Engineering topics

Fekel, F. C., Jr.

Publications and source records attributed to Fekel, F. C., Jr..

10 records

NASA NTRS1985

AY Ceti - A flaring, spotted star with a hot companion

AY Ceti is a late-type single-line spectroscopic binary, a bright X-ray source (L/x/ equal to about 1.5 x 10 to the 31st ergs/s), and a spotted star, as evidenced by its prominent photometric wave. In this paper, observations made with the IUE satellite and the VLA radio interferometer are reported. The 1200-2000 A UV spectrum of AY Cet shows a hot stellar continuum and a very broad Ly-alpha absorption line from a previously unobserved white dwarf secondary. The UV spectrum can be matched to the energy distribution of a (T/eff/ = 18,000 K, log g = 8) model atmosphere. Superposed on this hot continuum are high-excitation emission lines typical of chromospheres and transition regions of active late-type stars, e.g., the spotted RS CVn binaries. It is concluded that the bright lines and soft X-ray emission of AY Cet arise from the cool primary star, rather than from mass transfer and accretion onto the secondary as has recently been proposed for the similar system 56 Peg. Two strong radio flares on AY Cet were observed. The second was rapidly variable and left-hand circularly polarized at levels up to pi(c) = 86 + or - 5 percent at 20 cm wavelength. The most likely emission mechanism is an electron-cyclotron maser.

Simon, T.↗

NASA NTRS1983

Spectroscopy of V711 Tauri (= HR 1099) - Fundamental properties and evidence for starspots

New orbital elements have been determined for the bright RS CVn-type system V711 Tau. The spectroscopic period has been refined to 2.83774 d + or - 0.00001 d. The eccentricity is determined to be 0.014 + or - 0.009, and the inclination of the system is 33 deg + or - 2 deg. The masses, radii, and equatorial rotational velocities for each component are stated.Evolutionary models suggest that mass transfer may begin in 70 to 80 million years. High SNR Reticon observations at red wavelengths show substantial differences in rotational velocity and line strength between the two components, as well as asymmetries in all absorption lines of the more massive, active, cooler star. These asymmetries are correlated with photometric variations and move across the line profiles with time. They are the result of starspot regions rotating in and out of view.

Fekel, F. C., Jr.↗

NASA NTRS1983

HR 7578 - A K dwarf double-lined spectroscopic binary with peculiar abundances

The number of double-lined K and M dwarf binaries which is currently known is quite small, only a dozen or less of each type. The HR 7578 system was classified as dK5 on the Mount Wilson system and as K2 V on the MK ystem. A summary of radial-velocity measurements including the observatory and weight of each observation is given in a table. The star with the stronger lines has been called component A. The final orbital element solution with all observations appropriately weighted was computed with a differential corrections computer program described by Barker et al. (1967). The program had been modified for the double-lined case. Of particular interest are the very large eccentricity of the system and the large minimum masses for each component. These large minimum masses suggest that eclipses may be detectable despite the relatively long period and small radii of the stars.

Fekel, F. C., Jr.↗

NASA NTRS1983

Revised orbits for 105 Herculis and Pi Cephei A and a model for the Pi Cephei system

New orbital elements for the giant primary components of 105 Herculis and Pi Cephei A are derived using radial velocities from Dominion Astrophysical Observatory coude plates. These data are combined with those of Harper (1925) in order to estimate the velocity amplitude of Pi Cephei A in the visual orbit of this triple system. Two models of this system are developed. In the first model, the unseen spectroscopic secondary component is a single main-sequence star, although this seems unlikely, while in the alternative model the unseen secondary component is itself double.

Scarfe, C. D.↗

NASA NTRS1983

Observations of spectroscopic binaries at ultraviolet and red wavelengths

The use of IUE-satellite and ground-based-Reticon observations for the study of spectroscopic binaries is examined, and sample data from the Reticon are presented. IUE radial-velocity determinations with uncertainties as low as 2-5 km/sec should be possible for binaries with early-type secondary components, using UV spectral lines where contamination by the later-type primary is reduced. The Reticon solid-state photodiode-array detector has been used at the coudefocus of the 2.7-m telescope at McDonald Observatory for observation of complex multiple systems in the 400-950-nm range with a quantum efficiency of 40-80 percent and resolution of 20-30 pm at 440 pm/mm. The fundamental parameters of 15 systems observed with this apparatus are listed in a table, and two sample spectra are shown.

Fekel, F. C., Jr.↗

NASA NTRS1982

Secondaries of eclipsing binaries. IV - The triple system Lambda Tauri

High signal-to-noise ratio Reticon observations of Lambda Tauri have been obtained along with high-quality orbital elements for both the primary and secondary of the eclipsing system. The velocity curve of the secondary is determined for the first time. The findings include: K(1) = 56.9 + or - 0.6 km/s, K(2 = 215.6 + or - 0.7 km/s, m(1) = 7.18 + or - 0.09 solar masses, and m(2) = 1.89 + or - 0.04 solar masses. The 33-day periodicity in the residuals is confirmed and is present in the secondary velocities as well as those of the primary, and can unambiguously be ascribed to orbital motion about a third body. The K and f(m) for the 33-day orbit are 10.1 + or - 0.7 km/s and 0.0034 + or - 0.0008 solar masses. The photometry shows that the orbits are coplanar to within seven degrees. The mass of the third body is 0.7 + or - 0.2 solar masses; it is most probably a K dwarf.

Fekel, F. C., Jr.↗

NASA NTRS1982

HD 185151 - A new active-chromosphere binary

Spectroscopic and photometric observations of the K2III star HD 185151 are reported which establish it as a chromospherically active binary with an orbital period of 40.1 days. Reticon observation of the hydrogen alpha region shows a partially filled profile, owing presumably to chromospheric emission, as well as a blue emission wing extending out about 100 km/s. The light curve is effectively a double sine curve, and can be modeled by two starspots separated by almost exactly 180 deg in longitude.

Bopp, B. W.↗

NASA NTRS1981

HD 202908 - A young, solar-type triple system

HD 202908 is a solar-type, spectroscopic-visual triple system. High-dispersion spectroscopic observations show that the primary visual component is a double-lined spectroscopic binary with a period of 3.966 days and a mass ratio of 1.0. Velocity changes due to motion in the long-period, 76-year orbit are now perceptible. Over the next 5 years, these changes may amount to 30 km/s for the single star. Continued spectroscopic and visual observations through nodal and periastron passage of the highly eccentric visual orbit, which will occur nearly simultaneously about 1985.5, will permit the accurate determination of the masses and luminosities of the three components. Contrary to expectation, the short-period and long-period orbits are not coplanar. The large lithium abundances, strength of the Ca II emission lines, and rotational velocities all suggest that this multiple system has an age similar to that of the Hyades cluster.

Fekel, F. C., Jr.↗

NASA NTRS1981

The properties of close multiple stars

A reexamination of the properties of close multiple systems is conducted, taking into account recent numerical, analytical, and observational results. The orbital elements of 43 spectroscopic multiple systems are presented in a table. Tables with photometry data of the systems and data describing their properties are also provided. Attention is given to period ratios, mass ratios, orbital coplanarity, stability, lithium abundances and age estimates, and prospects of future observations. Numerical studies indicate that fragmentation produces binary components with mass ratios usually close to 1.0, while fission usually produces mass ratios in the range 0.1-0.5. Using analytical stability criteria, all 27 close multiple systems considered are stable if they are corotating. If they are counter-rotating, four systems are possibly unstable. However, other factors suggest that even these four are probably stable. The solar-type close multiple systems ranged in age from 100 million years to 2,000 million years.

Fekel, F. C., Jr.↗

NASA NTRS1981

The close multiple system mu Orionis - Masses and the mass-luminosity relation

The observations made of the secondary component B of the close visual binary mu Ori are described. The Reticon observations made at red wavelengths showed the secondary to be a double-lined spectroscopic binary with a period of 4.78 days and nearly identical components having minimum masses of 1.1 solar mass each. Previous estimates are corroborated by the large spectroscopic mass ratio of B to A and B. The discovery that B is a pair of late-F dwarfs solves the apparent mass-luminosity relation discrepancy noted in previous studies.

Fekel, F. C., Jr.↗