Bipolar Nebula Research Articles

Diamonds and polycyclic aromatic hydrocarbons in the circumstellar environment of the Herbig Ae/Be star Elias 1

We report long-slit spectroscopic observations of the Herbig Ae/Be star Elias 1 in the 3.2-3,6 μm region covering the C-H stretch emission features of hydrogen-terminated diamonds and polycyclic aromatic hydrocarbons (PAHs). The data were recorded at the United Kingdom Infrared Telescope using the UKIRT Imaging Spectrometer (UIST) and yield information on the profiles and intensities of the bands as a function of offset along the NS and EW axes centred on the close binary. The diamond and nearby infrared continuum emission arises from a symmetrical inner core region (≤0.34 arcsec or 48 au). The 3.3-μm PAH emission is extended along the EW axis up to ca. 100 au each side of the star. This result supports a suggestion of Haas, Leinert & Richichi of an EW oriented bipolar nebula in Elias 1.

Photometric and spectroscopic studies of very low mass YSOs and young Brown Dwarfs in S106

Young brown dwarfs have been identified in a significant population in various star forming regions. Some deep surveys have yielded less massive objects with planetary-mass (e.g., Oasa et al. 1999; Lucas & Roche 2000). Nevertheless, it is not yet clear how abundant these very low-mass objects are formed. S106 is one of the nearest massive star-forming regions associated with prominent bipolar nebulae and an HII region. We have conducted near-infrared photometric and spectroscopic observations of very low-mass young stellar objects (YSOs) in the S106 region.

Molecular Hydrogen Jets, Filaments, and Haloes in Planetary Nebulae

We present deep H images of planetary nebulae obtained with the CHFTIR camera of the Canada-France-Hawaii Telescope. Molecular hydrogen emissions are seen in the equatorial torus, bipolar lobes, as well as in extended haloes. Radial equatorial jets are also detected in a number of bipolar nebulae.

NIR high-resolution imaging and radiative transfer modeling of the Frosty Leo nebula

We present a $K\prime$ -band speckle image and $HK$ -band polarimetric images of the proto-planetary nebula Frosty Leo obtained using the 6 m SAO telescope and the 8 m Subaru telescope, respectively. Our speckle image revealed clumpy structures in the hourglass-like bipolar nebula. The polarimetric data, for the first time, detected an elongated region with small polarizations and polarization vector alignment on the east side of the central star. We have performed radiative transfer calculations to model the dust shell of Frosty Leo. We found that micron-size grains in the equatorial dense region and small grains in the bipolar lobes are required to explain the total intensity images, the polarization images, and the spectral energy distribution.

BIMA Array Observations of the Highly Unusual SiO Maser Source with a Bipolar Nebulosity IRAS 19312+1950

We report the results of mapping observations of the bipolar nebula with SiO maser emission, IRAS 19312+1950, in the CO (J = 1-0 and 2-1), 13CO (J = 1-0 and 2-1), C18O (J = 1-0), CS (J = 2-1), SO (JK = 32-21), and HCO+ (J = 3-2) lines with the Berkeley-Illinois-Maryland Association array. The evolutional status of this source has been evoking a controversy since its discovery, although SiO maser sources are usually identified as late-type stars with active mass loss. In line profiles, two kinematical components are found, as reported in previous single-dish observations: a broad pedestal component and a narrow component. Spatiokinetic properties of a broad-component region traced by 12CO lines are roughly explained by a simple spherical outflow model with an expanding velocity typical of an AGB star, although some properties of the broad-component region still conflict with properties of a typical AGB spherical outflow. A narrow-component region apparently exhibits a bipolar flow. The angular size of the narrow-component region is spatially larger than that of the broad-component region. The intensity distribution of the CS emission avoids the central region of the source, and that of the SO broad-component emission exhibits a small feature peaked exactly at the mapping center. According to the present results, if the broad component really originates in a spherical outflow, an oxygen-rich evolved stellar object seems to be a natural interpretation for the central star of IRAS 19312+1950.

A deep survey of brown dwarfs in Orion with Gemini

We report the results of a deep near infrared (JHK) survey of the outer parts of the Trapezium Cluster with Gemini South/Flamingos. 396 sources were detected in a 26 arcmin 2 area, including 138 brown dwarf candidates, defined as M 150 AU) binary companions. This result has modest statistical significance (96%) in our data but is supported at 93% confidence by analysis of an completely independent sample taken from the Subaru data of Kaifu et al.(2000). There is a statistically very significant excess of both stars and brown dwarfs with small separations from each other (< 6 arcsec or 2600 AU). This appears to be due to the presence of small N subgroups, which are likely to be dynamically unstable in the long term. Hence these results are consistent with the ’ejected stellar embryo’ hypothesis for brown dwarf formation (Reipurth & Clarke 2001). We also report the discovery of two new bipolar nebulae, which are interpreted as Class I protostars.

The Three‐dimensional Circumstellar Environment of SN 1987A

We present the detailed construction and analysis of the most complete map to date of the circumstellar environment around SN 1987A, using ground and space-based imaging from the past 16 years. PSF-matched difference-imaging analyses of data from 1988 through 1997 reveal material between 1 and 28 ly from the SN. Careful analyses allows the reconstruction of the probable circumstellar environment, revealing a richly-structured bipolar nebula. An outer, double-lobed ``Peanut,'' which is believed to be the contact discontinuity between red supergiant and main sequence winds, is a prolate shell extending 28 ly along the poles and 11 ly near the equator. Napoleon's Hat, previously believed to be an independent structure, is the waist of this Peanut, which is pinched to a radius of 6 ly. Interior to this is a cylindrical hourglass, 1 ly in radius and 4 ly long, which connects to the Peanut by a thick equatorial disk. The nebulae are inclined 41\degr south and 8\degr east of the line of sight, slightly elliptical in cross section, and marginally offset west of the SN. From the hourglass to the large, bipolar lobes, echo fluxes suggest that the gas density drops from 1--3 cm^{-3} to >0.03 cm^{-3}, while the maximum dust-grain size increases from ~0.2 micron to 2 micron, and the Si:C dust ratio decreases. The nebulae have a total mass of ~1.7 Msun. The geometry of the three rings is studied, suggesting the northern and southern rings are located 1.3 and 1.0 ly from the SN, while the equatorial ring is elliptical (b/a < 0.98), and spatially offset in the same direction as the hourglass.

A Cool Magnetized Shell Wrapped around the Hot HiiRegion S106: Geometry, Kinematics, Magnetic Vectors, and Pressure Balance

In the optical, the exciting star S106 IR resides in a conspicuous dust lane and it ionizes two bright, sharp gas lobes on both sides of the dust lane. Wrapped around this hot (10,000 K) ionized (H II) optical bipolar nebula (the two gas lobes), we see a cool shell in the millimeter-submillimeter radio. Outside the cool shell, there is an even colder (<22 K), large (20' = 4 pc), lower density molecular cloud. In this paper, we study the cool gas (spectroscopy in three lines), the cool dust (continuum imaging), and the magnetic field (polarimetry) in the shell, all made near a wavelength of 850 μm with the same angular resolution of 14'' using the James Clerk Maxwell Telescope (JCMT). Near a radial velocity of -1 km s-1, we used 12CO, 13CO, and C18O in the J = 3-2 lines to map the cool (32 K) gas in the shell peaks on both sides of the hot cavity walls, extending 2' (0.4 pc) in north-south length with a 100'' (0.3 pc) east-west diameter. Also, we used dust continuum emission and its linear polarization to map the cool shell. For the vertical cool shell, sandwiched between a hot region and a colder cloud, we find that the shell's combined pressure (made up mostly of turbulence and total magnetic field) can withstand the turbulent and thermal pressure of the hot ionized outflow, although the cool gas shell is slowly being eroded by the ionization process going on. The large-scale magnetic field appears roughly vertical along the roughly vertical gas shell. The magnetic field in the vertical shell (away from the central dust lane) has an estimated value near 400 μG. In the horizontal dust lane, the magnetic field appears roughly horizontal and parallel to the dust lane encompassing the IR and FIR components. Here the magnetic field derived from various methods has an estimated plane-of-sky median value near 570 μG, while the previously published Zeeman data indicated a line-of-sight strength near +240 μG.

The sub-arcsecond dusty environment of Eta Carinae

The core of the nebula surrounding Eta Carinae has been observed with the VLT Adaptive Optics system NACO and with the interferometer VLTI/MIDI to constrain spatially and spectrally the warm dusty environment and the central object. In particular, narrow-band images at 3.74 and 4.05 micron reveal the butterfly shaped dusty environment close to the central star with unprecedented spatial resolution. A void whose radius corresponds to the expected sublimation radius has been discovered around the central source. Fringes have been obtained in the Mid-IR which reveal a correlated flux of about 100Jy situated 0.3 south-east of the photocenter of the nebula at 8.7 micron, which corresponds with the location of the star as seen in other wavelengths. This correlated flux is partly attributed to the central object, and these observations provide an upper limit for the SED of the central source from 2.2 to 13.5 micron. Moreover, we have been able to spectrally disperse the signal from the nebula itself at PA=318 degree, i.e. in the direction of the bipolar nebula 310 degree) within the MIDI field of view of 3. A large amount of corundum (Al2O3) is discovered, peaking at 0.6-1.2 south-east from the star, whereas the dust content of the Weigelt blobs is dominated b silicates. We discuss the mechanisms of dust formation which are closely related to the geometry of this Butterfly nebulae.

The creation of the Helix planetary nebula (NGC 7293) by multiple events

A deep continuum-subtracted image of NGC 7293 has been obtained in the light of the Hα+[N ii] emission lines. New images of two filamentary halo structures have been obtained, and a possible detection of a collimated outflow made. Spatially resolved long-slit profiles of the Hα+[N ii] lines have been observed across several of these features with the Manchester echelle spectrometer combined with the San Pedro Martir 2.1-m telescope; these are compared with the [N ii] 6584 Å, [O iii] 5007 Å, He ii 6560 Å and Hα profiles obtained over the nebular core. The central He ii emission originates in a ≈ 0.34-pc diameter spherical volume expanding at ⩽12 km s−1, which is surrounded by, and partially coincident with, an [O iii] 5007 Å emitting inner shell expanding at 12 km s−1. The bright helical structure surrounding this inner region is modelled as a bipolar nebula with lobe expansions of 25 km s−1 whose axis is tilted at 37° to the sightline but with a toroidal waist itself expanding at 14 km s−1. These observations are compared with the expectations of the interacting two-winds model for the formation of planetary nebulae. Only after the fast wind has switched off could this global velocity structure be generated. Ablated flows must complicate any interpretation. It is suggested that the clumpy nature of much of the material could play a part in creating the radial ‘spokes’ shown here to be apparently present close to the central star. These ‘spokes’ could in fact be the persistent tails of cometary globules whose heads have now completely photoevaporated. A halo arc projecting from the north-east of the bright core has a counterpart to the south-east. Anomolies in the position-velocity arrays of line profiles could suggest that these are part of an expanding disc not aligned with the central helical structure, although bipolar lobes expanding along a tilted axis are not ruled out.

Hubble Space TelescopeNICMOS Imaging Polarimetry of Proto-Planetary Nebulae: Probing the Dust Shell Structure via Polarized Light

Using NICMOS on the Hubble Space Telescope, we have performed imaging polarimetry of proto–planetary nebulae (PPNs). Our objective is to study the structure of optically thin circumstellar shells of post–asymptotic giant branch (AGB) stars by separating dust-scattered, linearly polarized starlight from unpolarized direct starlight. This unique technique allows us to probe faint reflection nebulae around the bright central star, which can be buried under the point-spread function of the central star in conventional imaging. Our observations and archival search have yielded polarimetric images for five sources: IRAS 07134+1005 (HD 56126), 06530-0213, 04296+3429, (Z)02229+6208, and 16594-4656. These images have revealed the circumstellar dust distribution in unprecedented detail via polarized intensity maps, providing a basis for understanding the three-dimensional structure of these dust shells. We have observationally confirmed the presence of the inner cavity caused by the cessation of AGB mass loss, and the internal shell structures, which are strongly tied to the progenitor star's mass-loss history on the AGB. We have also found that equatorial enhancement in these circumstellar shells comes with various degrees of contrast, suggesting a range of optical depths in these optically thin shells. Our data support the interpretation that the dichotomy of PPN morphologies is due primarily to differences in optical depth and secondarily to the inclination effect. The polarization maps reveal a range of inclination angles for these optically thin reflection nebulae, dispelling the notion that elliptical nebulae are pole-on bipolar nebulae.

A New View of the Circumstellar Environment of SN 1987A

We summarize the analysis of a uniform set of both previously-known and newly-discovered scattered-light echoes, detected within 30 of SN 1987A in ten years of optical imaging, and with which we have constructed the most complete three-dimensional model of the progenitor's circumstellar environment. Surrounding the SN is a richly-structured bipolar nebula. An outer, double-lobed ``peanut,'' which we believe is the contact discontinuity between the red supergiant and main sequence winds, is a prolate shell extending 28 ly along the poles and 11 ly near the equator. Napoleon's Hat, previously believed to be an independent structure, is the waist of this peanut, which is pinched to a radius of 6 ly. Interior, the innermost circumstellar material lies along a cylindrical hourglass, 1 ly in radius and 4 ly long, which connects to the peanut by a thick equatorial disk. The nebulae are inclined 41o south and 8o east of the line of sight, slightly elliptical in cross section, and marginally offset west of the SN. The 3-D geometry of the three circumstellar rings is studied, suggesting the equatorial ring is elliptical (b/a 0.03 cm^{-3}; the maximum dust-grain size increases from ~0.2 micron to 2 micron; and the Si:C dust ratio decreases. The nebulae have a total mass of ~1.7 Msun, yielding a red-supergiant mass loss around 5*10^{-6} Msun yr^{-1}.

Study of the Bipolar Nebula IRAS 19312+1950. II. Circumstellar Chemistry

Abstract The bipolar nebula IRAS 19312$+$1950 is a unique SiO maser source exhibiting both properties of young and evolved objects. To clarify the nature of this object, we made molecular line observations with the Nobeyama 45-m radio telescope. We detected emission from O-bearing ($\mathrm{HCO}^{{+}}\mkern-2.0mu$, SiO, SO, and $\mathrm{SO}_2$), C–and N-bearing molecules (CN, CS, HCN, HNC, $\mathrm{NH}_{3}$, $\mathrm{N}_{2}\mathrm{H}^{+}\mkern-2.0mu$, $\mathrm{HC}_{3}\mathrm{N}$, $\mathrm{H}_2\mathrm{CS}$, and $\mathrm{CH}_3\mathrm{OH}$), and their isotopic species (C${{17\atop} \mathrm{O}}, {{13\atop} \mathrm{C}}$${{18\atop} \mathrm{O}}$, and C${{34\atop} \mathrm{S}}$). The line profiles consist of weak broad ($\Delta v \sim 30 \,\mathrm{km} \,\mathrm{s}^{-1}$) and/or strong narrow ($\Delta v \lesssim 5 \,\mathrm{km} \,\mathrm{s}^{-1}$) components, depending on the molecular species. Strong time variations of $\mathrm{H}_2\mathrm{O}$ and SiO masers were also observed. Numerical modeling of the envelope with the LVG-code resulted in a good fit of the model with a mass loss rate of $2.6 \times10^{-4} \,{{{M}_{\odot}}} \,\mathrm{yr}^{-1}$ to the observed intensities for the broad-component lines. On the other hand, non-O-bearing molecules, which only have narrow profiles, were found to have abundances typical of those in cool dust clouds. No isotopic enrichment was found, indicating little evidence of the narrow cool component being ejecta of the central AGB star or a possible companion. These facts compelled us to conclude that IRAS 19312$+$1950 is an exotic mass-losing evolved star embedded in a low-mass ($\sim 20 \; \,{{{M}_{\odot}}}$) dark cloud.

High‐Resolution Near‐Infrared Observations of the Circumstellar Disk System in the Bok Globule CB 26

We report on results of near-infrared and optical observations of the millimeter disk embedded in the Bok globule CB 26. The near-infrared images show a bipolar reflection nebula with a central extinction lane that coincides with the millimeter disk. Imaging polarimetry of this object yielded a polarization pattern that is typical of a young stellar object (YSO) surrounded by a large circumstellar disk and an envelope, seen almost edge-on. The strong linear polarization in the bipolar lobes is caused by single scattering at dust grains and reveals the location of the illuminating source that coincides with the center of the millimeter disk. The spectral energy distribution of the YSO embedded in CB 26 resembles that of a Class I source with a luminosity of 0.5 L☉. Using the pre-main-sequence evolutionary tracks and the stellar mass inferred from the rotation curve of the disk, we derive an age of the system of ≤106 yr. Hα and [S II] narrowband imaging as well as optical spectroscopy revealed a Herbig-Haro object 615 northwest of CB 26 YSO 1, perfectly aligned with the symmetry axis of the bipolar nebula. This Herbig-Haro object (HH 494) indicates ongoing accretion and outflow activity in CB 26 YSO 1. Its excitation characteristics show that the Herbig-Haro flow is propagating into a low-density environment. We suggest that CB 26 YSO 1 represents the transition stage between embedded protostellar accretion disks and more evolved protoplanetary disks around T Tauri stars in an undisturbed environment.

The Binarity of η Carinae and Its Similarity to Related Astrophysical Objects

I examine some aspects of the interaction between the massive star η Carinae and its companion, in particular during the eclipse-like event, known as the spectroscopic event or the shell event. The spectroscopic event is thought to occur when near periastron passages the stellar companion induces much higher mass-loss rate from the primary star and/or enters into a much denser environment around the primary star. I find that enhanced mass-loss rate during periastron passages, if it occurs, might explain the high eccentricity of the system. However, there is not yet a good model to explain the presumed enhanced mass-loss rate during periastron passages. In the region where the winds from the two stars collide, a dense slow flow is formed, such that large dust grains may be formed. Unlike the case during the 19th century Great Eruption, the companion does not accrete mass during most of its orbital motion. However, near periastron passages short accretion episodes may occur, which may lead to pulsed ejection of two jets by the companion. The companion may ionize a nonnegligible region in its surrounding, resembling the situation in symbiotic systems. I discuss the relation of some of these processes to other astrophysical objects, by incorporating η Car into a large class of astrophysical bipolar nebulae.

Menzel 3: a Multipolar Nebula in the Making

The nebula Menzel 3 (Mz 3) has arguably the most complex bipolar morphology, consisting of three nested pairs of bipolar lobes and an equatorial ellipse. Its three pairs of bipolar lobes share the same axis of symmetry but have very different opening angles and morphologies: the innermost pair of bipolar lobes shows closed-lobe morphology, whereas the other two have open lobes with cylindrical and conical shapes, respectively. We have carried out high-dispersion spectroscopic observations of Mz 3 and detected distinct kinematic properties among the different morphological components. The expansion characteristics of the two outer pairs of lobes suggest that they originated in an explosive event, whereas the innermost pair of lobes resulted from the interaction of a fast wind with the surrounding material. The equatorial ellipse is associated with a fast equatorial outflow, which is unique among bipolar nebulae. The dynamical ages of the different structures in Mz 3 suggest episodic bipolar ejections, and the distinct morphologies and kinematics among these different structures reveal fundamental changes in the system between these episodic ejections.

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.

Why a Single‐Star Model Cannot Explain the Bipolar Nebula of η Carinae

I examine the angular momentum evolution during the 1837-1856 Great Eruption of the massive star ? Carinae. I find that the new estimate of the mass blown during that eruption implies that the envelope of ? Car substantially spun down during the 20 yr eruption. Single-star models, most of which require the envelope to rotate at close to the break-up velocity, cannot account for the bipolar nebula?the Homunculus?formed from matter expelled in that eruption. The kinetic energy and momentum of the Homunculus further constrain single-star models. I discuss how ? Car can fit into a unified model for the formation of bipolar lobes in which two oppositely ejected jets inflate two lobes (or bubbles). These jets are blown by an accretion disk, which requires stellar companions in the case of bipolar nebulae around stellar objects.

High Spatial Resolution Mid‐ and Far‐infrared Imaging Study of NGC 2346

We present the first high spatial resolution mid-IR and far-IR images of the planetary nebula NGC 2346 using the Multiband Imaging Photometer for Spitzer (MIPS) on board the Spitzer Space Telescope. The morphology at 24 μm is strikingly similar to that seen in the optical image, with an additional unresolved hot dust component at the center. The 70 μm image reveals a torus-like structure near the narrow waist of the bipolar nebula, while the 160 μm image shows a very extended cold dust envelope around the nebula. Our new MIPS data provide direct evidence that the mass loss in the end of the asymptotic giant branch (AGB) phase diverts from spherical symmetry to axisymmetry and that the binary central star has played an important role in the bipolar nebular evolution.

Numerical Modeling of η Carinae Bipolar Outflows

In this paper, we present two-dimensional gasdynamic simulations of the formation and evolution of the ? Car bipolar outflows. Adopting the interacting nonspherical winds model, we have carried out high-resolution numerical simulations, which include explicitly computed time-dependent radiative cooling, for different possible scenarios of the colliding winds. In our simulations, we consider different degrees of nonspherical symmetry for the preoutburst wind and the great eruption of the 1840s produced by the ? Car wind. Different models show important differences in the shape and kinematical properties of the Homunculus structure. In particular, we search for the appropriate combination of wind parameters (which control the degree of nonspherical symmetry) to obtain the numerical results that best match both the observed morphology and the expansion velocity of the ? Car bipolar shell. In addition, our numerical simulations show the formation of a bipolar nebula embedded within the Homunculus (the little Homunculus) that developed from a secondary eruptive event suffered by the star in the 1890s, and also the development of tenuous, high-velocity ejections in the equatorial region that resulted from the impact of the eruptive wind of the 1840s with the preoutburst wind; these ejections could explain some of the high-speed features observed in the equatorial ejecta. The models were, however, unable to produce the equatorial ejections associated with the second eruptive event.