Ground-based Optical Observations Research Articles

RXTE,ROSAT,EUVE,IUE, and Optical Observations through the 45 Day Supercycle of V1159 Orionis

A complete 45 day supercycle of the cataclysmic variable V1159 Ori comprising a superoutburst and eight normal outbursts was observed. Coverage included ground-based optical observations as well as observations with RXTE for 38 days, ROSAT for 34 days, IUE for 27 days, and Extreme Ultraviolet Explorer (EUVE) for 10 days. The resulting light curves reveal that the optical and UV light variations are inversely correlated with the RXTE and ROSAT fluxes, with the largest change in intensity occurring in the ROSAT bandpass. There is no evidence for a strong EUV/soft X-ray component during outburst. An outflowing wind is evident from the C IV line profile during each brief outburst as well as the superoutburst. The transitions from outburst states of the disk to quiescent states take place on timescales of hours. Accretion disk models can fit the UV line and continuum energy distributions near outburst only if the disk radial temperature profile is modified from the standard case to produce a hotter distribution in the outer annuli. The high mass transfer rate, the hot disk distribution, and the similarity of outbursts and superoutbursts argue for outside-in outbursts in this system.

Multiwavelength Study of the Starburst Galaxy NGC 7714. I. Ultraviolet‐Optical Spectroscopy

We have studied the physical conditions in the central 300 pc of the prototypical starburst galaxy NGC 7714. Our analysis is based on ultraviolet spectroscopy with the HST/GHRS and ground-based optical observations, and it also covers X-ray and radio data taken from the literature. The data are interpreted using evolutionary models optimized for young starburst regions. The massive stellar population is derived in a self-consistent way using the continuum and stellar absorption lines in the ultraviolet and the nebular emission-line optical spectrum. The central starburst has an age of about 4.5 Myr, with little evidence for an age spread. Wolf-Rayet features at the ultraviolet indicate a stellar population of ~2000 Wolf-Rayet stars. The overall properties of the newly formed stars are quite similar to those derived, e.g., in 30 Doradus. A standard Salpeter initial mass function is consistent with all observational constraints. The nucleus of NGC 7714 has a bolometric luminosity of (0.5-1)×1010 L☉ and a mass of (5-10)×106 M☉ (if low-mass stars have formed). We find evidence for spatial structure within the central 300 pc sampled. Therefore it is unlikely that the nucleus of NGC 7714 hosts a single star cluster exceeding the properties of other known clusters. Contrary to previous suggestions, we find no evidence for a nuclear supernova rate that would significantly exceed the total disk-integrated rate. About one supernova event per century is predicted. Most of these events are associated with the core collapse of a hydrogen-free or -poor progenitor. An older stellar generation, with ages of tens of Myr and older, is suggested as well. This population is less concentrated toward the nucleus and extends over kiloparsec scales.

Link of the Hipparcos Catalogue to the ICRS

AbstractIn compliance with the 1991 IAU resolutions on reference frames, the merged Hipparcos Catalogue had to be aligned in such a way that it represents at optical wavelengths the International Celestial Reference System (ICRS). This was realized as a combination of particular solutions obtained from observations of radio stars by radio interferometry, observation of quasars relative to Hipparcos stars, photographic plates including galaxies and Hipparcos stars, star catalogues referred to extragalactic objects, HST observations, and comparison of Earth orientation parameters obtained by VLBI and ground-based optical observations reduced with Hipparcos positions and proper motions. The individual results generally agree within 10 mas in orientation at epoch and 1 mas/yr in spin of the system. Two methods were used to combine the results and yielded uncertainties of 0.6 mas in orientation and 0.25 mas/yr in spin.

Hubble Space Telescopeand Ground‐based Observations of I Zw 1 and MRK 486 and the Variability of Polarization in Radio‐quiet Active Galactic Nuclei

Hubble Space Telescope UV spectropolarimetry and new ground-based optical observations of the Seyfert 1/QSO I Zw 1 and highly polarized Seyfert 1 Mrk 486 are presented. I Zw 1 is found to be a polarimetric variable. Our data show that the polarization position angle has changed by ~50? compared to measurements obtained 10-15 yr ago. There is evidence that the degree of optical linear polarization may be variable as well, but for ? 4000 ?, P remained less than 1%. Optical/UV synchrotron radiation can be ruled out as the cause of the observed polarized flux and variations because the permitted lines are polarized. The optical polarization increases dramatically to the blue. In contrast, the UV polarization is roughly constant with wavelength at ~1% and falls far below the polarization level expected from ground-based observations. The overall wavelength dependence of the optical and UV polarization can be reconciled if the effect of starlight from the luminous host galaxy is taken into account. The strong increase in the optical polarization with decreasing wavelength for Mrk 486 continues into the UV and reaches nearly 8% by 2000 ?. This suggests that dust scattering may be the dominant polarizing mechanism in this object. Spectropolarimetry of H? and H? reveals complex polarization structure across the lines (mostly in the polarization position angle), leading to the conclusion that at least some of the scattering material is located within the broad-line region (BLR). These results are consistent with the BLR being composed of two distinct line-emitting regions: (1) a region of width ~1500 km s-1- (FWHM) polarized at P.A. 150?-160?, and (2) a region of width ~3000 km s-1- polarized at P.A. 100?-110?. Identification of these distinct regions in the BLR by their differing polarizations demonstrates the existence of an intermediate-line region in a low-luminosity AGN. Associated C IV absorption is detected in the UV spectrum of Mrk 486, in keeping with the general trend that high polarization in radio-quiet AGNs is somehow linked to the presence of absorbing gas. The object also shows evidence for variations in polarization. Observations acquired at two separate telescopes during 1994-1995 reveal a decrease of ~10? in polarization P.A. compared with earlier measurements. The polarization variability of these two objects, along with the deduced proximity of the scattering region to the nucleus of Mrk 486, argues that the structure of the scattering and/or emission-line regions in at least some radio-quiet AGNs evolve on relatively short time scales (a few years or less).

A compiled catalogue of optical positions of extragalactic radio sources

Based on 28 individual catalogues, in which the positions of optical counterparts of extragalactic radio sources are listed, we compiled a combined catalogue by means of a weighted least squares adjustment. The catalogue is in the system of FK5/J2000.0. It consists of about five hundred sources, among which there are 56 primary sources with position uncertainties as . Comparisons show that the orientation differences between optical and radio frames are Local relative deformations are not obvious within the precision of ground-based optical observations.

Ground-Based Optical Observations in the Near-Earth Space Chemical Releases: Apparatus and Principal Results

Optical diagnostic devices complex for investigations in near-Earth space was created. The optical data of 1983-1991 ionosphere active experiments with chemical releases show high efficiency of optical observations with the complex. The results of observation could be compared with model estimations of cloud dynamics.

A new perspective on solar active regions

A flood of new observations of the solar corona have been made with high spatial resolution, good temporal coverage and resolution, and large linear dynamic range by the Soft X-ray Telescope on Yohkoh. These data are changing our fundamental understanding of how solar magnetic fields emerge, interact, and dissipate. This paper reviews some of the results from Yohkoh in the context of earlier results from the Solar Maximum Mission and in conjunction with ground-based optical and radio observations.

X-ray bright point flares due to magnetic reconnection

Ground-based optical observations coordinated with Yohkoh/SXT X-ray observations of an old, disintegrating bipolar active region AR NOAA 7493 (May 1, 1993) provided a multiwavelength data base to study a flaring ‘active region’ X-ray bright point (XBP) of about 16 hr lifetime, and the activity related to it in different layers of the solar atmosphere. The XBP appeared to be related to a new minor bipole of about 1020 Mx. Superposed on a global evolution of soft X-ray brightness, the XBP displayed changes of brightness, lasting for 1–10 min. During the brightenings the XBP apparently had a spatial structure, which was (tiny) loop-like rather than point-like. The X-ray brightenings were correlated with chromospheric activity: (i) brightenings of underlying chromospheric faculae, and (ii) appearance of strong turbulent velocities in the arch filament system. We propose that the XBP brightenings were due to reconnection of the magnetic field lines (sketched in 3D) between the new bipole and a pre-existing plage field induced by the motion of one of the new pores (v = 0.2 km s−1) towards the plage, and that the XBP itself was a reconnected hot loop between them.

Ground-based optical observations of coronal mass ejections on the night sky

Attention is paid to the potential ability of ground-based optical observations of CMEs at large angular distances from the Sun on the night sky. Zodiacal light photometers on-board the Helios space probes have traced CMEs up to angular distance of 90° from the Sun. We present first results of our observation of the faint luminous extended object at the night sky at the distance of 50° from the Sun obtained on 6 June 1994. It is supposed to be a feature of coronal mass ejection.

Ground-based optical observations of daytime auroral emissions from Antarctica

First results obtained from ground-based observations on daytime amoral emission intensities from the Indian station, Maitri, in Antarctica, are presented and discussed. These results show striking increases in intensities in all the emissions (viz. low- and high-energy electron-induced and proton-induced emissions), during noon hours in a latitudinal region near the plasmapause and far from the conventional cusp zone. Wave-like disturbances are seen on moderately disturbed days in proton-induced emissions. Plausible causes for such enhancements and disturbances are discussed.

GINGA AND ROSAT OBSERVATIONS OF THE CATACLYSMIC VARIABLE S193

ABSTRACT The cataclysmic variable S193 was observed with the Ginga and ROSAT satellites along with ground-based optical observations. The bremsstrahlung temperatures and the column densities derived from these two observations are noticeably different. However, since the observations were separated by 3 years and took place at different optical magnitudes, it is not clear whether this is related to an intrinsic change in the system or to a two component source of X-rays. While the x-ray data are not sufficient to accomplish a detailed analysis for periodicities, the Ginga data place an upper limit of 40% on the amplitude of any sinusoidal modulation.

Hot gas and the origin of the nebular continuum in novae

A featureless blue continuum (with constant f(sub nu)) is a defining feature of declining classical novae. The fact that f(sub nu) is constant into the infrared, and the absence of a Balmer jump, suggests that this continuum originates in hot tenous gas. The electron temperature and density of the hot gas phase of classical nova QU Vul 1984 are estimated from ground-based optical and IUE ultraviolet observations. This region has a temperature of 10(exp 5) - 10(exp 6), and a density in the range of 2 x 10(exp 4) to 3 x 10(exp 5)/cu cm. In addition, a colder, denser shell composed of many 'clumps' or condensations is present, and it is responsible for most of the optical-to-ultraviolet emission lines. The hot has, however, may be much more massive and could dominate the energetics of the ejecta. The total returned mass could be as high as 10(exp -4) and 4 x 10(exp -3) solar mass, depending on conditions in the hot gas. The large mass of the shell, in combination with the high metallicity found in this nova, supports the idea that novae may be an important contributor to the chemical enrichment of the interstellar medium.

Two Year UV-Optical Monitoring of the Seyfert 1 Galaxy Markarian 335

We report on the results of a UV-Optical spectral monitoring of the bright Seyfert 1 galactic nuclei Mkn 335. This campaign began in June, 1989, and ended in June, 1991. Ultraviolet spectra of fourteen epochs at nearly uniform sampling of 30-day intervals, except when the object was inaccessible from the IUE satellite, have been obtained, of which twelve were coordinated with quasi-simultaneous ground-based optical observations made at Lick Observatory.

Hubble Space Telescope Faint Object Spectrograph and ground-based observations of the broad absorption line quasar 0226-1024

Faint Object Spectrograph data from the Hubble Space Telescope of the broad absorption line quasar 0226-1024 have revealed the presence of 8-10 absorbing ions between 680 and 1000 A (restframe): C III, N III, N IV, O III, O IV, O VI, S V, S VI, possibly Ne VIII, and possibly O V* arising from a metastable excited state. We also present ground-based optical observations of the broad line troughs for the following ions: H I, C IV, N V, Si IV, and possibly Fe III, S IV, P V, and C III* (also arising from a metastable excited state). The results of this fit are used to estimate the absorbing ionic column densities. There is evidence that the broad absorption line clouds are optically thick and either do not completely cover the continuum source or narrow unresolved lines are present.

Observations and modeling of the Jovian remote neutral sodium emissions

Groundbased optical imaging observations of the Jovian environment using a 4-in.-aperture telescope have revealed a large cloud of neutral sodium extending out to more than 400 Jovian radii ( R J) in the planet's equatorial plane. Preliminary analysis of one image, taken on 25 January 1990, has been published. This one image represents a small fraction of the data obtained during our initial observations conducted in November and December 1989 and January 1990 at the McDonald Observatory. The 1989 observational campaign consisted of low-dispersion imaging spectrograph observations, while the 1990 campaign consisted of direct imaging observations. In this work, we present analysis and modeling of our initial data sets, concentrating on such properties as morphology, abundances, source rates and mechanisms, and spatial asymmetries. In addition, a complete description is given of the observational and data reduction techniques employed in these pilot studies of an extended planetary atmosphere.

Optical observations of Io's neutral clouds and plasma torus

A review of ground-based optical observations of Io's neutral clouds and plasma torus is provided. The physical processes determining the spatial distribution and intensity of torus emissions are described with reference to a model based on Voyager spacecraft data. The model is then compared to ground-based observations. Inconsistencies and variations in torus conditions over long timescales are emphasized. Periodicities in the torus evident in Voyager and ground-based are critically discussed.

Comet Halley remote plasma tail observations and in situ solar wind properties: VEGA- [formula omitted] IMF/plasma observations and ground-based optical observations from 1 December 1985 to 1 May 1986

Properties of the interplanetary magnetic field and solar wind plasma are analysed from continuous observations from 1 December 1985 to 1 May 1986 made by the Vega spacecraft (Riedler et al., 1986, Nature 321, 288; Gringauz et al., 1986, Nature 321, 282). Several high speed streams and flare-related shocks are found; the magnetic field sector boundaries are also seen. Many Earth-based observations of disconnection events in the plasma tail of comet Halley are now available and several mechanisms [changes in the solar wind (Jockers, 1985, Astron. Astrophys. Suppl. Ser. 62, 791; 1986, Asteroids, Comets and Meteors II, Reprocentralen HSC, Uppsala), interplanetary magnetic field features, e.g. day-side reconnection (Niedner and Brandt, 1978, Astrophys. J. 223, 665) or night-side reconnection (Russell et al., 1986, J. geophys. Res. 91, 1417)] have been proposed to explain the occurrence of such events. We investigated the correlation between the IMF sector boundaries measured by Vega and the observed disconnection events; such a correlation would support the day-side reconnection explanation. It is found that only in 50% of the considered events does a correlation between these two phenomena exist. For the other cases, a sector boundary of the IMF sweeping over the comet cannot explain the occurrence of disruptions of the main plasma tail. An indication is also seen that density enhancements (e.g. as they occur for high speed streams) in the solar wind are connected with large tail events.

On the possible bipolar nature of 21 micron IRAS sources

The discovery of another IRAS source (22574 + 6609) showing the unidentified 21-micron emission feature is reported. Its overall energy distribution is similar to the well-known edge-on bipolar nebulae AFGL 2688 and AFGL 618. Ground-based optical and infrared observations of this object and two other 21-micron sources show that while all three have very similar infrared properties, they differ greatly in the visual region. All three of these 21-micron sources are intrinsically similar bipolar nebulae, viewed at different orientations.

Inner corona from solar radio observations

Abstract The solar corona is the region of transfer, transformation, accumulation and release of “nonthermal” energy generated in the subphotospheric levels. These processes are essentially connected with the plasma structures observed in the corona. Radio astronomy methods present an unique opportunity for measuring magnetic fields, particle acceleration, plasma turbulence in the corona as well as such parameters as electron density and temperature accessible also to other techniques. To be effective radio observations need a combination of high spatial resolution with good spectral coverage and accurate polarization measurements as well as plenty of observational time. No one of the existing systems meet all these demands. However, such structures as radio granulation, coronal holes, filaments and their cavities have been studied using such instruments as VLA, WSRT and RATAN-600. Local sources of active regions prove to be very complicated structures due to a number of different mechanisms of generation of the radio emission. Using the radio telescope RATAN-600 a new type of structure - peculiar sources have been found in centimeter wavelength range. They give evidence of stable ( lasting several days ) localized regions of energy release in the lower corona. The mechanism of generation of the radio emission of these peculiar sources as well as of a decimetric halo is still in the stage of discussion. Significant progress is expected as a result of current modificationsof the RATAN-600 solar program. Cooperative programs of ground-based radio and optical observations of plasma structures of the inner corona in combination with space observations in EUV and X-rays are most prominent in resolving the problems above.

The solar activity-oriented Japanese programme

There are two activity-oriented programmes in Japan; i) space programme, and ii) the programme of ground-based optical and radio observations. The space programme is carried out with Solar-A satellite, which will be launched in August/September 1991, and four instruments such as Hard X-ray Telescope (HXT), Soft X-ray Telescope (SXT), Bragg Crystal Spectrometer (BCS), and Wide-Band Spectrometer (WBS) are on board Solar-A satellite. A flare telescope is newly set up at Mitaka in order to observe magnetic field, velocity field, Hα features, and white light images in a flaring region. A radio heliograph is constructing at Nobeyama in order to observe flares at 17GHz with a spatial resolution of 7.3 arc sec × 16.5 arc sec and a time resolution of 50 ms.