Julie H. Lutz

DUST-DISTANCES TO PLANETARY NEBULAE.

The authors have measured accurate, new extinction constants for the planetary nebulae considered by Lutz in her earlier studies of distances, in which these were determined by comparing nebular extinctions with color excesses of surrounding O and B stars whose distances are known. Instead of fitting a curve to all the stellar data, the authors bracket the nebular extinction with a range in color excess, and average the distances of the stars that fall within the band. Two of the eight nebulae considered lie outside the range of the stellar data, illustrating the error that can be introduced into the method by insufficiently deep photometry, which can cause dust distances to be overestimated. For the others, the typical uncertainty is still high, averaging about ±55%. The derived distances marginally support the distance scale used by Cahn and Kaler as well as the distance method employed by Daub.

He 2-104 - A symbiotic proto-planetary nebula

CCD observations are presented for He 2-104, an object previously classified as both PN and symbiotic star, which show that this is in fact a protoplanetary nebula (PPN) with a dynamical age of about 800 yr. The presence of highly collimated jets, extending over 75 arcsec on the sky, combined with an energy distribution showing a hot as well as a cool component, indicates that He 2-104 is a binary PPN. Since the primary is probably a Mira with a 400-d period (as reported by Whitelock, 1988), it is proposed that the system is a symbiotic PPN. 16 refs.

He 2-104: A link between symbiotic stars and planetary nebulae

Ultraviolet, optical and infrared observations of He 2-104 are presented, and estimates for some of the physical properties of the nebular shell are made. It is argued that He 2-104 is in transition between the D-type symbiotic star and bipolar planetary nebula phases and, as such, represents a link between subclasses of these two types of objects. The model includes a binary system with a Mira variable and a hot, evolved star. Previous mass loss has resulted in the formation of a disk of gas and dust around the whole system, while the hot star has an accretion disk which produces the observed highly ionized emission line spectrum. Emission lines from cooler, lower density gas is also observed to come from the nebula. In addition, matter is flowing out of the system in a direction perpendicular to the disk with a high velocity and is impacting upon the previously-ejected red giant wind and/or the ambient interstellar medium.

Planetary Nebula Central Stars and Symbiotic Stars in the MACHO Galactic Bulge Database

We have examined central stars of planetary nebulae and symbiotic stars found in the MACHO Galactic bulge database to look for variability. We found four central stars of planetary nebulae and eight symbiotic stars that show variability. We examine thevariability and the nature of these objects in detail, as well as reporting on the objects that we did not find to be variable. catalogs 1 and the full database of detected sources. Sources from the full MACHO database of millions of objects were selected for the MGB Variable Star Catalog if the central 80% of points in the objects light curve failed to fit a constant magnitude in a χ-square test. This criterion resulted in 521,007 candidate variables in the Galactic bulge. 2 MACHO data were taken simultaneously in two nonstandard filters: red and blue. These can be transformed to Cousins V and R using the method of Bessell & Germany (1999), which was calibrated for metal-poor giants. We present these magnitudes here in the interest of providing rough estimates. When we only have data in one MACHO band, we assume a color of 0 for PNCS and 1 for SS

Misclassified and misidentified planetary nebulae and nuclei

Observations are reported for 17 objects that are listed in the Catalogue of Galactic Planetary Nebulae (CGPN). These have either been misclassified as planetary nebulae, have been identified incorrectly by their observers or in the CGPN, or have had peculiar central stars erroneously assigned to them. In about one-half of the cases, we confirm previous reclassifications. The general characteristics of each object are described, and we provide relative emission-line fluxes for two that are already known to be symbiotic stars.

Correlations between Lithium and Technetium Absorption Lines in the Spectra of Galactic S Stars

Correlations between the presence of the 6707 A line of lithium and the resonance lines of technetium (4238 and 4262 A) in a large sample of Galactic S stars are analyzed. Half of the sample stars are intrinsic S stars (those exhibiting technetium in their spectra), and 1/3 of these stars also have strong lithium lines in their spectra. Stars having both lithium and technetium in their spectra are interpreted as intermediate-mass thermally pulsating asymptotic giant branch (TP-AGB) stars in which lithium is produced by the Cameron-Fowler mechanism. The production of lithium is predicted to occur in high-luminosity (Mbol ≤ −6) TP-AGB stars by the hot-bottom burning (HBB) mechanism. Data on the carbon isotope ratios of stars in our sample agree with the predictions of HBB; however, oxygen isotope ratios in these stars do not agree with the predictions of HBB. Furthermore, the available luminosities for our sample stars are below the minimum value necessary for HBB to occur in available models. Cool-bottom processing (CBP) is one possible explanation for the presence of lithium in the spectra of these stars. Intrinsic S stars having technetium but no lithium in their spectra are interpreted as lower mass (1.5-3 M⊙) thermally pulsating AGB stars that have not undergone CBP. Extrinsic S stars constitute the remaining half of the sample. Carbon and oxygen isotope ratios, as well as the lack of technetium and lithium in the spectra of these stars, are consistent with these being low-mass red giant branch stars (1-2 M⊙), with mass transfer from a now extinct thermally pulsating AGB star being responsible for the enhanced abundance of s-process elements.

Interstellar dust and distances to planetary nebulae

S>UBV and H gamma data were used to construct diagrams of color excess versus distance for early-type stars within 1 deg 5 of six planetary nebulae. These diagrams were used in conjunction with the observed extinctions of the planetaries to derive distances for NGC 6741, NGC 6894, NGC 7026, NGC 7354, IC 1747, and IC 289. This method is independent of assumptions about optical thickness in the nebular shell or evolutionary stage. Assumptions of electron temperature and R, the ratio of total to selective absorption, are required. The method is limited in accuracy by the patchiness of the interstellar medium and by the possibility that R may vary from point to point in the Galaxy. (auth)

A case study of a WC planetary nebula nucleus - Henize 2-99

The WC spectrum of the nucleus of the planetary nebula Henize 2-99. Fluxes are given, emission lines are identified, and blends are described. The most powerful emissions are C III, C II, and C IV. O, H, and Si lines are also observed, but little stellar nitrogen is found except for N V. The interstellar extinction is estimated at c = 0.9 + or - 0.2. Blackbody, Zanstra, and Stoy temperatures are found to be 70,000 K, 26,000 K, and 27,000 K, respectively. It is shown that He 2-99 is binebulous with a prominent enhancement in H-alpha along the minor axis. The structural characteristics of He 2-99 are very similar to BD +30 deg 3639 and NGC 40. 69 refs.

High-Dispersion Spectroscopy of BF Cygni at the Beginning of the 2006 Outburst

BF Cygni (hereafter BF Cyg) is a symbiotic star that in 2006 July started into an optical outburst that has lasted for several years. Between 2006 August and 2007 January we obtained high-dispersion spectra (r ~ 35,000) over the wavelength range of 3800-10000 A of BF Cyg with the 3.5 m echelle spectrograph at Apache Point Observatory. The emission lines in the optical spectrum of BF Cyg changed dramatically during the interval of observations. The species found were mostly low-ionization emission lines of H, He, C, N, O, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, and Ni. Both permitted and forbidden lines were seen. In particular, Fe I was observed in emission, which is not a common phenomenon. We discuss the evolution of the BF Cyg spectrum during the 5 month interval of our observations. Some emission lines developed P-Cygni profiles indicating gas expanding at about 100-200 km s-1. Other lines changed from emission to absorption. A few absorption lines that had not been observed in 2006 August were evident on the spectra obtained in 2006 November and 2007 January. Some interesting (but unidentified) persistent broad features were observed in the continuum. Comparisons of our observations with previous spectroscopy of BF Cyg demonstrate that the emission spectrum is in a lower state of excitation during this outburst than during quiescence.

The peculiar object He 2--467

He 2--467 has been classified as a planetary nebula. However, the spectrum of this object shows emission lines superposed on the absorption spectrum of a G-type star. Image tube spectrograph and scanner observations of the emission and absorption features are presented. The emission spectrum is unusual in that no forbidden lines are seen, and the He i singlet to triplet ratios do not agree with recombination theory. (AIP)