scholarly journals Symbiotic star UV emission and theoretical models

1982 ◽  
Vol 70 ◽  
pp. 269-272
Author(s):  
M. Kafatos
Keyword(s):  
Line Emission ◽  
Theoretical Models ◽  
Symbiotic Star ◽  
Symbiotic Stars ◽  
Uv Emission

Observations of symbiotic stars in the far UV have provided important information on the nature of these objects. The canonical spectrum of a symbiotic star, e.g. RW Hya, Z And, AG Peg, is dominated by strong allowed and semiforbidden lines of a variety of at least twice ionized elements. Weaker emission from neutral and singly ionized species is also present. The Mg II doublet is usually very strong and may be associated with the M giant primary. A continuum may or may not be present in the 1200 - 2000 A range but is generally present in the range 2000 - 3200 A range, the latter arising from free-free and bound-free emission in the same nebula that is responsible for the UV line emission (CI Cyg, RW Hya, RX Pup). The suspected hot subdwarf continuum is seen in some cases in the range 1200 - 2000 A (RW Hya, AG Peg, SY Mus).

scholarly journals Ultraviolet properties of the symbiotic stars

1982 ◽  
Vol 70 ◽  
pp. 103-113
Author(s):  
Mark H. Slovak ◽  
David L. Lambert
Keyword(s):  
High Resolution ◽  
Broad Band ◽  
Symbiotic Star ◽  
Symbiotic Stars ◽  
Interim Report

Prior to the launch of the IDE satellite in early 1978, the only symbiotic star previously detected in the ultraviolet by earlier UV satellites, such as the 0A0-2, TD-1 and ANS experiments, was AG Pegasi = HD 207757 (Gallager et al. 1979). These broad-band observations indicated that the symbiotics as a class may show a significant ultraviolet flux and thus they became natural candidates for a survey with the IUE satellite. The following is an interim report on a survey of the symbiotics, both at low and, for AG Pegasi and CH Cygni, at high resolution.

Symbiotic Stars in the Local Group of Galaxies: POINT-AGAPE Catalogue Revisited

2017 ◽  
Vol 14 (S339) ◽  
pp. 291-294
Author(s):  
K. Drozd ◽  
J. Mikołajewska ◽  
M. Darnley ◽  
K. Iłkiewicz ◽  
N. Caldwell ◽  
...  
Keyword(s):  
Light Curve ◽  
Local Group ◽  
Light Curves ◽  
Symbiotic Star ◽  
Symbiotic Stars ◽  
Original Point

AbstractThis research was prompted by the discovery of 35 new or candidate symbiotic stars during a targeted search in the Local Group of Galaxies. A catalogue of a further 200 or so such objects has now been compiled. Many of them could be identified with counterparts in the POINT-AGAPE Catalogue. However, information in the Catalogue is limited to position, brightness and possible period, and light-curves are not available. The poster presented an example of a light-curve of a symbiotic star retrieved from original Point-Agape Catalogue data.

The nova type outburst of the symbiotic star AS 296

1990 ◽  
Vol 122 ◽  
pp. 440-441
Author(s):  
Ulisse Munari
Keyword(s):  
Orbital Period ◽  
Active Phase ◽  
Borderline Case ◽  
Symbiotic Star ◽  
Symbiotic Stars ◽  
Late Type ◽  
Type Giant ◽  
One Year

AbstractThe photometric and spectroscopic evolutions, displayed by AS 296 since the June 1988 outburst ([1]), are presented and discussed. The main features of the model outlined by [2], [3] and [4], are confirmed and further developped. An orbital period of about 3 years is inferred from Hα modulation (see [5]).The outburst originated from a TNR event in the accreted envelope of a WD. The IUE and optical spectroscopic evolution agrees with the expected scenario for degenerate conditions in the accreted material, while the high quiescence luminosity of the WD would indicate nondegenerate conditions.The late type giant passed unchanged the outburst. Also the region of Hα formation was not touched by the eruption.After one year the system has not yet reached the quiescence again. The photometric evolution displayed by AS 296 up to June 15, 1989 is presented in Fig.1.In Tab.1, the main features exhibited by symbiotic stars that have experienced a TNR event are summarized. The first 8 objects in the table are usually collectively called "symbiotic novae". They distinguish themselves for the very long outburst duration. At present, AS 296 appears to be a borderline case of such class, and a firm understanding needs to wait for the end of current active phase.

scholarly journals Spectroscopic observations of AG Dra

1982 ◽  
Vol 70 ◽  
pp. 185-189
Author(s):  
Huang Chang-Chun
Keyword(s):  
Radial Velocity ◽  
Spectral Type ◽  
Symbiotic Star ◽  
Symbiotic Stars ◽  
Spectroscopic Observations ◽  
Very High

AG Dra is an interesting symbiotic star, on account of its very high negative velocity and its earlier spectral type among the symbiotic stars. This star has been classified as dG7 (Wilson,1943), K1 II (Roman,1953) and K3 III (Boyarchuk,1966). It has a variable radial velocity.During summer 1981, spectroscopic observations of AG Dra were performed at the Haute-Provence Observatory using the Marly spectrograph with a dispersion of 80 A mm-1 at the 120 cm telescope and using the Coudé spectrograph of the 193 cm telescope with a dispersion of 40 A mm-1. Professor Ch. Fehrenbach very kindly given me a plate of the star which he had taken in July,1966, using the coudé spectrograph of the 193 cm telescope with a dispersion of 40 A mm-1.

scholarly journals On the Origin of the 6.4 keV line from the GRXE

2011 ◽  
Vol 7 (S279) ◽  
pp. 329-330
Author(s):  
Romanus Eze ◽  
Kei Saitou ◽  
Ken Ebisawa
Keyword(s):  
Galactic Plane ◽  
Cataclysmic Variables ◽  
Line Emission ◽  
Emission Lines ◽  
Symbiotic Stars ◽  
Line Flux ◽  
X Ray ◽  
Fluorescence Line ◽  
Magnetic Cataclysmic Variables ◽  
Cold Matter

AbstractThe Galactic Ridge X-ray Emission (GRXE) spectrum has strong iron emission lines at 6.4, 6.7, and 7.0 keV, each corresponding to the neutral (or low-ionized), He-like, and H-like iron ions. The 6.4 keV fluorescence line is due to irradiation of neutral (or low ionized) material (iron) by hard X-ray sources, indicating uniform presence of the cold matter in the Galactic plane. In order to resolve origin of the cold fluorescent matter, we examined the contribution of the 6.4 keV line emission from white dwarf surfaces in the hard X-ray emitting symbiotic stars (hSSs) and magnetic cataclysmic variables (mCVs) to the GRXE. In our spectral analysis of 4 hSSs and 19 mCVs observed with Suzaku, we were able to resolve the three iron emission lines. We found that the equivalent-widths (EWs) of the 6.4 keV lines of hSSs are systematically higher than those of mCVs, such that the average EWs of hSSs and mCVs are 180−10+50 eV and 93−3+20 eV, respectively. The EW of hSSs compares favorably with the typical EWs of the 6.4 keV line in the GRXE of 90–300 eV depending on Galactic positions. Average 6.4 keV line luminosities of the hSSs and mCVs are 9.2 × 1039 and 1.6 × 1039 photons s−1, respectively, indicating that hSSs are intrinsically more efficient 6.4 keV line emitters than mCVs. We estimated required space densities of hSSs and mCVs to account for all the GRXE 6.4 keV line emission flux to be 2 × 10−7 pc−3 and 1 × 10−6 pc−3, respectively. We also estimated the actual 6.4 keV line contribution from the hSSs, which is as much as 30% of the observed GRXE flux, and that from the mCV is about 50%. We therefore conclude that the GRXE 6.4 keV line flux is primarily explained by hSSs and mCVs.

scholarly journals X-Ray and Ultraviolet Observations of AG Draconis during Quiescence and Outburst

1987 ◽  
Vol 93 ◽  
pp. 763-763
Author(s):  
A. Cassatella ◽  
F.A. Córdova ◽  
M. Friedjung ◽  
J. Kenyom ◽  
L. Piro ◽  
...  
Keyword(s):  
Orbital Motion ◽  
Uv Light ◽  
Low Energy ◽  
Emission Lines ◽  
Symbiotic Star ◽  
Symbiotic Stars ◽  
Uv Spectrum ◽  
X Ray ◽  
High Ionization ◽  
Ultraviolet Observations

AbstractWe describe the first X-ray monitoring of a symbiotic star during phases of enhanced activity. AG Dra is a Pop II object with a composite spectrum, characterized by a cool K-type component, prominent high ionization emission lines and a strong UV continuum which is attributed to a hot dwarf companion. Periodic variability of the UV radiation during minimum could be attributed to the orbital motion of the system. In April 1980 HEAO-2 detected an intense, soft X-ray flux from AG Dra, stronger than in other symbiotic stars. After one major outburst of November 1980, which continued until 1983, two more outbursts occurred in February 1985 and January 1986, and coordinated X-ray (EXOSAT) and ultraviolet (IUE) observations were organized to study the behaviour of AG Dra during different activity phases. EXOSAT observations made during decline after the 1985 outburst, revealed a weak X-ray flux in the Thin Lexan filter of the Low Energy dedtector. Observations made during minimum, in June and November 1985, at phases 0.22 and 0.50 of the UV light curve, disclosed the presence of an intense X-ray flux, which was not occulted in November. AG Dra was again observed with EXOSAT in February 1986 when the stellar luminosity was still at maximum. No X-ray flux was detected, in spite of the prominent, high ionization UV spectrum observed with IUE.A detailed discussion of the X-ray and ultraviolet results on AG Dra in the light of possible models is in progress.

scholarly journals Theoretical Models of Magnetic Flux Tubes: Structure and Dynamics

1994 ◽  
Vol 154 ◽  
pp. 407-421
Author(s):  
O Steiner
Keyword(s):  
Magnetic Flux ◽  
Line Emission ◽  
Theoretical Models ◽  
Small Scale ◽  
Solar Photosphere ◽  
Model Calculations ◽  
Flux Tubes ◽  
Wide Range ◽  
Magnetic Flux Tubes ◽  
Lower Chromosphere

Two types of model calculations for small scale magnetic flux tubes in the solar atmosphere are reviewed. In the first kind, one follows the temporal evolution governed by the complete set of the MHD and radiative transfer equations to a (quasi) stationary solution. From such a solution the continuum contrasts of a photospheric flux tube in the visible and in the infrared continuum at 1.6 μm have been computed and are briefly discussed. The second, more empirical type of method assumes the flux tubes to be in magnetohydrostatic equilibrium. It is computationally faster and more flexible and allows us to explore a wide range of parameters. Models and insights obtained from such parameter studies are discussed in some detail. These include an explanation for the peculiar variation of the area asymmetry of Stokes V profiles across the solar disk in terms of mass motions in the surroundings of magnetic flux tubes.Furthermore, a two-dimensional model of the lower chromosphere that has been developed is presented. Emphasis is laid on the effect of thermal bifurcation of the lower chromosphere on the structure of the chromospheric magnetic field. If the cool carbon monoxide clouds, observed in the infrared, occupy the non-magnetic regions, the flux tubes expand very strongly and form a magnetic canopy with an almost horizontal base. This has consequences for the spatial distribution of the Ca II K spectral line emission.Finally, some consideration is given to the formation and destruction of intense magnetic flux tubes in the solar photosphere. The formation is described as a consequence of the flux expulsion process that leads to a convective instability. A possible observational signature of this mechanism is proposed.

scholarly journals Photoionization modelling of quiescence-phase spectra of novae and a symbiotic star

2020 ◽  
Vol 492 (2) ◽  
pp. 2326-2334 ◽  
Author(s):  
Anindita Mondal ◽  
Ramkrishna Das ◽  
G C Anupama ◽  
Soumen Mondal
Keyword(s):  
Physical Parameters ◽  
Symbiotic Star ◽  
Symbiotic Stars ◽  
Hydrogen Density ◽  
Elemental Abundances ◽  
Optical Region ◽  
Best Fitting ◽  
Best Fit ◽  
Absorption Features ◽  
Phase Spectra

ABSTRACT Using observed and published spectra in the optical region, we have studied a handful of novae and symbiotic stars that show novae-like variability in the quiescence phase. We present results for the novae T Coronae Borealis, GK Persei, RS Ophiuchi, V3890 Sagittarii and V745 Scorpii, and for a symbiotic star BX Monocerotis. Observations were carried out at the 2-m Himalayan Chandra Telescope (HCT). Generally, the spectra show prominent low-ionization emission features of hydrogen, helium, iron and oxygen and TiO absorption features resulting from the cool secondary component; T Coronae Borealis and GK Persei show higher ionization lines. We used the photoionization code cloudy to model these spectra. From the best-fitting models, we have estimated the physical parameters (e.g. temperature, luminosity and hydrogen density), the elemental abundances and other parameters related to the system. By matching the spectra of various giants with the absorption features and using the best fit, we have determined the types of secondaries and also their contribution to the spectra.

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