{A} to beyond 1 micron, enabling detection of nebular emission lines critical for spectral analysis as well as photoionization modeling. We obtained GTC spectra of 24 compact (angular diameter <5 arcsec) PNe located in the Galactic disk, ~3-20 kpc from the Galactic centre, and can be used to constrain stellar evolution models and derive radial abundance gradients of the Milky Way. We have observed 30 PNe in the outer halo of M31 using the GTC. These halo PNe are uniformly metal-rich and probably all evolved from low-mass stars, consistent with the conjecture that they all formed from the metal-rich gas in M31 disk but displaced to their present locations due to galaxy interactions.

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arXiv2024

Modernizing IRAF to Support Gemini Data Reduction

The US National Gemini Office (US NGO), part of the Community Science and Data Center (CSDC) at NSF's NOIRLab, has completed a project to upgrade the IRAF-based Gemini reduction software to provide a fully supported system capable of running natively on modern hardware. This work includes 64-bit platform ports of the GEMINI package and dependency tasks (e.g. from the STSDAS external package), upgrades to the core IRAF system and all other external packages to fix any platform and licensing problems, and the establishment of fully supported Help Desk and distribution systems for the user community. Early results show a 10-20X speedup of execution times using the native 64-bit software compared to the virtualized 32-bit solutions now in use. Results are even better on new Apple M1/M2 platforms where the additional overhead of Intel CPU emulation can be eliminated. Timing comparisons, science verification testing, and release plans are discussed.

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arXiv2023

US National Gemini Office in the NOIRLab era

This article presents an overview of the US National Gemini Office (US NGO) and its role within the International Gemini Observatory user community. Throughout the years, the US NGO charter changed considerably to accommodate the evolving needs of astronomers and the observatory. The current landscape of observational astronomy requires effective communication between stakeholders and reliable/accessible data reduction tools and products, which minimize the time between data gathering and publication of scientific results. Because of that, the US NGO heavily invests in producing data reduction tutorials and cookbooks. Recently, the US NGO started engaging with the Gemini user community through social media, and the results have been encouraging, increasing the observatory's visibility. The US NGO staff developed tools to assess whether the support provided to the user community is sufficient and effective, through website analytics and social media engagement numbers. These quantitative metrics serve as the baseline for internal reporting and directing efforts to new or current products. In the era of the NSF's National Optical-Infrared Astronomy Research Laboratory (NOIRLab), the US NGO is well-positioned to be the liaison between the US user base and the Gemini Observatory. Furthermore, collaborations within NOIRLab programs, such as the Astro Data Lab and the Time Allocation Committee, enhance the US NGO outreach to attract users and develop new products. The future landscape laid out by the Astro 2020 report confirms the need to establish such synergies and provide more integrated user support services to the astronomical community at large.

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arXiv2023

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

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

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arXiv2022

Carbon Abundances in Compact Galactic Planetary Nebulae: An Ultraviolet spectroscopic study with the Space Telescope Imaging Spectrograph (STIS)

We surveyed a sample of compact Galactic planetary nebulae (PNe) with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope (HST/STIS) to determine their gas-phase carbon abundances. Carbon abundances in PNe constrain the nature of their asymptotic giant branch (AGB) progenitors, as well as cosmic recycling. We measured carbon abundances, or limits thereof, of 11 compact Galactic PNe, notably increasing the sample of Galactic PNe whose carbon abundance based on HST ultraviolet spectra is available. Dust content of most targets has been studied elsewhere from Spitzer spectroscopy; given the compact nature of the nebulae, both UV and IR spectra can be directly compared to study gas- and dust-phase carbon. We found that carbon-poor (C/O<1) compact Galactic PNe have oxygen-rich dust type (ORD), while their carbon-enhanced counterparts (C/O>1) have carbon-rich dust (CRD), confirming the correlation between gas- and dust-phase carbon content which was known for Magellanic Cloud PNe. Based on models of expected final yields from AGB evolution we interpret the majority of the carbon-poor PNe in this study as the progeny of ~1.1-1.2 M$_{\odot}$ stars that experienced some extra-mixing on the red giant branch (RGB), they went through the AGB but did not go through the carbon star phase. Most PNe in this group have bipolar morphology, possibly due to the presence of a sub-solar companion. Carbon-enhanced PNe in our sample could be the progeny of stars in the ~1.5-2.5 M$_{\odot}$ range, depending on their original metallicity.

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arXiv2019

The population of Galactic planetary nebulae: a study of distance scales and central stars based on the second GAIA release

We matched the astrometry of central stars (CSs) of spectroscopically-confirmed Galactic planetary nebulae (PNe) with DR2 Gaia parallaxes ($p$), finding 430 targets in common with $p>0$ and $|σ_{\rm p}/p|<1$. A catalog of PNe whose CSs have DR2 Gaia parallaxes is presented in Table 1. We compared DR2 parallaxes with those in the literature, finding a good correlation between the two samples. We used PNe parallaxes to calibrate the Galactic PN distance scale. Restricting the sample to objects with 20$\%$ parallax accuracy, we derive the distance scale ${\rm log}(R_{\rm pc})=-(0.226\pm0.0155)\times{\rm log}(S_{\rm Hβ})-(3.920\pm0.215)$, which represents a notable improvement with respect to previous ones. We found that the ionized mass vs. optical thickness distance scale for Galactic PNe is not as well constrained by the Gaia calibrators, but gives important insight on the nature of the PNe, and is essential to define the domain for our distance scale application. We placed the CSs whose distance has been determined directly by parallax on the HR diagram, and found that their location on the post-AGB H-burning evolutionary tracks is typical for post-AGB stars.

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arXiv2019

Astro2020 Science White Paper: Radial Metallicity Gradients in Star-Forming Galaxies

Spiral star-forming galaxies are complex astrophysical objects whose baryonic component is dominated by the disk, where most of the star formation resides. The metallicity in the disk is not uniform, and it usually decreases with the distance to the galaxy center, in the so-called radial metallicity gradient. Radial metallicity gradients have been successfully used to set important constraints on galaxy formation and their chemical evolution. This paper focuses on the implications of radial metallicity gradients measured with different probes for a variety of galaxies, and on the foreseen advances in this field in the astronomical landscape of the 2020s.

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arXiv2019

Precision Analysis of Evolved Stars

Evolved stars dominate galactic spectra, enrich the galactic medium, expand to change their planetary systems, eject winds of a complex nature, produce spectacular nebulae and illuminate them, and transfer material between binary companions. While doing this, they fill the HR diagram with diagnostic loops that write the story of late stellar evolution. Evolved stars sometimes release unfathomable amounts of energy in neutrinos, light, kinetic flow, and gravitational waves. During these late-life times, stars evolve complexly, with expansion, convection, mixing, pulsation, mass loss. Some processes have virtually no spatial symmetries, and are poorly addressed with low-resolution measurements and analysis. Even a "simple" question as how to model mass loss resists solution. However, new methods offer increasingly diagnostic tools. Astrometry reveals populations and groupings. Pulsations/oscillations support study of stellar interiors. Optical/radio interferometry enable 2-3d imagery of atmospheres and shells. Bright stars with rich molecular spectra and velocity fields are a ripe opportunity for imaging with high spatial and spectral resolution, giving insight into the physics and modeling of later stellar evolution.

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arXiv2018

The role of the US National Office in the Gemini partnership

We follow the history of the US National Gemini Office from its origin when the US National New Technology Telescope was reshaped into two 8m telescopes for the International Gemini Observatory. The development of the office in the decade of the 1990s continues to shape its function to the present. The following decade, 2000-2010, marked major milestones including the dedication of the telescopes, the reshaping of the Gemini instrumentation program, and dissatisfaction of the US community as expressed in the ALTAIR report. Nationally funded facilities are under financial pressure, as new projects must be funded from a nearly fixed budget. We will discuss how the US NGO should be used to advocate for both the US community and the Gemini Observatory. This role could be an essential one in protecting open access to 8m-class facilities.

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arXiv2018

Galactic planetary nebulae as probes of radial metallicity gradients and other abundance patterns

We use planetary nebulae (PNe) as probes to determine the Galactic radial oxygen gradients, and other abundance patterns. We select data homogeneously from recent data sets, including PNe at large Galactocentric distances. The radial oxygen gradient calculated for the general PN population, which probes the region between the Galactic center and out to $\sim$28 kpc, is shallow, with slope $\sim$-0.02 dex kpc$^{-1}$, in agreement with previous findings. We looked for time evolution of the metallicity gradient using PNe with different age progenitors as metallicity probes. We identify PNe whose progenitor stars are younger than 1 Gyr (YPPNe), and those whose progenitor stars are older than 7.5 Gyr (OPPNe), based on the comparison between evolutionary yields and elemental abundances of the PNe. By studying OPPNe and YPPNe separately we found that: (i) The OPPNe oxygen gradient is shallower ($\sim-0.015$ dex kpc$^{-1}$) than that derived from YPPNe ($\sim-0.027$ dex kpc$^{-1}$); (ii) the OPPNe inner radial distribution of oxygen is compatible with no gradient to the radial extent of the thick disk population ($\sim$10 kpc), similarly to what has been observed in thick disk stars; (iii) planetary nebulae (especially OPPNe) indicate that significant gradient slope is limited to Galactocentric distances between $\sim$10 to $\sim$13.5 kpc, as observed for open clusters and field stars. Outside this range, the distribution is almost flat. We found that the radial oxygen gradient is steeper for a PN population closer to the Galactic disk, similarly to what is observed in the general stellar population by the SEGUE survey. We use our novel population dating to compare our results with current chemical evolutionary models, and with gradients from other Galactic populations, for insight on galaxy chemical evolution.

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arXiv2017

The Gaia Data Release 1 parallaxes and the distance scale of Galactic planetary nebulae

In this paper we gauge the potentiality of Gaia in the distance scale calibration of planetary nebulae (PNe) by assessing the impact of DR1 parallaxes of central stars of Galactic PNe (CSPNe) against known physical relations. For selected PNe targets with state-of-the-art data on angular sizes and fluxes, we derive the distance-dependent parameters of the classical distance scales, i.e., physical radii and ionized masses, from DR1 parallaxes; we propagate the uncertainties in the estimated quantities and evaluate their statistical properties in the presence of large relative parallax errors; we populate the statistical distance scale diagrams with this sample and discuss its significance in light of existing data and current calibrations. We glean from DR1 parallaxes 8 CSPNe with S/N$>$1. We show that this set of potential calibrators doubles the number of extant trigonometric parallaxes (from HST and ground-based), and increases by two orders of magnitude the domain of physical parameters probed previously. We then use the combined sample of suitable trigonometric parallaxes to fit the physical-radius-to-surface-brightness relation. This distance scale calibration, although preliminary, appears solid on statistical grounds, and suggestive of new PNe physics. With the tenfold improvement in PNe number statistics and astrometric accuracy expected from future Gaia releases the new distance scale, already very intriguing, will be definitively constrained.

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arXiv2017

Tests of the Galactic planetary nebula distance scale with the initial Gaia parallax distances of their central stars

We used the "primary dataset" of Gaia Data Release 1 (DR1) to search for parallax measurements of central stars (CSs) of Galactic planetary nebulae (PNe), to determine PN distances. We found that a trigonometric parallax is available for 16 CSs, seven of which with relative uncertainty below 80%. The limited comparison of these trigonometric distances to other reliable individual determinations discloses good correlation between the two sets, with the Gaia parallax distances being lower by a factor of ~0.1 dex in the logarithmic distances. We tested with the Gaia parallaxes the most popular Galactic PN distance scales, namely, the physical radius vs. surface brightness, and the ionized mass vs. inverse optical thickness scales. While the number of available calibrators may still be too low, and their relative uncertainties too high, to derive a working distance scale, we were able to assess the current sample and to reveal the very promising potential of the future Gaia releases for a recalibration of the distance scale of Galactic PNe.

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arXiv2016

Compact Planetary Nebulae in the Galactic Disk: Analysis of the Central Stars

We have obtained multi-wavelength observations of compact Galactic planetary nebulae (PNe) to probe post-Asymptotic Giant Branch (AGB) evolution from the onset of nebular ejection. We analyze new observations from HST to derive the masses and evolutionary status of their central stars (CSs) in order to better understand the relationship between the CS properties and those of the surrounding nebulae. We also compare this sample with others we obtained using the same technique in different metallicity environments: the Large and Small Magellanic Clouds. We work with HST/WFC3 images of 51 targets obtained in a snapshot survey (GO-11657). The high spatial resolution of HST allows us to resolve these compact PNe and distinguish the CS emission from that of their surrounding PNe. The targets were imaged through the filters F200LP, F350LP, and F814W from which we derive Johnson V and I magnitudes. We derive CS bolometric luminosities and effective temperatures using the Zanstra technique, from a combination of HST photometry and ground-based spectroscopic data. We present new unique photometric measurements of 50 CSs, and derived effective temperatures and luminosities for most of them. Central star masses for 23 targets were derived by placing the stars on a temperature-luminosity diagram and compare their location with the best available single star post-AGB evolutionary tracks, the remaining masses were indeterminate most likely because of underestimates of the stellar temperature, or because of substantial errors in the adopted statistical distances to these objects. The distribution of CS masses in the sample of compact PNe is different than sample in the LMC and SMC, but with a median mass of 0.59 solar masses it is similar to other Galactic samples. We conclude that the compact nature of many of the PNe is a result of their large distance, rather than their physical dimension.

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arXiv2016

Compact Galactic Planetary Nebulae: A HST/WFC3 Morphological Catalog, and a Study of their Role in the Galaxy

We present the images of a \textit{Hubble Space Telescope} (\textit{HST}/WFC3) snapshot program of angularly compact Galactic planetary nebulae (PNe), acquired with the aim of studying their size, evolutionary status, and morphology. PNe that are smaller than $\sim4\arcsec$ are underrepresented in most morphological studies, and today they are less well studied than their immediate evolutionary predecessors, the pre-planetary nebulae. The images have been acquired in the light of [\ion{O}{3}]$\lambda5007$, which is commonly used to classify the PN morphology, in the UV continuum with the aim of detecting the central star unambiguously, and in the $I-$band to detect a cool stellar companion, if present. The sample of 51 confirmed PNe exhibits nearly the full range of primary morphological classes, with the distribution more heavily weighted toward bipolar PNe, but with total of aspherical PNe almost identical to that of the general Galactic sample. A large range of microstructures is evident in our sample as well, with many nebulae displaying attached shells, halos, ansae, and internal structure in the form of arcs, rings, and spirals. Various aspherical structures in a few PNe, including detached arcs, suggest an interaction with the ISM. We studied the observed sample of compact Galactic PNe in the context of the general Galactic PN population, and explore whether their physical size, spatial distribution, reddening, radial metallicity gradient, and possible progenitors, are peculiar within the population of Galactic PNe. We found that these compact Galactic PNe, which have been selected based on apparent dimensions, constitute a diverse Galactic PN population that is relatively uniformly distributed across the Galactic disk, including the outskirts of our Galaxy. This unique sample will be used in the future to probe the old Galactic disk population.

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arXiv2016

SDSS IV MaNGA - Spatially resolved diagnostic diagrams: A proof that many galaxies are LIERs

We study the spatially resolved excitation properties of the ionised gas in a sample of 646 galaxies using integral field spectroscopy data from SDSS-IV MaNGA. Making use of Baldwin-Philips-Terlevich diagnostic diagrams we demonstrate the ubiquitous presence of extended (kpc scale) low ionisation emission-line regions (LIERs) in both star forming and quiescent galaxies. In star forming galaxies LIER emission can be associated with diffuse ionised gas, most evident as extra-planar emission in edge-on systems. In addition, we identify two main classes of galaxies displaying LIER emission: `central LIER' (cLIER) galaxies, where central LIER emission is spatially extended, but accompanied by star formation at larger galactocentric distances, and `extended LIER' (eLIER) galaxies, where LIER emission is extended throughout the whole galaxy. In eLIER and cLIER galaxies, LIER emission is associated with radially flat, low H$α$ equivalent width of line emission ($<$ 3 Å) and stellar population indices demonstrating the lack of young stellar populations, implying that line emission follows tightly the continuum due to the underlying old stellar population. The H$α$ surface brightness radial profiles are always shallower than $\rm 1/r^{2}$ and the line ratio [OIII]$λ$5007/[OII]$λ$3727,29 (a tracer of the ionisation parameter of the gas) shows a flat gradient. This combined evidence strongly supports the scenario in which LIER emission is not due to a central point source but to diffuse stellar sources, the most likely candidates being hot, evolved (post-asymptotic giant branch) stars. Shocks are observed to play a significant role in the ionisation of the gas only in rare merging and interacting systems.

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