Central Stars Of Planetary Nebulae Research Articles

HR Diagram of Evolved Stars

AbstractA short review is presented on the various methods to construct the HR diagram for central stars of planetary nebulae (CPN).

Evolution of planetary nebulae

A second argument in this direction was given by several astronomers in the 1950's. It had long been known from the double peaked emission lines observed in the nebulae, that they were expanding. The velocity of expansion is on the average 15 to 20 km s -t, with only exceptional cases differing by more than a factor 2 from this value. Since this nebular material presumably escaped from the central star, the question was asked: which stars have an escape velocity of the order of 20 km s-t? The answer is Red Giants. On considering this answer, other reasons for its correctness became apparent. A red giant actually has the characteristics of an early stage of a PN. Much of its mass is present in a high density core which could easily be the forerunner of the PN central star. Some of its mass is present in the enormous giant atmosphere which could easily become the nebula. It only remained to set the giant atmosphere in motion at the escape velocity. The solution the star has chosen to solve this problem is not yet completely understood. It is clear however that the mass lost by the star to form a PN occurs at a stage prior to its being observed as a PN. Thus the previous stage, whether OH/IR star, Mira variables and other types of red giants will also be discussed.

Ultraviolet Fe VII absorption and Fe II emission lines of central stars of planetary nebulae

The SWP camera of the IUE satellite was used in the high-dispersion mode to search for Fe VII absorption and Fe II high-excitation emission lines in five additional very hot central stars of planetary nebulae. Some of the Fe VII lines were detected at 1208, 1239, and 1332 A in all the objects of this program, LT 5, NGC 6058, NGC 7094, A43, and Lo 1 (= K1-26), as well as some of the Fe II emission lines at A 1360, 1776, 1869, 1881, 1884, and 1975 A. Two additional objects, NGC 2867 and He 2-131, were obtained from the IUE archive and were evaluated. The present study probably exhausts the list of candidates that are sufficiently bright and hot to be reached with the high-dispersion mode of the IUE.

PHOTOIONIZATION OF HIGH-LATITUDE GAS IN NGC 891

ABSTRACT NGC 891 by the UV radiation from various in situ stellar populations. We find that although OB stars dominate the production of stellar UV photons, models using only OB stars cannot reproduce the observed [N II] λ6584/Hα ratios seen throughout this diffuse ionized medium (DIM). Models that combine OB stars with the high-temperature end of the white-dwarf distribution and the central stars of planetary nebulae are capable of reproducing the observed [N II] λ6584/Hα ratios. Estimation of ionizing photon fluxes, using free-free and infrared emission, combined with these models requires the filling factor throughout the DIM in NGC 891 to be of order 10-2^ and that white dwarfs and planetary nebula central stars contribute ~25% of the ionizing photons at |z| = 250 pc. Our model results indicate that the filling factor of the DIM in the Milky Way is approximately 10-1^, in agreement with previous estimates.

Echelle spectroscopy of CD -41 deg 13967 - The young central star of a new planetary nebula

view Abstract Citations (12) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Echelle Spectroscopy of CD -41 degrees 13967: The Young Central Star of a New Planetary Nebula McCarthy, James K. ; Rich, R. Michael ; Becker, S. R. ; Butler, K. ; Husfeld, D. ; Groth, H. G. Abstract High-resolution CCD spectra obtained with the Palomar 60 inch (1.5 m) echelle spectrograph and subsequently confirmed and extended using the CTIO 4 m echelle spectrograph have revealed that the hot star CD -41° 13967 is the young central star of a previously unknown low-excitation planetary nebula. Presented in this paper is a detailed analysis of our CCD echelle spectra of CD -41° 13967, which are well fitted by non-LTE model atmosphere line profiles corresponding to Teff = 27,000 K, log (g) = 3.1, and a He abundance 3 times solar. These best-fit model parameters imply a mass of 0.63 Msun and a post-asymptotic giant branch (AGB) age of 1250 yr for the central star, based on a comparison with central star of planetary nebula (CSPN) evolutionary tracks in the distance-independent Teff-log (g) plane. Using recent UBVRI CCD photometry corrected for extinction along with the Eddington flux emerging from the best-fit non-LTE model atmosphere, we derive a spectroscopic distance estimate of 3.5 kpc to CD - 41° 13967. This together with the Galactic coordinates (lII = 359.0; bII = - 33.5) strongly suggests that CD -41° 13967 belongs to the Galactic halo population, a suggestion supported by the results of our stellar abundance analyses for silicon, [Si/H] = -0.20±0.10 and oxygen, [O/H] = -0.43±0.20 as well as by the mean of our stellar radial velocity measurements <Vr>* = -91±2 km s-1; compare also with our result, <Vr>PN = -97±2 km s-1). The surrounding planetary nebula, He 3-1863, shows an angular extent greater than 6" (FWHM) on the E/W slit of our CTIO spectrograms. The excitation class of the nebula is zero, with only Hα, Hβ, Hγ, Hδ, [N II] 5755, 6548, 6584 Å, [O I] 6300, 6364 Å, [O II] 7320, 7330 Å, and [S II] 6717, 6731 Å lines in evidence; lacking is any [O III] 4363, 4959, 5007 Å emission. This is consistent with the low Teff; determined for the central star. Subsequent narrow-band Hα CCD imaging reveals that He 3-1863 is a centrally concentrated elliptical nebula with a total E/W extent ≥17" and N/S extent ≥ 13" on the sky. Publication: The Astrophysical Journal Pub Date: April 1991 DOI: 10.1086/169898 Bibcode: 1991ApJ...371..380M Keywords: Early Stars; Echelle Gratings; Nonequilibrium Thermodynamics; Planetary Nebulae; Stellar Spectra; Charge Coupled Devices; Hot Stars; Stellar Atmospheres; nebulae: planetary; stars: abundances; stars: early-type; stars: individual (CD -41° 13967); Astrophysics full text sources ADS | data products SIMBAD (1)

Photospheric Abundances in Central Stars of Planetary Nebulae, and Evolutionary Implications

The available information about spectral characteristics and photospheric abundances of 115 CSPN is presented. About 33% of CSPN in the sample are H-deficient. Many (but not all) H-deficient CSPN show extremely high C abundances. There is also some evidence of a variety of C abundances among H-rich CSPN. The available evidence suggests that most CSPN leaving the AGB with a H-rich photosphere will become DA white dwarfs. The “late He shell flash + fast wind” (born-again) mechanism may offer a satisfactory way of explaining some of the H-deficient CSPN. However, at least in some cases, the complete ejection of the H-rich stellar envelope, and exposure of He-burned matter at the remnant stellar surface, must happen already at the time of departure from the AGB.

Winds in Central Stars of Planetary Nebulae

AbstractWe present the results of an examination of low-resolution IUE spectra of Galactic planetary nebulae in an effort to determine the occurence of stellar winds in their central stars. Our analysis confirms the results obtained in previous studies.

The observed position of planetary nebulae nuclei on the luminosity - temperature diagram

The position of the central stars of planetary nebulae on the T/L diagram provides an important test of the stellar evolution theory. In this paper, we present, at first, a brief review of the recent works presented on this subject. The confrontation of observational results with theoretical models allows to precise the range of the masses of the central stars, which represents the main parameter governing their evolution. In the second part, we present the results of our new spectrophotometric survey; we have computed temperatures and luminosities of the central stars, using newly derived observational parameters and statistical distances. Taking into account the limitation both on our observations and on the used methods, the T/L diagram obtained enables us to estimate the range of the mass distribution.

Evolutionary versus dynamical time scales for the evolution of the central stars of planetary nebulae

view Abstract Citations (51) References (51) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evolutionary versus Dynamical Time Scales for the Evolution of the Central Stars of Planetary Nebulae McCarthy, J. K. ; Mould, J. R. ; Mendez, R. H. ; Kudritzki, R. P. ; Husfeld, D. ; Herrero, A. ; Groth, H. G. Abstract The disagreement between evolutionary and dynamical time scales for the evolution of the central stars of planetary nebulae (CSPN) through the H-R diagram is investigated. Three possible reasons for the disagreement are examined: (1) the nebulae could have experienced a phase of rapid photoionization of material ejected previously while the stars were still on the AGB; (2) the central stars could have undergone a late helium shell flash and returned to the AGB; and (3) the AGB-CSPN evolutionary transition times could have been increased by small additional amounts of residual envelope material remaining after the superwind mass-loss phase. Mechanism (3) is favored here because it can account for evolutionary ages both less than and greater than the corresponding dynamical ages. Publication: The Astrophysical Journal Pub Date: March 1990 DOI: 10.1086/168458 Bibcode: 1990ApJ...351..230M Keywords: Asymptotic Giant Branch Stars; Planetary Nebulae; Stellar Evolution; Absorption Spectra; Hertzsprung-Russell Diagram; Photoionization; Stellar Envelopes; Stellar Mass; Stellar Winds; Astrophysics; NEBULAE: PLANETARY; STARS: EVOLUTION full text sources ADS | data products SIMBAD (23)

Properties of central stars in 13 faint, extended planetary nebulae

Temperatures and luminosities for 13 faint central stars in extended planetary nebulae have been derived and placed on the theoretical log L-log T diagram to infer their masses. Despite the initial expectation of finding predominantly higher-mass central stars, it was found rather that the masses cover almost the entire central star range, from less than 0.55 to about 1.1 solar mass and have a mean value of about 0.64 + or - 0.16 solar mass. This value is not significantly different from the average of 0.58 solar mass typically found for the mass distribution both of planetary nebula central stars and of white dwarfs. 27 refs.

Model atmospheres and parameters of central stars of planetary nebulae

Non-LTE hydrogen and helium model atmospheres have been obtained for temperatures and gravities relevant to the central stars of planetary nebulae. Low-resolution and high-resolution observations obtained by the IUE satellite have been used along with optical data to determine Zanstra temperatures of the central stars of NGC 1535, NGC 6210, NGC 7009, IC 418, and IC 4593. Comparison of the observed stellar continuum of these stars with theoretical results allowed further information on the stellar temperature to be derived. The final temperatures are used to calculate accurate stellar parameters. 62 refs.

Planetary nebulae as standard candles. II - The calibration in M31 and its companions

The results of a PN survey of M31's bulge are reported. A total of 429 PNs were detected, of which 104 are members of a statistically complete and homogeneous sample covering the top 2.5 mag of the PN luminosity function (PNLF). It is shown that the PNLF is not a power law, but instead has a sharp turnover. This behavior is most easily explained as arising from a sharp cutoff in the upper mass limit of PN central stars in combination with extremely rapid evolutionary time scales for more massive candidate progenitors. Analysis of the PN spatial distribution shows that the density of PN per unit luminosity is about the same in M31's bulge and disk, and the implied stellar death rate is in good agreement with theoretical estimates. Finally, a foundation for using the distinctive shape of the PNLF and the invariance of the luminosity-specific PN number density is laid by deriving two maximum likelihood equations. 77 refs.

The chemical composition of the emitting gas in HM Sagittae

view Abstract Citations (11) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Chemical Composition of the Emitting Gas in HM Sagittae de Freitas Pacheco, J. A. ; Codina-Landaberry, S. J. ; Lopes, Dalton F. Abstract Spectroscopic observations of HM Sge obtained in 1985 and 1986 using a 1.6-m telescope with a 0.5-A resolution are reported. It is found that the broad line component is formed in a region characterized by an electron temperature of 14,000 to 15,000 K and an electron density of 33,700,000/cu cm. Helium overabundance and nitrogen enhancement are observed in the emitting gas. It is shown that the source has a temperature of about 180,000 K and a radius and luminosity comparable to those of the central stars of planetary nebulae. Publication: The Astrophysical Journal Pub Date: February 1989 DOI: 10.1086/167120 Bibcode: 1989ApJ...337..520D Keywords: Astronomical Spectroscopy; Binary Stars; Emission Spectra; Stellar Composition; Symbiotic Stars; Abundance; Chemical Composition; Electron Density (Concentration); M Stars; Mira Variables; Red Giant Stars; White Dwarf Stars; Astrophysics; STARS: ABUNDANCES; STARS: INDIVIDUAL CONSTELLATION NAME: HM SAGITTAE; STARS: SYMBIOTIC full text sources ADS | data products SIMBAD (8)

Evolutionary Tracks for Central Stars of Planetary Nebulae

Our understanding of the evolution of Central Stars of Planetary Nebulae (CPN) has made considerable progress during the last years. This was possible since consistent computations through the asymptotic giant branch (AGB), with thermal pulses and (in some cases) mass loss taken into account, became available (Schönberner, 1979, 1983; Kovetz and Harpaz, 1981; Harpaz and Kovetz, 1981; Iben, 1982, 1984; Wood and Faulkner, 1986). It turned out that the evolution depends very sensitively on the inital conditions on the AGB. More precisely, the evolution of an AGB remnant is a function of the phase of the thermal-pulse cycle during which this remnant was created on the tip of the AGB by the planetary-nebula (PN) formation process (Iben, 1984, 1987). This was first shown by Schönberner (1979), and then fully explored by Iben (1984). In short, two major modes of PAGB evolution to the white dwarf stage are possible, according to the two main phases of a thermally pulsing AGB star: the hydrogen-burning or helium-burning mode. If, for instance, the PN formation, i.e. the removal of the stellar envelope by mass loss, happens during a luminosity peak that follows a thermal pulse of the helium-burning shell, the remnant leaves the AGB while still burning helium as the main energy supplier (Härm and Schwarzschild, 1975). On the other hand, PN formation may also occur during the quiescent hydrogen-burning phase on the AGB, and the remnant continues then to burn mainly hydrogen on its way to becoming a white dwarf.

Nonradial Pulsational Analyses of the Pulsating Central Stars of Planetary Nebulae

We have performed nonradial pulsation analyses of the central star of the planetary nebula K1-16. K1-16 is a very unusual nebulae which appears to have ejected material that is very rich in helium. The central star shows no evidence for hydrogen in its spectrum and the helium and carbon lines are in emission. Grauer and Bond (Ap. J., 277, 211, 1984) discovered that it is pulsating with periods around 1700 sec. Although its spectral characteristics are similar to those of the PG1159-035 variables, it is pulsating in much longer periods than they are.

Mass Loss Rates in Central Stars of Planetary Nebulae

Central stars of planetary nebulae (PNCS) frequently exhibit fast winds (cf. Cerruti-Sola and Perinotto, 1985; C.P. and Grewing, this volume). They may be important for the structure of the whole nebula as well as for the evolution of the central star. Their speed is typically two orders of magnitude higher than that of the classical optically visible nebula, which in turn expands a few times faster than the most external winds detected in few cases in the radio domain.I review here the status of art in the determination of the mass loss rates (M) associated with these fast winds. I restrict myself to the ‘observational’ determinations. Only at the end I will say something about the predictions of multi-scattering line radiation wind driven theory in connection with one best studied object: N6C 6543. This allows one to conclude that this theory may be the right explanation also for these winds.

Magnitude Measurements of Central Stars of Planetary Nebulae

Magnitudes have been measured for 44 faint central stars of planetary nebulae by imaging the star and nebula of a CCD detector. The nebula is 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 the 44 cases observed. Zanstra temperatures are calculated from the observed magnitudes, and discussed.

Model Atmospheres and Quantitative Spectroscopy of Central Stars of Planetary Nebulae

It is a good tradition in IAU Symposia about PN to have a paper on model atmospheres. However, this is always a difficult task for the authors, because the majority of the PN researchers still believe that the best model atmosphere for a Central Star is a black body. Of course, this puts a theorist in stellar atmospheres into a somewhat desperate position. However, Central Stars of Planetary Nebulae (hereafter CSPN) - as all other stars - show spectral lines. And we will try to use the opportunity of this paper to convince that - as for all other stars - the quantitative analysis of these lines on basis of model atmospheres yields extremely valuable information about the physical nature of the stars.

Spectroscopic Distances to Central Stars of Planetary Nebulae

We present spectroscopic distances for 22 central stars of planetary nebulae. These distances have been determined using information provided by our non-LTE model atmosphere analyses of the stellar H and He absorption line profiles. In this way, no assumptions about nebular properties are necessary.Our spectroscopic distances turn out to be larger than many other frequently cited values. We show that our distances are not in contradiction with the available information about the interstellar extinction, and we describe additional evidence supporting them.

Magnitudes, Spectra, and Temperatures of Planetary Nuclei

The purpose of this review is to examine the fundamental observational parameters of the central stars of planetary nebulae, namely their apparent magnitudes and gross spectral characteristics, and how these relate to the derivation or estimation of effective temperatures.