Author name code: pottasch ADS astronomy entries on 2022-09-14 author:Pottasch, Stuart ------------------------------------------------------------------------ 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. Bibcode: 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.
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.
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.
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. Title: Abundances of planetary nebulae in the Galactic bulge Authors: Pottasch, S. R.; Bernard-Salas, J. Bibcode: 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.
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.
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.
Results: Reliable abundances are obtained for O, N, Ne, S, and Ar for Galactic bulge PNe.
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.

Based on observations with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology. Title: Dust properties in the Galactic bulge Authors: Pottasch, S. R.; Bernard-Salas, J. Bibcode: 2013A&A...550A..35P Altcode: 2013arXiv1301.3732P Context. It has been suggested that the ratio of total-to-selective extinction RV in dust in the interstellar medium differs in the Galactic bulge from its value in the local neighborhood.
Aims: We attempt to test this suggestion.
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 RV can then be found.
Results: The ratio of total-to-selective extinction in the Galactic bulge is consistent with the value RV = 3.1, which is the same as has been found in the local neighborhood.
Conclusions: The suggestion that RV is different in the Galactic bulge is incorrect. The reasons for this are discussed.

Based on observations with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology. Title: OT2_spottasc_1: Carbon abundances in Galactic bulge planetary nebulae Authors: Pottasch, S. R. Bibcode: 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. Title: The history of the creation of Astronomy & Astrophysics Authors: Pottasch, S. R. Bibcode: 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. Title: Abundances in planetary nebulae: NGC 1535, NGC 6629, He2-108, and Tc1 Authors: Pottasch, S. R.; Surendiranath, R.; Bernard-Salas, J. Bibcode: 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.
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.
Methods: The mid-infrared spectra of the planetary nebulae NGC 1535, NGC 6629, He2-108, and Tc1 (IC 1266) 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.
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⊙ and 2.5 M⊙. 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⊙ and 0.63 M⊙.
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.

Based on observations with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology. Title: Adriaan Blaauw, 1914-2010 Authors: de Zeeuw, T.; Pottasch, S.; Wilson, R. Bibcode: 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. Title: Planetary nebulae abundances and stellar evolution II Authors: Pottasch, S. R.; Bernard-Salas, J. Bibcode: 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.
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.
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.
Results: Six of the seven bipolar nebulae can be identified as descendants of high mass stars (4-6 M⊙) 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".

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: NGC 2792 Authors: Pottasch, S. R.; Surendiranath, R.; Bernard-Salas, J.; Roellig, T. L. Bibcode: 2009A&A...502..189P Altcode: The mid-infrared spectrum of the rather circular planetary nebula NGC 2792 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.

Based on observations with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology. Title: Abundances in the planetary nebula NGC 6210 Authors: Pottasch, S. R.; Bernard-Salas, J.; Roellig, T. L. Bibcode: 2009A&A...499..249P Altcode: The spectra of the planetary nebula NGC 6210 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.

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. Title: Abundances of planetary nebulae NGC 3242 and NGC 6369 Authors: Pottasch, S. R.; Bernard-Salas, J. Bibcode: 2008A&A...490..715P Altcode: 2008arXiv0809.3745P The spectra of the planetary nebulae NGC 3242 and NGC 6369 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.

Based on observations with the Spitzer Space

Telescope, which is operated by the Jet Propulsion Laboratory,

California Institute of Technology. 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. Bibcode: 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. Title: Abundances in planetary nebulae: NGC 6826 Authors: Surendiranath, R.; Pottasch, S. R. Bibcode: 2008A&A...483..519S Altcode: Aims: We determine the chemical abundances and other parameters of the nebula NGC 6826 and its central star.
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.
Results: The results of these two methods are compared. In addition, we discuss the star exciting the nebula.

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: Abundances of planetary nebula NGC 2392 Authors: Pottasch, S. R.; Bernard-Salas, J.; Roellig, T. L. Bibcode: 2008A&A...481..393P Altcode: 2008arXiv0801.2767P The spectra of the planetary nebula NGC 2392 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.

Based on

observations with the Spitzer Space Telescope, which is operated

by the Jet Propulsion Laboratory, California Institute of

Technology. 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. Bibcode: 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 × 10-5 and 2.7 × 10-5 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 × 10-6 and 1.0 × 10-6. 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. Title: Abundances of planetary nebula M 1-42 Authors: Pottasch, S. R.; Bernard-Salas, J.; Roellig, T. L. Bibcode: 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⊙. The present temperature and luminosity of the central star is determined and at first sight may be inconsistent with such a high mass.

Based on

observations with the Spitzer Space Telescope, which is operated

by the Jet Propulsion Laboratory, California Institute of

Technology. 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. Bibcode: 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 CHβ=0.27 from hydrogen recombination lines and the radio to Hβ ratio. Forbidden line ratios give an electron density of 1860 cm-3 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. 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. Bibcode: 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.

(12 data files). Title: Abundances in planetary nebulae: Hb 5 Authors: Pottasch, S. R.; Surendiranath, R. Bibcode: 2007A&A...462..179P Altcode: The ISO spectra of the bilobal planetary nebula Hb 5 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.

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: 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. Bibcode: 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. Title: Planetary nebulae abundances and stellar evolution Authors: Pottasch, S. R.; Bernard-Salas, J. Bibcode: 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. 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. Bibcode: 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.
Methods: .We present low-resolution optical spectroscopy, finding charts and improved astrometric coordinates of a sample of 253 IRAS sources.
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.
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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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: Mz 3 Authors: Pottasch, S. R.; Surendiranath, R. Bibcode: 2005A&A...444..861P Altcode: ISO spectra of the bipolar planetary nebula Mz 3 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. Bibcode: 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 NGC 2022, NGC 6818 and IC 4191 Authors: Pottasch, S. R.; Beintema, D. A.; Feibelman, W. A. Bibcode: 2005A&A...436..953P Altcode: The ISO and IUE spectra of the elliptical nebulae NGC 2022, NGC 6818 and IC 4191 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: NGC 6886 Authors: Pottasch, S. R.; Surendiranath, R. Bibcode: 2005A&A...432..139P Altcode: ISO and IUE spectra of the round-shaped planetary nebula NGC 6886 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 NGC 6886 and its central star.

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 Hu1-2 Authors: Hyung, S.; Pottasch, S. R.; Feibelman, W. A. Bibcode: 2004A&A...425..143H Altcode: We have obtained high resolution optical spectra of the planetary nebula Hu 1-2 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 Nɛ ≃ 4000-10 000 cm-3, 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.

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. Bibcode: 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 IC 418, IC 2165 and NGC 5882 Authors: Pottasch, S. R.; Bernard-Salas, J.; Beintema, D. A.; Feibelman, W. A. Bibcode: 2004A&A...423..593P Altcode: The ISO and IUE spectra of the elliptical nebulae NGC 5882, IC 418 and IC 2165 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.

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: Me 2-1 Authors: Surendiranath, R.; Pottasch, S. R.; García-Lario, P. Bibcode: 2004A&A...421.1051S Altcode: 2004astro.ph..6534S ISO and IUE spectra of the round planetary nebula Me 2-1 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 Me 2-1 and its central star.

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.

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. Bibcode: 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. Bibcode: 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.

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. Bibcode: 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 Msun) 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 22Ne during thermal pulses, which would imply a reduced role of the 22Ne(alpha , n)25Mg reaction as neutron source to the s-process nucleosynthesis in these stars. Title: Abundances of Planetary Nebulae BD+30 3639 and NGC 6543 Authors: Bernard-Salas, J.; Pottasch, S. R.; Wesselius, P. R.; Feibelman, W. A. Bibcode: 2003A&A...406..165B Altcode: Infrared spectra taken with the Short Wavelength Spectrometer on board ISO and UV observations with IUE of planetary nebulae BD+30 3639 and NGC 6543 are presented. The extinction derived using infrared lines for BD+30 3639 is EB-V= 0.34, slightly higher than previous determinations. For NGC 6543 the extinction found from the hydrogen lines is EB-V= 0.07. Infrared, optical and ultraviolet data have been used to derive the physical parameters of the nebula. BD+30 3639 has an average Te= 8500 K and Ne= 11 000 CH_betam3. In the case of NGC 6543 a Te = 8200 K and Ne = 5000 CH_betam3 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.

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 NGC 7027 Authors: Bernard-Salas, J.; Pottasch, S. R.; Beintema, D. A.; Wesselius, P. R. Bibcode: 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 Hu 1-2 Authors: Pottasch, S. R.; Hyung, S.; Aller, L. H.; Beintema, D. A.; Bernard-Salas, J.; Feibelman, W. A.; Klöckner, H. -R. Bibcode: 2003A&A...401..205P Altcode: The ISO and IUE spectra of the ``elliptical'' nebula Hu 1-2 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.

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. Bibcode: 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. Bibcode: 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. Bibcode: 2003IAUS..209..376B Altcode: 2003IAUS..209..376S No abstract at ADS Title: Abundances of Planetary Nebula NGC 5315 Authors: Pottasch, S. R.; Beintema, D. A.; Bernard Salas, J.; Koornneef, J.; Feibelman, W. A. Bibcode: 2002A&A...393..285P Altcode: The ISO and IUE spectra of the elliptical nebula NGC 5315 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 NGC 2440 Authors: Bernard Salas, J.; Pottasch, S. R.; Feibelman, W. A.; Wesselius, P. R. Bibcode: 2002A&A...387..301B Altcode: The infrared and ultraviolet spectra of planetary nebula NGC 2440 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_Hbeta 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. Bibcode: 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. Bibcode: 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. Bibcode: 2002css1.book..913P Altcode: No abstract at ADS Title: Abundances of planetary nebulae NGC 7662 and NGC 6741 Authors: Pottasch, S. R.; Beintema, D. A.; Bernard Salas, J.; Feibelman, W. A. Bibcode: 2001A&A...380..684P Altcode: The ISO and IUE spectra of the elliptical nebulae NGC 7662 and NGC 6741 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 D1, D2 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 Teff = 8500K, log g = 1.5, Vturb = 13km/s-1 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 Texi = 6100K +/- 200 for the emission line region. Title: The ISO-SWS spectrum of planetary nebula NGC 7027 Authors: Bernard Salas, J.; Pottasch, S. R.; Beintema, D. A.; Wesselius, P. R. Bibcode: 2001A&A...367..949B Altcode: 2001A&A...367..949S We present the infrared spectrum of the planetary nebula NGC 7027 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 Msun. 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Msun 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. Bibcode: 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 t2 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. Bibcode: 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. Bibcode: 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-1 and considering the observed angular diameter of the nebula (4.1''), 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 D1, D2 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.

(2 data files). Title: Vier sterren die zichtbaar evolueren. Authors: Pottasch, S. Bibcode: 1995Zenit..22....8P Altcode: No abstract at ADS Title: Axial Symmetry in Planetary Nebulae Authors: Pottasch, S. R. Bibcode: 1995AnIPS..11....7P Altcode: No abstract at ADS Title: VLA measurements of a sample of planetary nebulae. Authors: Pottasch, S. R.; Zijlstra, A. A. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Lsun, 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. Bibcode: 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. Bibcode: 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* 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1993IAUS..155...40V Altcode: No abstract at ADS Title: The IUE Ultraviolet Spectrum of PC 11 Authors: Parthasarathy, M.; Pottasch, S. R.; Clavel, J. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Vr = +105 km/s and VLSR = +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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1991iue..prop.4117P Altcode: No abstract at ADS Title: Planetary nebulae as standard candles : the distance to the galactic center. Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 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.

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-1, 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 H2O 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.

The distance, derived from H I absorption, is about 4 kpc; the luminosity is a few times 105 Lsun. 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.

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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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-1. 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 Hβ and Hα profiles. The high resolution spectrum at Hα shows the presence of a sharp double-peaked central emission from a low expanding envelope at a velocity of 35±5 km s-1, together with a much broader emission with velocities of several hundred kilometers. The displacement between both components is about 130 km s-1. 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 VLSR=57 km s-1, 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1989IAUS..131..200S Altcode: No abstract at ADS Title: Expansion Velocities of Southern Planetary Nebulae Authors: Sahu, K. C.; Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1989IAUS..131..220M Altcode: No abstract at ADS Title: IRAS observations of extended planetary nebulae. Authors: Leene, A.; Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Msun 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 Bibcode: 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. Bibcode: 1989IAUS..131..302G Altcode: No abstract at ADS Title: Properties of planetary nebulae. II. Central star evolution. Authors: Gathier, R.; Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 mv = 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 ≡7×10-2M_sun;, ≡9×10-2M_sun;, and ≡6×10-2M_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. Bibcode: 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 10-2M_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. Bibcode: 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. Bibcode: 1988SSRv...48..370K Altcode: No abstract at ADS Title: Book-Review - Late Stages of Stellar Evolution Authors: Kwok, S.; Pottasch, S. R. Bibcode: 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. Bibcode: 1988mosg.proc..257M Altcode: No abstract at ADS Title: IUE Observations of Hen 401 and Related Stars Authors: Pottasch, S. R. Bibcode: 1988iue..prop.3321P Altcode: No abstract at ADS Title: IUE Observations of Young Planetary Nebulae Authors: Pottasch, S. R. Bibcode: 1988iue..prop.3351P Altcode: No abstract at ADS Title: Masses of Planetary Nebulae and Their Central Stars. Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 1988iue..prop.3329P Altcode: No abstract at ADS Title: Book-Review - Late Stages of Stellar Evolution Authors: Kwok, S.; Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1987S&T....74R.493K Altcode: No abstract at ADS Title: Misclassified planetary nebulae. Authors: Acker, A.; Chopinet, M.; Pottasch, S. R.; Stenholm, B. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 10-5M_sun;/yr. Title: Late stages of stellar evolution Authors: Kwok, S.; Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Mg0, Mn+, Fe+, Zn+ (all for the first time in a PN) and for Mg+, Al+, Al2+, Si+, O0. 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1986Natur.320..423A Altcode: It has been argued1 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 temperature2,3 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 Msolar 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-Msolar white dwarf are brought into question. Title: Distances to planetary nebulae. II. HI absorption observations. Authors: Gathier, R.; Pottasch, S. R.; Goss, W. M. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 10-2M_sun; to 10-3M_sun;, and for HD 101584 it is of the order of 10-3M_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. Bibcode: 1986iue..prop.2658P Altcode: No abstract at ADS Title: IRAS measurements of planetary nebulae Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 3×105cm-3 which is considerably higher of 104cm-3 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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-1)} = -10.1...-8.1 is derived, while the final wind velocity is v = 2200 km s-1. 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1984SSRv...37..399O Altcode: No abstract at ADS Title: Planetary nebulae. A study of late stages of stellar evolution Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 ne ∝ R-1.3. 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1983MNRAS.204...53S Altcode: Chemical abundances in a large and representative sample of galactic H II regions covering a wide range in galactocentric radius RG were measured using radio and optical spectroscopy. Accurate electron temperatures in 67 H II regions spanning the range RG = 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. Bibcode: 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. Bibcode: 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. Bibcode: 1983IAUS..103..547P Altcode: No abstract at ADS Title: Study of The Interstellar Medium in the Scorpius-Ophiuchus Region Authors: Pottasch, S. R. Bibcode: 1983iue..prop.1738P Altcode: No abstract at ADS Title: Kinematic distances of planetary nebulae. Authors: Maciel, W. J.; Pottasch, S. R. Bibcode: 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. Bibcode: 1983IAUS..103..541P Altcode: No abstract at ADS Title: Extinction - Distances to planetary nebulae. Authors: Gathier, R.; Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1982iue..prop.1215P Altcode: No abstract at ADS Title: Extinction to Planetary Nebulae Authors: Pottasch, S. R. Bibcode: 1982iue..prop.1376P Altcode: No abstract at ADS Title: Mass-Loss of Wolf-Rayet-Type Central Stars of Planetary Nebulae Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 × 105 °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. Bibcode: 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. Bibcode: 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. Bibcode: 1980A&A....91..378N Altcode: No abstract at ADS Title: Masses of planetary nebulae. Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1980iue..prop..685P Altcode: No abstract at ADS Title: Interstellar Line Measurements of High-Velocity Clouds Authors: Pottasch, S. R. Bibcode: 1980iue..prop..686P Altcode: No abstract at ADS Title: Cool gaseous nebulae Authors: Shaver, P. A.; McGee, R. X.; Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1979IUE1.symp...49P Altcode: No abstract at ADS Title: Central Stars of Planetary Nebulae Authors: Pottasch, S. R. Bibcode: 1979iue..prop..318P Altcode: No abstract at ADS Title: SDO and Nova-Like Stars Authors: Pottasch, S. R. Bibcode: 1979iue..prop..319P Altcode: No abstract at ADS Title: Black Hole Binaries Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1976uis..confA...1K Altcode: No abstract at ADS Title: On the iron abundance in interstellar gas. Authors: Olthof, H.; Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1974smws.conf..209P Altcode: 1974smws.proc..209P No abstract at ADS Title: Physics of Interstellar Medium Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1973A&A....29..453D Altcode: No abstract at ADS Title: A model of the interstellar medium. II. Interpretation of the Na0/Ca+ ratio. Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 1972SoPh...23..406D Altcode: No abstract at ADS Title: Abundances in the Solar Corona Authors: de Boer, K. S.; Olthof, H.; Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1970IAUS...39..272P Altcode: No abstract at ADS Title: Review of Astrophysical Conclusions from the UV Solar Spectra Authors: Pottasch, S. R. Bibcode: 1970IAUS...36..241P Altcode: No abstract at ADS Title: On the Abundance Determination in the Solar Chromosphere Authors: Pecker, J. C.; Pottasch, S. R. Bibcode: 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. Bibcode: 1969LIACo..15..377P Altcode: 1969MSRSL..17..377P No abstract at ADS Title: Forbidden line emission from the interstellar medium. Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 1968SoPh....4..104J Altcode: No abstract at ADS Title: On the Infrared Measurements from a Nebula in Orion Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 1968BAN....19..469P Altcode: No abstract at ADS Title: On the abundances in the solar corona. Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1967BAN....19...17T Altcode: No abstract at ADS Title: An interpretation of the spectrum of the recurrent nova RS Ophiuchi Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 1967BAN....19..113P Altcode: No abstract at ADS Title: On the radiative energy loss in the intergalactic medium Authors: Pottasch, S. R. Bibcode: 1966BAN....18..156P Altcode: No abstract at ADS Title: On the Oxygen-to-Iron Ratio in the Solar Corona Authors: Pottasch, Stuart R. Bibcode: 1966BAN....18..443P Altcode: No abstract at ADS Title: On the Chemical Composition of the Solar Corona Authors: Pottasch, S. R. Bibcode: 1966IAUS...26..200P Altcode: No abstract at ADS Title: On the iron lines observed in the solar ultraviolet spectrum Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 1965AnAp...28..148P Altcode: No abstract at ADS Title: The diffuse emission nebulae Authors: Pottasch, Stuart R. Bibcode: 1965VA......6..149P Altcode: No abstract at ADS Title: On the radiative cooling rate in stellar atmospheres Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1965IAUS...23..105P Altcode: No abstract at ADS Title: Determination of electron temperature in diffuse nebulae. Authors: Pottasch, S. R. Bibcode: 1965VA......6..173P Altcode: No abstract at ADS Title: On the Interpretation of the Solar Ultraviolet Emission Line Spectrum Authors: Pottasch, Stuart R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1964AnAp...27..252F Altcode: No abstract at ADS Title: On the chemical composition of the solar corona Authors: Pottasch, S. R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Title: The lower solar corona : the abundance of iron Authors: Pottasch, Stuart Robert Bibcode: 1963PGLO...52..544P Altcode: No abstract at ADS Title: The lower solar corona: the abundance of iron Authors: Pottasch, S. R. Bibcode: 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. Title: The lower solar corona : interpretation of the ultraviolet spectrum Authors: Pottasch, Stuart Robert Bibcode: 1963PGLO...51..945P Altcode: No abstract at ADS Title: Excitation conditions in H II regions in spiral and irregular galaxies Authors: Burbidge, Geoffrey R.; Gould, Robert Joseph; Pottasch, Stuart Robert Bibcode: 1963PGLO...56..945B Altcode: No abstract at ADS Title: Chemical Composition of the Outer Solar Atmosphere. Authors: Pottasch, Stuart R. Bibcode: 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 Title: The Effect of Optical Depth in the Spectrum of Helium (triplets) in Nebulae. Authors: Pottasch, Stuart R. Bibcode: 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. Title: Mouvement des bords brillants dans les nébuleuses diffuses Authors: Courtès, G.; Cruvellier, P.; Pottasch, S. R. Bibcode: 1962AnAp...25..214C Altcode: No abstract at ADS Title: Dynamics of Bright-Rim Structures Authors: Pottasch, S. R. Bibcode: 1962dmim.conf..205P Altcode: 1972dmim.conf..205P No abstract at ADS Title: Mouvement des bords brillants dans les nebuleuses diffuses Authors: Courtes, Georges; Cruvellier, Paul; Pottasch, Stuart Robert Bibcode: 1962POHP....6Q....C Altcode: No abstract at ADS Title: Balmer Line Emission from a Shell. Authors: Pottasch, Stuart K. Bibcode: 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. Title: Motions in Bright Rim Structures in Diffuse Nebulae. Authors: Courtes, G.; Pottasch, S. R. Bibcode: 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. Title: Balmer decrements. - II. The Be stars Authors: Pottasch, S. R. Bibcode: 1961AnAp...24..159P Altcode: No abstract at ADS Title: The Ultraviolet Radiation from O Stars in Diffuse Nebulae Authors: Pottasch, S. R. Bibcode: 1961LIACo..10..563P Altcode: 1961LIACo..10..562P; 1961MSRSL...4..562P No abstract at ADS Title: The Extent of H II Regions. Authors: Pottasch, Stuart R. Bibcode: 1960ApJ...132..269P Altcode: No abstract at ADS 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. Bibcode: 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. Title: The spectrum of RR Telescopii between May 1949 and August 1950 Authors: Pottasch, S. R.; Varsavsky, C. M. Bibcode: 1960AnAp...23..516P Altcode: No abstract at ADS Title: Comments on some physical processes in diffuse nebulae Authors: Pottasch, S. R. Bibcode: 1960AnAp...23..749P Altcode: No abstract at ADS Title: Use of the Equation Hydrostatic Equilibrium in Determining the Temperature Distribution in the Outer Solar Atmosphere. Authors: Pottasch, S. R. Bibcode: 1960ApJ...131...68P Altcode: No abstract at ADS Title: Balmer Decrements : the Diffuse Nebulae. Authors: Pottasch, S. R. Bibcode: 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. Title: Departures from the Saha Equation Under Varying Conditions of Lyman Continuous Opacity. Authors: Pottasch, S. R.; Thomas, R. N. Bibcode: 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). Title: The nova outburst: II. The radiative cooling of an expanding shell Authors: Pottasch, S. Bibcode: 1959AnAp...22..310P Altcode: No abstract at ADS Title: The nova outburst: V. The temperature and radius of the central exciting star and observation of elements other than hydrogen Authors: Pottasch, S. Bibcode: 1959AnAp...22..412P Altcode: No abstract at ADS Title: The nova outburst: I Authors: Pottasch, S. Bibcode: 1959AnAp...22..297P Altcode: No abstract at ADS Title: The nova outburst: III. The ionization of hydrogen gas by an exciting star Authors: Jefferies, J.; Pottasch, S. Bibcode: 1959AnAp...22..318J Altcode: No abstract at ADS Title: The nova outburst: IV. The intensity of H&alpha Authors: Pottasch, S. Bibcode: 1959AnAp...22..394P Altcode: No abstract at ADS Title: Bright Rims in Diffuse Nebulae Authors: Pottasch, Stuart R. Bibcode: 1958RvMP...30.1053P Altcode: No abstract at ADS Title: The Nova Outburst. Authors: Pottasch, Stuart Robert Bibcode: 1958PhDT.........1P Altcode: No abstract at ADS Title: Dynamics of bright rims in diffuse nebulae Authors: Pottasch, S. R. Bibcode: 1958BAN....14...29P Altcode: No abstract at ADS Title: A study of bright rims in diffuse nebulae Authors: Pottasch, S. R. Bibcode: 1956BAN....13...77P Altcode: No abstract at ADS