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NASA NTRS1988

Analysis of IUE data on V426 Ophiuchi - Outburst and orbital variability

Time-resolved IUE spectra throughout two orbits of the dwarf nova V426 Oph during quiescence are presented. It is found that the visual and C IV fluxes remain relatively constant during both orbits, whereas the UV coninua and Mg II lines vary by 20-30 percent. The time scales of this variability are discussed. Analysis of other spectra at brighter optical magnitudes shows that the UV lags the optical during a probable rise to outburst, similar to the behavior of SS Cyg. The reddening of V426 Oph is determined to be E(B-V) = 0.1. The contribution of the white dwarf to the UV flux at quiescence is estimated to be 25 percent, based on the system parameters of Hessman (1988) and the period-temperature relation of Sion (1987).

Szkody, Paula↗

NASA NTRS1989

The VV Cephei star V641 Cassiopeiae

Ultraviolet spectra of the variable star V641 Cas taken with the IUE satellite have confirmed the VV Cephei nature of this object. The observations are consistent with the variable being a M3 I + B2 V-III system with E(B-V) = 0.55 mag lying in the Perseus arm of the Galaxy. In spite of V641 Cas having the largest light variation in the visible of any VV Cephei type star, no correlation was found between variation in ultraviolet line or continuum and light variation in the visible wavelength region.

Shaw, J. Scott↗

NASA NTRS1989

Kinematic modeling of the Galaxy. I - The Yale Bright Star Catalogue

A code has been developed to investigate the kinematic properties of stellar populations of the Galaxy by modeling the distributions of proper motion and line-of-sight velocity. The coordinate frames of reference are discussed in detail and the general matrix transformations valid beyond the solar neighborhood are given. As a first application, the kinematic properties of the magnitude-selected sample of 3993 stars in the Bright Star Catalogue with V less than 6.0 and (B-V) greater than 0 are selected. The observed kinematic distributions are compared with a conventional model that has an exponential disk with scale heights, components of velocity dispersion ellipsoid, and asymmetric drift taken from the literature and defined as functions of spectral type. The comparisons suggest that a significant fraction of the Bright Star Catalogue belongs to a relatively young population that is not properly represented in the model.

Ratnatunga, Kavan U.↗

NASA NTRS1989

Photographic, near-infrared, and CCD photometry of the distant globular cluster AM-1

New photographic, CCD, and near-infrared photometry of stars in the distant globular cluster AM-1 are presented. Based on the photographic and CCD photometry down to the horizontal branch, a distance modulus (m-M)v = 20.4 mag is derived, with E(B-V) = 0.0 mag, corresponding to a distance of 120 kpc from the sun. Using the (V-K) colors of two giants in AM-1, a metallicity of Fe/H = -2.0 + or - 0.2 is deduced, in good agreement with earlier determinations. Using complete photometry and star counts, a core radius of 10 arcsec (6 pc) and a tidal radius of 100 arcsec (58 pc) are derived. Despite the low intrinsic luminosity (Mv = -5.0 mag) and the large galactocentric distance of this globular cluster, the apparent magnitude distribution of the giant branch stars of AM-1 is not found to be unusual.

Madore, Barry F.↗

NASA NTRS1989

The slow nova V1819 Cygni (Nova Cygni 1986)

Spectrophotometric and spectropolarimetric observations of the slow nova Cygni 1986 were obtained with the 36-in Pine Bluff Observatory telescope beginning about one week after maximum and continuing for one-two years after maximum. An E(B-V) value of about 0.35 is found. In the months following maximum light, the Balmer decrement was extremely steep and variable with time. Departures from case B radiative transfer noted throughout most of the observational period are consistent with self-absorption of the Balmer lines due to high densities in parts of the nova shell. The results suggest that at 11 months after maximum the shell density was about 10 to the 7th/cu cm, dropping to about 10 to the 6th/cu cm two years after maximum.

Whitney, Barbara A.↗

NASA NTRS1989

The region of formation of the ultraviolet high temperature resonance lines in the eclipsing binary Beta Persei (Algol)

A new series of IUE observations of Beta Persei has shown that the high temperature resonance lines of Si IV and C IV arise in a region that surrounds the brighter, early-type component of the system. The continuum spectrum corresponds to that of a B8V object, and the value of E(B-V) that yielded the best match between the two IUE regions was 0.06, the value quoted for Beta Per in Jamar et al.'s (1976) Catalog.

Brandi, E.↗

NASA NTRS1989

Problems with the Baade-Wesselink method

The discrepancy noted in radii obtained by the Baade-Wesselink method when different colors are used to determine the effective temperatures is explored. The discrepancy is found to be due to an inconsistency in the applied temperature-color calibrations. The assumption of the maximum likelihood method that beta (the effective temperature + 0.1 times the bolometric correction) is a linear function of the color is valid for the B-V and V-I colors, but not for the V-R colors. It is suggested that the errors introduced by the nonlinearity in the relation between beta and the V-R colors will produce radii which are too large. The radii derived from the V-B colors appear to be too small.

Bohm-Vitense, E.↗

NASA NTRS1989

The relationship between infrared, optical, and ultraviolet extinction

The parameterized extinction data of Fitzpatrick and Massa (1986, 1988) for the ultraviolet and various sources for the optical and near-infrared are used to derive a meaningful average extinction law over the 3.5 micron to 0.125 wavelength range which is applicable to both diffuse and dense regions of the interstellar medium. The law depends on only one parameter R(V) = A(V)/E(B-V). An analytic formula is given for the mean extinction law which can be used to calculate color excesses or to deredden observations. The validity of the law over a large wavelength interval suggests that the processes which modify the sizes and compositions of grains are stochastic in nature and very efficient.

Cardelli, Jason A.↗

NASA NTRS1989

IUE observations of the M dwarfs CM Draconis and Rossiter 137 B - Magnetic activity at saturated levels

IUE observations of two active M dwarfs with known rotation rate or age and presumed to be almost totally convective are presented. The first of these stars, CM Draconis (Gl 630.1), is an old Population II binary with its components in tidally induced rapid rotation (P = 1.27 d, dM 4 + dM 4). The other one, Rossiter 137 B, forms with HD 36705 (AB Dor) a visual pair of young active stars. The activity of CM Dra is due to the forced rotation in a close binary, while Rst 137 B is assumed to rotate fast enough to generate its magnetica activity. These results are compared with those for M dwarfs, particularly AU Mic and YZ CMi, that have known rotational periods and measured ultraviolet emission line fluxes. The chromospheric-coronal saturation levels of cool dwarfs between 0.3 less than B-V less than 1.6 is determined. It is found that saturated F stars have stronger chromospheres than saturated M stars, but the opposite is true for the corona. Results of these observations seem to favor a rotation-dependent distributed dynamo generating magnetic flux in totally convective stars.

Vilhu, O.↗

NASA NTRS1990

HR 1362 - A test case for stellar dynamo theories

An analysis of 11 yr of photometry of HR 1362 = EK Eri has shown a well-established photometric period of 335 days. This confirms an earlier period determination of about 310 days from 3 yr of APT data and is consistent with a new v sin i determination of 2 + or - 2 km/s. Recent Ca II H and K observations show moderately strong H and K emission lines at a flux level of log F prime (K) of about 6.5 ergs sq m/s. If the photometric period is interpreted as the rotation period, this surface flux is more than one order of magnitude larger than what can be expected from empirical activity versus rotation relationships. The spectrum and the U-B and B-V colors are consistent with a single G8 III-IV spectral classification, while the V-R and V-I values indicate a small color excess, typical of chromospherically active stars.

Strassmeier, Klaus G.↗

NASA NTRS1989

Asteroid magnitudes, UBV colors, and IRAS albedos and diameters

This paper lists absolute magnitudes and slope parameters for known asteroids numbered through 3318. The values presented are those used in reducing asteroid IR flux data obtained with the IRAS. U-B colors are given for 938 asteroids, and B-V colors are given for 945 asteroids. The IRAS albedos and diameters are tabulated for 1790 asteroids.

Tedesco, Edward F.↗

NASA NTRS1990

The orbit and companions of the classical Cepheid FF Aql

New radial velocities of the classical Cepheid FF Aql have been obtained and combined with previous observations to provide a revised orbit. A companion has been detected at 1800 A in IUE spectra with a spectral type of A9 V to F3 V. If the Cepheid has an evolutionary mass, then the mass ratio is M1/M2 = 3.8. A companion recently detected by speckle interferometry is in a longer-period orbit if it is a physical companion. In this case it is also an evolved star. The possible fourth member of the system, the visual companion, is unlikely to be a member of the system. The companion at 6 arcsec is unlikely to be a physical companion. Cepheids (in the 'free-fall' descending branch of the light curve) and nonvariable supergiants are shown to have a different spectral slope between 2900 and 1800 A for the same (B-V)0. IUE spectra of Polaris are rediscussed using other Cepheid spectra as comparison stars, and it is concluded that there is probably no sign of a companion.

Evans, Nancy Remage↗

NASA NTRS1990

WRA 751, a candidate for a new luminous blue variable

Results are presened on spectroscopic observations (carried out with the ESO 1.52-m telescope at La Silla, Chile) and measurements made by the Infrared Astronomical Satellite on the star WRA 751. It is estimated that the T(eff) of this star is 30,000 K and its E(B-V) is 1.8 mag. Comparison with evolutionary tracks of Maeder and Meynet (1980) indicates that WRA 751 is located in the region of luminous blue variables at a lower limit of the initial mass of about 50 solar masses. Its other physical characteristics, such as the light variability, strong Fe II lines, and the extinction-free spectral energy distribution, suggest that WRA 751 is a candidate for a new luminous blue variable.

Hu, J. Y.↗

NASA NTRS1990

Empirical relationships between gas abundances and UV selective extinction

Several studies of gas-phase abundances in lines of sight through the outer edges of dense clouds are summarized. These lines of sight have 0.4 less than E(B-V) less than 1.1 and have inferred spatial densities of a few hundred cm(-3). The primary thrust of these studies has been to compare gaseous abundances in interstellar clouds that have various types of peculiar selective extinction. To date, the most notable result has been an empirical relationship between the CN/Fe I abundance ratio and the depth of the 2200 A extinction bump. It is not clear at the present time, however, whether these two parameters are linearly correlated or the data are organized into two discrete ensembles. Based on 19 samples and assuming the clouds form discrete ensembles, lines of sight that have a CN/Fe I abundance ratio greater than 0.3 (dex) appear to have a shallow 2.57 plus or minus 0.55 bump compared to 3.60 plus or minus 0.36 for other dense clouds and compared to the 3.6 Seaton (1979) average. The difference in the strength of the extinction bump between these two ensembles is 1.03 plus or minus 0.23. Although a high-resolution IUE survey of dense clouds is far from complete, the few lines of sight with shallow extinction bumps all show preferential depletion of certain elements, while those lines of sight with normal 2200 A bumps do not. Ca II, Cr II, and Mn II appear to exhibit the strongest preferential depletion compared to S II, P II, and Mg II. Fe II and Si II depletions also appear to be enhanced somewhat in the shallow-bump lines of sight. It should be noted that Copernicus data suggest all elements, including the so-called nondepletors, deplete in diffuse clouds (Snow and Jenkins 1980, Joseph 1988). Those lines of sight through dense clouds that have normal 2200 A extinction bumps appear to be extensions of the depletions found in the diffuse interstellar medium. That is, the overall level of depletion is enhanced, but the element-to-element abundances are similar to those in diffuse clouds. In a separate study, the abundances of neutral atoms were studied in a dense cloud having a shallow 2200 A bump and in one with a normal strength bump.

Joseph, Charles L.↗

NASA NTRS1989

The detection of a broad interstellar extinction feature near 1700 A

A statistical examination of 126 extinction curves has revealed the presence of a second broad absorption feature similar in nature to the 2200 A feature. The feature is centered on wavelength 1706 A, has a full half-width of 350 A, and a mean central height of 0.21 magnitudes. The strength of the feature increases with E(B-V) supporting an interstellar origin, and on average it is 18 times weaker than the 2200 A feature.

Carnochan, David J.↗

NASA NTRS1989

The dependence of UV extinction properties on dust environment

UV extinction data, derived from the Savage et al. (1985) ANS extinction catalog, are analyzed. The data include the normalized extinction at 1550 A, the strength of the 2175 A bump, and a crude estimate of the bump width. The results confirm the systematic increase of far-UV extinction with galactic altitude first uncovered by Kiszkurno-Koziej and Lequeux (1987) and verify that this effect is in fact a result of the dust being away from the plane, and not a generalized density dependence. It is also shown that the width of the 2175 A bump is systematically broader in denser regions (defined by large values of E(B-V) per Kpc), implying that a similar galactic altitude effect seen in this parameter may only be a reflection of the lower densities encountered away from the plane. The dependence of bump width upon bump strength is also examined. It is shown that a relationship between these two parameters is expected for certain models of the bump, but none is found. However, two factors which could be complicating a straightforward interpretation of the observations are identified and discussed.

Massa, Derck↗

NASA NTRS1989

Does CO trace H2 at high galactic latitude

A CO survey of 342 Infrared Excess Clouds (IRECs) distributed uniformly across the sky is presented. Following comparison of the integrated CO brightness with the 100 micron infrared brightness B(sub 4) obtained from the IRAS data, evidence was found for a threshold in B(sub 4) of 4-5 MJy sr(exp -1) below which CO does not form. Evidence is also presented that the threshold effect can be seen within an individual cloud, providing evidence for a phase transition between atomic and molecular gas. While the main thrust was to examine the CO content of the IRECs, it was also attempted to detect CO toward a number of UV stars so that CO brightness could be correlated with direct measurements of H2 column density and E(B-V). Of the 26 observed stars CO was detected toward 6. It is consistent with the results obtained using infrared data.

Bazell, David↗

NASA NTRS1990

Observations and models of star formation in the tidal features of interacting galaxies

Multi-color surface photometry (BVri) is presented for the tidal features in a sample of interacting galaxies. Large color variations are found between the morphological components and within the individual components. The blue colors in the primary and the tidal features are most dramatic in B-V, and not in V-i, indicating that star formation instead of metallicity or age dominates the colors. Color variations between components is larger in systems shortly after interaction begins and diminishes to a very low level in systems which are merged. Photometric models for interacting systems are presented which suggest that a weak burst of star formation in the tidal features could cause the observed color distributions. Dynamical models indicate that compression occurs during the development of tidal features causing an increase in the local density by a factor of between 1.5 and 5. Assuming this density increase can be related to the star formation rate by a Schmidt law, the density increases observed in the dynamical models may be responsible for the variations in color seen in some of the interacting systems. Limitations of the dynamical models are also discussed.

Wallin, John F.↗