Martin Sergio Guerrero - Academia.edu (original) (raw)
Papers by Martin Sergio Guerrero
Wolf-Rayet (WR) stars are evolved massive stars whose H-rich envelopes have been stripped by copi... more Wolf-Rayet (WR) stars are evolved massive stars whose H-rich envelopes have been stripped by copious stellar winds at a red supergiant (RSG) or luminous blue variable (LBV) phase. The fast WR wind can sweep up the circumstellar material and form a bubble. Hydrodynamical models of WR bubbles have been calculated both analytically and numerically by García-Segura, Mac Low, and Langer.
Astrophysics and Space Science Library
An isolated massive star can blow a bubble, while a group of massive stars can blow superbubbles.... more An isolated massive star can blow a bubble, while a group of massive stars can blow superbubbles. In this paper, we examine three intriguing questions regarding bubbles and superbubbles: (1) why don't we see interstellar bubbles around every O star? (2) how hot are the bubble interiors? and (3) what is going on at the hot/cold gas interface in a bubble?
Planetary Nebulae, 1997
Planetary Nebulae (PNs) are highly representative of the late stages of intermediate mass stellar... more Planetary Nebulae (PNs) are highly representative of the late stages of intermediate mass stellar evolution. However, there are still many unresolved questions in their evolutionary scheme. Mass loss processes during the Asymptotic Giant Branch (AGB) are not fully understood. Binarity, rotation and magnetic fields may play an important role in PNs formation. The morphological study of PNs will help us to address those questions, and therefore a meaningful homogeneous database is needed. In recent years, an ESO catalog of images of more than 250 Southern PNs, observed through narrow-band filters, has been published (Schwarz, Corradi, & Melnick 1992). On the other hand, a complete morphological survey of the Northern sky PNs does not exist to date, and only limited samples of narrow-band PN imagery exist (Balick 1987; Chu, Jacoby, & Arendt 1987). We aim at filling the gap, earring out a complete catalog of extended Northern PNs. The catalog The sample was selected according to the following criteria: 1. We observe only those PNs that are spectroscopically confirmed by Acker et al (1992). 2. We include in our observing list PNs larger than 4". Objects larger than 12" were observed using the 0.8m IAC-80 telescope, while smaller objects were observed with the 2.5m NOT telescope. 3. Our PN sample suitably covers the Northern sky: PNs with-10° < δ < +80° and diameters larger than 4" were all included in the observing list. 4. We did not observe objects that had already been observed by Balick (1987) and Schwarz et al. (1992), to avoid obvious duplications. In order to obtain sharp images of the different ionized regions, we acquired the data through a choice of narrow-band filters: Ηα+[Ν II] (FWHM=50 Â), Ha and [Nil] λ 6584 Â(FWHM=10 Â), and [Ο ill] λ 5007 Â(FWHM=30 Â). The catalog contains 243 Northern PNs, for a total of589 gray-scale frames. For thirtytwo PNs we have produced a color picture, obtained combining the frames obtained through different narrow-band filters. The Morphological Classification We use the catalog images to improve previous morphological classifications (the most recent from Schwarz, Corradi, & Stanghellini 1992). Excluding the non-extended PNs,
Planetary Nebulae, 1997
There is a renewed interest in the study of the possible precession of the central sources of pla... more There is a renewed interest in the study of the possible precession of the central sources of planetary nebulae. Three different morphological features are considered the effect of precession: 1. Point-symmetric PNe: Objects whose morphological components are symmetrical with respect to reflection through the center. 2. Quadrupolar PNe: Characterized by two well-defined pairs of lobes which are symmetric, in pairs, with respect to two different axes. These PNe are very likely the result of two episodic nebular ejection processes, produced at different positions of the symmetry axis. 3. Bipolar, rotating episodic jets (or BRET’s): Spectacular structures (Lopez, Meaburn, & Palmer 1994) due to the precession of a symmetrical, collimated episodic outflow.
Astronomy & Astrophysics, 2000
We report high-sensitivity millimeter-wave CO observations of recently discovered bipolar planeta... more We report high-sensitivity millimeter-wave CO observations of recently discovered bipolar planetary nebulae (PNe). Three objects (BV 5-1, K 3-94 and K 3-24) have been detected, and one of them (BV 5-1) is resolved by the ~ 10{''} telescope beam. The envelopes of the three newly detected objects display values of the molecular to ionized mass ratio of ~ 0.2, and
The Astrophysical Journal, 1996
In the context of the Instituto de Astrofísica de Canarias (IAC) morphological survey of Galactic... more In the context of the Instituto de Astrofísica de Canarias (IAC) morphological survey of Galactic planetary nebulae (PNs), a new morphological class has been found, and we define their members as quadrupolar PNs. We have found five quadrupolar objects whose lobes are, in pairs, symmetric with respect to two different axes. Among these PNs, three (M2-46, K3-24, and M1-75) have well-defined pairs of lobes; another two (M3-28 and M4-14) are irregular and very possibly quadrupolar. For M2-46, we have measured the extension and the angle between the lobes, and the expansion velocities of the lobes by means of spectroscopic analysis. We propose that these nebulae have been formed by precession of the rotation axis of the central stars, possibly in the presence of a binary companion, associated with multiple shell ejection at the asymptotic giant branch. A simple binary mechanism not associated with precession cannot produce such a morphology.
The formation and shaping of planetary nebulae (PNe) is a complex process that involves the actio... more The formation and shaping of planetary nebulae (PNe) is a complex process that involves the action of multiple agents, including fast stellar winds and collimated outflows. Both fast stellar winds and collimated outflows can produce shock-heated gas that emits diffuse X-rays. Hot gas in PN interiors was hinted by ROSAT observations, but unambiguous detections of diffuse X-ray emission were not made until Chandra and XMM-Newton became available. The unprecedented angular resolution and sensitivity of these new X-ray observations allow us to investigate in detail the physical properties and origin of the hot gas content of PNe and to assess its dynamical effects on the shaping and expansion of PNe. This paper reviews the results from recent X-ray observations of PNe and discusses their implications to our understanding of the formation and evolution of PNe.
We present narrow-band images and high resolution long-slit spectra of the compact planetary nebu... more We present narrow-band images and high resolution long-slit spectra of the compact planetary nebulae M 1-66, He 2-115, K 3-1, K 3-13 and K 3-30, which present evidence of collimated outflows. Our data reveal the internal structure and kinematics of these objects for the first time.
Proceedings of the International Astronomical Union, 2011
NGC 6369 is a double-shell PN with a filamentary outer shell or envelope and faint bipolar extens... more NGC 6369 is a double-shell PN with a filamentary outer shell or envelope and faint bipolar extensions. We have used ground-and space-based narrowband optical and near-IR images, broadband mid-IR images, optical long-slit echelle spectra, and mid-IR spectra to investigate its physical structure. The observations confirm a bipolar structure for the inner shell of NGC 6369, but they also reveal evidence for H2 and strong polycyclic aromatic hydrocarbons (PAHs) emission from a photo-dissociation region (PDR) with molecular inclusions located outside the bright inner shell.
Diffuse X-ray emission has been detected in a small number of planetary nebulae (PNe), indicating... more Diffuse X-ray emission has been detected in a small number of planetary nebulae (PNe), indicating the existence of shocked fast stellar winds and providing support for the interacting-stellar-winds formation scenario of PNe. However, the observed X-ray luminosities are much lower than expected, similar to the situation seen in bubbles or superbubbles blown by massive stars. Ad hoc assumptions have been made to reconcile the discrepancy between observations and theoretical expectations. We have initiated FUSE programs to observe O VI absorption and emission from PNe, and our preliminary results indicate that O VI emission provides an effective diagnostic for hot gas in PN interiors.
The Astrophysical Journal, 1998
We present spatially resolved echelle spectroscopy, obtained at high spectral resolution, for 15 ... more We present spatially resolved echelle spectroscopy, obtained at high spectral resolution, for 15 multiple-shell planetary nebulae. Most exhibit faint detached halos (IC 1295, MA 3, M 2-2, M 2-40, NGC 6804, NGC 6826, NGC 6884, NGC 6891, NGC 7662, PM 1-295, and Vy 2-3). Furthermore, we have included some with attached shells (IC 1454, K 1-20, K 3-73, and PM
The Astrophysical Journal, 2004
Superbubbles surrounding OB associations provide ideal laboratories to study the stellar energy f... more Superbubbles surrounding OB associations provide ideal laboratories to study the stellar energy feedback problem because the stellar energy input can be estimated from the observed stellar content of the OB associations and the interstellar thermal and kinetic energies of superbubbles are well-defined and easy to observe. We have used DEM L 192, also known as N 51D, to carry out a detailed case study of the energy budget in a superbubble, and we find that the expected amount of stellar mechanical energy injected into the ISM, (18 ± 5) × 10 51 ergs, exceeds the amount of thermal and kinetic energies stored in the superbubble, (6 ± 2) × 10 51 ergs. Clearly, a significant fraction of the stellar mechanical energy must have been converted to other forms of energy. The X-ray spectrum of the diffuse emission from DEM L 192 requires a power-law component to explain the featureless emission at 1.0-3.0 keV. The origin of this power-law component is unclear, but it may be responsible for the discrepancy between the stellar energy input and the observed interstellar energy in DEM L 192.
The Astrophysical Journal, 1996
We discuss in detail the evolutionary path of the multiple-shell planetary nebula M1-46, in the l... more We discuss in detail the evolutionary path of the multiple-shell planetary nebula M1-46, in the light of our new observations. The velocities of the halo and main nebula correspond to a dynamical time lap between the shells of about 6.8 x 104 yr. By means of a non-LTE analysis of the central star's spectrum, we derived a stellar temperature of Teff = 45,000 K, which, coupled to the visual magnitude and an appropriate bolometric correction, gives a stellar luminosity of 5370 Lsun. The mass of the central star has been evaluated to be 0.6 Msun, and its interpulse time on the asymptotic giant branch is 7.6 x 104 yr. The agreement between the observed intershell time lap and the evolutionary interpulse time lap points to the fact that the formation of this planetary nebula could be ascribed to the gasping mass loss associated with the thermal pulses at the thermally pulsating asymptotic giant branch. The high-resolution spatially resolved observations reveal the presence of different kinematical components in the main nebula which cannot be understood in a homogeneous expanding shell scenario. As regards the chemical abundances, M1-46 has the typical abundances of a type II planetary nebula. No definite abundance gradient between the shells is found.
The Astrophysical Journal, 1999
We present narrowband imagery and long-slit intermediate-resolution spectroscopy of the multiples... more We present narrowband imagery and long-slit intermediate-resolution spectroscopy of the multipleshell planetary nebulae NGC 2438 and NGC 5882. A comparative study of the chemical abundances of the main nebulae and their surrounding halos shows a moderate N/O enrichment of the central regions. The oxygen abundances appear constant throughout the nebulae, but there are some indications of a moderate helium enrichment in the NGC 5882 main nebula. This study, along with with data published in the literature for six other multiple-shell planetary nebulae (M1-46, NGC 6543, NGC 6720, NGC 6751, NGC 6826, and NGC 7662), provides insight into the chemical enrichment and physical conditions of halos. All the nebulae in this sample have chemical abundances typical of type II planetary nebulae, thus indicating a small chemical enrichment. In addition, we do not Ðnd evidence to support a strong chemical enrichment of the main nebulae relative to the halos. The conclusion is that the third dredgeup, in these nebulae, is of small or null e †ect. Finally, we Ðnd a clear evidence that the gas in the halos is ionized by stellar UV radiation leaking through the material of the main nebula.
![Research paper thumbnail of [ITAL]Chandra[/ITAL] Reveals the X-Ray Glint in the Cat’s Eye](https://attachments.academia-assets.com/86997014/thumbnails/1.jpg)
](The Astrophysical Journal, 2001
We have obtained Chandra ACIS-S observations of NGC 6543, the Cat's Eye Nebula. The X-ray emissio... more We have obtained Chandra ACIS-S observations of NGC 6543, the Cat's Eye Nebula. The X-ray emission from NGC 6543 is clearly resolved into a point source at the central star and diffuse emission confined within the central elliptical shell and two extensions along the major axis. Spectral analysis of the diffuse component shows that the abundances of the X-ray-emitting gas are similar to those of the fast (1,750 km s −1) stellar wind but not those of the nebula. Furthermore, the temperature of this gas is ∼1.7×10 6 K, which is 100 times lower than the expected post-shock temperature of the fast stellar wind. The combination of low temperature and wind abundances is puzzling. The thermal pressure of this hot gas is about twice the pressure in the cool nebular shell; thus, the hot gas plays an essential role in the ongoing evolution of the nebula.
The Astronomical Journal, 2009
We present intermediate resolution long-slit spectra and narrow-band Hα, [N ii] and [O iii] image... more We present intermediate resolution long-slit spectra and narrow-band Hα, [N ii] and [O iii] images of PM 1-242, PM 318 and PM 1-333, three IRAS sources classified as possible planetary nebulae. The spectra show that the three objects are true planetary nebulae and allow us to study their physical properties; the images provide a detailed view of their morphology. PM 1-242 is a medium-to-high-excitation (e.g., He iiλ4686/Hβ ∼ 0.4; [N ii]λ6584/Hα ∼ 0.3) planetary nebula with an elliptical shape containing [N ii] enhanced point-symmetric arcs. An electron temperature [T e ([S iii])] of ∼ 10250 K and an electron density [N e ([S ii])] of ∼ 2300 cm −3 are derived for PM 1-242. Abundance calculations suggest a large helium abundance (He/H ∼ 0.29) in PM 1-242. PM 1-318 is a high-excitation (He iiλ4686/Hβ ∼ 1) planetary nebula with a ring-like inner shell containing two enhanced opposite regions, surrounded by a fainter round attached shell brighter in the light of [O iii]. PM 1-333 is an extended planetary nebula with a high-excitation (He iiλ4686/Hβ up to ∼ 0.9) patchy circular main body containing two low-excitation knotty arcs. A low N e ([S ii]) of ∼ 450 cm −3 and T e ([O iii]) of ∼ 15000 K are derived for this nebula. Abundance calculations suggest that PM 1-333 is a type I planetary nebula. The lack of a sharp shell morphology, low electron density, and highexcitation strongly suggest that PM 1-333 is an evolved planetary nebula. PM 1-333
Publications of the Astronomical Society of Australia, 2010
Planetary nebulae (PNe) can be roughly categorized into several broad morphological classes. The ... more Planetary nebulae (PNe) can be roughly categorized into several broad morphological classes. The high quality images of PNe acquired in recent years, however, have revealed a wealth of fine structures that preclude simplistic models for their formation. Here we present narrow-band, sub-arcsecond images of a sample of relatively large PNe that illustrate the complexity and variety of small-scale structures. This is especially true for bipolar PNe, for which the images reveal multi-polar ejections and, in some cases, suggest turbulent gas motions. Our images also reveal the presence or signs of jet-like outflows in several objects in which this kind of component has not been previously reported.
Planetary Nebulae (PNe) consist of material ejected by stars with masses <=8-10 M&sun; and for... more Planetary Nebulae (PNe) consist of material ejected by stars with masses <=8-10 M&sun; and form through the interaction between the current fast stellar wind and previous asymptotic giant branch (AGB) wind. PNe exhibit a large variety of shapes but most can be classified as either elliptical or bipolar. Different scenarios have been suggested for these two broad classes of PNe, including non-isotropic mass loss in the AGB phase, early shaping of the nebula through fast collimated outflows, and binarity. The impact of the fast stellar winds or collimated outflows, with velocities often >1000 km s-1, produces shock-heated gas that fills the interior of the PN and is expected to emit X-rays. Indeed, XMM-Newton and Chandra have detected diffuse X-ray emission from several elliptical PNe, but the large number of Chandra observations of bipolar PNe have yielded positive detections in only two young nebulae - NGC 7027 and Mz 3. We have used XMM-Newton to observe two evolved bipolar P...
Wolf-Rayet (WR) stars are evolved massive stars whose H-rich envelopes have been stripped by copi... more Wolf-Rayet (WR) stars are evolved massive stars whose H-rich envelopes have been stripped by copious stellar winds at a red supergiant (RSG) or luminous blue variable (LBV) phase. The fast WR wind can sweep up the circumstellar material and form a bubble. Hydrodynamical models of WR bubbles have been calculated both analytically and numerically by García-Segura, Mac Low, and Langer.
Astrophysics and Space Science Library
An isolated massive star can blow a bubble, while a group of massive stars can blow superbubbles.... more An isolated massive star can blow a bubble, while a group of massive stars can blow superbubbles. In this paper, we examine three intriguing questions regarding bubbles and superbubbles: (1) why don't we see interstellar bubbles around every O star? (2) how hot are the bubble interiors? and (3) what is going on at the hot/cold gas interface in a bubble?
Planetary Nebulae, 1997
Planetary Nebulae (PNs) are highly representative of the late stages of intermediate mass stellar... more Planetary Nebulae (PNs) are highly representative of the late stages of intermediate mass stellar evolution. However, there are still many unresolved questions in their evolutionary scheme. Mass loss processes during the Asymptotic Giant Branch (AGB) are not fully understood. Binarity, rotation and magnetic fields may play an important role in PNs formation. The morphological study of PNs will help us to address those questions, and therefore a meaningful homogeneous database is needed. In recent years, an ESO catalog of images of more than 250 Southern PNs, observed through narrow-band filters, has been published (Schwarz, Corradi, & Melnick 1992). On the other hand, a complete morphological survey of the Northern sky PNs does not exist to date, and only limited samples of narrow-band PN imagery exist (Balick 1987; Chu, Jacoby, & Arendt 1987). We aim at filling the gap, earring out a complete catalog of extended Northern PNs. The catalog The sample was selected according to the following criteria: 1. We observe only those PNs that are spectroscopically confirmed by Acker et al (1992). 2. We include in our observing list PNs larger than 4". Objects larger than 12" were observed using the 0.8m IAC-80 telescope, while smaller objects were observed with the 2.5m NOT telescope. 3. Our PN sample suitably covers the Northern sky: PNs with-10° < δ < +80° and diameters larger than 4" were all included in the observing list. 4. We did not observe objects that had already been observed by Balick (1987) and Schwarz et al. (1992), to avoid obvious duplications. In order to obtain sharp images of the different ionized regions, we acquired the data through a choice of narrow-band filters: Ηα+[Ν II] (FWHM=50 Â), Ha and [Nil] λ 6584 Â(FWHM=10 Â), and [Ο ill] λ 5007 Â(FWHM=30 Â). The catalog contains 243 Northern PNs, for a total of589 gray-scale frames. For thirtytwo PNs we have produced a color picture, obtained combining the frames obtained through different narrow-band filters. The Morphological Classification We use the catalog images to improve previous morphological classifications (the most recent from Schwarz, Corradi, & Stanghellini 1992). Excluding the non-extended PNs,
Planetary Nebulae, 1997
There is a renewed interest in the study of the possible precession of the central sources of pla... more There is a renewed interest in the study of the possible precession of the central sources of planetary nebulae. Three different morphological features are considered the effect of precession: 1. Point-symmetric PNe: Objects whose morphological components are symmetrical with respect to reflection through the center. 2. Quadrupolar PNe: Characterized by two well-defined pairs of lobes which are symmetric, in pairs, with respect to two different axes. These PNe are very likely the result of two episodic nebular ejection processes, produced at different positions of the symmetry axis. 3. Bipolar, rotating episodic jets (or BRET’s): Spectacular structures (Lopez, Meaburn, & Palmer 1994) due to the precession of a symmetrical, collimated episodic outflow.
Astronomy & Astrophysics, 2000
We report high-sensitivity millimeter-wave CO observations of recently discovered bipolar planeta... more We report high-sensitivity millimeter-wave CO observations of recently discovered bipolar planetary nebulae (PNe). Three objects (BV 5-1, K 3-94 and K 3-24) have been detected, and one of them (BV 5-1) is resolved by the ~ 10{''} telescope beam. The envelopes of the three newly detected objects display values of the molecular to ionized mass ratio of ~ 0.2, and
The Astrophysical Journal, 1996
In the context of the Instituto de Astrofísica de Canarias (IAC) morphological survey of Galactic... more In the context of the Instituto de Astrofísica de Canarias (IAC) morphological survey of Galactic planetary nebulae (PNs), a new morphological class has been found, and we define their members as quadrupolar PNs. We have found five quadrupolar objects whose lobes are, in pairs, symmetric with respect to two different axes. Among these PNs, three (M2-46, K3-24, and M1-75) have well-defined pairs of lobes; another two (M3-28 and M4-14) are irregular and very possibly quadrupolar. For M2-46, we have measured the extension and the angle between the lobes, and the expansion velocities of the lobes by means of spectroscopic analysis. We propose that these nebulae have been formed by precession of the rotation axis of the central stars, possibly in the presence of a binary companion, associated with multiple shell ejection at the asymptotic giant branch. A simple binary mechanism not associated with precession cannot produce such a morphology.
The formation and shaping of planetary nebulae (PNe) is a complex process that involves the actio... more The formation and shaping of planetary nebulae (PNe) is a complex process that involves the action of multiple agents, including fast stellar winds and collimated outflows. Both fast stellar winds and collimated outflows can produce shock-heated gas that emits diffuse X-rays. Hot gas in PN interiors was hinted by ROSAT observations, but unambiguous detections of diffuse X-ray emission were not made until Chandra and XMM-Newton became available. The unprecedented angular resolution and sensitivity of these new X-ray observations allow us to investigate in detail the physical properties and origin of the hot gas content of PNe and to assess its dynamical effects on the shaping and expansion of PNe. This paper reviews the results from recent X-ray observations of PNe and discusses their implications to our understanding of the formation and evolution of PNe.
We present narrow-band images and high resolution long-slit spectra of the compact planetary nebu... more We present narrow-band images and high resolution long-slit spectra of the compact planetary nebulae M 1-66, He 2-115, K 3-1, K 3-13 and K 3-30, which present evidence of collimated outflows. Our data reveal the internal structure and kinematics of these objects for the first time.
Proceedings of the International Astronomical Union, 2011
NGC 6369 is a double-shell PN with a filamentary outer shell or envelope and faint bipolar extens... more NGC 6369 is a double-shell PN with a filamentary outer shell or envelope and faint bipolar extensions. We have used ground-and space-based narrowband optical and near-IR images, broadband mid-IR images, optical long-slit echelle spectra, and mid-IR spectra to investigate its physical structure. The observations confirm a bipolar structure for the inner shell of NGC 6369, but they also reveal evidence for H2 and strong polycyclic aromatic hydrocarbons (PAHs) emission from a photo-dissociation region (PDR) with molecular inclusions located outside the bright inner shell.
Diffuse X-ray emission has been detected in a small number of planetary nebulae (PNe), indicating... more Diffuse X-ray emission has been detected in a small number of planetary nebulae (PNe), indicating the existence of shocked fast stellar winds and providing support for the interacting-stellar-winds formation scenario of PNe. However, the observed X-ray luminosities are much lower than expected, similar to the situation seen in bubbles or superbubbles blown by massive stars. Ad hoc assumptions have been made to reconcile the discrepancy between observations and theoretical expectations. We have initiated FUSE programs to observe O VI absorption and emission from PNe, and our preliminary results indicate that O VI emission provides an effective diagnostic for hot gas in PN interiors.
The Astrophysical Journal, 1998
We present spatially resolved echelle spectroscopy, obtained at high spectral resolution, for 15 ... more We present spatially resolved echelle spectroscopy, obtained at high spectral resolution, for 15 multiple-shell planetary nebulae. Most exhibit faint detached halos (IC 1295, MA 3, M 2-2, M 2-40, NGC 6804, NGC 6826, NGC 6884, NGC 6891, NGC 7662, PM 1-295, and Vy 2-3). Furthermore, we have included some with attached shells (IC 1454, K 1-20, K 3-73, and PM
The Astrophysical Journal, 2004
Superbubbles surrounding OB associations provide ideal laboratories to study the stellar energy f... more Superbubbles surrounding OB associations provide ideal laboratories to study the stellar energy feedback problem because the stellar energy input can be estimated from the observed stellar content of the OB associations and the interstellar thermal and kinetic energies of superbubbles are well-defined and easy to observe. We have used DEM L 192, also known as N 51D, to carry out a detailed case study of the energy budget in a superbubble, and we find that the expected amount of stellar mechanical energy injected into the ISM, (18 ± 5) × 10 51 ergs, exceeds the amount of thermal and kinetic energies stored in the superbubble, (6 ± 2) × 10 51 ergs. Clearly, a significant fraction of the stellar mechanical energy must have been converted to other forms of energy. The X-ray spectrum of the diffuse emission from DEM L 192 requires a power-law component to explain the featureless emission at 1.0-3.0 keV. The origin of this power-law component is unclear, but it may be responsible for the discrepancy between the stellar energy input and the observed interstellar energy in DEM L 192.
The Astrophysical Journal, 1996
We discuss in detail the evolutionary path of the multiple-shell planetary nebula M1-46, in the l... more We discuss in detail the evolutionary path of the multiple-shell planetary nebula M1-46, in the light of our new observations. The velocities of the halo and main nebula correspond to a dynamical time lap between the shells of about 6.8 x 104 yr. By means of a non-LTE analysis of the central star's spectrum, we derived a stellar temperature of Teff = 45,000 K, which, coupled to the visual magnitude and an appropriate bolometric correction, gives a stellar luminosity of 5370 Lsun. The mass of the central star has been evaluated to be 0.6 Msun, and its interpulse time on the asymptotic giant branch is 7.6 x 104 yr. The agreement between the observed intershell time lap and the evolutionary interpulse time lap points to the fact that the formation of this planetary nebula could be ascribed to the gasping mass loss associated with the thermal pulses at the thermally pulsating asymptotic giant branch. The high-resolution spatially resolved observations reveal the presence of different kinematical components in the main nebula which cannot be understood in a homogeneous expanding shell scenario. As regards the chemical abundances, M1-46 has the typical abundances of a type II planetary nebula. No definite abundance gradient between the shells is found.
The Astrophysical Journal, 1999
We present narrowband imagery and long-slit intermediate-resolution spectroscopy of the multiples... more We present narrowband imagery and long-slit intermediate-resolution spectroscopy of the multipleshell planetary nebulae NGC 2438 and NGC 5882. A comparative study of the chemical abundances of the main nebulae and their surrounding halos shows a moderate N/O enrichment of the central regions. The oxygen abundances appear constant throughout the nebulae, but there are some indications of a moderate helium enrichment in the NGC 5882 main nebula. This study, along with with data published in the literature for six other multiple-shell planetary nebulae (M1-46, NGC 6543, NGC 6720, NGC 6751, NGC 6826, and NGC 7662), provides insight into the chemical enrichment and physical conditions of halos. All the nebulae in this sample have chemical abundances typical of type II planetary nebulae, thus indicating a small chemical enrichment. In addition, we do not Ðnd evidence to support a strong chemical enrichment of the main nebulae relative to the halos. The conclusion is that the third dredgeup, in these nebulae, is of small or null e †ect. Finally, we Ðnd a clear evidence that the gas in the halos is ionized by stellar UV radiation leaking through the material of the main nebula.
The Astrophysical Journal, 2001
We have obtained Chandra ACIS-S observations of NGC 6543, the Cat's Eye Nebula. The X-ray emissio... more We have obtained Chandra ACIS-S observations of NGC 6543, the Cat's Eye Nebula. The X-ray emission from NGC 6543 is clearly resolved into a point source at the central star and diffuse emission confined within the central elliptical shell and two extensions along the major axis. Spectral analysis of the diffuse component shows that the abundances of the X-ray-emitting gas are similar to those of the fast (1,750 km s −1) stellar wind but not those of the nebula. Furthermore, the temperature of this gas is ∼1.7×10 6 K, which is 100 times lower than the expected post-shock temperature of the fast stellar wind. The combination of low temperature and wind abundances is puzzling. The thermal pressure of this hot gas is about twice the pressure in the cool nebular shell; thus, the hot gas plays an essential role in the ongoing evolution of the nebula.
The Astronomical Journal, 2009
We present intermediate resolution long-slit spectra and narrow-band Hα, [N ii] and [O iii] image... more We present intermediate resolution long-slit spectra and narrow-band Hα, [N ii] and [O iii] images of PM 1-242, PM 318 and PM 1-333, three IRAS sources classified as possible planetary nebulae. The spectra show that the three objects are true planetary nebulae and allow us to study their physical properties; the images provide a detailed view of their morphology. PM 1-242 is a medium-to-high-excitation (e.g., He iiλ4686/Hβ ∼ 0.4; [N ii]λ6584/Hα ∼ 0.3) planetary nebula with an elliptical shape containing [N ii] enhanced point-symmetric arcs. An electron temperature [T e ([S iii])] of ∼ 10250 K and an electron density [N e ([S ii])] of ∼ 2300 cm −3 are derived for PM 1-242. Abundance calculations suggest a large helium abundance (He/H ∼ 0.29) in PM 1-242. PM 1-318 is a high-excitation (He iiλ4686/Hβ ∼ 1) planetary nebula with a ring-like inner shell containing two enhanced opposite regions, surrounded by a fainter round attached shell brighter in the light of [O iii]. PM 1-333 is an extended planetary nebula with a high-excitation (He iiλ4686/Hβ up to ∼ 0.9) patchy circular main body containing two low-excitation knotty arcs. A low N e ([S ii]) of ∼ 450 cm −3 and T e ([O iii]) of ∼ 15000 K are derived for this nebula. Abundance calculations suggest that PM 1-333 is a type I planetary nebula. The lack of a sharp shell morphology, low electron density, and highexcitation strongly suggest that PM 1-333 is an evolved planetary nebula. PM 1-333
Publications of the Astronomical Society of Australia, 2010
Planetary nebulae (PNe) can be roughly categorized into several broad morphological classes. The ... more Planetary nebulae (PNe) can be roughly categorized into several broad morphological classes. The high quality images of PNe acquired in recent years, however, have revealed a wealth of fine structures that preclude simplistic models for their formation. Here we present narrow-band, sub-arcsecond images of a sample of relatively large PNe that illustrate the complexity and variety of small-scale structures. This is especially true for bipolar PNe, for which the images reveal multi-polar ejections and, in some cases, suggest turbulent gas motions. Our images also reveal the presence or signs of jet-like outflows in several objects in which this kind of component has not been previously reported.
Planetary Nebulae (PNe) consist of material ejected by stars with masses <=8-10 M&sun; and for... more Planetary Nebulae (PNe) consist of material ejected by stars with masses <=8-10 M&sun; and form through the interaction between the current fast stellar wind and previous asymptotic giant branch (AGB) wind. PNe exhibit a large variety of shapes but most can be classified as either elliptical or bipolar. Different scenarios have been suggested for these two broad classes of PNe, including non-isotropic mass loss in the AGB phase, early shaping of the nebula through fast collimated outflows, and binarity. The impact of the fast stellar winds or collimated outflows, with velocities often >1000 km s-1, produces shock-heated gas that fills the interior of the PN and is expected to emit X-rays. Indeed, XMM-Newton and Chandra have detected diffuse X-ray emission from several elliptical PNe, but the large number of Chandra observations of bipolar PNe have yielded positive detections in only two young nebulae - NGC 7027 and Mz 3. We have used XMM-Newton to observe two evolved bipolar P...