A. Gutierrez-Moreno

STUDIES OF SOUTHERN PLANETARY NEBULAE. I. FLUXES FROM BRIGHT PLANETARY NEBULAE.

A study of spectrophotometric observations of some southern planetary nebulae, made during 1980 and 1981, to increase and improve the absolute data for some of them and to detect objects of special interest, is discussed. Observed H-beta fluxes, logarithmic reddening correctitons, and intrinsic forbidden-line intensities relative to H-beta are given for 14 bright southern planetary nebulae. The results of the study, as well as those obtained from other authors, are listed in tables and compared.

A STUDY OF ATMOSPHERIC EXTINCTION AT CERRO TOLOLO INTER-AMERICAN OBSERVATORY. II

The behavior of the atmospheric extinction at CTIO during 1984 is analyzed. Rayleigh scattering, aerosol extinction, and ozone absorption parameters are determined. The behavior of the extinction during different months of the year is discussed.

New Spectroscopic Observations of the Planetary Nebula PC 11

New observations of the planetary nebula PC 11, made in 1991, are presented and discussed. The object is a compact planetary nebula, small and dense, with a low mass of ionized gas. It is losing matter through one or more jets, formed mainly by O iii. The central star is a binary, with a cool component of spectral type F0-F1 V. The hot component has an energy balance temperature of 105,000 K, a mass of 0.638 M,, and very low luminosity, estimated as 11 L,, with a radius of the order of 0.01 R,. The position of PC 11 in the H-R diagram is peculiar, since it seems incompatible with its being a very young planetary nebula, as suggested by its small size and high density.

Ultraviolet and Optical Observations of Hen 1213, Hen 1341, and Hen 1761

We present UV observations of the symbiotic stars Hen 1213, Hen 1341, and Hen 1761, made almost simultaneously with optical observations during 1995; previous optical observations were made during 1987 and 1991. The UV spectrum of Hen 1213 was badly affected by background radiation, and only a rough description of the spectrum could be given here; for this reason, only the observations of Hen 1341 and Hen 1761 are discussed. They have the typical spectra of symbiotic stars, with a late giant component, with many emission lines superimposed. It is found that for both objects the reddening determined from He II λ1640/He II λ4686 is smaller than that obtained from the Balmer decrement, including optical depth effects. Hen 1341 does not show important variations for the three observing periods. Hen 1761 shows P Cygni profiles for He II λ4686 and He I λ4471, with expansion velocities of the order of 900 and 600 km s-1, respectively. The 1991 observations give the lower temperature of the hot component with the larger size of the nebula and the lowest He contents. Rough estimates indicate that the hot component of Hen 1761 is smaller and less luminous than that of Hen 1341.

SPECTROSCOPIC OBSERVATIONS OF THE PLANETARY NEBULAE ME 2-1

Observations of the planetary nebula Me2-1 were obtained with different set-ups, in order to analyze some effects of contamination produced by the second order ultraviolet spectrum in the first order red, for wavelengths longer than approximately 6000 A. This contamination problem will be discussed elsewhere. Here we present the observations of Me2-1, which include a wide wavelength range, from about 3100 to 10200 A. A comparison with previous results is shown for the wavelength intervals in common. From these data, the most relevant nebular parameters are derived, using lines in the optical and near IR regions. Some parameters corresponding to the central star are also determined. The results are compared with previously obtained values.

STUDIES OF SOUTHERN PLANETARY NEBULAE. II. ELECTRON TEMPERATURES AND DENSITIES.

Electron temperatures and densities for 14 bright southern planetary nebulae, obtained from data previously published, are presented here. It is found that the difference between the logarithmic electron densities obtained from the ratio of nebular lines and from the ratio of auroral or transauroral lines to nebular lines is linearly correlated with the electron densities. It is also found that the ratio of the temperatures in the O III and N II forbidden line regions, TH/TL, is linearly correlated with the degree of excitation, measured through the intensity of He II 4686A. The relation is double valued, with values of TH/TL both larger and smaller than 1 for the same degree of excitation. Up to this moment, no physical parameter giving a unique correlation with TH/TL has been found.

OBSERVATIONS OF FIVE SUSPECTED SYMBIOTIC STARS

We present observations of five objects previously classified as suspected symbiotic stars: CD -36 8436, He 2-101, Sa 3-43, Th 4-4 and V3804 Sgr. We find that they are all symbiotic, and deduce some of their physical characteristics.

ATMOSPHERIC EXTINCTION IN THE (U-B) COLOR INDEX.

Various methods for obtaining the atmospheric extinction in the (U-B) color index taking into account the dependence of extinction coefficient on the intrinsic color index of the star are examined. Numerical integrations are performed to determine synthetic color indices for 32 stars of spectral classes O9 to M0 and luminosity classes I, III and V through 0, 1 and 2 air masses, resulting in three (u-b) color indices for each star. Photometric reduction of the color indices to the (U-B) color index was then performed by the classical method, by the method proposed by Gutierrez-Moreno et al. (1966) and various modifications of it, and by the method proposed by Moffat and Vogt (1977). Comparison with observations of 71 stars in the standard region E5, nine extinction standard stars and 25 Johnson standard stars in the UBV reveals that the reduction of (U-B) by the classical method gives internal errors between two and three times larger than those obtained for (B-V) and V, while the methods of Gutierrez-Moreno et al. and Moffat and Vogt provide greatly improved accuracy.

Ultraviolet observations of the symbiotic star AS 296

AS 296 is a well-known S-type symbiotic star which underwent an optical outburst during 1988. In this paper, UV data based on IUE observations obtained both during the quiescent and outburst stages are presented and discussed, correlating them to observations made in the optical region. It is concluded that the object is a symbiotic nova, in which the outburst is due to a thermonuclear runaway produced in the hydrogen-burning shell of a white dwarf with M of about 0.5 solar masses, accreting from the late-type giant at a rate M(acc) of about 9.7 x 10 exp -9 solar mass/year. It is not possible to determine from the observations if the hydrogen flash is degenerate or nondegenerate.

THREE TYPE I PLANETARY NEBULAE

Observations of three planetary nebulae (PNe) with [N II] lambda-6583 > H-alpha are presented. They are He 2-111, He 2-145, and He 2-152. He 2-111 has already been classified by several authors as a type I PN. It is concluded that He 2-145 and He 2-152 are both type I PNe. Physical parameters of the nebulae and the central stars are given. It is found that He 2-152 has an extremely high He contents. The luminosities of the central stars run from 340 L* for He 2-152 to 1090 L* for He 2-111. When using distance independent parameters for the determination of the luminosity, much higher values are obtained, running from 5200 L* for He 2-145 to 19800 L* for He 2-111.