T. Barker

THE CASE FOR THIRD BODIES AS THE CAUSE OF PERIOD CHANGES IN SELECTED ALGOL SYSTEMS

Many eclipsing binary star systems show long-term variations in their orbital periods, evident in their O - C (observed minus calculated period) diagrams. With data from the Robotic Optical Transient Search Experiment (ROTSE-I) compiled in the SkyDOT database, New Mexico State University 1 m data, and recent American Association of Variable Star Observers (AAVSO) data, we revisit Borkovits and Hegeduss best-case candidates for third-body effects in eclipsing binaries: AB And, TV Cas, XX Cep, and AK Her. We also examine the possibility of a third body orbiting Y Cam. Our new data support their suggestion that a third body is present in all systems except AK Her, as is revealed by the sinusoidal variations of the O - C residuals. Our new data suggest that a third body alone cannot explain the variations seen in the O - C residuals of AK Her. We also provide a table of 143 eclipsing binary systems that have historical AAVSO O - C data with new values computed from the SkyDOT database.

The ionization structure of planetary nebulae. X - NGC 2392

Spectrophotometric observations of emission-line intensities over the spectral range 1400 to 7200 A were made in six positions in the planetary nebula NGC 2392. Standard equations used to correct for the existence of elements in other than the optically observable ionization stages give consistent results for the different positions that are in excellent agreement with abundances calculated using ultraviolet lines, and there is no evidence for any abundance gradient in the nebula. The logarithmic abundances agree well with determinations by Aller and Keyes. 26 refs.

The ionization structure of planetary nebulae. III - NGC 7009

Spectrophotometric observations of emission line intensities were made in 8 positions in the planetary nebula NGC 7009. For the 6 brightest positions, the coverage is from 1400 A to 10,000 A. Standard equations used to correct for the existence of elements in other than the optical observable ionization stages give results over a wide range of ionization that are consistent and agree with abundances calculated using ultraviolet lines. This result is particularly gratifying for N because previously the standard formula gave inconsistent abundances in NGC 7009. The major outstanding problem is that the lambda 4267 CII line implies a C(2+) abundance as much as 12 times greater than that determined from the UV lines. This discrepancy is greatest nearest the central star, as is the case in the planetary nebula NGC 6720. The logarithmic abundances (relative to H=12.00) are: He=11.07, 0=8.68, N=8.10, Ne=8.16, C=8.18, Ar=6.36, and S=7.12. The average of the Ne, Ar, and S abundances agrees to within 5% of that for NGC 6720, but the O, N, nd C abundances average 1.9 times lower in NGC 7009, suggesting that here may have been mixing of processed material in the planetary precursor in NGC 6720.

The ionization structure of the ring nebula. I. Sulfur and argon

Measurements of line intensities in the Ring Nebula have been made in four of the six positions observed by Hawley and Miller over a wider wavelength range. The conclusions of Hawley and Miller about the physical conditions and ionization of He, O, Ne, and N are generally confirmed. New observations of S and Ar line intensities have been made, and new ionization correction formulae for these elements are examined.

The ionization structure of planetary nebulae. VI - NGC 7662

Spectrophotometric observations of NGC 7662, obtained in the UV using the IUE in May 1983 and at 340-720 nm using the 90-cm and 2.1-m telescopes at KPNO during 1982-1984, are reported and analyzed. The line intensities and the temperatures, densities, and ionic abundances determined from them are presented in tables and characterized in detail. Generally good agreement is found among these UV/optical abundances, abundances derived from optical data alone, and the model predictions of Harrington et al. (1982).

The ionization structure of planetary nebulae. IV - NGC 6853

Upgraded UV and IR data were taken of the planetary nebula NGC 6853 in the same region as previous optical data to improve the data base on various ionized species in the nebula. The spectral range 1400-9600 A was scanned, and good agreement was obtained between UV and optical ionization abundance data, although the 4267 A C II line yielded a C(2+) abundance larger than indicated by the UV data. The discrepancy concentrated around the central star. Ionization abundances were determined for He, O, N, NC, C, Ar, and S relative to H, and the causes of discrepancies in the abundances compared to those of previous investigators are discussed. It is noted that, as in the planetary nebula NGC 6720, lighter element abundances are higher than solar values, which suggests mixing of processed materials in the envelope of the two nebulae.

The ionization structure of the Ring Nebula. II - Ultraviolet observations

Ultraviolet observations of emission line intensities have been made in four positions in the Ring Nebula previously studied optically. There is good agreement for O and N abundances, and the importance of charge-transfer reactions to the ionization of Ne is confirmed. The Ne/O abundance of 0.25 +- 0.03 is close to the average value for planetary nebulae found by Kaler; the C/H abundance is (3.9 +- 0.4) x 10/sup -4/, also in good agreement with other measurements in planetaries. The most surprising result is that the C/sup 2 +/ abundance inferred from the optical lambda4267 recombination line is as much as 10 times higher than that measured from the UV lines. This discrepancy is greatest nearest the central star. This phenomenon warrants further observational and theoretical study; at the present time, the most attractive explanation seems to be resonance fluorescence due to light from the central star.

Monitoring the Mass Accretion Rate in Scorpius X-1 Using the Optical Johnson B Filter

The emission from low-mass X-ray binaries (LMXBs) arises from the accretion of mass onto a neutron star or black hole. A knowledge of the amount of mass being accreted as well as changes in this value are therefore essential inputs into models of these systems. Despite the need for this information, we currently lack an easily applied method that allows the accretion rate to be measured. X-ray color-color plots and UV observations can be used for this purpose, but these methods require access to oversubscribed satellites. Even if time is granted on these facilities, there is no guarantee that the source will be in a desired state when the observations take place. In this paper we show that an estimate of the ratio of the mass accretion rate to the Eddington rate can be obtained for Sco X-1 by using the Johnson B magnitude. Based on correlated X-ray and ground-based observations, we find that for Sco X-1, /E = -(0.123 ± 0.007)B + 2.543 ± 0.085. This relation is valid when the system is on its normal and lower flaring branches. Based on theoretical models, we suggest that similar relations should also exist for other LMXBs.

The Ionization Structure of Planetary Nebulae

Ground-based and satellite spectrophotometric observations of emission-line intensities over the spectral range 1400–7200 A have been made in 5 or more positions in a total of 9 planetary nebulae.

The ionization structure of planetary nebulae. IX - NGC 1535

The ionization structure of planetary nebula NGC 1535 was investigated using spectrophotometric observations of emission-line intensities over the spectral range 1400-7200 A, which were carried out in five positions in this nebula. The results obtained on the ionic abundances of He, O, N, Ne, C, and Ar in NGC 1535 suggest that it is a planetary nebula that formed initially in a somewhat metal-poor region and has undergone little or no enhancement of its original abundances by mixing with nuclear-processed material. 19 refs.