A family of unidentified infrared emission (UIE) bands is widely observed in planetary nebulae. We suggest that the carriers of the UIE bands are mixed aromatic/aliphatic organic nanoparticles (MAONs) synthesized over thousand-year time scales in the nebulae. The possible chemical pathways of synthesis is discussed. These organics are ejected into the interstellar medium and could have enriched the primordial Solar System, leading to the reservoir of complex organics in comets, asteroids, planetary satellites, and interplanetary dust particles.

The Sun’s global inertial modes are very sensitive to the solar differential rotation and to properties of the deep solar convection zone which are currently poorly constrained. These properties include the superadiabatic temperature gradient, the latitudinal entropy gradient, and the turbulent viscosity. The inertial modes also play a key role in controlling the Sun’s large-scale structure and dynamics, in particular the solar differential rotation. This paper summarizes recent observations and advances in the (linear and nonlinear) modeling of the solar inertial modes.

I present a short overview of the COST Action NanoSpace (“Carbon molecular nanostructures in space”; CA21126) together with the most recent updates. This includes the main motivation and scientific challenges, Action structure and organization (e.g., working groups, tasks, etc.) as well as the main objectives and deliverables. A special emphasis is given to the interdisciplinary approach proposed to attack the Action challenge and the main needs to drive the field forward. Planetary nebulae (PNe) are wonderful astrochemistry laboratories and a dominant source of complex carbon molecular nanostructures (i.e., nanocarbons) in space, being key astronomical objects for NanoSpace. The main goal is to show the power of networking as a tool to understand nanocarbons in PNe as well as to encourage the participation and collaborations between the PNe community and the multiple interdisciplinary research fields represented in NanoSpace.

The newly discovered inertial modes in the Sun offer the opportunity to probe the solar convective zone down to the tachocline. While linear analysis predicts the frequencies and eigenfunctions of the modes, it gives no information about their excitation or their amplitudes. We present here a theoretical formalism for the stochastic excitation of the solar inertial modes by turbulent convection. The amplitudes predicted by our model are in complete agreement with observations, thus supporting the assumption that they are stochastically excited. Our work also uncovers a qualitative transition in the shape of the inertial mode spectrum, between m ≲ 5 where the modes are clearly resolved in frequency, and m ≳ 5 where the modes overlap. This complicates the interpretation of the high-m data, and suggests that a model for the whole shape of the power spectrum is necessary to exploit the full seismic potential of solar inertial modes.

We use nearly two decades of helioseismic data obtained from the GONG (2002–2020) and HMI (2010–2020) ring-diagram pipelines to examine the temporal variations of the properties of individual equatorial Rossby modes with azimuthal orders in the range 6 ≤ m ≤ 10. We find that the mode parameters obtained from GONG and HMI are consistent during the data overlapping period of 2010–2020. The power and the frequency of each mode exhibit significant temporal variations over the full observing period. Using the GONG data during solar cycles 23 and 24, we find that the mode power averaged over 6 ≤ m ≤ 10 shows a positive correlation with the sunspot number (0.42), while the averaged frequency shift is anti-correlated (–0.91). The anti-correlation between the average mode power and frequency shift is –0.44.

A high sensitivity and high-angular resolutions infrared space telescope, the James Webb Space Telescope (JWST), allowed us to study dust and molecules in unprecedented details. This contribution highlights the first year of JWST’s scientific operation, and reports prospects of dust and molecular studies in the coming future.

We study the m = 1 high-latitude inertial mode and its contribution to the latitudinal transport of the Sun’s angular momentum. Ring-diagram helioseismology applied to 5° tiles is used to obtain the horizontal flows near the surface of the Sun. Using 10 years of data from SDO/HMI, we report on the horizontal eigenfunction and Reynolds stress $\[{Q_{\theta \phi }} = \langle {u'_\theta }{u'_\phi }\rangle \]$ for the m = 1 high-latitude inertial mode (frequency –86.3 nHz, critical latitudes ±58°). We find that Qθφ takes significant values above the critical latitude and is positive (negative) in the northern (southern) hemisphere, implying equatorward transport of angular momentum. The Qθφ peaks above latitude 70° with a value of 38 m2/s2.

The Red Rectangle is a nebula surrounding the post-AGB star HD 44179. It is the prototype of a particular class of nebulae associated with post-AGB binaries characterised by the presence of stable circumbinary disks in (quasi-)Keplerian rotation. Here we present the results of new high-resolution (0.″ 02″05) ALMA observations of continuum and line emissions at 0.9 mm. The continuum maps are analysed through a simple model of dust emission, which can reproduce the observational data. We find that most dust emission in the Red Rectangle is concentrated in the central regions of the rotating disk and that the settlement of dust grains onto the equatorial plane is very significant, particularly in comparison with the much larger scale height displayed by the gas distribution. The diameter of the dust-emitting region is about 250 au, with a total width of about 50 au. This region coincides with the warm PDR where certain molecules (like HCN), CI, and CII are presumably formed, as well as probably PAHs. From the spectral index, we confirm the presence in the disk of large grains, with a typical radius of about 150 μm, which supports the long-lived hypothesis for this structure. We also confirm the existence of a compact ionised wind at the centre of the nebula, probably emerging from the accretion disk around the companion, for which we derive an extent of about 10 au and a total flux of 8 mJy. We also briefly present the results on molecular lines of 12CO, 13CO, and other less abundant species.

We performed numerical simulations of the common envelope (CE) interaction between two intermediate-mass asymptotic giant branch (AGB) stars and their low-mass companions. For the first time, formation and growth of dust in the envelope is calculated explicitly. We find that the first dust grains appear as early as ∼1–3 yrs after the onset of the CE, and are smaller than grains formed later. As the simulations progress, a high-opacity dusty shell forms, resulting in the CE photosphere being up to an order of magnitude larger than it would be without the inclusion of dust. At the end of the simulations, the total dust yield is ∼8.2×10−3 M⊙ (∼2.2×10−2 M⊙) for a CE with a 1.7 M⊙ (3.7 M⊙) AGB star. Dust formation does not substantially lead to more mass unbinding or substantially alter the orbital evolution.

Our understanding of solar convection is incomplete. A crucial gap is the unknown superadiabaticity in the solar convection zone, δ = ▽–▽ad. Global modes of oscillations in the inertial frequency range are sensitive to δ and serve as a novel tool to explore solar convection. Here, we address the forward problem where the superadiabaticity δ(r) varies with radius. We solve the 2.5D eigenvalue problem, considering the linearized equations for momentum, mass and energy conservation with respect to a realistic solar model. We find that the frequency and eigenfunction of the m = 1 high-latitude mode are influenced by δ in the lower convection zone. Our prescribed setup suggests that the superadiabaticity in the lower half of the convection zone is below 2.4×10-7 to reach a qualitative agreement with the observed eigenfunction.

Magnetic fields are important physics in stellar evolutionary theory, which seriously affects the stellar structure and evolutionary statues. The small-scale magnetic fields in the photosphere are ubiquitous, and float on the stellar surface, which usually couple with the acoustic waves, affecting the propagation of the acoustic waves. Considering the effect of the magnetic fields in the stellar photosphere on the oscillation frequencies, we calculate the asteroseismology for solar-like star KIC 11295426 and KIC 10963065. We obtain the stellar fundamental parameters, especially the strength of small-scale magnetic fields in the stellar photosphere. We find that the small-scale magnetic fields in the stellar photosphere may obviously improve the agreement between the observations and the theoretical models for two stars. The magnetic strength for KIC 11295426 and KIC 10963065 from asteroseismology are in agreement with the stellar period-activity relation.

The modelling of the evolutionary phases beyond the asymptotic giant branch attracts the interest of the astrophysical community because it allows the determination of the properties of progenitor stars and to deduce the efficiency of the mechanisms able to alter the surface chemistry of the stars evolving through the asymptotic giant branch. This has been possible since improvements in the modelling of these phases, which allow a reliable determination of the luminosity with which stars evolve after the termination the asymptotic giant branch evolution.

The surface chemistry of post-asymptotic giant branch stars and planetary nebulae is shown to be tightly correlated to the various processes taking place during the asymptotic giant branch evolution. The possibility of using the observed infrared excess of these evolved stars to derive information on the dust formation process during the previous evolutionary phases is also discussed.

Classical and recurrent novae are luminous eruptions taking place in binary star systems in which a white dwarf accretes material from a non-degenerate stellar companion. After the nova event, a shell of gas is expelled and expands into the surrounding environment at hundreds to thousands of km s−1. This shell, the so-called nova remnant, experiences interactions with the binary system, the accretion disk, the surrounding environment, and very notably with continuous winds from the white dwarf powered by radiation from nuclear burning on its surface. The similarities with the formation of planetary nebulae are obvious, yet the shaping of nova remnants occurs on much shorter time-scales. This results in the prevalent round to mild elliptical 3D shape of nova remnants. Here we describe the morphology, kinematics and dynamics of nova remnants based on our multi-epoch imaging and long-slit and integral field spectroscopic studies and compare them with those of planetary nebulae.

As is well known, low-mass stars constitute the most abundant class of stars in our galaxy. In stars less massive than the Sun, the density within stellar interiors increases as the stellar mass decreases. Therefore, for low-mass stars, the significance of electrostatic effects in stellar interiors cannot be neglected, as these interactions can alter the properties of matter.

In our study, we focus on exploring the outer layers of stars less massive than the Sun. We have computed a range of stellar models, ranging from 0.4 to 0.9 solar masses, to investigate the effects of two physical processes on the acoustic oscillations in the envelopes of these stars: partial ionization of chemical elements and electrostatic interactions between particles in the outer layers. In addition to partial ionization, we demonstrate that Coulomb effects also influence the acoustic oscillation spectrum. Our investigation reveals the following findings:

1. Coulomb effects can indeed influence the acoustic oscillations in low-mass stars.

2. The model with a mass of inline1 serves as a transition point. For models less massive than inline1, their acoustic spectrum is more affected by electrostatic interactions, whereas models more massive than inline1 have their acoustic spectrum more impacted by partial ionization processes.

Our work unveils the promising possibilities that future discoveries related to the detection of solar-like oscillations in stars less massive than the Sun could offer in terms of understanding the connections between the internal structure of low-mass stars and their observable characteristics.

Bipolar or multipolar lobes in pre-planetary nebulae (pPNe) often exhibit intertwined outer whorled patterns, resulting from stellar wind matter accumulation during the asymptotic giant branch (AGB) phase. These structures are likely triggered by stellar or substellar companions. We regard that CW Leonis currently stands at a critical transition moment, providing a vivid illustration of the progression from an AGB star in a binary system to a pPN. We have found that CW Leonis has shown significant enhancements in its optical and near-infrared light curves over the past two decades, with the recent Hubble Space Telescope image finally revealing the long-awaited central star. Utilizing an eccentric-orbit binary model, we can reproduce the position-angle dependence of the expansion velocity in the whorled pattern around CW Leonis, suggesting a nearly face-on orbital inclination. Its contradiction to the features in the innermost circumstellar envelope, corresponding to a nearly edge-on inclination, may imply the presence of an additional companion. Our updated theoretical framework explores the complexity of the whorled pattern. Further identifying and monitoring phase-transition candidates at the tip of the AGB will provide valuable insights into the AGB-pPN transition and the role of companions in shaping the morphological evolution of these stellar objects.

The solar dynamo is a physical process of magnetic field generation due to conversion of kinetic energy of plasma flows into magnetic energy. However, in the mean-field dynamo theory, one needs to segregate scales and consider separately large-scale dynamo and small-scale dynamo. The large-scale dynamo produces the large-scale mean field and unavoidable fluctuations of the mean field. Both are cycle-dependent. The small-scale dynamo is supposed to produce only the small-scale field, and this field is cycle-independent. There is no sharp boundary between the intervals of the large-scale and small-scale dynamos. An unavoidable presence of a smooth transition implies that there is a region where the properties of the large-scale global dynamo and fluctuations inherent to small-scale dynamo co-exist on some intermediate scales. Recent achievements in observations of the small-scale dynamo operation on the smallest observable scales and on the intermediate scales of typical active regions are discussed in the review.

In this article, the physical processes occurring in the convective layer and the photosphere of the Sun and their connection to the formation of active regions (ARs) and the development of the corresponding magnetic field are explored. Specifically, we test the magnetic flux emergence hypothesis and based on the line-of-sight magnetic field and Doppler shift data obtained from the Global Oscillation Network Group (GONG) observations. The study encompasses the analysis of 24 ARs observed during the period from 2011 to 2022. We find a strong correlation between the magnetic flux and the imbalance of radial velocity fluxes. The results indicate that the magnetic flux emergence hypothesis cannot fully explain the evolution of ARs during their early stages of development.

We present a radial velocity and model atmosphere analysis of both components of the spectroscopic binary central star of NGC 1514, based on high-resolution, high-signal-to-noise-ratio spectrograms taken with the CFH and Subaru telescopes at Maunakea, Hawaii. Together with the Gaia parallax and other data from the literature, all this information permits to determine the basic stellar parameters (Teff, L, log g, masses) of both binary components. This allows us to empirically test the theoretical post-AGB mass-luminosity relation.

We investigate the evolution of subsurface flows during the emergence and the active phase of sunspot regions using the time–distance helioseismology analysis of the full-disk Dopplergrams from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We present an analysis of emerging active regions of various types, including delta-type active regions and regions with the reverse polarity order (‘anti-Hale active regions’). The results reveal strong vortical and shearing flows during the emergence of magnetic flux, as well as the process of formation of large-scale converging flow patterns around developing active regions, predominantly in the top 6 Mm deep layers of the convection zone. Our analysis revealed a significant correlation between the flow divergence and helicity in the active regions with their flaring activity, indicating that measuring characteristics of subsurface flows can contribute to flare forecasting.