scholarly journals Fallback in bipolar planetary nebulae?

2021 ◽  
Vol 21 (11) ◽  
pp. 275
Author(s):  
Willem A. Baan ◽  
Hiroshi Imai ◽  
Gabor Orosz
Keyword(s):  
Low Power ◽  
Accretion Rate ◽  
Planetary Nebulae ◽  
Equatorial Region ◽  
Alternative Scenario ◽  
Bipolar Outflow ◽  
Total Luminosity

Abstract The subclass of bipolar Planetary Nebulae (PNe) exhibits well-defined low-power outflows and some shows shock-related equatorial spiderweb structures and hourglass structures surrounding these outflows. These structures are distinctly different from the phenomena associated with spherical and elliptical PNe and suggest a non-standard way to simultaneously energise both kinds of structures. This paper presents evidence from the published literature on bipolar PN Hb 12 and other sources in support of an alternative scenario for energising these structures by means of accretion from material shells deposited during earlier post-AGB and pre-PNe evolutionary stages. In addition to energising the bipolar outflow, a sub-Eddington accretion scenario could hydrodynamically explain the spiderweb and outer hourglass structures as oblique shockwaves for guiding the accreting material into the equatorial region of the source. Estimates of the accretion rate resulting from fallback-related spherical accretion could indeed help to drive a low-power outflow and contribute to the total luminosity of these sources.

scholarly journals Masers: Probing the mass loss process in PPN

1997 ◽  
Vol 180 ◽  
pp. 348-349
Author(s):  
Dieter Engels
Keyword(s):  
Mass Loss ◽  
Large Amplitude ◽  
Planetary Nebulae ◽  
Transition Process ◽  
Main Line ◽  
Agb Stars ◽  
Loss Process ◽  
Bipolar Outflow ◽  
Sky Survey ◽  
Sizeable Number

With the advent of the IRAS All-Sky Survey a sizeable number of transition objects between the AGB and the PN-phase were found - the Proto Planetary Nebulae (PPN). Oxygen-rich AGB stars often show prominent masers of SiO, H2O, and OH, which are lost during the transition process. The heavy mass loss on the AGB however does not stop abruptly and a new axisymmetric wind develops during the PPN phase. These winds both may host new masers and they can be used to study the changes of the mass loss process after that the stars have stopped their large-amplitude variations on the AGB. Several PPN are known to have OH masers, and at least in one case, HD 101584, the presence of a bipolar outflow could be proven (te Lintel Hekkert et al. 1992). Lewis (1989) found that main-line OH masers become prominent again. I will discuss here conclusions, which can be drawn from observations of H2O masers in PPN.

scholarly journals The Structure of Accretion Flow at the Base of Jets in AGN

2002 ◽  
Vol 19 (1) ◽  
pp. 125-128 ◽  
Author(s):  
Alina-C. Donea ◽  
Peter L. Biermann
Keyword(s):  
Boundary Layer ◽  
Black Hole ◽  
Angular Momentum ◽  
Low Power ◽  
Accretion Disk ◽  
Gravitational Energy ◽  
Kerr Geometry ◽  
Narrow Region ◽  
Stable Circular Orbit ◽  
Total Luminosity

AbstractThis paper discusses the boundary layer and the emission spectrum from an accretion disk having a jet anchored at its inner radius, close to the black hole. We summarise our earlier work and apply it to the accretion disks of some blazars. We suggest that the ‘accretion disk with jet’ (ADJ) model could make the bridge between standard accretion disk models (suitable for quasars and FRii sources) and low-power advection dominated accretion disk models (suitable for some of the low-power BL Lacs and FRi sources).The jet is collimated within a very narrow region close to the black hole (nozzle). In our model it is assumed that the boundary layer of the disk is the region between radius Rms — the last marginally stable circular orbit calculated for a Kerr geometry — and the radius Rjet, which gives the thickness of the ‘footring’, i.e. the base of the jet. We analyse the size of the boundary layer of the disk where the jet is fed with energy, mass, and angular momentum. As a consequence of the angular momentum extraction, the accretion disk beyond Rjet no longer has a Keplerian flow. A hot corona usually surrounds the disk, and entrainment of the corona along the flow could also be important for the energy and mass budget of the jet.We assume that the gravitational energy available at the footring of the jet goes into the jet, and so the spectrum from the accretion disk gives a total luminosity smaller than that of a ‘standard’ accretion disk, and our ADJ model should apply for blazars with low central luminosities. Variations of the boundary layer and nozzle may account for some of the variability observed in active galactic nuclei.

scholarly journals Molecular Hydrogen in the Lagoon: H2 Line Emission from Messier 8

2002 ◽  
Vol 19 (2) ◽  
pp. 260-264 ◽  
Author(s):  
Michael G. Burton
Keyword(s):  
Line Intensity ◽  
Molecular Cloud ◽  
Molecular Hydrogen ◽  
Line Emission ◽  
Molecular Gas ◽  
Line Centre ◽  
Bipolar Outflow ◽  
Total Luminosity

AbstractThe 2.12 μm v = 1−0 S(1) line of molecular hydrogen has been imaged in the Hourglass region of M8. The line is emitted from a roughly bipolar region, centred around the O7 star Herschel 36. The peak H2 1−0 S(1) line intensity is 8.2 × 10−15 erg s−1 cm−2arcsec−2. The line centre emission velocity varies from −25 kms−1 in the SE lobe to +45 kms−1 in the NW lobe. The distribution is similar to that of the CO J = 3−2 line. The H2 line appears to be shock-excited when a bipolar outflow from Herschel 36 interacts with the ambient molecular cloud. The total luminosity of all H2 lines is estimated to be ˜16 L⊙ and the mass of the hot molecular gas ˜9 × 10−4 M⊙ (without any correction for extinction).

scholarly journals Dust in Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 117-128 ◽  
Author(s):  
Patrick F. Roche
Keyword(s):  
Thermal Emission ◽  
Planetary Nebulae ◽  
Central Star ◽  
Infrared Emission ◽  
Significant Fraction ◽  
Dust Grains ◽  
Ionized Gas ◽  
Total Luminosity

The presence of dust in planetary nebulae can be deduced in several ways - from the observed depletions of condensable elements, internal extinction and, most directly, through the detection of infrared emission from the dust grains. We know that there is a substantial amount of dust in planetary nebulae, and that a significant fraction of the total luminosity emerges in the infrared through thermal emission in most objects. However, a number of questions still largely remain unsolved, and perhaps the most pressing of these are that we do not yet have a satisfactory understanding of the ultraviolet, optical or infrared properties of the dust grains and we also do not yet know exactly where the emitting grains are located within the nebulae; for example, are they mixed with the ionized gas, or in neutral inclusions or perhaps in a disk around the central star?

scholarly journals HST spectra reveal accretion in MY Lupi

2019 ◽  
Vol 629 ◽  
pp. A108 ◽  
Author(s):  
J. M. Alcalá ◽  
C. F. Manara ◽  
K. France ◽  
C. P. Schneider ◽  
N. Arulanantham ◽  
...  
Keyword(s):  
Accretion Rate ◽  
Space Telescope ◽  
Low Contrast ◽  
Mass Accretion Rate ◽  
Excess Emission ◽  
Total Luminosity ◽  
Significant Difference ◽  
Chromospheric Emission ◽  
Order Of Magnitude ◽  
Far Ultraviolet

The mass accretion rate is a crucial parameter for the study of the evolution of accretion discs around young low-mass stellar and substellar objects (YSOs). We revisit the case of MY Lup, an object where VLT/X-shooter data suggested a negligible mass accretion rate, and show it to be accreting on a level similar to other Class II YSOs in Lupus based on Hubble Space Telescope (HST) observations. In our HST-Cosmic Origins Spectrograph (HST-COS) and -Space Telescope Imaging Spectrograph (HST-STIS) spectra, we find many emission lines, as well as substantial far-ultraviolet (FUV) continuum excess emission, which can be ascribed to active accretion. The total luminosity of the C IV λ1549 Å doublet is 4.1 × 10−4 L⊙. Using scalings between accretion luminosity, Lacc, and C IV luminosity from the literature, we derive Lacc ~2 × 10−1 L⊙, which is more than an order of magnitude higher than the upper limit estimated from the X-shooter observations. We discuss possible reasons for the X-shooter-HST discrepancy, the most plausible being that the low contrast between the continuum excess emission and the photospheric+chromospheric emission at optical wavelengths in MY Lup hampered detection of excess emission. The luminosity of the FUV continuum and C IV lines, strong H2 fluorescence, and a “1600 A Bump” place MY Lup in the class of accreting objects with gas-rich discs. So far, MY Lup is the only peculiar case in which a significant difference between the HST and X-shooter Ṁacc estimates exists that is not ascribable to variability. The mass accretion rate inferred from the revisited Lacc estimate is Ṁacc ~ 1(−0.5+1.5) × 10−8 M⊙ yr−1. This value is consistent with the typical value derived for accreting YSOs of similar mass in Lupus and points to less clearing of the inner disc than indicated by near- and mid-infrared observations. This is confirmed by Atacama Large Millimeter Array (ALMA) data, which show that the gaps and rings seen in the sub-millimetre are relatively shallow.

Less Power, Greater Conflict

2018 ◽  
Vol 49 (1) ◽  
pp. 47-62 ◽  
Author(s):  
Petra C. Schmid
Keyword(s):  
Low Power ◽  
High Power ◽  
Goal Pursuit ◽  
Goal Conflict ◽  
Personal Goals ◽  
Multiple Goals ◽  
Objective Performance ◽  
The Future ◽  
The Way

Abstract. Power facilitates goal pursuit, but how does power affect the way people respond to conflict between their multiple goals? Our results showed that higher trait power was associated with reduced experience of conflict in scenarios describing multiple goals (Study 1) and between personal goals (Study 2). Moreover, manipulated low power increased individuals’ experience of goal conflict relative to high power and a control condition (Studies 3 and 4), with the consequence that they planned to invest less into the pursuit of their goals in the future. With its focus on multiple goals and individuals’ experiences during goal pursuit rather than objective performance, the present research uses new angles to examine power effects on goal pursuit.

An interdependence account of sexism and power: Men’s hostile sexism, biased perceptions of low power, and relationship aggression.

2019 ◽  
Vol 117 (2) ◽  
pp. 338-363 ◽  
Author(s):  
Emily J. Cross ◽  
Nickola C. Overall ◽  
Rachel S. T. Low ◽  
James K. McNulty
Keyword(s):  
Low Power ◽  
Hostile Sexism ◽  
Relationship Aggression
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