scholarly journals Eruptive Phenomena as a Source of the Observed Variations of Intrinsic Polarization in Long Period and T Tau Variables

1983 ◽  
Vol 71 ◽  
pp. 515-518
Author(s):  
M. Sole ◽  
G. Strazzulla
Keyword(s):  
Temperature Dependence ◽  
Equivalent Width ◽  
Emission Lines ◽  
Rapid Rise ◽  
Intrinsic Polarization ◽  
Colour Centres ◽  
Long Period ◽  
Uv Photons ◽  
T Tau

ABSTRACTThe correlation between the rapid rise of intrinsic polarization, increasing U-B and enhanced equivalent width of Balmer, H and K emission lines is interpreted as a consequence of the activation of colour centres in circumstellar silicate dust by X/UV photons from flares. The temperature dependence of bleaching is discussed and the number of centres producing polarization changes is estimated.

Determination of the term Symbiotic Star

1982 ◽  
Vol 70 ◽  
pp. 225-230
Author(s):  
A. A. Boyarchuk
Keyword(s):  
Spectral Type ◽  
Emission Lines ◽  
Symbiotic Star ◽  
Symbiotic Stars ◽  
Absorption And Emission ◽  
Long Period ◽  
T Tau Type Stars ◽  
The Common ◽  
T Tau

Symbiotic stars have been studied for many years. But the common determination of the term “symbiotic star” does not exist even now. Merrill (1958) introduced this term in order to emphasize unusual spectral features – absorption TiO bands and emission lines belonging to highly ionized ions.If we look on the eruptive stars spectra we well see absorption and emission features in the spectra of many stars which we cannot certainly consider as symbiotic stars. For example the U Gem type stars have absorption and emission features in their spectra. A similar situation exists in the case of the old novae. The T Tau type stars have many emission lines, and their spectral type corresponds to G-K. Even the long period variables have some emission lines though their spectral type is M. On the other hand, there are also the BQ[]type stars which are characterized by the presence in their optical spectrum of forbidden emission lines and of a rather hot absorption spectrum.

scholarly journals X-ray variability of the HMXB Cen X-3: evidence for inhomogeneous accretion flows.

2020 ◽  
Author(s):  
G Sanjurjo-Ferrín ◽  
J M Torrejón ◽  
K Postnov ◽  
L Oskinova ◽  
J J Rodes-Roca ◽  
...  
Keyword(s):  
Equivalent Width ◽  
Compact Star ◽  
Timing Analysis ◽  
Roche Lobe ◽  
The Other ◽  
Emission Lines ◽  
High Mass ◽  
X Ray ◽  
Accretion Flows ◽  
Inner Radius

Abstract Cen X-3 is a compact high mass X-ray binary likely powered by Roche lobe overflow. We present a phase-resolved X-ray spectral and timing analysis of two pointed XMM-Newton observations. The first one took place during a normal state of the source, when it has a luminosity LX ∼ 1036 erg s−1. This observation covered orbital phases φ = 0.00 − 0.37, i.e. the egress from the eclipse. The egress lightcurve is highly structured, showing distinctive intervals. We argue that different intervals correspond to the emergence of different emitting structures. The lightcurve analysis enables us to estimate the size of such structures around the compact star, the most conspicuous of which has a size ∼0.3R*, of the order of the Roche lobe radius. During the egress, the equivalent width of Fe emission lines, from highly ionized species, decreases as the X-ray continuum grows. On the other hand, the equivalent width of the Fe Kα line, from near neutral Fe, strengthens. This line is likely formed due to the X-ray illumination of the accretion stream. The second observation was taken when the source was 10 times X-ray brighter and covered the orbital phases φ = 0.36 − 0.80. The X-ray lightcurve in the high state shows dips. These dips are not caused by absorption but can be due to instabilities in the accretion stream. The typical dip duration, of about 1000 s, is much longer than the timescale attributed to the accretion of the clumpy stellar wind of the massive donor star, but is similar to the viscous timescale at the inner radius of the accretion disk.

scholarly journals Quasars Disks and Cosmology

1987 ◽  
Vol 124 ◽  
pp. 695-696
Author(s):  
Hagai Netzer
Keyword(s):  
Black Hole ◽  
Ultraviolet Radiation ◽  
Equivalent Width ◽  
Selection Effect ◽  
Emission Lines ◽  
Line Of Sight ◽  
Apparent Brightness ◽  
Central Black Hole ◽  
New Ideas ◽  
Thin Disks

Much of the optical and ultraviolet radiation of bright quasars may originate in a massive accretion disk around a central black hole. Most searches for the signature of such disks gave ambiguous results but lately there are new ideas that may lead to their discovery. In particular, the apparent brightness of thin disks depend on their inclination to the observer's line of sight and this may be detected by the equivalent width of some emission lines (Netzer 1985, 1986). This idea may change our view on the inner structure of quasars and other AGN. In addition, it points to a potential selection effect that has not been taken into account so far. Magnitude limited optical quasar samples may contain, preferentially, face-on disks, thus cosmological evolution based on such samples may be biased. There are other implications, especially to the observed correlation of Lop with Lx in quasars.

scholarly journals Metallicity and Binarity in WC and WO Stars

2003 ◽  
Vol 212 ◽  
pp. 566-567
Author(s):  
Laura Norci ◽  
V. Francesco Polcaro ◽  
Roberto F. Viotti
Keyword(s):  
Statistical Analysis ◽  
Equivalent Width ◽  
Emission Lines ◽  
Physical Conditions ◽  
Maximum Value ◽  
Ionization Effect ◽  
Significant Difference ◽  
Increasing Trend ◽  
The Difference

Median values of the fwhm and equivalent width Wλ of the C iv 581 nm, O v 559 nm and 465 nm emission lines were derived from an extended statistical analysis of WC and WO stars (Norci et al. 2002; see Table 1). We find that the C iv equivalent width shows an increasing trend towards earlier WC subtypes, reaching a maximum value of 95 nm (± 32 %) for the Galactic WC4-6 stars, and decreases by about a factor of three in the hotter WO stars (Figure 1, left). The line appears about twice as strong in the LMC than in the Galactic WC4 stars, and the difference is particularly evident in the non-Galactic WO stars. Such an effect is absent in the O v 559 nm line, which smoothly increases towards WCE and WO stars, with no significant difference between Galactic and non-Galactic WC4 and WO stars. Thus this C anomaly is not an ionization effect; it is, therefore, probably due to a cause that selectively operates on C rather than on O. Different physical conditions in the winds of Galactic and non-Galactic stars, possibly related to the different initial metallicity Z, could be responsible for the anomaly.

scholarly journals On the Formation of Hydrogen Emission Lines in Miras

1995 ◽  
Vol 155 ◽  
pp. 419-420
Author(s):  
Patrick de Laverny ◽  
Christian Magnan
Keyword(s):  
Deep Layer ◽  
Emission Lines ◽  
Hydrogen Emission ◽  
Long Period ◽  
Hydrogen Recombination ◽  
Long Period Variables ◽  
Hydrogen Emission Lines ◽  
Cyclic Variations ◽  
Recombination Zone

AbstractWe investigate non-LTE effects in the hydrogen recombination zone of Long-Period Variables of Mira type. We propose that the Balmer hydrogen emission lines could be formed in this deep layer. We show how the spectral cyclic variations of Miras could be mimicked with this interpretation. As a result the radius of a Mira in the Balmer transitions could be much smaller than its radius in the molecular absorptions, which are formed in higher layers.

scholarly journals Ultraviolet Spectropolarimetry of Classical Novae in Outburst: Evidence for Aspherical Ejecta

1996 ◽  
Vol 158 ◽  
pp. 315-316
Author(s):  
J.J. Johnson ◽  
C.M. Anderson ◽  
K.S. Bjorkman ◽  
A.D. Code ◽  
G.K. Fox ◽  
...  
Keyword(s):  
Space Shuttle ◽  
Emission Lines ◽  
Intrinsic Polarization ◽  
Classical Novae

AbstractWe used the Wisconsin Ultraviolet Photo-Polarimeter Experiment during the Astro-2 mission aboard the Space Shuttle Endeavour, to obtain ultraviolet spectropolarimetry of three classical novae that had recently gone into outburst. All three novae appear to have intrinsic polarization, with polarization changes across emission lines. This result indicates that, geometrically, the ejecta were quite aspherical.

scholarly journals Hydrogen Emission Lines from Extended Pulsating Atmospheres

1993 ◽  
Vol 139 ◽  
pp. 281-282
Author(s):  
P. de Laverny ◽  
C. Magnan
Keyword(s):  
Emission Lines ◽  
Cold Environment ◽  
Dilution Factor ◽  
Hydrogen Emission ◽  
Long Period ◽  
Evolved Stars ◽  
Lyman Continuum ◽  
Long Period Variables ◽  
Hydrogen Emission Lines ◽  
Hydrogen Lines

AbstractIn order to study the basic radiative mechanisms in the extended envelopes of evolved stars (e.g. Long Period Variables), we determine the spectrum emerging from a very optically thick Non-LTE hydrogen layer surrounding a core of high temperature (see figure 1). Such a model was first proposed by Sobolev (1960) and Menzel (1946). It is consistent with the fact that LPVs are likely evolving toward planetary nebulae. The main parameters of the model are the temperature of the illuminating star (Tr), the dilution factor (ω) and the Lyman continuum optical depth of the envelope (τ1c). We examine their influence upon the emerging intensities in the lines and in the continua.The model could explain some observations related to evolved stars and especially the presence of emission features in an otherwise cold environment. Furthermore atmospheric pulsation phenomena produce large variations in the emerging spectra: reddening, emission/absorption transition of the hydrogen lines, profile deformations…

scholarly journals UV and optical spectrum variability of T Tau and RY Tau

2012 ◽  
Vol 8 (S292) ◽  
pp. 44-44
Author(s):  
N. Z. Ismailov ◽  
N. Kh. Quliyev ◽  
O. V. Khalilov ◽  
H. N. Adigezalzade
Keyword(s):  
Emission Line ◽  
Brightness Variation ◽  
Emission Lines ◽  
Spectral Energy ◽  
Spectral Radiation ◽  
Line Intensities ◽  
T Tauri ◽  
Spectral Ranges ◽  
T Tau ◽  
Archive Data

AbstractIn this report we have presented results of spectral observations of classical T Tauri type stars T Tau and RY Tau. Observational dates were obtained from following sources: spectrograms of the UV range from the IUE archive data, and spectrograms of the visual range obtained in the 2 m telescope of ShAO of the NAS of Azerbaijan (Ismailov et al. 2010). For both of stars on the Scargle method we have searched a periodicity of variations in equivalent widths of emission lines in the optical and UV ranges. In the RY Tau firstly was detected the periodic variability in MgII λ2800 Å emission doublet intensities with a period of 23 days. The observed period had also revealed with the equivalent widths and displacements of components of Hα and H+Hϵ and K CaII emission.The lines were found to be shifted to short wavelengths as the emission line intensities increased in both UV and optical spectral ranges. The lack of a correlation between the brightness variation and the emission line intensity also suggests that, on the whole, the contribution from the radiation in emission lines for the star RY Tau is insignificant.On the analysis of T Tau we conclude that there is a significant variation of spectral emission lines in the optical and UV on a time scale of about 33 days and that this variations is periodic. Both of stars shows the periodicity also for observed group of such lines as CIV λ1450 Å, HeII λ 1640 Å, SII λ1756 Å (Ismailov et al. 2010, Ismailov et al. 2011).Additionally we have carried out spectral energy distributions of this stars in the range 0.36-100 μm which have indicated the excess of spectral radiation in the IR range of spectrum. These excesses of radiations can be explained by the thermal radiation of still unformed bodies at the circumstellar environment. The periodic variability in the spectrum together with the excess of the spectral radiation may be occurred by protoplanets and/or protostars in these young systems. It is showed that possible, planet formation processes mainly to be completed at the time of the formation of classical T Tauri type stars.

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