Search Results (50)

We present recent progress in our understanding of the physical interaction mechanisms at work in evolved binaries of low-to-intermediate initial mass, which are surrounded by a stable disc of gas and dust. These systems are known as post-asymptotic giant-branch (post-AGB) binaries, but recently, it has been shown that some systems are too low in luminosity and should be considered as post-red-giant branch (post-RGB) instead. While the systems are currently well within their Roche lobe, they still show signs of active ongoing interaction between the different building blocks. We end this contribution with some future research plans. Full article

We present the results of photometric and spectroscopic observations of a poorly studied B-type supergiant with infrared excess, the hot post-AGB star IRAS 21546+4721. Based on our photometric observations in the $UBV{R}_C{I}_C$ bands, we detected rapid, night-to-night, non-periodic brightness variations in the star with peak-to-peak amplitudes up to $0{.}^{m}3$ in the V band, as well as color–color and color–brightness correlations. Based on its variability characteristics, IRAS 21546+4721 appears similar to other hot post-AGB stars. Possible causes of the photometric variability are discussed. Additionally, we acquired low-resolution spectra in a wavelength range from 3500 to 7500 Å. The spectrum contains absorption lines typical of an early B-type star, along with a set of emission lines of H I, He I, [O I], [O II], [N II], [S II], and C II originating from an ionized circumstellar envelope. An analysis of the emission spectrum allowed us to estimate the parameters of the gas envelope ($N_e$∼ 10⁴ cm⁻³, $T_e$∼ 10,000 K) and the star’s temperature (∼26,500 K). The radial velocity measured from the emission lines was $V_r=-141\pm 7$ km s⁻¹. Full article

A new spectroscopic study of HR 4049, a post-AGB star in a binary system, based on échelle spectra taken between 2019 and 2025 with the 0.81 m telescope of the Three College Observatory (North Carolina, USA) at a resolution of R ≈ 12,000 is reported. A cross-correlation analysis of 73 spectra of a single C i multiplet in the 4760–4780 Å range yielded the following orbital parameters: the orbital period $P=428.474\pm 0.002$ days, eccentricity $e=0.29\pm 0.01$, argument of periastron $\omega ={242.3}^{\circ }\pm {0.3}^{\circ }$, epoch of periastron $T_0=\mathrm{2,458,383.2}\pm 0.6$, heliocentric systemic radial velocity $\gamma =-30.12\pm 0.09$ km s⁻¹, and semi-amplitude of the radial velocity curve $K_1=15.52\pm 0.13$ km s⁻¹. Phase-dependent variations of the Hα line profile indicate dynamic processes in the circumstellar environment. The luminosity of HR 4049 was refined using the Gaia EDR3 parallax ($0.71\pm 0.10$ mas), corresponding to a distance of $1397\pm 170$ pc, and the average visual magnitude in the brightest state ($m_V=5.35$ mag). The derived luminosity, $log(L/L_{\odot })=4.22\pm 0.12$, suggests an initial mass of 3.0–4.0 $M_{\odot }$. Analysis of the mass function and most probable orbital inclinations (60°–75°) leads to current masses of $\sim 0.75M_{\odot }$ for the primary and $0.70$–$0.82M_{\odot }$ for the secondary component. The results confirm the system’s long-term orbital stability and provide further insights for future research into the nature of post-AGB binaries. Full article

AS 314 (V452 Sct) is a poorly studied early-type emission-line star, which exhibits an infrared excess at wavelengths longer than 10 $\mathsf{\mu }$m. Its earlier studies have been limited to small amounts of observational data and led to controversial conclusions about its fundamental parameters and evolutionary status. Comparison of high-resolution spectra of AS 314 taken over 20 years ago with those of Luminous Blue Variables and other high-luminosity objects suggested its observed properties can be explained by a strong stellar wind from a distant (D∼10 kpc) massive star, possibly in a binary system. However, a recent assessment of its low-resolution spectrum along with a new distance from a Gaia parallax (∼1.6 kpc) resulted in an alternative hypothesis that AS 314 is a low-mass post-asymptotic giant branch (post-AGB) star. The latter hypothesis ignored the high-resolution data, which gave rise to the former explanation. We collected over 30 mostly high-resolution spectra taken in 1997–2023, supplemented them with results of long-term photometric surveys, compared the spectra and the spectral energy distribution with those of post-AGB objects and B/A supergiants, and concluded that the observed properties AS 314 are more consistent with those of the latter. Full article

Understanding the transition from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) phase is crucial for advancing our knowledge of galaxy evolution and the chemical enrichment of the universe. In this manuscript, we analyze 137 carbon-rich, evolved low- and intermediate-mass stars (LIMSs) from both the Magellanic Clouds (MCs) and the Milky Way (MW). We focus on AGB, post-AGB, and PN sources, tracing the evolution of their emission through spectral energy distribution (SED) modeling. Consistent with previous studies, we observe that more evolved LIMSs exhibit cooler dust temperatures and lower optical depths. Amorphous carbon (amC) is the dominant dust species in all the evolutionary stages examined in this work, while silicon carbide (SiC) accounts for 5–30% of the total dust content. Additionally, we analyze color–color diagrams (CCDs) in the infrared using data from IRAC, WISE, and 2MASS, uncovering significant evolutionary trends in LIMS emission. AGB stars evolve from bluer to redder colors as they produce increasing amounts of dust. Post-AGB and PN sources are clearly differentiated from AGB stars, reflecting shifts in both effective stellar and dust temperatures as the stars transition through these evolutionary phases. Full article

Planetary nebulae (PNe) are the ejected gas and dust shells of evolved low- and intermediate-mass stars (LIMSs). We present an abundance comparison between PNe and their progenitors to reveal their similarities and differences since such a comparison has rarely, and not recently, been performed in the Milky Way. The dynamical expulsion of the outer envelope of an evolved LIMS produces the PN. We expected similarities in most $\alpha$-element distributions across the stellar and nebular populations, given that these elements are only marginally produced and destroyed during the LIMS evolution. Differences found in the Fe and S abundances allow us to determine their depletion due to grain condensation in the post-AGB phases. Differences in N and C between PNe and their progenitors set new limits to the low- and intermediate-mass star contributions to these elements. Finally, radial metallicity gradients from evolved LIMS and PNe and Gaia-calibrated distances constrain Galactic evolution in the framework of the current chemical evolutionary models. We found the following: (1) Gas-phase iron is significantly depleted in PNe compared to their progenitor stars, with an average depletion factor of <D[Fe/H]> = 1.74 ± 0.49. (2) Sulfur is also depleted in PNe, though to a much lesser extent than iron. (3) The median enrichment levels for carbon and nitrogen relative to the median stellar population of the same metallicity are approximately [C/H] ∼ +0.3 and [N/H] ∼ +0.4, respectively. PNe with progenitors that experienced hot-bottom burning (HBB) exhibit extreme nitrogen enrichment. (4) With the data available to date, the radial metallicity gradient derived from evolved LIMSs and PNe are compatible within the uncertainties. Full article

The asymptotic giant branch (AGB) phase, experienced by low- and intermediate-mass stars (LIMSs), plays a crucial role in galaxies due to its significant dust production. Planetary nebulae (PNe) offer a novel perspective, providing valuable insights into the dust production mechanisms and the evolutionary history of LIMSs. We selected a sample of nine PNe from the Large Magellanic Cloud (LMC), likely originating from single stars. By modeling their spectral energy distributions (SEDs) with photoionization techniques, we successfully reproduced the observed photometric data, spectra, and chemical abundances. This approach enabled us to constrain key characteristics of the central stars (CSs), dust, and gaseous nebulae, which were then compared with predictions from stellar evolution models. By integrating observational data across ultraviolet (UV) to infrared (IR) wavelengths, we achieved a comprehensive understanding of the structure of the PNe in our sample. The results of the SED analysis are consistent with evolutionary models and previous studies that focus on individual components of the PN, such as dust or the gaseous nebula. Our analysis enabled us to determine the metallicity, the progenitor mass of the CSs, and the amount of dust and gas surrounding the CSs, linking these properties to the previous AGB phase. The PN phase provides critical insights into the physical processes active during earlier evolutionary stages. Additionally, we found that higher progenitor masses are associated with greater amounts of dust in the surrounding nebulae but lower amounts of gaseous material compared to sources with lower progenitor masses. Full article

We present a brief review of the formation and evolution of hydrogen-deficient central stars of planetary nebulae. We include a detailed description of the main observable features of both the central stars and their surrounding nebulae and review their main classifications. We also provide a brief description of the possible progenitor systems of hydrogen-deficient central stars as well as of transients, which are closely connected to the formation of these stars. In particular, we offer a detailed theoretical explanation of the main evolutionary scenarios, both single and binary, which is devised to explain these stars and nebulae. Particular emphasis is made in the description of the so-called born again scenario, their quantitative predictions, and uncertainties. Finally, we discuss the pros and cons of both binary and single evolution channels, draw some conclusions, and discuss open questions in the field. Full article

We present the first hydrodynamical simulations of common envelope evolution that include the formation of dust and the effect of radiation pressure on dust grains. We performed smoothed particle hydrodynamics simulations of the CE evolution for two systems made of a 1.7 $M_{\odot }$ and 3.7 $M_{\odot }$ AGB star primary with a 0.6 $M_{\odot }$ binary companion. The results of our calculations indicate that dust formation has a negligible impact on the gas dynamics essentially because dust forms in the already unbound material. The expansion and cooling of the envelope yield very early and highly efficient production of dust. In our formalism, which does not consider dust destruction, almost 100% of the available carbon that is not locked in CO condensates in dust grains. This massive dust production, thus, strongly depends on the envelope mass and composition, in particular, its C/O ratio, and has a considerable impact on the observational aspect of the object, resulting in a photospheric radius that is approximatively one order of magnitude larger than that of a non-dusty system. Full article

²²Ne(α, γ)²⁶Mg is pivotal in the understanding of several open astrophysical questions, as the nucleosynthesis beyond Fe through the s-process, but its stellar reaction rate is still subject to large uncertainties. These mainly arise from its extremely low rate in the Gamow energy region, whose measurement is hampered by the unavoidable presence of the cosmic ray background noise. A possibility to overcome this issue is to perform the measurement in a quasi background-free environment, such as that offered by the underground Bellotti Ion Beam Facility at LNGS. This is the key idea of EASγ experiment. In this study, the signal from the de-excitation of the compound nucleus ²⁶Mg has been simulated and its detection has been investigated both on surface and deep-underground laboratories. The simulation results show the enhancement in sensitivity achieved by performing the measurement deep underground and with an additional shielding, yielding to unprecedented sensitivity. Full article

Stellar evolution models serve as tools to derive stellar parameters from elemental and isotopic abundance ratios. For low-to-intermediate mass evolved stars, C/O, ¹²C/¹³C, and ¹⁷O/¹⁸O ratios are proxies of the initial mass, a largely unknown parameter in post-AGB sources, yet fundamental to establish correlations with the main properties of their post-AGB envelopes, progressing in understanding their formation and evolution. In these sources, the C/O ratio can be constrained from the detection of C- or O-bearing species in addition to CO, while the ¹⁷O/¹⁸O ratio is straightforwardly determined from the C¹⁷O-to-C¹⁸O intensity ratio of rotational lines. However, the theory is at odds with the observations. We review the status of the question, including new accurate ¹⁷O/¹⁸O ratios for 11 targets (totaling 29). Comparing the results for the ¹⁷O/^$18$O ratios and C-rich/O-rich chemical composition, we find that ∼45% of the cases are canonical, i.e., the observations align with standard model predictions. O-rich non-canonical sources, with ^$17$O/^$18$O ratios above the expected, can be explained by a premature interruption of their AGB evolution as a consequence of a quasi-explosive ejection of a large fraction of the initial mass. For non-canonical C-rich sources, with ^$17$O/^$18$O ratios below predictions, we suggest the possibility they are extrinsic C-rich stars. Full article

After the synthesis of carbon in the core of asymptotic giant branch (AGB) stars, carbon is dredged up to the surface by convection. Many carbon-based molecules are formed in the subsequently developed stellar wind. These include acetylene, which can link together to form benzene in post-AGB evolution. The emergence of the spectral signatures of aromatic and aliphatic compounds in the transition phase between AGB stars and planetary nebulae suggests that complex organic compounds can be formed in the circumstellar environment over very short (10³ yr) timescales. We suggest that the carrier of the family of unidentified infrared emission bands is an amorphous carbonaceous compound—mixed aromatic/aliphatic nanoparticles (MAONs). The implications of the synthesis of complex organics in evolved stars are discussed. Full article

Ongoing improvements in the sensitivity of sub-mm- and mm-range interferometers and single-dish radio telescopes allow for the increasingly detailed study of AGB and post-AGB objects in molecular species other than ${}^{12}\mathrm{CO}$ and ${}^{13}\mathrm{CO}$. With a new update introduced in the modelling tool SHAPE + shapemol, we can now create morpho-kinematical models to reproduce observations of these AGB and post-AGB circumstellar shells in different molecular species, allowing for an accurate description of their physical features as well as their molecular abundances and isotopic ratios. The pre-planetary nebula M1-92 (Minkowski’s Footprint) is one of the most complex objects of this kind, with a wide range of physical conditions and more than 20 molecular species detected. We model this nebula, reproducing the observational data from IRAM-30m and HSO/HiFi spectra and NOEMA interferometric maps, trying to understand the unusual evolution of its central star in the last phases of its life. The results show interesting features that tell us the story of its death. According to standard evolution models, a ${}^{17}\mathrm{O}$/${}^{18}\mathrm{O}$ isotopic ratio of 1.6 implies a stellar initial mass of ∼1.7$M_{\odot }$. Such a star should have turned C-rich by the end of the AGB phase, in striking contrast to the O-rich nature of the nebula. The most plausible way of reconciling this discrepancy is that M1-92 resulted from a sudden massive ejection event, interrupting the AGB evolution of the central source and preventing its transformation into a C-rich star. We also detect a changing ${}^{12}\mathrm{C}$/${}^{13}\mathrm{C}$ ratio across the nebula, which is particularly relevant in the inner equatorial region traced by ${\mathrm{HCO}}^{+}$ and ${\mathrm{H}}^{13}$${\mathrm{CO}}^{+}$, indicating an isotopic ratio variation taking place at some point during the last 1200 yr. Full article

Proto- and young planetary nebulae comprise dense circumstellar envelopes made of molecular gas and dust, some of which hide compact ionized cores that host stellar systems with hot objects, and show high-velocity bipolar outflows launched from inside their cores by means of still unknown mechanisms. We present high-angular-resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations (HPBW ≃ 30–50 mas) of CRL 618 at 1.35 mm covering the H30$\alpha$ recombination line as well as ≃150 molecular lines. The ionized core is resolved, showing a size of ≃0${.}^{″}8\times 0{.}^{″}5$ and is elongated along the east–west direction. This region exhibits a remarkable incomplete ring-like structure with two bright spots to the north and south that are separated by ≃$0_{.}^{″}2$ and shows deprojected velocity gradients ranging from 0.2 to 0.6 km ${\mathrm{s}}^{-1}$${\mathrm{au}}^{-1}$. The 1 mm wavelength continuum emission is mostly produced by free–free emission with a small contribution from dust with an average spectral index of 0.28 ($S_{\nu }\propto {\nu }^{\alpha }$). The ionized core can roughly be modeled as a tilted hollow cylinder with a denser, incomplete equatorial band lacking its back side. Molecular emission traces the neutral component of the same structures enclosing the ionized matter. Full article

The Medium-Resolution Spectrometer on the Mid-Infrared Instrument on the JWST obtained spectra of three carbon stars in the Large Magellanic Cloud. Two of the spectra differ significantly from spectra obtained ∼16–19 years earlier with the Infrared Spectrograph on the Spitzer Space Telescope. The one semi-regular variable among the three has changed little. The long-period Mira variable in the sample shows changes consistent with its pulsation cycle. The short-period Mira shows dramatic changes in the strength of its molecular absorption bands, with some bands growing weaker and some stronger. Whether these variations result from its pulsation cycle or its evolution is not clear. Full article