Engineering topics

Takalo, L. O.

Publications and source records attributed to Takalo, L. O..

6 records

NASA NTRS1988

Phase-resolved IUE observations of AM Herculis system E1405-451

The first phase-resolved IUE observations of the AM Herculis system E1405-451 is reported. The spectra show bright emission lines from N V, C IV, and He II, whose centroids vary drastically during the 101.5 minute period. The radial velocities measured from the line centroids show a sinusoidal variation with a semiamplitude of 300 km/s. An explanation for the observed emission line velocities is considered using a model for the system having inclination i = 60 deg and magnetic colatitude Delta = 20 deg.

Takalo, L. O.↗

NASA NTRS1988

Spectroscopic observations of X-ray selected late type stars

A spectroscopic survey of nine X-ray selected late type stars was conducted. These stars are serendipitously discovered EINSTEIN X-ray sources, selected from two large x-ray surveys: the Columbia Astrophysical Laboratory survey (five stars) and the CFA Medium Sensitivity survey (four stars). Four of the Columbia survey stars were found to be short period binaries. The fifth was found to be an active single G dwarf. None of the Medium Sensitivity survey stars were found to be either binaries or active stars. Activity was measured by comparing the H-alpha and the CaII infrared triplet (8498, 8542) lines in these stars to the lines in inactive stars of similar spectral type. A correlation was found between the excess H-alpha lime emission and V sin(i) and between the excess H-alpha line emission and X-ray luminosity. No correlation was found between the infrared line emission and any other measured quantity.

Takalo, L. O.↗

NASA NTRS1986

X-ray-selected M dwarfs and the diffuse X-ray background

A systematic optical identification program was carried out for serendipitous X-ray sources discovered by the Einstein Observatory. A total of 104 were detected above the threshold flux of 3 x 10 to the -13th ergs/sq cm per sec in the 114 sq deg survey region; 11 of these 104 sources are dM stars. Including X-ray-selected M dwarfs from the LMC survey, the Medium Sensitivity Survey, and the Einstein Deep Survey, a dwarf M star composite X-ray spectrum was constructed; the best-fit thermal model yields kT = 1.3 + or - 0.3 keV, consistent with typical active star spectra. An M dwarf X-ray luminosity function was also constructed and it is concluded that the integrated contribution to the diffuse soft (0.28-1.0 keV) X-ray background from such stars is less than 10 percent, a factor of more than about 2 lower than previous estimates. This result is consistent with a limit on the dwarf M star contribution derived from a spectral decomposition of the observed X-ray background spectrum.

Caillault, J.-P.↗

NASA NTRS1985

E2000 + 223 - A newly discovered old nova?

The X-ray source, E2000 + 223, serendipitously discovered by the Einstein Observatory, has been tentatively identified with an old nova shell. Spectroscopic observations of the diffuse optical counterpart show a heavily reddened continuum with bright forbidden S II emission lines at double lambda 6716, 6732. Radio observations at the VLA show a weak (about 1.2 mJy) extended radio source, with a nonthermal spectrum, concident with the optical emission. The observations can be best explained by assuming the object is an old nova which erupted sometime in the eighteenth or nineteenth century, similar to GK Per (Nova 1901) but at a distance of 1.4 kpc.

Takalo, L. O.↗

NASA NTRS1985

The peculiar X-ray and radio star AS431

Einstein observations are reported which reveal that the highly reddened emission-line star AS431 has a highly absorbed X-ray spectrum and a relatively strong intrinsic flux of 5 x 10 to the -12th erg/sq cm/s or more. Observations at 20 cm and 6 cm with the National Radio Astronomy Observatory Very Large Array are also reported which show that AS431 is also a moderately strong radio source (about 35 mJy). These data, together with optical and infrared observations, suggest a model in which both the radio and X-ray emissions arise in a chaotic stellar wind emerging from a single luminous Wolf-Rayet star.

Caillault, J.-P.↗

NASA NTRS1984

E2003 + 225 - A 3h 42m AM Herculis type binary system

The bright soft X-ray source E2003 + 225, originally discovered by the HEAO 1 low-energy detectors, has been found to be a new AM Herculis type binary. The optical counterpart shows a rich emission spectrum of He II, He I, and H as well as circular and linear polarization. Larger polarization in the near-infrared than in the ultraviolet argues for its origin as high harmonic cyclotron emission. Optical photometry, polarimetry, spectroscopy, and the X-ray light curves are all consistent with an orbital period of 222.51 m, the longest period known for AM Herculis systems, and only the second on the long side of the 2-3 hour cataclysmic variable period gap.

Takalo, L. O.↗