Engineering topics

Remillard, R. A.

Publications and source records attributed to Remillard, R. A..

35 records · Page 2

NASA NTRS1990

1H 0709-360 - A cataclysmic variable with an orbital period inside the 'period gap'

The discovery is reported of the second cataclysmic variable with a binary period lying well inside the nominal 2-3 hr period gap. The object, 1H 0709-360, is an X-ray source which has been identified on the basis of positional data from the instruments of the HEAO 1 survey. The X-ray source was also detected by the Uhuru and Ariel 5 surveys. Multicolor photometry has revealed eclipsing behavior at an orbital period of 2.444 hr. Radial velocity measurements show modulations at the same period, with an offset between the spectroscopic and photometric conjunctions. Both the eclipse profile and a clear rotational disturbance in the radial velocities of emission lines during eclipse provide unambiguous evidence for the existence of an accretion disk. Thus the object cannot be an AM Herculis variable, a conclusion supported by the absence of circular polarization. Instead, the evidence suggests that the object could be a DQ Herculis magnetic variable that is close to synchronism. The evolutionary implications of this rare object are discussed.

Tuohy, I. R.↗

NASA NTRS1990

LB 1800 - A bright eclipsing cataclysmic variable and a transient X-ray source

The star LB 1800 has been discovered to be a 13th mag high-excitation cataclysmic variable exhibiting novalike characteristics and partial eclipses in its light curve. It has subsequently been identified as the optical counterpart of the transient hard X-ray source 4U 0608-49 following analysis of HEAO 1 data. Both the radial velocity and photometric variations have a period of 5.56 hr, while the K-velocity of the relatively uncomplicated radial velocity curves is 134 + or - 9 km/s, leading to a mass function of 0.058 + or - 0.003 solar mass. The dynamical and eclipse solutions point to an orbital inclination of 87 deg + or - 3 deg and a mass ratio of 0.46 + or - 0.04 for the empirical secondary mass 0.55 solar mass. The implied white dwarf mass is therefore quite high at about 1.2 solar mass. The disk size, from timings of first and last contact, was estimated to be very close to that of the secondary star. Phase-dependent, double-peak emission lines are sometimes observed. It is argued that the orbital variations in the relative strengths of the red and blue peaks arise from changing hot-spot visibility.

Buckley, D. A. H.↗

NASA NTRS1990

H1722 + 119 - A highly polarized X-ray-selected BL Lacertae object

A 15th-mag, X-ray-selected BL Lac object, H1722 + 119, has been discovered to possess a steep X-ray spectrum with power-law energy index near 1.3; radio measurements indicate a variable, compact source with 1.4-4.9 GHz power-law energy index of 0.04. The optical-IR polarization of H1722 + 119 reaches a maximum of 17 percent, which is much higher than other X-ray-selected BL Lac objects. The degree of polarization is found to be wavelength-dependent, decreasing monotonically toward the IR.

Brissenden, R. J. V.↗

NASA NTRS1990

The X-ray Timing Explorer

The capabilities of the X-ray Timing Explorer (XTE) are described with particular attention paid to current scientific problems it will address from galactic neutron star systems to active galactic nuclei. It features a low-background continuous 2-200 keV response with large apertures (a 0.63 sq m proportional counter array and a 0.16 sq m dual rocking NaI/CsI scintillation array). Rapid response (in hours) to temporal phenomena, e.g. transients, is obtained by virtue of a scanning all-sky monitor and rapid maneuverability. XTE will carry out detailed energy-resolved studies of phenomena close to neutron stars (e.g. QPO's) because of its submillisecond timing, its high telemetry rates, and the high throughput of its data system.

Bradt, H. V.↗

NASA NTRS1989

Two X-ray-selected BL Lacertae objects observed with the HEAO 1 scanning modulation collimator

Two 16th magnitude BL Lac objects, H1101 - 232 and H1426 + 428, have been discovered. Each is a persistent and relatively bright X-ray source. A 2.7 percent linear polarization is measured in the optical emission or H101 - 232. The X-ray identification of H1426 + 428 is confirmed in an Exosat observation. The X-ray spectrum is well-modeled by a power law with an energy index of 1.19. Both BL Lac objects exhibit high f(x)/f(opt) ratios and they show a distinct resemblance to other X-ray selected BL Lac objects. The host galaxies are about 18th mag with angular diameters of about 20 arcsec and each may be the dominant member of a cluster of galaxies. Additional wide-slit spectroscopy reveals faint absorption features with redshifts of 0.129 for H1426 + 428 and 0.186 for H1101 - 232. The implied X-ray and optical luminosities exceed 10 to the 45th ergs/s for both BL Lac nuclei, assuming isotropic emission.

Remillard, R. A.↗

NASA NTRS1987

Discovery of three new RS Canum Venaticorum-like counterparts to HEAO I X-ray sources

The identification of three high-latitude HEAO I Scanning Modulation Collimator X-ray sources with the chromospherically active RS CVn-like stars HD 113816, HD 146413, and HD 39576 is reported. Optical observations, including coude spectroscopy and broad-band and narrow band photoelectric photometry are presented. The Ca II emission strength of all three stars shows that they are chromospherically active. HD 146413 and HD 39576 exhibit variable X-ray emission in the 1-13 keV energy range, while HD 113816 is a softer and steadier source. The level of X-ray flux detected from these three stars is some one to two orders of magnitude higher than predicted empirically from the Ca II emission fluxes. It is proposed that this emission results from flarelike activity.

Buckley, D. A. H.↗

NASA NTRS1986

Identification of two southern X-ray emitting cataclysmic variables

The optical identification of two faint HEAO 1 X-ray sources with previously uncataloged cataclysmic variables is reported. The two cataclysmic variables, 1H 0542 - 407 and H0534 - 581, have average V magnitudes of about 15.7 and about 14.9, and have similar high excitation spectra with moderate to strong He II 4686 A emission. X-ray measurements and multicolor optical photometry for both objects establish 1H 0542 - 407 as a new DQ Herculis magnetic variable having a white dwarf rotation period of about 1920 s and an orbital period near 6.2 hr. 1H 0542 - 407 is unusual among DQ Her systems in having a large soft X-ray pulse fraction of about 70 percent semiamplitude below 1 keV. No definitive X-ray or optical periodicities were detected from H0534 - 581, but it appears to be either a nova-like variable or a DQ Her system. Both cataclysmic variables have very hard X-ray spectra, with evidence for iron line emission at about 6.7 keV from 1H 0542 - 407.

Tuohy, I. R.↗

NASA NTRS1986

Simultaneous X-ray and optical observations of GX 339-4 in an X-ray high state

Optical emission, soft X-rays, and hard X-rays have been observed simultaneously from the black hole candidate GX 3339-4 in a typical high state. Each of these components is interpreted as arising from a characteristic region of the accretion disk. Considered as a black hole, GX 339-4 lacks the variable 2 keV blackbody component that would be emitted from the 'solid' surface of a neutron star in the low-mass neutron star binaries. The X-ray emission in the high state is therefore extremely soft and stable in time. The intermediate disk region is optically thick and geometrically thin. The observed soft X-ray component with a 'disk blackbody' spectrum comes from this region. The innermost disk region is dynamically unstable due to the effect of general relativity and possibly due to radiation pressure. This region is responsible for the generation of the hard X-ray tail through Comptonization.

Makishima, K.↗

NASA NTRS1986

The black hole binary A0620-00

CCD photometry obtained with the 1.3-m McGraw-Hill telescope during 1981-1985 and 490-560-nm spectra obtained at KPNO on Jan. 17, 1985, are reported for A0620-00. The mass of the compact X-ray source is found to have lower limit 3.20 solar mass, strongly implying that it is a black hole; its mass is shown to exceed 7.3 solar mass if the K dwarf fills its Roche lobe during quiescence.

Mcclintock, J. E.↗

NASA NTRS1986

H0538 + 608 - A bright AM Herculis-type X-ray source

The discovery of an AM Herculis-type magnetic variable, an accreting binary system that contains a magnetic white dwarf and a late-type companion, is reported. The proposed optical counterpart to the detected X-ray source exhibits all the optical emission characteristics of its class: circular polarization, strongly modulated brightness variations, intense flickering on time scales of seconds, historical 'low states', and intense emission lines, including very strong lines of He II. The modulations in the polarization and the photometric magnitude suggest an orbital period of 3.1 + or -0.2 hr.

Remillard, R. A.↗

NASA NTRS1986

The discovery of eight bright active galactic nuclei observed with the HEAO 1 scanning modulation collimator

The eight 14th- and 15th-magnitude active galactic nuclei (AGNs) considered include one QSO and seven type 1 Seyferts; all were discovered in the course of a systematic program for the identification of the fainter X-ray sources of the HEAO 1 survey. While the X-ray and optical luminosities, and many of the optical emission features of the AGNs resemble other bright Seyfert 1s nearby, three of the galaxies exhibit very strong Fe II emission, and two show very weak forbidden line spectra. Photometric magnitudes and selected emission line intensities are given for each of the AGNs.

Remillard, R. A.↗

NASA NTRS1985

Optical observations of new X-ray emitting cataclysmic variables

Two X-ray emitting cataclysmic variables were discovered as a result of a program to identify faint X-ray sources located by the HEAO-A3 modulation collimator experiment. The objects, H0534-581 and 1H0542-407, have similar high excitation spectra with intense emission lines showing broad and narrow components. Photometry shows that H0534-581 and 1H0542-407 have average magnitudes of V=14.9 and 15.7 respectively, leading to Lx/Lopt ratios of 1.5 (typical of dwarf novae in quiescence). While pronounced variability of delta B or = 1.5 mag is observed from both systems, there is no clear evidence for repeatable orbital periods between 1 and 4 hr.

Tuohy, I. R.↗

NASA NTRS1984

Cygnus X-2 - Neutron star or degenerate dwarf?

Some conflicting models have been proposed for Cyg X-2: a degenerate dwarf model which predicts a distance of 250 + or 50 pc; and a neutron star model which implies a distance of about 8000 pc. Based on a reddening study, it is found that the distance to Cyg X-2 is greater than 1100 pc, which rules strongly against the degenerate dwarf model. This conclusion is based on observations of the 2200 A feature in the spectrum of Cyg X-2 made with the International Ultraviolet Explorer (IUE), and UBV and spectroscopic observations of 38 field stars. For the reddening of Cyg X-2 values of E(B-V) = 0.40 + or - 0.07 (1 sigma) are found and are consistent with the reddening to infinity in that direction inferred from radio data. Consequently, Cyg X-2 may be located in the halo at about 8 kpc as proposed in 1979 by Cowley, Crampton, and Hutchings.

Mcclintock, J. E.↗

NASA NTRS1984

SAS 3 observations of Cygnus X-1 - The intensity dips

In general, the dips are observed to occur near superior conjunctions of the X-ray source, but one pair of 2-minute dips occurs when the X-ray source is closer to the observer than is the supergiant companion. The dips are analyzed spectrally with the aid of seven energy channels in the range 1.2-50 keV. Essentially, there is no change in the spectral index during the dips. Reductions in the count rates are observed at energies exceeding 6 keV for some of the dips, but the dip amplitude is always significantly greater in the 1.2-3 keV band. It is believed that absorption by partially ionized gas may best explain these results, since the observations of Pravdo et al. (1980) rule out absorption by unionized material. Estimates for the intervening gas density, extent, and distance from the X-ray source are presented. Attention is also given to the problems confronting the models for the injection of gas through the line of sight, believed to be inclined by approximately 30 deg from the binary pole.

Remillard, R. A.↗

NASA NTRS1981

A UBV photometric study of the 5.2 hour X-ray binary 4U 2129+47

The paper presents results derived from UBV photometric observations of the 5.2 X-ray binary 4U 2129+47 which were made on 11 nights between 1978 October and 1979 August. The light curves observed during this period are relatively stable in shape and amplitude (Delta B = 1.5 mag) and are a surprisingly close match to the time-averaged light curves observed for HZ Her. There is a significant asymmetry in their shape which is independent of color and varies in amplitude by a factor of approximately 2. The UBV colors at minimum light suggest a considerably earlier spectral type (G or earlier) than is inferred by assuming that the star fills its Roche lobe (late K or early M). Optical pulsations were studied, and a 3 sigma limit of 0.5% was set on the fraction of the flux which is pulsed for periods between 60 ms and 300 s. Assuming that the optical companion is a normal main-sequence star filling its Roche lobe, its mass is approximately 0.65 solar mass. Assuming also that the compact object has a mass of 1.3 solar masses and that the orbital inclination of the system is approximately 90 deg, it is found that the orbital separation is approximately 1.9 solar radii and K-opt is approximately 300 km/s.

Mcclintock, J. E.↗

NASA NTRS1980

The discovery of an O subdwarf in the globular cluster NGC 6712

Spectral data for C49 in the globular cluster NGC 6712 are examined with reference to evolutionary models for low-mass stars that are contracting into white dwarfs. The spectrum of this star is found to be almost identical to that of the first sdO star found in a globular cluster, star A in NGC 6397. Analysis of the spectral data using nonlocal thermodynamic equilibrium models gives surface parameters T not less than 50,000 K, log g = 5.5 plus or minus 0.5, and N(He)/N(H) approximately equal to 0.1. The results are consistent with the models considered.

Remillard, R. A.↗

NASA NTRS1979

Optical studies of the Seyfert 2 X-ray galaxy NGC 2110

Spectrophotometry of the nucleus of the X-ray galaxy NGC2110 shows a typical Seyfert Type 2 spectrum with a strong galactic continuum. The widths of the forbidden lines are about 360 km/s (FWHM), H-beta being somewhat broader. The moderate Balmer decrement implies that the interstellar reddening is approximately 2.1 mag. The average electron density and temperature in the line-emitting region are approximately 300 per cu cm and 35,000 K, respectively. From measurements of the nebulium line, it is found that the extent of the nucleus measured along the major axis of the galaxy is about 10 arcsec (2100 pc) and the full range of gas velocities is about 700 km/s. A direct plate is discussed which shows faint spirallike features in NGC2110, a galaxy currently classified as elliptical. NGC2110 is a member of a new class (about 5 members) of very nearby (cz less than 2500 km/s) X-ray galaxies. Bradt et al. (1978) tentatively concluded that they are Seyfert Type 2 galaxies. This conclusion is supported, and it is shown that this is not inconsistent with the narrowness (less than 500 km/s FWHM) of their emission line.

Mcclintock, J. E.↗