Large Magellanic Cloud Planetary Nebula Morphology: Probing Stellar Populations and Evolution

Planetary nebulae (PNe) in the Large Magellanic Cloud (LMC) offer the unique opportunity to study both the population and evolution of low- and intermediate-mass stars, by means of the morphological type of the nebula. Using observations from our LMC PN morphological survey, and including images available in the Hubble Space Telescope Data Archive and published chemical abundances, we find that asymmetry in PNe is strongly correlated with a younger stellar population, as indicated by the abundance of elements that are unaltered by stellar evolution (Ne, Ar, and S). While similar results have been obtained for Galactic PNe, this is the first demonstration of the relationship for extragalactic PNe. We also examine the relation between morphology and abundance of the products of stellar evolution. We found that asymmetric PNe have higher nitrogen and lower carbon abundances than symmetric PNe. Our two main results are broadly consistent with the predictions of stellar evolution if the progenitors of asymmetric PNe have on average larger masses than the progenitors of symmetric PNe. The results bear on the question of formation mechanisms for asymmetric PNe-specifically, that the genesis of PNe structure should relate strongly to the population type, and by inference the mass, of the progenitor star and less strongly on whether the central star is a member of a close binary system.     

行星状星云NGC 2242的红外辐射

被Zwicky等人列为星系的NGC 2242,后来刘继英等人发现它具有发射特征并认为可能是行星状星云。前原英夫等人用有缝光谱肯定了它是一个行星状星云。我们证认它是IRAS06304+4448。根据IRAS Point Source Catalog所提供的25μm和60μm的辐射流量,我们得到了这一行星状星云的尘埃温度T_d=130K,光学厚度τ_(25μm)=1.98×10~(-7)和尘埃的总质量M_d=1.0×10~(-7)到1.8×10~(-6)M_⊙之间。     

The Planetary Nebula Luminosity Function at the dawn of Gaia

The [O?iii] λ5007 Planetary Nebula Luminosity Function (PNLF) is an excellent extragalactic standard candle. In theory, the PNLF method should not work at all, since the luminosities of the brightest planetary nebulae (PNe) should be highly sensitive to the age of their host stellar population. Yet the method appears robust, as it consistently produces ?10?% distances to galaxies of all Hubble types, from the earliest ellipticals to the latest-type spirals and irregulars. It is therefore uniquely suited for cross-checking the results of other techniques and finding small offsets between the Population?I and Population?II distance ladders. We review the calibration of the method and show that the zero points provided by Cepheids and the Tip of the Red Giant Branch are in excellent agreement. We then compare the results of the PNLF with those from Surface Brightness Fluctuation measurements, and show that, although both techniques agree in a relative sense, the latter method yields distances that are ～15?% larger than those from the PNLF. We trace this discrepancy back to the calibration galaxies and argue that, due to a small systematic error associated with internal reddening, the true distance scale likely falls between the extremes of the two methods. We also demonstrate how PNLF measurements in the early-type galaxies that have hosted Type?Ia supernovae can help calibrate the SN?Ia maximum magnitude-rate of decline relation. Finally, we discuss how the results from space missions such as Kepler and Gaia can help our understanding of the PNLF phenomenon and improve our knowledge of the physics of local planetary nebulae.     

The Variability and Radial Velocity of Planetary Nebula Central Stars

The extremely accurate estimates of stellar variability and radial velocity in the Gaia Data Release 3(Gaia DR3)have enabled us to examine the close binarity and radial velocity(RV) of central stars(CSs) of planetary nebulae(PNe). This study is twofold:(1) searching for new close binary CS candidates to better understand how binarity affects the formation and evolution of PNe; and(2) extending the sample size of known RVs of PNe in order to understand their kinematics and the dynamics of the Mil...     

The Planetary Nebula Spectrograph elliptical galaxy survey: the dark matter in NGC 4494

We present new Planetary Nebula Spectrograph observations of the ordinary elliptical galaxy NGC 4494, resulting in positions and velocities of 255 planetary nebulae out to seven effective radii (25 kpc). We also present new wide-field surface photometry from MMT/Megacam, and long-slit stellar kinematics from VLT/FORS2. The spatial and kinematical distributions of the planetary nebulae agree with the field stars in the region of overlap. The mean rotation is relatively low, with a possible kinematic axis twist outside  1 R _e  . The velocity dispersion profile declines with radius, though not very steeply, down to  ∼70 km s⁻¹  at the last data point.
We have constructed spherical dynamical models of the system, including Jeans analyses with multi-component Λ cold dark matter (CDM) motivated galaxies as well as logarithmic potentials. These models include special attention to orbital anisotropy, which we constrain using fourth-order velocity moments. Given several different sets of modelling methods and assumptions, we find consistent results for the mass profile within the radial range constrained by the data. Some dark matter (DM) is required by the data; our best-fitting solution has a radially anisotropic stellar halo, a plausible stellar mass-to-light ratio and a DM halo with an unexpectedly low central density. We find that this result does not substantially change with a flattened axisymmetric model.
Taken together with other results for galaxy halo masses, we find suggestions for a puzzling pattern wherein most intermediate-luminosity galaxies have very low concentration haloes, while some high-mass ellipticals have very high concentrations. We discuss some possible implications of these results for DM and galaxy formation.     

The Macquarie/AAO/Strasbourg Hα Planetary Nebula Catalogue: MASH

We present the Macquarie/AAO/Strasbourg Hα Planetary Nebula Catalogue (MASH) of over 900 true, likely and possible new Galactic planetary nebulae (PNe) discovered from the AAO/UKST Hα survey of the southern Galactic plane. The combination of depth, resolution, uniformity and areal coverage of the Hα survey has opened up a hitherto unexplored region of parameter space permitting the detection of this significant new PN sample. Away from the Galactic bulge the new PNe are typically more evolved, of larger angular extent, of lower surface brightness and more obscured (i.e. extinguished) than those in most previous surveys. We have also doubled the number of PNe in the Galactic bulge itself and although most are compact, we have also found more evolved examples. The MASH catalogue represents the culmination of a seven-year programme of identification and confirmatory spectroscopy. A key strength is that the entire sample has been derived from the same, uniform observational data. The 60 per cent increase in known Galactic PNe represents the largest ever incremental sample of such discoveries and will have a significant impact on many aspects of PN research. This is especially important for studies at the faint end of the PN luminosity function which was previously poorly represented.     

Spectroscopic Variability of the Compact Planetary Nebula Hb 12

Astronomy Letters - We present the results of our new low-resolution spectroscopic observations of the young compact planetary nebula Hb 12 performed in 2011–2020 with SAI MSU telescopes. We...     

行星状星云NGC2346核星的食光变现象的消失

本文给出了对行星状星云NGC2346核星AGK3—0°695从1981年到1987年这段期间内所做的照相观测结果。从中我们看到该天体自1981年底开始出现的大变幅食光变现象持续数年之后,从1986年开始其光变幅度迅速减小,由85年的Δm～4~m减小到86年的Δm～1~m.1。而且到1987年其光变曲线仅存Δm～0~m.4的不规则亮度起伏,已无明显的周期性光变现象,文中对此现象做了初步分析讨论。     

Discovery of an Optical Jet in the Rosette Nebula： Rosette HH2

We report on the discovery of an optical jet-Rosette HH2-in the Rosette Nebula. The jet system bears unique features for residing at the center of a giant HII region, and its energy source is visible with apparently very low extinction along the line of sight. Unlike most other Herbig-Haro jets, this jet indicates a high-excitation origin, and its extended portion shows a seemingly intact structure, instead of normally a shocked working surface, which is attributed to photoablation.     

Astronomical Engineering Revisited: Planetary Orbit Modification Using Solar Radiation Pressure

As the Sun evolves along the main sequence its luminosity will grow, leading to a steadily increasing solar flux at the Earth with corresponding catastrophic consequences for the biosphere. A novel means of avoiding this terminal route to human evolution has recently been proposed by Korycansky et al. which utilises a series of grazing fly-pasts of the Earth with a small solar system body to increase the orbit radius of the Earth over a timescale of order 10⁹ years. This short paper will propose an alternative strategy which utilises a large reflective sail to generate a propulsive thrust due to solar radiation pressure. It will be shown that if the sail is configured to be in static equilibrium relative to the Earth, the centre-of-mass of the Earth-sail system slowly accelerates. This scheme offers some advantages in that the mass of the sail is four orders of magnitude less than the mass to be processed in the scheme of Korycanskyet al. for trajectory correction manoeuvres alone. In addition, the severe hazard posed by multiple grazing fly-pasts of the Earth by a small solar system body is avoided. Although offering significant advantages, any thoughts of engineering on an astronomical scale clearly requires a leap of the imagination and a ready use of liberal assumptions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Surprising Variability of the Planetary Nebula IC 4997 $$=$$ QV Sge

Astronomy Letters - We present the results of a new epoch (2009–2019) of a long-term (50 years) photometric monitoring of the variable planetary nebula IC 4997 (QV Sge). The integral (star +...     

The Crab Nebula: Interpretation of Chandra observations

We interpret the observed X-ray morphology of the central part of the Crab Nebula (torus + jets) in terms of the standard theory by Kennel and Coroniti (1984). The only new element is the inclusion of anisotropy in the energy flux from the pulsar in the theory. In the standard theory of relativistic winds, the Lorentz factor of the particles in front of the shock that terminates the pulsar relativistic wind depends on the polar angle as γ = γ₀ + γ _m sin² θ, where γ₀∼200 and γ_m∼4.5×10⁶. The plasma flow in the wind is isotropic. After the passage of the pulsar wind through the shock, the flow becomes subsonic with a roughly constant (over the plerion volume) pressure P=1/3;n∈ where n is the plasma particle density and ∈ is the mean particle energy. Since ∈∼γmc ², a low-density region filled with the most energetic electrons is formed near the equator. A bright torus of synchrotron radiation develops here. Jet-like regions are formed along the pulsar rotation axis, where the particle density is almost four orders of magnitude higher than that in the equatorial plane, because the particle energy there is four orders of magnitude lower. The energy of these particles is too low to produce detectable synchrotron radiation. However, these quasijets become comparable in brightness to the torus if additional particle acceleration takes place in the plerion. We also present the results of our study of the hydrodynamic interaction between an anisotropic wind and the interstellar medium. We compare the calculated and observed distributions of the volume emissivity of X-ray radiation.     

Search for a Periodic Signal in the Emission from the Crab Nebula at High Energies

Astronomy Letters - The emission from the Crab nebula exhibits a significant gamma-ray variability. In this paper we have analyzed this variability in terms of periodicity. Using the pulsar...     

Preliminary Analysis of Photometric Variations of the Central Star of the Planetary Nebula Sh 2-71

We confirm the presence of regular UBV(RI)_C light variations of the object in the center of the planetary nebula Sh 2-71, with an improved period of P = 68.132 ± 0.005 days. The shapes and amplitudes of light curves, in particular colours, are briefly discussed.     

The dynamics of the Orion Nebula

A model is constructed of a spherically symmetric self-gravitating condensation of neutral hydrogen immersed in anHii region. The structure of the condensation is represented by the isothermal gas sphere at a temperature of 100°K. Typical parameters of such a condensation compatible with the estimated ultra-violet radiation field in the central regions of the Orion Nebula are, mass 1M ; radius 10¹⁶ cm; mean density 10^–15 gm cm^–3. The condensations are not static configurations but evolve because of mass loss by ionization from their surfaces. Perhaps 5% become gravitationally unstable and collapse. The remainder act as sources of ionized gas which flows into the surrounding nebula.     

The Stingray Nebula: watching the rapid evolution of a newly born planetary nebula

The formation and early evolution of planetary nebulae represent one of the most poorly understood phases of stellar evolution (Kwok, 1987; Maddox, 1995). One of the youngest, the Stingray Nebula (He3-1357) (Henize, 1967; Henize, 1976), shows all the tell-tale signs of a newly born planetary nebula: it has become ionized only within the past few decades (Parthasarathy et al., 1993); the mass-loss from the central star has ceased within the past few years; and the central star is becoming hotter and fainter as expected from a star on its way to becoming a DA white dwarf (Parthasarathy et al., 1995). The Stingray Nebula thus provides the ideal laboratory for examining the early structure and evolution of this class of objects. Images of the Stingray Nebula, obtained with the Hubble Space Telescope, show for the first time that its multiple expulsions of matter are focused by an equatorial ring and bubbles of gas located on opposite sides of the ring (Bobrowsky et al., 1995). The position angle of the outflows has changed, possibly as a result of precessional motion induced by the presence of a companion star. This is consistent with the precessing jet model by Livio & Pringle (1996). Indeed, we have reported the discovery of a companion star in the Stingray Nebula (Bobrowsky et al., 1998). Finally, we present evidence of the companion star dynamically distorting the gas in this newly-born planetary nebula.     

The Orion Nebula: structure,dynamics, and population

The physical nature and evolution of the Orion Nebula has begun to be revealed by calibrated emission line images and high resolution spectroscopy. We review the evidence that the nebula is a thin wall of emission on the near side of the Orion Molecular Cloud and that its separation from the dominant ionizing star is about 0.3 pc. The density of the nebula decreases rapidly away from the ionization front and the ionized gas is moving at 8 km s^–1 away from the front. A three dimensional model of the surface is presented and its peaks and valleys interpreted as due to irregularities in the density of the molecular cloud. The front is moving rapidly into the molecular cloud, so that objects previously shielded from ionization are continuously being revealed. Recent Hubble Space Telescope images are reviewed and they indicate that protoplanetary disks around pre-main sequence stars are both common and rendered visible by ionization and projection against the bright nebula. A large body of velocity data is discussed and it is seen that Kolmogorov type turbulence seems to only apply to material in the ionization front and the statistical fluctuations become less correlated away from the front.