scholarly journals H Atom Observations in Near-Stellar Environments

1992 ◽  
Vol 150 ◽  
pp. 351-355
Author(s):  
Luis F. Rodriguez
Keyword(s):  
Atomic Hydrogen ◽  
Molecular Form ◽  
Planetary Nebulae ◽  
Line Of Sight ◽  
Theoretical Knowledge ◽  
H Ii Regions ◽  
Physical Conditions ◽  
Photodissociation Regions ◽  
Reflection Nebulae

Interferometric observations of the 21-cm line of atomic hydrogen resolve out the emission from extended, line-of-sight clouds and allow the detailed study of compact H I structures in the surroundings of some stars. These atomic hydrogen components most probably are the result of photodissociation of gas that originally was in molecular form. They have been observed in H II regions, reflection nebulae, and planetary nebulae. The study of this atomic hydrogen component is important to determine the mass and physical conditions of gas in the environment of luminous stars and to test our theoretical knowledge of photodissociation regions.

scholarly journals Plasma diagnostics for planetary nebulae and H ii regions using N ii and O ii optical recombination lines

2011 ◽  
Vol 7 (S283) ◽  
pp. 432-433
Author(s):  
Ian A. McNabb ◽  
Xuan Fang ◽  
Xiao–Wei Liu ◽  
Peter J. Storey
Keyword(s):  
Plasma Diagnostics ◽  
Planetary Nebulae ◽  
Coupling Scheme ◽  
H Ii Regions ◽  
Diagnostic Analysis ◽  
Plasma Diagnostic ◽  
Intermediate Coupling ◽  
Physical Conditions ◽  
Cold Metal ◽  
Intermediate Coupling Scheme

AbstractWe carry out plasma diagnostic analysis for a number of planetary nebulae (PNe) and H ii regions. We use N ii and O ii optical recombination lines (ORLs) with new effective recombination coefficients calculated under the intermediate coupling scheme, for a range of electron temperatures (Te) and densities (Ne), and fitted against the most reliable measurements. Comparing Te derived from ORLs, collisionally excited lines (CELs), the hydrogen Balmer Jump, and/or He i if available, we find the relation Te (ORLs) < Te (He i) < Te (H i BJ) < Te (CELs), confirming the physical conditions in the bi-abundance model postulated by Liu et al., i.e. the nebula contains another cold, metal-rich and probably H-deficient component.

scholarly journals Photodissociation Regions and Planetary Nebulae

1993 ◽  
Vol 155 ◽  
pp. 155-162 ◽  
Author(s):  
A.G.G.M. Tielens
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Time Dependent ◽  
Molecular Gas ◽  
Dense Gas ◽  
Physical Conditions ◽  
Thermal Spectrum ◽  
Ngc 7027 ◽  
Photodissociation Regions

FUV photons (<13.6eV) from the central star create a region of warm (≈1000K) atomic and molecular gas around Planetary Nebulae (PN). This paper reviews theoretical and observational characteristics of such regions, commonly called photodissociation regions or PDRs. PDRs around PN differ in some aspects from those in other galactic objects and this is briefly discussed with an emphasis on time dependent effects. It is concluded that, in evolved PN (texp>103 yr), molecules will only survive inside dense clumps (>106 cm−3). H2 emission from such dense gas will show a thermal spectrum in the low v states. Finally, the physical conditions in the PDR associated with NGC 7027 are compared to those in other galactic and extragalactic PDRs

scholarly journals Planetary Nebulae and their parent stellar populations. Tracing the mass assembly of M87 and Intracluster light in the Virgo cluster core

2015 ◽  
Vol 11 (S317) ◽  
pp. 69-76
Author(s):  
Magda Arnaboldi ◽  
Alessia Longobardi ◽  
Ortwin Gerhard
Keyword(s):  
Planetary Nebulae ◽  
Major Axis ◽  
Large Magellanic Cloud ◽  
Virgo Cluster ◽  
Star Formation History ◽  
Cluster Core ◽  
Line Of Sight ◽  
Cluster Galaxy ◽  
Mass Assembly ◽  
Intracluster Light

AbstractThe diffuse extended outer regions of galaxies are hard to study because they are faint, with typical surface brightness of 1% of the dark night sky. We can tackle this problem by using resolved star tracers which remain visible at large distances from the galaxy centers. This article describes the use of Planetary Nebulae as tracers and the calibration of their properties as indicators of the star formation history, mean age and metallicity of the parent stars in the Milky Way and Local Group galaxies. We then report on the results from a deep, extended, planetary nebulae survey in a 0.5 deg2region centered on the brightest cluster galaxy NGC 4486 (M87) in the Virgo cluster core, carried out with SuprimeCam@Subaru and FLAMES-GIRAFFE@VLT. Two planetary nebulae populations are identified out to 150 kpc distance from the center of M87. One population is associated with the M87 halo and the second one with the intracluster light in the Virgo cluster core. They have different line-of-sight velocity and spatial distributions, as well as different planetary nebulae specific frequencies and luminosity functions. The intracluster planetary nebulae in the surveyed region correspond to a luminosity of four times the luminosity of the Large Magellanic Cloud. The M87 halo planetary nebulae trace an older, more metal-rich, parent stellar population. A substructure detected in the projected phase-space of the line-of-sight velocity vs. major axis distance for the M87 halo planetary nebulae provides evidence for the recent accretion event of a satellite galaxy with luminosity twice that of M33. The satellite stars were tidally stripped about 1 Gyr ago, and reached apocenter at a major axis distance of 60–90 kpc from the center of M87. The M87 halo is still growing significantly at the distances where the substructure is detected.

scholarly journals Atomic hydrogen in the planetary nebula IC 4997

1987 ◽  
Vol 122 ◽  
pp. 501-502
Author(s):  
C. Giovanardi ◽  
D.R. Altschuler ◽  
S.E. Schneider ◽  
P.R. Silverglate
Keyword(s):  
Atomic Hydrogen ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Expansion Velocity ◽  
Hydrogen Emission

In the course of a sensitive search for atomic hydrogen emission associated with planetary nebulae having high velocities relative to Galactic HI (Schneider et al. 1986), we detected absorption in the spectrum of IC 4997 (PK 58-10.1). This is only the second definite detection of HI associated with a PN. The velocity of the feature coincides precisely with that expected if the gas is expanding with the measured optical expansion velocity of 14 km s−1 (Sabbadin 1984), strongly suggesting an association.

scholarly journals Planetary Nebulae in Local Group Galaxies

1983 ◽  
Vol 103 ◽  
pp. 443-460
Author(s):  
Holland C. Ford
Keyword(s):  
Local Group ◽  
Planetary Nebulae ◽  
Stellar Populations ◽  
Chemical Compositions ◽  
H Ii Regions ◽  
Helium Abundance ◽  
Abundance Gradient ◽  
Star Forming ◽  
Ic 10 ◽  
Ngc 6822

Recent surveys for planetary nebulae have given the first identifications in Fornax, NGC 6822, M33, IC 10, Leo A, Sextans A, Pegasus, WLM, NGC 404, and M81, and extended the identifications in the SMC, the LMC, and M31. Observations of planetaries have established chemical compositions in old or intermediate age populations in 8 Local Group galaxies. The chemical compositions show that i) the helium abundance is higher in planetary nebulae than in H II regions in the same galaxy, and ii) nitrogen is overabundant relative to H II regions by factors of 4 to 100. Planetary nebulae are not a major source of helium in star-forming galaxies, and are a major source of nitrogen. The planetary in Fornax has a relatively high O abundance, and, together with Fornax's carbon stars, establishes the presence of at least 2 stellar populations. The abundance gradient derived from 3 planetaries in M31 is very shallow, and gives high abundances at ~ 20 kpc. By using planetary nebulae as standard candles, upper and lower distance limits have been set for 10 Local Group candidates, and a new distance estimated for M81.

scholarly journals Influence of galactic arm scale dynamics on the molecular composition of the cold and dense ISM III. Elemental depletion and shortcomings of the current physico-chemical models

2020 ◽  
Vol 497 (2) ◽  
pp. 2309-2319
Author(s):  
V Wakelam ◽  
W Iqbal ◽  
J-P Melisse ◽  
P Gratier ◽  
M Ruaud ◽  
...  
Keyword(s):  
Gas Phase ◽  
Molecular Form ◽  
Dense Medium ◽  
Chemical Model ◽  
Physical Conditions ◽  
Dense Cores ◽  
Chemical Models ◽  
Physico Chemical ◽  
Galactic Model ◽  
Elemental Depletion

ABSTRACT We present a study of the elemental depletion in the interstellar medium. We combined the results of a Galactic model describing the gas physical conditions during the formation of dense cores with a full-gas-grain chemical model. During the transition between diffuse and dense medium, the reservoirs of elements, initially atomic in the gas, are gradually depleted on dust grains (with a phase of neutralization for those which are ions). This process becomes efficient when the density is larger than 100 cm−3. If the dense material goes back into diffuse conditions, these elements are brought back in the gas phase because of photo-dissociations of the molecules on the ices, followed by thermal desorption from the grains. Nothing remains on the grains for densities below 10 cm−3 or in the gas phase in a molecular form. One exception is chlorine, which is efficiently converted at low density. Our current gas–grain chemical model is not able to reproduce the depletion of atoms observed in the diffuse medium except for Cl, which gas abundance follows the observed one in medium with densities smaller than 10 cm−3. This is an indication that crucial processes (involving maybe chemisorption and/or ice irradiation profoundly modifying the nature of the ices) are missing.

scholarly journals Intracluster Planetary Nebulae

2003 ◽  
Vol 209 ◽  
pp. 597-604 ◽  
Author(s):  
John J. Feldmeier
Keyword(s):  
Velocity Field ◽  
Stellar Population ◽  
Planetary Nebulae ◽  
Line Of Sight ◽  
Galaxy Groups ◽  
The Past ◽  
Star Production ◽  
Intracluster Light ◽  
Lower Luminosity

We review the progress of research on intracluster planetary nebulae (IPN). In the past five years, hundreds of IPN candidates have been detected in the Virgo and Fornax galaxy clusters and searches are also underway in poorer galaxy groups. From the observations to date, and applying the known properties of extragalactic planetary nebulae, the intracluster light in Virgo and Fornax: 1) is significant, at least 20% of the total cluster stellar luminosity, 2) is elongated in Virgo along our line of sight, and 3) may derive from lower-luminosity galaxies, consistent with some models of intracluster star production. A fraction of IPN candidates are not true IPN, but emission-line sources of very large observed equivalent width (≥ 200 Å). The most likely source for these contaminating objects are Lyman-α galaxies at z ≈ 3.1. Follow-up spectroscopy of the IPN candidates will be crucial to discriminate against high red-shift galaxies and to derive the velocity field of the intracluster stellar population.

scholarly journals Planetary Nebulae and the Pregalactic Helium Abundance

1989 ◽  
Vol 131 ◽  
pp. 213-213 ◽  
Author(s):  
Walter J. Maciel
Keyword(s):  
Chemical Composition ◽  
Recent Work ◽  
Planetary Nebulae ◽  
H Ii Regions ◽  
Helium Abundance

Recent work has emphasized the determination of the pregalactic helium abundance by mass Yp and the slope ΔY/ΔZ based on the chemical composition of both galactic and extragalactic H II regions (Pagel, 1987; Pagel et al., 1986).

scholarly journals Distribution of star-forming complexes and the structure of our Galaxy

2003 ◽  
Vol 212 ◽  
pp. 431-440 ◽  
Author(s):  
Delphine Russeil
Keyword(s):  
Large Scale ◽  
Stellar Population ◽  
Line Of Sight ◽  
H Ii Regions ◽  
Spiral Arms ◽  
Ob Stars ◽  
Star Forming ◽  
Optical Images ◽  
External Galaxies

The determination of the external galaxies morphology is generally based on their appearance on optical images. At these wavelengths young stellar population and their associated H ii regions, which can be grouped into star-forming complexes, appear preferentially located along spiral arms. Hence, it is naturally to use the same tracers to delineate the arms of our own Galaxy. But, where for external galaxies the distribution of star-forming complexes along the spiral arms is generally evident from direct imaging, for our Galaxy the spiral arms are strung out along the line of sight, leading to the superposition and mixing of information from the different complexes in the spiral arms making it difficult to distinguish them. Thus to access to the spatial distribution of young objects, hence to the large scale structure of our Galaxy, it is required first to identify and collect star-forming complexes (molecular clouds – H ii regions – OB stars) and then to determine their distance. In this framework I review the observational results and difficulties concerning the distribution of star-forming complexes and the determination of the structure of our Galaxy.

scholarly journals What do planetary nebulae and H II regions reveal about the chemical evolution of nearby dwarf galaxies?

2018 ◽  
Vol 14 (S344) ◽  
pp. 161-177 ◽  
Author(s):  
Denise R. Gonçalves
Keyword(s):  
Chemical Evolution ◽  
Local Group ◽  
Planetary Nebulae ◽  
H Ii Regions ◽  
Chemical Abundances ◽  
Local Universe ◽  
Time Line ◽  
Nearby Galaxies ◽  
H Ii Region ◽  
Age Range

AbstractThe Local Group contains a great number of dwarf irregulars and spheroidals, for which the spectroscopy of individual stars can be obtained. Thus, the chemical evolution of these galaxies can be traced, with the only need of finding populations spanning a large age range and such that we can accurately derive the composition. Planetary nebulae (PNe) are old- and intermediate-age star remnants and their chemical abundances can be obtained up to 3-4 Mpc. H ii regions, which are brighter and much easily detected, represent galaxies young content. PNe and H ii regions share similar spectroscopic features and are analysed in the same way. Both are among the best tracers of the chemical evolution allowing to draw the chemical time line of nearby galaxies. The focus in this review are the PN and H ii region populations as constraints to the chemical evolution models and the mass-metallicity relation of the local universe.

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