Content uploaded by Michael A. Dopita
Author content
All content in this area was uploaded by Michael A. Dopita
Content may be subject to copyright.
Hubble Space Telescope Observations of Planetary Nebulae in the Magellanic Clouds. I. The Extreme Type I SMP 83/WS 35
Abstract
We have obtained Hubble Space Telescope Planetary Camera images in
both the Hα and the [O III] λ5007 emission lines of the
planetary nebula SMP 83 alias WS35, alias N66 in the Large Magellanic
Cloud. By combining these results with optical and UV
spectrophotometry, absolute flux measurements, and dynamical and
density information, we have been able to construct a fully
self-consistent nebular model. This proves that SMP 83 is an extremely
massive type I object having a central star having an effective
temperature of 170,000 K and a luminosity of nearly 3 ×
104 Lsun. The core mass is estimated in the
range 1.0-1.2 Msun, for which the main-sequence mass was
greater than ˜6 Msun. The nebular abundances are higher
than the average for the LMC and show evidence for hot-bottom burning.
... Regan et al. 2001;Wong & Blitz 2002;Leroy et al. 2008;Barrera-Ballesteros et al. 2021;Pessa et al. 2021) that has been described as a pressure-molecular gas correlation (e.g. Wong & Blitz 2002;Blitz & Rosolowsky 2006;Leroy et al. 2008), an extended star formation relation (Dopita et al. 1993;Shi et al. 2011;Sánchez et al. 2021), or a resolved star-forming main sequence (Lin et al. 2019). ...
We identify stellar structures in the PHANGS sample of 74 nearby galaxies and construct morphological masks of sub-galactic environments based on Spitzer 3.6 μ m images. At the simplest level, we distinguish five environments: centres, bars, spiral arms, interarm regions, and discs without strong spirals. Slightly more sophisticated masks include rings and lenses, which are publicly released but not explicitly used in this paper. We examine trends with environment in the molecular gas content, star formation rate, and depletion time using PHANGS–ALMA CO(2–1) intensity maps and tracers of star formation. The interarm regions and discs without strong spirals clearly dominate in area, whereas molecular gas and star formation are quite evenly distributed among the five basic environments. We reproduce the molecular Kennicutt–Schmidt relation with a slope compatible with unity within the uncertainties and without significant slope differences among environments. In contrast to what has been suggested by early studies, we find that bars are not always deserts devoid of gas and star formation, but instead they show large diversity. Similarly, spiral arms do not account for most of the gas and star formation in disc galaxies, and they do not have shorter depletion times than the interarm regions. Spiral arms accumulate gas and star formation, without systematically boosting the star formation efficiency. Centres harbour remarkably high surface densities and on average shorter depletion times than other environments. Centres of barred galaxies show higher surface densities and wider distributions compared to the outer disc; yet, depletion times are similar to unbarred galaxies, suggesting highly intermittent periods of star formation when bars episodically drive gas inflow, without enhancing the central star formation efficiency permanently. In conclusion, we provide quantitative evidence that stellar structures in galaxies strongly affect the organisation of molecular gas and star formation, but their impact on star formation efficiency is more subtle.
... The density we estimate is in agreement with previous measurements (Bernard-Salas et al. 2004 and references therein). The temperature of the central source is the same as that estimated by Dopita et al. (1993) with MAPPINGS 2 and a multizone model combining an optically thick ring with optically thin extensions. They found densities of 1000 and 3600 cm −3 in the thin and thick components, respectively. ...
The MIPSGAL 24 ?m Galactic Plane Survey has revealed more than 400 compact-extended objects. Less than 15% of these MIPSGAL bubbles (MBs) are known and identified as evolved stars. We present Spitzer observations of four MBs obtained with the InfraRed Spectrograph to determine the origin of the mid-IR emission. We model the mid-IR gas lines and the dust emission to infer physical conditions within the MBs and consequently their nature. Two MBs show a dust-poor spectrum dominated by highly ionized gas lines of [O IV], [Ne III], [Ne V], [S III], and [S IV]. We identify them as planetary nebulae with a density of a few 103 cm?3 and a central white dwarf of 200,000?K. The mid-IR emission of the two other MBs is dominated by a dust continuum and lower-excitation lines. Both of them show a central source in the near-IR (Two Micron All Sky Survey and IRAC) broadband images. The first dust-rich MB matches a Wolf-Rayet star of ~60,000?K at 7.5?kpc with dust components of ~170 and ~1750?K. Its mass is about 10?3M
? and its mass loss is about 10?6M
? yr?1. The second dust-rich MB has recently been suggested as a Be/B[e]/luminous blue variable candidate. The gas lines of [Fe II] as well as hot continuum components (~300 and ~1250?K) arise from the inside of the MB while its outer shell emits a colder dust component (~75?K). The distance to the MB remains highly uncertain. Its mass is about 10?3M
? and its mass loss is about 10?5M
? yr?1.
The proximity, accurately known distance and low line-of-sight reddening give the ideal circumstances to pursue studies of individual stellar populations in the Magellanic Clouds. Here we show how our understanding of the evolution and chemical composition of the planetary nebulae in the Magellanic Clouds has been impacted by imaging and UV spectroscopic studies using the Hubble Space Telescope. Images provide sizes, internal morphological structure, absolute fluxes, and dynamical ages, while spectra allow us to place the central stars accurately on the H-R Diagram, and we can also examine the details of the evolution, of mass- and age- dependent chemical dredge-up processes, and infer the star-formation history of the Magellanic Clouds.
We present the results of our major HST study of the evolution of PN in the Magellanic Clouds. This consists of imaging studies in [O III] and FOS UV spectroscopy. These data are then used in theoretical photoionisation models in conjuction with ground-based spectrophotometry, absolute flux and expansion velocity and density to derive self consistent diameters, ages, masses, and nebular abundances and to accurately place the central stars on the H-R Diagram. We find that observed sizes and ages can be reconciled with evolutionary theory provided that the He-burners outnumber the H-burners in the approximate ratio 2:1. For the LMC observed abundance patterns are qualitatively consistent with the (mass-dependent) operation of the various chemical dredge-up processes as predicted by theory. However, the observed dredge-up efficiencies do not agree with current theory. Finally, since core masses are determined with adequate precision, we are able to derive, for the first time, the metallicity age relation for of the LMC. We find that the base metallicity of the LMC rapidly increased ∼ 2 Gyr ago, consistent with the age of the burst of star formation inferred from field stars and clusters.
The variability of P Cygni profiles is important because of its connection with the mechanism of wind production and with the behaviour of the associated mass loss rates.
N66 (WS 35, SMP 83) is a Type I (He-N rich) PN in the LMC with a high ionization degree. It shows a bipolar morphology with a filamentary structure (Dopita et al. 1993). Its central star has shown very impressive changes, in short time scale, that have been investigated. Here we describe the history of these changes:
Planetary Nebulae (PNe) are amongst the most spectacular objects produced by
stellar evolution, but the exact identity of their progenitors has never been
established for a large and homogeneous observational sample. We investigate
the relationship between PNe and their stellar progenitors in the Large
Magellanic Cloud (LMC) through the statistical comparison between a highly
complete spectroscopic catalog of PNe and the spatially resolved age
distribution of the underlying stellar populations. We find that most PN
progenitors in the LMC have main-sequence lifetimes in a narrow range between 5
and 8 Gyr, which corresponds to masses between 1.2 and 1.0 M$_{\odot}$, and
produce PNe that last $26^{+6}_{-7}$~kyr on average. We tentatively detect a
second population of PN progenitors, with main-sequence lifetimes between 35
and 800~Myr, i.e., masses between 8.2 and 2.1 M$_{\odot}$, and average PN
lifetimes of $11^{+6}_{-7}$ kyr. These two distinct and disjoint populations of
progenitors strongly suggest the existence of at least two physically distinct
formation channels for PNe. Our determination of PN lifetimes and progenitor
masses has implications for the understanding of PNe in the context of stellar
evolution models, and for the role that rotation, magnetic fields, and binarity
can play in the shaping of PN morphologies.
We have measured the electron-impact-induced fluorescence spectrum of neon in the wavelength range 120-270 nm at a spectral resolution of 0.43 nm (FWHM). The strongest lines observed in the far-ultraviolet (FUV) spectrum of neon are assigned to terms of the doublet system of Ne II (2s22p4nl) and the triplet system of Ne III (2s22p33l). Our FUV spectral data, obtained at 300 eV electron-impact energy, provide absolute emission cross sections of these Ne II and Ne III lines, and are compared to previous measurements where available. In addition, the excitation function of the strongest Ne II line observed at 191.6 nm was measured from threshold to 1000 eV electron-impact energy.
Morphology of the planetary nebula LMC-N66 (ionized by a [WN] star) indicates that the nebula is a multipolar object with a very narrow waist. It shows several jets, knots and filaments in opposite directions from the central star. A couple of twisted long filaments could be interpreted as due to point-symmetric type ejection. If such is the case, the progenitor would be a binary precessing system. High resolution spectroscopy shows that most of the material is approaching or receding from the star. However the line profiles are very complex, showing several components at different velocities. Our high resolution spectroscopic data show that the different structures (knots, filaments, ...) present different radial velocities spreading from 240 to more than 400 km s-1. The system velocity is 300 km s-1. There are high velocity knots located to the north of the central star, moving at more than 100 km s-1 relative to the system velocity.
N66 (WS 35, SMP 83) is a Type I (He-N rich) PN in the LMC with a high ionization degree. It shows a bipolar morphology with a filamentary structure (Dopita et al. 1993). Its central star has shown very impressive changes, in short time scale, that have been investigated. Here we describe the history of these changes:
1.
-In 1987, as derived from nebular parameters (Peña & Ruiz 1987), the central star had a weak continuum with T* ~ 120 000 K and L* ~ 25 000 L⨀. From evolutionary tracks, a stellar mass of ~ 1M
⨀ was obtained, which is one of the highest of those that have been determined with reasonable accuracy.
2.
-In 1990 the star began a spectacular mass-loss event. Its UV and optical continua increased by factors ranging from 2 to 4 magnitudes and it developed WR features resembling a Population I WN4.5 (or earlier) star (Peña et al. 1995).
3.
-The strong wind has persisted for more than 5 years, showing some variations in the emission line ionization degree and a sudden disappearance of the WR features which lasted some weeks in August-September, 1995. From ground-based telescopes and the IUE satellite we have followed the central star evolution; the changes in the stellar fluxes are presented in Table 1.
4.
-N66 central star is the only nucleus of a PN showing a WN type spectrum. All the other CSPNe with WR features (in the Galaxy and the Magellanic Clouds) are of WC type. 5.- These spectacular changes have no theoretical explanation at present. The possibilities that the star is undergoing a late thermal pulse or suffering a violent instability due to its high luminosity are being explored.
Self-consistent photoionization modeling of 44 Magellanic Cloud PNe is used to construct an H-R diagram for the central stars in both Clouds and is used to obtain the nebular chemical abundances and the physical parameters of the nebulae. The type I PNe are the youngest PNe in the clouds, have the highest core masses, and lie on the descending branch of the evolutionary tracks. These objects show correlated He and N/O abundance enhancements. The nebulae mass of the optically thick objects is well correlated with the nebular radius. Clear evidence is found for an abundance scatter in the material which formed the precursor star of the PNe in both Clouds. The metallicity range in the LMC is a factor of about 10, while that in the SMC is about 3-4. A core-mass:metallicity relationship is discovered for the LMC and is interpreted as a transformed age:metallicity relationship.
Optical spectroscopy in the range 3300-7800 A is presented for a total of 37 planetary nebulae in the LMC and seven in the SMC. Reddening estimates from Balmer line ratios have been determined, and the line intensities have been dereddened accordingly. Nebular forbidden O III electron temperatures, and where measurable forbidden S II densities, are derived. Forbidden O II electron densities are recalculated using appropriate electron temperatures. Zanstra temperatures are derived for 22 objects possessing detectable stellar continua. These temperatures are in agreement with photoionization modeling of this sample. 35 refs.
Using the Faint Object Camera on-board the Hubble Space Telescope, we have obtained images of four planetary nebulae (PNe) in the Magellanic Clouds, namely N2 and N5 in the SMC and N66 and N201 in the LMC. Each nebula was imaged through two narrow-band filters isolating [O III] λ5007 and Hβ, for a nominal exposure time of 1000 s in each filter. Significant detail is evident on the raw images and, after deconvolution using the Richardson-Lucy algorithm, structures as small as 0″.06 are easily discernible. In [O III], SMC N5 shows a circular ring structure, with a peak-to-peak diameter of 0″.26 and a FWHM of 0″.35, while SMC N2 shows an elliptical ring structure with a peak-to-peak diameter of 0″.26 × 0″.21 (FWHM 0″.40 × 0″.35). The expansion ages corresponding to the observed structures in SMC N2 and N5 are of the order of 3000 yr. Such low ages appear more easy to reconcile with helium-burning rather than hydrogen-burning central star evolutionary tracks. LMC N201 is very compact, with a FWHM of 0″.21 in Hβ. The Type I PN LMC N66 is a multipolar nebula, with the brightest part having an extent of about 2″ and with fainter structures extending over 4″. The [O III] image reveals structures unprecedented for a planetary nebula, with several bright knots and faint loops visible outside the two main bright lobes.
The paper describes categorization of galactic planetary nebulas and the
implications of their abundances of H, He, C, N, O, and Ne, determined
mainly by photoelectric observations in the visual spectral range. The
four types of planetary nebulas in the order of decreasing heavy element
abundances are (1) He and N rich, (2) intermediate population, (3) high
velocity, and (4) halo population. The second type is associated with
well defined He, N, and O gradients across the galactic disk, and the
oxygen gradient is similar to the metallicity gradient derived from GK
giants and F main sequence stars. Evidence suggesting that the O, Ne,
and S enrichment in the galaxy occurred before the Fe enrichment is
reported.
An extensive grid of optically thick model PN is computed in order to
determine the extent to which the emission-line fluxes used in the
planetary nebular distance scale are affected by the stellar effective
temperature and the nebular and stellar metallicity. It is concluded
that the nebular flux in the H-beta line is closely related to the
luminosity of the central star, but that the more commonly used flux in
the forbidden O III line at 5007 A can also be calibrated to give a
reliable estimate of this quantity. A simple method is presented for
determining the stellar effective temperature and the luminosity, and
the nebular metallicity using only the Balmer lines and the lines of
forbidden O III in the optical. As an absolute calibration of the
planetary nebular distance scale, the excitation, extinction, and
metallicity-corrected cutoff in the luminosity function are derived for
the planetary nebulae in both the SMC and LMC, and the true distance
modulus to the LMC is derived by a new hydrogen-reignition clump-fitting
technique based on self-consistent helium-burning evolutionary models
for the central stars.
Absolute H-beta nebular fluxes are presented for a total of 97 planetary
nebulae (PN) in the Magellanic Clouds. These new fluxes are compared
with all previously published data. Nebular masses are derived for 54
objects and are found to lie mainly in the range 0.01-0.35 solar masses.
A relationship between density and ionized mass for a subset of the
nebulae is used to show that these objects are optically thick. Another
relationship between H-beta flux and nebular density is examined. The
point at which the nebulae become optically thin is seen as a change in
the slope of this curve. From these relationships a nebular mass-radius
relation is found to apply to optically thick nebulae.
The observed chemical abundances of the Magellanic Clouds are
interpreted in terms of the star formation histories of the Clouds and
the relationships between the chemical evolutionary histories of each of
the Clouds and with the solar evolution in the Galaxy. It is found that
the interstellar medium (ISM) of the LMC has a mean metallicity 0.2 dex
lower than the local ISM, and the metallicity of the SMC is 0.6 dex
lower. However, the interstellar media of both the Magellanic Clouds and
the Galaxy have significantly nonsolar elemental ratios. It is also
shown that the stellar carbon abundances in the clouds appear normal,
and therefore it is the H II regions that must be overdefficient in this
element.