arXiv subjects

Bruce Balick

Publications and source records attributed to Bruce Balick.

65 records · Page 4Linked to original sources

arXiv2005

Kinematic Structure of H2 and [Fe II] in the Bipolar Planetary Nebula M 2-9

We present high-dispersion long-slit IR spectra of the double-shell bipolar planetary nebula M 2-9 in the emission lines [Fe II] 16435 and H2 v=1--0 S(1) 21218. H2 spectra reveal for the first time the kinematic structure of the outer shell in M 2-9. Kinematics of the inner shell, traced by [Fe II], resemble those of optical lines like [N II]. [Fe II] and H2 shells have expansion speeds roughly proportional to distance from the star (``Hubble'' flows) and share the same dynamical age of 1200--2000 yr, depending on the distance to M 2-9. Thus, the inner ionized lobes and outer molecular lobes, as well as the molecular torus and ``outer loops'' measured by other observers, were all formed around the same time. Consequently, their nested structure likely arises from an excitation gradient rather than independent ejections. H2 and [Fe II] emission is distributed more uniformly than [N II], and IR lines are not dominated by the moving ionization pattern like visual-wavelength lines. We suggest that this is because IR lines of [Fe II] and H2 are excited by relatively isotropic far-UV radiation (Balmer continuum), whereas optical lines respond to a directed rotating beam of Lyman continuum. Finally, we highlight intriguing similarities between M 2-9 and the Homunculus of eta Carinae, despite the different central engines powering the two nebulae.

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arXiv2004

Simultaneous Production of Disk and Lobes: A Single-Wind MHD Model for the Eta Carinae Nebula

The luminous blue variable Eta Carinae is surrounded by a complex and highly structured nebula of ejected material. The best-studied and axisymmetric components of this outflow consist of bipolar lobes (the ``homunculus'') and an equatorial ``skirt.'' Recent proper motion measurements suggest that the skirt was ejected at the same time as the lobes, contrary to the assumptions of all current theoretical models for the formation of the nebula (which use the skirt to collimate stellar winds into lobes). We present a magnetohydrodynamic (MHD) stellar wind model that produces an outflowing disk and bipolar lobes in a single, steady-state wind. The basic model consists of a wind from a rotating star with a rotation-axis-aligned dipole magnetic field. The azimuthal component of the magnetic field, generated by stellar rotation, compresses the wind toward the equator and also toward the rotation axis, simultaneously producing an outflowing disk and jet. We use numerical MHD simulations to study the wind for various amounts of stellar rotation and to show a range of wind morphologies. In order to produce wide angle lobes similar to the homunculus (which have roughly a 30 degree opening angle), a high-speed polar wind (with enhanced energy density) from the star is also required. In that case, the structure of the wind bears a remarkable resemblance to the skirt plus homunculus morphology of the Eta Car nebulae, and a significant fraction of the stellar angular momentum is carried away by the wind. Although the model assumes a steady-state wind (rather than an eruption) and thermal wind driving (rather than radiation pressure), the structure of the wind is encouraging.

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arXiv2004

Menzel 3: Dissecting the ant

The structure and kinematics of the bipolar nebula Mz 3 have been investigated by means of HST, CTIO and ESO images and spectra. At least four distinct outflows have been identified which, from the inside to the outside, are the following: a pair of bright bipolar lobes, two opposite highly collimated column-shaped outflows, a conical system of radial structure, and a very dim, previously unnoticed, low-latitude and flattened (ring-like) radial outflow. A simple Hubble-law describes the velocity field of the ballisticaly expanding lobes, columns and rays, suggesting that their shaping has being done at very early stages of evolution, in a sort of eruptive events with increasing degree of collimation and expansion ages ranging from ~600 for the inner structures to ~1600 years (per kpc to the nebula) for the largest ones.

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arXiv2004

Sulfur, Chlorine, and Argon Abundances in Planetary Nebulae. IV: Synthesis and the Sulfur Anomaly

We have compiled a large sample of O, Ne, S, Cl, and Ar abundances which have been determined for 85 galactic planetary nebulae in a consistent and homogeneous manner using spectra extending from 3600-9600 Angstroms. Sulfur abundances have been computed using the near IR lines of [S III] 9069,9532 along with [S III] temperatures. We find average values, expressed logarithmically with a standard deviation, of log(S/O)=-1.91(+/-.24), log(Cl/O)=-3.52(+/-.16), and log(Ar/O)=-2.29(+/-.18), numbers consistent with previous studies of both planetary nebulae and H II regions. We also find a strong correlation between [O III] and [S III] temperatures among planetary nebulae. In analyzing abundances of Ne, S, Cl, and Ar with respect to O, we find a tight correlation for Ne-O, and loose correlations for Cl-O and Ar-O. All three trends appear to be colinear with observed correlations for H II regions. S and O also show a correlation but there is a definite offset from the behavior exhibited by H II regions and stars. We suggest that this S anomaly is most easily explained by the existence of S^+3, whose abundance must be inferred indirectly when only optical spectra are available, in amounts in excess of what is predicted by model-derived ionization correction factors. Finally for the disk PNe, abundances of O, Ne, S, Cl, and Ar all show gradients when plotted against galactocentric distance. The slopes are statistically indistinguishable from one another, a result which is consistent with the notion that the cosmic abundances of these elements evolve in lockstep.

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arXiv2003

Space Telescope Imaging Spectrograph slitless observations of Small Magellanic Cloud Planetary Nebulae: a study on morphology, emission line intensity, and evolution

A sample of 27 Planetary Nebulae (PNs) in the Small Magellanic Clouds (SMC) have been observed with the Hubble Space Telescope Imaging Spectrograph (HST/STIS) to determine their morphology, size, and the spatial variation of the ratios of bright emission lines. The morphologies of SMC PNs are similar to those of LMC and Galactic PNs. However, only a third of the resolved SMC PNs are asymmetric, compared to half in the LMC. The low metallicity environment of the SMC seems to discourage the onset of bipolarity in PNs. We measured the line intensity, average surface brightness (SB), and photometric radius of each nebula in halpha, hbeta, [O III] lambda4959 and 5007, [NII] 6548 and 6584, [S II] lambda6716 and 5731, He I 6678, and [OI] 6300 and 6363. We show that the surface brightness to radius relationship is the same as in LMC PNs, indicating its possible use as a distance scale indicator for Galactic PNs. We determine the electron densities and the ionized masses of the nebulae where the [S II] lines were measured accurately, and we find that the SMC PNs are denser than the LMC PNs by a factor of 1.5. The average ionized mass of the SMC PNs is 0.3 Msun. We also found that the median [O III]/hbeta intensity ratio in the SMC is about half than the corresponding LMC median. We use Cloudy to model the dependence of the [O III]/hbeta ratio on the oxygen abundance. Our models encompass very well the average observed physical quantities. We suggest that the SMC PNs are principally cooled by the carbon lines, making it hard to study their excitation based on the optical lines at our disposal.

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arXiv2003

A Compact X-ray Source and Possible X-ray Jets within the Planetary Nebula Menzel 3

We report the discovery, by the Chandra X-ray Observatory, of X-ray emission from the bipolar planetary nebula Menzel 3. In Chandra CCD imaging, Mz 3 displays hot (3-6x10^6 K) gas within its twin, coaxial bubbles of optical nebulosity, as well as a compact X-ray source at the position of its central star(s). The brightest diffuse X-ray emission lies along the polar axis of the optical nebula, suggesting a jet-like configuration. The observed combination of an X-ray-emitting point source and possible X-ray jet(s) is consistent with models in which accretion disks and, potentially, magnetic fields shape bipolar planetary nebulae via the generation of fast, collimated outflows.

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arXiv2002

Slitless Spectroscopy of LMC Planetary Nebulae. A Study of the Emission Lines and Morphology

HST STIS slitless spectroscopy of LMC PNs is the ideal tool to study their morphology and their ionization structures at once. We present the results from a group of 29 PNs that have been spatially resolved, for the first time, in all the major optical lines. Images in the light of \ha, \nii, and \oiii are presented, together with line intensities, measured from the extracted 1D and 2D spectra. A study on the surface brightness in the different optical lines, the electron densities, the ionized masses, the excitation classes, and the extinction follows, illustrating an ideal consistence with the previous results found by us on LMC PNs. In particular, we find the surface brightness decline with the photometric radius to be the same in most emission lines. We find that asymmetric PNs form a well defined cooling sequence in the excitation -- surface brightness plane, confirming their different origin, and larger progenitor mass.

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arXiv2002

Hubble Space Telescope Expansion Parallaxes of the Planetary Nebulae NGC 6578, NGC 6884, NGC 6891, and IC 2448

We have combined two epochs of Hubble Space Telescope WFPC2 imaging data with ground-based expansion velocities to determine distances to three planetary nebulae (NGC 6578, NGC 6884, and IC 2448). We used two variants of the expansion parallax technique--a gradient method and a magnification method--to determine the distances. The results from the two methods agree to within the errors. A fourth nebula was included in the study (NGC 6891), but the expansion was too small to determine the distance, and only a lower limit was obtained. This is the first paper in a series which will examine at least 24 nebulae in total.

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arXiv2000

Morphology and Evolution of LMC Planetary Nebulae

The LMC is ideal for studying the co-evolution of planetary nebulae (PNe) and their central stars, in that the debilitating uncertainties of the Galactic PN distance scale and selection biases from attenuation by interstellar dust do not apply. We present images and analyze slit-less spectra which were obtained in a survey of Large Magellanic Cloud PNe. These data on 29 targets were obtained with HST using the Space Telescope Imaging Spectrograph. The data permit us to determine the nebular dimensions and morphology in the monochromatic light of several emission lines, including those that have traditionally been used for morphological studies in the Galaxy: H-alpha, [N II] 6583 and [O III] 5007, plus others of varying ionization, including [O I], He I, and [S II]. Together with the 31 resolved LMC PNe for which monochromatic images exist in the HST archive, these data show that the incidence of non-symmetric nebulae, including bipolar nebulae (which is an indicator of Population I ancestry in the Galaxy), is significantly higher than that reported for the Galaxy. The onset of asymmetric features appears even in very young nebulae (with dynamical ages of ~1400 yr), suggesting that at least the gross features of the nebular morphology may be more closely tied to PN formation, and that subsequent shaping of the expanding envelope by the radiation field and wind from the central star may play the lesser role of amplifying these gross features. There is some evidence of evolution between two morphological types, in the sense that bipolar core (BC) nebulae may evolve to pure bipolars late in the PN lifetime.

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arXiv2000

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 HST 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, S). While similar results have been obtained for Galactic PNe, this is the first demonstration of the relationship for extra-galactic 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.

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arXiv1997

Photo-evaporation of clumps in Planetary Nebulae

We study the evolution of dense neutral clumps located in the outer parts of planetary nebulae. These clumps will be photo-ionized by the ionizing radiation from the central star and change their structure in the process. The main effect of the ionization process is the setting up of a photo-evaporation flow and a shock running through the clump. Once this shock has moved through the entire clump it starts to accelerate because of the `rocket effect'. This continues until the entire clump has been photo-ionized. We present an analytic model for the shock and accelerating phases and also the results of numerical simulations which include detailed microphysics. We find a good match between the analytic description and the numerical results and use the numerical results to produce some of the clump's observational characteristics at different phases of its evolution. We compare the results with the properties of the fast moving low ionization knots (ansae or FLIERs) seen in a number of planetary nebulae. We find that the models match many of the kinematic and emission properties of FLIERs.

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