scholarly journals A New Search for Nebulae Surrounding Wolf-Rayet Stars

1982 ◽  
Vol 99 ◽  
pp. 463-468
Author(s):  
Joy N. Heckathorn ◽  
Frederick C. Bruhweiler ◽  
Theodore R. Gull
Keyword(s):  
Milky Way ◽  
Narrow Band ◽  
Interference Filter ◽  
Emission Lines ◽  
List Type ◽  
Type Number ◽  
Filamentary Structure ◽  
Line Survey ◽  
Ring Nebulae ◽  
Rayet Star

We have used the plate data from An Emission Line Survey of the Milky Way by Parker, Gull and Kirschner(1979) to make a new search for ring nebulae around Wolf-Rayet stars. The Survey consists of narrow-band interference filter direct imagery centered on the emission lines of Hα + [N II] at λ6570, [O III] at λ5007, and [S II] at λ6730. We have discovered at least five new ring nebulae. of the fifteen ring nebulae we were able to detect on the Survey, including our new discoveries, eleven were brighter in the [O III] bandpass than in the Hα + [N II] bandpass, and were filamentary in [O III]. All of the nebulosities we were able to detect were rated on the basis of three criteria: 1)Sharp, filamentary structure present in any or all bandpasses.2)Wolf-Rayet star centered in projected nebulosity, or, if off-center, the segment of the ring nearest the star proportionally brighter than the rest of the ring.3)Absence of any O stars within the nebulosity, or O star in off-centered position not adjacent to the brightest or sharpest portion of the ring.

scholarly journals Dynamics and variability of winds from single Wolf-Rayet stars

1999 ◽  
Vol 193 ◽  
pp. 157-167
Author(s):  
Stanley P. Owocki ◽  
Kenneth G. Gayley
Keyword(s):  
Mass Loss ◽  
Multiple Scattering ◽  
Optical Depth ◽  
Spectral Distribution ◽  
Radiation Flux ◽  
Emission Lines ◽  
List Type ◽  
Type Number ◽  
Ob Stars ◽  
Realistic Line

We review the dynamics of winds from single Wolf-Rayet stars, with emphasis on the following specific points: (a)The classical “momentum problem” (to explain the large inferred ratio of wind to radiative momentum, η Mv∞/(L/c) ≫ 1) is in principle readily solved through multiple scattering of radiation by an opacity that is sufficiently “gray” in its spectral distribution. In this case, one simply obtains η ≃ τ, where τ is the wind optical depth;(b)Lines with a Poisson spectral distribution yield an “effectively gray” cumulative opacity, with multi-line scattering occuring when the velocity separation between thick lines Δv is less than the wind terminal speed v∞. In this case, one obtains η ≃ v∞/Δv;(c)However, realistic line lists are not gray, and leakage through gaps in the line spectral distribution tends to limit the effective scattering to η ≲ 1;(d)In WR winds, ionization stratification helps spread line-bunches and so fill in gaps, allowing for more effective global trapping of radiation, and thus η > 1;(e)However, photon thermalization can reduce the local effectiveness of line-driving near the stellar core, making it difficult for radiation alone to initiate the wind;(f)The relative complexity of WR wind initiation may be associated with the extensive turbulent structure inferred from observed variabililty in WR wind emission lines;(g)Overall, the understanding of WR winds is perhaps best viewed as an “opacity problem”, i.e., identifying the enhanced opacity that can adequately block the radiation flux throughout the wind, and thus drive a WR mass loss that is much greater than from OB stars of comparable luminosity.

scholarly journals A 100-Year Astronomical-Data Bank: Collaboration Possibilities and Some Problems

2001 ◽  
Vol 24 (3) ◽  
pp. 233-233
Author(s):  
Salakhutdin N. Nuritdinov
Keyword(s):  
Milky Way ◽  
Data Bank ◽  
List Type ◽  
Type Number ◽  
Uzbek Academy ◽  
Astronomical Data ◽  
Research Complex ◽  
Galactic Astronomy ◽  
Academy Of Sciences ◽  
Working Out

Our Department of Galactic astronomy and Cosmogony of the Astronomical Institude of Uzbek Academy of Sciences has rich photo meterials obtained over more than 100 years by two telescopes (Normal Astrograph with F= 3500 mm, D= 330 mm and Zeiss Double Astrograph with F= 3000 mm, D= 400 mm). The main objects studied are: 1Open and Globular star clusters,2Regions of the Milky Way and the Pulkovo Observatory program.3Comets and Asteroids4Planets and their Satellites.There are also astronomical data received in the framework of a number of International programmes. Now we are working out some research-complex programmes of these objects. We are ready to collaborate on these programmes.

scholarly journals Molecular gas around the Wolf-Rayet star WR 18 (WN4)

2003 ◽  
Vol 212 ◽  
pp. 732-733
Author(s):  
Anthony P. Marston
Keyword(s):  
Mass Loss ◽  
Optical Emission ◽  
Emission Lines ◽  
Molecular Gas ◽  
Evolved Stars ◽  
Ring Nebula ◽  
History Of ◽  
Optical Ring ◽  
Ring Nebulae ◽  
Rayet Star

Optically observed ring nebulae and H i cavities around Wolf-Rayet stars have enabled us to obtain information on the history of mass-loss associated with these massive evolved stars. However, such studies have left a number of unanswered questions regarding the amount of mass-loss and the conditions of the stars during a sequence of mass-loss phases. Here we discuss the molecular gas environments of the WR star WR 18, which has an associated optical ring nebula NGC 3199. Our observations show that significant amounts of molecular gas appear close to and associated with the star. Mapping of molecular CO near the star shows that molecular materials appear to substantially avoid areas of optical emission and, instead, form a distorted clumpy shell interior to NGC 3199. Molecular emission lines are broader than lines seen in the interstellar medium and suggest the shell is composed of ejecta. This is further corroborated by the enhanced abundances of molecules containing C, N and O. Implications of the observations for the evolution of WR 18 are discussed.

scholarly journals Observations of Southern Dwarf Novae

1979 ◽  
Vol 53 ◽  
pp. 497-497
Author(s):  
N. Vogt
Keyword(s):  
Orbital Period ◽  
White Dwarf ◽  
Photometric Data ◽  
Emission Lines ◽  
List Type ◽  
Type Number ◽  
Dwarf Novae ◽  
Broad Emission ◽  
Cataclysmic Binaries ◽  
Short Period

Preliminary results of spectroscopic and photometric data for five dwarf novae are presented : 1) V 436 Cen. The orbital period of 0.0669 days was determined from radial velocity variations. The RV half amplitude of the primary, K1. = 159 km/s, implies very small masses of M1 ≲ 0.20 M⊙ and M2 = 0.18 M⊙ for the binary components.2) Z Cha. Broad emission (Hβ, Hγ, Hδ) and superimposed narrow absorption lines of Hβ-HII, HeI 4471, Cal 4427 and Call K characterize the spectrum during quiescence. Apparently, the cool, optically thin outer disc is seen on the background of a hot continuum, originating from the white dwarf or the inner disc. The RV half amplitude K1 = 87 km/s results in masses of M1 = 1.10 M⊙ and M⊙ = 0.21 M⊙.3) EX Hya. The RV half amplitude K1 = 68 km/s reveals masses of M1 = 1.4 M⊙ and M2 = 0.19 M⊙ The equivalent widths of the emission lines of H, HeI 4471 and HeII 4686 vary with the phase of the recently detected 67 minute cycle (maximal EW coincides nearly with maximal continuum intensity).4) 0Y Car is an eclipsing binary with an orbital period of 0.0631 days. The eclipses show strong variations in shape and amplitude in the course of an outburst, similar as those of Z Cha. The observations seem to confirm that the location of the eruption is the central part of the disc which increases in size and luminosity.5) EK TrA shows periodic superhumps (P = 0.0645 days) during supermaximum, and therefore belongs to the SU UMa sub-group of dwarf novae which are also characterized by a quasi-periodic occurence of super-maxima. The SU UMa sub-group comprises 70% of the ultra-short period cataclysmic binaries, and at least 18% of all dwarf novae.

scholarly journals Using Narrow Emission Lines to Test Physical Models Unifying AGNs

1989 ◽  
Vol 134 ◽  
pp. 305-307 ◽  
Author(s):  
Steve Rawlings ◽  
Richard Saunders
Keyword(s):  
Large Scale ◽  
Line Strength ◽  
Physical Models ◽  
Emission Lines ◽  
Continuum Emission ◽  
List Type ◽  
Type Number ◽  
X Ray ◽  
Central Engine ◽  
Narrow Emission

We contend that quantitative measurements of nuclear narrow emission line strength can strongly constrain models that unify AGNs. The reasons for the importance of narrow-line luminosity LNLR are: a)The lines normally arise via photoionisation by the integrated UV/soft X-ray luminosity LPHOT of the central source. Thus LNLR is directly linked to a physical quantity intimately connected with the central engine but not observable from the ground. For constant covering factor we expect an approximate proportionality between LNLR and LPHOT; this has been confirmed observationally for AGNs by estimating LPHOT from either optical non-stellar luminosity or effective ionisation parameter.b)NLRs are far enough from the photoionising source to avoid the excessive obscuration that appears able to attenuate broad-line and continuum emission. Narrow-lines are radiated isotropically unlike, eg, the radio core which may be Doppler boosted. Their variability timescale of 103–4 years is intermediate between those of LPHOT and any large-scale radio emission.

scholarly journals Discussion

1957 ◽  
Vol 3 ◽  
pp. 173-174
Keyword(s):  
Binary Systems ◽  
Classification Scheme ◽  
Eclipsing Binaries ◽  
Emission Lines ◽  
Velocity Variation ◽  
List Type ◽  
Type Number ◽  
Simple Manner ◽  
Gas Streams ◽  
Spectral Class

Following the papers on instability in binary systems, Dr S. Gaposchkin described a classification scheme that he had devised to describe the eclipsing binaries having emission lines, gas streams, or thick atmospheres. Such stars Gaposchkin calls the ‘camouflaged eclipsing variables’, and divides them into five groups: (1)Typical members are UX Mon and SX Cas: the spectral type of the brighter star is B or A, that of the fainter is G or later. The minima are of equal depth. Balmer emission is present.(2)Prototypes are β Lyr and ν Sgr: only one component can be seen distinctly, but two minima are present in the light curve. The spectroscopic behaviour is most complicated.(3)Prototypes are RT And and YY Gem: the spectral class is G or later. Ca 11 emission is present. The depths of the minima are roughly equal, and the dimensions of the components are about the same.(4)The prototype is DN Ori: both components are so well camouflaged that no definite velocity variation has been observed.(5)Prototypes are V444 Cyg or UX UMa: the bright lines are strong, and their displacements and intensities do not vary in a simple manner with phase.

scholarly journals Wolf-Rayet Phenomena

1982 ◽  
Vol 99 ◽  
pp. 3-22
Author(s):  
P. S. Conti
Keyword(s):  
Continuous Spectrum ◽  
Emission Lines ◽  
List Type ◽  
Type Number ◽  
Balmer Series ◽  
Intrinsic Absorption ◽  
Wide Range ◽  
Emission Line Spectrum ◽  
Hydrogen Lines ◽  
Future Work

I have been asked to review in broad terms the concept of Wolf-Rayet (W-R) phenomena, that is, to outline what we currently know about the properties of stars showing such phenomena and to indicate the directions in which future work is leading. I thought I would begin by listing the characteristics of W-R spectra to which probably all the participants at this Symposium will be able to agree. These can readily be adapted from Thomas (1968) who discussed them at the Boulder W-R Symposium. The characteristics of W-R spectra are as follows: (1)They are primarily an emission line spectrum superimposed on a “hot” continuous spectrum.(2)P Cygni absorption components are observed for some lines in some stars; a fact not realized in 1968 was that a very few W-R stars have intrinsic absorption lines (e.g. The Balmer series in HD 92740 — Niemela (1973).(3)The emission lines represent a wide range of excitation and ionization. This level is often higher than indicated by simple modeling of the continuous spectrum.(4)The emission lines are broad, corresponding to widths of hundreds to thousands of kilometers per second; widths often differ among various ions in the same star.(5)The W-R stars can be divided into two subtypes: These are the WN types, in which the ions of nitrogen dominate, and the WC types, in which the ions of carbon (and oxygen) dominate. Both sub-types have strong lines of helium; in a few cases, hydrogen lines, in emission, are also observed (Underbill 1968).

scholarly journals Optical Differences Between Radio-Loud and Radio-Quiet QSOs

1994 ◽  
Vol 159 ◽  
pp. 503-503
Author(s):  
Paul J. Francis
Keyword(s):  
Equivalent Width ◽  
Rest Frame ◽  
Uv Spectra ◽  
Emission Lines ◽  
List Type ◽  
Type Number ◽  
Complete Sample ◽  
Broad Absorption ◽  
Broad Absorption Line ◽  
Radio Power

We analyse the rest-frame UV spectra of a complete sample of optically selected radio-loud and radio-quiet QSOs. Our results are: 1:Broad absorption-line QSOs (BALQSOs) are all radio quiet, but they are strongly clustered toward the top end of the radio-quiet population in radio power.2:Radio-loud QSOs have higher equivalent-width, narrower high ionisation emission-lines than radio-quiet QSOs.3:Further ReadingSee Francis, Hooper & Impey, 1993, Astronomical Journal 106, 417 and references therein for more details and discussion.

scholarly journals The Filamentary Structure of the Ring Nebula

1978 ◽  
Vol 76 ◽  
pp. 289-289
Author(s):  
L.E. Goad
Keyword(s):  
Narrow Band ◽  
Emission Lines ◽  
Low Density ◽  
High Excitation ◽  
Filamentary Structure ◽  
Interference Filters ◽  
Stellar Radiation ◽  
Ionization Structure ◽  
Ring Nebula ◽  
Structure Calculations

Image-tube photographs taken through narrow-band interference filters have been used to obtain monochromatic surface brightnesses of the Ring Nebula (NGC 6720) in the strongest emission lines of H I, He I, He II, [N II], [O I], [O II], [O III], and [S II]. These data have been used to analyze the spatial distribution of the various ionized species within the nebula. The bulk of the observed emission is shown to arise from a network of neutral filaments whose inner surfaces are ionized by the incident stellar radiation. The filamentary network is embedded in a low-density, high-temperature medium which is the source of most of the observed high-excitation lines. The ionization structure of several prominent filaments is examined in detail and comparisons are made to recent ionization structure calculations.

Open discussion

1982 ◽  
Vol 99 ◽  
pp. 605-613
Author(s):  
P. S. Conti
Keyword(s):  
Buenos Aires ◽  
Large Mass ◽  
List Type ◽  
Common Phenomenon ◽  
Open Discussion ◽  
The Stability ◽  
Ring Nebulae

Conti: One of the main conclusions of the Wolf-Rayet symposium in Buenos Aires was that Wolf-Rayet stars are evolutionary products of massive objects. Some questions:–Do hot helium-rich stars, that are not Wolf-Rayet stars, exist?–What about the stability of helium rich stars of large mass? We know a helium rich star of ∼40 MO. Has the stability something to do with the wind?–Ring nebulae and bubbles : this seems to be a much more common phenomenon than we thought of some years age.–What is the origin of the subtypes? This is important to find a possible matching of scenarios to subtypes.

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