scholarly journals Cataclysmic Variables, Hubble-Sandage Variables and η Carinae

1980 ◽  
Vol 88 ◽  
pp. 155-160
Author(s):  
G. T. Bath
Keyword(s):  
Cataclysmic Variables ◽  
Emission Lines ◽  
Quiescent State ◽  
High Luminosity ◽  
Dwarf Novae ◽  
Blue Colour ◽  
External Galaxies ◽  
Distance Indicators ◽  
Colour Indices

The Hubble-Sandage variables are the most luminous stars in external galaxies. They were first investigated by Hubble and Sandage (1953) for use as distance indicators. Their main characteristics are high luminosity, blue colour indices, and irregular variability. Spectroscopically they show hydrogen and helium in emission with occasionally weaker Fell and [Fell], and no Balmer jump (Humphreys 1975, 1978). In this respect they closely resemble cataclysmic variables, particularly dwarf novae. In the quiescent state dwarf novae show broad H and HeI, together with a strong UV continuum. Weak FeII in emission has been observed in U Gem and SS Aur (Warner 1976). The Balmer jump is either not present, or weakly in emission. The principal spectroscopic difference is the increased breadth of the occasionally doubled emission lines.

scholarly journals The Nature of the Difference Between Novae, Dwarf Novae, and Novalikes

1980 ◽  
Vol 88 ◽  
pp. 431-437
Author(s):  
I. G. Mitrofanov
Keyword(s):  
Accretion Disk ◽  
Binary Systems ◽  
Hot Spot ◽  
Cataclysmic Variables ◽  
Emission Lines ◽  
Close Binary ◽  
Dwarf Novae ◽  
Ultraviolet Continuum ◽  
Close Binary Systems ◽  
The Difference

Novae (N) and Dwarf Novae (DN) are considered to belong to the class of the Cataclysmic Variables (CVs). The Novalike stars and recently discovered Polars (the AM Herculis-type stars) seem to have the same nature as CVs and probably are members of this class. It is usually assumed that CVs are close binary systems, each system contains a degenerate dwarf and a nondegenerate second component, their period being usually less than 16h (e.g. see: Robinson 1976). A second star is believed to overfill its Roche lobe and its matter flows onto the degenerated component. Then around the degenerated dwarf there arises an accretion disk. This disk and the hot spot where the interaction between the disk and outflowing stream occurs are the main sources of the blue and ultraviolet continuum and strong H and He emission lines.

scholarly journals Voracious vortices in cataclysmic variables

2020 ◽  
Vol 642 ◽  
pp. A100
Author(s):  
V. V. Neustroev ◽  
S. V. Zharikov
Keyword(s):  
Cataclysmic Variables ◽  
Accretion Disc ◽  
Emission Lines ◽  
Quiescent State ◽  
Doppler Tomography ◽  
Time Resolved ◽  
Balmer Lines ◽  
Cool Gas ◽  
The Right ◽  
Three Body

Context. In Paper I we showed that the accretion disc radius of the dwarf nova HT Cas in its quiescent state has not changed significantly during many years of observations. It has remained consistently large, close to the tidal truncation radius. This result is inconsistent with the modern understanding of the evolution of the disc radius through an outburst cycle. Aims. Spectroscopic observations of HT Cas during its superoutburst offered us an exceptional opportunity to compare the properties of the disc of this object in superoutburst and in quiescence. Methods. We obtained a new set of time-resolved spectra of HT Cas in the middle of its 2017 superoutburst. We used Doppler tomography to map emission structures in the system, which we compared with those detected during the quiescent state. We used solutions of the restricted three-body problem to discuss again the location of emission structures and the disc size of HT Cas in quiescence. Results. The superoutburst spectrum is similar in appearance to the quiescent spectra, although the strength of most of the emission lines decreased. However, the high-excitation lines significantly strengthened in comparison with the Balmer lines. Many lines show a mix of broad emission and narrow absorption components. Hα in superoutburst was much narrower than in quiescence. Other emission lines have also narrowed in outburst, but they did not become as narrow as Hα. Doppler maps of Hα in quiescence and of the Hβ and He I lines in outburst are dominated by a bright emission arc at the right side of the tomograms, which is located at and even beyond the theoretical truncation limit. However, the bulk of the Hα emission in outburst has significantly lower velocities. Conclusions. We show that the accretion disc radius of HT Cas during its superoutburst has become hot but remained the same size as it was in quiescence. Instead, we detected cool gas beyond the Roche lobe of the white dwarf that may have been expelled from the hot disc during the superoutburst.

scholarly journals Kinematics of Nuclei of Sc Galaxies

1980 ◽  
Vol 5 ◽  
pp. 191-191
Author(s):  
V. C. Rubin
Keyword(s):  
High Velocity ◽  
Stellar Population ◽  
Hii Regions ◽  
Emission Lines ◽  
High Luminosity ◽  
Rotation Curves ◽  
Velocity Gradients ◽  
Wide Range ◽  
Central Regions ◽  
Velocity Dispersions

For a sample of 21 Sc galaxies with a wide range of luminosities, of radii, and of masses, W. K. Ford and I have obtained spectra and determined rotation curves. By their kinematical behavior in their central regions, the Sc’s can be separated into two groups. Some galaxies, generally small and of low luminosity, have shallow central velocity gradients, reflecting their low central masses and densities. Other galaxies, most often large ones of high luminosity, have steep central velocity gradients. One reason this separation by central velocity gradients is of interest is because these galaxies exhibit other significant spectral differences which go hand-in-hand with the kinematical differences.The small, low luminosity galaxies show emission lines of Hα and [NII], with nuclear Ha sharp and stronger than [NII], and little or no stellar nuclear continuum, just as conventional HII regions. In contrast, the high luminosity galaxies show broad nuclear emission, with [NII] stronger than Ha. These galaxies have a strong red stellar continuum, arising from a red stellar population. The cause of the Hα[NII] intensity reversal in the nuclei of some galaxies remains unknown. However, the strong [NII] emission in generally high luminosity galaxies with massive nuclei, nuclei which show strong red continua, suggests that [Nil] intensity correlates with nuclear luminosity, and in turn with the density and velocity properties of the nuclear populations. We would expect high velocity dispersions and high bulge luminosities for galaxies with strong nuclear [NII] and steep central velocity gradients.

scholarly journals Ultraviolet Observations of Cataclysmic Variables

1987 ◽  
Vol 93 ◽  
pp. 205-205 ◽  
Author(s):  
F. Verbunt
Keyword(s):  
Orbital Period ◽  
Cataclysmic Variables ◽  
Type Systems ◽  
Terminal Velocity ◽  
Dwarf Novae ◽  
Preliminary Results ◽  
System Type ◽  
International Ultraviolet Explorer ◽  
Flux Level ◽  
Ultraviolet Observations

AbstractThe preliminary results of the analysis of more than 1000 spectra of cataclysmic variables in the archive of the International Ultraviolet Explorer were presented at the meeting. To characterize the slope of the spectra I use F = log(f1460Å/f2880Å). For most spectra F lies between 0.2 and 0.7. No correlation of F with orbital period, inclination, system type or (for dwarf novae) length of the interoutburst interval are found, apart from somewhat lower values of F for DQ Her type systems. Out of 16 dwarf novae for which spectra both at outburst maximum and minimum are available 11 show no large difference in F between maximum and minimum, and in 5 F declines with the flux level. Out of 6 dwarf novae 5 show very red spectra during the rise to maximum, and 1 shows slopes during rise similar to those during decline.In the ultraviolet resonance lines, due to a wind from the disc, no correlation is found between inclination and terminal velocity.

scholarly journals X-Ray Emission from Flare Stars

1983 ◽  
Vol 71 ◽  
pp. 125-129
Author(s):  
P.C. Agrawal ◽  
A.R. Rao ◽  
B.V. Sreekantan
Keyword(s):  
Emission Lines ◽  
Quiescent State ◽  
X Ray ◽  
Uv Emission ◽  
Chromospheric Emission ◽  
Flare Stars ◽  
Einstein Observatory

Flare stars are a group of mostly dMe stars, which show intense flaring activity in the optical as well as in the radio and X-ray bands. These stars are characterized by the presence of chromospheric emission lines like % and Call H and K which are present even during the quiescent state. The presence of transition regions and coronae have been inferred from the detection of UV emission lines like NV, CIV, SiIV etc. with IUE and X-ray observations made with the Einstein Observatory. We report here X-ray observations of flare stars made with Einstein to measure their coronal X-ray emission during the quiescent state.

scholarly journals H2 Emission from External Galaxies

1992 ◽  
Vol 150 ◽  
pp. 103-107
Author(s):  
Kimiaki Kawara
Keyword(s):  
Uv Radiation ◽  
Supernova Remnants ◽  
Emission Lines ◽  
Hot Stars ◽  
Shock Excitation ◽  
X Ray ◽  
Spectroscopic Observations ◽  
Near Ir ◽  
Bare Nucleus ◽  
External Galaxies

2 μm spectroscopic observations by many authors have revealed significant rotation-vibrational H2 emission is widespread from starburst to bare nucleus galaxies. Near-IR H2 emission lines can arise from various excitation sources: UV radiation by hot stars, shock excitation by supernova remnants or AGN driven winds, and UV/X-ray radiation by an AGN. In this review recent data will be compared with such H2 excitation models.

scholarly journals Peculiar Red Giants in External Galaxies

1989 ◽  
Vol 106 ◽  
pp. 35-50 ◽  
Author(s):  
Harvey B. Richer
Keyword(s):  
Star Formation ◽  
Stellar Evolution ◽  
Hubble Constant ◽  
Red Giants ◽  
Stellar Content ◽  
Late Type ◽  
External Galaxies ◽  
Distance Indicators ◽  
Luminosity Evolution ◽  
Local Value

AbstractStudy of the late-type stellar content in external galaxies provides numerous clues for the theory of stellar evolution, for star-formation scenarios in galaxies, and for proper models of the luminosity evolution of galaxies which are then used in cosmological studies. In addition, these late-type stars can be used as distance indicators themselves and yield a local value of the Hubble constant consistent with recent Cepheid determinations.

scholarly journals A Fuse Survey of Disk-Accreting Cataclysmic Variables

2004 ◽  
Vol 194 ◽  
pp. 251-251
Author(s):  
C. S. Froning ◽  
K. S. Long ◽  
P. Szkody ◽  
B. T. Gänsicke
Keyword(s):  
Cataclysmic Variables ◽  
Dwarf Novae ◽  
X Ray ◽  
Intermediate Polars ◽  
Far Ultraviolet ◽  
X Ray Binaries ◽  
Initial Results

We present initial results of a survey of the FUV spectra of disk-accreting cataclysmic variables obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).FUSE covers the 905 - 1188 Å range at spectral resolutions ≃0.1 Å. To date, FUSE has observed more than 65 cataclysmic variables (CVs). Publicly-available data include observations of 11 dwarf novae (DN), 15 non-magnetic novalikes (NLs), 7 intermediate polars and DQ Her stars, at least 15 polars, and 4 super-soft X-ray binaries.

Stark-broadened emission lines in the accretion disks of cataclysmic variables

1988 ◽  
Vol 327 ◽  
pp. 234 ◽  
Author(s):  
D. N. C. Lin ◽  
R. E. Williams ◽  
R. J. Stover
Keyword(s):  
Accretion Disks ◽  
Cataclysmic Variables ◽  
Emission Lines

scholarly journals Physical Interpretation of Dwarf Nova Primary Effective Temperatures

2004 ◽  
Vol 194 ◽  
pp. 192-193
Author(s):  
Dean M. Townsley ◽  
Lars Bildsten
Keyword(s):  
Gravitational Radiation ◽  
Accretion Rate ◽  
Thermal State ◽  
Cataclysmic Variables ◽  
Theoretical Work ◽  
Dwarf Novae ◽  
Radiation Losses ◽  
Accretion Rates ◽  
The Masses ◽  
The Impact

AbstractWe have undertaken a theoretical study of the impact of the accumulating envelopes on the thermal state of the underlying white dwarf (WD). This has allowed us to find the equilibrium WD core temperatures, the classical nova ignition masses and the thermal luminosities for WDs accreting at rates of 10–11 – 10–8M⊙ yr–1. These accretion rates are most, appropriate to WDs in cataclysmic variables (CVs) of (Porb ≲ 7 hr), many of which accrete sporadically as Dwarf Novae. Over twenty Dwarf Novae have been observed in quiescence, when the accretion rate is low and the WD photosphere is detected and Teff measured. Comparing our theoretical work to these observations allows us to constrain the WD mass and the time averaged accretion rate, ⟨Ṁ⟩. If ⟨Ṁ⟩ is that given by gravitational radiation losses alone, then the WD masses are > 0.8 M⊙. An alternative conclusion is that the masses are closer to 0.6M⊙ and ⟨Ṁ⟩ is 3-4 times larger than that expected from gravitational radiation losses.

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