bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Short-Term Variability in the X-Ray-Selected BL Lac Object IE 0317+186 and the Radio-Selected BL Lac Object ON231
Authors: Cheng F.Z. , Lu J.F. , Xie G.Z. , Li K.H. , Li Z.L. , Wang L.F.
Published: June 2019

In order to compare X-ray-selected BL Lac objects with radio-selected BL Lac objects, we have carried out optical monitoring of some of these objects for about three years at Yunnan Observatory in China. All observations have been made with a CCD-image system at the f/13.3 Cassegrain focus of the 102-cm RCC telescope. The CCD-image system was developed by Ye et al. in Kitt Peak National Observatory of USA (Ye et al., 1985). The filters used were as follows: B-GG385(2mm)+BG12(1mm)+BG18(1mm), V-GG495(2mm)+BG18(2mm). After observing many times, more complete light curves have obtained for the X-ray-selected BL Lac object IE 0317+186 and the radio-selected BL Lac object ON 231, respectively(Fig 1 and Fig 2). Fig 1 shows that IE 0317+186 has a characteristic timescale of about 4.5hours with an amplitudes of ΔV≃0.65 mag. Fig 2 indicates that a timescale of short-term variability in ON 231 is about 70 min with an amplitudes of ΔB≃0.8 mag.
The Character of the Optical Variability for the BL Lacertae Objects OJ 287
Authors: Miller H. Richard , Carini Michael T.
Published: June 2019

The BL Lacertae objects, OJ 287, has long been known to exhibit large amplitude variations on time scales as short as a few days. The time rate of change in brightness for these variations has been observed to be in excess of 1.0 mag. per day on several occasions. However, the nature of the optical variations on time scales significantly shorter than a day has not been well established, and in many cases the results have been controversial (Carrasco et al, 1985, Lawrence et al 1987, McHardy and Czerny, 1987). In order to address this problem, we have obtained observations of OJ 287 on four different nights during the past two years using the KPNO 0.9 meter telescope equipped with the direct CCD camera. Variations were detected for OJ 287 on each night with ranges of 0.05 mag. to 0.10 mag. The variations detected on 1986 November 9 are typical of those observed on each of the nights and is shown in Figure 1. A power spectrum analysis of the data was performed and no convincing evidence for the presence of any periodicity was found. Based on this analysis, the short term optical variations observed for OJ 287 have a very different character than the rapid x-ray flickering observed for Seyfert galaxies which have been characterized by 1/f - noise. Therefore, these observations would imply sizes for the source region 3 × 10−5 pc. If one assures that the underlying engine is a supermassive blackhole, then the time scales of the variability suggests masses for the blackhole of 107M⊙ – 108M⊙.
The Complex Structure of the CIV Emission Line in the Seyfert 1 Galaxy NGC 4151 at Minimum States
Authors: Ulrich M.-H.
Published: June 2019

NGC 4151 passes rather frequently through states of deep minima characterized by a weak UV continuum and a nearly complete fading of the broad components of CIV and other permitted lines. The phenomenon described in this short article is best observed during these minima [7]. Other properties of the UV and X-ray continuum and of the emission and absorption lines of NGC 4151 have been presented and discussed elsewhere [1–6].
CaII – FeII Correlation in Active Galactic Nuclei
Authors: Joly Monique
Published: June 2019

The presence of Call emission in the red spectra of AGN is now commonly observed. A sample of forty AGN has been surveyed by Persson (1988): fourteen of his objects show a clear emission of the Call triplet at 8498, 8542, 8662A (CaIIT) with a strength correlated with that of the optical Fell emission. The study of the Call triplet puts new constraints to the physical conditions in the low ionisation region of the BLR.
Quasar Emission Line Profile Modelling
Authors: Kallman T. R. , Krolik J. H. , Wilkes B. J.
Published: June 2019

We present fits of models for the C IV λ 1549, N V λ1240 and Lα lines to observed profile data. Since these lines depend sensitively on the cloud ionization parameter (defined as the ratio of the illuminating flux to the cloud pressure; c.f. Krolik, McKee, and Tarter, 1981) and pressure, their relative strengths constrain the distribution of clouds in quasar broad line regions. We make the following assumptions: That the distribution of clouds around the continuum source is spherical and that the cloud motion relative to the continuum source is radial; that the clouds are in pressure equilibrium with hot intercloud medium (ICM) whose mass flux is conserved; and that the line fluxes emitted by the clouds as a consequence of the continuum illumination is given by “standard” (e.g. Kwan and Krolik, 1981) photoionization models. The cloud mass flux is not assumed to be constant, but is allowed to vary with velocity in order to fit the data. For the purposes of illustration, we have chosen a specific dynamical model: isothermal freefall with TICM = 108K. The cloud column density is assumed to be fixed at 1023cm−2.
Observations of Quasar Broad-Line Profiles in the Optical and Infrared
Authors: Thompson Keith Louis
Published: June 2019

Seven low redshift QSOs have been observed spectroscopically at infrared and optical wavelengths at McDonald Observatory. The two instruments used were the infrared grating spectrometer (IRGS; see Lester, Harvey, and Carr 1988 for a description) on the 2.7m reflector, and the es-2 cassegrain spectrometer on the 2.1m. Table 1 shows the objects and spectra taken.
Is There a Relation Between Optical Emission Line Strengths and Continuum Shapes?
Authors: Wilkes Belinda J. , Elvis Martin , McDowell Jonathan
Published: June 2019

Until recently there have been very few measurements of the ionizing continuum in quasars. With the combination of Einstein X-ray slopes and IUE spectra for a sample of quasars, this continuum can now be better constrained. Here we take a preliminary look for relations between the shape of this continuum and the emission lines produced over the observed range of continuum properties.
A Comparison of the X-ray Spectra of Quasars and BL Lac Objects
Authors: Worrall D. M. , Wilkes B. J.
Published: June 2019

Quasars with similar core-compact radio properties can be classified by their differences at optical and infrared frequencies. Their X-ray properties might be expected to be similar if the synchrotron self-Compton mechanism relates their radio and X-ray emission. We have compared the 0.2–3.5 keV mean power-law energy spectral indices, , for 4 quasar classes: 12 Highly Polarized QSOs (HPQs), 19 Flat Radio Spectrum, core-compact, low-polarization, QSOs (FRS QSOs), 24 radio-selected BL Lac objects, and 7 X-ray-selected BL Lac objects.
A Multi-Wavelength Study of X-ray Selected AGN
Authors: Brissenden R. J. V. , Tuohy I. R. , Bicknell G. V. , Remillard R. A. , Schwartz D. A.
Published: June 2019

A sample of Active Galactic Nuclei (AGN) have been discovered during a program to identify the optical counterparts of X-ray sources detected by the Modulation Collimator experiment of the High Energy Astronomy Observatory-1 (HEAO-1). UV-excess techniques were used to identify the X-ray sources (Remillard et al. 1986) and the details of the identifications are given elsewhere (Remillard et al. 1988, Brissenden et al. 1988). We report here the preliminary results of a multi-wavelength study of these new AGN.
Spectral Index Versus Frequency and Models for the Continua of AGN and QSOs
Authors: Stein Wayne A.
Published: June 2019

The observed spectral index as a function of frequency of QSO continua must be explained in models. It is generally increasing (F(ν) ∝ ν−α, α increasing) with higher frequency in the infrared (downward curvature). The visual to ultraviolet continuum has been shown to be a broken power law with F(ν) ∝ ν−0.5 at low frequency and a break to larger α at νo ∼ 3×1015 Hz. X-ray observations frequently exhibit a flat continuum with α < 1. One prominent example is 3C273 for which α1–3μm → 2, αvis ∼ 0.5 and αx ∼ 0.5. These spectral indices arise naturally in Secondary Electron Synchrotron Self-Compton (SESSC) models. Some accretion disk models approach these spectral indices for the visual-ultraviolet portion of the spectral distribution.
Cosmic X-ray Background from Early Active Galactic Nuclei
Authors: Zdziarski Andrzej A.
Published: June 2019

A model for the origin of the cosmic X-ray background (hereafter XRB) is presented. The component of the background left after subtraction of the known classes of sources is explained by emission from a population of black hole sources at the redshift of z ∼ 4–5. The model is presented in more detail elsewhere (Zdziarski 1988). Here, we summarize its most important results.
Relativistic Neutrons in Active Galactic Nuclei
Authors: Sikora Marek , Rudak Bronisław , Begelman Mitchell
Published: June 2019

A substantial fraction of the radiation from an active galactic nucleus (AGN) is apparently nonthermal in origin, and is probably produced by ultrarelativistic electrons. How much energy goes into relativistic protons is uncertain, but it is likely to be comparable to the electron energy or larger. Indeed, several authors (Sikora et al. 1987; Kazanas and Ellison 1986; Zdziarski 1986) have shown that proton-photon and proton-proton collisions can be efficient sources of relativistic pairs in the central engine of an AGN. Thus it is not necessary for electrons to be accelerated directly in AGNs, provided that protons are accelerated with high enough efficiency.
Revisiting the Geometry of the BLR in AKN120: Preliminary Results from UV Data and Line Profile Analysis
Authors: Alloin D. , Baribaud T. , Boisson C. , Pelat D.
Published: June 2019

From continuum and line intensity light-curves in the ultraviolet range, we find that the CIV peak-emission lies at about 2 ± 0.5 light-month from the centre. Line profile variations in the Ha and CIV emission suggest that the BLR is made of two regions with distinct kinematical properties:

•

a spherically distributed set of clouds, responsible for the broad HIL emission and responding to ionizing flux variations with a time-lag of 2 light-months at most

•

a disc-like structure from which most of the LIL emission arises, with a slow response to ionizing flux changes: hence larger is size.
Is the Lyman Absorption Edge a Good Observational Test for AGN Accretion Disks?
Authors: Sun Wei-Hsin , Malkan Matthew A.
Published: June 2019

Geometrically thin and optically thick accretion disk models which use non-LTE stellar atmospheres predict a Lyman absorption edge near 912Å in the quasar rest frame (Sun and Malkan 1987; Sun 1987). The detailed spectral shapes around the Lyman limit have been calculated for both Kerr and Schwarzschild metrics. The Lyman absorption edge, especially in the (more realistic) Kerr case, is markedly distorted and displaced by the relativistic effects of the strong gravitational field of the black hole and the large Doppler motions of the disk surface. Figure 1 shows a Kerr disk model accreting at 10% of its Eddington luminosity (LEdd), typical for quasars, viewed from five different angles.
Is the Flat Spectrum Double 1830-211 a Result of Gravitational Lensing?
Authors: Swarup G. , Subrahmanyan R. , Narasimha D. , Rao A. P.
Published: June 2019

In this paper we present recent observational data on the flat spectrum double (1 arcsec.) radio source 1830-211 (Rao and Subrahmanyan, 1988, MNRAS, 231, 229) and discuss why gravitational imaging appears to be the most plausible explanation for its unique nature.
Theory of the Intermediate Zone
Authors: Krolik Julian H.
Published: June 2019

The “intermediate zone” is the several decades in radius between the broad and narrow emission line regions in active galactic nuclei. As Antonucci and Miller (1985) first discovered, it comprises two basic structures: an obscuring torus, and a reflection region which fills the hole of the torus and extends some ways above its top. Recent theoretical work, reviewed here, has concentrated on understanding both the thermal/ionization state, and the dynamical state of both regions. The torus is probably composed of a large number of dusty, molecular clouds of large column density and unusually high temperature and ionization fraction, while the reflection region is hot and highly ionized. Spectroscopic diagnostics exist for both. The key problem, still essentially unsolved, in the dynamics of the torus is its geometrical thickness. The reflection region is probably a pressure-driven transonic wind whose source is material evaporated by photoionization from the inner surface of the torus, but a small fraction of it may actually be accreting onto the nucleus.
Near-Infrared Spectroscopy of Seyfert and Starburst Galaxies
Authors: Nishida Minoru , Kawara Kimiaki
Published: June 2019

The Brackett α and γ lines of atomic hydrogen, molecular hydrogen H2 v=1-0 S(1) line and [FeII] 1.644 μm line were observed in type 1 and type 2 Seyferts, LINERS, starburst galaxies, and interacting galaxies. For the observations, the Infrared Spectrometer (IRS) with an array of eight InSb detectors was used on the CTIO 4 m and 1.5 m telescopes. The effective size of the slit is 6.8″x4.3″ on the 4 m and 10.3″x20.7″ on the 1.5 m. The resolution of the IRS was 290 km s−1 at 2 μm.
Red Giant Winds as Emission Line Clouds (Broad or Narrow) in Active Galactic Nuclei
Authors: Kazanas Demosthenes
Published: June 2019

It is proposed that the clouds thought responsible for the line emission in AGN are not of uniform density but stratified. Such a stratification may be a result either of their self-gravity or of gas dynamics associated with each cloud (e.g. winds). To fix ideas we assume the latter possibility, we examine the consequences and compare with the observations and the phenomenology of emission line clouds.(For the general properties of these clouds see review by Netzer in this volume). Given the successes of the standard model the reader may wonder why is there any need for revisions. The reasons are given in detail elsewhere (see also Scoville and Norman this volume). In brief these are the drag of clouds though the confining medium, the excessive accretion rates implied by the standard model, the response of the line radiation to changes in the continuum, and the lack of a dynamical mechanism for cloud formation. Finally, in the “standard” picture the narrow line clouds are a distinct population with separate dynamics and origin.
Photopolarimetry of Seyfert Galaxies - NGC 2992, NGC 3081, NGC 3227 and IC 4329 A
Authors: Joshi U.C. , Jain Rekha , Deshpande M.R.
Published: June 2019

Photopolarimetric observations in UBVRI bands of Seyfert galaxies NGC 2992, NGC 3081, NGC 3227 and IC 4329A were carried between 1984–87. Measurements were made with PRL polarimeter (Deshpande et al. 1985) on 1 meter telescope of Indian Institute of Astrophysics, Kavalur. Method of observations and reduction is same as discussed elsewhere (Joshi et al. 1987).
Polarization of IRAS Quasars and the Inner Structure of Active Galactic Nuclei
Authors: Wills Beverley J. , Wills D. , Evans N. J. , Natta A. , Thompson K. L. , Breger M. , Sitko M. L. , Lester D. F. , Garnett D. R. , Sawyer S. R.
Published: June 2019

We have found that 4 new, bright IRAS quasars, out of 7 observed, have strong, non-variable, wavelength-dependent polarization. Three show degrees of polarization, pλ, increasing from infrared to UV wavelengths (Fig. 1), which implies a combination of a polarized, scattered spectrum and a much redder, unpolarized spectrum. Detailed IR and optical polarimetry and spectrophotometry of one, IRAS 13349+2438 (Wills et al.), shows a polarized flux spectrum, pλxFλ, (continuum and Pa α, Hα, and Hβ broad hydrogen lines) typical of unreddened, luminous quasars. This suggests that the path of scattered light from a central, luminous quasar is low in dust and that the polarization of the scattered spectrum is wavelength independent. The latter is most easily explained by electron scattering although the data do not exclude dust scattering. When this polarized flux spectrum is subtracted from the total spectrum, we are left with a very reddened line and continuum spectrum, E(B-V) = 0.3 to 0.7, which we attribute to the same luminous quasar seen through a thick dusty torus. The angle of polarization is parallel to the major axis of the r-band image, presumed to be that of the host galaxy. If the torus is in the plane of the galaxy, the axial ratio suggests a viewing angle of 40° to the plane of the torus. Fig. 2 illustrates the geometry. The appearance of the quasar at optical and UV wavelengths will depend strongly on viewing angle, suggesting that present samples of quasars selected by colours, optical flux density, or quasi-stellar appearance, may be seriously biased, with important consequences for studies of the space density and evolution of AGN.
A Separation of Systematic and Turbulent Motions in the Narrow-Line Region of NGC 4151
Authors: Schulz Hartmut , Boer Berto
Published: June 2019

Line profiles from the spatially resolved narrow-line region of NGC 4151 are separated into several bulk-motion components which show velocity dispersions two to three times larger than starburst nuclei with similar luminosity. The components are suggested to arise within the galactic disk and by filaments entrained in or situated along the shells of two super-bubbles. The large cone-like SW bubble is able to account for the SW soft-X ray excess and the hole in the NLR disk through which a UV-radiation cone emerges. The bubbles appear to be related to the nuclear radio source.
Hα Emission Lines in High Redshift Quasars
Authors: Espey B.R. , Carswell R.F. , Bailey J.A. , Smith M.G. , Ward M.J.
Published: June 2019

We present new data on the redshifts and Hα profiles of 18 medium to high redshift QSOs observed by us using the FIGS spectrometer at the Anglo-Australian Telescope facility and compare the data to that of the strong UV lines obtained in spectra taken at nearly the same time. We find that the Hα line is redshifted by an average of 1100 km s−1 with respect to CIVλ1549. Low ionization lines, such as OIλ1305 and MgIIλ2798 are shifted by similar amounts. These results are difficult to reconcile with any simple models currently available, including those where dust obscuration is solely responsible for the observed velocity shifts. The similarity between the velocities of Hα and MgII, OI provides some support for models where the Balmer lines are produced predominantly in a warm HI region, perhaps by X-ray heating, while the Lyman lines arise mainly in a population of optically thin clouds. A velocity separation between the two cloud populations, along with some obscuration, could explain the main features. However, detailed differences between lines of similar ionization suggest that the true situation is more complex.

A search for correlations between the velocity shift and other quantities revealed only one, namely with the ratio of the CIII]λ1909 and CIVλ1549 line fluxes. The meaning of this is obscure, but may relate to density or projection effects. A number of other correlations proposed by previous workers as tests for their models were sought but not found.
New Millimetre Measurements and the Radio to X-ray Continua of Active Galactic Nuclei
Authors: Lawrence A.
Published: June 2019

I am one of a large team studying an X-ray flux limited sample of 35 AGN, at radio (Unger et al 1987 MNRAS 228 521), IR (Ward et al 1987 ApJ 315 74 and Carleton et al 1987 ApJ 318 595), optical-UV (Boisson et al in preparation), and X-ray (Turner PhD thesis, Leicester) wavelengths. A gap in the data which we have just started to fill is the millimetre region. (Lawrence, Ward, Elvis, Robson, Smith, Duncan, and Rowan-Robinson). In Jan/Feb 1988 we made measurements of twelve objects at 800 and 1100 micron, using the ROE/QMC bolometer, UKT14, on the new UK/Dutch/Canadian facility on Mauna Kea, the James Clerk Maxwell Telescope, reaching 1 sigma sensitivity of ∼15–20 mJy, an order of magnitude improvement over previous data. The four radio loud objects measured were easily detected, as expected. These all have a strong blazar component, showing smooth but curved spectra over many decades, possibly log-Gaussian in form (Landau et al 1986 ApJ 308 78), or alternatively explicable by a small number of power-law components (Robson et al 1988 MNRAS in press). In any case, other evidence points to non-thermal radiation by a relativistically moving feature (high polarization, strong variability, superluminal motion). Eight radio quiet objects were measured, and upper limits only found, except for a possible four sigma detection of N2992. In all cases, the mm limits are far below the 100 micron IRAS fluxes. In four of the nearest objects, this is not too surprising, as fluxes are rising steeply throughout 12 to 100 micron, a sign that the IRAS data is dominated by cool interstellar dust emission (“cirrus”) from the discs of the parent galaxies. However we can also say that any postulated power law component of spectral index ∼1 dominating the near-IR, must become self-absorbed around ∼200 micron if the mm limits are not to be exceeded. Four rather more interesting objects are shown in Fig. 1. Again, any underlying power-law component must be self-absorbed by ∼100 micron, but is not clear that such a power-law is needed. N5506 and IC4329A have falling optical energy distributions, and large H α/Hβ ratios; on the other hand, the IR continuum lies well above the X-ray level, so there is good argument for absorption and re-radiation by dust. N4151, while flat through the near-IR-optical, has a large hump centred at ∼25 micron. Particularly important here are further new measurements by Engargiola et al (1987, ApJ in press),and Edelson et al (1988, preprint) which show the energy distribution to be falling so steeply from 155 to 438 micron that self-absorbed synchrotron is ruled out in this region. In fact, the whole energy distribution from mm to UV can be modelled without a power law at all, as shown in Fig 2. This uses a starburst component (from Rowan-Robinson and Crawford 1988, MNRAS in press), hot dust represented by three greybodies at 200K, 500K, and 1000K, starlight from a nuclear cusp, and a blackbody at 30,000K. Even MKN590, which at first sight looks like a power-law, can be modelled by similar components (Fig. 3).
Dust-Embedded AGN in Unusually Warm IRAS Galaxies
Authors: Vader J. P. , Frogel J. A. , Gillett F. C. , de Grijp M. H. K.
Published: June 2019

The IRAS Point Source Catalog contains only 61 sources identified as galaxies whose energy distribution peaks at 60 mμ. The scarcity of such galaxies has prompted a search for possible common properties. This sample of ‘60 mμ peakers’, 21 of which are previously identified galaxies, partially overlaps with that of warm IRAS galaxies studied by de Grijp et al. (1987) and contains similar percentages of Seyfert (65%) and starburst galaxies on the one hand, and of strong and weak radio sources on the other hand. A remarkable characteristic is, however, that about half of the 60 mμ peakers seem to be early-type galaxies. The fact that such galaxies are rarely IRAS sources and, if so, have FIR energy distributions peaking at 100 mμ similar to those of spirals, implies that we are sampling active or nuclear starburst early-type galaxies with a very large success rate. The observational data accumulated so far further show that:

(i)

objects with smaller FIR to near-IR flux ratios have redder J-K colors and warmer 60 to 25 mμ colors, i.e., an infared spectrum dominated by warmer dust and/or a nonthermal source (Figs. 1a,b);

(ii)

out of 32 objects with radio data, the 5 compact radio sources with luminosities intermediate between those af radio-quiet and radio-loud AGN have among the warmest 60 to 25 mμ colors (Fig. 2). Such warm FIR colors are not a common characteristic of radio galaxies and quasars (Golombek et al. 1987, Neugebauer et al. 1986).

(iii)

the 60 mμ luminosities range from 109 to 1012 L0, and are largest for Mkn 231, 2306+0505 (Hill et al. 1987) and 2046+1925 (Frogel et al. 1988). The latter 2 objects, along with 0052-7054 (Frogel and Elias 1987) which also belongs to our sample, are Seyfert 2 galaxies with evidence for the presence of a dust-obsured broad line region.
Long-Slit Spectroscopy of IC 5135 and NGC 4388
Authors: Shields Joseph C. , Filippenko Alexei V.
Published: June 2019

The nucleus of the peculiar Sa galaxy IC 5135 has strong emission lines whose relative intensities resemble those of Seyfert 2 galaxies (Phillips, Charles, and Baldwin 1983). However, the galaxy exhibits relative line intensities such as [O III] λ5007/Hβ = 6.5 and He II λ4686/Hβ = 0.17 that are considerably smaller than typical Seyfert 2 values of 11 and 0.3, respectively (Koski 1978). New, high-resolution spectra (FWHM ≈ 2Å) obtained at Las Campanas Observatory reveal that the Hβ emission-line profile actually consists of a relatively strong, narrow component (FWHM ≈ 250 km s−1) superposed on a much weaker, broad base (FWHM ≈ 1000 km s−1; Fig. 1). A similar two-component profile is evident in [O I] λ6300, whose narrow core probably comes from circumnuclear H II regions that produce little [O III] and He II emission. The strong, high-order Balmer absorption lines are consistent with the presence of a young stellar population in the nucleus.
Long Slit CCD Observations of Active and Normal Galaxies
Authors: Carone T. E.
Published: June 2019

Most studies of active galaxies have concentrated on their unresolved nuclear regions because this is where their prodigous energy output originates. With the advent of CCDs, recent work has centered on determining how an AGN affects its host galaxy. To isolate the effect of an AGN on its host galaxy, a comparison between a set of galaxies containing active nuclei and a set of normal galaxies would be useful. In principle, if the active and normal galaxy samples are chosen properly, then any systematic differences found between the two samples in the line emission and/or continuum properties of the host galaxy can be attributed to nuclear activity.
Multicolor Images of a Complete z ∼ 1 Sample of 3CR Galaxies
Authors: Stockton Alan , Lilly Simon J.
Published: June 2019

In order to look at relationships among various optical and radio properties of powerful radio galaxies at high redshifts in a systematic way, we have observed a nearly complete subsample of the Laing et al. (1984; henceforth LRL) revision of the 3CR extragalactic source list. Our sample comprises the 14 radio galaxies in the LRL list with δ < 50° and 0.8 < z < 1.3. We have obtained images of 13 of the 14 galaxies (we are missing 3CR 175.1) in each of three bands. The filters used typically gave ∼ 200 Å (rest-frame) passbands shortward of 3700 Å and longward of 4000 Å (in order to give us a 4000 Å break index), as well as a 50 Å passband centered on the [O II] λ3727 line. The images were obtained with the Galileo/IfA TI 500 × 500 CCD system on the UH 2.2 m and CFHT 3.6 m telescopes on Mauna Kea. Absolute calibrations of the images were based on observations of Gunn-Oke spectrophotometric standard stars through the various filters. The photometry we discuss here used synthetic circular apertures closely matched for each object to those used by Lilly and Longair (1984), who give K magnitudes, at least, and sometimes J and H as well, for all objects in our sample.
Photometric Properties of AGNs from the Absolute Spectrophotometry of De Bruyn and Sargent
Authors: Kalinkov M. , Kuneva I. , Tsvetanov Z. , Filipov L.
Published: June 2019

The absolute spectrophotometry of 66 AGNs (de Bruyn and Sargent, 1978) is used to compute synthetic magnitudes and colors, and K-corrections in the UBV system. In our preliminary contribution (Kalinkov et al., 1988) only some results of (U-B)s and (B-V)s colors were given. Here we use the whole observational data given by de Bruyn and Sargent. Synthetic spectra for 41 Sy1, 7 Sy1.5 and 15 Sy2 galaxies are constructed in relative units, assuming f(λ5470) = 1000. Colors and K-corrections are obtained from the synthetic spectra. The variations with the redshift are presented in the polynomial approximation form X = aizi, i = 0,1,‥, where X = (U-B)ss, (B-V)ss, KB, KV (Table 1). The largest deviation in mag. from the computed curves is denoted by Q. The relations in Table 1 are very good approximations in the corresponding redshift ranges.
On Why We Need a Good Theory of Star Formation
Authors: Lynden-Bell D.
Published: June 2019

In this conference we have had good lead speakers who have produced fine summaries of what has been achieved. Rather than summarise these summaries I have decided to ask how the type of work discussed here will influence the rest of astronomy. By comparing what we now know about star formation with what other parts of astronomy need from us, we shall see what is still needed and put in perspective what has been achieved.
Planetary Searches Using Optical Astrometric Interferometers
Authors: Staelin D. H. , Colavita M. M. , Shao M.
Published: June 2019

Detection of planets by virtue of their gravitational perturbations of nearby visible stars generally requires relative astrometric accuracies of ~ 3 × 10−4 arc sec for Jovian planets and ~ 3 × 10−7 arc sec for terrestrial planets. Two-color optical astrometric interferometers on earth should be capable of ~ 10−4 arc sec rms accuracy for stars brighter than magnitude 7–10, while small one-color space systems should achieve at least ~ 10−5 arc sec. Two-color systems permit correction every few milliseconds for the random wavefront tilt due to atmospheric turbulence; the correction is based on the observed offset between the red and blue fringes, and the known atmospheric dispersion. A 3.4-meter baseline interferometer on Mount Wilson has demonstrated ~ 0.02 arc sec rms fluctuations for 1-second samples.
Titan's Organic Chemistry
Authors: Sagan C. , Thompson W. R. , Khare B. N.
Published: June 2019

Voyager discovered nine simple organic molecules in the atmosphere of Titan. Complex organic solids, called tholins, produced by irradiation of simulated Titanian atmosphere are consistent with measured properties of Titan from ultraviolet to microwave frequencies, and are the likely main constituents of the observed red aerosols. The tholins contain many of the organic building blocks central to life on Earth. At least 100 m and possibly kms thickness of complex organics have been produced on Titan during the age of the solar system, and may exist today as submarine deposits beneath an extensive ocean of simple hydrocarbons.
Universal Protein Ancestors from Hydrogen Cyanide and Water
Authors: Matthews Clifford N.
Published: June 2019

Current research in cosmochemistry shows that crude organic solids of high molecular weight are readily formed in planetary, interplanetary and interstellar environments. What are the components of these intractable materials and how are they connected, if at all, with the beginnings of life? It is proposed here that underlying much of this ubiquitous chemistry is a low energy route leading directly to the synthesis of heteropolypeptides from hydrogen cyanide and water. Evidence from laboratory and extraterrestrial investigations suggests that this hydrogen cyanide polymerization is a truly universal process that accounts not only for the past synthesis of protein ancestors on Earth but also for reactions proceeding elsewhere today within our solar system, on planetary bodies around other stars and in the dusty molecular clouds of spiral galaxies. The existence of this preferred pathway adds greatly to the probability of life being widespread in the universe.
The Universal Diagrams and Life in the Universe
Authors: Kafatos M.
Published: June 2019

In any statement concerning extraterrestrial life one has to present the best amount of information concerning life as we know it here on earth. One way to do this is to put many classes of known objects in the universe on common plots. I call these plots the “Universal Diagrams”. The quantities plotted are mass, luminous output, temperature, size and entropy change. It is interesting to speculate where etraterrestrial life may lie on these diagrams but it seems that it will have to lie in regions more or less occupied by terrestrial life.
SETI: The Microwave Search Problem and the Targeted Search Approach
Authors: Seeger Charles L. , Wolfe John H.
Published: June 2019

The targeted search component of the NASA SETI program is limited to time sharing in the usual fashion on existing large radio telescopes. Unless the consequences of this restriction are compensated by increased capability in the SETI electronic systems, an undesirable loss in sensitivity must be accepted in order to prevent a more costly and humanly unattractive lengthening of the projected five-year observing program to a duration of some decades.
Exponential Expansion: Galactic Destiny or Technological Hubris?
Authors: Finney B. R.
Published: June 2019

Is it our destiny to expand exponentially to populate the galaxy, or is such a vision but an extreme example of technological hubris? The overall record of human evolution and dispersion over the Earth can be cited to support the view that we are a uniquely expansionary and technological animal bound for the stars, yet an examination of the fate of individual migrations and exploratory initiatives raises doubts. Although it may be in keeping with our hubristic nature to predict ultimate galactic expansion, there is no way to specify how far expansionary urges may drive our spacefaring descendants.
Where Are They? Implications of Ancient and Future Migrations
Authors: Jones Eric M.
Published: June 2019

Some of my more strident space-enthusiast friends wear T-shirts that say, “The meek shall inherit the Earth…the rest of us are going to the stars!” That may strike some as being overly optimistic at best, but I believe there is a grain of truth to it. Whenever I talk about space colonization or one-way voyages to the stars someone usually asks, “Who would want to go?” Usually someone else will the chime in, “I'll go!” Not only do people come in various sizes and shapes and colors, they look at the world in many different ways. I grew up in the suburbs of New York and knew people who had literally never been west of the Hudson River and had no intention of ever going. New York was comfortable. There is nothing wrong with that attitude. It is just that for many people such a life is not right for them. I went west as soon as I had the chance. I do not regret having left and am much more comfortable where I am now. As I have gotten older, I have found myself settling in and, although I like to travel, I am beginning to understand how those sedentary New Yorkers felt. The only difference is that I settled down a little later in life and in a different place from where I started. But some people never lose that need for adventure, that wanderlust, that need for a radical change, and new places. These are the people who will blaze the trail to the stars.
Dynamical Modeling of M13 Proper Motions
Authors: Cudworth Kyle , Lin D.N.C. , Oh Kap-Soo
Published: June 2019

Proper motion data of M13 cluster members are very useful for the investigation of the cluster's internal dynamics. We introduce a maximum likelihood method to fit these data in terms of conventional King-Michie models.
Observed Dynamical Parameters of Star Clusters in the SMC
Authors: Kontizas E. , Kontizas M.
Published: June 2019

The dynamical study of the SMC clusters is very important for many reasons. (a) The disk “blue” clusters are more massive and older than the galactic open clusters whereas the “halo” red clusters are less massive and younger than the galactic globulars (Kontizas, Danezis, Kontizas, 1982; Kontizas and Kontizas, 1983). (b) All clusters show density profiles that fit the available theoretical models (King, 1962) giving evidence of relaxed systems, even for the young clusters with evolutionary ages 106−108yr. The relaxation mechanism has to be reconsidered for the SMC and possibly in connection to the metal abundance. (c) The ellipticities of young and old SMC clusters have shown that there is no obvious age-ellipticity dependance and that the SMC clusters are statistically more elliptical than the clusters of the LMC and our Galaxy (Frenk and Fall, 1982, Kontizas et al, 1984).
Precollapse Evolution of Globular Clusters
Authors: Spitzer Lyman
Published: June 2019

The dynamical evolution of a cluster in which N, the number of stars, is large, results primarily from encounters between pairs of stars; these tend to modify the system so that it approaches a more probable configuration. In statistical equilibrium, the distribution of stars among states of different energy, Ei, per unit mass would be determined to a first approximation by the probability Pi, where

here giis the statistical weight of each state, proportional to the amount of phase space available, and B is a constant. Evidently dynamical evolution tends a) towards stellar states which are more tightly bound by their mutual gravitational attraction and have a correspondingly lower Ei, and b) towards the free state, where the volume of available phase space is very large. The only relatively stable state for an isolated cluster is one in which a central, non-evolving massive configuration (a compact object, or tight binary, or a hierarchical multiple system) has all the initial binding energy of the cluster and all other stars have escaped.
Black-Hole Remnants in Globular Clusters
Authors: Larson Richard B.
Published: June 2019

Many presentations at this meeting have discussed the phenomenon of “core collapse”, and it seems agreed that a stellar system like a globular cluster will, within a few half-mass relaxation times, undergo a runaway increase in central density and achieve a nearly singular density distribution with a logarithmic gradient slightly steeper than −2. The collapse is halted by the formation of binaries when the core has shrunk to contain only a small number of stars, and the system subsequently expands gradually while maintaining a density profile approximating that of a singular isothermal sphere. Light profiles resembling the predicted nearly singular form have been found in a small number of globular clusters (Djorgovski, this meeting), but a puzzle remains in that many more clusters should have undergone core collapse, yet they show quite flat light profiles in their cores.
The Dynamical Evolution of Young Open Clusters
Authors: Margulis Michael , Lada Charles J. , Dearborn David
Published: June 2019

Using numerical N-body calculations we have simulated the dynamical evolution of young clusters as they emerge from molecular clouds. Starting with initially virialized systems of stars and gas we follow the evolution of these systems from the time immediately after the stars have formed in a cloud until a time long after all the residual star-forming gas has been dispersed. In the models stellar systems were composed of 50, and in some cases 100, stars and these stars were represented as point masses. The stellar mass function followed a power law with an index of −2.5 and ranged over two decades in mass (Scalo 1978). Gas in the models was represented as an extra term in the gravitational potential function governing stellar motions, and was set to follow a density distribution corresponding to a spherically symmetric Plummer potential function (Plummer 1911). Starting with these initial conditions, stellar motions were then integrated and evolution of each stellar system was followed as gas was dispersed from the vicinity of the stars as a function of time.
Most Probable Phase Distribution in Spherical Star Systems and Conditions for Its Existence
Authors: Antonov V. A.
Published: June 2019

The initial stages of the evolution of a spherical star system can be pictured in the following way. The stars have their beginning in a comparatively small region; the mechanism of the origin of initial velocities is not known exactly. From the point of view of the contemporary state of stellar astronomy, it is an acceptable view that the initial velocities have their origin in the attraction of each individual star towards the center of gravity of the system. The second possible assumption is to attribute the origin of initial velocities to forces of an explosive character. But in either case, initially, all orbits have to be almost exactly radial.
Present problems in relativistic Celestial Mechanics
Authors: Brumberg V. A.
Published: June 2019

Review of the present problems of relativistic celestial mechanics. Advantage is taken of the method suggested earlier by the author and based on using quasi-Galilean coordinates with arbitrary coordinate functions or parameters. As compared with the previous papers the new elements are post-post-Newtonian approximation for the circular motion in the Schwarzschild problem and reduction of the artificial satellite problem including the main solar perturbations to the Schwarzschild problem. Some current questions of time scales definitions, reference frames and reduction of observations are briefly discussed.
Simulation of general relativistic corrections in long term numerical integrations of planetary orbits
Authors: Nobili Anna M. , Roxburgh Ian W.
Published: June 2019

Long term numerical integrations of planetary orbits designed to study the stability of the Solar System over timescales comparable to its age have become very promising thanks to the availability of very powerful computers and to a substantial improvement in our methods of investigating the stability of hierarchical dynamical systems. The stability of such numerical integrations relies on the ability to control all possible sources of error. Among the errors caused by the inadequacy of the physical model are those due to the fact that Newton's theory of gravitation is used instead of general relativity. We show that the secular advance of perihelia predicted by general relativity can be simulated exactly by a 1/r2 perturbing potential with almost negligible additional cost in computer time.
Libration of the Moon: shape of the Earth and motion of the ecliptic plane
Authors: Moons M.
Published: June 2019

Very accurate theories of the libration of the Moon have been recently built by Migus (1980), Eckhardt (1981, 1982) and Moons (1982, 1984). All of them take into account the perturbation due to the Earth and the Sun on the motion of a rigid Moon about its center of mass. Additional perturbations (influence of the planets, shape of the Earth, elasticity of the Moon, …) are also often included.

We present here the perturbations due to the shape of the Earth and the motion of the ecliptic plane on our theory which already contains planetary perturbations. This theory is completely analytical with respect to the harmonic coefficients of the lunar gravity field which is expanded in spherical harmonics up to the fourth order. The ELP 2000 solution (Chapront and Chapront-Touzé, 1983) supplies us with the motion of the center of mass of the Moon.
Relativistic effects in geodetic VLBI measurements
Authors: Soffel M. , Ruder H. , Schneider M. , Campbell J. , Schuh H.
Published: June 2019

The various relativistic effects occuring in VLBI measurements are discussed. A concrete example showing the influence of the gravitational delay due to the Sun upon the delay residuals from fit in a Mark III geodetic VLBI experiment is given. It is argued that regular geodetic VLBI observations might provide the best test of Einstein's theory of gravity on the post-Newtonian level in the near future.
Coordinate time in the vicinity of the Earth
Authors: Allan D. W. , Ashby N.
Published: June 2019

Atomic clock accuracies continue to improve rapidly, requiring the inclusion of general relativity for unambiguous time and frequency clock comparisons. Atomic clocks are now placed on space vehicles and there are many new applications of time and frequency metrology. This paper addresses theoretical and practical limitations in the accuracy of atomic clock comparisons arising from relativity, and demonstrates that accuracies of time and frequency comparison can approach a few picoseconds and a few parts in 1016, respectively.
General Relativity confronts experiment
Authors: Will Clifford M.
Published: June 2019

We review the status of experimental tests of general relativity. These include tests of the Einstein Equivalence Principle, which requires that gravitation be described by a curved-spacetime, “metric” theory of gravity. General relativity is consistent with all tests to date, including the “classical tests”: light deflection using radio interferometers, radar time delay using Viking Mars landers, and the perihelion shift of Mercury; and tests of the strong equivalence principle, such as lunar laser ranging tests of the “Nordtvedt effect”, and tests for variations in G. We also review ten years of observations of the Binary Pulsar, in which the first evidence for gravitational radiation has been found.
Prospects for observations of relativistic effects in the solar system
Authors: Reasenberg R. D. , Shapiro I. I.
Published: June 2019

The solar system is the traditional laboratory for testing theories of gravitation. The results of all tests are consistent with the predictions of general relativity. The differences between these predictions and those of Newton's theory of gravitation have been confirmed with uncertainties as small as one part in a thousand. To enhance significantly the accuracy of such tests, one must investigate novel techniques. In this paper we concentrate on an experiment that promises a dramatic improvement in a classical test of general relativity – the deflection of light by solar gravity. The goal is to measure the post-post-Newtonian contribution of nearly 11 microarcseconds to this deflection. The technique we propose is based on use of an astrometric optical interferometer, POINTS, which could be operated from the bay of the Space Shuttle, mounted on the proposed Space Station, or supported by an independent spacecraft. POINTS should be able to measure the separation of stars about 90° apart with an uncertainty of only a few microarcseconds.
New relativistic effects in the motion of the Moon
Authors: Mashhoon Bahram
Published: June 2019

A summary of the main relativistic effects in the motion of the Moon is presented. The results are based on the application of a novel approach to the restricted three-body problem in general relativity to the lunar motion. It is shown that the rotation of the Sun causes a secular acceleration in the relative Earth-Moon motion. This might appear to be due to a temporal “variation” of the gravitational constant.
Evidence for Dark Matter in Galactic Systems
Authors: Davis Marc
Published: June 2019

The evidence for dark matter in binaries and groups of galaxies is very strong, and is seen in all recent observational studies. Measurements of mass in galactic systems is possible on scales ranging from 50 kpc using virial analysis of binary galaxies to 15 Mpc using Virgocentric infall analysis. The Ω estimates derived from these studies are generally consistent with Ω < 0.2, with a fairly weak trend toward larger Ω estimates on larger scales. However, measurements of the galaxy distribution in the IRAS catalog yields a dipole anisotropy consistent in direction with the microwave dipole anisotropy, suggesting that the local galaxy distribution is responsible for the microwave velocity. This will eventually provide the most reliable estimate of Ω, and is likely to result in a value somewhat larger than previous estimates on smaller scales. Study of the velocity field around large clusters in cosmological n-body experiments provides a useful guide for understanding the limitations of the spherically symmetric models of Virgocentric infall. We point out a number of biases that could affect the existing Virgocentric flow studies.