bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Hα Image of Nova V1500 Cygni Twelve Years After Outburst
Authors: Wade Richard A. , Ciardullo R. , DeVeny J.B. , Jacoby G.H. , Schoening W.E. 
Published: July 2016

We obtained a narrow band Hα image of V1500 Cyg during an engineering run at the R-C focus of the KPNO 4 m telescope on UT 1987 July 19. Our detector was an 800 × 800 format TI CCD, which yielded a plate scale of 0.1013 arcsec/pixel. The exposure was 2000 sec and was made through a 75 Å wide filter centered at 6563 Å. The seeing was ~ 1.2 arcsec.Our reductions were accomplished with the DAOPHOT photometry package (Stetson 1987) and IRAF data reduction facility. After performing standard bias level subtraction and flat field division, we used DAOPHOT to find the frame’s normalized point spread function (PSF) by summing the images of several field stars. We then scaled the PSF to calculate the instrumental magnitudes of the stars and of V1500 Cyg. This procedure overestimates the brightness of the nova, since the nebula contributes extra light to the central object and modifies the expected intensity distribution. (This is especially true in the narrow Hα bandpass.) Hence, in a frame where the PSF has been used to remove the fitted images, all the stars have satisfactorily small residuals around the mean sky level, except the nova itself. The image of V1500 Cyg shows sky level at the center, but a halo that rises from the center and then falls away.
Ultraviolet spectroscopy of the shell of RR Pic
Authors: Duerbeck H. W. , Seitter W. C. , Bode M. F. , Evans A. 
Published: July 2016

Spectroscopy of the nebular (as opposed to the stellar) remnants of old novae can be a powerful diagnostic of physical conditions in, and mode of excitation of, nova shells. While optical spectroscopy of nova shells has been widely used in this way, few are sufficiently well resolved, and sufficiently bright, to be observed with IUE.Combined optical and ultraviolet spectroscopy of only two nova remnants–those of GK Per and DQ Her–have been reported to date. Ferland et al. (1984) demonstrated that the shell of DQ Her is extremely cool (Te ≃ 500 K) and is excited by a hot central source. Bode et al. (1988) showed that the ultraviolet and optical lines in the spectrum of the GK Per nebula can best be understood in terms of shock excitation, consistent with its observed properties at radio wavelengths (Seaquist et al. 1989).
The Ionization of Novae Ejecta
Authors: Williams R.E. 
Published: July 2016

AbstractNovae ejecta pass through four distinct phases of evolution of the emission-line spectrum, caused by different ionization characteristics of the shell. These include a neutral (I), an auroral (II), a coronal (III), and a nebular (IV) phase. Photoionization from the contracting photosphere of the hot white dwarf is the source of the ionization, including the highly ionized coronal phase. Changing emission line ratios in certain novae that develop dust are caused by condensation of grains from the gas, and can be used to determine the composition of the dust. In V1370 Aql, substantial silicate grain formation appears to have taken place, probably within the ionized gas.
Winds from Disks
Authors: Drew J.E. 
Published: July 2016

The disks referred to in the title of this paper are specifically those present in cataclysmic variables in which the accreting white dwarf has a relatively weak magnetic field (≪ 1 MG). Such systems are classified either as nova-like variables or as dwarf novae, and are of interest here because they are believed to be novae in quiescence (Ritter and Livio discuss this point elsewhere in this volume).This review aims to do two things: i) to summarise what has been learned about the winds associated with non-magnetic cataclysmic variables both from observation and from numerical modelling, and ii) to outline ideas about the nature of the mass loss mechanism. By contrast with the certainty that nova outflows are the consequence of thermonuclear runaway, it shall be seen that the fundamental cause of mass loss from cataclysmic variables remains obscure. An earlier review of this subject is by Cordova and Howarth (1986). Also of interest are some sections of the monograph on dwarf novae and nova-like variables by LaDous (1989).
Ionization and temperature structure in nova shells
Authors: Beck H. , Gail H.-P. , Gass H. , Sedlmayr E. 
Published: July 2016

AbstractIt is well known from observations that some novae show infrared continuum excesses indicating dust heating by the strong ultraviolet radiation field. It seems, however, that dust formation in nova shells depends on some yet unknown intrinsic parameters since the characteristic infrared excesses are not observed in all objects. To study the conditions under which dust nucleation may occur in nova shells, as a first step we investigate the time dependend ionization and temperature structure.
The Cyclic Evolution of Classical Novae
Authors: Prialnik Dina 
Published: July 2016

The cyclic evolution of classical novae (CN) cannot be observed, as in the case of recurrent or dwarf novae. The duration of a typical cycle may range from a few thousand to a few 105 years. Thus we have to rely on theoretical studies for understanding the periodic outbursts — due to thermonuclear runaways (TNR) — on the surface of accreting white dwarfs (WD). One may distinguish between two kinds of studies: a) detailed investigations of a specific aspect or a particular evolutionary phase; b) studies which emphasize the cyclic behavior of novae and their long-term evolution. The latter, which form the subject of this brief review, may be divided into four groups, each adopting a different approach to the problem:1.Steady-state (semi-analytic) solutions;2.One- (or two-) zone models;3.Quasi-static (and/or steady burning) numerical calculations;4.Full-scale hydrodynamic evolutionary computations.
The Symbiotic Novae
Authors: Viotti R. 
Published: July 2016

AbstractSymbiotic Novae are composite spectrum variables, whose light history is characterized by a single nova-like outburst. Their behaviour and time evolution is rather similar to that of classical novae, except for the much longer time scale, and the associated physics could be the same. We give an overview of the basic characteristics of the symbiotic novae, and their time behaviour in different frequencies. We find that the observed amplitude of outburst is mostly determined by the red star visual luminosity. The actual luminosity increase of the compact object might be much larger than that observed, and closer to that of classical novae. In some systems, the red star luminosity is possibly weakened by circumstellar dust. In symbiotic novae accretion should occur from the red star wind. Although the actual value of the accretion rate is still uncertain, thermonuclear runaway seems to better describe the symbiotic novae phenomenon. But new observational and theoretical work is needed.
High Resolution Spectroscopy of Symbiotic Stars
Authors: Schwarz Hugo E. , Duerbeck Hilmar W. , Seitter Waltraut C. 
Published: July 2016

A high resolution spectroscopy survey of symbiotic stars is conducted in the southern hemisphere by the authors, using the Coudé Echelle Spectrograph (CES), equipped with a CCD at the ESO Coudé Auxiliary Telescope (CAT), and concurrently in the northern hemisphere by Bode, Evans, Meaburn and collaborators, using the UK facilities at La Palma. So far, more than 400 spectra of about 70 stars have been obtained, mostly during 1988 and 1989. The southern part of the work will be described below.The discussion of symbiotic stars in the context of novae is not far-fetched. A number of symbiotics are known to have nova-like outbursts, and several novae are not easily distinguished from symbiotic stars. A noteworthy example is the most recently recognized recurrent nova, V745 Sco, first observed by Liller on July 24, 1989. It is described here, both because in late decline it represents a link between novae and symbiotic stars, and because of its current interest.
Disk Structure in U Geminorum
Authors: Madej J. , Paczyński B. 
Published: July 2016

AbstractA hot spot at the outer rim of the accretion disk dominates the light of U Geminorum at minimum light. We take this as evidence that there is no accretion from the disk onto the white dwarf between the eruptions, and we assume there is no viscosity in the disk at that time. The hot spot is produced by dissipation of the radial component of velocity of stream falling from the inner Lagrangian point. Angular momentum per unit massis smaller in the stream than it is in the outer parts of the disk. This leads to angular momentum redistribution in the outer part of the disk. The difference of tangential velocity between the stream and the disk is dissipated in few orbital periods. These processes make the outer parts of the disk look like a torus. We calculated the structure of the torus in U Geminorum between the eruptions and we obtained the following oarameters: mass of the torus: 10-9 - 10-8 M⊙ (assumed), its optical thickness: 106, the large radius (i.e. the radius of the disk): 0.5 R⊙ (assumed), the small radius (i.e. the half thickness of the outer parts of the disk): 0.05 R⊙. Conditions at the surface of the torus are similar as on the solar surface.
The Evolution of a Slow Nova Model with a Z = .03 Envelope from Pre-explosion to Extinction
Authors: Prialnik D. , Shara M.M. , Shaviv G. 
Published: July 2016

AbstractA model for slow nova explosions is presented. The model consists of a 0.8 Mθ C/0 core and an envelope of 10−4 Mθ with solar composition. The envelope is assumed to have been accreted from a companion. The nuclear runaway produces luminosity close to the Eddington luminosity; this ejects 95% of the envelope. We findICNO equilibrium burning on a timescale of 105.5 seconds produces enough energy for mass ejection.IIThe rise in luminosity stops close to the Eddington limit and the outer envelope layers accelerate via the continuous action of radiation pressure.IIIThe mass outflow has two phases: a gentle outflow at the beginning and then a rapid outflow. In both phases we find ṁ ⋍ const., or equivalently, steady state outflow.IVThe nova’s “shut-off” mechanism is the exhaustion of the envelope’s mass. In this “slow nova” model it took about 200 days for 95% of the envelope to be ejected and to leave behing a hot white dwarf.VThe isotope ratios C12/C13, N14/N15 and O16/O17 are in good agreement with observations.VIThe behaviour of LBOL(t) agrees well with observations. Several additional consequences are discussed.
Mass Loss and Cepheid Pulsation
Authors: Davis Cecil G. 
Published: July 2016

AbstractThis paper serves two purposes: 1) to discuss the latest improvements in nonlinear pulsation theory indicating the ability to resolve features such as the “Christy bump” on the light curves and 2) to show from the results of a bump model and recent observations that mass loss is one of the possible explanations for the mass discrepancy problem between evolutionary and pulsation theories. Recent observations by Sanford and Gow of Los Alamos and Bernat (McDonald Observatory) show that extensive mass loss has occurred in the evolution of the M supergiant α Orionis.
The Interstellar and Circumstellar Environment of White Dwarfs
Authors: Barstow M.A. , Dobbie P.D. , Holberg J.B. 
Published: July 2016

AbstractWe have studied the EUV spectra of 13 DA white dwarfs, observed by the EUVE satellite, paying attention to the possible sources of absorbing material along the lines-of-sight in both the local interstellar medium and in the photospheres of the stars themselves. The range of interstellar column densities seen are consistent with our previous understanding of the local distribution of material. Absorption from interstellar He II is found in the direction of five stars, allowing us to measure directly the He ionization fraction and estimate, indirectly, that of H. The weighted mean ionization fractions along these lines-of-sight are 0.27 ± 0.04 and 0.35 ± 0.1 respectively. Where He II is directly detected, the observed ionization fractions are not correlated with direction or with the volume/column density of material along the line-of-sight. Furthermore, the limits on the amount of He II established in all other directions completely encompass the range of observed values. Indeed, all the data can be consistent with more or less constant He and H ionization fractions throughout the local ISM. However, observation of very hot DA stars, indicating higher He II columns, might contradict this picture if the material is not photospheric or circumstellar.
The Soft X-ray Background Spectrum from DXS
Authors: Sanders W.T. , Edgar R.J. , Liedahl D.A. , Morgenthaler J.P. 
Published: July 2016

AbstractThe Diffuse X-ray Spectrometer (DXS) obtained spectra of the low energy X-ray (44 – 83 Å) diffuse background near the galactic plane from galactic longitudes 150° ≲ l ≲ 300° with ≲ 3 Å spectral resolution and ~ 15° angular resolution. Thus, DXS measured X-ray spectra that arise almost entirely from within the Local Bubble. The DXS spectra show emission lines and emission-line blends, indicating that the source of the X-ray emission is thermal – hot plasma in the Local Bubble. The measured spectra are not consistent with those predicted by standard coronal models, either with solar abundances or depleted abundances, over the temperature range 105 – 107 K. The measured spectra are also inconsistent with the predictions of various non-equilibrium models. A nearly acceptable fit to DXS spectra can be achieved using a hybrid model that combines the Raymond & Smith ionization balance calculation with recently calculated (by DAL) ionic emission lines.
Planned Observations of Hot Gas in the LISM
Authors: McLean R. , Green J.C. , Gunderson K.S. 
Published: July 2016

AbstractWe plan to observe hot gas in the local interstellar medium (LISM) at high resolution using a rocket-borne spectrograph that can simultaneously observe OVI, NV and CIV at resolutions of 1 – 2kms−1. Data from a single flight will have sufficient signal to noise ratio to detect a broad 50kms−1 component down to a column density of N ≥ 0.5 × 1013cm−2. High-velocity components as fast as 300kms−1 can be detected. New high resolution observations of hot gas absorption line profiles will probe the kinematics of the local bubble, and comparison between the carbon, nitrogen and oxygen profiles will allow discrimination between the various production models.
Interstellar C IV and Si IV in the Direction of Loop I
Authors: Freire Ferrero Rubens 
Published: July 2016

AbstractNearby late-B and early-A stars show clear IS absorptions in Mg II, C II and other lines (IUE spectra). Some of them, in the Sco Cen direction, also show absorption features at C IV and Si IV line wavelengths. We discuss the possible formation of these lines in an intermediate temperature gas region between the dense and cold H I wall and the hot ISM, a region that could be the collision interaction between the Local Bubble and the Loop I supershell. Some individual stellar spectra are presented and discussed.
A New View of the LHB and ¼ keV X-ray Halo
Authors: Snowden S.L. 
Published: July 2016

AbstractThe X-ray sky at ¼ keV is completely dominated by diffuse emission. It has become clear that it originates as at least three separate components: local emission within the nearest ~ 100 pc from the Sun, halo emission from beyond most of the neutral material of the Galactic disk, and the superposition of unresolved extragalactic sources. The only way to determine the temperatures and relative emission measures of the hot plasma responsible for the Galactic components is to use the X-ray intensity variations due to column density variations in the intervening Hi to separate the components. “Shadowing” studies have been pursued for individual objects using ROSAT data, from both pointed observations and the all-sky survey with considerable success.This paper presents the results of an all-sky analysis of the ¼ keV background from the ROSAT survey. A Local Hot Bubble is found consistent with, although somewhat smaller than, previous models. It has a temperature of 106.1 K and an emission measure which varies by a factor of ~ 3.3 over large angles. The halo emission has a temperature near 106.0 K with an emission measure which varies from near zero to more than five times that of the local emission.
ISOPHOT Observations of a Cold Filament in the Local Hot Bubble
Authors: Herbstmeier Uwe , Alexandre Wennmacher  
Published: July 2016

AbstractWe report on FIR measurements of the dust component towards LVC 88+36–2, a dense neutral filament in the Local Hot Bubble. The measurements were performed with ISOPHOT, the photometer on-board ESA’s Infrared Space Observatory ISO. The dust temperature derived is about 18 K and stays constant across the filament. Limb brightening at 60μm is measured in agreement with cirrus clouds not located in the Local Hot Bubble. No evidence for an increased UV radiation field along the boundaries of the cloud is found.
Interaction of Interstellar Shocks with Dense Obstacles: Formation of “Bullets”
Authors: Gvaramadze V.V. 
Published: July 2016

AbstractThe so-called cumulative effect take place in converging conical shock waves arising behind dense obstacles overtaken by incident interstellar shock. A significant part of energy of converging flow of matter swept-up by a radiative conical shock can be transferred to a dense jet-like ejection (“bullet”) directed along the cone axis. Possible applications of this effect for star-forming regions (e.g., OMC-1) and supernova remnants (e.g., Vela SNR) are discussed.
The Line of Sight of ϵ Canis Majoris: Depletion and Extent of the Local Cloud
Authors: Gry Cécile , Dupin Olivier 
Published: July 2016

AbstractWith new high resolution UV spectra of ϵ CMa we show that the gas column density in this sight-line is less than 4 1017 cm−2, that the neutral gas density is less than 10−5 cm−3 after the first 3 parsecs, and that the Local Cloud seems to be almost undepleted and to extend to no more than 0.6 pc in this direction.
The Magnetic Field Near the Local Bubble
Authors: Heiles Carl 
Published: July 2016

AbstractThere are almost no direct observational indicators of the magnetic field inside the local bubble. Just outside the bubble, the best tracers are stellar polarization and HI Zeeman splitting. These show that the local field does not follow the large-scale Galactic field. Here we discuss whether the deformation of the large-scale field by the local HI shells is consistent with the observations. We concentrate on the Loop 1 region, and find that the field lines are well-explained by this idea; in addition, the bright radio filaments of Radio Loop 1 delineate particular field lines that are “lit up” by an excess of relativistic electrons.
Measurements of the Size and Pressure of the Local Bubble Towards Eridanus
Authors: Burrows D.N. , Guo Z. 
Published: July 2016

AbstractWe have measured the size and pressure of the Local Bubble in the direction of the constellation Eridanus using ROSAT PSPC observations of soft X-ray “shadows” cast by neutral clouds against the bright X-ray emission from the Orion-Eridanus superbubble. We discuss the technique and present our results for the size of the Local Bubble in the directions of our shadowing fields. Using these distances and the measured soft X-ray emission measures, we derive the Local Bubble’s thermal pressure. For four lines of sight in Eridanus, we obtain pressures of about 1.2 × 104 K cm−3, in good agreement with measurements in several other directions.
Interaction of the Local Bubble with its environment
Authors: Egger Roland 
Published: July 2016

AbstractThe Local Bubble (LB), a volume of roughly 100 pc radius filled with ionized gas of high temperature and low density, is not a unique object. It is obviously surrounded by several interstellar bubbles of similar properties. Some of them are as close as to undergo interaction with the LB. Our most prominent neighbour is the Loop I superbubble formed by the Sco-Cen OB association. It is shown that this huge shell is in collision with our Local Bubble. The product of this interaction is an annular cloud of dense neutral gas at the boundary between the two bubbles. Other examples for close neighbouring bubbles are the Gum nebula, the Eridanus bubble and possibly the two radio loops II and III.
ASCA SIS X-ray Observations of the Wind Blown Bubble NGC 6888
Authors: Wrigge Matthias , Chu You-Hua , Magnier Eugene A. , Kamata Yuichi 
Published: July 2016

AbstractWe present ASCA SIS observations of the wind-blown bubble NGC 6888. Because the ASCA SIS is sensitive to higher energy photons and has a higher spectral resolution compared to the ROSAT PSPC, we are able to detect a T ≈ 8×106 K plasma component besides the T ≈ 1.5×106 K component known from previous PSPC observations. The existence of a high-temperature component, the observed limb-brightened X-ray surface brightness profile, and the observed level of X-ray surface brightness cannot be satisfactorily explained by currently available models. Reducing heat conduction at the contact discontinuity may raise the central temperature and produce a limb-brightening; however, the expected X-ray surface brightness is still considerably higher than the observed surface brightness.
The Galactic HI Halo
Authors: Kalberla P.M.W. , Westphalen G. , Mebold U. , Hartmann D. , Burton W.B. 
Published: July 2016

AbstractWe find indications for diffuse HI gas at substantial z heights in our Galaxy, with a velocity dispersion of 60 km s−1 and a vertical projected column density of 1.41019 cm−2. This pervasive component of the emission spectrum could be identified in the Leiden/Dwingeloo 21 cm Survey (LDS) after increasing the accuracy further by correcting the observations for reflections from ground. Assuming hydrostatic equilibrium an exponential scale height of 4.4 kpc for the observed diffuse high-dispersion Hi component is deduced. This differs from the scale height of lkpc derived by Lockman & Gehman (1991), which corresponds to a velocity dispersion of 34kms−1, based on an analysis of the the Bell Laboratories HI Survey (BLS). A comparison of BLS and LDS data explains the differences in the derived model parameters in terms of baseline uncertainties at a level of ≈ 30 mK. We find additional indications for baseline uncertainties in the BLS data. Concerning the LDS we cannot, however, exclude that this survey may also be affected by baseline uncertainties. Receiver bandpass and stray-radiation effects need a more thorough analysis before drawing firm conclusions.
3D Hydrodynamical Simulations of a Galactic Fountain
Authors: de Avillez M.A. , Berry D.L. , Kahn F.D. 
Published: July 2016

AbstractGalactic fountains are thought to be responsible for the formation of the observed intermediate and high velocity clouds in the Galactic halo. Threedimensional simulations have been carried out to determine the evolution of the disk gas as it enters the fountain, cools and returns to the Galactic disk. The descending cold gas, headed by a shock, sweeps up the ascending flow, triggering the formation of an unstable layer where Rayleigh-Taylor instabilities grow, which may provoke the formation of the observed clouds.