Distances for galactic planetary nebulae using mean forbidden [O II] doublet ratio electron densities

We present [O II| 3726, 3729-Å doublet ratios and electron densities for 68 galactic planetary nebulae (PN). For 45 of the objects, the doublet ratios represent integrations over the whole of the nebula. Distances have been derived for the majority of the nebulae, using calibrations recently derived from Magellanic Cloud PN. For PN which are optically thin in the hydrogen Lyman continuum, we have derived distances using a variant of the Shklovsky method (constant ionized hydrogen mass) which uses the mean [O II] electron density and the measured radio flux and which does not require knowledge of the filling factor or nebular angular radius. For PN which are optically thick in the Lyman continuum, the constant Hβ flux method was used to derive distances. The typical [O II] density at the transition point between an optically thick and thin nebula is 4500 cm−3. Since the optically thin and thick methods both over-estimate the distance when applied to inappropriate nebulae, the smaller of the two distance estimates is adopted for each nebula. An extensive comparison is made between the distances derived here and previously published distances and distance scales. It is shown that the present distances, based on Magellanic Cloud calibrations, give consistency with independent distance estimates. They also yield much greater self-consistency between central star masses derived from luminosity versus Teff comparisons on the one hand, and from absolute magnitude versus evolutionary age comparisons on the other hand. For the PN in our sample, rms electron densities, filling factors and absolute radii have also been derived. The derived filling factors are found to decrease with increasing absolute angular radius, but we argue that this effect can be attributed entirely to the effects of measurement uncertainties in the adopted angular radii

DR 1: a WO3 star in IC 1613 and its surrounding nebula, S3

We present an analysis of the WO3 star, DR 1, which is located in the dwarf irregular galaxy IC 1613, and is surrounded by an HII region which shows nebular HeII 4686 A in emission, a rare phenomenon in nebulae surrounding Wolf-Rayet stars. We have derived E(B-V)=0.07 via a comparison of the observed Balmer line ratios to those predicted by theory, using the electron temperature of T_e_=17100K derived from our nebular analysis. We find O/H=4.99x10^-5^ by number for the nebula, in agreement with the O/H ratios found for other emission-line regions in IC 1613. We derive the following nebular mass fractions: X=0.761, Y=0.238 and Z=0.00091. After allowance for the contribution by the nebular continuum, we have derived a stellar absolute magnitude of M_V_=-3.6 for DR 1, a stellar effective temperature of T_*_=75000K via a HI and HeII Zanstra analysis, and a stellar luminosity of 10^6^Lsun_. A terminal wind velocity of vinfinity_=2850km/s is derived for DR 1 from the width of the strongest stellar emission lines. We also performed an abundance analysis of the stellar wind via a recombination theory analysis of the stellar emission-line features, and derive X(C)=0.48, X(O)=0.27 and X(He)=0.25. These values are within the range found for other WO stars by Kingsburgh et al. (1994) and agree with those predicted by the Z=0.004 massive star evolutionary models of Meynet et al. (1994), but not with their Z=0.001 models. Our observations confirm the prediction that WO stars in low-metallicity galaxies should be much more luminous than their counterparts in higher metallicity galaxies

Elemental abundances for a sample of southern galctic planetary nebulae

We present spectrophotometric observations of a sample of 80 southern galactic planetary nebulae (PN), and derive elemental abundances for 68 objects, supplementing the optical observations with UV data in 25 cases. We define Type I PN as those objects that have experienced envelope-burning conversion to nitrogen of dredgedup primary carbon. Such nebulae are recognised by their having nitrogen abundances that exceed the total C + N abundance of H II regions in the same galaxy. In our own galaxy, this criterion corresponds to N/O > 0.8. In the current sample, 11 nebulae having N/O > 0.8 are thereby classified as Type I. For these Type I PN, no evidence is found for oxygen depletion, compared with non-Type I PN. No trend is found between the N/O and O/H ratios for the entire sample, and the mean O/H ratios for the non-Type I and Type I PN are the same within the errors; O/H=(4.93±2.22)×10−4 by number for 42 non-Type I PN and O/H=(4.42±1.44)×10−4 for 11 Type I PN. Also, no difference is found between the oxygen abundances in the PN in this sample and the oxygen abundances in galactic H II regions. Hence we find no evidence for the ON cycle (which is predicted to operate during the second dredge-up) to have significantly altered the surface abundances of the progenitor stars, even for the Type I PN. The helium abundances derived for the non-Type I PN are in accord with those predicted by Becker&Iben for the first and third dredge-up phases. A comparison between the nitrogen abundances in the PN and the carbon+ nitrogen abundances in galactic H II regions indicates that roughly 36 per cent of the initial carbon is converted into nitrogen in the case of the non-Type I PN, consistent with predictions for the first dredge-up by Becker&Iben. In order to explain the high nitrogen abundances derived for the Type I PN, however, envelope-burning of dredged-up carbon into nitrogen, following the third dredge-up, is definitely required. Total C + N + O abundances are found to be correlated with C/H for the combined nonType I and Type I sample; the carbon has been enhanced by He-burning processed material brought up by the third dredge-up

Properties of the WO Wolf-Rayet stars

We present optical spectrophotometry for five WO Wolf-Rayet stars, three of them in our own Galaxy and one in each of the SMC and LMC. IUE ultraviolet spectrophotometry has also been obtained for the two Magellanic Cloud WO stars, including a high resolution spectrum for one of them. Quantitative spectral typing criteria are defined for WO subtypes spanning WO1 to WO5 and, for the case of the two WO stars in spectroscopic binaries, spectral types for the O-type primaries are derived. From our spectrophotometry we derive reddenings and magnitudes for each star. Absolute visual magnitudes of -2.5 and -1.8 are derived for a WO4 star and for a WO2 star, respectively, each star lying at a known distance. Wind terminal velocities ranging from 4200km/s to 5500km/s are derived from the black absorption edge of an ultraviolet P Cygni profile and from the FWZI of strong optical emission lines. The relative abundances of helium, carbon and oxygen in the winds of each of the WO stars are derived using a recombination theory analysis of selected ultraviolet and optical emission lines to determine the ionic abundances of He^2+^, C^4+^, O^4+^, O^5+^ and O^6+^. The derived abundance ratios show relatively narrow ranges. C/He number ratios of 0.51-0.52 are derived for two Galactic WO stars and one LMC WO star, with their C/O ratios ranging between 4.6 and 5.2, and their (C+O)/He ratios equal to 0.62. The one SMC WO star has a C/He ratio of 0.81, a C/O ratio of 2.7 and a (C+O)/He number ratio of 1.10. These abundance ratios are broadly consistent with evolutionary models for the advanced stages of massive stars, and promising agreement as a function of initial metallicity is found with the most recent evolutionary models

Physical Properties of Wolf-Rayet Stars

The striking broad emission line spectroscopic appearance of Wolf-Rayet (WR) stars has long defied analysis, due to the extreme physical conditions within their line and continuum forming regions. Recently, model atmosphere studies have advanced sufficiently to enable the determination of stellar temperatures, luminosities, abundances, ionizing fluxes and wind properties. The observed distributions of nitrogen (WN) and carbon (WC) sequence WR stars in the Milky Way and in nearby star forming galaxies are discussed; these imply lower limits to progenitor masses of ~25, 40, 75 Msun for hydrogen-depleted (He-burning) WN, WC, and H-rich (H-burning) WN stars, respectively. WR stars in massive star binaries permit studies of wind-wind interactions and dust formation in WC systems. They also show that WR stars have typical masses of 10-25 Msun, extending up to 80 Msun for H-rich WN stars. Theoretical and observational evidence that WR winds depend on metallicity is presented, with implications for evolutionary models, ionizing fluxes, and the role of WR stars within the context of core-collapse supernovae and long-duration gamma ray bursts.Comment: 76 pages, 8 figures. Minor revision to "Annual Review of Astronomy & Astrophysics" review article Volume 45 (2007) following editors comments. Version with full resolution figures is available from ftp://astro1.shef.ac.uk/pub/pac/AnnRev_revised.pd

Physical conditions and chemical abundances in photoionized nebulae from optical spectra

This chapter presents a review on the latest advances in the computation of physical conditions and chemical abundances of elements present in photoionized gas H II regions and planetary nebulae). The arrival of highly sensitive spectrographs attached to large telescopes and the development of more sophisticated and detailed atomic data calculations and ionization correction factors have helped to raise the number of ionic species studied in photoionized nebulae in the last years, as well as to reduce the uncertainties in the computed abundances. Special attention will be given to the detection of very faint lines such as heavy-element recombination lines of C, N and O in H II regions and planetary nebulae, and collisionally excited lines of neutron-capture elements (Z >30) in planetary nebulae.Comment: Book Chapter. 31 pages. 6 Figures. Accepted for publication in the book "Reviews in Frontiers of Modern Astrophysics: From Space Debris to Cosmology" (eds Kabath, Jones and Skarka; publisher Springer Nature) funded by the European Union Erasmus+ Strategic Partnership grant "Per Aspera Ad Astra Simul" 2017-1-CZ01-KA203-03556

The extinction and distance of Maffei 1

We have obtained low- and high-resolution spectra of the core of the highly reddened elliptical galaxy Maffei 1. From these data, we have obtained the first measurement of the Mg-2 index and have measured the velocity dispersion and radial velocity with improved accuracy. To evaluate the extinction, a correlation between the Mg-2 index and effective V-I color has been established for elliptical galaxies. Using a new method for correcting for effective wavelength shifts, the V-I color excess reveals that the optical depth of Galactic dust at 1 mum is 1.69 +/- 0.07. Thus, A(V) = 4.67 +/- 0.19 mag, which is lower by 0.4 mag than previously thought. To establish the distance, the fundamental plane for elliptical galaxies has been constructed in I. The velocity dispersion of Maffei 1, measured to be 186.8 +/- 7.4 km s(-1), in combination with modern wide. field photometry in I, leads to a distance of 2.92 +/- 0.37 Mpc. The D-n-sigma relation, which is independently calibrated, gives 3.08 +/- 0.85 and 3.23 +/- 0.67 Mpc from photometry in B and K', respectively. The weighted mean of the three estimates is 3.01 +/- 0.30 Mpc, which is lower than distances judged with reference to M32 and the bulge of M31 from the brightest stars seen at K'. Since the luminosity of asymptotic giant branch stars at K' is strongly dependent on age, the lower distance suggests that the last epoch of star formation in Maffei 1 occurred farther in the past than in these other systems. The distance and luminosity make Maffei 1 the nearest giant elliptical galaxy. In the absence of extinction, the galaxy would be among the brightest in the sky and would have an apparent size 2/3 that of the full Moon. The radial velocity of Maffei 1 is + 66.4 +/- 5.0 km s(-1), significantly higher than the accepted value of -10 km s(-1). The Hubble distance corresponding to the mean velocity of Maffei 1, Maffei 2, and IC 342 is 3.5 Mpc. Thus, it is unlikely that Maffei 1 has had any influence on Local Group dynamics