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At least 163 records · Page 9

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NASA NTRS1981

Identification of 4U 1849-31 with V1223 Sagittarii and discovery of optical pulsations

The X-ray source 4U 1849-31 is identified with the 13 mag star V1223 Sgr, on the basis of a precise HEAO 1 modulation collimator X-ray position uniquely selected by the Ariel-5 sky survey location. It is shown by optical spectroscopy and photometry that V1223 Sgr is a cataclysmic variable, displaying a photometric period of 13.2 min that is interpreted as being due to the rotation of a degenerate dwarf. The similarity of this system to H2252-035 is noted.

Steiner, J. E.↗

NASA NTRS1982

Long term X-ray observations of systems with unusual optical counterparts and modulation measurement of selected astronomical sources

The OAO-3 satellite was used for several months' observation of the loss mass X-ray binary sources 2A18822-371 and 4U2129+47 in a search for variability similar to the 35 day on-off cycle observed in Her X-1. The related system Cyg X-2 was observed both optically and in X-rays covering one complete binary cycle of 9.8 days. The UCL X-ray telescope observations revealed no periodities nor obvious variability other than the known orbital periods; however, the ground-based optical spectroscopy supports the interpretation of the photometry periodicities as representing orbital motion in 2A1822-371 and detected radial velocity motions on the photometric period in 4U2129+47. The shape and the length of the 4.8 hour periodicity in the X-ray emission from Cyg X-3 was also studied. The quality OAO-3 data obtained to measure the light curve and look for a change in the period and/or obtain improved measurement of the slope of the light curve was insufficient.

Bowyer, C. S.↗

NASA NTRS1982

A new intermediate Seyfert galaxy - X-ray, optical, and radio properties

It is shown that the X-ray source X0459 + 034 is a Seyfert galaxy of intermediate type, and optical spectroscopy and radio observations were performed to study the nature of the object. The object appears almost stellar and slightly diffuse on Palomar Sky Survey prints. The source is identified as a Type 1.5 Seyfert with broad and narrow line components of redshift 0.016 + or - 0.001, according to H-Beta line profile. In addition, the broad line component H-Beta equivalent width is larger than that of the narrow line component by a factor of three. Finally, it is shown that this is a weak radio source with a steep nonthermal spectrum and an angular extent of approximately 3 in., and the composite radio-to-X-ray spectrum suggests that in different spectral regions, different relativistic electron populations or emission mechanisms are contributing factors.

Ghigo, F. D.↗

NASA NTRS1982

0351+026 - A QSO spawned by interacting galaxies

The results of a detailed investigation into the nature of the H I-rich quasi-stellar object 0351+026 are presented. An improved H I profile reveals the presence of two distinct components. A high-quality CCD image clearly shows the presence of two galaxies. The brighter galaxy hosts the QSO while the less luminous companion has a prominent, apparently stellar nucleus. Moreover, this image also shows streamers of nebulosity emanating from the two galaxies and has an overall morphology which is highly reminiscent of that seen in other strongly interacting galaxies. Optical spectroscopy of the system shows that the forbidden O III emission lies between the two nuclei and there is strong evidence of stellar absorption lines in both the host and companion galaxies. Overall, the data suggest that this system represents a violent encounter between two low-luminosity H I-rich galaxies. The possibility exists that this collision has triggered the QSO activity in the brighter galaxy.

Bothun, G. D.↗

NASA NTRS1983

The extraordinary extragalactic supernova remnant in NGC 4449. II - X-ray and optical investigations

Einstein Observatory X-ray observations indicate that the SNR in NGC 4449 is the most luminous X-ray, as well as optical and radio, SNR known. New optical spectroscopy, together with the X-ray data, suggest this exceptional luminosity to be due to chemically enriched material at unusually high densities. A model is proposed in which this SNR resulted from the explosion of a massive star in a medium of nearly 25/cu cm density about 100 years ago. The chemistry in question further suggests that the SNR in NGC 4449 resulted from the explosion of a star whose mass was greater than 25 solar masses.

Blair, W. P.↗

NASA NTRS1983

Observation of winds in cool stars

Sufficient observational material - ultraviolet spectroscopic measures, quantitative optical spectroscopy, and X-ray photometry exists to enable discernment of the presence and character of mass loss in cool stars and to establish meaningful constraints on theoretical models. Two determinants of atmospheric wind structure - temperature and gravity - may suffice in a most superficial way to define the wind and atmospheric structure in a star; however more extensive observations demonstrate the importance of magnetic surface activity and its particular geometrical configuration. Successive observations of an active binary system and a supergiant star reveal that magnetic activity and perhaps mass loss occur on restricted regions of a stellar surface and that long lived structures are present in a wind.

Dupree, A. K.↗

NASA NTRS1985

A summary of the UV, optical and IR properties of disks in CV's

The available observations of dwarf novae and novalike systems that are relevant to the study of accretion in cataclysmic variables are reviewed. This includes UV data from IUE and optical spectroscopy and infrared photometry. The flux distributions are compared to available steady state models to obtain an estimate of the mass accretion and the range of this parameter among the dwarf novae (U Gem, Z Cam and SU UMa types) and the novalikes (UX UMa, AM Her, DQ Her types). The normal and abnormal range of variation in the continuum and line fluxes is discussed.

Szkody, P.↗

NASA NTRS1986

Coordinated Exosat and spectroscopic observations of flare stars and coronal heating

Some results of simultaneous monitoring of the two flare stars UV Ceti and EQ Peg with Exosat and ground-based optical spectroscopy are presented. Short-timescale variability is observed in the 0.1-2 keV emission from both these objects and, in the case of UV Ceti, a strong correlation is found between the soft X-ray and H-gamma fluctuations. These results imply that much of the low-level X-ray flux previously considered 'quiescent' probably originates from small flare events.

Butler, C. J.↗

NASA NTRS1987

Circumnuclear starbursts in Seyfert galaxies

Observational diagnostics for the recognition of circumnuclear star formation in Seyfert galaxies are described and illustrated. These methods include: (1) spatially resolved optical spectroscopy, which allows the emission lines for HII regions to be separated from those originating in gas ionized by the Seyfert nucleus; (2) radio continuum mapping, where the linear radio sources characteristic of the nuclear activity may be distinguished from the diffuse morphology of multiple supernova remnants generated in a starburst; (3) infrared spectroscopic searches for emission features of dust, which are seen in starbursts but not in Seyfert nuclei; (4) the shape of the IRAS spectrum. These various diagnostics agree well as to the presence or absence of ongoing star formation. The IRAS spectra of a significant fraction of Seyferts are dominated by emission from dust heated by stars, not the Seyfert nucleus itself. In these cases, the spectrum is curved, being steep between 25 and 60 microns and flatter between 60 and 100 microns. When the Seyfert nucleus dominates, the 25 to 100 micron spectrum is much flatter. It is suggested that the location of a Seyfert galaxy in the IRAS color-color diagram reflects primarily the relative contributions of the active nucleus and dust heated by stars to the infrared fluxes.

Wilson, Andrew S.↗

NASA NTRS1987

IRAS observations of AGN candidates at low flux levels

IRAS additional observations were used to obtain a sample of point sources at much fainter flux levels than hitherto available through the IRAS Point Source Catalogue. This sample is being used to compile an incomplete but representative catalogue of faint IRAS candidate Active Galactic Nuclei (AGNs) and to study the evolution of the infrared bright galaxies. Ground based follow up observations (optical spectroscopy) are mainly hampered by identification confusion.

Degrijp, Marinus H. K.↗

NASA NTRS1987

Far-infrared properties of optically-selected quasars and Seyfert galaxies

Pointed IRAS observations and ground based observations are used to determine the infrared properties of optically selected galaxies and quasars. The use of complete, unbiased, optically selected samples means that statistical tests can be applied to probe the underlying properties of active galactic nuclei (AGNs). The near infrared to millimeter spectral energy distributions (SEDs) were studied of the CfA Seyfert galaxies, a well defined, unbiased sample of 25 Type 1 and 23 Type 2 Seyfert galaxies selected by optical spectroscopy. Data given show strong trends in the infrared SEDs. Strong evidence is also given that the infrared spectra of Seyfert 2 galaxies are dominated by thermal emission from warm dust, while nonthermal emission is more important in the spectra of quasars and luminous Seyfert 1 nuclei.

Edelson, R. A.↗

NASA NTRS1990

An IRAS survey of the Taurus-Auriga molecular cloud

IRAS data are used to search for young premain-sequence stars not previously associated with molecular cloud cores in the Taurus-Auriga region. NIR photometry and optical spectroscopy suggest that many of the objects are young stars. The sample includes six new embedded sources with luminosities comparable to that of the average T Tauri star, suggesting that surveys for premain-sequence stars in the cloud are essentially complete for luminosities greater than 0.5 solar luminosities. A disagreement is found between accretion rates derived from the duration of the embedded phase and those derived from the bolometric luminosity. It is found that this disagreement may be reconciled if a star accretes most of its mass in a time that is short compared to the duration of the embedded phase or if the ages of T Tauri stars have been underestimated.

Kenyon, Scott J.↗

NASA NTRS1990

Nuclear outflow from the edge-on galaxy NGC 3628

New evidence is presented for collimated outflow from a starburst nucleus in the edge-on galaxy NGC 3628. A plume of X-ray emission along the minor axis of this galaxy is suggested by the distribution of counts in the softer energy channels of the Einstein Observatory IPC. Plumes of H-alpha emission are visible in a CCD image of the southern minor axis region, at a position angle consistent with that of the X-ray plume, while extended, possibly filamentary, H-alpha emission is visible in the north. Optical spectroscopy along the northern minor axis clearly detects line emission, with line ratios of H-alpha, N II, and S II changing from those characteristic of normal H II regions near the nucleus, to a low-ionization state, consistent with shock heating, farther out. All this evidence, and the IR and radio continuum properties of this galaxy, make NGC 3628 another member of the growing class of galaxies with starburst nuclear activity and outflowing winds, to which NGC 253 and M82 already belong.

Fabbiano, G.↗

NASA NTRS1990

Coordinated optical and ultraviolet observations of DH Leo

Results are reported from contemporaneous KPNO optical spectroscopy, IUE UV spectroscopy, and KPNO R photometry of the DH Leo triple system in spring 1987. The data are presented in tables, graphs, and spectral phase images and discussed in detail. The H-alpha, H-beta, H-gamma, H-delta, and Ca II H and IRT lines are found to have excess emission, and the phase modulation in H-alpha, H-beta, and Ca II is well correlated with the photometric modulation. This result is attributed to the combination of (1) a small amount of global chromospheric emission and (2) emission from plagelike regions associated with cool starspots. The (H-alpha)/(H-beta) ratio is found to be significantly lower than that in longer-period RS CVn systems.

Newmark, Jeffrey S.↗

NASA NTRS1990

Emission-line properties of the composite Seyfert/Starbust galaxy IC 5135

The galaxy IC 5135 is host for Seyfert activity and vigorous star formation in its nucleus. Results of a study based on optical spectroscopy and imaging are presented that reveal the ionization properties of the nucleus and near-nucleus region, as well as the global morphology of this galaxy. The dual nature of the nucleus is evident in emission-line profiles, which show two kinematic components. Line intensity ratios in the nucleus are typical of Seyfert 2 galaxies, but evolve with increasing radius to values generally characteristic of H II regions. IC 5135 provides an illustration of the importance of the O I 6300 forbidden line as a tracer of a hard-spectrum, photoionizing continuum; the presence at large radii of ionizing radiation from nucleus is clearly revealed by the relative strength of this line.

Shields, Joseph C.↗

NASA NTRS1990

Multiband observations of Cygnus A: A study of pressure balance in the core of a powerful radio galaxy

Cygnus A is a powerful double radio source associated with a giant elliptical galaxy at the center of a poor cluster of galaxies. The radio source also sits within the core radius of a dense, cooling flow, x ray emitting cluster gas. Optical spectroscopy and narrow band imaging have revealed copious amounts of narrow line emission from the inner 20 kpc of the associated galaxy. Researchers assume H sub o = 75 km sec (-1) Mpc(-1). Discussed here are the pressures in the three components of the Interstellar Medium (ISM) (i.e., the radio, x ray, and line emitting fluids) within a radius of about 15 kpc of the active nucleus of the Cygnus A galaxy.

Carilli, Chris↗

NASA NTRS1990

Blue ellipticals in compact groups

By studying galaxies in compact groups, the authors examine the hypothesis that mergers of spiral galaxies make elliptical galaxies. The authors combine dynamical models of the merger-rich compact group environment with stellar evolution models and predict that roughly 15 percent of compact group ellipticals should be 0.15 mag bluer in B - R color than normal ellipticals. The published colors of these galaxies suggest the existence of this predicted blue population, but a normal distribution with large random errors can not be ruled out based on these data alone. However, the authors have new ultraviolet blue visual data which confirm the blue color of the two ellipticals with blue B - R colors for which they have their own colors. This confirmation of a population of blue ellipticals indicates that interactions are occurring in compact groups, but a blue color in one index alone does not require that these ellipticals are recent products of the merger of two spirals. The authors demonstrate how optical spectroscopy in the blue may distinguish between a true spiral + spiral merger and the swallowing of a gas-rich system by an already formed elliptical. The authors also show that the sum of the luminosity of the galaxies in each group is consistent with the hypothesis that the final stage in the evolution of compact group is an elliptical galaxy.

Zepf, Stephen E.↗

NASA NTRS1990

The kinematics and morphology of NGC 520: One, two, or three galaxies

The peculiar galaxy NGC 520 (Arp 157) is often interpreted as an interacting pair of galaxies. The identification of the two bulges and overall morphology of the two galaxies has long been a puzzle which the authors attempt to solve here. New longslit optical spectroscopy and near-infrared images of NGC 520 are presented. These data suggest that the northwest peak is the bulge of one of two galaxies in the system. The other larger bulge is clearly evident in the K band image in the middle of the dust lane. The stellar radial velocity profile in the central 10 seconds of the larger bulge is consistent with counterrotation seen in the molecular gas component. This kinematic subsystem could be the remains of a merged gas-rich irregular.

Stanford, S. A.↗