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Eaton, J. A.

Publications and source records attributed to Eaton, J. A..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The unusual carbon star HD 59643 - Alternative models

A binary model for the carbon star HD 59643 is discussed in which the secondary spectrum is formed in an accretion disk. If this hot, ultraviolet-emitting disk radiates like a 20,000 K black-body, it must be 0.03 solar radii or less across at minimum emission. Large widths of C IV multiplet UV1 on high-resolution spectra indicate its formation in the inner parts of a disk. The semiforbidden C III and Si III lines, however, are much narrower and could be formed in the outer parts of a disk or in the carbon star's chromosphere. The electron density in the region of formation of C III is about 10 to the 10th/cu cm.

Johnson, H. R.↗
NASA NTRS1985

Stratification of the extended atmosphere of the Wolf-Rayet component of V444 Cygni

Ultraviolet spectra covering both eclipses of V444 Cygni have been obtained. Longward of 1570 angstroms, the continuum brightness showed essentially the same variation seen in the optical (at 4244 angstroms). Striking atmospheric eclipses of up to 0.7 mag in depth were detected, however, in individual strong lines as well as over large ranges of the continuum shortward of 1500 angstroms. IUE data are used to estimate the degree of interstellar extinction and terminal expansion velocity of the system and to study the phase dependence of the continuum and line absorptions.

Eaton, J. A.↗
NASA NTRS1985

Analysis of ultraviolet atmospheric eclipses in the Wolf-Rayet binary CV Serpentis

While no eclipses deeper than 0.04 mag are noted in the present UV spectra, covering one-half of an orbital cycle of CV Ser, in the electron scattering continuum at 2400-3200 A or in fine error sensor observations, marked atmospheric eclipses of up to 0.5 mag depth are observed in individual strong lines and over large ranges of the continuum at shorter wavelengths. The flux above the continuum in the C II 1247 A, Si IV 1400 A, and Si IV 1723 lines showed similar phase dependence with emission weakening, as well as with the emission's going into absorption as phase progresses from superior to inferior conjunction of the WC star (primary eclipse). These observations show effects very similar to the behavior of WN stars in the UV.

Eaton, J. A.↗
NASA NTRS1985

Ultraviolet spectra and chromospheres of R stars

Long-wavelength IUE spectra of 13 normal R stars and two hydrogen-deficient R0 supergiants were obtained. Early R stars are noted to have line spectra and levels of flux in the ultraviolet characteristic of G5-K2 III stars, whereas late R stars were observed to have colors and line spectra similar to late K and M stars, but with greatly enhanced strength of low-lying multiplets of neutral metals. Hydrogen-deficient carbon stars show readily apparent differences from the normal early R stars, reflecting their luminosity and somewhat higher temperatures. The lines of neutral metals in these stars are weakened, while those of ionized metals are strengthened.

Eaton, J. A.↗
NASA NTRS1985

Ultraviolet spectra of N, R, and S stars

Ultraviolet IUE spectra of N, R, and S stars are displayed and discussed. Carbon stars of type N have IUE spectra similar to M stars except that the Mg II lines are much weaker and low-excitation lines from neutral metals are stronger. Spectra of early R stars (R0-R3) closely resemble those of late G or early K in both lines and continuum with no significant emission lines. Late R stars (R5-R8) show spectra like late K or early M stars except that lines from low levels of excitation are stronger. Ultraviolet spectra of S stars show a wide variation in the strength of Mg II lines.

Johnson, H. R.↗
NASA NTRS1984

Line identifications in the ultraviolet (2590-3230 A) spectrum of the hydrogen-deficient carbon star HD 182040

Identifications for absorption features detected in the ultraviolet spectrum of the hydrogen-deficient supergiant carbon star HD 182040 observed at high resolution with the IUE satellite are presented. The spectrum in this range is filled with blended lines of the iron-peak elements, with Fe I and Cr II dominating the spectrum. Spectra definitely and probably detected are given, as well as those searched for and not detected. In the investigated range, the spectrum resembles that of a middle-G supergiant. The absorption-line spectrum is similar to the spectra of the sun and other late-type stars, but neutral metal lines are weaker than in K and M giants. The level of ionization is significantly higher than in the sun, Zeta Cap, and Epsilon Gem.

Johnson, H. R.↗
NASA NTRS1984

Ultraviolet photometry from the Orbiting Astronomical Observatory. XXXIX - The structure of the eclipsing Wolf-Rayet binary V444 Cygni as derived from light curves between 2460 A and 3. 5 microns

The WN5 component of V444 Cyg is characterized on the basis of light curves constructed using 1971 OAO observations at 425, 332, 298, and 246 nm and the broadband data at 2.2 and 3.5 microns of Hartmann (1978). Data and calculation results are presented in tables and graphs and discussed. Parameters estimated include core radius 2.9 solar radii, surface temperature 90,000 K, surface electron density 9 x 10 to the 12th/cu cm, surface outflow velocity 400 km/s, and terminal velocity (at about 10 solar radii) 2500 km/s, suggesting that the flow is He. These results are found to agree with the model of Wolf-Rayet atmospheres proposed by Beals (1929, 1944).

Cherepashchuk, A. M.↗
NASA NTRS1983

The photometric period of 39 AY Ceti

A photometric period of 77.65 days is derived for 39 AY Ceti through a comparison of photoelectric photometry obtained in 1971 and 1972 with that obtained in the periods 1980-1981 and 1981-1982. JD 2444636.0 is an epoch of minimum light, and the full amplitude is found to have been as large as 0.18 mag in V. It is noted that the mean light level has dropped by almost 0.2 mag over the last decade. The present binary star is also noteworthy in light of the recently discovered white dwarf secondary component, and because radial velocity measurements indicate an eccentricity as large as 0.1 and an orbital period which, at 57.1 days, differs considerably from the photometric period presented.

Hopkins, J. L.↗
NASA NTRS1983

Five years of photometry of Sigma Geminorum

Thirteen observatories have collaborated in obtaining five years of photoelectric photometry for the bright, K1 III RS CVn binary Sigma Geminorum. Except for one year, the light curve has exhibited two minima which are separated by approximately half a cycle. At the 1977.2 epoch of discovery one minimum was shallower, but as of 1982.2 they have become comparable in depth. During the 1979-80 season, the light curve changed shape rapidly, with the shallower minimum becoming as deep as the other within a period of no more than 80 days. The overall brightness range during the five years in V has been 4.13-4.29 mag, and it is found that the times of both minima can be fit with a photometric period of 19.423 days.

Fried, R. E.↗
NASA NTRS1983

Chromospheric emission of W Ursae Majoris-type stars and its relation to the structure of their common envelopes

Short-wavelength IUE spectra of 14 W UMa binary systems were analyzed. All but the A2 V system GK Cep and possibly the A8 system AG Vir show chromospheric and transition-region emission lines. This property extends to at least as early as A8-9. The luminosity in transition-region emission lines is roughly proportional to bolometric luminosity. The strength of transition-region emission relative to chromospheric emission is roughly independent of spectral type and is at least as great as for other stars with enhanced surface activity. The enhanced chromospheric activity and light curve peculiarities of the hotter systems seem to disagree with the predictions of the contract-discontinuity models for contract binary structure.

Eaton, J. A.↗
NASA NTRS1983

ANS spectrophotometry - Delta Pictoris as an upper-main-sequence algol system

The early-type eclipsing binary Delta Pictoris has been studied with 260 observations in each of five UV bands. These are the most accurate observations to date, and no strong evidence for light-curve complications produced by circumstellar material has been found. Combined light curves from four epochs separated by intervals of six months do not show any strong dips or shoulders as seen in earlier investigations. The strength of th C IV wavelength 1550 line is independent of phase to better than 0.01 m. The root-mean-square scatterer shown by the light curves ranges from 0.006 m to 0.014 and may be evidence that either or both of the components are intrinsically variable. The integrated colors of the system are consistent with a B1 V spectral type and very little interstellar extinction. A detached solution of the light curves for a Roche model well with the spectroscopic mass ratio, but a semidetached solution cannot be ruled out.

Eaton, J. A.↗
NASA NTRS1983

Five years of photometry of Lambda Andromedae

Photoelectric photometry of the bright variable RS CVn-type binary Lambda And obtained in 1977-78 and 1980-81 is presented and used, together with earlier photometry, to derive the photometric period and discuss the changing shape of the light curve. The best ephemeris for times of minimum light is 2443829.2 + 53.95 d E. Because times of minimum and maximum extending back to those of Calder in 1933-37 can be phased together properly, the principal dark region must have maintained its identity for almost 50 yr. Over the last five years the brightness range has been between 3.70 and 4.05 m. During 1980-81 shallow secondary minima developed at phases where maxima occurred in previous years. Lambda And remains the only well-established case of nonsynchronous rotation among the known RS CVn variables.

Boyd, R. W.↗
NASA NTRS1983

Three years of photometry of IM Pegasi = HR 8703

Differential photometry of this K1 IV-III p RS CVn-type binary in 1978-79, 1979-80, and 1980-81 at eight different observatories shows that the variability, discovered originally by Herbst, is periodic. The mean of three different determinations of the photometric period was 24(d).39 + or 0(d).03, about 1 percent shorter than the orbital period of 24(d).649 determined spectroscopically by Harper. The total range observed during these three years was for V from 5(m).60 to 5(m).85. The light curve was nearly sinusoidal but always noticieably asymmetric, with the sense reversing sometime between 1979-80 and 1980-81.

Eaton, J. A.↗
NASA NTRS1982

Four years of photometry of DK Draconis = HR 4665

Differential BV photometry of the K0 III + K0 III long-period RS CVn-type binary DK Dra = HR 4665 in 1977, 1978, 1979, and 1980 at eight different observatories is presented. A least squares fit to times of maximum and minimum light yields the ephemeris JD = 2,443,219.5 + 63.75 d E for times of minimum. This photometric period is 1% shorter than the spectroscopically determined orbital period 64.44 d. The light curve was symmetrical and roughly sinusoidal in 1979 and 1980 but was asymmetrical in 1977 and 1978, with a faster rise to maximum. During these four years DK Dra varied between V = 6.07 and 6.35 m.

Eaton, J. A.↗
NASA NTRS1982

HR 7275 - A new variable star

Three years of photometry in V and B of the UBV system are presented to confirm the suspicion of Herbst (1973) that HR 7275 is a variable star. The photometry is used to derive the photometric period, which proves to be about 3% shorter than the spectroscopically determined optical period of 28.59 d. Total variation observed during the three years was 0.22 m in the V, and the light curve was always asymmetrical.

Fried, R. E.↗
NASA NTRS1982

ANS spectrophotometry - The bright X-ray binaries Hercules X-1 /HZ Herculis/ and Cygnus X-1 /HDE 226868/

Complete ultraviolet light curves for HZ Her immediately after a well-defined X-ray turn-on in 1975 are obtained. The features of the curve are found to correspond well with features seen in the optical. The absolute level of emission at maximum light at 1550 A is in good agreement with the calculations of the X-ray reflection effect of Milgrom and Salpeter (1975). It is found that at 1550 A approximately 20% of the light at maximum comes from the accretion disk. Similar observations of Cyg X-1 make it possible to determine the degree of reddening, equivalent to E(B-V) = 0.95 + or - 0.07, from the strength of the 2200 A interstellar absorption feature. The distance inferred from this amount of reddening requires that the optical star be luminous and, therefore, massive. Observations obtained during the May 1975 X-ray transition show ultraviolet excess when compared with the data obtained six months later.

Wu, C.-C.↗
NASA NTRS1981

54 Cam - A new variable star

Differential photometry of the RS CVn-type binary 54 Cam is presented, which shows that the light was variable with a period of 10.163 + or - 0.009 d, and with an amplitude increase from 0.03 to 0.06 m between 1979 and 1980. The photometric period of 10.163 d is 9% shorter than the orbital period of 11.0764 d, and is suggested as an explanation for the radio emission from 54 Cam due to a process of connection, disruption, and reconnection of magnetic field lines.

Hall, D. S.↗