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Moffett, T. J.

Publications and source records attributed to Moffett, T. J..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

A survey of chromospherically active stars

Photometric and/or spectroscopic observations have been obtained of 52 late-type stars which are suspected or known to be chromospherically active. Although not all types of observations were obtained for each star, these observations include all-sky BVRI Johnson photometry, ultraviolet spectrograms, low-dispersion blue-wavelength spectrograms, and high-dispersion red-wavelength spectrograms. From the spectroscopic observations v sin i's, radial velocities, and the appearance of the Ca II H and K emission lines have been determined as well as the H-alpha line. The photometric observations indicate that chromospherically active stars have V - R and V - I color excesses. Such excesses will affect the surface fluxes determined with the surface brightness-color relationship. On the other hand all-sky BVRI photometry appears to be an excellent way to identify chromospherically active stars. A small group of moderately rapidly rotating, possibly single G8-K2 giants has been found. These stars have very modest chromospheric activity and so are not FK comae stars. A number of other unusual chromospherically active stars are identified.

Fekel, F. C.↗
NASA NTRS1981

The visual surface brightness relation and the absolute magnitudes of RR Lyrae stars. II - RR Lyrae and X Arietis

The theoretical surface brightness relation for RR Lyrae stars has been combined with new VR photometry to determine distances, radii, and absolute magnitudes for X Arietis and RR Lyrae. For X Arietis, a pulsational variation in the radius from 5.06 solar radii to 5.96 solar radii, a distance of 495 + or - 50 pc, and an intensity mean absolute magnitude of +0.59 + or - 0.25 is obtained. The corresponding quantities for RR Lyrae are 4.81-5.67 solar radii, 263 + or - 39 pc, and an intensity mean absolute magnitude of +0.61 + or - 0.35. The larger errors quoted for RR Lyrae are due to uncertainties arising from the Blazhko effect. Results are discussed in the context of the dependence of RR Lyrae absolute magnitudes on metal abundance.

Manduca, A.↗
NASA NTRS1981

On the mass of the Cepheid X Cygni

Using a new non-Lagrangian hydrodynamic radiation transport code, models of the Cepheid X Cygni have been calculated and compared with new observations. Adopting an effective temperature of 5300 K, the luminosity was varied for stellar masses of 6, 8, and 9 solar masses in order to obtain a period of 16.4d. The results indicate that in order to find reasonable agreement between the light curves as calculated and observed, the mass used in the models must be nearly the evolutionary mass, not some 60% less as found in earlier work for Cepheids with periods from 7d to 10d. In addition, the new observations support the physical reality of the so-called 'artificial viscosity dip'.

Davis, C. G.↗
NASA NTRS1980

Observational studies of Cepheids. I - BVRI photometry of bright Cepheids

Over 1,000 differentially determined photoelectric BVRI observations and the resulting light curves are presented for 24 bright Cepheids accessible from Northern Hemisphere observatories. The internal precision of these data is shown to be better than + or - 0.01 mag, and the accuracy of transformation to the Johnson BVRI system is nearly as good.

Moffett, T. J.↗
NASA NTRS1980

Photoelectric observations of lunar occultations

Photoelectric observations of 13 lunar occultation disappearances during a March 1979 Hyades passage are reported. Three double stars (SAO 93925 = Fin 342 = 70 Tau, SAO 93961 = ADS 3248, and SAO 95419 = Kui 24) and one possible double (SAO 93950 = 75 Tau) were detected. A brief description is given of the Purdue University pulse-counting photometer as modified for occultation observations.

Fekel, F. C.↗
NASA NTRS1979

A UBVRI equatorial extinction star network

An equatorial-extinction star network, based on 1503 observations of 37 stars, is presented. These results together with those of Crawford et al. (1971) provide a well-determined UBVRI extinction network. Identification charts are included.

Barnes, T. G., III↗
NASA NTRS1979

Equatorial UBVRI photoelectric sequences

From 1335 BVRI observations of 189 stars in selected areas 92-115, Landolt's (1973) network of faint UBV standards has been extended to R I. Of these stars, 173 have four or more observations. The (U-B) values of Landolt are adopted, and a well-observed equatorial faint-star network is presented on the Johnson UBVRI photometric system.

Moffett, T. J.↗
NASA NTRS1979

Secondary standards for BVRI photometry

A thorough test of Fernie's instrumentation system for matching the Johnson BVRI photometric system has been made. From 1,526 observations of 186 stars in the Arizona-Tonantzintla Catalogue, there were found excellent transformations, except for a slight curvature in the (B-V) transformation, which is easily removed, and a difficulty in (R-I) for highly reddened stars. Photometric values and their uncertainties are given for all the stars, and these are of sufficient quality to serve as secondary standards in BVRI for small- to moderate-size telescopes (1-m).

Moffett, T. J.↗
NASA NTRS1978

Coordinated photometric and spectroscopic observations of strong extragalactic 90 GHz sources

Nearly simultaneous radio and infrared-optical observations were obtained for several extragalactic radio sources which are strong at 90 GHz. The spectral-flux distributions are generally peaked or flat over the radio portion of the spectrum with a steeper, power-law behavior at infrared-optical frequencies. For all sources, the radio and infrared-optical portions of the spectral-flux distributions can be smoothly joined by physically sensible interpolations over the spectral gap, although spectral breaks are required. For many of the sources, this is consistent with a common (synchrotron) origin of the radio, millimeter, and infrared-optical radiation. However, proof, in terms of correlated temporal variations and polarization properties, is still generally lacking.

Odell, S. L.↗
NASA NTRS1978

Further observations of nonperiodic optical flickering in HZ Herculis

High-speed photometric observations of the HZ Her/Her X-1 system show that nonperiodic optical flickering is present during both the ON and OFF portions of the 35-day cycle. The optical flickering is broad band and not confined to emission lines. There is a weak correlation between the amplitude of the flickering and orbital phase but efforts to identify the source of the flickering were unsuccessful.

Vanden Bout, P. A.↗
NASA NTRS1978

A search for centimetric wavelength emission from UV Ceti stars

Simultaneous radio and optical observations were obtained on three UV Cet flare stars: YZ CMi, AD Leo, and Wolf 424. The total simultaneous monitoring time was 33.9 hours during which time 41 optical flares were detected. Two enhancements were detected at 1420 MHz in close temporal association with optical flares, but are of uncertain validity. The results presented indicate that 1420 MHz emission during a typical stellar flare is less than 0.10 Jy.

Moffett, T. J.↗
NASA NTRS1976

Coordinated X-ray optical and radio observations of YZ Canis Minoris

Coordinated X ray, optical, and radio observations of the flare star YZ CMi are reported. Twenty-two minor optical flares and twelve radio events were recorded. No major optical flares, greater than 3 magnitudes, were observed. Although no flare related X ray emission was observed, the measured upper limits in this band enable meaningful comparisons with published flare star models. Three of the five models predicting the relative X ray to optical or radio flare luminosities are in serious disagreement with the observations. For the largest optical flare with coincident X ray coverage, the 3 sigma upper limit on X ray emission in the 0.15 to 0.8 keV band is 8.7 x 10 to the 28th power erg/s, corresponding to a ratio of X ray to B-band luminosity of less than 0.3. Based on the present results, the contribution of the flares UV Ceti flare stars to the galactic component of the diffuse soft X ray background is less than 0.2 percent.

Karpen, J. T.↗
NASA NTRS1976

Comments on the optical counterpart of the X-ray source 3U 0352 + 30

Spectral and photometric observations of ADS 2859 B, the faint companion to X Per, show it to be a normal M giant rather than a T Tauri star as previously reported in the literature. Consequently, there is no substantive reason to associate it with the X-ray source 3U 0352 + 30. A search for rapid light variations of X Per itself proved negative.

Moffett, T. J.↗
NASA NTRS1976

Simultaneous radio and optical observations of UV Ceti-type flare stars

The UV Ceti-type stars, YZ Canis Minoris, AD Leonis, and Wolf 424 AB, were monitored for 57.8 hours from January 15 to February 22, 1974, using the 1000-foot (305-m) radio telescope at Arecibo, Puerto Rico, and the 91-cm or 76-cm reflector at McDonald Observatory. Radio observations were made at frequencies of 430, 318, and 196 MHz, and optical monitoring was done in the Johnson U or B band, the Stromgren u band, or white light. During the period of simultaneous observations, 62 optical flares were detected. A total of 13 RF flares were independently identified, of which 10 reached maximum flux within 10 min of the peak time of an optical flare. Using times of optical-flare events as reference data, an additional 15 cases of radio enhancements associated with optical flares are identified. The most probable delay interval between the optical-flare maximum and 318-MHz radio peak was found to be 0 to 5 min, with the optical flare occurring first. Aside from this statistical delay of peak occurrence and a general tendency for radio and optical flares to be associated, no systematic correlations of optical and radio amplitudes or morphology were found. The possible consequences of the radio emission's being due to a coherent process are discussed.

Spangler, S. R.↗
NASA NTRS1975

A search for X-rays from UV Ceti flare stars

A search of MIT/OSO-7 data was made for evidence of X-ray emission from flares of UV Ceti flare stars. Observations from McDonald Observatory were used to identify the times of optical flares. The only instance of coincident coverage occurred on 1974 January 21 UT at 03:43:26 GMT for delta m(u)=0.86 flare of YZ CMi. No radio coverage of this particular event was obtained. Upper limits (3 sigma) of 0.8, 1.0, and 0.7 photons/sq cm-sec on the observed X-ray flux were set for the energy ranges greater than or approximately equal to 15, greater than or approximately equal to 3, and 1-10 keV, respectively.

Crannell, C. J.↗
NASA NTRS1975

A search for X rays from UV Ceti flare stars

A search of the MIT/OSO-7 data has been made for evidence of X-ray emission from flares of UV Ceti flare stars. Observations from McDonald Observatory have been used to identify the times of optical flares. The only instance of coincident coverage occurred on 1974, January 21, UT at 03:43:26 GMT for a flare of YZ CMi with a u magnitude increment of 0.86. No radio coverage of this particular event was obtained. Upper limits (3 sigma) of 0.8, 1.0, and 0.7 photons/sq cm sec on the observed X-ray flux have been set for the energy ranges greater than 15, greater than 3, and 1-10 keV, respectively.

Crannell, C. J.↗