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Author name code: pottasch
ADS astronomy entries on 2022-09-14
author:Pottasch, Stuart
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Title: Neon, sulphur, and argon abundances of planetary nebulae in
the sub-solar metallicity Galactic anti-centre
Authors: Pagomenos, G. J. S.; Bernard-Salas, J.; Pottasch, S. R.
2018A&A...615A..29P Altcode: 2017arXiv171208827P
Context. Spectra of planetary nebulae show numerous fine structure
emission lines from ionic species, enabling us to study the overall
abundances of the nebular material that is ejected into the interstellar
medium. The abundances derived from planetary nebula emission show
the presence of a metallicity gradient within the disk of the Milky
Way up to Galactocentric distances of 10 kpc, which are consistent
with findings from studies of different types of sources, including
H II regions and young B-type stars. The radial dependence of these
abundances further from the Galactic centre is in dispute. <BR />
Aims: We aim to derive the abundances of neon, sulphur and argon from
a sample of planetary nebulae towards the Galactic anti-centre, which
represent the abundances of the clouds from which they were formed, as
they remain unchanged throughout the course of stellar evolution. We
then aim to compare these values with similarly analysed data from
elsewhere in the Milky Way in order to observe whether the abundance
gradient continues in the outskirts of our Galaxy. <BR /> Methods:
We have observed 23 planetary nebulae at Galactocentric distances of
8-21 kpc with Spitzer IRS. The abundances were calculated from infrared
emission lines, for which we observed the main ionisation states of
neon, sulphur, and argon, which are little affected by extinction
and uncertainties in temperature measurements or fluctuations within
the planetary nebula. We have complemented these observations with
others from optical studies in the literature, in order to reduce
or avoid the need for ionisation correction factors in abundance
calculations. <BR /> Results: The overall abundances of our sample of
planetary nebulae in the Galactic anti-centre are lower than those in
the solar neighbourhood. The abundances of neon, sulphur, and argon
from these stars are consistent with a metallicity gradient from the
solar neighbourhood up to Galactocentric distances of 20 kpc, albeit
with varying degrees of dispersion within the data.
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Title: Abundances of planetary nebulae in the Galactic bulge
Authors: Pottasch, S. R.; Bernard-Salas, J.
2015A&A...583A..71P Altcode:
Context. Planetary nebulae (PNe) abundances are poorly known for
those nebulae in the Galactic bulge. This is because of the high
and uneven extinction in the bulge which makes visual spectral
measurements difficult. In addition, the extinction corrections may be
unreliable. Elements considered are O, N, Ne, S, Ar, and Cl. <BR />
Aims: We determine the abundances in 19 PNe, 18 of which are located
in the bulge. This doubles the number of PNe abundance determinations
in the bulge. The Galactic abundance gradient is discussed for five
elements. <BR /> Methods: The mid-infrared spectra measured by the
Spitzer Space Telescope are used to determine the abundances. This part
of the spectrum is little affected by extinction for which an uncertain
correction is no longer necessary. In addition the connection with the
visible and ultraviolet spectrum becomes simpler because hydrogen lines
are observed both in the infrared and in the visible spectra. In this
way we more than double the number of PNe with reliable abundances. <BR
/> Results: Reliable abundances are obtained for O, N, Ne, S, and Ar
for Galactic bulge PNe. <BR /> Conclusions: The Galactic abundance
gradient is less steep than previously thought. This is especially
true for oxygen. The sulfur abundance is reliable because all stages
of ionization expected have been measured. It is not systematically low
compared to oxygen as has been found for some Galactic PNe. <P />Based
on observations with the Spitzer Space Telescope, which is operated
by the Jet Propulsion Laboratory, California Institute of Technology.
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Title: Dust properties in the Galactic bulge
Authors: Pottasch, S. R.; Bernard-Salas, J.
2013A&A...550A..35P Altcode: 2013arXiv1301.3732P
Context. It has been suggested that the ratio of total-to-selective
extinction R<SUB>V</SUB> in dust in the interstellar medium differs
in the Galactic bulge from its value in the local neighborhood. <BR
/> Aims: We attempt to test this suggestion. <BR /> Methods: The
mid-infrared hydrogen lines in 16 Galactic bulge PNe measured by
the Spitzer Space Telescope are used to determine the extinction
corrected Hβ flux. This is compared to the observed Hβ flux to
obtain the total extinction at Hβ. The selective extinction is
obtained from the observed Balmer decrement in these nebulae. The
value of R<SUB>V</SUB> can then be found. <BR /> Results: The ratio of
total-to-selective extinction in the Galactic bulge is consistent with
the value R<SUB>V</SUB> = 3.1, which is the same as has been found
in the local neighborhood. <BR /> Conclusions: The suggestion that
R<SUB>V</SUB> is different in the Galactic bulge is incorrect. The
reasons for this are discussed. <P />Based on observations with the
Spitzer Space Telescope, which is operated by the Jet Propulsion
Laboratory, California Institute of Technology.
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Title: OT2_spottasc_1: Carbon abundances in Galactic bulge planetary
nebulae
Authors: Pottasch, S. R.
2011hers.prop.1719P Altcode:
Carbon (and nitrogen) abundances, which can be used to constrain stellar
evolution theory, are not well known in Galactic bulge planetary
nebulae because the lines used are in the ultraviolet and are weak
and difficult to measure accurately. We propose to measure the C(+)
abundance in a selection of low ionization PNe where it is the dominant
ion, by measuring the CII line at 157 microns. The nitrogen line at
122 microns is used in conjunction with the line at 6584 angstroms
to accurately determine the electron temperature, which not only will
make the nitrogen abundance more accurate, but will enable abundances
to be determined for other ions measured in the visual spectrum.
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Title: The history of the creation of Astronomy & Astrophysics
Authors: Pottasch, S. R.
2011EAS....49...23P Altcode:
Dutch astronomer S.R. Pottasch, who was appointed as one of the two
first Editors-in-Chief of A&A together with J.L. Steinberg, recalls
the events that led to the creation of the first European astronomy
journal. This account is based on the author's notes and documents and
also on an article relating ESO's early history written by A. Blaauw
and published in The ESO Messenger No. 60, pp. 23-34 (1990). C. Bertout
added footnotes giving a few biographical details about the actors.
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Title: Abundances in planetary nebulae: NGC 1535, NGC 6629, He2-108,
and Tc1
Authors: Pottasch, S. R.; Surendiranath, R.; Bernard-Salas, J.
2011A&A...531A..23P Altcode: 2011arXiv1107.4041P
Context. Models have been made of stars of a given mass that produce
planetary nebulae that usually begin on the AGB (although they may begin
earlier) and run to the white dwarf stage. While these models cover the
so-called dredge-up phases when nuclear reactions occur and the newly
formed products are brought to the surface, it is important to compare
the abundances predicted by the models with the abundances actually
observed in PNe. <BR /> Aims: The aim of the paper is to determine the
abundances in a group of PNe with uniform morphological and kinematic
properties. The PNe we discuss are circular with rather low-temperature
central stars and are rather far from the galactic plane. We discuss
the effect these abundances have on determining the evolution of the
central stars of these PNe. <BR /> Methods: The mid-infrared spectra
of the planetary nebulae <ASTROBJ>NGC 1535</ASTROBJ>, <ASTROBJ>NGC
6629</ASTROBJ>, <ASTROBJ>He2-108</ASTROBJ>, and <ASTROBJ>Tc1</ASTROBJ>
(<ASTROBJ>IC 1266</ASTROBJ>) taken with the Spitzer Space Telescope are
presented. These spectra were combined with the ultraviolet IUE spectra
and with the spectra in the visual wavelength region to obtain complete,
extinction-corrected spectra. The chemical composition of these
nebulae is then found by directly calculating and adding individual ion
abundances. For two of these PNe, we attempted to reproduce the observed
spectrum by making a model nebula. This proved impossible for one of the
nebulae and the reason for this is discussed. The resulting abundances
are more accurate than earlier studies for several reasons, the most
important is that inclusion of the far infrared spectra increases the
number of observed ions and makes it possible to include the nebular
temperature gradient in the abundance calculations. <BR /> Results:
The abundances of the above four PNe have been determined and compared
to the abundances found in five other PNe with similar properties
studied earlier. These abundances are further compared with values
predicted by the models of Karakas (2003). From this comparison we
conclude that the central stars of these PNe originally had a low mass,
probably between 1 M<SUB>⊙</SUB> and 2.5 M<SUB>⊙</SUB>. A further
comparison is made with the stellar evolution models on the HR diagram,
from which we conclude that the core mass of these PNe is between
0.56 M<SUB>⊙</SUB> and 0.63 M<SUB>⊙</SUB>. <BR /> Conclusions:
A consistent picture of the evolution of this group of PNe is found
that agrees with the predictions of the models concerning the present
nebular abundances, the individual masses, and luminosities of these
PNe. The distance of these PNe can be determined as well. <P />Based
on observations with the Spitzer Space Telescope, which is operated
by the Jet Propulsion Laboratory, California Institute of Technology.
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Title: Adriaan Blaauw, 1914-2010
Authors: de Zeeuw, T.; Pottasch, S.; Wilson, R.
2011Msngr.143....2D Altcode:
In the last issue of The Messenger (142, p. 51) only a brief obituary of
Adriaan Blaauw, the second Director General of ESO, could be included
at the time of going to press. There follow three tributes to Adriaan
Blaauw: by Tim de Zeeuw, current ESO Director General; by his long-term
colleague at the Kapteyn Institute, Stuart Pottasch; and by Raymond
Wilson, who led the Optics Group during his tenure as Director General.
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Title: Planetary nebulae abundances and stellar evolution II
Authors: Pottasch, S. R.; Bernard-Salas, J.
2010A&A...517A..95P Altcode: 2010arXiv1005.3042P
Context. In recent years mid- and far infrared spectra of planetary
nebulae have been analysed and lead to more accurate abundances. It may
be expected that these better abundances lead to a better understanding
of the evolution of these objects. <BR /> Aims: The observed abundances
in planetary nebulae are compared to those predicted by the models
of Karakas (2003, Thesis, Monash Univ. Melbourne) in order to predict
the progenitor masses of the various PNe used. The morphology of the
PNe is included in the comparison. Since the central stars play an
important role in the evolution, it is expected that this comparison
will yield additional information about them. <BR /> Methods: First the
nitrogen/oxygen ratio is discussed with relation to the helium/hydrogen
ratio. The progenitor mass for each PNe can be found by a comparison
with the models of Karakas. Then the present luminosity of the central
stars is determined in two ways: first by computing the central star
effective temperature and radius, and second by computing the nebular
luminosity from the hydrogen and helium lines. This luminosity is also
a function of the initial mass so that these two values of initial mass
can be compared. <BR /> Results: Six of the seven bipolar nebulae can
be identified as descendants of high mass stars (4-6 M<SUB>⊙</SUB>)
while the seventh is ambiguous. Most of the elliptical PNe have central
stars which descend from low initial mass stars, although there are a
few caveats which are discussed. There is no observational evidence
for a higher mass for central stars which have a high carbon/oxygen
ratio. The evidence provided by the abundance comparison with the models
of Karakas is consistent with the HR diagram to which it is compared. In
the course of this discussion it is shown how "optically thin" nebulae
can be separated from those which are "optically thick". <P />Based
on observations with ISO, an ESA project with instruments funded by
ESA Member States (especially the PI countries: France, Germany, the
Netherlands and the United Kingdom) and with the participation of ISAS
and NASA.
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Title: Abundances in planetary nebulae: NGC 2792
Authors: Pottasch, S. R.; Surendiranath, R.; Bernard-Salas, J.;
Roellig, T. L.
2009A&A...502..189P Altcode:
The mid-infrared spectrum of the rather circular planetary nebula
<ASTROBJ>NGC 2792</ASTROBJ> taken with the Spitzer Space Telescope
is presented. This spectrum is combined with the ultraviolet IUE
spectrum and with the spectrum in the visual wavelength region to
obtain a complete, extinction corrected, spectrum. The chemical
composition of the nebula is then calculated in two ways. First
by directly calculating and adding individual ion abundances, and
secondly by building a model nebula that attempts to reproduce the
observed spectrum. Because it is now possible to include the nebular
temperature gradient, the chemical composition is more accurate than has
been given earlier in the literature. Discussion of both the central
star and the evolution of the star-nebula is then given. <P />Based
on observations with the Spitzer Space Telescope, which is operated
by the Jet Propulsion Laboratory, California Institute of Technology.
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Title: Abundances in the planetary nebula NGC 6210
Authors: Pottasch, S. R.; Bernard-Salas, J.; Roellig, T. L.
2009A&A...499..249P Altcode:
The spectra of the planetary nebula <ASTROBJ>NGC 6210</ASTROBJ> is
reanalysed using spectral measurements made in the mid-infrared with
the Spitzer Space Telescope and the Infrared Space Observatory. The
aim is to determine the chemical composition of this object. We also
make use of IUE and ground based spectra. Abundances determined from
the mid-infrared lines, which are insensitive to electron temperature,
are used as the basis for the determination of the composition, which
is found to differ somewhat from earlier results. The abundances found,
especially the low value of helium and oxygen, indicate that the central
star was originally of rather low mass, probably ≤1 M_⊙. Abundances
of phosphorus, iron, silicon, sodium, potassium and chlorine have
been determined, some for the first time in this nebula. The electron
temperature in this nebula is constant. The temperature, radius
and luminosity of the central star is also discussed. It is shown
that the luminosity is consistent with that predicted for a star of
0.9 M_⊙. But the predicted nebular age is inconsistent with the
observed kinetic age. <P />Based on observations with the Spitzer
Space Telescope, which is operated by the Jet Propulsion Laboratory,
California Institute of Technology and with ISO, an ESA project with
instruments funded by ESA member states and with participation of ISAS
and NASA.
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Title: Abundances of planetary nebulae NGC 3242 and NGC 6369
Authors: Pottasch, S. R.; Bernard-Salas, J.
2008A&A...490..715P Altcode: 2008arXiv0809.3745P
The spectra of the planetary nebulae <ASTROBJ>NGC 3242 and NGC
6369</ASTROBJ> are reanalysed using spectral measurements made in the
mid-infrared with the Spitzer Space Telescope and the Infrared Space
Observatory (ISO). The aim is to determine the chemical composition
of these objects. We also make use of International Ultraviolet
Explorer (IUE) and ground based spectra. These elliptical PNe are
interesting because they are well-studied, nearby, bright objects
and therefore allow a reasonably complete comparison of this type of
nebulae. Abundances determined from the mid-infrared lines, which are
insensitive to electron temperature, are used as the basis for the
determination of the composition, which are found to differ somewhat
from earlier results. The abundances found, especially the low value
of helium and oxygen, indicate that the central star was originally
of rather low mass. The abundance of phosphorus has been determined
for the first time in NGC 3242. The electron temperature in both
of these nebulae is roughly constant unlike NGC 6302 and NGC 2392
where a strong temperature gradient is found. The temperature of the
central star is discussed for both nebulae. Finally a comparison of
the element abundances in these nebulae with the solar abundance is
made. The low abundance of Fe and P is noted and it is suggested that
these elements are an important constituent of the nebular dust. <P
/>Based on observations with the Spitzer Space <P />Telescope, which
is operated by the Jet Propulsion Laboratory, <P />California Institute
of Technology.
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Title: Chemical Abundances and Dust in Planetary Nebulae in the
Galactic Bulge
Authors: Gutenkunst, S.; Bernard-Salas, J.; Pottasch, S. R.; Sloan,
G. C.; Houck, J. R.
2008ApJ...680.1206G Altcode: 2008arXiv0803.1828G
We present mid-infrared Spitzer spectra of 11 planetary nebulae in the
Galactic bulge. We derive argon, neon, sulfur, and oxygen abundances
for them using mainly infrared line fluxes combined with some optical
line fluxes from the literature. Due to the high extinction toward
the bulge, the infrared spectra allow us to determine abundances for
certain elements more accurately than previously possible with optical
data alone. Abundances of argon and sulfur (and in most cases neon and
oxygen) in planetary nebulae in the bulge give the abundances of the
interstellar medium at the time their progenitor stars formed; thus,
these abundances give information about the formation and evolution
of the bulge. The abundances of bulge planetary nebulae tend to be
slightly higher than those in the disk on average, but they do not
follow the trend of the disk planetary nebulae, thus confirming the
difference between bulge and disk evolution. In addition, the bulge
planetary nebulae show peculiar dust properties compared to the disk
nebulae. Oxygen-rich dust features (crystalline silicates) dominate
the spectra of all of the bulge planetary nebulae; such features are
more scarce in disk nebulae. In addition, carbon-rich dust features
(polycyclic aromatic hydrocarbons) appear in roughly half of the bulge
planetary nebulae in our sample, which is interesting in light of the
fact that this dual chemistry is comparatively rare in the Milky Way
as a whole.
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Title: Abundances in planetary nebulae: <ASTROBJ>NGC 6826</ASTROBJ>
Authors: Surendiranath, R.; Pottasch, S. R.
2008A&A...483..519S Altcode:
Aims: We determine the chemical abundances and other parameters of
the nebula NGC 6826 and its central star. <BR />Methods: We present
new ISO spectra and combine them with archival IUE and optical
spectra from the literature to get a complete, extinction-corrected,
spectrum. The chemical composition of the nebula is then calculated
in two ways, first by directly calculating and adding individual
ion abundances, and second by building a model nebula that will
reproduce the observed spectrum. <BR />Results: The results of these
two methods are compared. In addition, we discuss the star exciting
the nebula. <P />Based <P />on observations with ISO, an ESA project
with instruments funded <P />by ESA Member States (especially the PI
countries: France, <P />Germany, The Netherlands, and the UK) and with
the <P />participation of ISAS and NASA.
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Title: Abundances of planetary nebula NGC 2392
Authors: Pottasch, S. R.; Bernard-Salas, J.; Roellig, T. L.
2008A&A...481..393P Altcode: 2008arXiv0801.2767P
The spectra of the planetary nebula <ASTROBJ>NGC 2392</ASTROBJ> is
reanalysed using spectral measurements made in the mid-infrared with
the Spitzer Space Telescope. The aim is to determine the chemical
composition of this object. We also make use of IUE and ground based
spectra. Abundances determined from the mid-infrared lines, which are
insensitive to electron temperature, are used as the basis for the
determination of the composition, which are found to differ somewhat
from earlier results. The abundances found, especially the low value
of helium and oxygen, indicate that the central star was originally of
rather low mass. Abundances of phosphorus, iron, silicon and chlorine
have been determined for the first time in this nebula. The variation
of electron temperature in this nebula is very clear, reaching quite
high values close to the center. The temperature of the central star is
discussed in the light of the observed high stages of ionization. The
nebular information indicates that the spectrum of the star deviates
considerably from a blackbody. <P />Based on <P />observations with the
Spitzer Space Telescope, which is operated <P />by the Jet Propulsion
Laboratory, California Institute of <P />Technology.
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Title: Neon and Sulfur Abundances of Planetary Nebulae in the
Magellanic Clouds
Authors: Bernard-Salas, J.; Pottasch, S. R.; Gutenkunst, S.; Morris,
P. W.; Houck, J. R.
2008ApJ...672..274B Altcode: 2007arXiv0709.3292B
The chemical abundances of neon and sulfur for 25 planetary nebulae
(PNe) in the Magellanic Clouds are presented. These abundances
have been derived using mainly infrared data from the Spitzer Space
Telescope. The implications for the chemical evolution of these elements
are discussed. A comparison with similarly obtained abundances of
Galactic PNe and H II regions and Magellanic Cloud H II regions is
also given. The average neon abundances are 6.0 × 10<SUP>-5</SUP> and
2.7 × 10<SUP>-5</SUP> for the PNe in the Large and Small Magellanic
Clouds, respectively. These are ~1/3 and 1/6 of the average abundances
of Galactic planetary nebulae to which we compare. The average sulfur
abundances for the LMC and SMC are, respectively, 2.7 × 10<SUP>-6</SUP>
and 1.0 × 10<SUP>-6</SUP>. The Ne/S ratio (23.5) is on average higher
than the ratio found in Galactic PNe (16), but the range of values in
both data sets is similar for most of the objects. The neon abundances
found in PNe and H II regions agree with each other. It is possible
that a few (3-4) of the PNe in the sample have experienced some neon
enrichment, but for two of these objects the high Ne/S ratio can be
explained by their very low sulfur abundances. The neon and sulfur
abundances derived in this paper are also compared to previously
published abundances using optical data and photoionization models.
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Title: Abundances of planetary nebula <ASTROBJ>M 1-42</ASTROBJ>
Authors: Pottasch, S. R.; Bernard-Salas, J.; Roellig, T. L.
2007A&A...471..865P Altcode: 2007arXiv0706.3407P
The spectra of the planetary nebula M 1-42 is reanalysed using
spectral measurements made in the mid-infrared with the Spitzer
Space Telescope. The aim is to determine the chemical composition
of this object. We also make use of ISO, IUE and ground based
spectra. Abundances determined from the mid- and far-infrared lines,
which are insensitive to electron temperature, are used as the basis for
the determination of the composition, which are found to substantially
differ from earlier results. High values of neon, argon and sulfur
are found. They are higher than in other PN, with the exception of NGC
6153, a nebula of very similar abundances. The high values of helium and
nitrogen found indicate that the second dredge-up and hot bottom burning
has occurred in the course of evolution and that the central star was
originally more massive than 4 M<SUB>⊙</SUB>. The present temperature
and luminosity of the central star is determined and at first sight may
be inconsistent with such a high mass. <P />Based on <P />observations
with the Spitzer Space Telescope, which is operated <P />by the Jet
Propulsion Laboratory, California Institute of <P />Technology.
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Title: The Spitzer IRS Infrared Spectrum and Abundances of the
Planetary Nebula IC 2448
Authors: Guiles, S.; Bernard-Salas, J.; Pottasch, S. R.; Roellig, T. L.
2007ApJ...660.1282G Altcode: 2007astro.ph..3090G
We present the mid-infrared spectrum of the planetary nebula IC 2448. In
order to determine the chemical composition of the nebula, we use the
infrared line fluxes from the Spitzer spectrum along with optical line
fluxes from the literature and ultraviolet line fluxes from archival
IUE spectra. We determine an extinction of C<SUB>Hβ</SUB>=0.27 from
hydrogen recombination lines and the radio to Hβ ratio. Forbidden line
ratios give an electron density of 1860 cm<SUP>-3</SUP> and an average
electron temperature of 12,700 K. The use of infrared lines allows
us to determine more accurate abundances than previously possible
because abundances derived from infrared lines do not vary greatly
with the adopted electron temperature and extinction, and additional
ionization stages are observed. Elements left mostly unchanged by
stellar evolution (Ar, Ne, S, and O) all have subsolar values in IC
2448, indicating that the progenitor star formed out of moderately
metal deficient material. Evidence from the Spitzer spectrum of IC
2448 supports previous claims that IC 2448 is an old nebula formed
from a low-mass progenitor star.
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Title: VizieR Online Data Catalog: A spectroscopic atlas of post-AGB
stars and planetary nebulae selected from the IRAS point source
catalogue.
Authors: Suarez, O.; Garcia-Lario, P.; Manchado, A.; Manteiga, M.;
Ulla, A.; Pottasch, S. R.
2007yCat..34580173S Altcode:
The spectroscopic observations were conducted during several runs
spanning 15 years from March 1988 to June 2003. The observations from
the Southern Hemisphere were carried out in most cases at the European
Southern Observatory (ESO, La Silla, Chile) with the 1.5m ESO telescope,
equipped with a Boller & Chivens spectrograph. The first and last
runs of observations were carried out at the 3.6m ESO telescope, located
at the same site, using the ESO Faint Object Spectrograph and Camera
EFOSC1 in the first run and EFOSC2 in the last one. The observations
from the Northern Hemisphere were carried out at the 2.5m Isaac Newton
Telescope at the Observatorio del Roque de los Muchachos (La Palma,
Spain), using the IDS spectrograph, and at the 2.2m telescope at the
Observatorio Hispano-Aleman (Calar Alto, Spain), also equipped with
a Boller & Chivens spectrograph. <P />(12 data files).
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Title: Abundances in planetary nebulae: <ASTROBJ>Hb 5</ASTROBJ>
Authors: Pottasch, S. R.; Surendiranath, R.
2007A&A...462..179P Altcode:
The ISO spectra of the bilobal planetary nebula <ASTROBJ>Hb 5</ASTROBJ>
are presented. These spectra are combined with the spectra in the
visual wavelength region to obtain a complete, extinction corrected,
spectrum. The chemical composition of the nebula is then calculated
in several ways. First by directly calculating and adding individual
ion abundances, assuming that all the ionic lines are formed in an
ionized region surrounding the ionizing star. Secondly by building an
"end-to-end model" nebula in which we have included a neutral region
and a photodissociation region (PDR) beyond the ionized nebula. In this
way we attempt to interpret the molecular hydrogen lines observed by
ISO in a more self-consistent way. In the final analysis, the model
is found to be basically heuristic, but gives new insights about the
PDR and the PN. The implications of these are discussed. <P />Based on
observations with ISO, an ESA project with instruments funded <P />by
ESA Member States (especially the PI countries: France, <P />Germany,
the Netherlands and the UK) and with the <P />participation of ISAS
and NASA.
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Title: IRS Observations of LMC and SMC Planetary Nebulae
Authors: Bernard-Salas, J.; Houck, J. R.; Morris, P. W.; Sloan, G. C.;
Pottasch, S. R.; Barry, D. J.
2006ASPC..357..157B Altcode:
By the ejection of the outer parts of its envelope, a Planetary Nebula
(PN) contributes to the elemental enrichment of the interstellar
medium. PNe offer for the first time in the life of a star,
the possibility to reliably probe the products of the stellar
nucleosynthesis. Furthermore, the evolution and characteristics of
the dust can also be studied. We present the GTO program which has
been designed to study a number of planetary nebulae in the LMC and
SMC. Preliminary results of the IRS observations of planetary nebula
LMC-SMP83 are also given.
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Title: Planetary nebulae abundances and stellar evolution
Authors: Pottasch, S. R.; Bernard-Salas, J.
2006A&A...457..189P Altcode: 2006astro.ph..8001P
A summary is given of planetary nebulae abundances from ISO
measurements. It is shown that these nebulae show abundance gradients
(with galactocentric distance), which in the case of neon, argon,
sulfur and oxygen (with four exceptions) are the same as HII regions and
early type star abundance gradients. The abundance of these elements
predicted from these gradients at the distance of the Sun from the
center are exactly the solar abundance. Sulfur is the exception
to this; the reason for this is discussed. The higher solar neon
abundance is confirmed; this is discussed in terms of the results
of helioseismology. Evidence is presented for oxygen destruction
via ON cycling having occurred in the progenitors of four planetary
nebulae with bilobal structure. These progenitor stars had a high mass,
probably greater than 5 M⊙. This is deduced from the high values of
He/H and N/H found in these nebulae. Formation of nitrogen, helium and
carbon are discussed. The high mass progenitors which showed oxygen
destruction are shown to have probably destroyed carbon as well. This
is probably the result of hot bottom burning.
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Title: A spectroscopic atlas of post-AGB stars and planetary nebulae
selected from the IRAS point source catalogue
Authors: Suárez, O.; García-Lario, P.; Manchado, A.; Manteiga, M.;
Ulla, A.; Pottasch, S. R.
2006A&A...458..173S Altcode: 2006astro.ph..8080S
Aims.We study the optical spectral properties of a sample of stars
showing far infrared colours similar to those of well-known planetary
nebulae. The large majority of them were unidentified sources or poorly
known in the literature at the time when this spectroscopic survey
started, some 15 years ago.<BR /> Methods: .We present low-resolution
optical spectroscopy, finding charts and improved astrometric
coordinates of a sample of 253 IRAS sources.<BR /> Results: .We have
identified 103 sources as post-AGB stars, 21 as "transition sources",
and 36 as planetary nebulae, some of them strongly reddened. Among
the rest of sources in the sample, we were also able to identify 38
young stellar objects, 5 peculiar stars, and 2 Seyfert galaxies. Up
to 49 sources in our spectroscopic sample do not show any optical
counterpart, and most of them are suggested to be heavily obscured
post-AGB stars, rapidly evolving on their way to becoming planetary
nebulae.<BR /> Conclusions: .An analysis of the galactic distribution
of the sources identified as evolved stars in the sample is presented
together with a study of the distribution of these stars in the IRAS
two-colour diagram. Finally, the spectral type distribution and other
properties of the sources identified as post-AGB in this spectroscopic
survey are discussed in the framework of stellar evolution.
---------------------------------------------------------
Title: Planetary Nebulae abundances and stellar evolution
Authors: Pottasch, S. R.; Bernard-Salas, J.
2006IAUJD...4E..38P Altcode:
A summary is given of planetary nebulae abundances from ISO
measurements. It is shown that these nebulae show abundance gradients
(with galactocentric distance), which in the case of neon, argon,
sulphur and oxygen (with four exceptions) are the same as HII
regions and early type star abundance gradients. The abundance of
these elements predicted from these gradients at the distance of
the Sun from the center are exactly the solar abundance. Sulfur is
the exception to this; the reason for this is discussed. The higher
solar neon abundance is confirmed; this is discussed in terms of
the results of helioseismology. Evidence is presented for oxygen
destruction via ON cycling having occurred in the progenitors of four
planetary nebulae with bi-lobal structure. These progenitor stars had
a high mass, probably greater than 5M_smallsun. This is deduced from
the high values of He/H and N/H found in these nebulae. Formation of
nitrogen, helium and carbon are discussed. The high mass progenitors
which showed oxygen destruction are shown to have probably destroyed
carbon as well. This is probably the result of hot bottom burning.
---------------------------------------------------------
Title: Revealing the nature of Bulge Planetary Nebulae
Authors: Houck, James R.; Bernard-Salas, Jeronimo; Morris, Patrick W.;
Pottasch, Stuart R.; Sloan, Greg C.
2006sptz.prop30550H Altcode:
We propose observing a sample of 11 bulge planetary nebulae using the
IRS spectrograph on board Spitzer. The goal is to study their chemical
composition and physical parameters in order to understand their
nature and evolution. Because of their brightness bulge planetary
nebulae are ideal to study the dynamics of the Galaxy and their
abundances can be used to determine the metallicity gradient toward
the Galactic Center. Despite their importance, the nature of these
objects is still not well understood. For instance, do the bulge
planetary nebulae belong to an old population or are they part of a
population with recent star formation? One way to study this problem is
by simply deriving the abundances of certain elements, like sulfur and
argon. These elements are neither produced nor destroyed in the course
of evolution and therefore represent the composition at the time of
star formation. Abundance determination of these elements have been
attempted but sulfur and argon emit most of their lines in the IR,
and therefore optical or UV studies have been inconclusive. Spitzer
posseses the ideal wavelength coverage to obtain accurate abundances
for these elements and give a good insight in the evolutionary and
nucleosynthesis properties of the stellar progenitors. Moreover,
it's sensitivity allows one to observe these objects in very short
integration times, and for the first time have a look into the dust
of these objects in a metal--rich environment in our own Galaxy. In
the same framework of study we have included in this sample a very
interesting PN (NGC3132) which doesn't belong to the bulge but which
shows very unusual characteristics. This unusual behavior should be
studied in the infrared, both to study the dust and to account for
unseen ions to derive accurate abundances. Spitzer's spectra will
be of invaluable value obtain a consistent theoretical evolutionary
picture of these objects.
---------------------------------------------------------
Title: Infrared-Mapping of the extended planetary nebulae NGC2392
and NGC2346
Authors: Houck, James R.; Bernard-Salas, Jeronimo; Peeters, Els;
Pottasch, Stuart R.; Sloan, Greg C.; Smith, John-David
2006sptz.prop30482H Altcode:
We propose a pilot spectroscopic study of the extended PNe NGC2392
(classical spherical), and NGC2346 (classical bipolar) using the IRS
spectrograph on board Spitzer. The analysis will be done using CUBISM,
a tool developed for constructing spectral cubes, maps, and arbitrary
aperture 1D spectral extractions from IRS data. The main goal of this
proposal is to study the ionization structure of a PN and test whether
the assumptions of homogeneity often used in the literature is valid,
and to study the spatial behavior of dust features across an extended
planetary nebula. This pilot study will be of great value for the
interpretation of observations of the abundances and PAH emission
features in the wide range of objects that are known to show these
bands both in the near universe and in galaxies far away.
---------------------------------------------------------
Title: Spitzer-IRS's view of Halo PNe
Authors: Bernard-Salas, Jeronimo; Morris, Patrick W.; Peeters, Els;
Pottasch, Stuart R.
2006sptz.prop30652B Altcode:
We propose to observe a sample of 4 Halo planetary nebulae (PNe) using
the IRS spectrograph on board Spitzer. The planetary nebula phase is
ideal to obtain accurate abundances and the study of halo planetary
nebulae offers a great opportunity to understand the chemical evolution
of the Galactic halo which is still in debate. Halo PNe are very rare,
out of 2000 known PNe in the Galaxy only 10 belong to the halo. They
presumably have low progenitor masses and seem to show subsolar oxygen
abundance, as well as low abundance of other heavier elements. However,
several studies have clearly shown that the oxygen abundance can be
strongly affected by nucleosynthesis, rendering the Ar/O and S/O ratios
(often used in the literature) not useful. In addition, the study of
the abundance of sulfur and argon (elements not suppose to change
in the course of evolution of low- and intermediate-mass stars) is
hampered by the fact that these elements emit most of their energy in
the infrared. For these reasons, The abundances variations from source
to source haven't been able to be confirmed. Ground based efforts have
been made to measure lines of these elements in the infrared, but only
in one halo PN this has been successful. The IRS spectrograph on board
the Spitzer Space Telescope covers the ideal wavelength range where
most of the lines from these elements are emitted, plus it has the
superb sensitivity to study these objects. Because of this, Spitzer
provides an ideal opportunity to obtain accurate abundances and give
important insight in the halo composition. Moreover, the infrared
data offer a good opportunity to study the dust, and the halo PNe
provides a perfect laboratory to study the properties of the dust in
a low metallicity environment in our own Galaxy.
---------------------------------------------------------
Title: Abundances in planetary nebulae: <ASTROBJ>Mz 3</ASTROBJ>
Authors: Pottasch, S. R.; Surendiranath, R.
2005A&A...444..861P Altcode:
ISO spectra of the bipolar planetary nebula <ASTROBJ>Mz 3</ASTROBJ>
are used to determine the element abundances in the bright lobes
of the nebula. The ISO spectra alone are sufficient to determine
nitrogen, neon, argon, sulfur and iron abundances. These spectra are
combined with spectra in the visual wavelength region (taken from the
literature) to obtain an extinction corrected spectrum which is used
to determine the abundance of oxygen and some other elements using
a classical determination. We have tried abundance determination
using photoionization modeling using cloudy, which is essential
for determining the helium, silicon and chlorine abundances. It was
found difficult to model the entire spectrum. New information about
the central star could be determined. The abundances determined
are found to differ somewhat from earlier results using only visual
spectra. The reasons for this difference are discussed. An elevated
helium abundance is found, agreeing with the determination of Smith
2003. Taken together with the high nitrogen abundance found, it is
concluded that the exciting star of Mz 3 had a high progenitor mass.
---------------------------------------------------------
Title: Mid-IR Spectroscopy of Planetary Nebulae in the Large
Magellanic Cloud
Authors: Bernard-Salas, J.; Houck, J. R.; Pottasch, S. R.; Peeters, E.
2005AIPC..804...56B Altcode:
The use of infrared observations has improved the abundance
determination in galactic nebulae because it avoids/reduces many
problems usually encountered when deriving abundances using optical or
ultraviolet data. Furthermore, the peak of dust emission occurs in the
infrared and features such as PAHs and silicates can only be studied
in this part of the spectrum. The unprecedented sensitivity of the
Spitzer Space Telescope makes the study of planetary nebulae outside the
Milky Way in the infrared possible. We present the first results of the
guaranteed-time-observations program which has been designed to study
a number of planetary nebulae in the Large and Small Magellanic Clouds
using the Infrared Spectrograph on board the Spitzer Space Telescope.
---------------------------------------------------------
Title: Abundances of planetary nebulae <ASTROBJ>NGC 2022</ASTROBJ>,
<ASTROBJ>NGC 6818</ASTROBJ> and IC 4191
Authors: Pottasch, S. R.; Beintema, D. A.; Feibelman, W. A.
2005A&A...436..953P Altcode:
The ISO and IUE spectra of the elliptical nebulae <ASTROBJ>NGC 2022,
NGC 6818 and IC 4191</ASTROBJ> are presented. These spectra are combined
with the spectra in the visual wavelength region to obtain a complete,
extinction corrected, spectrum. The chemical composition of the
nebulae is then calculated and compared to previous determinations. A
discussion is also given of the exciting stars of the nebulae, and
possible evolutionary effects.
---------------------------------------------------------
Title: Abundances in planetary nebulae: <ASTROBJ>NGC 6886</ASTROBJ>
Authors: Pottasch, S. R.; Surendiranath, R.
2005A&A...432..139P Altcode:
ISO and IUE spectra of the round-shaped planetary nebula <ASTROBJ>NGC
6886</ASTROBJ> are combined with spectra in the visual wavelength
region taken from the literature to obtain a complete, extinction
corrected spectrum from ultraviolet to infrared wavelengths. The
characteristics of the nebula and its central star are determined by
various methods including photoionization modeling using Cloudy. The
results of the modeling are checked against the observational data and
compared to those derived from a more classical abundance determination
approach. The abundances determined are found to differ substantially
from earlier results although the observations used are essentially the
same, except for the inclusion of the ISO results. The reasons for this
difference are discussed. Finally, the main results are interpreted in
terms of the evolutionary stage of <ASTROBJ>NGC 6886</ASTROBJ> and its
central star. <P />Based on observations with ISO, an ESA project with
instruments funded by ESA Member States (especially the PI countries:
France, Germany, The Netherlands and the UK) and with the participation
of ISAS and NASA. This work has also used IUE and HST archival data.
---------------------------------------------------------
Title: Photoionization model analysis of the planetary nebula
<ASTROBJ>Hu1-2</ASTROBJ>
Authors: Hyung, S.; Pottasch, S. R.; Feibelman, W. A.
2004A&A...425..143H Altcode:
We have obtained high resolution optical spectra of the planetary
nebula <ASTROBJ>Hu 1-2</ASTROBJ> in the wavelength region of 3700
Å-10 050 Å, with the Hamilton Echelle Spectrograph (HES) at Lick
Observatory. Diagnostic analysis indicates that the nebular gas can be
represented by inhomogeneous shells of electron density N<SUB>ɛ</SUB>
≃ 4000-10 000 cm<SUP>-3</SUP>, and a gas temperature of 12 000-18
000 K. Using the spherically symmetric photoionization model with
appropriate abundances, we tried to accommodate the observed physical
conditions and high electron temperatures. The chemical composition of
the nebula was derived from calculations using a photoionization model
which predicts the observed IUE, HES and ISO line intensities; and the
composition was then compared to previous determinations. Model analysis
confirms the semi-empirically determined abundance derivations carried
out in earlier studies. He and N abundances are high, but those of C,
O, Ne and S are very low. <P />Table \ref{tab3} is only available in
electronic form at http://www.edpsciences.org
---------------------------------------------------------
Title: Spitzer Infrared Spectrograph (IRS) Observations of Large
Magellanic Cloud Planetary Nebula SMP 83
Authors: Bernard-Salas, J.; Houck, J. R.; Morris, P. W.; Sloan, G. C.;
Pottasch, S. R.; Barry, D. J.
2004ApJS..154..271B Altcode:
The first observations of the infrared spectrum of the LMC planetary
nebula SMP 83 as observed by the recently launched Spitzer Space
Telescope are presented. The high-resolution (R~600) spectrum shows
strong emission lines but no significant continuum. The infrared
fine-structure lines are used, together with published optical spectra,
to derive the electron temperature of the ionized gas for several
ions. A correlation between the electron temperature and the ionization
potential is found. Ionic abundances for the observed infrared ions
have been derived, and the total neon and sulfur abundances have been
determined. These abundances are compared to average LMC abundances
of H II regions in order to better understand the chemical evolution
of these elements. The nature of the progenitor star is also discussed.
---------------------------------------------------------
Title: Abundances of Planetary Nebulae <ASTROBJ>IC 418, IC 2165 and
NGC 5882</ASTROBJ>
Authors: Pottasch, S. R.; Bernard-Salas, J.; Beintema, D. A.;
Feibelman, W. A.
2004A&A...423..593P Altcode:
The ISO and IUE spectra of the elliptical nebulae <ASTROBJ>NGC 5882,
IC 418 and IC 2165</ASTROBJ> are presented. These spectra are combined
with the spectra in the visual wavelength region to obtain a complete,
extinction corrected, spectrum. The chemical composition of the
nebulae is then calculated and compared to previous determinations. A
discussion is given of: (1) the recombination line abundances; (2)
the exciting stars of the nebulae; and (3) possible evolutionary
effects. <P />Based on observations with ISO, an ESA project with
instruments funded by ESA Member States (especially the PI countries:
France, Germany, The Netherlands and the United Kingdom) and with the
participation of ISAS and NASA.
---------------------------------------------------------
Title: Abundances in planetary nebulae: <ASTROBJ>Me 2-1</ASTROBJ>
Authors: Surendiranath, R.; Pottasch, S. R.; García-Lario, P.
2004A&A...421.1051S Altcode: 2004astro.ph..6534S
ISO and IUE spectra of the round planetary nebula <ASTROBJ>Me
2-1</ASTROBJ> are combined with visual spectra taken from the
literature to obtain for the first time a complete extinction-corrected
spectrum. With this, the physico-chemical characteristics of the nebula
and its central star are determined by various methods including
photoionization modeling using Cloudy. The results of the modeling
are compared to those derived from a more classical, simple abundance
determination approach. A discussion is presented on the validity of the
different methods used and assumptions made. Finally, the main results
are interpreted in terms of the evolutionary stage of <ASTROBJ>Me
2-1</ASTROBJ> and its central star. <P />Based on observations with ISO,
an ESA project with instruments funded by ESA Member States (especially
the PI countries: France, Germany, The Netherlands and the UK) and
with the participation of ISAS and NASA. This research has also used
archival IUE and HST data. <P />Tables \ref{tab-4} and \ref{tab-7}
are only available in electronic form at http://www.edpsciences.org
---------------------------------------------------------
Title: IRS observations of the LMC planetary nebula SMP83
Authors: Bernard-Salas, J.; Houck, J. R.; Morris, P. W.; Sloan, G. C.;
Pottasch, S. R.; Barry, D. J.
2004astro.ph..6170B Altcode:
The first observations of the infrared spectrum of the LMC planetary
nebula SMP83 as observed by the recently launched Spitzer Space
Telescope are presented. The high resolution R~600 spectrum shows
strong emission lines but no significant continuum. The infrared fine
structure lines are used, together with published optical spectra,
to derive the electron temperature of the ionized gas for several
ions. A correlation between the electron temperature with ionization
potential is found. Ionic abundances for the observed infrared ions
have been derived and the total neon and sulfur abundances have been
determined. These abundances are compared to average LMC abundances
of HII regions to better understand the chemical evolution of these
elements. The nature of the progenitor star is also discussed.
---------------------------------------------------------
Title: Abundances of planetary nebulae NGC 40 and NGC 6153
Authors: Pottasch, S. R.; Bernard-Salas, J.; Beintema, D. A.;
Feibelman, W. A.
2003A&A...409..599P Altcode:
The ISO and IUE spectra of the elliptical nebulae NGC 40 and NGC 6153
are presented. These spectra are combined with the spectra in the
visual wavelength region to obtain a complete, extinction corrected,
spectrum. The chemical composition of the nebulae is then calculated
and compared to previous determinations. A discussion is given of:
(1) the recombination line abundances, (2) the exciting stars of
the nebulae, and (3) possible evolutionary effects. <P />Based on
observations with ISO, an ESA project with instruments funded by
ESA Member States (especially the PI countries: France, Germany,
The Netherlands and the UK) and with the participation of ISAS and NASA.
---------------------------------------------------------
Title: Probing AGB nucleosynthesis via accurate Planetary Nebula
abundances
Authors: Marigo, P.; Bernard-Salas, J.; Pottasch, S. R.; Tielens,
A. G. G. M.; Wesselius, P. R.
2003A&A...409..619M Altcode: 2003astro.ph..7252M
The elemental abundances of ten planetary nebulae, derived with high
accuracy including ISO and IUE spectra, are analysed with the aid of
synthetic evolutionary models for the TP-AGB phase. The accuracy on the
observed abundances is essential in order to make a reliable comparison
with the models. The advantages of the infrared spectra in achieving
this accuracy are discussed. Model prescriptions are varied until we
achieve the simultaneous reproduction of all elemental features, which
allows placing important constraints on the characteristic masses and
nucleosynthetic processes experienced by the stellar progenitors. First
of all, it is possible to separate the sample into two groups of PNe,
one indicating the occurrence of only the third dredge-up during the
TP-AGB phase, and the other showing also the chemical signature of
hot-bottom burning. The former group is reproduced by stellar models
with variable molecular opacities (see Marigo \cite{Marigo2002}),
adopting initial solar metallicity, and typical efficiency of the
third dredge-up, lambda ~ 0.3-0.4. The latter group of PNe, with
extremely high He content (0.15 <=He/H <=0.20) and marked
oxygen deficiency, is consistent with original sub-solar metallicity
(i.e. LMC composition). Moreover, we are able to explain quantitatively
both the N/H-He/H correlation and the N/H-C/H anti-correlation, thus
solving the discrepancy pointed out long ago by Becker & Iben
(\cite{Becker1980}). This is obtained only under the hypothesis that
intermediate-mass TP-AGB progenitors (M >~ 4.5-5.0 M<SUB>sun</SUB>)
with LMC composition have suffered a number of very efficient,
carbon-poor, dredge-up events. Finally, the neon abundances of the
He-rich PNe can be recovered by invoking a significant production of
<SUP>22</SUP>Ne during thermal pulses, which would imply a reduced
role of the <SUP>22</SUP>Ne(alpha , n)<SUP>25</SUP>Mg reaction as
neutron source to the s-process nucleosynthesis in these stars.
---------------------------------------------------------
Title: Abundances of Planetary Nebulae <ASTROBJ>BD+30 3639</ASTROBJ>
and <ASTROBJ>NGC 6543</ASTROBJ>
Authors: Bernard-Salas, J.; Pottasch, S. R.; Wesselius, P. R.;
Feibelman, W. A.
2003A&A...406..165B Altcode:
Infrared spectra taken with the Short Wavelength Spectrometer on board
ISO and UV observations with IUE of planetary nebulae <ASTROBJ>BD+30
3639</ASTROBJ> and <ASTROBJ>NGC 6543</ASTROBJ> are presented. The
extinction derived using infrared lines for <ASTROBJ>BD+30
3639</ASTROBJ> is E<SUB>B-V</SUB>= 0.34, slightly higher than previous
determinations. For <ASTROBJ>NGC 6543</ASTROBJ> the extinction found
from the hydrogen lines is E<SUB>B-V</SUB>= 0.07. Infrared, optical and
ultraviolet data have been used to derive the physical parameters of
the nebula. <ASTROBJ>BD+30 3639</ASTROBJ> has an average T<SUB>e</SUB>=
8500 K and N<SUB>e</SUB>= 11 000 C<SUB>H_beta</SUB>m3. In the case of
<ASTROBJ>NGC 6543</ASTROBJ> a T<SUB>e</SUB> = 8200 K and N<SUB>e</SUB>
= 5000 C<SUB>H_beta</SUB>m3 have been found, in agreement with previous
determinations. The element abundances have been derived and compared
to those found in the Sun and O, B stars. This comparison gives a hint
of the mass of the progenitor stars from which they evolved. <P />Based
on observations with ISO, an ESA project with instruments funded by
ESA Member States (especially the PI countries: France, Germany, The
Netherlands and the United Kingdom) and with the participation of ISAS
and NASA.
---------------------------------------------------------
Title: Erratum: The ISO-SWS spectrum of planetary nebula <ASTROBJ>NGC
7027</ASTROBJ>
Authors: Bernard-Salas, J.; Pottasch, S. R.; Beintema, D. A.;
Wesselius, P. R.
2003A&A...406..175B Altcode:
Based on observations with ISO, an ESA project with instruments funded
by ESA Member States (especially the PI countries: France, Germany,
The Netherlands and UK) and with the participation of ISAS and NASA.
---------------------------------------------------------
Title: Abundances of the planetary nebula <ASTROBJ>Hu 1-2</ASTROBJ>
Authors: Pottasch, S. R.; Hyung, S.; Aller, L. H.; Beintema, D. A.;
Bernard-Salas, J.; Feibelman, W. A.; Klöckner, H. -R.
2003A&A...401..205P Altcode:
The ISO and IUE spectra of the “elliptical” nebula <ASTROBJ>Hu
1-2</ASTROBJ> are presented. These spectra are combined with new, high
resolution spectra in the visual wavelength region to obtain a complete,
extinction corrected, spectrum. The chemical composition of the nebula
is then calculated and compared to previous determinations. The
abundances determined are the lowest yet found in the analysis of
ISO data. The evolutionary significance is discussed. <P />Based
on observations with ISO, an ESA project with instruments funded by
ESA Member States (especially the PI countries: France, Germany, the
Netherlands and the United Kingdom) and with the participation of ISAS
and NASA.
---------------------------------------------------------
Title: CNO Abundances in Planetary Nebulae
Authors: Bernard-Salas, J.; Wesselius, P. R.; Pottasch, S. R.;
Marigo, P.
2003ASPC..304..163B Altcode: 2003cnou.conf..163B
No abstract at ADS
---------------------------------------------------------
Title: Abundances in Planetary Nebulae: Including ISO Results
(invited review)
Authors: Pottasch, S. R.; Beintema, D. A.; Bernard-Salas, J.;
Feibelman, W. A.
2003IAUS..209..353P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Accurate Abundances Determination of Planetary Nebulae
Authors: Bernard-Salas, J.; Pottasch, S. R.; Wesselius, P. R.;
Marigo, P.
2003IAUS..209..376B Altcode: 2003IAUS..209..376S
No abstract at ADS
---------------------------------------------------------
Title: Abundances of Planetary Nebula <ASTROBJ>NGC 5315</ASTROBJ>
Authors: Pottasch, S. R.; Beintema, D. A.; Bernard Salas, J.;
Koornneef, J.; Feibelman, W. A.
2002A&A...393..285P Altcode:
The ISO and IUE spectra of the elliptical nebula <ASTROBJ>NGC
5315</ASTROBJ> is presented. These spectra are combined with the
spectra in the visual wavelength region to obtain a complete, extinction
corrected, spectrum. The chemical composition of the nebulae is then
calculated and compared to previous determinations. The HST NICMOS
observations of the nebula in 3 emission lines are also presented. These
observations are used to determine the helium abundance as a function of
position in the nebula. A discussion is given of possible evolutionary
effects. Based on observations with ISO, an ESA project with instruments
funded by ESA Member States (especially the PI countries: France,
Germany, The Netherlands and the UK) and with the participation of
ISAS and NASA.
---------------------------------------------------------
Title: An ISO and IUE study of planetary nebula <ASTROBJ>NGC
2440</ASTROBJ>
Authors: Bernard Salas, J.; Pottasch, S. R.; Feibelman, W. A.;
Wesselius, P. R.
2002A&A...387..301B Altcode:
The infrared and ultraviolet spectra of planetary nebula <ASTROBJ>NGC
2440</ASTROBJ> are presented. The observations were made by the Infrared
Space Observatory (ISO) and the International Ultraviolet Explorer
(IUE). These data, in conjunction with published optical observations
have been used to derive electron temperature and density. The electron
temperature increases with increasing ionization potential, from 11
000 to 18 000 K. The electron density has a constant value of 4500
C_H<SUB>beta </SUB>m3 in agreement with previous determinations. The
chemical abundance has been derived for the following elements; helium,
carbon, nitrogen, oxygen, neon, sulfur and argon. The ionization
correction factor turns out to be very small for all species except
sulfur. Based on observations with ISO, an ESA project with instruments
funded by ESA Member States (especially the PI countries: France,
Germany, The Netherlands and the UK) and with the participation of
ISAS and NASA.
---------------------------------------------------------
Title: Chemical Composition of Planetary Nebulae: Including ISO
Results
Authors: Pottasch, S. R.; Beintema, D. A.; Bernard Salas, J.;
Feibelman, W. A.
2002RMxAC..12..100P Altcode:
The method of determining abundances using Infrared Space Observatory
spectra is discussed. The results for seven planetary nebula are
given. Using these data, a preliminary discussion of their evolution
is given.
---------------------------------------------------------
Title: Physics and Chemistry of Planetary Nebulae with ISO-SWS
Authors: Bernard Salas, J.; Hony, S.; Pottasch, S. R.; Wesselius,
P. R.; Beintema, D. A.
2002RMxAC..12..160B Altcode:
Infrared spectra of the four planetary nebulae, NGC7027, BD+303639,
NGC6153 and NGC6543 have been taken by the ISO Short Wavelength
Spectrometer (SWS). These ISO data have been complemented with the
already existing optical and ultraviolet observations. By comparing
the nebular abundances for NGC7027 and BD+303639 with those given by
new theoretical evolutionary models, the mass of the progenitor star
of these nebulae has been constrained.
---------------------------------------------------------
Title: Planetary nebulae
Authors: Pottasch, S. R.
2002css1.book..913P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Abundances of planetary nebulae <ASTROBJ>NGC 7662</ASTROBJ>
and <ASTROBJ>NGC 6741</ASTROBJ>
Authors: Pottasch, S. R.; Beintema, D. A.; Bernard Salas, J.;
Feibelman, W. A.
2001A&A...380..684P Altcode:
The ISO and IUE spectra of the elliptical nebulae <ASTROBJ>NGC
7662</ASTROBJ> and <ASTROBJ>NGC 6741</ASTROBJ> are presented. These
spectra are combined with the spectra in the visual wavelength region
to obtain a complete, extinction corrected, spectrum. The chemical
composition of the nebulae is then calculated and compared to previous
determinations. The abundances found are compared to determinations
made in other nebulae using ISO data. A discussion is given to see
if possible evolutionary effects can be found from the abundance
differences. Based on observations with ISO, an ESA project with
instruments funded by ESA Member States (especially the PI countries:
France, Germany, The Netherlands and the UK) and with the participation
of ISAS and NASA.
---------------------------------------------------------
Title: IUE and ISO observations of the bipolar proto-planetary nebula
Hen 401 (IRAS 10178-5958)
Authors: Parthasarathy, M.; García-Lario, P.; Gauba, G.; de Martino,
D.; Nakada, Y.; Fujii, T.; Pottasch, S. R.; San Fernández de
Córdoba, L.
2001A&A...376..941P Altcode:
We present ultraviolet (IUE) and infrared (ISO) observations of the
bipolar proto-planetary nebula Hen 401 which, combined with previously
available optical and near infrared data, are used to reconstruct the
overall spectral energy distribution from 1150 Å to 100 mu m. The ISO
spectrum is dominated by strong PAH emission superimposed on a very
cold continuum which is interpreted as thermal emission originating in
the C-rich cool dust ( ~ 106 K) present in the circumstellar envelope,
the remnant of the previous AGB phase. In addition, a second, hotter
component detected in the near infrared is attributed to thermal
emission from hot dust ( ~ 640 K), suggesting that mass loss and dust
grain formation is still on-going during the current post-AGB phase. The
ultraviolet (IUE) spectrum shows a stellar continuum in the wavelength
interval 2400 Å to 3200 Å which corresponds to a moderately reddened
B8-type central star. Unexpectedly, the UV flux in the wavelength
interval 1150 Å to 1900 Å is very weak or absent with no evidence of a
hotter binary companion which could explain the detection of the nebular
emission lines observed in the available ground-based optical spectra
of Hen 401. HST WFPC2 high resolution images also show no indication
of a hot companion to the B8-type central star observed both in the
optical and in the UV. The evolutionary implications of a possible
single nature for the central star of Hen 401 are discussed. Based on
observations obtained with the International Ultraviolet Explorer,
retrieved from the INES Archive at VILSPA, Madrid, Spain, and
observations made with ISO, an ESA project with instruments funded
by ESA Member States (especially the PI countries: France, Germany,
The Netherlands and the UK) with the participation of ISAS and NASA.
---------------------------------------------------------
Title: Optical Survey of Post-AGB Candidates
Authors: Manchado, Arturo; Suárez, Olga; García-Lario, Pedro;
Manteiga, Minia; Pottasch, Stuart R.
2001ASSL..265...21M Altcode: 2001pao..conf...21M
Over the past 12 years we have been conducting a survey of IRAS (PSC)
sources with dust temperatures between 100 and 250 K, which is the
temperature of AGB shells after mass loss has ceased. About 1000
PSC sources fulfill this criterion, about half of them identified
previously in the literature: most are PNe (49%) and post-AGB stars
(27%), but there is also a small fraction of young stellar objects
and active galaxies. In order to classify the unidentified sources,
we took low resolution spectra of these objects, in the range from
3500 to 9000 Å. The region between 3600 and 5050 Å has been used
to carry out the spectral classification of most of the unidentified
sources. Partial results are presented here: of the 187 objects studied,
34 were PNe, 10 proto-PNe and 103 post-AGB candidates with or without
Hα emission. The rest have been identified as young stellar objects
(34), LBVs (2), and active galaxies (3).
---------------------------------------------------------
Title: Spectroscopy of Post-AGB A-Supergiant HD 101584 (IRAS
11385-5517)
Authors: Sivarani, T.; Parthasarathy, M.; García-Lario, P.; Manchado,
A.; Pottasch, S. R.
2001ASSL..265..295S Altcode: 2001pao..conf..295S
In the high resolution optical spectra we identified forbidden lines
of [OI] and [CI], which indicate the presence of low excitation
nebula. There are many emission lines due forbidden and permitted
lines of neutral and singly ionised metals. The Hα, FeII 6383Å,
NaI D<SUB>1</SUB>, D<SUB>2</SUB> lines and the CaII IR triplet lines
show P-Cygni profiles indicating a mass outflow. From the spectrum
synthesis analysis of NI lines, we find the atmospheric parameters
to be T<SUB>eff</SUB> = 8500K, log g = 1.5, V<SUB>turb</SUB> =
13km/s<SUP>-1</SUP> and [Fe/H] = 0.0. Carbon and nitrogen are found to
be overabundant. From the analysis of Fe emission lines and forbidden
lines, we derived T<SUB>exi</SUB> = 6100K +/- 200 for the emission
line region.
---------------------------------------------------------
Title: The ISO-SWS spectrum of planetary nebula <ASTROBJ>NGC
7027</ASTROBJ>
Authors: Bernard Salas, J.; Pottasch, S. R.; Beintema, D. A.;
Wesselius, P. R.
2001A&A...367..949B Altcode: 2001A&A...367..949S
We present the infrared spectrum of the planetary nebula <ASTROBJ>NGC
7027</ASTROBJ> observed with the Short Wavelength Spectrometer
(SWS), on board the Infrared Space Observatory (ISO). These data
allow us to derive the electron density and, together with the IUE
and optical spectra, the electron temperature for several ions. The
nebular composition has been determined, the evolutionary status of the
central star is discussed and the element depletion in the nebula is
given. We conclude that the progenitor was a C-rich star with a mass
between 3 and 4 M<SUB>sun</SUB>. Based on observations with ISO, an
ESA project with instruments funded by ESA Member States (especially
the PI countries: France, Germany, The Netherlands and the UK) and
with the participation of ISAS and NASA.
---------------------------------------------------------
Title: VizieR Online Data Catalog: NIR photometry of IRAS sources. III
(Garcia-Lario+, 1997)
Authors: Garcia-Lario, P.; Manchado, A.; Pych, W.; Pottasch, S. R.
2000yCat..41260479G Altcode:
We present the near infrared photometry of a new sample of 225 IRAS
sources, many of them previously unidentified in the literature,
selected because their far infrared colours are similar to those
shown by known planetary nebulae. The results obtained are used to
establish the main source of near infrared emission. Combining this
information with the far infrared IRAS data and a few additional
criteria we determine the nature and evolutionary stage of
all the sources observed so far, including those for which near
infrared photometry was previously reported in Papers I (Manchado
et al., 1989A&A...214..139M) and II (Garcia-Lario et al.,
1990A&AS...82..497G). (5 data files).
---------------------------------------------------------
Title: The Refereeing System in Astronomy
Authors: Pottasch, Stuart R.
2000ASSL..256..111P Altcode: 2000osa1.book..111P
No abstract at ADS
---------------------------------------------------------
Title: Abundances in Planetary Nebulae: ISO spectra
Authors: Pottasch, S. R.; Beintema, D. A.
2000ign..confE..45P Altcode:
The far infrared spectra of planetary nebulae have several important
advantages. First, these spectral lines originate from levels so
close to the ground level that the electron temperature (and possible
temperature fluctuations) is unimportant. The resultant ionic abundances
are thus independent of temperature. Second,there are many ions
present which are not found in other observed spectral regions. Used
in conjunction with the visual and ultraviolet observations, many
more ions of a given element are present. This reduces the necessity
to use 'ionization correction factors'. For several elements they
are unimportant. This makes abundance determinations much more
reliable. When both infrared lines and optical or UV lines of the
same ion are present, both the ion abundance and the average electron
temperature for that particular ion can be determined. In this way
a plot of the electron temperature against ionization potential can
be made, which helps greatly in determining abundances of ions not
represented in the infrared. Results are given for seven nebulae, and
are compared to other recent abundance determinations. It is shown
that earlier determinations are sometimes in error: sometimes by a
factor 1.5 to 2, occasionally by almost an order of magnitude.
---------------------------------------------------------
Title: Abundance in the planetary nebulae NGC 6537 and He2-111
Authors: Pottasch, S. R.; Beintema, D. A.; Feibelman, W. A.
2000A&A...363..767P Altcode:
The ISO and IUE spectra of the bipolar planetary nebulae NGC 6537 and
He2-111 are presented. These spectra are combined with the spectrum
in the visual wavelength region from the nebulae to obtain a complete
spectrum that is corrected for extinction. The chemical abundance of the
nebulae is then determined and compared to previous determinations. The
abundance of the two nebulae is quite similar. A comparison is then
made with the abundance of two other bipolar planetary nebulae whose
abundance is also determined with the help of ISO observations. It
is shown that not all bipolar nebulae have similar abundance. NGC
6445 has a much lower nitrogen to oxygen ratio, similar to NGC 7027,
but still not as low as the Orion nebula.
---------------------------------------------------------
Title: The ISO-SWS Line Spectrum of Planetary Nebula NGC 7027
Authors: Bernard Salas, J.; Pottasch, S. R.; Beintema, D. A.;
Wesselius, P. R.
2000ESASP.456..175B Altcode: 2000ibp..conf..175B
We present the spectrum of the brightest planetary nebula NGC 7027 as
was observed by the Short Wavelength Spectrometer (SWS), on board the
Infrared Space Observatory (ISO). These data allows us to derive the
electron density, and in conjunction with the IUE and optical spectra,
we have derived the electron temperature for several ions. The nebular
composition has been determined, and a discussion of the evolutionary
status of the central star is given.
---------------------------------------------------------
Title: The central star of the Planetary Nebula NGC 6537
Authors: Pottasch, S. R.
2000A&A...362L..17P Altcode:
The fact that Space Telescope WFPC2 images of the planetary nebula
NGC 6537 fail to show the central star is used to derive a limit
to its magnitude: it is fainter than a magnitude of 22.4 in the
visible. This is used to derive a lower limit to the temperature of
the star. The Zanstra temperature is at least 500 000 K. The Energy
Balance temperature is found to be consistent with this value, as
is the ionization state of the nebula. Assuming a reasonable range
of distances for the nebula, the radius of the star can be found. It
is consistent with the mass-radius relation of a white dwarf of 0.9
M<SUB>sun</SUB> or higher.
---------------------------------------------------------
Title: Properties of Dust Grains in Planetary Nebulae. I. The Ionized
Region of NGC 6445
Authors: van Hoof, Peter A. M.; Van de Steene, Griet C.; Beintema,
Douwe A.; Martin, P. G.; Pottasch, Stuart R.; Ferland, Gary J.
2000ApJ...532..384V Altcode: 1999astro.ph.10400V
One of the factors influencing the spectral evolution of a planetary
nebula is the fate of the dust grains that are emitting the infrared
continuum. Several processes have been proposed that either destroy
the grains or remove them from the ionized region. To test whether
these processes are effective, we study new infrared spectra of the
evolved nebula NGC 6445. These data show that the thermal emission
from the grains is very cool and has a low flux compared to Hβ. A
model of the ionized region is constructed, using the photoionization
code CLOUDY 90.05. Based on this model, we show from depletions in the
gas-phase elements that little grain destruction can have occurred in
the ionized region of NGC 6445. We also argue that dust-gas separation
in the nebula is not plausible. The most likely conclusion is that
grains are residing inside the ionized region of NGC 6445 and that
the low temperature and flux of the grain emission are caused by the
low luminosity of the central star and the low optical depth of the
grains. This implies that the bulk of the silicon-bearing grains in
this nebula were able to survive exposure to hard-UV photons for at
least several thousands of years, contradicting previously published
results. A comparison between optical and infrared diagnostic line
ratios gives a marginal indication for the presence of a t<SUP>2</SUP>
effect in the nebula. However, the evidence is not convincing and the
differences could also be explained by uncertainties in the absolute
flux calibration of the spectra, the aperture corrections that have
been applied, or the collisional cross sections. The photoionization
model allows an accurate determination of the central star temperature
based on model atmospheres. The resulting value of 184 kK is in good
agreement with the average of all published Zanstra temperatures
based on blackbody approximations. The off-source spectrum taken
with LWS clearly shows the presence of a warm cirrus component with a
temperature of 24 K as well as a very cold component with a temperature
of 7 K. Since our observation encompasses only a small region of the
sky, it is not clear how extended the 7 K component is and whether it
contributed significantly to the Far-Infrared Absolute Spectrophotometer
(FIRAS) spectrum taken by COBE. Because our line of sight is in the
Galactic plane, the very cold component could be a starless core.
---------------------------------------------------------
Title: A spatio-kinematic study of the interaction of the planetary
nebula NGC 246 with the interstellar medium
Authors: Muthu, C.; Anandarao, B. G.; Pottasch, S. R.
2000A&A...355.1098M Altcode:
Spatio-Kinematic observations were made on NGC 246 in the [OIII]
5007 Å line using an Imaging Fabry-Perot Spectrometer. Evidence
for the deceleration effect was found in the leading edge of the
nebular shell, possibly due to its interaction with the interstellar
medium. Further, we show that the [OIII] electron temperature derived
from spectrographic data in the leading half is larger than that in
the trailing half possibly due to the compressional heating.
---------------------------------------------------------
Title: The UV (IUE) spectrum of the planetary nebula PC 11 (HD 149427)
Authors: Parthasarathy, M.; García-Lario, P.; Pottasch, S. R.;
de Martino, D.; Surendiranath, R.
2000A&A...355..720P Altcode:
The UV spectrum of PC 11 is found to show variations in the strength of
the O III] 1666Ä , N III] 1750Ä and C III] 1909Ä emission lines. The
detection of continuum emission in the wavelength interval 2650Ä to
3200Ä indicates that the central star of PC 11 has an early F-type
dwarf companion. The very low level of UV continuum in the wavelength
interval 1150Ä to 1900Ä and the non-detection of the central star in
the UV images recently taken with HST suggest that the hot whitedwarf
or sub-dwarf like central star may be obscured by a dusty disk. The
variations in the UV emission lines observed during the period 1987
to 1994 may be the consequence of variable emission coming from
high-velocity jet-like emission visible in optical images also taken
with HST in the light of [O III]. Based on our UV observations, we
confirm our identification of PC 11 as a planetary nebula with a close
binary central star. Adopting the absolute magnitude of a F0V companion
yields a distance of 485 pc to PC 11. If we assume a typical expansion
velocity of 12.5 km s<SUP>-1</SUP> and considering the observed angular
diameter of the nebula (4.1<SUP>”</SUP>), we find the age of PC 11 to
be 376 years. The AGB phase of evolution of the central star seems to
have been terminated only recently. Based on observations obtained with
the International Ultraviolet Explorer, retrieved from the IUE Final
Archive at VILSPA and on observations made with the NASA/ESA Hubble
Space Telescope, obtained from the data Archive at the Space Telescope
Science Institute, which is operated by the Association of Universities
for Research in Astronomy, Inc., under NASA contract NAS5-26555
---------------------------------------------------------
Title: A Spatio-Kinematic Study of the Interaction of the PN NGC
246 with the Interstellar Medium
Authors: Muthu, C.; Anandarao, B. G.; Pottasch, S. R.
2000ASPC..199..317M Altcode: 2000apn..conf..317M
Spatio-Kinematic observations were made on NGC 246 in the [OIII]
5007Å line using an IFPS. Deceleration was detected in the leading
edge of the nebular shell, possibly due to its interaction with the
interstellar medium. Shell fragmentation and stopping time scales
are found to be larger than the nebular age. The electron temperature
derived from spectrographic data in the leading half is larger than
that in the trailing half due possibly to the compressional heating.
---------------------------------------------------------
Title: Abundances and Morphology in Planetary Nebulae
Authors: Pottasch, Stuart R.
2000ASPC..199..289P Altcode: 2000apn..conf..289P
The abundances of 16 well studied have been determined. New ISO
measurements have been combined with optical and ultraviolet data from
the literature, in an attempt to obtain accurate values. Only He, O,
C, N, Ne, Ar, and S are considered. High values of N/O are sometimes,
but not always, found in bipolar nebulae. On the other hand, some
bipolar nebulae show low values of N/O, and it is concluded that no
simple relationship between morphology and composition exists.
---------------------------------------------------------
Title: The history of the creation of Astronomy and Astrophysics.
Authors: Pottasch, S. R.
1999A&A...352..349P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The ISO spectrum of the planetary nebula NGC
6302. I. Observations
Authors: Beintema, D. A.; Pottasch, S. R.
1999A&A...347..942B Altcode:
The spectrum of the planetary nebula NGC 6302 is presented, as it was
observed by the ISO short-wavelength spectrometer. The IUE spectrum
observed at the same position with the same aperture is also presented.
---------------------------------------------------------
Title: The ISO spectrum of the planetary nebula NGC 6302. II. Nebular
abundances
Authors: Pottasch, S. R.; Beintema, D. A.
1999A&A...347..975P Altcode:
The ISO spectrum of NGC 6302 is used, in conjunction with the visible
and ultraviolet spectrum, to determine the nebular composition. In
addition to being considerably more accurate than previous
determinations, the abundances of many more elements (and ions) can
be found. A discussion of the previous evolution of the central star,
in the light of these abundances, is given. A discussion is also given
of the composition of the dust.
---------------------------------------------------------
Title: Spectroscopy of the post-AGB star HD 101584 (IRAS 11385-5517)
Authors: Sivarani, T.; Parthasarathy, M.; García-Lario, P.; Manchado,
A.; Pottasch, S. R.
1999A&AS..137..505S Altcode: 1999astro.ph..7310S
From an analysis of the spectrum (4000 Ä to 8800 Ä) of HD 101584 it
is found that most of the neutral and single ionized metallic lines are
in emission. The forbidden emission lines of [OI] 6300 Ä and 6363 Ä
and [CI] 8727 Ä are detected, which indicate the presence of a very
low excitation nebula. The Hα , FeII 6383 Ä, NaI D<SUB>1</SUB>,
D<SUB>2</SUB> lines and the CaII IR triplet lines show P-Cygni
profiles indicating a mass outflow. The Hα line shows many velocity
components in the profile. The FeII 6383 Ä also has almost the same
line profile as the Hα line indicating that they are formed in the same
region. From the spectrum synthesis analysis we find the atmospheric
parameters to be T_eff=8500 K, log g=1.5, V_turb=13 km s(-1) and [Fe/H]
= 0.0. From an analysis of the absorption lines the photospheric
abundances of some of the elements are derived. Carbon and nitrogen
are found to be overabundant. From the analysis of Fe emission lines
we derived T_exi=6100 K +/- 200 for the emission line region. Based
on observations obtained at the European Southern Observatory (ESO),
Chile and the Vainu Bappu Observatory, Kavalur, India.
---------------------------------------------------------
Title: Properties of the dust emission of the planetary nebula
NGC 6445
Authors: van Hoof, P. A. M.; van Steene, G. C.; Beintema, D. A.;
Martin, P. G.; Pottasch, S. R.; Ferland, G. J.
1999ESASP.427..417V Altcode: 1999usis.conf..417V
In this paper we present new infrared spectra of the planetary nebula
NGC 6445. These data show that the thermal emission from the grains
is unusually cool and has a very low flux compared to Hβ. A model
of the ionized region is constructed, using the photo-ionization code
Cloudy 90.05. Based on this model we show from depletions in the gas
phase elements that little grain destruction can have occurred in the
ionized region of NGC 6445. We also find that there is no indication
for dust-gas separation in the nebula. The most likely conclusion is
that grains are residing inside the ionized region of NGC 6445 and
that the low temperature and flux of the grain emission is caused by
the low luminosity of the central star and the low optical depth of
the grains. This implies that the grains in this nebula could survive
exposure to hard UV photons for at least several thousands of years.
---------------------------------------------------------
Title: A sample of planetary nebulae observed by HIPPARCOS
Authors: Acker, A.; Fresneau, A.; Pottasch, S. R.; Jasniewicz, G.
1998A&A...337..253A Altcode:
By using HIPPARCOS data (magnitudes, parallaxes, proper motions), (1)
we determine new values of the apparent luminosity of the central stars
of 19 planetary nebulae, (2) we discuss their distance and position
on the T/L diagram. By comparison with the distances determined by
individual or statistical methods, we see that most of these “ground"
distances look overestimated when we trust the HIPPARCOS trigonometric
parallaxes. It seems that for compact nebulae, the nebula itself could
influence the parallax measurement. In particular, the very small
HIPPARCOS distances to SwSt 1 and Hu 2-1 are unexpected and are not
trustworthy. Peculiar motions are analyzed, in terms of astrophysical
parameters of the binary system A 35, and in relation with asymmetric
morphology.
---------------------------------------------------------
Title: HST photometry of the stars near the center of PN NGC 650
Authors: Koornneef, J.; Pottasch, S. R.
1998A&A...335..277K Altcode:
Colours and magnitudes of the central star of NGC 650 and its two
companions have been obtained from HST images. The spectral types of
the companions, which have been deduced from the colours, suggest a
probable distance to the companions of between 5 and 6 kpc. Using the
spectral and photometric characteristics of the central star, which
are very similar to the very well studied PN PG 1159, we show that its
distance is probably close to 1.2 kpc. Thus it appears unlikely that
the central star is physically related to the two visible companions.
---------------------------------------------------------
Title: Crystalline silicates in planetary nebulae with [WC]
central stars
Authors: Waters, L. B. F. M.; Beintema, D. A.; Zijlstra, A. A.;
de Koter, A.; Molster, F. J.; Bouwman, J.; de Jong, T.; Pottasch,
S. R.; de Graauw, Th.
1998A&A...331L..61W Altcode: 1998astro.ph..2289W
We present ISO-SWS spectroscopy of the cool dusty envelopes surrounding
two Planetary Nebulae with [WC] central stars, BD+30 3639 and
He 2-113. The lambda < 15 mu m region is dominated by a rising
continuum with prominent emission from C-rich dust (PAHs), while the
long wavelength part shows narrow solid state features from crystalline
silicates. This demonstrates that the chemical composition of both
stars changed very recently (less than 1000 years ago). The most likely
explanation is a thermal pulse at the very end of the AGB or shortly
after the AGB. The H-rich nature of the C-rich dust suggests that the
change to C-rich chemistry did not remove all H. The present-day H-poor
[WC] nature of the central star may be due to extensive mass loss
and mixing following the late thermal pulse. Based on observations
with ISO, an ESA project with instruments funded by ESA Member States
(especially the PI countries: France Germany, the Netherlands and the
United Kingdom) and with the participation of ISAS and NASA
---------------------------------------------------------
Title: A comparison of HIPPARCOS parallaxes with planetary nebulae
spectroscopic distances
Authors: Pottasch, S. R.; Acker, A.
1998A&A...329L...5P Altcode:
The Hipparcos satellite has measured the parallax of a small sample
of planetary nebulae. In this paper we consider the results for 3
planetary nebulae (PN) for which spectroscopic distances have also
been determined from stellar gravities. These gravities in turn have
been derived from profile fitting of selected hydrogen and helium lines
(Mendez et al., 1988 a, b, 1992). A comparison of these distances shows
that the Hipparcos distances are all considerably smaller. This same
effect has been found in two other PN central stars, whose distance has
been determined from the VLA measured nebular expansion. The question
of the mass of the central star of PHL 932 is also discussed.
---------------------------------------------------------
Title: Near infrared photometry of IRAS sources with colours like
planetary nebulae. III
Authors: Garcia-Lario, P.; Manchado, A.; Pych, W.; Pottasch, S. R.
1997A&AS..126..479G Altcode:
We present the near infrared photometry of a new sample of 225 IRAS
sources, many of them previously unidentified in the literature,
selected because their far infrared colours are similar to those
shown by known planetary nebulae. The results obtained are used to
establish the main source of near infrared emission. Combining this
information with the far infrared IRAS data and a few additional
criteria we determine the nature and evolutionary stage of all the
sources observed so far, including those for which near infrared
photometry was previously reported in Papers I and II. Among
the unidentified IRAS sources in our sample we find only a small
percentage of planetary nebulae, many of them very young and dusty,
showing peculiar near infrared colours. Most of the new objects
observed in the near infrared are identified as transition objects
in the previous stages of the stellar evolution. Among them, we find
heavily obscured late-AGB stars, early post-AGB stars still obscured by
thick circumstellar envelopes which are probably the true progenitors
of planetary nebulae, and a significant fraction of stars with bright
optical counterparts showing little or no near infrared excess, which we
associate with highly evolved post-AGB stars with low mass progenitors,
which may never become planetary nebulae. In addition, we also find a
small percentage of young stellar objects, as well as a few Seyfert
galaxies. We conclude that, in most cases, based on near infrared
data alone, it is not possible to give a confident classification
of the unidentified IRAS source. However, the near infrared is shown
to be a powerful tool, specially when dealing with objects which are
heavily obscured in the optical. In this case, the detection of the
near infrared counterpart is the only way in which we can extend the
study of these sources to other spectral ranges and may be crucial
to understand the short-lived phase which precedes the formation of a
new planetary nebula. Based on observations collected at the European
Southern Observatory, La Silla (Chile) and at the Spanish Observatorio
del Teide, Tenerife, Spain. Table 6 is only available electronically
at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/Abstract.html
---------------------------------------------------------
Title: Abundances in planetary nebulae near the galactic
centre. I. Abundance determinations
Authors: Ratag, M. A.; Pottasch, S. R.; Dennefeld, M.; Menzies, J.
1997A&AS..126..297R Altcode: 1997A&AS..126..297M
Abundance determinations of about 110 planetary nebulae, which are
likely to be in the Galactic Bulge are presented. Plasma diagnostics
have been performed by making use of the available forbidden line ratios
combined with radio continuum measurements. Chemical abundances of
He, O, N, Ne, S, Ar, and Cl are then derived by employing theoretical
nebular models as interpolation devices in establishing the ionization
correction factors (ICFs) used to estimate the distribution of atoms
among unobserved ionization stages. The overall agreement between
the results derived by using the model-ICFs and those obtained from
the theoretical models is reasonably good. The uncertainties related
to the total abundances show a clear dependence on the level of
excitation. In most cases, the abundances of chlorine can be derived
only in objects with a relatively high Cl-abundance. Contrary to the
conclusion previously drawn by \cite[Webster (1988)]{we88}, we found
the excitation classes are not uniformly distributed. A clear peak at
about classes 5 and 6 is noticed. The distribution is shifted toward
a lower excitation range with respect to that of the nearby nebulae,
reflecting the difference in the central star temperature distribution
between the two samples.
---------------------------------------------------------
Title: A multiwavelength study of LS II+34 26: a hot post-AGB star
in the process of becoming a planetary nebula.
Authors: Garcia-Lario, P.; Parthasarathy, M.; de Martino, D.; Sanz
Fernandez de Cordoba, L.; Monier, R.; Manchado, A.; Pottasch, S. R.
1997A&A...326.1103G Altcode:
We present the results from a multiwavelength analysis of LS II+34
26, recently identified as a low mass post-AGB star and not a massive
population I B-type star, as previously thought. We confirm that the
central star is a carbon-poor post-AGB star surrounded by a very low
excitation and compact nebula. Spectroscopic monitoring carried out
since 1991 reveals variations which suggest that this star has had a
mass loss episode in the period 1993-1995. The asymmetric profiles in
a few absorption lines in high resolution optical spectra indicate the
presence of complex motions in the outer layers of the atmosphere. The
radial velocity variations (several tens of km/s) observed in spectra
taken in a single epoch can be attributed to stellar pulsation. For
a few lines stronger variations over the years (up to 70km/s) can
be explained if these lines are formed in the outflow. The anomalous
extinction observed in the UV suggests that part of the reddening is of
circumstellar origin and that the standard interstellar extinction law
is not applicable. On the other hand, the absence of a significant near
infrared excess in LS II+34 26 suggests that the mass loss enhancement
corresponds to a short-lived episode of modest intensity. Although
non-LTE effects prevent the accurate determination of the atmospheric
parameters and abundances of LS II+34 26, a comparative analysis with
LS IV-12 111 indicates that both stars are very similar. Both are
identified as low mass carbon-poor hot post-AGB stars belonging to
the halo population of our Galaxy.
---------------------------------------------------------
Title: The changeover from H to He rich mass loss in PN
Authors: Pottasch, Stuart
1997hst..prop.7837P Altcode: 1997hst..prop.4163P
We image three bright planetary nebulae, which have helium rich
stellar atmospheres and helium poor nebulae. However, we think that
the inner nebulae must be helium rich on a spatial scale that is very
accessible with the NIC1 camera on HST. We would expect the images
to show a helium-enriched shell on a scale of app. 1". If observed,
this would be the first observation of the changeover from hydrogen
rich mass loss to helium rich mass loss in planetary nebulae.
---------------------------------------------------------
Title: Comments on PN evolution (Invited Review)
Authors: Pottasch, S. R.
1997IAUS..180..483P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fading and variations in the spectrum of the central star of
the young Planetary Nebula SAO 244567 (Hen 1357)
Authors: Parthasarathy, M.; Garcia-Lario, P.; de Martino, D.; Pottasch,
S. R.; de Cordoba, S. F.
1997IAUS..180..123P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The central stars of the Planetary Nebulae NGC 7027 and
NGC 6S43
Authors: van Hoof, P. A. M.; Beintema, D. A.; Lahuis, F.; Pottasch,
S. R.
1997IAUS..180..134V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The SWS Line Spectrum of the Planetary Line Nebula NGC 6302
Authors: Pottasch, S. R.; Beintema, D.
1997ESASP.419...73P Altcode: 1997fiso.work...73P
A preliminary analysis is given of the emission line spectrum of the
planetary nebula NCC 6302, observed with the ISO Short-Wavelength
Spectrometer.
---------------------------------------------------------
Title: The central star of the planetary nebula NGC 6302.
Authors: Pottasch, S. R.; Beintema, D.; Dominguez-Rodriguez, F. J.;
Schaeidt, S.; Valentijn, E.; Vandenbussche, B.
1996A&A...315L.261P Altcode:
Selected results from the ISO spectrum of NGC 6302 are reported. The
intensity of the high ionization [Mg VIII] line is given. The
controversy concerning the mechanism of ionization of the high
ionization stages, and especially the [NeV] lines is discussed. It
is concluded that all lines can be reproduced in a photoionization
model, if the temperature of the central star is about 380,000 K. The
abundances of several elements in the nebula is given, as well as the
intensities of the lines involved.
---------------------------------------------------------
Title: The central stars of the planetary nebulae NGC 7027 and
NGC 6543.
Authors: Beintema, D. A.; van Hoof, P. A. M.; Lahuis, F.; Pottasch,
S. R.; Waters, L. B. F. M.; de Graauw, T.; Boxhoorn, D. R.;
Feuchtgruber, H.; Morris, P. W.
1996A&A...315L.253B Altcode: 1999astro.ph..6166B
Infrared spectra of NGC 7027 and NGC 6543 ranging from 2.4 to 45μm were
obtained with the Short Wavelength Spectrometer on board the Infrared
Space Observatory. A first analysis of these spectra, with the aid of
photo-ionization models, is presented. We report the first detection
of the [ArVI] 4.53μm and [NeVI] 7.65μm lines in the spectrum of
NGC 7027. When compared with older observations it is clear that the
[ArVI] line and possibly also other lines have increased in strength
since 1981. We argue that a likely explanation for this variability
is a change in the spectral energy distribution of the central star,
possibly an increase in effective temperature. However, this result
needs to be confirmed by further observations. We also report a
non-detection of the [OIV] 25.9μm line and the first detection of the
[NaIII] 7.32μm line in the spectrum of NGC 6543. The non-detection is
not expected based on a blackbody approximation for the spectrum of
the central star. The ionization threshold for O^3+^ is just beyond
the HeII limit, and the absence of this line shows that the stellar
flux drops at least by a factor 350 at the HeII limit. Modeling the
[OIV] line may prove to be a valuable test for atmosphere models.
---------------------------------------------------------
Title: Optical observations of southern planetary nebula candidates.
Authors: van de Steene, G. C.; Sahu, K. C.; Pottasch, S. R.
1996A&AS..120..111V Altcode:
We present Hα+[N II] images and low resolution spectra of 16
IRAS-selected, southern planetary nebula candidates previously detected
in the radio continuum. The Hα+[N II] images are presented as finding
charts. Contour plots are shown for the resolved planetary nebulae. From
these images mean optical angular diameters were determined. Optical
spectra show that these IRAS-selected and radio detected planetary
nebula candidates are indeed planetary nebulae. The values for their
extinction coefficient is generally very high. More than half of the
planetary nebulae seem to be of low excitation, having central stars
with an effective temperature of probably ~60000K or less.
---------------------------------------------------------
Title: Optical observations of planetary nebula candidates from the
northern hemisphere.
Authors: van de Steene, G. C.; Jacoby, G. H.; Pottasch, S. R.
1996A&AS..118..243V Altcode:
We present Hα+[N II] images of 17 and low resolution spectra of 14
IRAS-selected planetary nebula candidates. The Hα+[N II] images are
presented as finding charts. Contour plots are shown for the resolved
planetary nebulae. From these images accurate optical positions and
mean optical angular diameters were determined. Optical spectra show
that the IRAS-selected and radio detected planetary nebula candidates
are indeed planetary nebulae. Three planetary nebula candidates,
previously not detected in the radio continuum were seen in Hα . They
are larger, low surface brightness planetary nebulae. Most of these
IRAS planetary nebulae are heavily extinct, having an average A_V_
of 7 magnitudes. About half of the planetary nebulae seem to be of
low excitation, having central stars with an effective temperature
probably ~60.000 K or less.
---------------------------------------------------------
Title: Properties of planetary nebulae with WR central stars
(Invited paper)
Authors: Pottasch, Stuart R.
1996Ap&SS.238...17P Altcode:
A review of the observational properties of the Wolf-Rayet central
stars is given.
---------------------------------------------------------
Title: Local space density and formation rate of planetary nebulae.
Authors: Pottasch, S. R.
1996A&A...307..561P Altcode:
Individual distances of 50 nearby planetary nebulae are determined using
a variety of methods, but excluding statistical methods or distance
scales. These distances, together with a discussion of the sample
completeness, are used to determine local PN formation rate. Together
with the brightness of the nebula, its ionized mass is derived. The
evolution of the ionized mass is discussed. As a by-product, the
Zanstra temperature of the central stars of the optically thick
nebulae is found. Interestingly this temperature indicates that the
DA white dwarfs in the sample are considerably hotter than previously
thought. Finally, with the help of the galactic bulge PN, a luminosity
function for PN in the galaxy is derived.
---------------------------------------------------------
Title: IRAS 17423-1755: a massive post-AGB star evolving into the
planetary nebula stage?
Authors: Riera, A.; Garcia-Lario, P.; Manchado, A.; Pottasch, S. R.;
Raga, A. C.
1995A&A...302..137R Altcode:
IRAS 17423-1755 has been recognized as a new bipolar nebula during a
multi-wavelength observational program of unidentified IRAS sources with
far infrared colours similar to those of known planetary nebulae. B,
V, R and Hα CCD images show a clearly marked bipolar structure
with a total extension of ~11 arcsec. The spectrum of the core shows
strong emission lines of HI (Balmer and Paschen series), HeI, FeII,
[FeII], OI, CaII and [CaII]. Strong P-Cygni profiles are clearly seen
in the Balmer lines and in some other emission lines, indicating the
presence of a strong mass outflow. This is confirmed by the presence
of a very steep density gradient in the nebula, strong near infrared
excess and the detection of highly symmetric bipolar emission at very
large velocities in the lobes (>~425km/s). The highest velocity,
however, is observed in the innermost region of the bipolar outflow,
where a jet-like structure is detected with v=870km/s, while its
velocity decreases to 750km/s a few arcsecs away from the central
star. This has been interpreted as the result of sporadic mass loss
events with a time-dependent ejection velocity. The position-velocity
diagram is well reproduced assuming an inclination angle of 150deg. The
emission observed in the lobes shows an extraordinary line width
and double-peaked profiles, indicating that the emission arises from
the cooling region behind a bow-shock. From the high values of the
[NII]/Hα ratios, we deduce that the outflowing material is nitrogen
enriched gas of stellar origin, which can only be explained if IRAS
17423-1755 is an evolved star and not a young stellar object. The
morphology and kinematics closely resemble those observed in well
known bipolar proto-planetary nebulae, while the luminosity is far
below the values found in known LBV's (Luminous Blue Variables). The
characteristics of the OH maser emission found in IRAS 17423-1755 are
consistent with the presence of an equatorial disk of neutral material
(perpendicular to the bipolar axis) expanding at v_e_=50km/s, which
could be the responsible for the collimation of the outflow.
---------------------------------------------------------
Title: Fading and variations in the spectrum of the central star of
the very young planetary nebula SAO 244567 (Hen 1357).
Authors: Parthasarathy, M.; Garcia-Lario, P.; de Martino, D.; Pottasch,
S. R.; Kilkenny, D.; Martinez, P.; Sahu, K. C.; Reddy, B. E.; Sewell,
B. T.
1995A&A...300L..25P Altcode:
The optical spectrum of SAO 244567 obtained in 1971 shows that it
was a post-AGB B1 or B2 supergiant at that time. It has turned into a
planetary nebula (PN ) within the last 20 years. The IUE ultraviolet
spectra obtained during the last seven years show that the central
star is rapidly evolving. It is found that the central star of this
young PN has faded by a factor of 2.83 within the last seven years. The
terminal velocity of the stellar wind has decreased from -3500km/s in
1988 to almost zero in 1994. In 1988 the CIV (1550A) line which was a
P-Cygni profile with strong absorption component has almost vanished
by 1994. The UV absorption and nebular features show variations in
strength. This may be due to the fading of the central star and also
possibly to expansion of the nebula. These results suggest that in the
central star the nuclear fuel is almost extinct as a result of post-AGB
mass loss. The main stellar energy may be gravothermal energy. Typical
for hydrogen-burning AGB remnants is a very fast drop in luminosity
by an order of magnitude when the burning cannot be sustained any
longer. These results suggest that the central star of this young
PN is rapidly evolving to become a DA white dwarf. An alternative
interpretation is that the present fading could be due to an episode
of high mass loss, which is now just completed. If the ultraviolet
fading was a factor of 2.83 from 1988 to 1995, the luminosity would
remain the same if the temperature increased from 37500K to 47500K in
the same period. It may b that these changes occur in steps which are
triggered by episodic mass loss periods during the post-AGB evolution,
and that the hydrogen burning has not stopped or stopped temporarily.
---------------------------------------------------------
Title: Radio continuum observations of planetary nebula candidates
from the northern hemisphere.
Authors: van de Steene, G. C.; Pottasch, S. R.
1995A&A...299..238V Altcode:
We analyzed radio continuum observations of unidentified IRAS
point sources with far IR colors that are typical of planetary
nebulae. These IRAS-selected planetary nebula candidates are located
outside the galactic bulge and were observed with the Westerbork
Radio Synthesis Telescope. We have detected 20 new planetary nebulae
out of 82 observed candidates. The detected sources are very close to
the galactic plane. The detection rate is highest in that part of the
color-color diagram, where planetary nebulae are expected to spend most
time during their evolution. The radio and IR properties are compared
with PN detected in the same way in the galactic bulge and with optical
planetary nebulae which fulfill the same selection criteria. On average,
the IR excess of the IRAS-selected and radio detected planetary nebula
candidates is higher than for the optical planetary nebulae.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Radio observations of PN candidates
(Van de Steene+, 1995)
Authors: van de Steene, G. C.; Pottasch, S. R.
1995yCat..32990238V Altcode:
We analyzed radio continuum observations of unidentified IRAS
point sources with far IR colors that are typical of planetary
nebulae. These IRAS-selected planetary nebula candidates are located
outside the galactic bulge and were observed with the Westerbork
Radio Synthesis Telescope. We have detected 20 new planetary nebulae
out of 82 observed candidates. The detected sources are very close
to the galactic plane. The detection rate is highest in that part
of the color-color diagram, where planetary nebulae are expected to
spend most time during their evolution. The radio and IR properties
are compared with PN detected in the same way in the galactic bulge
and with optical planetary nebulae which fulfill the same selection
criteria. On average, the IR excess of the IRAS-selected and radio
detected planetary nebula candidates is higher than for the optical
planetary nebulae. <P />(2 data files).
---------------------------------------------------------
Title: Vier sterren die zichtbaar evolueren.
Authors: Pottasch, S.
1995Zenit..22....8P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Axial Symmetry in Planetary Nebulae
Authors: Pottasch, S. R.
1995AnIPS..11....7P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: VLA measurements of a sample of planetary nebulae.
Authors: Pottasch, S. R.; Zijlstra, A. A.
1994A&A...289..261P Altcode: 1994astro.ph..3062P
We report on new radio measurements of Galactic planetary nebulae,
aimed at resolving the controversies on the reliability of older
VLA flux densities and the suggested deviations from the standard
Galactic extinction law found for planetary nebulae. We show that
for faint (<10mJy) objects observed at high angular resolution,
previous determinations are indeed too low. For the bright objects we
find no significant differences. The new values are the most accurate
flux determinations yet for planetary nebulae, reaching 1% for the
brightest objects in the sample. Based on the new data, we confirm
that there is a systematic difference between the extinction derived
from the radio/Hβ flux ratio and derived from the Balmer decrement,
which led to the suggestion of deviations from the standard extinction
law. However, final confirmation of this has to await the availability
of more, accurate measurements of the Balmer (and/or Paschen) lines.
---------------------------------------------------------
Title: Adriaan Blaauw at 80.
Authors: Pottasch, S. R.
1994Msngr..76...62P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Nebular emission lines in IRAS 10215-5916
Authors: Garcia-Lario, P.; Manchado, A.; Parthasarathy, M.; Pottasch,
S. R.
1994A&A...285..179G Altcode:
From low and high resolution spectroscopic observations of IRAS
10215-5916 we have discovered the presence of nebular emission lines
in this G-type supergiant star in the post-AGB stage. From its high
resolution spectrum we derived an expansion velocity of 17 km/s for
the shell, similar to the values usually observed in planetary and
proto-planetary nebulae. The images taken in the near infrared show
that IRAS 10215-5916 is slightly extended and asymmetric. Although we
cannot rule out a possible binary nature for the central star of this
IRAS source, in which a hot component could be the responsible for the
observed nebular emission, no indications of binarity have been found
so far. We suggest that the observed spectrum and morphology could be
produced by the asymmetric mass loss of a single star in the post-AGB
phase. Post-AGB mass loss can play a fundamental role on shortening
the transition time towards the planetary nebula stage and favour
the formation of the bipolar structures commonly observed in evolved
planetary nebulae. In this sense, it is shown that this mass loss is
more intense and frequent for massive progenitors of PNe.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Radio observations of South. PN
Candidates (Van de Steene+ 1993)
Authors: van de Steene, G. C. M.; Pottasch, S. R.
1994yCat..32740895V Altcode:
IRAS sources having IR colours typical of planetary nebulae and located
outside the Galactic bulge were observed in the radio continuum at
6cm with the Australian Compact Array (ACA). 18 new planetary nebulae
were discovered among 89 candidates. The observations were performed
in March and April 1991. (2 data files).
---------------------------------------------------------
Title: Imaging and spectroscopy of Abell 63 (UU Sge).
Authors: Walton, N. A.; Walsh, J. R.; Pottasch, S. R.
1993A&A...275..256W Altcode:
UU Sge, the eclipsing binary central star of the low- surface-brightness
planetary nebula (PN) Abell 63, has been observed spectroscopically
in the visible throughout its 11.2 hour period and especially during
the minimum. A determination of the spectral types of the components
of the binary system has been made. The primary hot central star is an
`sdO' type PN nucleus of temperature ∼50 000 K, consistent with the
low excitation of the nebular spectrum. From the spectrum at minimum
light, the secondary star can be identified as a cool dwarf star
around late G, if on the main sequence. Measurement of the magnitude
of the secondary during the eclipse of the primary enabled an upper
limit to the distance to the PN to be directly determined as ∼3.6
kpc. For this distance the luminosity of the hot star is ∼2400
L<SUB>sun</SUB>, in agreement with evolutionary tracks for (single)
PN nuclei. Deep CCD images of Abell 63 reveal it to have a `butterfly'
morphology implying that the close binary central system may have had
a strong effect on the nebula shaping.
---------------------------------------------------------
Title: Radio continuum observations of southern planetary nebulae
candidates.
Authors: van de Steene, G. C. M.; Pottasch, S. R.
1993A&A...274..895V Altcode:
We report on radio continuum observations of unidentified IRAS
point sources with far IR colors that are typical of planetary
nebulae. These planetary nebulae candidates are located outside the
Galactic bulge and observable from the southern hemisphere. The IR
and radio properties of the observed and detected planetary nebulae
candidates are discussed. We have detected 18 new planetary nebulae
out of 89 observed candidates. These seem to belong to the class of
small, radio-bright planetary nebulae with IR excess, primarily found
within a few degrees of the Galactic plane. They appear to be quite
young planetaries.
---------------------------------------------------------
Title: Circumstellar dust in Mira variables and the mass loss
mechanisms.
Authors: Anandarao, B. G.; Pottasch, S. R.; Vaidya, D. B.
1993A&A...273..570A Altcode:
IRAS data on 92 oxygen-rich Mira variables are analysed to evaluate the
role of pulsations in mass loss among these stars. Using a radiative
model, equilibrium temperature, size, mass, and optical depth of
circumstellar dust shells have been estimated. A two-component dust
shell model was found necessary for fitting the photometric data. The
LRS data required only a single shell which agrees very well with the
inner hotter shell obtained from the photometric data. The mass of the
inner shell shows a positive correlation with the pulsation period while
that of the outer shell shows no such correlation. We suggest that the
outer shell is a result of the mass loss during the pre-AGB stage while
the inner shell represents AGB mass loss caused by pulsation with the
possible support of radiation pressure. Dust was estimated to condense
at ∼3-10R<SUB>*</SUB> lending support to the two-step process of mass
loss involving the pulsations and radiation pressure. The recently
reported variability of far infrared fluxes during pulsation period
does not seem to alter these results significantly.
---------------------------------------------------------
Title: High Velocity Outflows in IRAS 17423-1755
Authors: Riera, A.; Garcia-Lario, P.; Manchado, A.; Pottasch, S. R.
1993IAUS..155..348R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Effect of Mass Loss in the IRAS Two-Colour Diagram
Authors: García-Lario, P.; Manchado, A.; Pottasch, S. R.
1993ESOC...46..129G Altcode: 1993mlab.conf..129G
No abstract at ADS
---------------------------------------------------------
Title: On the Relation of Core Mass with Chemical Composition in PN
Authors: Pottasch, S. R.
1993IAUS..155..449P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: IRAS 06562-0337 : final mass-loss episodes before the formation
of a planetary nebula ?
Authors: Garcia-Lario, P.; Manchado, A.; Sahu, K. C.; Pottasch, S. R.
1993A&A...267L..11G Altcode:
The onset of forbidden line emission in the spectrum of a
proto-planetary nebula has been detected for the first time in the lapse
of only two years. IRAS 06562-0337 was first observed in December 1987
and October 1988, showing only the Balmer lines in emission. A third
spectrum obtained in February 1990 shows a quite different appearance,
with forbidden emission lines typical of a low excitation planetary
nebula. The effective temperature of the central star has clearly
increased over these two years. Another spectrum obtained in March
1992 however, shows that the forbidden lines have disappeared. This,
combined with the nature of the H-alpha profiles at different times,
reveals the episodic nature of the mass loss mechanism which most
likely precedes the formation of a planetary nebula.
---------------------------------------------------------
Title: Radio Continuum Observations of Southern Planetary Nebulae
Candidates
Authors: van de Steene, G. C.; Pottasch, S. R.
1993IAUS..155...40V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The IUE Ultraviolet Spectrum of PC 11
Authors: Parthasarathy, M.; Pottasch, S. R.; Clavel, J.
1993IAUS..155..398P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Spectroscopic Study of Binary Star Planetary Nebulae
Authors: Walsh, J. R.; Walton, N. A.; Pottasch, S. R.
1993IAUS..155..390W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A New Object in the Transition Phase Post-AGB to PN
Authors: Manchado, A.; García-Lario, P.; Sahu, K. C.; Pottasch, S. R.
1993ESOC...46..273M Altcode: 1993mlab.conf..273M
No abstract at ADS
---------------------------------------------------------
Title: Slowly Evolving Post-AGB Stars?
Authors: Oudmaijer, R. D.; Waters, L. B. F. M.; Pottasch, S. R.
1993ESOC...46..122O Altcode: 1993mlab.conf..122O
No abstract at ADS
---------------------------------------------------------
Title: A New Evolutionary Interpretation of the IRAS Two-Colour
Diagram
Authors: Garcia-Lario, P.; Manchado, A.; Pottasch, S. R.
1993IAUS..155..332G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Chemical Composition of Post-Agb Stars
Authors: Parthasarathy, M.; Garcia-Lario, P.; Pottasch, S. R.
1993ASPC...45..185P Altcode: 1993lhls.work..185P
No abstract at ADS
---------------------------------------------------------
Title: The Chemical Composition of POST AGB Stars
Authors: Parthasarathy, M.; Garcia-Lario, P.; Pottasch, S. R.
1993IAUS..155..352P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: SAO 244567 : a post-AGB star which has turned into a planetarey
nebula within the last 40 years.
Authors: Parthasarathy, M.; Garcia-Lario, P.; Pottasch, S. R.;
Manchado, A.; Clavel, J.; de Martino, D.; van de Steene, G. C. M.;
Sahu, K. C.
1993A&A...267L..19P Altcode:
SAO 244567 (Hen 1357 = CPD -59 deg 6926 = IRAS 17119-5926) is an
IRAS source with far infrared colors and flux distribution similar
to those of planetary nebulae. The IUE ultraviolet spectra obtained
in July 1988 and April 1992 show nebular emission lines, and also the
changes in the spectra suggest the formation of the planetary nebula
and the rapid evolution of the central star. The optical spectrum of
this star obtained by Henize around 1950 shows only the H-alpha line
in emission, while the most recent one, obtained in 1990 shows strong
forbidden emission lines corresponding to a low excitation and young
planetary nebula. The IUE ultraviolet spectra show evidence for the
presence of stellar wind and mass loss. The stellar lines show P-Cygni
type profiles and the terminal velocity of the stellar wind is about -
3000 km/s. The spectral type of the central star is O8 V. The presence
of a detached cold dust shell (125 K), high galactic latitude and
abundances suggest that SAO 244567 has recently evolved from a low or
intermediate mass progenitor star which has ejected its outer envelope
during the AGB stage of evolution and is rapidly evolving towards
hotter spectral types.
---------------------------------------------------------
Title: Last Stages of Stellar Evolution
Authors: Pottasch, Stuart R.
1993inas.conf...63P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Planetary and Proto-Planetary Nebulae in the IRAS Two-Colour
Diagram
Authors: Garcia-Lario, P.; Manchado, A.; Pottasch, S. R.
1993IAUS..155..331G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: IRAS10215-5916: A Post-AGB Star with Nebular Emission Lines
Authors: García-Lario, P.; Manchado, A.; Pottasch, S. R.
1993ESOC...46..262G Altcode: 1993mlab.conf..262G
No abstract at ADS
---------------------------------------------------------
Title: Imaging and Spectroscopy of Abell 63 (UU Sge)
Authors: Walton, N. A.; Walsh, J. R.; Pottasch, S. R.
1993IAUS..155..394W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Very Rapid-Evolving Young Planetary Nebula
Authors: Manchado, A.; Garcia-Lario, P.; Sahu, K. C.; Pottasch, S. R.
1993IAUS..155..357M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Kinematical Studies of Planetary Nebulae Using Taurus+CCD
Authors: Sahu, K. C.; Walsh, J. R.; Walton, N. A.; Pottasch, S. R.
1993IAUS..155..378S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The chemical composition of the high velocity POST AGB star
(HD 56126 (F 51).
Authors: Parthasarathy, M.; Garcia Lario, P.; Pottasch, S. R.
1992A&A...264..159P Altcode:
From an analysis of high-resolution spectra of the IRAS source HD 56126
(F5I), it is found that its photospheric abundances of C, O, S are
nearly solar and N is overabundant by about -0.2 dex. The abundance of
Fe and related elements suggest that HD 56126 is metal-poor (Fe/H is not
greater than -1.0). The atmospheric parameters of HD 56126 are found to
be T(eff) = 6500 K, log g = 0.5, Fe/H = 1.0, and zeta = 4 km/s. The
radial velocity measurements yield V<SUB>r</SUB> = +105 km/s and
V<SUB>LSR</SUB> = +52.3 km/s, and show that HD 56126 is a high-velocity
star belonging to the old disk population. The large abundance ratios
of CNO and S elements with respect to Fe are due to depletions of Fe
and related elements but not of CNO and S elements. It is suggested
that in the recent past, during the AGB stage of the evolution of these
star, they extended cool denser outer envelopes in which the temperature
reached to the limit of condensation temperature of refractory elements,
resulting in the formation of dust grains close to the star.
---------------------------------------------------------
Title: Shklovsky distances to galactic bulge planetary nebulae.
Authors: Pottasch, S. R.; Zijlstra, A. A.
1992A&A...256..251P Altcode:
The authors analyze a sample of planetary nebulae in the bulge to judge
the validity of the Shklovsky method for distance determination. Based
on a similar study, Stasinska et al. (1991) find that the method gives
acceptable results. The authors conclude the opposite: the agreement of
the Shklovsky distances with the actual distance to the bulge is poor,
and cannot be explained by observational uncertainties; the errors are
systematic rather than random. The difference is mainly caused by the
use of radio diameters in preference to optical values. The implications
for the mass distribution of planetary nebulae are discussed.
---------------------------------------------------------
Title: Abundances in planetary nebulae near the galactic
center. II. Abundance distributions.
Authors: Ratag, Mezak A.; Pottasch, Stuart R.; Dennefeld, Michel;
Menzies, John W.
1992A&A...255..255R Altcode:
The general distribution pattern of various abundance ratios, with
respect to hydrogen and oxygen, in the planetary nebulae (PNe) in
the galactic bulge is investigated, and the results are compared
with the disk nebulae, the solar values, and the prediction based
on the observed gradients in the disk. It was found that, excluding
the He and N elements (which are affected by nucleosynthesis and
mixing processes in the parent stars) and the Cl (which is likely to
be affected by incompleteness), the mean values of the heavy element
abundances in the bulge PNe are, on average, 25 percent lower than the
solar values. The abundance distributions resemble those of the disk
sample, with a slightly higher mean abundance in the case of oxygen.
---------------------------------------------------------
Title: Circumstellar Dust in Mira Variables; the Pulsational Mass Loss
Authors: Anandarao, B. G.; Pottasch, S. R.; Seema, P.; Vaidya, D. B.
1992ASPC...26..474A Altcode: 1992csss....7..474A
No abstract at ADS
---------------------------------------------------------
Title: IUE Observations of Post AGB Stars Which Show Spectrum
Variation
Authors: Pottasch, S. R.
1992iue..prop.4424P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Planetary nebulae near the galactic center : III. The WSRT
measurements.
Authors: Ratag, M. A.; Pottasch, S. R.
1991A&AS...91..481R Altcode:
The detections of radio continuum emission at 6 cm from 74 IRAS sources
with a typical far-infrared color of planetary nebulae, located within
15 deg of the Galactic center, are reported. Results based mainly on
SWRT observations in the period 1987-1989 are presented. The detections
are reported of 30 known planetary nebulae, 11 of them for the first
time, and their radio measurements are given.
---------------------------------------------------------
Title: Radio recombination line observations of the planetary nebula
NGC 7027.
Authors: Roelfsema, P. R.; Goss, W. M.; Pottasch, S. R.; Zijlstra, A.
1991A&A...251..611R Altcode:
The planetary nebula NGC 7027 has been observed in the 76-alpha and
110-alpha radio recombination lines. An electron temperature of 14,500
+/-1000 K is found in most of the nebula. The observed H110-alpha
and H76-alpha line to continuum ratios are in good agreement with a
true electron density of n(e,true) = 6 x 10 exp 4/cu cm. The velocity
structure of the line emission implies that the ionized gas in NGC 7027
is expanding anisotropically. A radially expanding prolate spheroidal
shell model for the ionized gas distribution is found to be consistent
both with the observed recombination line velocities and with the
observed continuum brightness distribution. The relation between the
outflowing ionized gas and the molecular cloud surrounding NGC 7027
is discussed.
---------------------------------------------------------
Title: IRAS 22568+6141 : a new bipolar planetary nebula.
Authors: Garcia Lario, P.; Manchado, A.; Riera, A.; Mampaso, A.;
Pottasch, S. R.
1991A&A...249..223G Altcode:
The identification of a bipolar planetary nebula is reported with
a description of its characteristics. The nebula IRAS 22568 + 6141
has an extension of 8 arcsec, a high extinction of 2.37, and electron
temperature and density of 11,500 K and 20,000/cu cm respectively. The
distance to the object is estimated at 6 kpc by means of the Shklovskii
method which is consistent with the H-alpha radial velocity of -80
km/s. The IRAS data suggest that the source has a total dust + gas
enevelope of 0.4 solar mass, and the mass-loss rate and progenitor
type are calculated for the young planetary nebula.
---------------------------------------------------------
Title: On the scale height of planetary nebulae.
Authors: Zijlstra, A. A.; Pottasch, S. R.
1991A&A...243..478Z Altcode:
Based on the distribution at high galactic latitudes, the local scale
height of planetary nebulae (PNe) is determined. The authors find
a value of 250±50 pc, assuming an exponential disk, or 190±40 pc
in case of an isothermal disk. This agrees well with the old stellar
disk. The result is considerably higher than earlier determinations;
the difference can be explained by the use of statistical distance
scales in the earlier work. The majority of the nearby planetary
nebulae therefore originates from old stars. The total number of PNe
in the galactic disk is found to be ≡23000±6000. The birthrate of
planetary nebulae is consistent with the white dwarf birthrate.
---------------------------------------------------------
Title: IUE Observations of New Proto- Planetary Nebulae from IRAS
Survey
Authors: Pottasch, S. R.
1991iue..prop.4117P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Planetary nebulae as standard candles : the distance to the
galactic center.
Authors: Pottasch, S. R.
1990A&A...236..231P Altcode:
Luminosity functions for planetary nebulae in the galactic bulge and
the Magellanic Clouds are presented. In combination with the known
luminosity function of PN in M 31, they are used to determine the
distance to the galactic center.
---------------------------------------------------------
Title: Mapping the outflow of OH 5.89-0.39
Authors: Zijlstra, A. A.; Pottasch, S. R.; Engels, D.; Roelfsema,
P. R.; Te Lintel Hekkert, P.; Umana, G.
1990MNRAS.246..217Z Altcode:
A fast, massive bipolar outflow is found to be associated with
5.89-0.39, a luminous, compact H II region. Using VLA observations,
we have mapped the source in the continuum, in several OH lines, in
H I absorption, and in the H76α recombination line. <P />The inner
ionized region, with a radius of 0.06 pc, shows a disc-like geometry,
with some evidence for rotation in the outer part of the disc. The
main-line OH masers in the surrounding neutral gas trace a biconical
rapid outflow, with a total velocity width of 60 km s<SUP>-1</SUP>,
perpendicular to the disc. The OH outflow is aligned with a much more
extended flow observed in CO. Evidence for outflow is also seen in H I
absorption, albeit at lower velocities. We conclude that the outflowing
gas originates outside the ionized region. The H<SUB>2</SUB>O masers
also trace an outflow, but with a velocity gradient opposite to the
OH and CO. They may arise from one or more other young stars in the
region. <P />The distance, derived from H I absorption, is about 4 kpc;
the luminosity is a few times 10<SUP>5</SUP> L<SUB>sun</SUB>. The
central star is most likely a massive star of late O-type, still
surrounded by an accretion disc left over from the star-formation
process. <P />5.89-0.39 is among the most massive and luminous,
and contains the most luminous H II region, of the known outflow
objects. The characteristics of the OH emission differ from other
outflow sources: in 5.89-0.39 the OH is situated in the outflowing
gas, while in other known cases it is either aligned with the disc,
or shows a chaotic velocity field. This makes 5.89-0.39 very suitable
for studying the dynamics of massive molecular outflows. We suggest
that the OH emitting clumps arise from a disrupting circumstellar disc.
---------------------------------------------------------
Title: Three new young objects from the IRAS Point Source Catalogue.
Authors: Manchado, A.; Garcia-Lario, P.; Sahu, K. C.; Pottasch, S. R.
1990A&AS...84..517M Altcode:
Three new young objects have been found when carrying out a survey
of IRAS sources with infrared colors like planetary nebulae, via low
resolution spectroscopy. IRAS 14592 - 6311 and IRAS 07173 - 1733 are
bright cometary nebulae, showing metal line emission very similar
to V1331 Cyg, which is the prototype of a certain number of T-Tauri
stars. They present strong P-Cygni profiles and some other peculiar
characteristics. IRAS 07173 - 1733 is located on the edge of the dark
cloud KHAV 201. In the case of IRAS 05506 + 2414, it presents a bipolar
structure with Herbig-Haro emission characteristics in one of the lobes,
produced by shocked gas.
---------------------------------------------------------
Title: Molecular gas in cometary globules : CG 1.
Authors: Harju, J.; Sahu, M.; Henkel, C.; Wilson, T. L.; Sahu, K. C.;
Pottasch, S. R.
1990A&A...233..197H Altcode:
Detailed molecular line maps of the cometary globule CG 1, which is
located toward the Gum nebula, are presented. Spectra of the CO (J =
1-0 and 2-1), (C-13)O (J = 1-0 and 2-1), (C-18)O (1-0), HCN (1-0), HNC
(1-0), and CS (2-1) transitions lead to the following main results: (1)
the CO emission is seen over the entire optically visible structure;
(2) the total molecular mass is 20-45 solar masses; (3) the bulk of
the mass is located in the tail; (4) the H2 column densities reach
a few 10 to the 21st/sq cm and the H2 densities a few 10,000/cu cm;
(5) the gas kinetic temperature from CO is about 15 K in both the
central part and the head of the globule; and (6) the star formation
efficiency is at least 10 percent.
---------------------------------------------------------
Title: Planetary nebulae near the galactic center.
Authors: Ratag, M. A.; Pottasch, S. R.; Zijlstra, A. A.; Menzies, J.
1990A&A...233..181R Altcode:
Radio measurements using the VLA on newly discovered PNe within 15 deg
from the Galactic center are reported in a continuation from a previous
paper. The sample of new Galactic bulge PNe is increased by adding
48 PNe, which are listed and described. Six optically known PNe were
also detected in the fields and are briefly discussed. The findings
strengthen the conclusion that on the average the newly discovered
nebulae have IR excesses (IREs) higher than the nearby nebulae. The
presence of a strong correlation between IRE and nebular age in the
nearby nebulae suggests that the known bulge nebulae are generally
younger than the nearby ones and on average the newly discovered
nebulae are even younger. Possible causes for this are the disruption
of nebulae at a younger age in the bulge due to the higher density
ISM combined with the very high velocity dispersion and the presence
of a strong interstellar radiation field.
---------------------------------------------------------
Title: Circumnebular neutral hydrogen in planetary nebulae.
Authors: Taylor, A. R.; Gussie, G. T.; Pottasch, S. R.
1990ApJ...351..515T Altcode:
Centimeter line observations of six compact planetary nebulae are
reported. Circumnebular atomic hydrogen absorption has been observed
in NGC 6790, NGC 6886, IC 418, IC 5117, and BD +30 deg 3639, while H I
was not observed to a high upper limit in NGC 6741. Hydrogen was also
detected in emission from BD +30 deg 3639. The expansion velocities of
the circumnebular envelopes are similar to the expansion velocities
observed for the ionized nebula. The optical depth of circumnebular
H I appears to decrease with increasing linear radius of the ionized
nebulae, indicating that these nebulae are ionization bounded and that
the amount of atomic hydrogen decreases as young nebulas evolve.
---------------------------------------------------------
Title: Near infrared survey of IRAS sources with colours like
planetary nebulae. II.
Authors: Garcia-Lario, P.; Manchado, A.; Suso, S. R.; Pottasch, S. R.;
Olling, R.
1990A&AS...82..497G Altcode:
Near infrared standard photometry (J, H, K, L and M bands) of 38 IRAS
sources with far infrared colours similar to those of known planetary
nebulae is presented. They are classified according to their infrared
global energy distribution from 1 to 100 micron though it is not
possible to reach a definitive conclusion about their evolutionary
stage, there are clear indications that most of them are in the
transition phase from AGB and post-AGB stars to proto-planetary and
planetary nebulae.
---------------------------------------------------------
Title: Misclassified planetary nebulae.
Authors: Zijlstra, A.; Pottasch, S.; Bignell, C.
1990A&AS...82..273Z Altcode:
VLA Radio observations of a number of suspected planetary nebulae
are presented. Based on the morphology of the source, and on the
IRAS far infrared colours, some of these are shown to be compact H
Il regions. Most of the other sources show no radio emission down
to a level of 1 mJy and are either emission line stars, reflection
nebulae, or galaxies. The radio images of the resolved sources are
presented, along with a discussion of the detected sources. Also a
brief description of some of the sources is given.
---------------------------------------------------------
Title: Newly Discovered Young Planetary Nebulae
Authors: Pottasch, S. R.; Ratag, M. A.; Olling, R.
1990fmpn.coll..381P Altcode:
Potential planetary nebulae are selected from the IRAS point source
catalog by their colors. From a list of 600 candidates in the direction
of the Galactic bulge, about 20 percent have been confirmed by the
presence of radio continuum emission. It is argued that the percentage
of PN in the group is much higher, but the others have a radio flux
density below the 1 mJy limit imposed by the observations. A substantial
fraction of the new PN have very high infrared excesses, indicating
that the central star temperature is very low, sometimes less than
13,000 K. The position of these nebulae on the H-R diagram is discussed.
---------------------------------------------------------
Title: Two new Seyfert galaxies from the IRAS Point Source Catalogue.
Authors: Perez, E.; Manchado, A.; Garcia-Lario, P.; Pottasch, S. R.
1990A&A...227..407P Altcode:
Two sources selected from the IRAS Point Source Catalogue (PSC)
have been spectroscopically identified as galaxies with a Seyfert
type active nucleus. The brightest of the two sources, IRAS 20210 +
1121, is in close interaction with a companion galaxy at a projected
distance of 1.1 kpc and has a perturbed spiral-like morphology. This
galaxy presents some features which make it a candidate for an obscured
Seyfert type 1. The second source, IRAS 01475-0740, has an elliptical
morphology and might be located at the centre of a group of galaxies.
---------------------------------------------------------
Title: C-Rich Planetary Nebulae - Descendents of Carbon-Stars
Authors: Pottasch, S. R.
1990fmpn.coll..306P Altcode:
A sample of planetary nebulae whose carbon abundance is well determined
is considered, with a view to answering the question: is there evidence
for a connection of those nebulae with high carbon abundance with carbon
stars. Evidence concerning the spatial distribution, expansion velocity,
morphology, and luminosity are presented.
---------------------------------------------------------
Title: A Possible Nova from the IRAS Point Source Catalogue
Authors: Garcia-Lario, P.; Manchado, A.; Sahu, K. C.; Pottasch, S. R.
1990LNP...369...55G Altcode: 1990IAUCo.122...55G; 1990pcn..conf...55G
During a spectroscopic survey of IRAS sources with infrared colours
similar to those in planetary nebulae, IRAS 06518-1041 revealed itself
as a possible novalike object. The spectrum of IRAS 06518 - 1041, which
is shown in Figure 1, presents strong and broad hydrogen Balmer lines
together with broad permitted lines of He and C. This spectrum also
shows a much weaker narrow nebular component, with forbidden lines of
[OIII] and narrow Ha. The mean velocity associated to the observed
line widths is about 800 km s<SUP>-1</SUP>. The observed emission
lines correspond well to typical post-novae objects in the quiescent
phase (Warner, 1989). Another argument which supports the idea of this
object being a nova-like star is that there are some indications of the
binarity of the source if we attend to the asymmetries observed both
in the H<SUB>β</SUB> and H<SUB>α</SUB> profiles. The high resolution
spectrum at H<SUB>α</SUB> shows the presence of a sharp double-peaked
central emission from a low expanding envelope at a velocity of
35±5 km s<SUP>-1</SUP>, together with a much broader emission with
velocities of several hundred kilometers. The displacement between
both components is about 130 km s<SUP>-1</SUP>. This broad component
could be due to the presence of an accretion disk around the system
with hydrogen-rich material falling onto the compact companion. This
is supported by the fact that the broad emission looks like the
combination of different velocity components giving rise to a complex
and asymmetric line profile. From this high resolution spectrum
we derive a V<SUB>LSR</SUB>=57 km s<SUP>-1</SUP>, which points to
a distance of 5.5 kpc if we adopt the model rotation curve of the
Galaxy given by Pottasch (1984) and a distance of 9 kpc from the Sun
to the galactic center. The large infrared excess detected by the IRAS
satellite is probably the result of the formation of dust grains in
the outer parts of the common envelope at a temperature of about 160 K,
as can be derived from the infrared data. This infrared excess is also
present in other nova-like objects and is specially important in old
and slow novae (Callus et al, 1987) where the continuous ejection of
mass produces dust shells which are strong emitters in the infrared.
---------------------------------------------------------
Title: Near Infrared Photometry of IRAS Sources with Colours like
Planetary Nebulae
Authors: Garcia-Lario, P.; Manchado, A.; Pottasch, S. R.; Suso, J.;
Olling, R.
1990fmpn.coll..474G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A New Proto Planetary Nebula
Authors: Manchado, A.; Riera, A.; Mampaso, A.; Garcia Lario, P.;
Pottasch, S. R.
1990fmpn.coll..554M Altcode:
Low and high resolution spectra of IRAS 22568 + 6141 have been
obtained. Physical parameters and abundances and flux densities are
given for the object. The mass loss rate is the expected value for
objects at the start of the evolution off the AGB. The elemental values
of the object, its location in the H-R diagram, and its kinematical
age indicate that it is a young PN.
---------------------------------------------------------
Title: Abundances in the galactic bulge planetary nebulae
Authors: Ratag, M. A.; Pottasch, S. R.; Dennefeld, M.; Menzies, J.
1990ESOC...35...93R Altcode: 1990bg...work...93R
The abundance distributions in a large sample of Galactic bulge
planetary nebulae (PNe) are discussed. They are, in general, similar to
those of the non-bulge PNe. Almost all the mean abundances are lower
than the solar values. Helium and nitrogen show overabundances with
respect to both the solar values and the non-bulge PNe.
---------------------------------------------------------
Title: The argon abundance in planetary nebulae.
Authors: Ratag, M. A.; Pottasch, S. R.
1990A&A...227..207R Altcode:
The important ionization stages of argon in planetary nebulae are
studied. The summation of Ar(2+) and Ar(3+) range, approximately from
2 to 8 with a peak at about class 4. Ar(2+) alone clearly predominates
in the classes 2 to 6. The fraction of ions in lower stages competes
with that of Ar(2+) and Ar(3+) in very low excitation nebulae, while
in very high excitation nebulae (excitation class greater than 8), the
summation of ions in higher stages becomes equally important compared
to Ar(2+) and Ar(3+). This study provides also alternative ionization
correction factors (ICFs) which are reasonably accurate in deriving
the total argon abundance based only on a single ion, either Ar(2+)
or Ar(3+), as well as on the summation of them.
---------------------------------------------------------
Title: The far-infrared (IRAS) excess in BQ and related stars.
Authors: Parthasarathy, M.; Pottasch, S. R.
1989A&A...225..521P Altcode:
The FIR IRAS flux distributions and color of 12 peculiar emission-line
objects (HD 51585, Hen 401, Hen 591, Hen 1013, He 2-138, M 2-9, HD
326971, Hen 1357, Hen 1428, Tc 1, Hen 1475, and M 1-26) are found to
be similar to that observed in young compact planetary nebulae. From
the FIR fluxes the temperatures, luminosities, and masses of the dust
envelopes are estimated. The results suggest that these 12 peculiar
emission line stars suffered extensive mass loss in the past on their
AGB stage of evolution. These objects appear to be evolving toward the
early stages of planetary nebulae and may be described as transition
objects or possible protoplanetary nebulae.
---------------------------------------------------------
Title: IRAS 22568+6141: a new bipolar nebula.
Authors: Manchado, A.; Riera, A.; Mampaso, A.; García Lario, P.;
Pottasch, S. R.
1989RMxAA..18..182M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chemical abundances and masses of the haloes around the
planetary nebulae NGC 6543 and NGC 6826.
Authors: Manchado, A.; Pottasch, S. R.
1989A&A...222..219M Altcode:
Spatial resolved low resolution spectroscopy of the haloes around the
planetary nebulae NGC 6543 and NGC 6826 were conducted. The results
imply that the radiation is thermal and not due to dust reflection. From
those data chemical abundances and masses were calculated. Chemical
abundances decrease in the haloes, while masses increase up to ten
times in NGC 6543 reaching a value of 1 solar mass. The mass loss
required to form these haloes coincides with that expected at the
beginning of the evolution off the AGB.
---------------------------------------------------------
Title: A catalogue of VLA radio continuum observations of planetary
nebulae with the Very Large Array.
Authors: Zijlstra, A. A.; Pottasch, S. R.; Bignell, C.
1989A&AS...79..329Z Altcode:
An extended VLA survey of about 300 planetary nebulae, ranging in
size from 4 arcsec to 8 arcmin, has been completed. The maps and the
measured parameters, such as radio flux density, diameter, and position,
are presented. The brightness temperatures, total far-infrared flux,
and infrared excess are derived. Newly measured optical positions are
given for a few sources. A compilation of all published VLA data of
planetary nebulae is also included. High-resolution radio synthesis
observations are now available for approximately 400 nebulae.
---------------------------------------------------------
Title: Evolution of planetary nebulae in the galactic bulge.
Authors: Pottasch, S. R.; Acker, A.
1989A&A...221..123P Altcode:
The luminosity of the central stars planetary nebulas near the
galactic center is discussed. The distance to these objects is
quite well known, removing the most common source of uncertainty in
luminosity determinations. The resulting luminosities are compared to
theoretical models and to empirical determinations from nearby nebulas
using different methods.
---------------------------------------------------------
Title: IRAS observations of the star-forming dark cloud ESO 210-6A
and the associated near-infrared source HH 47/46 IRS.
Authors: Sahu, M.; Sahu, K. C.; Pottasch, S. R.
1989A&A...218..221S Altcode:
Maps of the dark cloud ESO 210-6A and the associated NIR source
HH 46/47 were constructed using IRAS data. The 60/100 micron color
temperature distribution in the cloud shows that the temperature in
the cloud ranges from 20 to 40 K, with the maximum temperature at the
position of the NIR source. On the other hand, the 12/25 micron color
temperature distribution shows temperatures ranging from 200 to 400
K, and exhibits a minimum at the position of the NIR source. Such an
anticorrelation between 12/25 micron and 60/100 micron temperature
distributions extends to all parts of the cloud. The dust mass and
the FIR luminosity of the ESO 210-6A dark cloud, derived from the
60-micron and 100-micron fluxes, were found to be about 0.08 solar
mass and 44 solar luminosities, respectively.
---------------------------------------------------------
Title: IRAS 16455-3455 and IRAS 15154-5258 : two new southern
planetary nebulae.
Authors: Manchado, A.; Garcia-Lario, P.; Pottasch, S. R.
1989A&A...218..267M Altcode:
The identification of two new southern planetary nebulae, IRAS
16455-3455 and IRAS 15154-5258, via low resolution spectroscopy,
is reported. IRAS 16455-3455 is a high excitation planetary nebula
with an extension of 9 arcsec, m(V) = 8.95 and E(B-V) = 1.21. Chemical
abundances in this nebula are similar to the mean values for planetaries
in the Galaxy. IRAS 15154-5258 is a hydrogen-poor nebula with a high
infrared excess. The central star has a WC4 Wolf-Rayet spectrum.
---------------------------------------------------------
Title: Abundance Gradient for 13 Planetary Nebulae in the Galaxy
Authors: Manchado, A.; Mampaso, A.; Pottasch, S. R.
1989Ap&SS.157...23M Altcode:
Via optical low-resolution long slit spectroscopy conducted at the 2.5
m INT in La Palma, He, O, N, Ne, A, and S abundances in 13 extended PN
were calculated. The analysis of these results allowed us to infer that
the nitrogen and oxygen abundances do not correlate, which implies
that probably not all the nitrogen found was produced in the CNO
cycle. Furthermore, the oxygen and neon abundances seem to correlate
well enough which indicate a common origen of these two elements during
stellar evolution. The values of He, O, N, and Ne abundances obtained,
yield a gradient of those abundances with the position of the nebulae
with respect to the galactic plane. This is consistent with the
existence of different types of populations amonst the PN in the Galaxy.
---------------------------------------------------------
Title: OH maser emission from young planetary nebulae.
Authors: Zijlstra, A. A.; te Lintel Hekkert, P.; Pottasch, S. R.;
Caswell, J. L.; Ratag, M.; Habing, H. J.
1989A&A...217..157Z Altcode:
OH emission, primarily in the 1612 MHz satellite line and also in the
main lines, is detected in a number of young planetary nebulae. These
objects form a direct observational link between the evolved OH/IR
stars and planetary nebulae. In this paper, the observations are
presented and the implications for various aspects of Post-Asymptotic
Giant Branch evolution are discussed. Lifetimes and birthrates of this
evolutionary stage are calculated. A scheme for classifying preplanetary
nebula objects is proposed.
---------------------------------------------------------
Title: Low mass planetary nebulae near the galactic centre.
Authors: Zijlstra, Albert A.; Pottasch, Stuart R.
1989A&A...216..245Z Altcode:
A group of weak, low-excitation planetary nebulae in the galactic
bulge are studied. The properties of the nebulae are within the normal
range for planetary nebulae, but some have a very low total ionized
mass. From the observed properties of the nebulae the temperatures of
the central stars are estimated. With two possible exceptions, the
stars have not yet entered the cooling track in the HR diagram. It
is shown that, if the planetary nebulae are optically thick to the
ionizing stellar radiation, the total luminosity can be derived
from the H-beta luminosity in a way analogous to the Zanstra (1931)
method for determining stellar temperatures. The resulting position in
the HR diagram is in most cases not consistent with the theoretically
predicted evolutionary tracks. Thus, the nebulae may be optically thin,
in spite of the very low mass of some of the objects.
---------------------------------------------------------
Title: A Search for New Objects in the Transition Phase Between
Agb-Stars and Planetary Nebulae
Authors: Manchado, A.; Garcia Lario, P.; Pottasch, S. R.
1989Ap&SS.156...57M Altcode:
We present the first results of a spectroscopy survey of iras sources
with colours similar to those of planetary nebulae. Two new planetary
nebulae, some Hα emission line stars, one peculiar source which is
probably a pre-Main-Sequence object and a new Seyfert I galaxy have
been found.
---------------------------------------------------------
Title: IRAS 09149-6206, a new Seyfert I galaxy.
Authors: Perez, E.; Manchado, A.; Pottasch, S. R.; Garcia-Lario, P.
1989A&A...215..262P Altcode:
We report on the serendipitous discovery of a new type I Seyfert galaxy,
IRAS 09149-6206, found during a search for planetary nebulae using
the IRAS Point Source Catalogue (PSC). The optical spectrum of this
galaxy shows very strong broad Balmer and Fe II emission, indicating
the existence of large optical depths, while the emission spectrum
from the narrow line region (NLR) is relatively weak, with only the
high excitation lines present. The object presents extended [O III]
emission and from the rotation curve we calculate a mass of 8 10^9^
M_sun_ within a radius of 3 kpc. It is suggested that the activity
could have been triggered by interaction with a close faint companion
---------------------------------------------------------
Title: Near-infrared survey of IRAS sources with colours like
planetary nebulae.
Authors: Manchado, A.; Pottasch, S. R.; Garcia-Lario, P.; Esteban,
C.; Mampaso, A.
1989A&A...214..139M Altcode:
Near-IR photometry of 38 objects associated with unidentified
IRAS PSC sources, which have colors in the FIR similar to those of
planetary nebulae are presented. From their IR flux distribution,
from their low-resolution IR spectra and from their position in the
near-IR color-color diagrams, their precise nature is identified. They
fall in different categories: six are possible post-AGB stars, five
Mira variables or OH/IR stars, fifteen very likely new planetary
nebulae while the last twelve are objects showing large amounts of
extinction. Some of them could be photoplanetary nebulae while others
could represent premain-sequence objects.
---------------------------------------------------------
Title: Kinematic structure and chemical composition of the double
shell PN NGC 3242.
Authors: Sahu, K. C.; Pottasch, S. R.; Anandarao, B. G.; Desai, J. N.
1989IAUS..131..200S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Expansion Velocities of Southern Planetary Nebulae
Authors: Sahu, K. C.; Pottasch, S. R.
1989IAUS..131..196S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: OH maser emission from young planetary nebulae.
Authors: Zijlstra, A.; Pottasch, S. R.; te Lintel Hekkert, P.;
Bignell, C.
1989IAUS..131..210Z Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High resolution long-slit spectroscopy of A 78.
Authors: Manchado, A.; Pottasch, S. R.; Mampaso, A.
1989IAUS..131..184M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Low Resolution Spectroscopy of 13 Low Surface Brightness
Planetary Nebulae
Authors: Manchado, A.; Pottasch, S. R.; Mampaso, A.
1989IAUS..131..220M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: IRAS observations of extended planetary nebulae.
Authors: Leene, A.; Pottasch, S. R.
1989IAUS..131..174L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The central star of NGC 7027.
Authors: Walton, N. A.; Pottasch, S. R.; Reay, N. K.; Spoelstra, T.
1989IAUS..131..301W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A VLA radio continuum survey of planetary nebulae.
Authors: Zijlstra, A.; Pottasch, S. R.; Bignell, C.
1989IAUS..131...60Z Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Infrared Search for New Planetary Nebulae
Authors: Pottasch, S. R.; Esteban, C.; Manchado, A.; Mampaso, A.
1989IAUS..131R..63P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Planetary Nebulae Near the Galactic Center - Part One -
Method of Discovery and Preliminary Results
Authors: Pottasch, S. R.; Bignell, C.; Olling, R.; Zijlstra, A. A.
1989IAUS..131Q..63P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The halos of NGC 6543 and NGC 6826.
Authors: Manchado, A.; Pottasch, S. R.; Mampaso, A.
1989IAUS..131..196M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: New Young Objects from the IRAS Point Source Catalogue
Authors: Manchado, A.; García Lario, P.; Sahu, K. C.; Pottasch, S. R.
1989LNP...350..301M Altcode: 1989IAUCo.120..301M; 1989sdim.conf..301M
No abstract at ADS
---------------------------------------------------------
Title: The peculiar planetary nebula M1-78.
Authors: Pottasch, S. R.; Zijlstra, A. A.; Ukita, N.; Manchado, A.;
Ratag, M.
1989IAUS..131..216P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The position of the central stars of PN on the HR diagram.
Authors: Pottasch, S. R.
1989IAUS..131..481P Altcode:
Central stars can be placed on the HR diagram if their effective
temperature and radii are known. The distance, which always plays
an important, really critical role, is not well known. The author has
approached the problem in a somewhat different way (Pottasch, 1983). The
statistical methods of determining distance were discared. Only
those central stars were used whose distance could be determined
in an independent way. The fact that they are independent of the
statistical methods does not mean they are correct, because determining
accurate distances is difficult. The general conclusions indicated:
(1) the existence of less luminous central stars than predicted by
the Schönberner (1981) 0.55 M<SUB>sun</SUB> evolutionary track, and
(2) the existence of very high temperature central stars.
---------------------------------------------------------
Title: Primordial lithium abundance from interstellar lithium lines
towards SN 1987A
Authors: Sahu, Kailash C.; Pottasch, S. R.; Sahu, Meenakshi
1989AIPC..183..420S Altcode: 1989cam..conf..420S
The primoridal lithium abundance is known to be one of the best
probes to test the standard as well as the non-standard Big Bang
nucleosynthesis theories, and to measure the nucleon abundance in the
early universe in the standard Big Bang (SSB) model. We have obtained
high-resolution ((λ)/(δλ)\bartil 100,000), high signal-to-noise
(S/N>~1,500) spectra of SN 1987A around the Li:I λ6708 A˚ region,
using the ESO 1.4m CAT and the Coudé Echelle Spectrograph. The
non-detection of any lithium feature in our sepctra places an upper
limit on the lithium abundance. (AIP)
---------------------------------------------------------
Title: Magnitude Measurements of Central Stars of Planetary Nebulae
Authors: Gathier, R.; Pottasch, S. R.
1989IAUS..131..302G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Properties of planetary nebulae. II. Central star evolution.
Authors: Gathier, R.; Pottasch, S. R.
1989A&A...209..369G Altcode:
The evolution of central stars is studied, using a sample of planetary
nebulae with accurate, individually determined distances. The
central star luminosities and effective temperatures are calculated
from central star magnitudes. The central star positions in the HR
diagram are compared with theoretical evolutionary track, showing
that the observed ages of planetary nebulae with central stars are
much smaller than predicted. Also, relatively cool central stars
with luminosities lower than 1,000 solar luminosity are observed,
suggesting that planetary nebulae formation can take place at lower
luminosities than previously assumed.
---------------------------------------------------------
Title: Search for primordial lithium in the interstellar medium
towards SN 1987A.
Authors: Sahu, K. C.; Sahu, M.; Pottasch, S. R.
1988A&A...207L...1S Altcode:
The supernova SN 1987A provides the first possibility to directly
observe the primordial lithium in the galactic halo, and to derive the
lithium abundance from the observations of the interstellar medium
of an external galaxy. We have obtained high resolution (λ/δλ~
100,000), high signal-to-noise (S/N >~ 1,500) spectra of SN 1987A
around the Li I λ 6708 A region, using the ESO 1.4m CAT and the Coude
Echelle Spectrograph. The non-detection of any lithium feature in
our spectra places an upper limit on the lithium abundance. This was
used to derive the primordial lithium abundance taking all possible
correction factors, like depletion onto grains etc., into account. The
resulting primordial lithium abundance is N(Li)/N(H) <~ 0.8 x 10^-10^
(with a maximum uncertainty of a factor of 2). This value is consistent
with the abundance derived from the observations of halo dwarfs but
a factor of 10 lower than that derived from the observations of the
galactic ISM. This lithium abundance is marginally consistent with the
SBB nucleosynthesis and places severe constraints on the other recent
non-SBB nucleosynthesis theories. The resulting baryon to photon ratio
is the SBB model is ~3.2 x 10^-10^ which implies that the nucleons
fall short by a factor of 14 to 160 to close the universe.
---------------------------------------------------------
Title: Planetary nebulae near the galactic center. I. Method of
discovery and preliminary results.
Authors: Pottasch, S. R.; Bignell, C.; Olling, R.; Zijlstra, A. A.
1988A&A...205..248P Altcode:
A method is described for finding planetary nebulae (PN). Use is made
of the far infrared IRAS colors and radio continuum measurements. The
method is applied here to a region within 15° of the galactic
center. The first results are given, including 36 new PN. The
characteristics of the nebulae are described. While they are generally
similar to known nebulae, the method of selection gives an emphasis
to younger objects. A substantial number of the new nebulae may be in
the transition phase between OH/IR stars and PN.
---------------------------------------------------------
Title: Comparison of astronomical journals.
Authors: Pottasch, S. R.; Praderie, F.
1988Msngr..53...16P Altcode:
At the request of the Board of Oirectors of Astronomy and Astrophysics
(AA), we have undertaken a comparison of the more important astronomical
journals. The original reports covered the amount of material published,
financial aspects, time delays in publication, aspects of refereeing and
rejection of articles and the very difficult question of the overall
scientific quality. Because of the general interest among astronomers
in publishing and publications we have prepared this summary of the
reports. Some of the information used has been supplied by Or. H. Abt,
editor of the Astrophysical Journal (ApJ) and Prof. R.J. Tayler,
editor of the Monthly Notices of the Royal Astron. Soc. (MNRAS). We
have limited our comparison mainly to the three journals mentioned,
plus the Astronomical Journal (AJ).
---------------------------------------------------------
Title: Dust emission from symbiotic stars : an interpretation of
IRAS observations.
Authors: Anandarao, B. G.; Taylor, A. R.; Pottasch, S. R.
1988A&A...203..361A Altcode:
The Infrared Astronomical Satellite (IRAS) data (photometric and
low-resolution spectroscopic) on six symbiotic systems are analysed
to find out the circumstellar dust parameters. The two S-type systems
(UV Aur and CH Cyg) showed circumstellar dust-shell temperatures of
≡800K, while the other four systems, HM Sge, V1016 Cyg, RR Tel and RX
Pup (which happen to be D type nova-like objects), showed much lower
temperatures (≡300K). It is shown that among the nova-like systems
themselves, the dust-shell temperatures decrease with increasing age
of the nova-like outburst. Further, the observed ratio of the fluxes
in the silicate features at 10 and 18 μm, for these systems, decreases
with increasing age.
---------------------------------------------------------
Title: IUE observations of high galactic latitude F supergiants HD
161796 and HD 187885.
Authors: Parthasarathy, M.; Pottasch, S. R.; Wamsteker, W.
1988A&A...203..117P Altcode:
Low resolution (6 A) IUE ultraviolet spectra of the high galactic
latitude F supergiants HD 161796 (F3 Ib) and HD 187885 (F2-3I) are
analyzed. The UV spectrum (1250 A to 3250 A) of HD 161796 shows no
excess UV flux attributable to a hot degenerate companion. From the UV
spectrum the temperature is found to be 6300 K. There is no evidence for
significant metal deficiency. Except for the semiforbidden N IV 1487
A line the rest of the transition region emission lines are weak. In
spite of the large IR (IRAS) excess, the 2200 A region shows no evidence
for circumstellar reddening. The UV spectrum (1250 A to 1900 A) of HD
187885 is peculiar. A broad emission feature with emission peak centered
around 1580 A is present. A broad absorption feature nearly 100 A wide
centered around 1657 A appears to be present. This absorption feature
may be due to C I or due to quasi-molecular absorption of the H2.
---------------------------------------------------------
Title: IRAS pointed observations of planetary nebulae.
Authors: Leene, A.; Pottasch, S. R.
1988A&A...202..203L Altcode:
The pointed observations made by IRAS satellite have been analyzed in
order to find extended planetary nebulas. Of the 67 nebulas observed
only 10 were larger than the IRAS beams. IR data of these nebulas have
been compared with optical data. Also a comparison with other IRAS data
products has been made. The major part of the IR emission originates
in the ionized region. No evidence for weak extended IR haloes could
be found. The IR emission has a single temperature and its brightness
drops suddenly at the IR edge. In BD + 30 3639 and NGC 6543 there
is evidence for IF emission which envelopes the ionized region. This
dust could be a remnant of the progenitor shell. IR sizes have been
determined by model fits. The calculations indicate a mass loss rate
in dust between 10 to the -7th and 10 to the -6th solar masses/yr,
which is caused by the onset of some 'superwind'. The models support
the existence of a temperature gradient in NGC 6543 and BD + 30 3639.
---------------------------------------------------------
Title: The central star of NGC 7027.
Authors: Walton, N. A.; Pottasch, S. R.; Reay, N. K.; Taylor, A. R.
1988A&A...200L..21W Altcode:
Narrow band continuum images of NGC 7027 have been taken using a
charge-coupled device (CCD) at the prime focus of the 2.5 m Isaac Newton
Telescope. The central star of NGC 7027 is clearly detected, its visual
magnitude being measured at m<SUB>v</SUB> = 17.0±0.2. The effects of
varying extinction across the nebula were analysed by comparing the
optical Hβ map with a high resolution 2 cm radio map. This showed that
the central star lies at a position of low extinction. Hence the usual
value of extinction quoted for this nebula is too high when considering
the extinction at the central star. When this difference in extinction
at the central star is taken into account then the temperature of the
central star as determined using the Zanstra method is ≡310,000K.
---------------------------------------------------------
Title: Magnitudes of central stars of planetary nebulae.
Authors: Gathier, R.; Pottasch, S. R.
1988A&A...197..266G Altcode:
Magnitudes have been measured for 44, mostly faint central stars of
planetary nebulae by imaging the star and nebula on a CCD detector. The
nebular lines are suppressed by using a continuum filter. The remaining
nebular continuum is then subtracted as background as long as the star
can be clearly seen. This is true in 41 of 44 cases observed. Zanstra
temperatures are calculated from the observed magnitudes, and discussed.
---------------------------------------------------------
Title: The rapidly evolving source OH 5.89-0.39 : H II region or
proto-planetary nebula ?
Authors: Zijlstra, A. A.; Pottasch, S. R.
1988A&A...196L...9Z Altcode:
VLA observations have shown strong radio continuum emission associated
with 5.89-0.39, an object previously known as an OH/IR star. The
1612 MHz OH maser is rapidly disappearing. In this letter the VLA
observations are described. The authors discuss the properties of this
object, assuming that it is a young Planetary Nebula. Alternative
interpretations as a peculiar H II region or a post main sequence
massive star are also discussed.
---------------------------------------------------------
Title: Cometary globules in the GUM nebula. I. Infrared and optical
properties of CG 22.
Authors: Sahu, M.; Pottasch, S. R.; Sahu, K. C.; Wesselius, P. R.;
Desai, J. N.
1988A&A...195..269S Altcode:
The authors have undertaken a detailed study of the structure and
physical properties of cometary globules in the Gum nebula. This
paper reports the properties of CG 22, the largest cometary globule
in the system, derived from the IR and optical data. The cometary
globule clearly splits into 3 individual blobs. The dust temperature
distribution in the cometary globule shows temperatures ranging from 25
to 35K. The observed temperature and its gradient seem to be consistent
with the heating of the dust by Interstellar Radiation Field. From
the infrared fluxes, the dust masses for the three blobs have been
derived to be ≡7×10<SUP>-2</SUP>M_sun;, ≡9×10<SUP>-2</SUP>M_sun;,
and ≡6×10<SUP>-2</SUP>M_sun;. Star formation in the head of the
cometary globule seems to be evident.
---------------------------------------------------------
Title: The far-infrared (IRAS) excess in luminous F-G stars.
Authors: Pottasch, S. R.; Parthasarathy, M.
1988A&A...192..182P Altcode:
The far-infrared IRAS excesses are found in ten luminous F-G stars. The
far-IR fluxes from these stars are due to large amounts of dust
around them. The far-IR flux distribution, far-IR luminosities and
dust masses are similar to those in observed planetary nebulae. The
mass of the dust around HD 187885 and HD 179821 is of the order of
10<SUP>-2</SUP>M_sun;. These ten stars may be in the AGB - post-AGB
stage of evolution.
---------------------------------------------------------
Title: Abundance variations in the planetary nebula A 78.
Authors: Manchado, A.; Pottasch, S. R.; Mampaso, A.
1988A&A...191..128M Altcode:
The authors present long slit low dispersion flux calibrated spectra
for the planetary nebula A 78, and from these they obtain the chemical
abundances and their variation within the nebula. In the central part
of the nebula almost no hydrogen is found implying that the envelope
of the central star is burning helium. The authors also measured an
over-abundance of processed material which has been convected from
the centre of the star. In the outer part of the nebula the abundances
are close to solar.
---------------------------------------------------------
Title: Book-Review - Late State of Stellar Evolution
Authors: Kwok, S.; Pottasch, S. R.; Doom, C.
1988SSRv...48..370K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Late Stages of Stellar Evolution
Authors: Kwok, S.; Pottasch, S. R.
1988ApL&C..27..288K Altcode: 1988ApL....27..288K
No abstract at ADS
---------------------------------------------------------
Title: Shell Formation and Mass Loss in the Planetary Nebula A78.
Authors: Manchado, A.; Mampaso, A.; Pottasch, S. R.
1988mosg.proc..257M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: IUE Observations of Hen 401 and Related Stars
Authors: Pottasch, S. R.
1988iue..prop.3321P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: IUE Observations of Young Planetary Nebulae
Authors: Pottasch, S. R.
1988iue..prop.3351P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Masses of Planetary Nebulae and Their Central Stars.
Authors: Pottasch, S. R.
1988ASSL..142..109P Altcode: 1988mosg.proc..109P
Techniques for estimating the masses of PN and PN central stars
are described and demonstrated. The importance of accurate distance
estimates is stressed, and observational data on samples of Galactic
and extragalactic PN with well established distances are compiled in
tables and graphs and briefly characterized. Plots of PN mass versus
radius are shown to have significant real scattering, but a general
relation is derived. Central-star masses of about 0.5-1.1 solar mass
are then estimated on the basis of core-mass/luminosity relations for
H- and He-shell-burning stars. Predicted PN lifetimes and observed PN
ages are compared in a table and found to be in poor agreement.
---------------------------------------------------------
Title: IUE Observations of Proto-Planetary Nebulae
Authors: Pottasch, S. R.
1988iue..prop.3329P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Late Stages of Stellar Evolution
Authors: Kwok, S.; Pottasch, S. R.
1988Sci...239..301K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Dust Emission from Symbiotic Stars: Interpretation of IRAS
Observations
Authors: Anandarao, B. G.; Taylor, A. R.; Pottasch, S. R.
1988ASSL..145...65A Altcode: 1988syph.book...65A; 1988IAUCo.103...65A
No abstract at ADS
---------------------------------------------------------
Title: Internal dynamics of the Gum nebula.
Authors: Srinivasan, M.; Pecker, J. C.; Pottasch, S. R.; Sahu, K. C.
1987Msngr..50...11S Altcode: 1987Mgr....50...11S
The state of knowledge of the Gum Nebula is reviewed, and the results of
new observations are reported. Findings made by previous observations
are summarized. A new study is reported which found the expansion
velocity of the nebula and failed to detect forbidden O III emission
in any of the 14 positions observed. None of the H-alpha profiles
showed splitting.
---------------------------------------------------------
Title: Book-Review - Late Stages of Stellar Evolution
Authors: Kwok, S.; Pottasch, S. R.
1987S&T....74R.493K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Misclassified planetary nebulae.
Authors: Acker, A.; Chopinet, M.; Pottasch, S. R.; Stenholm, B.
1987A&AS...71..163A Altcode:
The authors present their opinion on 266 objects, taken from catalogues
and lists of planetary nebulae. These opinions are based on observations
given in the literature, on the vast photometric information collected
by the IRAS satellite, as well as on the observations from the ongoing
project of a spectroscopic survey of all planetary nebulae. 199 objects
are definitely rejected as planetary nebulae, 63 others are possibly
not planetary nebulae.
---------------------------------------------------------
Title: Book-Review - Late Stages of Stellar Evolution
Authors: Kwok, S.; Pottasch, S. R.
1987JBAA...97..321K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The unusual radio outburst of Nova Vulpeculae 1984 No 2.
Authors: Taylor, A. R.; Seaquist, E. R.; Hollis, J. M.; Pottasch, S. R.
1987A&A...183...38T Altcode:
Multifrequency radio monitoring of Nova Vulpeculae 1984 No. 2 has
revealed a unique radio light curve, exhibiting a strong outburst which
precedes the appearance of normal radio emission from the principal
ejecta of the nova by at least 100 days. The early emission is extremely
optically-thick and has brightness temperature in excess of 100,000
K. A model is discussed in which the radiation is produced by a strong
shock propagating outward through the principal ejecta of the nova,
as a result of an interaction with a later, high velocity wind from
the central source. It is shown that the general features of the radio
light curve can be explained by the presence of a central wind with a
mass loss rate of about 0.00001 solar masses/yr, lasting for a period
of 200 to 300 days after the optical outburst. The first radio map of
nova ejecta shortly after outburst is presented. Comparison of the
angular expansion rate to the ejection velocity implies a distance
of 3.6 kpc, and preliminary analysis of the main outburst emission
indicates a mass and kinetic energy of the ejecta respectively of
about 0.0008 solar masses and 8 x 10 to the 45th erg.
---------------------------------------------------------
Title: IRAS observations of the Dumbell nebula.
Authors: Zhang, C. Y.; Leene, A.; Pottasch, S. R.; Mo, J. E.
1987A&A...178..247Z Altcode:
Results of IRAS observations of the Dumbbell Nebula are presented. The
contribution from line emission of ions to the radiation at the four
IRAS bands has been estimated. Two components of dust grains are likely
to be mixed with ionized gas. The mass and temperature of dust have
been estimated.
---------------------------------------------------------
Title: Gradientes de abundancias en la nebulosa planetaria A78.
Authors: Manchado, A.; Mampaso, A.; Pottasch, S. R.
1987RMxAA..14..528M Altcode:
New bidimensional spectroscopic observations of A78 allow the authors to
determine the He, O, Ne, and N abundances and their variations along
the nebula. A clear overabundance of these elements is found in the
central region of the nebula, suggesting different nebular ejections of
material processed in the stellar interior and dredged-up subsequently
to the envelope.
---------------------------------------------------------
Title: Two new OH emitting planetary nebulae.
Authors: Pottasch, S. R.; Bignell, C.; Zijlstra, A.
1987A&A...177L..49P Altcode:
A search for radio continuum emission from OH/IR stars has been
made. Two stars were detected. These detections bring the total number
of known objects in the transition phase between OH/IR star and
planetary nebula to three. The two new objects do not have optical
counterparts, but are strong infrared sources. Both objects lie in
the galactic bulge and contain central stars of above average mass,
low temperature and large radius. One has the lowest temperature and
largest radius of any known central star. This star may be in rapid
transition to a higher temperature. The ionized masses of both nebulae
are determined.
---------------------------------------------------------
Title: Detection of neutral hydrogen in the planetary nebula IC 418.
Authors: Taylor, A. R.; Pottasch, S. R.
1987A&A...176L...5T Altcode:
Sensitive observations of the 21-cm neutral hydrogen line toward the
compact planetary nebula IC418 reveal an absorption feature at the
velocity of the near side of the expanding nebula, plus an emission
line red-shifted with respect to the system velocity. For a distance of
2 kpc, the emission line flux implies a total neutral hydrogen mass of
0.07 solar masses, similar to the mass of the central ionized nebula. If
the neutral gas is undergoing symmetric outflow, the relative intensity
of the emission and absorption features indicate a spin-excitation
temperature of about 1000 K.
---------------------------------------------------------
Title: IRAS measurements of HII regions.
Authors: Antonopoulou, E.; Pottasch, S. R.
1987A&A...173..108A Altcode:
Far-infrared broad band (IRAS) measurements of 71 compact H II
regions and IRAS Low Resolution Spectra (LRS) of some of them, are
presented. Ly-alpha does not contain sufficient energy to heat the dust,
and another energy source (probably direct absorption of radiation from
the exciting star) is required for all the H II regions studied. The
observed infrared excess is between 4 and 38. The infrared luminosities
for H II regions with known distances give information concerning the
spectral type of the exciting star. Neon and sulfur abundances have
been estimated from IRAS Low Resolution Spectra when the amount of
hydrogen can be determined (from the continuous radio emission). The
range of neon and sulfur abundance is unexpectedly large. Finally,
objects are discussed having an LRS spectrum similar to an H II region
but lacking radio emission.
---------------------------------------------------------
Title: Observations of extended planetary nebulae. I. NGC 7293 :
the Helix Nebula.
Authors: Leene, A.; Pottasch, S. R.
1987A&A...173..145L Altcode:
IRAS data have been used to determine the far-infrared flux density
of NGC 7283. The broadband IRAS flux densities at 12 and 25 μm are
mainly due to atomic line emission; only a small fraction is due to
emission from a dust continuum. The 60 and 100 μm emission however is
due to dust. Abundance estimates are made for some of the important
ions. Due to the large angular size of the nebula it is possible to
derive radial abundance profiles. These support the assertion that
line emission plays an important role. A limited comparison with other
nebulae has been made.
---------------------------------------------------------
Title: Contribution of line emission to the IRAS measurements:
NGC 6853.
Authors: Zhang, C. Y.; Leene, A.; Pottasch, S. R.; Mo, J. E.
1987IAUS..122..219Z Altcode:
The contribution from the line emission of ions to the radiation at
four IRAS bands has been estimated. The dust grains are likely to be
mixed with ionized gas.
---------------------------------------------------------
Title: Infrared Emission from Young Planetary Nebulae
Authors: Pottasch, S. R.
1987ASSL..132..355P Altcode: 1987lsse.proc..355P
Measurements of planetary nebulae in the far infrared, especially from
IRAS, are presented and discussed. The dust temperature and intrinsic
luminosity are found to vary as the nebula evolves. The source of
energy which heats the dust is discussed and it is shown that heating
by nebular Lyman alpha is usually insufficient, especially in young
nebulae. The problem as to whether the far infrared emission only comes
from the ionized region of the nebula or whether the neutral material
is also important is argued. The dust mass of the nebula is found to
evolve, the dust to gas mass ratio having a high value for very young
nebulae. It is argued that the dust is being constantly destroyed. The
dust emission spectra of many young nebulae are presented and they are
found to fall in three distinct categories. Finally, an estimate of
the spatial distribution of young nebulae near the galactic center,
as deduced from IRAS measurements, is given.
---------------------------------------------------------
Title: A comparison of some physical properties of planetary nebulae
in the Magellanic Clouds with those in the Galaxy.
Authors: Pottasch, S. R.
1987ESOC...27..531P Altcode: 1987sedo.work..531P
The intrinsic brightness of the nebulae is compared and found to extend
over a factor of at least 1000 both in the Magellanic Clouds and in
the galactic bulge. Some of the faint nebulae are highly evolved,
but a large number are young nebulae with low-temperature central
stars. The existence of these low-luminosity nuclei is not predicted
by current theories. Finally a discussion of the abundances of helium,
oxygen and nitrogen is given.
---------------------------------------------------------
Title: The effect of line emission on the IRAS data of planetary
nebulae.
Authors: Leene, A.; Pottasch, S. R.
1987ASSL..135..233L Altcode: 1987PN86.......233L; 1987pppn.work..233L
The effect of line emission on the IRAS flux densities of planetary
nebulae is discussed. IRAS observations of NGC 7293 are presented
and show the important effect of the S IV and O IV lines on the flux
densities of the 12 and 25 μm band. The effect of line emission on
the colour-colour plots is discussed.
---------------------------------------------------------
Title: Planetarnye tumannosti. Izuchenie pozdnikh stadij zvezdnoj
ehvolyutsii.
Authors: Pottasch, S. R.
1987ptip.book.....P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Far infrared observations on the peculiar variable star
R Aquarii.
Authors: Anandarao, B. G.; Pottasch, S. R.
1987IAUS..122..477A Altcode:
For the full paper see Abstr. 42.112.005.
---------------------------------------------------------
Title: IRAS additional observations of planetary nebulae.
Authors: Leene, A.; Zhang, C. Y.; Pottasch, S. R.
1987ASSL..135...39L Altcode: 1987PN86........39L; 1987pppn.work...39L
Data from special pointed observations of PN obtained with the IRAS
SA and CPC instruments are presented in tables and contour maps and
briefly reviewed. The major aims of these observations were to check
the integrated flux densities reported in the IRAS point-source and
small-structure catalogs and determine the source sizes. The only major
flux-density discrepancy detected was for NGC 6853, which was found
to be extended relative to the IRAS beams; otherwise the errors of
the additional observations were similar to those of the surveys and
due entirely to the repeatability of IRAS. Of the 33 sources analyzed
for size, seven were found to be extended; the accuracy of the data,
however, did not justify beam deconvolution for quantitative size
estimation.
---------------------------------------------------------
Title: Infrared Emission from Young Planetary Nebulae
Authors: Pottasch, S. R.
1987ASSL..135....1P Altcode: 1987pppn.work....1P; 1987PN86.........1P
Measurements of planetary nebulae in the far infrared, especially from
IRAS, are presented and discussed. The dust temperature and intrinsic
luminosity are found to vary as the nebula evolves. The source of
energy which heats the dust is discussed. The problem as to whether
the far infrared emission only comes from the ionized region of the
nebula or whether the neutral material is also important is argued. The
dust mass of the nebula is found to evolve, the dust to gas mass ratio
having a high value for very young nebulae. It is argued that the dust
is being constantly destroyed. The dust emission spectra of many young
nebulae are presented and they are found to fall in three distinct
categories. Finally an estimate of the spatial distribution of young
nebulae near the galactic center, as deduced from IRAS measurements,
is given.
---------------------------------------------------------
Title: Contribution of nebular emission lines to IRAS photometric
survey fluxes.
Authors: Preite Martinez, Andrea; Pottasch, S. R.
1987ASSL..135..197P Altcode: 1987pppn.work..197P; 1987PN86.......197P
In a recent paper (Pottasch et al., 1984) far-infrared IRAS measurements
of 46 planetary nebulae were presented and discussed. It was also
pointed out that line emission could contribute significantly to the
observed fluxes, especially in the 12 μm band. The authors examine
in detail this problem, presenting also results of a best-fit of line
emissivities as a function of electron density and temperature.
---------------------------------------------------------
Title: Radio continuum spectra of compact planetary nebulae :
a wind-shell model.
Authors: Taylor, A. R.; Pottasch, S. R.; Zhang, C. Y.
1987A&A...171..178T Altcode:
An analysis of the radio continuum spectra of 18 compact planetary
nebulae, based on published flux densities plus new observations at 327
MHz with the Westerbork Synthesis Radio Telescope, is presented. It
is shown that the radio spectra are well represented by a model in
which the radio emission arises in a photon-limited, ionized shell of
a stellar wind type envelope. A comparison of predicted and observed
angular radii indicates a radial density power law in the shell of
the form r exp -2. The model also accounts for an evolutionary trend
in the radio spectra revealed by a correlation between spectral shape
and the linear dimensions of the nebulae. The results suggest that
planetary nebulae are ionized shells of stellar wind ejecta produced
during the precursor, red giant stage. The derived mass loss rates
are typicaly a few 0.00001 solar masses/yr.
---------------------------------------------------------
Title: The Position of Planetary Nebulae Nuclei in the H-R Diagram -
Present Status
Authors: Pottasch, S. R.
1987ASSL..135...79P Altcode: 1987pppn.work...79P
Recent improvements in the determination of the distances to various
planetary nebulae are discussed. This increases the accuracy of
the luminosities to a selected group of nebulae. The central star
temperature determination has also been substantially improved for a
large group of very faint hot objects. This involves especially new
measurements of the central star magnitudes. The results are combined
in giving an improved H-R diagram.
---------------------------------------------------------
Title: A Wind Shell Model for Radio Emission from Compact Planetary
Nebulae
Authors: Taylor, A. R.; Pottasch, S. R.; Zhang, C. Y.
1987ASSL..132..399T Altcode: 1987lsse.proc..399T
The authors present an analysis of the radio continuum spectra of a
sample of compact planetary nebulae. A correlation is found between
the slope of the optically thick portion of the spectrum and linear
radius of the nebula. This correlation, and the shapes of individual
spectra are well explained by a model in which the radio emission
arises in a photon-limited, ionized shell of a stellar wind type
envelope. Theoretical fits are used to derive parameters of the
wind-shell. Typical mass loss rates inferred for the precursor red
giant are a few 10<SUP>-5</SUP>M_sun;/yr.
---------------------------------------------------------
Title: Late stages of stellar evolution
Authors: Kwok, S.; Pottasch, S. R.
1987ASSL..132.....K Altcode: 1987lsse.proc.....K
Various papers on the late stages of stellar evolution are
presented. The general topics addressed include: observations of
OH/IR and Mira stars, observations of carbon stars, evolutionary
and theoretical considerations, mass loss and late age evolution,
and young planetary nebulae.
---------------------------------------------------------
Title: Evidence for Pulsationally Driven Mass-Loss from Mira Variables
Authors: Whitelock, P. A.; Pottasch, S. R.; Feast, M. W.
1987ASSL..132..269W Altcode: 1987lsse.proc..269W
Quasi-simultaneous JHKL and IRAS observations of 18 Miras and one
symbiotic star are analysed. A relationship is shown to exist between
the luminosity of a Mira, its pulsation amplitude and the mass of its
dust shell. This shows that pulsation is an important factor in the
mechanism which leads to mass-loss in these stars. The symbiotic Mira,
R Aqr, is shown to have a higher dust temperature than single Miras
but a similar dust mass. It therefore appears that although the dust
is produced by normal Mira mass-loss, some contribution to its heating
is made by the hot component of the binary system.
---------------------------------------------------------
Title: IRAS catalogues and atlases. Atlas of low-resolution spectra.
Authors: Olnon, F. M.; Raimond, E.; Neugebauer, G.; van Duinen,
R. J.; Habing, H. J.; Aumann, H. H.; Beintema, D. A.; Boggess, N.;
Borgman, J.; Clegg, P. E.; Gillett, F. C.; Hauser, M. G.; Houck, J. R.;
Jennings, R. E.; de Jong, T.; Low, F. J.; Marsden, P. L.; Pottasch,
S. R.; Soifer, B. T.; Walker, R. G.; Emerson, J. P.; Rowan-Robinson,
M.; Wesselius, P. R.; Baud, B.; Beichman, C. A.; Gautier, T. N.;
Harris, S.; Miley, G. K.; Young, E.
1986A&AS...65..607O Altcode: 1986A&AS...65..607I
The authors present plots of all 5425 spectra in the IRAS catalogue
of low-resolution spectra. The LRS catalogue contains the average
spectra of most IRAS point sources with 12 μm flux densities above
10 Jy. More than 95 percent of the LRS sources are stars, most of them
with circumstellar envelopes.
---------------------------------------------------------
Title: Magnitudes of selected central stars of planetary nebulae
Authors: Walton, N. A.; Reay, N. K.; Pottasch, S. R.; Atherton, P. D.
1986ESASP.263..497W Altcode: 1986NIA86......497W; 1986niia.conf..497W
Narrow band continuum images of 21 planetary nebulae were obtained using
a CCD camera at the prime focus of the Anglo-Australian Telescope. The
nebulae were selected on the basis that their central stars were
previously poorly detected or undetected. The images were used to
determine visual magnitude for the nuclei of the planetary nebulae and
calculate their corresponding Zanstra temperatures. The distribution of
the planetary nebulae on the Log L-Log T plane is discussed in terms
of theories of the evolution of the nuclei of planetary nebulae. A
number of the central stars studied have high temperatures which can
be explained with present theories if their masses are 1 solar mass.
---------------------------------------------------------
Title: Abundances in the planetary nebula BD +30 3639.
Authors: Pwa, T. H.; Pottasch, S. R.; Mo, J. E.
1986A&A...164..184P Altcode:
High resolution IUE spectra of the low excitation nebula BD
+30°3639 show absorption lines of nebular material and of the
intervening ISM. With the method described in Pwa et al. (1984)
ionic abundances were derived for Mg<SUP>0</SUP>, Mn<SUP>+</SUP>,
Fe<SUP>+</SUP>, Zn<SUP>+</SUP> (all for the first time in a PN) and
for Mg<SUP>+</SUP>, Al<SUP>+</SUP>, Al<SUP>2+</SUP>, Si<SUP>+</SUP>,
O<SUP>0</SUP>. Using ratios of collisionally excited emission lines in
the UV and of available optical and IR data abundances of some ions were
(re)derived or upper limits deduced. It has been found: C = 8.6, O =
8.4, Mg = 6.6, Al = 5.4, Si = 6.3, S = 6.8, Mn ≥ 4.7, Fe ≥ 6.3,
Zn ≥ 5.0. The authors also estimate the possible dust mass assuming
that the depletion of the refractory elements has been caused by their
forming grains.
---------------------------------------------------------
Title: Detailed analysis of the ISM toward dzeta OPH and 9 Sgr.
Authors: Pwa, T. H.; Pottasch, S. R.
1986A&A...164..116P Altcode:
Data from high-resolution spectra obtained with the IUE at 115-210 nm
and 185-310 nm toward Zeta Oph and 9 Sqr are combined with published
laboratory atomic and molecular data and supplementary Copernicus
FUV observations to determine the abundances, temperatures, and
densities in both H I clouds and the Zeta Oph H II region. The results
are presented in extensive tables and graphs and characterized in
detail. Consideration is given to velocity structures, the relationship
of depletion to condensation temperature, the origin of the highly
ionized species of the H II region, the ionization and energy balance,
C photoionization, dust-grain photoelectrons, and ionization of H2 by
cosmic rays.
---------------------------------------------------------
Title: Far-infrared observations of the peculiar variable star
R Aquarii.
Authors: Anandarao, B. G.; Pottasch, S. R.
1986A&A...162..167A Altcode:
The first results on the peculiar Mira variable star R Aquarii obtained
by the IRAS satellite in the far-infrared region are presented. A simple
model in terms of circumstellar dust emission is given to interpret the
far-infrared excess. A two-dust shell model with silicate grains of size
1 μm at temperatures 800±80K and 87±8K seems to fit the observations
remarkably well in addition to the stellar emission at 2800K. It is
shown that this model explains the near and mid-infrared fluxes as
well. In comparison, another Mira variable U Ori also showed two dust
shells but with lower temperatures and smaller grain sizes. Implications
of these results on the nature of R Aquarii are discussed.
---------------------------------------------------------
Title: Erratum - the Far Infrared IRAS Excess in HD161796 and
Related Stars
Authors: Parthasarathy, M.; Pottasch, S. R.
1986A&A...161..417P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: IRAS spectra of planetary nebulae. III.
Authors: Pottasch, S. R.; Preite-Martinez, A.; Olnon, F. M.; Mo,
J. E.; Kingma, S.
1986A&A...161..363P Altcode:
Measurements of the IRAS spectra of planetary nebulae are presented. The
spectra cover the wavelength 7.5 to 23 microns. The lines observed are
mainly from ions of neon and sulfur. The abundance of these two elements
is determined and compared to results found in other astronomical
objects. It is also found that the Ne(4+) ion, when present, is formed
in a region whose density is an order of magnitude higher than the
region whose density is an order of magnitude higher than the region
where most of the line emission originates. IUE measurements of the
Ne(3+) line of many of the nebulae are presented.
---------------------------------------------------------
Title: Detection of the very hot central star in NGC2440
Authors: Atherton, P. D.; Reay, N. K.; Pottasch, S. R.
1986Natur.320..423A Altcode:
It has been argued<SUP>1</SUP> that the extremely faint central stars
of some planetary nebulae must be very hot, with most of their energy
output in the ultraviolet. We now report the detection of the central
star of the planetary nebula NGC2440 in a narrow-band continuum
image using a CCD (charge-coupled device) camera at the prime focus
of the Anglo-Australian telescope. Its visual magnitude has been
measured as 18.9+/-0.2. Its Zanstra temperature<SUP>2,3</SUP> is about
350,000 K, so that it is one of the hottest stars ever observed. Its
radius corresponds to that of a nearly degenerate star. Theoretical
calculations can explain the observed temperature and luminosity if
it has a mass of at least 1.0 M<SUB>solar</SUB> and is in its cooling
stage, but the predicted age of the nebula is considerably less than
that required by the calculations. Furthermore, the present estimates
of the progenitor mass of a 1-M<SUB>solar</SUB> white dwarf are brought
into question.
---------------------------------------------------------
Title: Distances to planetary nebulae. II. HI absorption observations.
Authors: Gathier, R.; Pottasch, S. R.; Goss, W. M.
1986A&A...157..191G Altcode:
Measurements of 21-cm absorption spectra for 24 PN have been carried
out, together with the 21-cm absorption spectrum of a background source
in each case. The 21-cm emission spectra in the direction towards the
PN have also been measured. Kinematic distances to the PN are either
derived using a flat galactic rotation curve or using distances
and radial velocities of H II regions to determine the galactic
structure. For 12 planetary nebulae, the final distance derived has
an uncertainty of less than 50 percent, a significant improvement
over previous distance determinations. H I, which is thought to be
associated with the PN, was found only in the absorption spectrum of
NGC 6790. A rough estimate of the lower limit to the total mass of
the H I involved gives 0.01 solar mass.
---------------------------------------------------------
Title: Distances to planetary nebulae. I. The reddening-distance
method.
Authors: Gathier, R.; Pottasch, S. R.; Pel, J. W.
1986A&A...157..171G Altcode:
Distances to 12 planetary nebulae are derived from the increase
of interstellar reddening with distance along the lines of sight
of the nebulae. The reddening-distance relations are determined
using Walraven VBLUW photometry of stars in small fields around
the planetary nebulae. With a theoretical calibration of the VBLUW
colors the effective temperature, surface gravity and reddening
are determined for early type stars. Distances are then determined
by means of a luminosity calibration which is based on the stellar
evolution models of Hejlesen (1980). The reddenings of the planetary
nebulae are determined using a number of different methods. The amount
of internal reddening is estimated. The planetary nebula distances
derived from the reddening-distance relations have accuracies of 10 to
40 percent. This is a substantial improvement compared to accuracies
of previously determined distances. As a byproduct, the distance to
the young open cluster NGC 2453 is determined.
---------------------------------------------------------
Title: Nova Vulpeculae 1984 No. 2
Authors: Taylor, A. R.; Seaquist, E. R.; Pottasch, S. R.
1986IAUC.4184....1T Altcode: 1986IAUC.4184....0T
A. R. Taylor, Kapteyn Astronomical Institute; E. R. Seaquist,
University of Toronto; and S. R. Pottasch, Kapteyn Astronomical
Institute, report the radio detection of Nova Vul 1984 No. 2 with the
Very Large Array. Multi-frequency observations show a steeply rising
spectrum with the flux density at longer wavelengths increasing with
time. Measured flux densities (in mJy) at 5 GHz were: 1985 July 16,
4.1; Oct. 7, 7.0; Dec. 18, 11.0. A high- resolution map at 15 GHz on
Oct. 7 revealed a main radio source plus a lobe of emission extending
~ 0"25 to the southeast. There is no counterpart of the lobe to the
northwest of the main component. Radio coordinates of the nova are
R.A. = 20h24m40s52, Decl. = +27deg40'48"1 (equinox 1950.0).
---------------------------------------------------------
Title: Infrared emission from young planetary nebulae.
Authors: Pottasch, S. R.
1986CRJS....8...97P Altcode: 1986nepl.conf...97P
Measurements of planetary nebulae in the far infrared, especially from
IRAS, are presented and discussed. The dust temperature and intrinsic
luminosity are found to vary as the nebula evolves. The source of energy
which heats the dust is discussed. The problem as to whether the far
infrared emission only comes from the ionized region of the nebula or
whether the neutral material is also important is argued. The dust
mass of the nebula is found to evolve. The dust emission spectra of
many young nebulae are presented. Finally an estimate of the spatial
distribution of young nebulae near the galactic center is given.
---------------------------------------------------------
Title: Abundances in the planetary nebula NGC 6153.
Authors: Pottasch, S. R.; Dennefeld, M.; Mo, J.
1986A&A...155..397P Altcode:
Spectra in the visual, infrared and ultraviolet, of the planetary nebula
NGC 6153 are presented. They are analysed to obtain the abundance and
physical conditions in the nebula. It is found that NGC 6153 is a very
unusual nebula, its abundance of many elements being higher than any
other nebula.
---------------------------------------------------------
Title: Infrared Observations of an Extended Planetary Nebula -
NGC7293 - the Helix Nebula
Authors: Leene, A.; Pottasch, S. R.
1986ASSL..124..143L Altcode: 1986lodm.conf..143L
In this paper it is shown that the broadband fluxes as measured by
IRAS in the nebula NGC 7293 are mainly due to atomic line emission;
this is probably even true for the long wavelength bands. All the
emission in these bands can be explained by line emission, but it is
likely that some emission is also due to dust.
---------------------------------------------------------
Title: Detection of the very hot Central Star in NGC 2440
Authors: Atherton, P. D.; Reay, N. K.; Pottasch, S. R.
1986mone.work..116A Altcode:
The central star of the planetary nebula NGC 2440 has been detected
in a narrow band continuum image using a CCD at the prime focus of the
Anglo Australian telescope. Its visual magnitude has been measured as
18.9. Its Zanstra temperature is about 350,000K and it is thus one
of the hottest stars ever seen. Its radius corresponds to that of
a nearly degenerate star. Theoretical calculations can explain its
observed temperature and luminosity if it has a mass of 1.0 M_sun;
and it is in its cooling stage. However the theory predicts an age for
the nebula which is considerably less than that observed. Furthermore,
the present estimates of the progenitor mass of a 1 M_sun; white dwarf
are brought into question.
---------------------------------------------------------
Title: IUE Observations of High Galactic Latitude F Supergiants HD
161796 and 163075
Authors: Pottasch, S. R.
1986iue..prop.2571P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hydrogen Deficient Planetary Nebulae: Preliminary Results
Authors: Pottasch, S. R.; Mampaso, A.; Manchado, A.; Menzies, J.
1986ASSL..128..359P Altcode: 1986IAUCo..87..359P; 1986hdsr.proc..359P
New spectra of A78 and A58 at different positions in the nebulae are
presented. An abundance gradient is found in A78, extending quite
close to the center. Similarly, the nebulous knot near the center of
A58 has considerably higher heavy element abundances than the outer
regions of this nebula. The ionization state is considerably lower
in A58 than A78. In A78 most of the neon is in the form of Ne(3+) and
Ne(4+), indicating that the standard ionization correction factor as
used by Jacoby and Ford (1983), is substantially in error. Finally,
the very high infrared excesses found in these nebulae are discussed.
---------------------------------------------------------
Title: The far-infrared (IRAS) excess in HD 161796 and related stars.
Authors: Parthasarathy, M.; Pottasch, S. R.
1986A&A...154L..16P Altcode:
The far infrared IRAS measurements of the high galactic latitude
F-supergiant HD 161796 and related stars are found to show
strong far infrared excesses, due to large amounts of dust around
them. For HD 161796 the dust mass is found to be of the order of
10<SUP>-2</SUP>M_sun; to 10<SUP>-3</SUP>M_sun;, and for HD 101584 it
is of the order of 10<SUP>-3</SUP>M_sun;. These results suggest that
HD 161796 and other similar high galactic latitude F-supergiants have
suffered extensive mass loss in the past as a result of superwind
phenomenon on their AGB stage of evolution.
---------------------------------------------------------
Title: Observations of Planetary Nebulae with Anomalously High
Ne Abundance
Authors: Pottasch, S. R.
1986iue..prop.2658P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: IRAS measurements of planetary nebulae
Authors: Pottasch, S. R.
1986ASSL..124..131P Altcode: 1986lodm.conf..131P
Low resolution IRAS spectra are described and their significance
discussed, along with the survey measurements. The relative
importance of line and continuum emission in the survey measurements
is evaluated. The interpretation of the continuum emission as dust
radiation is considered. The energy balance is used as a probe for
the source of dust heating. An evolution of the dust 'temperature'
is shown to exist and simple interpretations are given. The gas to
dust mass ratio is presented and its evolution is discussed. Finally,
the possibility of using the IRAS data to extend the known number of
planetary nebulae substantially is examined.
---------------------------------------------------------
Title: IRAS Measurements of Planetary Nebulae
Authors: Pottasch, S. R.
1986mone.work...89P Altcode:
The low resolution IRAS spectra are described and a discussion of their
importance is given. The survey measurements are then discussed. The
relative importance of line and continuum emission in the survey
measurements is evaluated. The interpretation of the continuum emission
as dust radiation is considered. The energy balance is used as a probe
for the source of dust heating. An evolution of the dust 'temperature'
is shown to exist and simple interpretations are given. The gas to
dust mass ratio is presented and its evolution is discussed. Finally
the possibility of using the IRAS data to substantially extend the
known number of planetary nebulae is examined.
---------------------------------------------------------
Title: The compact radio source near G 357.7-0.1.
Authors: Shaver, P. A.; Pottasch, S. R.; Salter, C. J.; Patnaik,
A. R.; van Gorkom, J. H.; Hunt, G. C.
1985A&A...147L..23S Altcode:
Since the compact source near the SNR G357.7-0.1 is probably a normal
H II region, it is held to be an unlikely site for an accreting
binary system powering G357.7-0.1, as suggested by Helfand and Becker
(1985). It may instead be a line-of-sight object totally unassociated
with the SNR, or the two objects could be located in the same OB
association. It is suggested that G357.7-0.1's unusual morphology may
be due to the occurrence of a supernova explosion near the edge of a
molecular cloud containing the H II region.
---------------------------------------------------------
Title: Fine-structure lines.
Authors: Pottasch, S. R.
1985Obs...105....5P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Highly ionized neon in the planetary nebula NGC 6302.
Authors: Pottasch, S. R.; Preite-Martinez, A.; Olnon, F. M.; Raimond,
E.; Beintema, D. A.; Habing, H. J.
1985A&A...143L..11P Altcode:
The (low resolution) spectrum of the planetary nebula NGC 6302 in the
wavelength range from 7.5 μm to 22 μm is presented. The strongest
feature in the spectrum is due to a line at 7.7 μm, which is identified
as Ne VI seen for the first time. The Ne V line at 14.3 μm is also
seen for the first time. The weakness of this line relative to Ne V
lines in the visible spectrum indicates that it is formed at a density
of 3×10<SUP>5</SUP>cm<SUP>-3</SUP> which is considerably higher of
10<SUP>4</SUP>cm<SUP>-3</SUP> at which the S II, O II and C III lines
are formed. The Ne II and Ne III lines are also observed, making it
possible to accurately derive the total neon abundance.
---------------------------------------------------------
Title: Chemical composition of interstellar material
Authors: Pottasch, S. R.
1985IAUS..106..575P Altcode:
Abundances in interstellar clouds, as determined from interstellar
absorption lines, are discussed first, including abundances in
"abnormal" (high-velocity) clouds. H II-region abundances are then
discussed and compared to results from the interstellar clouds. The
present status of an abundance gradient as determined from H II regions
is given. Abundances in planetary nebulae are then given for various
categories of nebulae, and compared to H II regions. Finally a short
status report on abundances near the galactic center is given.
---------------------------------------------------------
Title: Nebular Abundances for a sample of planetary nebulae with
accurate distances.
Authors: Gathier, R.; Pottasch, S. R.
1985ESOC...21..307G Altcode: 1985pdcn.conf..307G; 1985pdce.work..307G
A sample of planetary nebulae with recently obtained accurate distances
is used to study nebular enrichment as a function of central star
position in the Hertzsprung-Russell diagram. The results show that
theory is correct in predicting that the more massive intermediate-mass
stars produce He- and N-rich planetary nebulae. This confirms tentative
conclusions from previous studies. It appears that nebular enrichment
becomes significant for planetary nebulae which originate from stars
that are more massive than about 2.5-3 solar masses.
---------------------------------------------------------
Title: Wind distances for planetary nebulae.
Authors: Kaler, J. B.; Mo, J. -E.; Pottasch, S. R.
1985ApJ...288..305K Altcode:
A new method for the determination of distances to planetary nebulae is
presented. If a star has a strong wind that produces a P Cygni profile
in its spectrum, an escape velocity may be inferred from the terminal
velocity, which provides a relation involving stellar temperature,
luminosity, and mass. The theory of stellar evolution provides a
second relation among these three variables, so that once the star's
temperature is known, it is possible to simultaneously derive its mass
and luminosity, and hence its distance. The method is applied to several
test cases that illustrate its viability and current limitations.
---------------------------------------------------------
Title: Abundances in planetary nebulae near the galactic center.
Authors: Pottasch, S. R.; Dennefeld, M.
1985ESOC...21..303P Altcode: 1985pdcn.conf..303P; 1985pdce.work..303P
Preliminary results of a program to measure the abundances of planetary
nebulae near the galactic center are given. It appears that both oxygen
and nitrogen have approximately solar abundances in these nebulae. The
high abundances found in the nearby nebula NGC 6153 are discussed in
this context.
---------------------------------------------------------
Title: Book-Review - Planetary Nebulae
Authors: Pottasch, S. R.; Mallik, D. C. V.
1984BASI...12..424P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Mass loss from the central star of NGC 3242.
Authors: Hamann, W. -R.; Kudritzki, R. -P.; Mendez, R. H.; Pottasch,
S. R.
1984A&A...139..459H Altcode:
The central star of NGC 3242, which was classified to be of
"continuous type" before Kudritzki et al. (1981) discovered and
analysed photospheric absorptions, has been observed with IUE in high
resolution. The N V resonance doublet exhibits a weak P Cygni profile
with photospheric components. Theoretical profiles are obtained from
comoving-frame calculations, and the nitrogen ionization balance
is computed. A mass loss rate of log{M/(M_sun;yr<SUP>-1</SUP>)} =
-10.1...-8.1 is derived, while the final wind velocity is v = 2200
km s<SUP>-1</SUP>. The authors compare these wind parameters with
the parameters of the central star, which is probably the hottest
mass-losing star studied so far, and find that the usual relations
established for winds from early-type stars are fulfilled.
---------------------------------------------------------
Title: Nebular and interstellar absorption lines in planetary nebulae
: the case of NGC 6543.
Authors: Pwa, T. H.; Mo, J. E.; Pottasch, S. R.
1984A&A...139L...1P Altcode:
Using high resolution IUE spectra it is possible to separate the
narrow absorption lines due to the interstellar material and the
nebular matter. The analysis of nebular absorption lines has three
advantages. First the column densities of ions different from those
observed in emission can be determined. The abundance of the elements
are then readily derived without applying ionization correction. Second
the population ratio of the fine structure levels and the ground level
of certain ions and the ionization balance can yield an independent
estimate of the electron density. Third using Lyman α absorption and
interstellar measurements of S and Zn in the foreground extinction
can be estimated. The authors use the above method for NGC 6543. They
derive the abundance of C, Si, S and Al.
---------------------------------------------------------
Title: Book-Review - Planetary Nebulae
Authors: Pottasch, S. R.; Friedjung, M.
1984SSRv...39..216P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: IRAS measurements of planetary nebulae.
Authors: Pottasch, S. R.; Baud, B.; Beintema, D.; Emerson, J.; Habing,
H. J.; Harris, S.; Houck, J.; Jennings, R.; Marsden, P.
1984A&A...138...10P Altcode:
Far-infrared IRAS measurements of 46 of the brighter planetary nebulae
are presented. Dust temperatures are computed. Higher dust temperatures
are found in the younger, denser nebulae. Lyman α is shown to be a
sufficient source of energy to heat the dust for the larger, older
nebulae, but another energy source (probably the exciting star) is
required for the younger nebulae.
---------------------------------------------------------
Title: The magnitudes and temperatures of central stars of planetary
nebulae.
Authors: Reay, N. K.; Pottasch, S. R.; Atherton, P. D.; Taylor, K.
1984A&A...137..113R Altcode:
In order to determine the Zanstra temperature of the central star of
a planetary nebula, it is necessary to know the visual continuum flux
emitted by the star. When the central star is very hot, great care
is required to distinguish the weak stellar flux from the sometimes
relatively strong nebular continuum. A technique is adopted which
involves imaging the nebulae and central star temperatures between 10
to the 5th K and emission lines are found. The technique is applied to
nine planetary nebulae and central star temperature between 10 to the
5th K and 2 x 10 to the 5th K is found. For the central star of NGC
2440 the temperature is a lower limit since no star can be detected
against the nebular background.
---------------------------------------------------------
Title: Hot central stars in planetary nebulae.
Authors: Mo, J.; Pwa, T. H.; Pottasch, S. R.
1984ESASP.218..329M Altcode: 1984iue..conf..329M
The Zanstra temperature is determined for five hot stars using IUE
spectra. The ultraviolet part of the spectrum is much more favourable
than the visual region for such a determination because the stellar
continuum flux density is much stronger relative to the nebular
continuum in the ultraviolet.
---------------------------------------------------------
Title: Interstellar and nebular absorption lines in planetary nebulae.
Authors: Pwa, T. H.; Mo, J. E.; Pottasch, S. R.
1984ESASP.218..175P Altcode: 1984iue..conf..175P
High resolution IUE spectra were used to separate the narrow absorption
lines due to the interstellar material and the nebular matter in
NGC 6543. Column densities of ions in both regions were determined
and the ionic and elemental abundances were derived. Lines from the
fine structure levels yield the electron density in the nebula: log
n = 3, consistent with the current value found for eNGC 6543. Using
Lyman alpha absorption and interstellar absorption lines of S and Zn
the foreground extinction was estimated: E(B-V) = 0.04. The hydrogen
column density towards NGC 6543 is found to have log NH = 20.35.
---------------------------------------------------------
Title: The interstellar medium in the Scorpius-Ophiuchus region.
Authors: Pwa, T. H.; Pottasch, S. R.
1984ESASP.218..167P Altcode: 1984iue..conf..167P
Lines of sight from stars in the Sco-Oph complex are analyzed. Data
are high resolution IUE spectra with visual and 21 cm radio
observations. Abundances are compared to solar values. Zinc proves to
be a good metallicity tracer since it is only depleted by a factor
of 2; P and Cl are slightly depleted; Mg, Si and Fe are depleted
by 0.04 to 0.08. The most severely depleted are Ni, Cr and Al, at
0.003. Carbon monoxide is well observed in one of the stars in isotopes
C12O and C13O. Their respective column densities are 14.5 and 13.4
(logarithmically), giving a low isotope ratio of 11. Using ionization
equilibria electron densities are computed. It is found that ne varies
from 0.02 to 0.20. From excitation balance total particle density in
the neutral cloud of 1.5 to 2.2 is derived.
---------------------------------------------------------
Title: Mass loss from the central star of NGC 3242.
Authors: Hamann, W. R.; Kudritzki, R. P.; Mendez, R. H.; Pottasch,
S. R.
1984ESASP.218..333H Altcode: 1984iue..conf..333H
The central star of NGC 3242 was observed with IUE in high
resolution. The N V resonance doublet exhibits a weak P Cygni profile
with photospheric components. Theoretical profiles are obtained from
comoving-frame calculations, and the nitrogen ionization balance is
computed. A mass loss rate of -10.1 to -8.1 is derived, while the final
velocity is 2200 km/sec. Wind parameters compared with the parameters
of the central star show that the usual relations established for
winds from early-type stars are fullfilled.
---------------------------------------------------------
Title: Observations of Planetary Nebulae with Anomalously High
Neon Abundance
Authors: Pottasch, S. R.
1984iue..prop.2090P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Planetary Nebulae - a Study of Late Stages of
Stellar Evolution
Authors: Pottasch, S. R.
1984Natur.309R.477P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Planetary Nebulae - a Study of Late Stages of
Stellar Evolution
Authors: Pottasch, S. R.
1984Sci...224.1266P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: IRAS observations of OH/IR stars.
Authors: Olnon, F. M.; Baud, B.; Habing, H. J.; de Jong, T.; Harris,
S.; Pottasch, S. R.
1984ApJ...278L..41O Altcode:
Preliminary results of IRAS survey observations of a sample of 40 very
evolved stars, all detected originally as OH maser emission sources,
are presented. In several cases, the spectrum is very much redder than
for those sources identified from the ground. Color-color plots show
that there is a continuous sequence from classical Mira variables to
the reddest OH/IR stars. However, the reddest stars differ somewhat:
they pulsate only weakly or not at all. Probably, they have reached
the end of their evolution on the asymptotic giant branch.
---------------------------------------------------------
Title: The Infrared Astronomical Satellite (IRAS) mission.
Authors: Neugebauer, G.; Habing, H. J.; van Duinen, R.; Aumann,
H. H.; Baud, B.; Beichman, C. A.; Beintema, D. A.; Boggess, N.; Clegg,
P. E.; de Jong, T.; Emerson, J. P.; Gautier, T. N.; Gillett, F. C.;
Harris, S.; Hauser, M. G.; Houck, J. R.; Jennings, R. E.; Low, F. J.;
Marsden, P. L.; Miley, G.; Olnon, F. M.; Pottasch, S. R.; Raimond,
E.; Rowan-Robinson, M.; Soifer, B. T.; Walker, R. G.; Wesselius,
P. R.; Young, E.
1984ApJ...278L...1N Altcode:
The Infrared Astronomical Satellite (IRAS) consists of a spacecraft
and a liquid helium cryostat that contains a cooled IR telescope. The
telescope's focal plane assembly is cooled to less than 3 K, and
contains 62 IR detectors in the survey array which are arranged so
that every source crossing the field of view can be seen by at least
two detectors in each of four wavelength bands. The satellite was
launched into a 900 km-altitude near-polar orbit, and its cryogenic
helium supply was exhausted on November 22, 1983. By mission's end, 72
percent of the sky had been observed with three or more hours-confirming
scans, and 95 percent with two or more hours-confirming scans. About
2000 stars detected at 12 and 25 microns early in the mission, and
identified in the SAO (1966) catalog, have a positional uncertainty
ellipse whose axes are 45 x 9 arcsec for an hours-confirmed source.
---------------------------------------------------------
Title: IRAS spectra of planetary nebulae.
Authors: Pottasch, S. R.; Beintema, D. A.; Raimond, E.; Baud, B.;
van Duinen, R.; Habing, H. J.; Houck, J. R.; de Jong, T.; Jennings,
R. E.; Olnon, F. M.; Wesselius, P. R.
1984ApJ...278L..33P Altcode:
Low-resolution spectra in the 7 - 23 μm range of five planetary nebulae
observed with IRAS are presented and analyzed. The Ne III line at 15.5
μm is observed for the first time. This line is a sensitive indicator
of electron temperature. The Ne III line and the S IV line at 11.5 μm
dominate the short wavelengths in the spectra of the three observed
medium-excitation nebulae.
---------------------------------------------------------
Title: Book reviews
Authors: Ooms, O.; van der Woerd, Hans; Lamers, Henny J. G. L. M.;
Kleczek, Josip; Kovalevsky, J.; Gathier, R.; Jarzebowski, T.; Swings,
J. P.; van der Hucht, K. A.; Namba, O.; Mewe, R.; Lynden-Bell,
D.; Kuijpers, Jan; van der Klis, M.; de Hoop, D.; Wittenberg, H.;
Iwanowska, W.; Thé, P. S.; Schrijver, J.; Pottasch, S. R.
1984SSRv...37..399O Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Planetary nebulae. A study of late stages of stellar evolution
Authors: Pottasch, S. R.
1984ASSL..107.....P Altcode: 1984assl..107.....P
A detailed description of planetary nebulae, including the relevant
astronomical observations and their interpretation, is presented. The
distribution of planetary nebulae in the galaxy, the interpretation
of emission lines and nebular abundances, nebular continuum emission,
the distance to nebulae, and morphology, expansion, and mass loss
of nebulae are considered. The temperature of the central stars,
infrared and millimeter radiation, the evolution of the central star,
the evolution from red giant to planetary nebula, and the influence
of planetary nebulae on the interstellar medium are addressed.
---------------------------------------------------------
Title: Book-Review - Diffuse Matter in Galaxies
Authors: Audouze, J.; Lequeux, J.; Levy, M.; Vidal-Madjar, A.;
Pottasch, S. R.
1984SSRv...37..407A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Planetary Nebulae - a Study of Late Stages of
Stellar Evolution
Authors: Pottasch, S. R.
1984S&T....67..527P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Distances, radii, and masses of the planetary nebulae.
Authors: Phillips, J. P.; Pottasch, S. R.
1984A&A...130...91P Altcode:
The authors have used recently published data on planetary nebulae
densities, radio continuum fluxes, and gas kinetic temperatures, to
determine nebular distances, masses, and radii. Distances are found
to differ from those determined through the Shklovky method by a mean
factor ≡2; nebular radii are found to take values R ≤ 0.3 pc,
and the mean shell mass is determined to be <log(M/M_sun;)>
= -1.31±0.13. Evidence is presented for an intrinsic variation in
ionised shell masses, ranging over some two orders of magnitude or
more. Finally, density is found to change with nebular radius as
n<SUB>e</SUB> ∝ R<SUP>-1.3</SUP>. This result, together with the
proposed mass variation, may indicate the presence of substantial H
I zones outside the observed ionised shells.
---------------------------------------------------------
Title: VLA observations of planetary nebulae at the Galactic Centre.
Authors: Gathier, R.; Pottasch, S. R.; Goss, W. M.; van Gorkom, J. H.
1983A&A...128..325G Altcode:
The authors have observed a sample of 42 planetary nebulae in the
direction of the Galactic Centre (GC). They used the Very Large Array
(VLA) at a frequency of 4.9 GHz. They expect that ≡90% of the sample
is physically associated to the GC region. About 25% of the nebulae show
structures that indicate a shell distribution of the ionized gas. For
all the detected sources the radio map, radio position, 6 cm flux
density, deconvolved angular diameter and total ionized nebular mass
are presented. The distribution of flux densities of the GC planetaries
differs considerably from the distribution for nearby and Magellanic
Clouds nebulae. This difference is explained by the strong selection
effect of studying only optically confirmed planetary nebulae at the GC.
---------------------------------------------------------
Title: A VLA observation of the planetary nebula K 648 in Messier 15.
Authors: Gathier, R.; Pottasch, S. R.; Goss, W. M.
1983A&A...127..320G Altcode:
The authors have made a VLA observation at 6 cm of K 648, the
planetary nebula in the globular cluster M15. The angular resolution is
0arcsec.4 and the rms noise is 0.1 mJy. K 648 has an angular diameter
of 1arcsec.0±0arcsec.3 and a flux density of 3.1±0.6 mJy. With the
known distance to M15 the physical size, total ionized nebular mass
and electron density are derived. These quantities are comparable to
"typical" planetary nebulae in the solar neighbourhood.
---------------------------------------------------------
Title: The temperature of central stars of planetary nebulae :
the energy-balance method.
Authors: Preite-Martinez, A.; Pottasch, S. R.
1983A&A...126...31P Altcode:
A method is developed for determining the color temperature of the
ionizing continuum of the central star photoionizing a surrounding
nebula. The basis of this method rests on the assumption that
energy balance holds in the photoionized nebula. This method is a
generalization of Stoy's first derivation (1933) to several possible
situations in actual nebulae, including the optically thin, partially
thick, and completely optically thick nebulae. An analytical expression
is obtained for the energy balance temperature of the central stars of
low excitation nebulae. The energy balance temperature for 51 planetary
nebulae are derived and the results are shown to be fairly insensitive
to the optical depth of the surrounding nebula. A good consistency
is obtained between the computed energy balance temperatures and
the Zanstra temperatures. These findings are employed to predict the
apparent visual magnitude of central stars not yet observed or only
marginally detected.
---------------------------------------------------------
Title: The galactic abundance gradient.
Authors: Shaver, P. A.; McGee, R. X.; Newton, L. M.; Danks, A. C.;
Pottasch, S. R.
1983MNRAS.204...53S Altcode:
Chemical abundances in a large and representative sample of galactic H
II regions covering a wide range in galactocentric radius R<SUB>G</SUB>
were measured using radio and optical spectroscopy. Accurate electron
temperatures in 67 H II regions spanning the range R<SUB>G</SUB> =
3.5-13.7 kpc were determined using radio recombination lines and
these temperatures were applied to optical spectra of 33 of the
same H II regions in order to determine the abundances of O, N,
S, Ne, Ar, and He(+). Among other results, it is found that some
H II regions have electron temperatures below 5000 K and that the
radio-determined electron temperatures agree well with those obtained
from the optical line ratios, in the light of standard models of
H II regions. A gradient of H II region electron temperature with
distance from the galactic center is found which equals +433 + or -
40 K/kpc, while the oxygen abundance gradient is -0.07 + or - 0.015
dex/kpc. The nitrogen abundance gradient is similar to that of oxygen,
-0.09 + or 0.015 dex/kpc, while the sulfur abundance gradient (-0.01 +
or - 0.02 dex/kpc) is significantly flatter than that of oxygen. No
significant gradient in He(+)/H(+) is detected. In addition, evidence
indicates that the abundance gradients may be steeper over the inner
regions of the galactic disk.
---------------------------------------------------------
Title: Distances of the central stars and their position in the
HR diagram.
Authors: Pottasch, S. R.
1983IAUS..103..391P Altcode:
Determination of the distance to individual planetary nebulae (PN)
is discussed. Seven independent methods are considered and used
to obtain approximate distances to 50 PN. The accuracy of these
distances is tested by comparing nebular properties derived from
them with properties of nebulae at the galactic center or in the
Magellanic clouds. A comparison is also made with statistical distance
determinations. It is concluded that the assumption of constant mass
often leads to an overestimate of the distance, while the assumption of
constant H-beta flux leads to distances having individual uncertainties
of up to a factor of three. The determination of the temperature of
the central star is summarized. Individual central stars are placed on
the HR diagram and compared with theoretical predictions. Evolutionary
deductions made from the observations are discussed.
---------------------------------------------------------
Title: VLA Observations of Planetary Nebulae at the Galactic Centre
Authors: Gathier, R.; Pottasch, S. R.; Goss, W. M.; van Gorkom, J. H.
1983IAUS..103..423G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Temperatures of Central Stars of Planetary Nebulae -
the Energy-Balance Method
Authors: Preite-Martinez, A.; Pottasch, S. R.
1983IAUS..103..547P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Study of The Interstellar Medium in the Scorpius-Ophiuchus
Region
Authors: Pottasch, S. R.
1983iue..prop.1738P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Kinematic distances of planetary nebulae.
Authors: Maciel, W. J.; Pottasch, S. R.
1983IAUS..103..541M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Distance determinations from 21 CM interstellar absorption-line
measurements.
Authors: Pottasch, S. R.; Gathier, R.; Goss, W. M.
1983IAUS..103..541P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Extinction - Distances to planetary nebulae.
Authors: Gathier, R.; Pottasch, S. R.
1983IAUS..103..540G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Abandances in the planetary nebula NGC 6853.
Authors: Pottasch, S. R.; Gilra, D. P.; Wesselius, P. R.
1982A&A...109..182P Altcode:
IUE ultraviolet spectra have been analysed of several portions of
planetary nebula NGC 6853. Combining these measurements with those made
from the ground, we are able to determine the relative abundances of C,
N, O, and Ne, without making any important assumption concerning the
ionization of any of these elements. C, O, and Ne have solar abundances
whereas N is overabundant by a factor of three. The UV nebular continuum
is also discussed.
---------------------------------------------------------
Title: Analysis of the IUE and optical spectra of the peculiar Be
star HD 87643.
Authors: de Freitas Pacheco, J. A.; Gilra, D. P.; Pottasch, S. R.
1982A&A...108..111D Altcode:
IUE observations of the peculiar Be star HD 87643 are presented. The
broad absorptions seen at 2400 A, 2600 A, and 2750 A are interpreted as
being produced by Fe II transitions from the ground-state and the low
lying metastable states. The optical lines of Fe II seen in emission are
most probably excited by continuum fluorescence. This interpretation
allows us to estimate the rate of mass loss through the analysis of
the iron lines. The calculated value is about 7/10 millionths solar
mass per yr, which is in good agreement with that obtained from the
analysis of the H-beta (P Cygni) profile. This mass loss rate is two
to three orders of magnitude higher than the values deduced from the
UV lines for other Be stars, leading to the conclusion that a very
active short-lived phase in the star's evolution is being observed.
---------------------------------------------------------
Title: The Galactic Abundance Gradient
Authors: Shaver, P. A.; Danks, A. C.; McGee, R. X.; Newton, L. M.;
Pottasch, S. R.
1982Msngr..27...19S Altcode:
The study of chemical abundances and their variation from one galaxy
to another or within individual galaxies is of fundamental importance
for our understanding of the evolution of galaxies. The abundances
of heavy elements in the interstellar medium provide a fossil record
of the enrichment which has taken place due to nucleosynthesis in
successive generations of stars. Gradients of heavy element abundances
with distance from the galactic centre are predicted by models in
which the rate of star formation varies across the galactic disk,
and by dynamical collapse models of galactic evolution which involve
fresh infall of primordial gas onto the disk over long periods of
time. Different models predict different abundance gradients (in slope
and shape). and abundance measurements give constraints on these models
(see Pagel and Edmunds, 1981, Ann. Rev. Astron. Astrophys. 19, 77,
for arecent review).
---------------------------------------------------------
Title: The distance to the P.N. NGC 7027.
Authors: Pottasch, S. R.; Goss, W. M.; Arnal, E. M.; Gathier, R.
1982A&A...106..229P Altcode:
Various direct methods for determining the distance to NGC 7027 are
discussed. The first, 21 cm absorption in the intervening material,
is shown to give very clear limits to the distance. These limits are
still further sharpened by two other methods: a comparison of the
intrinsic H-beta luminosities of NGC 7027 and extragalactic planetary
nebulae; and a comparison of the density determined by H beta flux,
which is dependent on the distance, with the density as determined by
forbidden lines and radio recombination lines, which is not distance
dependent. The result is a distance of between 1 and 1.5 kpc.
---------------------------------------------------------
Title: Photoelectric heating of H II regions
Authors: Maciel, W. J.; Pottasch, S. R.
1982A&A...106....1M Altcode:
It is determined through the study of H II region heating by electrons
ejected from grains after absorption of stellar photons, as well as by
recombination of Lyman-alpha photons, that the nebula is heated further
by photoionization of H and He, and cooled by collisional excitation
of low-lying, abundant ion levels. It is found that this mechanism can
influence nebula thermal structure at 20-60% of the Stromgren radius,
depending on assumed electron density.
---------------------------------------------------------
Title: Continuum Radiation From Hot Central Stars of Planetary Nebulae
Authors: Pottasch, S. R.
1982iue..prop.1215P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Extinction to Planetary Nebulae
Authors: Pottasch, S. R.
1982iue..prop.1376P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Mass-Loss of Wolf-Rayet-Type Central Stars of Planetary Nebulae
Authors: Pottasch, S. R.
1982iue..prop.1380P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The ultraviolet spectrum of the planetary nebula NGC 2371
and its exciting star.
Authors: Pottasch, S. R.; Gathier, R.; Gilra, D. P.; Wesselius, P. R.
1981A&A...102..237P Altcode:
Low resolution IUE spectra have been taken of the planetary nebula
NGC 2371. Some were centered on the exciting star while other spectra
measure only nebula emission. We discuss the nebula line and continuum
spectrum in terms of the physical state of the nebula gas and its
abundance. The stellar spectrum yields information on the atmospheric
temperature and mass loss rate.
---------------------------------------------------------
Title: Aperture synthesis observations of recombination lines from
compact H II regions. II - The radio sources near K 3-50
Authors: van Gorkom, J. H.; Shaver, P. A.; Pottasch, S. R.; Blair,
G. N.; Matthews, H. E.
1981A&A....94..259V Altcode:
Observations of the H 109 (alpha) line with the Westerbork Synthesis
Radio Telescope showed compact H II regions near K 3-50. The H2CO
absorption detectors were directed towards the brightest components
A and C using the Effelsberg 100 m telescope; the more compact line
sources of the H II (alpha) have lower line to continuum ratios due to
pressure broadening, with very strong H2CO absorption towards C. The
most compact H II regions A and C velocities differ from the neutral
material by -7 and +7 km/s, indicating that both sources are examples
of the 'blister model'.
---------------------------------------------------------
Title: Hot central stars of planetary nebulae.
Authors: Pottasch, S. R.
1981A&A....94L..13P Altcode:
A substantial fraction of the central stars are hot objects. The
temperature of some of the hottest of the stars is investigated and
found to be between 1O5°K and 6 × 10<SUP>5</SUP> °K. The radii
and luminosities of these stars are found, and their evolution is
discussed. In particular, some of the hottest of these stars are
associated with recently formed nebulae, while others are substantially
older.
---------------------------------------------------------
Title: High-Resolution Observations of Planetary Nebulae
Authors: Pottasch, S. R.
1981iue..prop..905P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The position of the central stars of planetary nebulae in
the Hertzsprung-Russell diagram
Authors: Pottasch, S. R.
1981ASSL...88..447P Altcode: 1981pprg.work..447P
The methods for determining the effective temperature of the nuclei
of planetary nebulae are reviewed. The determination of the radius
and luminosity is also discussed. Special attention is given to the
very-high-temperature objects. Distance determinations are reviewed,
as well as determination of the nebular mass. A comparison of the
observations with theory is given, and it is concluded that the
mass of the central star is often about 0.5 solar mass but that the
very-high-temperature objects must be about 1 solar mass or more.
---------------------------------------------------------
Title: The far ultraviolet emission of the central stars of planetary
nebulae - erratum .
Authors: Natta, A.; Pottasch, S. R.; Preite-Martinez, A.
1980A&A....91..378N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Masses of planetary nebulae.
Authors: Pottasch, S. R.
1980A&A....89..336P Altcode:
A new determination of the ionized mass of planetary nebulae
is given. The total mass is also discussed. Aside from the mass
determination, the most important conclusions are that the ionized mass
usually is only a small fraction of the total mass (i.e., the nebulae
are usually optically thick to ionizing radiation) and the so-called
Shklovsky method of determining the distance of nebulae usually gives
a substantial overestimate of the distance.
---------------------------------------------------------
Title: Distances of planetary nebulae.
Authors: Maciel, W. J.; Pottasch, S. R.
1980A&A....88....1M Altcode:
The distances to 121 planetary nebulae are calculated through the
use of an empirical relationship between the nebular ionized mass
and radius. Such relation is established on the basis of recently
determined electron densities and selected distances. The new distances
are compared with values previously published, and reasons are given
for their adoption, based on observed radio and H-beta fluxes. Finally,
the adopted model is compared with the results produced by simple
theoretical models for the central stars.
---------------------------------------------------------
Title: Abundances and physical conditions in a high-velocity cloud.
Authors: Pottasch, S. R.; Wesselius, P. R.; Arnal, E. M.
1980ESASP.157...13P Altcode: 1980IUE2n.......13P; 1980iue..conf...13P
The physical conditions in the 'high-velocity cloud' in the direction
of HD 175754 are discussed, based on the high-dispersion International
Ultraviolet Explorer (IUE) measurements. It was found that the
abundances are very close to solar. Although the oxygen (and presumably
also the hydrogen) is mostly neutral, the ionization is higher than
expected from a neutral cloud. Consequences for the ionization and
heating of the interstellar medium in general are discussed.
---------------------------------------------------------
Title: Observations of the exciting stars of NGC 2023 and M 43 -
Interstellar extinction.
Authors: Gilra, D. P.; Arnal, E. M.; Wesselius, P. R.; Pottasch,
S. R.; de Vries, J.
1980ESASP.157...19G Altcode: 1980iue..conf...19G; 1980IUE2n.......19G
Both low and high resolution International Ultraviolet Explorer (IUE)
observations of the exciting stars of two nebulosities in Orion, NGC
2023 (HD 37903) and M43 (HD 37061) are discussed. Comparison with
Astronomical Netherlands Satellite (ANS) observations shows that,
in the 2.5 min X 2.5 min ANS field of view, a substantial nebular
contribution is included. The extinction curve for HD 37903 is smilar
to that of the inner region of the rho Oph cloud whereas for HD 37061
it is even lower throughout UV with the normalized extinction at 2200
being only 3.8. It appears that the ratio of small aperture to large
aperture data is not wavelength independent in the long wavelength
range. From the high resolution observations it seems that carbon may
be less and oxygen may be more under/abundant in these directions.
---------------------------------------------------------
Title: The far ultraviolet emission of the central stars of planetary
nebulae.
Authors: Natta, A.; Pottasch, S. R.; Preite-Martinez, A.
1980A&A....84..284N Altcode:
The paper deals with the far UV (100 - 900A) flux emitted by the
central stars of planetary nebulae. The method used to determine the
flux is discussed together with observation parameters. The procedure
discussed can be applied to abundance analysis.
---------------------------------------------------------
Title: C, N and O in the planetary nebula 2371.
Authors: Pottasch, S. R.; Gilra, D. P.; Natta, A.; Preite-Martinez,
A.; Wesselius, P. R.
1980ESASP.157..185P Altcode: 1980iue..conf..185P; 1980IUE2n......185P
Low resolution IUE spectra were taken of NGC 2371, some centered on
the central star, while other spectra include only the nebula. The
resultant abundances are discussed.
---------------------------------------------------------
Title: Observations of HII regions in the Magellanic Clouds.
Authors: Gilra, D.; Dennefeld, M.; Pottasch, S. R.
1980ESASP.157..205G Altcode: 1980IUE2n......205G; 1980iue..conf..205G
International Ultraviolet Explorer observations of 5 positions in the
30 Doradus region and one in N79A in the Large Magellanic Cloud, and,
N81 and N66 in the Small Magellanic Cloud were obtained. The C (III)
line at 1909 A was present in almost all the objects. Dust scattered
light was detected in 30 Dor and N66. A preliminary analysis of the
abundances in N81 shows that carbon is underabundant by about a factor
of 10.
---------------------------------------------------------
Title: The Peculiar Slow Nova HD 87643
Authors: Pottasch, S. R.
1980iue..prop..685P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Interstellar Line Measurements of High-Velocity Clouds
Authors: Pottasch, S. R.
1980iue..prop..686P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Cool gaseous nebulae
Authors: Shaver, P. A.; McGee, R. X.; Pottasch, S. R.
1979Natur.280..476S Altcode:
Radio recombination line observations of several low-density nebulae
are made, in order to determine the electron temperatures in the absence
of such effects as collisional de-excitation, stimulated emission, and
pressure broadening. Two nebulae, RCW94 and G339.1-0.2, are examined
in detail. Their most striking feature is the width of their spectral
lines (14.9 km/s), determined by employing two simultaneous 512-channel
spectra of a 10 MHz band, containing the H109 alpha, H137 beta, and
He109 alpha lines. The measured electron temperatures were found to
be 4,600 K for RCW94 and 3800 K for G339.1-0.2. These relatively low
temperatures are caused by a high metal abundance, which was found to
be higher than the solar values by a factor of 4 to 5.
---------------------------------------------------------
Title: The effective temperatures of the O stars.
Authors: Pottasch, S. R.; Wesselius, P. R.; van Duinen, R. J.
1979A&A....77..189P Altcode:
Far-ultraviolet photometric observations (in 5 bands between 1550 A
and 3300 A) are presented for ten O stars which are also the exciting
stars of diffuse nebulae. Since the number of photons shortwards of
the Lyman limit is known for these stars, sufficient information on the
total flux is available to determine the effective temperature without
making any assumptions concerning a model atmosphere. Conversely,
the distribution of flux with wavelength can be used to determine
the applicability of a given model. A detailed discussion of this is
presented. It is concluded that existing models with log g = 4 or 4.5
fail to reproduce the observations, while the few models with log g =
3.5 are in better agreement. A comparison of these 'normal' O stars and
stars with O-type spectra that excite planetary nebulae is given. It is
concluded that the atmospheres of these two types of O star are very
similar; they probably have the same effective gravity. A discussion
of the Zanstra He II temperature is also presented.
---------------------------------------------------------
Title: Determination of cooling rates in the interstellar medium.
Authors: Pottasch, S. R.; Wesselius, P. R.; van Duinen, R. J.
1979A&A....74L..15P Altcode:
The cooling in most interstellar 'clouds' is due to fine-structure line
emission by C(+). An estimate of the cooling rate can be obtained
from the measurement, in the ultraviolet, of the column density
N(C(+) 2 P 3/2) relative to N(H(0) + H(+)). The measurement of these
column densities for eight interstellar 'clouds' is discussed. In
equilibrium the cooling rate equals the heating rate. The rate
obtained is too high to be explained either by the ionization of C by
the interstellar radiation field or by ionization of H by low-energy
cosmic rays. Photoelectric emission from 'dust' could explain the
observed heating rate.
---------------------------------------------------------
Title: Population ratios of fine structure levels.
Authors: Smeding, A. G.; Pottasch, S. R.
1979A&AS...35..257S Altcode:
Population ratios of the fine-structure levels in the ground state are
calculated for Si II, C II, N III, N II, O I, and C I. These elements
have observed interstellar absorption lines arising from these levels,
and the population ratios can be used to determine the temperature and
density of the absorbing gas. Excitations induced by the interstellar
radiation field and by collisions with electrons, hydrogen atoms, and
protons are considered. The calculations are performed for temperatures
between 10 and 15,000 K and densities between 0.001 and 1000 per cu
cm. Limiting values of ionization are given for which recombination
to an excited level can be neglected.
---------------------------------------------------------
Title: The effective temperatures of the O stars
Authors: Pottasch, S. R.; Wesselius, P. R.; van Duinen, R. J.
1979IAUS...83..113P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Determination of Cooling Rates in the Interstellar Medium
Authors: Pottasch, S. R.; Wesselius, P. R.; van Duinen, R. J.
1979IUE1.symp...49P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Central Stars of Planetary Nebulae
Authors: Pottasch, S. R.
1979iue..prop..318P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: SDO and Nova-Like Stars
Authors: Pottasch, S. R.
1979iue..prop..319P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Black Hole Binaries
Authors: Pottasch, S. R.
1979iue..prop..357P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ultraviolet observations of planetary nebulae. IV. The C IV
lines at lambda 1550 Å.
Authors: Pottasch, S. R.; Wesselius, P. R.; van Duinen, R. J.
1978A&A....70..629P Altcode:
Summary. We present measurements and upper limits to the flux of the C
iv lines at A = 1550 A originating from planetary nebulae. We compare
the measured line fluxes with theoretical predictions and discuss
the possible effects of dust absorption on the fluxes. We conclude
that line fluxes can be used to determine carbon abundances in these
nebulae. The resultant abundances vary between the solar abundance to
an order of magnitude lower than this. Key words: planetary nebulae -
ultraviolet observations - abundances of carbon
---------------------------------------------------------
Title: Book reviews
Authors: Roberts, Paul H.; Scholer, Manfred; de Jager, C.; Ceplecha,
Zdeněk; Grewing, M.; Kresák, L.; Bumba, Václav; Pottasch, S. R.;
Sehnal, L.; Pagel, Bernard; Reijnen, G. C. M.; Ness, Norman F.;
de Jager, Cornelis
1978SSRv...22..213R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ultraviolet observations of planetary nebulae. III. Variability
of the central star.
Authors: Gilra, D. P.; Pottasch, S. R.; Wesselius, P. R.; van Duinen,
R. J.
1978A&A....63..297G Altcode:
UV photometric observations of 39 planetary nebulae performed with the
Astronomical Netherlands Satellite have been searched for variability
of the central stars. No photometric variations of more than about
15% are found, but detectable variations are observed in the nuclei
of five objects: IC 418, NGC 6543, A78, He2-131, and V-V 1-7. The
results indicate that: (1) the only definite variations occurred in
emission-line central stars with Of characteristics; (2) the variations
in A78, NGC 6543, and He2-131 may be entirely spectroscopic in origin;
(3) the variations in IC 418 appear to be both spectroscopic and
photometric; and (4) V-V 1-7 is probably not a planetary nebula.
---------------------------------------------------------
Title: Ultraviolet photometric variations in the central star of
IC 418.
Authors: Gilra, D. P.; Pottasch, S. R.; Wesselius, P. R.; van Duinen,
R. J.
1978IAUS...76..210G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ultraviolet radiation from planetary nebulae. II. Radiation
from the central stars.
Authors: Pottasch, S. R.; Wesselius, P. R.; Wu, C. -C.; Fieten, H.;
van Duinen, R. J.
1978A&A....62...95P Altcode:
Intermediate-band observations of about 30 planetary nebulae in the
spectral region from 1500 to 3300 A are used to obtain information
about the atmospheres, particularly the effective temperatures, of
the central exciting stars. Separation of the nebular emission and
the emission from the central star is described in detail, and the
resultant UV fluxes from the central stars are presented for stars of
various spectral types, including 10 O stars, two continuum stars,
three Wolf-Rayet stars, three O VI stars, four Abell objects, and
three unclassified central stars. It is shown that the central stars
often do not radiate as blackbodies over the spectral range from 1550
to 5500 A. Zanstra temperatures are determined for the central stars,
effective temperatures are derived from total fluxes, and a criterion
is formulated for distinguishing optically thick and optically thin
planetaries. The radii of the central stars and their positions on
the H-R diagram are briefly examined.
---------------------------------------------------------
Title: Advances in ultraviolet observations.
Authors: Pottasch, S. R.
1978IAUS...76...93P Altcode:
The accuracy of available ultraviolet measurements of planetary
nebulae is examined, and some interpretations of the data are made. The
observed dip in flux at 2200 A can be used to measure extinction if
(1) the intrinsic spectrum of the object is relatively smooth over the
interval 1700-2600 A, and (2) the intervening medium is characterized
by a uniform extinction curve with known properties. It is argued that
these conditions are likely to hold, and the extinction calculated
on this basis and expressed at E(B-V) is in good correlation with the
extinction calculated from the ratio of the H-beta flux to the radio
flux. Methods of separating nebular emission from central star emission
and measuring the nebular continuum are briefly mentioned.
---------------------------------------------------------
Title: Stellar Lyman alpha and Lyman beta profiles.
Authors: Vader, J. P.; Pottasch, S. R.; Bohlin, R. C.
1977A&A....60..211V Altcode:
Measurements of Lyman-alpha and Lyman-beta profiles, as obtained by
the Copernicus satellite for 20 early-type stars, are reported. The
profiles are compared with theoretical profiles computed using
unblanketed non-LTE model atmospheres. The Ly-alpha profiles are found
to be systematically broader than the Ly-beta profiles, contrary
to the theoretical predictions; this discrepancy is ascribed to
line-blanketing effects.
---------------------------------------------------------
Title: NGC 1510: a young elliptical galaxy?
Authors: Disney, M. J.; Pottasch, S. R.
1977A&A....60...43D Altcode:
NGC 1510 is a southern E0 galaxy with an A-type spectrum, strong
emission lines, and extremely blue colors. It has the relaxed light
distribution of a normal elliptical, and there is no sign of interaction
with its brighter SBO companion NGC 1512. There is an abnormally large
amount of hydrogen in the whole system, while the emission lines in
NGC 1510 yield a normal abundance of helium but a deficiency in other
elements by a factor 10. The UBV colors and multichannel spectrum scans
are well matched to single-burst models with a Salpeter initial mass
function and an age of a few hundred million years. It is suggested
that NGC 1510 may be a young galaxy that has formed from the large
amount of hydrogen near NGC 1512.
---------------------------------------------------------
Title: On the physical conditions in the "high-velocity" cloud near
zeta Ori.
Authors: Drake, J. F.; Pottasch, S. R.
1977A&A....54..425D Altcode:
The problem of the 'high-velocity' clouds is rediscussed. Recent OAO-C
Copernicus observations of lines of four atoms and ions have been used
to estimate the density and temperature in both the 'high-velocity'
and 'normal' interstellar clouds in the line-of-sight to Zeta Ori. The
temperature and densities in the normal cloud are similar to previous
results for interstellar clouds, yielding temperatures of the order of
100 K and compositions underabundant relative to the sun by factors
of 3 or more. The high-velocity cloud, however, is warmer (at least
1000 K) and appears to have a normal solar abundance.
---------------------------------------------------------
Title: Ultraviolet observations of planetary nebulae. I. Determination
of extinction.
Authors: Pottasch, S. R.; Wesselius, P. R.; Wu, C. -C.; van Duinen,
R. J.
1977A&A....54..435P Altcode:
The problem of interstellar extinction in UV observations of planetary
nebulae is discussed. Methods used to determine extinction are reviewed,
and it is proposed that the excess interstellar extinction at 2200 A
can be employed to determine the extinction along the line of sight
to a planetary. Observational data are presented which confirm the
two assumptions implicit in this technique, viz., that a common
normalized extinction curve exists in all directions and that the
intrinsic spectrum of a planetary is roughly continuous. (B-V) color
excesses derived according to the proposed technique are given for
31 planetaries, and the values are compared with observed ratios of
6-cm radio flux to H-beta flux. The IR excess of planetary nebulae is
examined, showing that the matter responsible for the measured excess
is not the same as that responsible for the extinction. A value of
approximately 3.2 is obtained for the ratio of total to selective
extinction.
---------------------------------------------------------
Title: Physical conditions in the normal and high velocity clouds
near zeta Ori.
Authors: Drake, J. F.; Pottasch, S. R.
1976BAAS....8..428D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ultraviolet photometry of Eta Carinae and its interpretation.
Authors: Pottasch, S. R.; Wesselius, P. R.; van Duinen, R. J.
1976A&A....47..443P Altcode:
Measurements of Eta Carinae in the ultraviolet are reported and used to
determine the extinction. It is concluded that the foreground material
will produce the observed extinction and that there is no need to
introduce anomalous additional extinction, as has been argued by
previous authors. The consequences of this for the infrared radiation
are discussed along with the intrinsic properties of Eta Carinae
---------------------------------------------------------
Title: Preliminary results obtained with the UV spectrophotometer,
onboard ANS.
Authors: Wesselius, P. R.; Aalders, J. W. G.; van Albada, T. S.;
Andriesse, C. D.; de Boer, K. S.; Borgman, J.; van Duinen, R. J.;
Koornneef, J.; Pottasch, S. R.; Vader, J. P.; Wu, C. -C.
1976sgov.meet...67W Altcode:
Some preliminary results obtained with a five-channel UV
spectrophotometer aboard the Astronomical Netherlands Satellite are
reported which concern hot subluminous stars, planetary nebulae,
globular clusters, extinction laws in the Large Magellanic Cloud as
well as in the Carina region, and properties of dust particles in
the Merope reflection nebula. Data on 12 hot subluminous subdwarfs
and white dwarfs are presented; three of these stars are found to
have an effective temperature of the order of 100,000 K but visual
magnitudes of 10.5, 12.1, and 12.3, respectively. Observations of 17
planetary nebulae and 10 globular clusters are very briefly reviewed,
and attempts to determine an extinction law for the Carina region
are mentioned. It is noted that the UV albedo and scattering phase
factor of dust particles in the Merope nebula will be derived from
observations of five positions in the nebula and of its exciting star.
---------------------------------------------------------
Title: A new analysis of solar XUV limb brightening observations by
OSO 4.
Authors: Koornneef, J.; Nijenhuis, A.; Pottasch, S. R.
1976uis..confA...1K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the iron abundance in interstellar gas.
Authors: Olthof, H.; Pottasch, S. R.
1975A&A....43..291O Altcode:
The iron abundance is determined in the Orion nebula from the observed
emission lines of Fe(+) and Fe(++). A comparison of the derived value
with the iron abundance in the sun and the interstellar medium is made.
---------------------------------------------------------
Title: Measurements of interstellar absorption lines between 3241
and 3969 Å.
Authors: de Boer, K. S.; Pottasch, S. R.
1974A&A....36..463D Altcode:
Key words: Ca ii K Ti ii CN interstellar lines Summary. We present
profiles for the interstellar Ca ii K absorption lines towards a Car,
1 Sco, Oph, HD 154090 and y Ara, as well as some results on interstellar
Ti ii and CN
---------------------------------------------------------
Title: Oscillator strengths for ionized iron and manganese.
Authors: de Boer, K. S.; Morton, D. C.; Pottasch, S. R.; York, D. G.
1974A&A....31..405D Altcode:
Summary. The observed strengths of interstellar absorption lines of
Fe ii and Mn ii in the spectra of oc Vir, P Cen, Sco, and Oph along
with laboratory f values of some of these lines between 2343 and 2606
A have been used to determine curves of growth for these ions and the
f-values of 10 lines of Fe ii and 3 lines of Mn ii between 1055 and
1261 A. The Fe and Mn abundances are derived. Key words: oscillator
strengths - interstellar absorption lines
---------------------------------------------------------
Title: Observations of interstellar NA 3302 doublet and the
interstellar sodium abundance.
Authors: de Boer, K. S.; Pottasch, S. R.
1974A&A....32....1D Altcode: 1974A&A....32....1B
Summary. Observations are presented of the interstellar neutral sodium
UV doublet at 3302 A (to be called Na U doublet). Together with
the scarce U line data in the literature, these form the basis for
deriving accurate Na0 column densities, which are an order of magnitude
larger than values derived from the D lines alone. After allowance for
ionization balance we find that in these clouds with strong D lines,
the ratio of total sodium to hydrogen is close to the solar abundance
value. Using both doublets (U and D) we find that the internal doppler
velocities are of the order of 1-3 km s 1in most clouds. Key words:
interstellar absorption lines - abundances - Na 1 lines - curve
of growth
---------------------------------------------------------
Title: A Model of Compact H II Regions Emitting in the Infrared
Authors: Pottasch, S. R.
1974A&A....30..371P Altcode:
Summary. The compact H ii regions, which are strong emitting sources in
the infrared, are studied. The following conclusions are drawn. (1)The
size of the region is determined by the luminosity of the source of
radiative energy, and the density of the region. (2)The dust grains in
these compact regions have the same properties as the dust grains in
the general interstellar medium. (3)The correlation between observed
infrared flux and observed radio flux can be explained for those cases
in which a single star is the energy source; this correlation s a result
of the correlation between the temperature and the luminosity of the
star. In those H ii regions in which many stars are responsible for the
heating, it is predicted that no correlation will be observed. (4) The
absorption efficiency of the dust grains as a function of wavelength
between 20 and 350 cannot have the form - over the entire range,
regardless of the value of n, if the optical depth is small in this
wavelength region. Key words: dust grains - absorption and emission
by dust - interstellar matter - compact H ii regions
---------------------------------------------------------
Title: Interpretation of Far Infrared Observations (Invited Lecture)
Authors: Pottasch, S. R.
1974smws.conf..209P Altcode: 1974smws.proc..209P
No abstract at ADS
---------------------------------------------------------
Title: Physics of Interstellar Medium
Authors: Pottasch, S. R.
1974ASIC....6..127P Altcode: 1974inme.conf..127P
No abstract at ADS
---------------------------------------------------------
Title: On the Photoionization Rates in Interstellar Gas
Authors: de Boer, K. S.; Koppenaal, K.; Pottasch, S. R.
1973A&A....28..145D Altcode:
Key words: interstellar gas - photoionization rates
Summary. Photoionization rates in the interstellar gas are calculated
using OAO -2 data for the interstellar radiation density. A comparison
is given with earlier results.
---------------------------------------------------------
Title: On the composition of the interstellar gas towards zeta Pup.
Authors: de Boer, K. S.; Pottasch, S. R.
1973A&A....28..155D Altcode:
Summary. UV-interstellar absorption lines measured in the direction
of Pup by the S 59 satellite spectrograph are presented. These data
are combined with other interstellar line measurements in the same
star, to derive a curve of growth and element abundances. Key words:
interstellar lines - abundances - (Pup - Gum nebula
---------------------------------------------------------
Title: On the observability of far infrared line emission originating
from the interstellar medium.
Authors: Pottasch, S. R.
1973A&A....24..305P Altcode:
Summary. Recent measurements of interstellar absorption lines in the
ultraviolet, originating from energy levels above the ground level, can
be used to directly compute the expected infrared line radiation. This
is done for the 156 t line of C+ in the directions of Oph and Sco and
lines of C0. O and Si+. The computed line strengths are considerable
and may be strong enough to be detectable with present techniques. Key
words: interstellar medium - infrared line radiation
---------------------------------------------------------
Title: Erratum; On the Photoionization Rates in Interstellar Gas
Authors: de Boer, K. S.; Koppenaal, K.; Pottasch, S. R.
1973A&A....29..453D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A model of the interstellar medium. II. Interpretation of
the Na<SUP>0</SUP>/Ca<SUP>+</SUP> ratio.
Authors: Pottasch, S. R.
1972A&A....20..245P Altcode:
Summary. An attempt is made to explain the observed variation of
the ratio Na0/Ca+ in interstellar "clouds", assuming the abundances
of sodium and calcium are everywhere the same. The results of this
analysis are applied to about thirty observed "clouds", and it is
shown that it is possible to derive values of electron temperature,
electron density, and state of ionization for each "cloud" (Table
2). It is shown that at least two and possibly four different groups
of clouds exist. These results are compared with other observations
of the interstellar medium, especially the pulsar dispersion measures
and the low frequency radio absorption measurements. A discussion
of the "cloud" properties is given. Key words: interstellar matter -
abundances - pulsar dispersion measures - low frequency radio absorption
---------------------------------------------------------
Title: On the Abundance of Calcium in the Solar Corona
Authors: De Boer, K. S.; Pottasch, S. R.
1972SoPh...23..406D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Abundances in the Solar Corona
Authors: de Boer, K. S.; Olthof, H.; Pottasch, S. R.
1972A&A....16..417D Altcode:
On the basis of the coronal measurements of the 30 May 1965 eclipse,
and using improved atomic parameters, we discuss the coronal abundance
determination. Two new line identffications are suggested and several
existing suggestions for possible identffications are discussed on the
basis of predicted intensities and abundances. Finally an extensive
list is given of lines which are possibly observable, together with
predicted intensity and equivalent width. Key words: corona - abundances
- forbidden line identffications
---------------------------------------------------------
Title: A model of the interstellar medium based on the interstellar
calcium and sodium lines.
Authors: Pottasch, S. R.
1972A&A....17..128P Altcode:
Use is made of the Ca0 to Ca+ ratio in the interstellar medium to
deduce the conditions of electron density and temperature prevailing
there. The deductions which can be made from the sodium lines
combined with the 21-cm hydrogen line both conflrm the results of
the calcium ratio and indicate that all these lines are formed in the
same medium. The properties of this medium are further investigated
using the observations of the pulsar dispersion measure and the
"background" radio recombination line measurements. It is shown that
the model previously developed can be refined so that it can account
for all these measurements. The problem of the abundances in the
interstellar medium is also discussed. Key-words:interstellar lines -
pulsar dispersion measure - abundances in interstellar matter
---------------------------------------------------------
Title: Infrared line radiation from the neighbourhood of the galactic
center.
Authors: Pottasch, S. R.
1972saim.conf..327P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: UV interstellar absorption lines in the spectrum of zeta Pup.
Authors: de Boer, K. S.; Hoekstra, R.; van der Hucht, K. A.; Kamperman,
T. M.; Lamers, H. J.; Pottasch, S. R.
1972A&A....21..447D Altcode:
Summary. Interstellar absorption lines have been detected in the
spectrum of the OS star Pup. They are due to the resonance lines of
Mg II 2803, 2796, Mg 2852, Fen 2586 and Mnll 2576, and possibly Fei
2522. Key words: interstellar medium - interstellar absorption lines -
satellite ultraviolet stellar spectra
---------------------------------------------------------
Title: Infrared Line Radiation from the Neighbourhood of the
Galactic Center
Authors: Pottasch, S. R.
1971A&A....13..152P Altcode:
Calculations are made on the amount of line radiation in the infrared
(between 2Oit and 200it) to be expected from the "thermal" regions in
the neighbourhood of the galactic center. A comparison is made with the
observed radiation in this wavelength region. Although the predicted
line radiation is an order of magnitude lower than the observed
radiation, the predicted flux depends on the assumed abundances, which
may be higher than the solar values used. Th any case, at least 10 lines
are expected to be present in observable strength, and observation of
these lines can provide an accurate determination of the abundances
of five elements at the galactic center. Key words: galactic center -
interstellar matter - thermal radio emission - infrared line radiation
---------------------------------------------------------
Title: Mass Loss from Stars
Authors: Pottasch, S. R.
1970IAUS...39..272P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Review of Astrophysical Conclusions from the UV Solar Spectra
Authors: Pottasch, S. R.
1970IAUS...36..241P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Abundance Determination in the Solar Chromosphere
Authors: Pecker, J. C.; Pottasch, S. R.
1969A&A.....2...81P Altcode:
We show that abundances of the metals can be obtained from observations
of the solar chromosphere; departures from local thermodynamic
equilibrium are taken into account. Results are given for iron,
titanium, scandium, strontium and barium.
---------------------------------------------------------
Title: 44. Forbidden Line Emission from the Interstellar Medium,
Introductory Report
Authors: Pottasch, S. R.
1969LIACo..15..377P Altcode: 1969MSRSL..17..377P
No abstract at ADS
---------------------------------------------------------
Title: Forbidden line emission from the interstellar medium.
Authors: Pottasch, S. R.
1969MSRSL..25..377P Altcode: 1969tisa.conf..377P
No abstract at ADS
---------------------------------------------------------
Title: Distances to the Pulsating Radio Sources
Authors: Habing, H. J.; Pottasch, S. R.
1968Natur.219.1137H Altcode:
IN several of the recent discussions of pulsating radio sources,
it is assumed that the distance of these objects is of the order of
100 pc or less. We wish to show that it is just as likely that these
objects lie at distances at least 10 times greater.
---------------------------------------------------------
Title: The Relative Abundance of Silicon and Iron in the Solar Corona
Authors: Jordan, Carole; Pottasch, S. R.
1968SoPh....4..104J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Infrared Measurements from a Nebula in Orion
Authors: Pottasch, S. R.
1968ApJ...151L..67P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The infrared lines and the temperature and ionization of the
interstellar medium
Authors: Pottasch, S. R.
1968BAN....19..469P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the abundances in the solar corona.
Authors: Pottasch, S. R.
1968ode..conf..183P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Relative Abundances in the Solar Corona as Determined
from the Ultraviolet Spectrum
Authors: Pottasch, S. R.
1967ApJ...150..361P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Low-Energy Cosmic Rays and the Electron Density in H i Regions
Authors: Habing, H. J.; Pottasch, S. R.
1967ApJ...149L.119H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: RS Ophiuchi: Reduction of spectra from the 1958 outburst
(Errata: 20 224)
Authors: Tolbert, C. R.; Pecker, J. C.; Pottasch, S. R.
1967BAN....19...17T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An interpretation of the spectrum of the recurrent nova
RS Ophiuchi
Authors: Pottasch, S. R.
1967BAN....19..227P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The inclusion of dielectronic recombination processes in the
interpretation of the solar ultraviolet spectrum
Authors: Pottasch, S. R.
1967BAN....19..113P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the radiative energy loss in the intergalactic medium
Authors: Pottasch, S. R.
1966BAN....18..156P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Oxygen-to-Iron Ratio in the Solar Corona
Authors: Pottasch, Stuart R.
1966BAN....18..443P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Chemical Composition of the Solar Corona
Authors: Pottasch, S. R.
1966IAUS...26..200P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the iron lines observed in the solar ultraviolet spectrum
Authors: Pottasch, S. R.
1966BAN....18..237P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the determination of the solar chemical composition from
a study of the ultraviolet resonance lines
Authors: Pottasch, S. R.
1965AnAp...28..148P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The diffuse emission nebulae
Authors: Pottasch, Stuart R.
1965VA......6..149P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the radiative cooling rate in stellar atmospheres
Authors: Pottasch, S. R.
1965BAN....18....7P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Balmer line profiles in Nova RS Ophiuchi 1958
Authors: Folkart, B.; Pecker, J. -C.; Pottasch, S. R.
1965nns..conf...60F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The narrow emission and absorption lines in Nova RS Ophiuchi
1958
Authors: Folkart, B.; Pecker, J. -C.; Pottasch, S. R.
1965nns..conf...50F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the determination of the solar chemical composition from
a study of the ultra-violet resonance lines
Authors: Pottasch, S. R.
1965IAUS...23..105P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Determination of electron temperature in diffuse nebulae.
Authors: Pottasch, S. R.
1965VA......6..173P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Interpretation of the Solar Ultraviolet Emission
Line Spectrum
Authors: Pottasch, Stuart R.
1964SSRv....3..816P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Balmer line profiles in Nova RS Ophiuchi, 1958
Authors: Folkart, B.; Pecker, J. -C.; Pottasch, S. R.
1964AnAp...27..249F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A comparison of the chemical composition of the solar
atmosphere with meteorites
Authors: Pottasch, S. R.
1964AnAp...27..163P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The narrow emission and absorption lines in Nova RS Ophiuchi
Authors: Folkart, B.; Pecker, J. -C.; Pottasch, S. R.
1964AnAp...27..252F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the chemical composition of the solar corona
Authors: Pottasch, S. R.
1964MNRAS.128...73P Altcode:
The abundance of nine elements is determined relative to hydrogen,
using the observations of the forbidden lines in the corona obtained
principally at the eclipse of 1952 February 25. The errors inherent in
the analysis, those of observation, physical parameters, and theoretical
assumption, are discussed in demil. An empirical method is developed
for finding the total abundance of an element when only a single
stage of ionization is observed. The results indicate disagreement
with the photospheric abundances but good agreement with the meteorite
compositions.
---------------------------------------------------------
Title: Excitation Conditions in H II Regions in Spiral and Irregular
Galaxies.
Authors: Burbidge, G. R.; Gould, R. J.; Pottasch, S. R.
1963ApJ...138..945B Altcode:
A review is given of possible explanations for the variation in
the Ha/[N "intensity ratio which decreases from 3 in spiral arm
regions to 0.1 in the nuclear regions of some spiral galaxies. It
is concluded that this behavior can be most easily understood in
terms of an increase in the electron temperature from about 6000
K in spiral arm regions to about 20000 K in nuclear regions. The
problem of the electron temperature in galactic H ii regions is
reinvestigated in the light of better data on element abundances
and electron-ion collisional excitation cross sections. From the
[0 iij/Ha and [0 iii]/Ha intensity ratios an electron temperature of
roughly 6000 K is found for two diffuse nebulae in our Galaxy. The
heating and cooling processes are considered. A more accurate method
for the calculation of the photoelectric heating rate yields values
about 60 per cent as large as those computed by Spitzer. The cooling
by electron-ion collisions is computed for the abundant ions. It
is found that excitation of low- lying fine structure levels of
the ground state term of a number of ions, especially Ne+, leads to
considerable cooling at moderate or low electron temperatures. The
results of these calculations show that, for most spiral arm H ii
regions, equilibrium electron temperatures in the approximate range
K can be expected and that, under certain excitation conditions,
temperatures as low as 1000 K may be attained. All considerations of
electron temperatures in normal spiral arm H ii regions seem to point
to a temperature appreciably below the value 10000 K which has often
been assumed. Possible mechanisms for the production of high ( 20000O
K) electron temperatures are considered. While photoelectric heating
can definitely be ruled out, the ejection of particles from stars
(probably in the form of clouds of plasma with proton energies above
about a kilovolt) can produce the necessary heating without disrupting
the observed ionization equilibrium in nuclei of galaxies.
---------------------------------------------------------
Title: The Lower Solar Corona: Interpretation of the Ultraviolet
Spectrum.
Authors: Pottasch, Stuart R.
1963ApJ...137..945P Altcode:
An analysis of the resonance lines of nine elements (27 ions) formed in
the chromosphere and corona of the sun yields the following results: (a)
the chemical composition of this region of the sun can be determined,
without any knowledge of the detailed temperature-density structure
in this region; (b) a further clue concerning the detailed structure
of this region may be obtained. A prediction of the expected emission
of the sun in radio frequencies can be used both as a check on the
correctness of the present work and as a means of obtaining the ratio
of the observed elements to hydrogen.
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Title: The lower solar corona : the abundance of iron
Authors: Pottasch, Stuart Robert
1963PGLO...52..544P Altcode:
No abstract at ADS
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Title: The lower solar corona: the abundance of iron
Authors: Pottasch, S. R.
1963MNRAS.125..543P Altcode:
The data on the intensities of the emission lines of [Fe x], [Fe xi] and
[Fe xiv] as a function of height in the solar atmosphere is assembled
(for the height range from 8ooo km above the limb to 100,000 km). It
is shown that, assuming spherical synametry, it is possible to derive
separately for each stage of ionization both the abundance of iron
(relative to hydrogen) and the electron temperature as a function of
height. The abundance of iron found assuming spherical symmetry is
in good agreement with previous coronal analyses, but is about 20
times higher than that found in the photospheric' curve of growth'
analysis. The case of a non-symmetrical atmosphere is then considered
and several general examples are discussed. It is found that it is
difficult to lower the iron abundance using a reasonable model.
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Title: The lower solar corona : interpretation of the ultraviolet
spectrum
Authors: Pottasch, Stuart Robert
1963PGLO...51..945P Altcode:
No abstract at ADS
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Title: Excitation conditions in H II regions in spiral and irregular
galaxies
Authors: Burbidge, Geoffrey R.; Gould, Robert Joseph; Pottasch,
Stuart Robert
1963PGLO...56..945B Altcode:
No abstract at ADS
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Title: Chemical Composition of the Outer Solar Atmosphere.
Authors: Pottasch, Stuart R.
1962AJ.....67..280P Altcode:
The observations of the resonance lines of 9 elements in 27 stages of
ionization in the far-ultraviolet region of the spectrum permits the
deduction of the relative abundance of these elements in the tipper
solar atmosphere (roughly between 3000 and 40 000 km above the solar
limb). The determination of the composition can be made without a
detailed knowledge of the temperature-density distribution in this
region of the atmosphere. The observations also give an indication
of the structure of the atmosphere. This indication is sufficient,
however, to enable the prediction of the radio frequency continuum,
which provides a check of the correctness of the assumptions which
have been made. The accuracy of the relative abundances is believed
to be about a factor of 2. The abundances, which follow, show a marked
discrepancy with a recent photospheric determination (Goldberg, Muller,
and Aller). Oxygen 100 Neon 10 Nitrogen 30 Magnesium 20 Carbon 350
Iron 12 Sulfur 8 Helium 25 000 Silicon 50 Hydrogen 150000
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Title: The Effect of Optical Depth in the Spectrum of Helium
(triplets) in Nebulae.
Authors: Pottasch, Stuart R.
1962ApJ...135..385P Altcode:
The relative intensities of the emission lines in the triplet system of
neutral helium are determined as a function of the optical depth of an
atmosphere in X 3889. The atmosphere considered is one of low density,
comparable to nebulae, so as to minimize the importance of effects
due to electron collisions. The range of optical depth considered is
limited so that only lines originating from the metastable level show
effects of optical depth. This limits us to r(1083Q < 10 , since
above this value the population of the 23P level becomes large enough
that one cannot ignore the optical depth in lines arising from that
level. A comparison with the helium observations of five well-known
nebulae indicates positively the effects of optical depth in at least
three and probably four of these nebula.
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Title: Mouvement des bords brillants dans les nébuleuses diffuses
Authors: Courtès, G.; Cruvellier, P.; Pottasch, S. R.
1962AnAp...25..214C Altcode:
No abstract at ADS
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Title: Dynamics of Bright-Rim Structures
Authors: Pottasch, S. R.
1962dmim.conf..205P Altcode: 1972dmim.conf..205P
No abstract at ADS
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Title: Mouvement des bords brillants dans les nebuleuses diffuses
Authors: Courtes, Georges; Cruvellier, Paul; Pottasch, Stuart Robert
1962POHP....6Q....C Altcode:
No abstract at ADS
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Title: Balmer Line Emission from a Shell.
Authors: Pottasch, Stuart K.
1961AJ.....66..294P Altcode:
We have attempted to determine the Balmer line ratio : H~ from a
consideration of the equations of statistical equilibrium for a shell
of hydrogen gas at a constant electron and temperature. This present
work differs from that of Menzel and associates in the three following
respects: (1) A wide range of electron densities is considered, from
10~ cm-3 to 10'~ cm-3 (although this value is kept constant in a given
atmosphere). This requires that collisional transitions between levels
be included. (2) Radiation in the Balmer and Paschen continua impinging
on the atmospheres is included, although the atmospheres are always
assumed thin enough so that these radiations remain roughly constant
through an atmosphere. (3) The atmospheres considered have varying
opacities to Ho~ radiation (from completely thin to completely thick)
and so it is necessary to consider the transfer of the Balmer line
radiation. Since we assume a four-level atom plus continuum, it is
necessary to solve simultaneously the transfer equations for H~ and
H~. The principal effort of this work is so directed.
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Title: Motions in Bright Rim Structures in Diffuse Nebulae.
Authors: Courtes, G.; Pottasch, S. R.
1961AJ.....66T..41C Altcode:
ibid. 14, 29, 1958) regards the bright rim structures in diffuse nebulae
as ionization fronts, the result of interaction of ionizing radiation
from an exciting star with dense un-ionized matter in the nebulae. This
theory can be definitely confirmed by observing the predicted motion of
the ionized material away from the ionization front at about the speed
of sound. Proper motion studies will not reveal this motion because
there is no way of marking a particular point in the ionized gas, so
that recourse must be made to radial velocity measurements. Because
these bright rim structures are observed primarily in the plane of the
sky any radial velocity shift will be observed at the same position
as the dark matter. The observations were taken at the Newtonian
focus of the 193-cm telescope of the Observatory of Haute Provence,
with a Fabry-Perot interferometer, especially built for this purpose
(Courtes, G., Ann. astrophys. 23, 115, 1960). It enables one to obtain
a field of view 6' on a side and is equipped with a filter which limits
the spectral range to Ha and the [NIll lines. Motions greater than 1.5
km/sec can be detected. Pictures of bright rim structures in NGC 6611,
IC 1396, and NGC 7000 have been obtained.
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Title: Balmer decrements. - II. The Be stars
Authors: Pottasch, S. R.
1961AnAp...24..159P Altcode:
No abstract at ADS
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Title: The Ultraviolet Radiation from O Stars in Diffuse Nebulae
Authors: Pottasch, S. R.
1961LIACo..10..563P Altcode: 1961LIACo..10..562P; 1961MSRSL...4..562P
No abstract at ADS
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Title: The Extent of H II Regions.
Authors: Pottasch, Stuart R.
1960ApJ...132..269P Altcode:
No abstract at ADS
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Title: Thermodynamic Structure of the Outer Solar
Atmosphere.VI. Effect of Departures from the Saha Equation on Inferred
Properties of the Low Chromosphere.
Authors: Pottasch, S. R.; Thomas, R. N.
1960ApJ...132..195P Altcode:
We apply the methodology of our preceding treatment of the Saha equation
under conditions of high Lyman continuous opacity to a reanalysis of
the continuous emission from the lowest chromosphere. The result is
a greatly steepened Trgradient, relative to the results of an earlier
analysis based on the neglect of non-LTE effects.
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Title: The spectrum of RR Telescopii between May 1949 and August 1950
Authors: Pottasch, S. R.; Varsavsky, C. M.
1960AnAp...23..516P Altcode:
No abstract at ADS
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Title: Comments on some physical processes in diffuse nebulae
Authors: Pottasch, S. R.
1960AnAp...23..749P Altcode:
No abstract at ADS
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Title: Use of the Equation Hydrostatic Equilibrium in Determining
the Temperature Distribution in the Outer Solar Atmosphere.
Authors: Pottasch, S. R.
1960ApJ...131...68P Altcode:
No abstract at ADS
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Title: Balmer Decrements : the Diffuse Nebulae.
Authors: Pottasch, S. R.
1960ApJ...131..202P Altcode:
The possibility that diffuse nebulae may have a total optical depth
in the early Balmer lines of the order of unity is considered. The
Balmer decrement is found as a function of the total optical depth of
a plane atmosphere in Ha, assuming that the atmosphere has a constant
temperature and density (less than 10 electrons/cm3) and is optically
thick to Lyman-line radiation. It is found that the Ha/H ratio increases
with increasing optical depth in Ha The observations of Ha/H in diffuse
nebulae are high enough to make any other interpretation beside that
of optical thickness in Ha appear doubtful The measurements of H and
H tend to confirm this interpretation.
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Title: Departures from the Saha Equation Under Varying Conditions
of Lyman Continuous Opacity.
Authors: Pottasch, S. R.; Thomas, R. N.
1959ApJ...130..941P Altcode:
A general method for determining the departure from the Saha equation in
a hydrogen atmosphere is presented. The usually stated, vague condition
of "high opacity in the Lyman continuum" is not sufficient to insure
LTE; departures from LTE may amount to several orders of magnitude
even under this condition (Fig. 2). For illustration, application
of the method is made to an atmosphere of constant T and n (Fig. 1)
and to an approximate chromospheric model (Fig. 3).
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Title: The nova outburst: II. The radiative cooling of an expanding
shell
Authors: Pottasch, S.
1959AnAp...22..310P Altcode:
No abstract at ADS
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Title: The nova outburst: V. The temperature and radius of the
central exciting star and observation of elements other than hydrogen
Authors: Pottasch, S.
1959AnAp...22..412P Altcode:
No abstract at ADS
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Title: The nova outburst: I
Authors: Pottasch, S.
1959AnAp...22..297P Altcode:
No abstract at ADS
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Title: The nova outburst: III. The ionization of hydrogen gas by an
exciting star
Authors: Jefferies, J.; Pottasch, S.
1959AnAp...22..318J Altcode:
No abstract at ADS
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Title: The nova outburst: IV. The intensity of H&alpha
Authors: Pottasch, S.
1959AnAp...22..394P Altcode:
No abstract at ADS
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Title: Bright Rims in Diffuse Nebulae
Authors: Pottasch, Stuart R.
1958RvMP...30.1053P Altcode:
No abstract at ADS
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Title: The Nova Outburst.
Authors: Pottasch, Stuart Robert
1958PhDT.........1P Altcode:
No abstract at ADS
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Title: Dynamics of bright rims in diffuse nebulae
Authors: Pottasch, S. R.
1958BAN....14...29P Altcode:
No abstract at ADS
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Title: A study of bright rims in diffuse nebulae
Authors: Pottasch, S. R.
1956BAN....13...77P Altcode:
No abstract at ADS
