scholarly journals The Shocking Truth About some “Proto-PN”

1989 ◽  
Vol 131 ◽  
pp. 447-447
Author(s):  
R. W. Goodrich ◽  
Luciana Bianchi
Keyword(s):  
Emission Lines ◽  
Excitation Mechanism ◽  
Strong Emission ◽  
Shock Heating ◽  
Central Stars

A small number of bipolar planetaries -including M2-9, M1-91, GL 618, and M2-56- exhibit very strong emission lines of low ionization species such as [O I], [N I], [N II], and [S II]. Most previous authors have attempted to analyze the spectra of these objects assuming that they are photoionized by their central stars. Closer examination, however, suggests that a different excitation mechanism may be at work -that of shock heating.

scholarly journals Excitation Mechanism of Cometary Lines

1987 ◽  
Vol 120 ◽  
pp. 447-453
Author(s):  
K.S. Krishna Swamy
Keyword(s):  
Solar Radiation ◽  
Emission Lines ◽  
Resonance Fluorescence ◽  
Excitation Mechanism ◽  
Strong Emission

The Cometary Spectra in the visible and ultraviolet regions are dominated by the strong emission lines of various molecules. These can be explained in terms of the resonance fluorescence process in the solar radiation.

scholarly journals [WN] central stars of planetary nebulae

2016 ◽  
Vol 12 (S323) ◽  
pp. 174-178
Author(s):  
H. Todt ◽  
B. Miszalski ◽  
J. A. Toalá ◽  
M. A. Guerrero
Keyword(s):  
Surface Composition ◽  
Planetary Nebulae ◽  
Emission Lines ◽  
Evolutionary Status ◽  
Low Mass Stars ◽  
Strong Emission ◽  
The Status ◽  
New Type ◽  
Low Mass ◽  
Central Stars

AbstractWhile most of the low-mass stars stay hydrogen-rich on their surface throughout their evolution, a considerable fraction of white dwarfs as well as central stars of planetary nebulae have a hydrogen-deficient surface composition. The majority of these H-deficient central stars exhibit spectra very similar to massive Wolf-Rayet stars of the carbon sequence, i.e. with broad emission lines of carbon, helium, and oxygen. In analogy to the massive Wolf-Rayet stars, they are classified as [WC] stars. Their formation, which is relatively well understood, is thought to be the result of a (very) late thermal pulse of the helium burning shell. It is therefore surprising that some H-deficient central stars which have been found recently, e.g. IC 4663 and Abell 48, exhibit spectra that resemble those of the massive Wolf-Rayet stars of the nitrogen sequence, i.e. with strong emission lines of nitrogen instead of carbon. This new type of central stars is therefore labelled [WN]. We present spectral analyses of these objects and discuss the status of further candidates as well as the evolutionary status and origin of the [WN] stars.

scholarly journals 3.31. Tri-dimensional observation of the superbubble in the starburst galaxy NGC 2782

1998 ◽  
Vol 184 ◽  
pp. 151-152
Author(s):  
M. Yoshida
Keyword(s):  
Spatial Distribution ◽  
Emission Line ◽  
Emission Lines ◽  
Starburst Galaxy ◽  
Two Dimensional ◽  
Excitation Mechanism ◽  
Ionized Gas ◽  
Shock Heating

We present results of an optical tri-dimensional observation of the central 2′ × 12″ region of the starburst galaxy NGC 2782. The circumnuclear Hα emission lines consist of broad (δv ~ 300 km s−1), blue-shifted component and narrow (δv < 100 km s−1) component and we first revealed the two-dimensional spatial distribution of those two components. The broad Hα emitting region is extended to 6″ (> 1 kpc) south from the nucleus and the emission-line ratios indicates that shock heating may be the main excitation mechanism of the ionized gas in the region. We conclude that this region is a superbubble outflowing from the nuclear starburst region.

scholarly journals New WR Central Stars of PNe identified on the AAO/UKST Hα Survey

2003 ◽  
Vol 209 ◽  
pp. 46-46
Author(s):  
D. H. Morgan ◽  
Q. A. Parker
Keyword(s):  
Milky Way ◽  
Central Star ◽  
Emission Lines ◽  
Early Type ◽  
Strong Emission ◽  
Ring Nebula ◽  
The Galaxy ◽  
Early Type Stars ◽  
The Many ◽  
Central Stars

Candidate central stars can be seen in some (≤10%) of the many (~1000) new planetary nebulae found during scans of the AAO/UKST Hα survey of the Milky Way (Parker et al. 2002). Spectroscopic observations have identified seven with Wolf-Rayet emission features, thereby adding significantly to the 56 [WR] central stars already known (Jeffery et al. 1996). Two of these are late-type stars – [WC8] and [WC9-10], and four are early-type around [WC4] or possibly [WO4]. Two of the early-type stars have unusual strong emission features near 4610Å which may be attributed to [N V] and could be indicative of enhanced nitrogen in their atmospheres and unusual stellar evolution. The seventh star is of the [WN] sequence and, if confirmed, would be the only known [WN] central star in the Galaxy. Its surrounding circular nebula has emission lines with expansion velocities exceeding 150 km/s suggesting that the object may not a conventional planetary nebula. The possibility that it is a Population I star with a ring nebula, although looking increasingly less likely, cannot be finally ruled out at this stage. Full details of the [WC] stars have been given by Morgan, Parker, & Russeil (2001) and Parker & Morgan (2002). The candidate [WN] star is described by Morgan & Parker (2002).

scholarly journals Parameters of Wolf-Rayet Stars

1986 ◽  
Vol 116 ◽  
pp. 199-214
Author(s):  
Peter S. Conti
Keyword(s):  
Absorption Spectrum ◽  
Mass Loss ◽  
Stellar Wind ◽  
Planetary Nebulae ◽  
Emission Lines ◽  
Helium Ions ◽  
Strong Emission ◽  
Optical Region ◽  
Central Stars ◽  
Intrinsic Feature

Wolf-Rayet (W-R) stars are objects with strong emission lines in the optical region due to a substantial stellar wind. They are found among the extreme Population I stars which are the topic of this Symposium and also this talk, and as central stars of planetary nebulae which I will not discuss here. The mass loss rates, Ṁ, are typically several 10−5 solar masses per year. W-R stars come in two major subtypes, the WN, in which strong lines of helium and nitrogen are seen, and the WC, in which strong lines of carbon and oxygen are found, along with the helium ions. In a few WN stars hydrogen appears to be present but the spectra of W-R stars are notable for the absence of this element. Absorption lines are generally not found in W-R stars, except in some instances due to a binary companion, or a more distant companion, or as a P-Cygni profile associated with certain emission features. An absorption spectrum appears to be an intrinsic feature in a very few WN stars.

scholarly journals The SAMI Galaxy Survey: reconciling strong emission line metallicity diagnostics using metallicity gradients

2021 ◽  
Vol 502 (3) ◽  
pp. 3357-3373
Author(s):  
Henry Poetrodjojo ◽  
Brent Groves ◽  
Lisa J Kewley ◽  
Sarah M Sweet ◽  
Sebastian F Sanchez ◽  
...  
Keyword(s):  
Emission Line ◽  
Electron Temperature ◽  
Gas Phase ◽  
Mass Range ◽  
Accurate Method ◽  
Emission Lines ◽  
Mass Relation ◽  
Strong Emission ◽  
Data Release ◽  
Accurate Comparison

ABSTRACT We measure the gas-phase metallicity gradients of 248 galaxies selected from Data Release 2 of the SAMI Galaxy Survey. We demonstrate that there are large systematic discrepancies between the metallicity gradients derived using common strong emission line metallicity diagnostics. We determine which pairs of diagnostics have Spearman’s rank coefficients greater than 0.6 and provide linear conversions to allow the accurate comparison of metallicity gradients derived using different strong emission line diagnostics. For galaxies within the mass range 8.5 &lt; log (M/M⊙) &lt; 11.0, we find discrepancies of up to 0.11 dex/Re between seven popular diagnostics in the metallicity gradient–mass relation. We find a suggestion of a break in the metallicity gradient–mass relation, where the slope shifts from negative to positive, occurs between 9.5 &lt; log (M/M⊙) &lt; 10.5 for the seven chosen diagnostics. Applying our conversions to the metallicity gradient–mass relation, we reduce the maximum dispersion from 0.11 dex/Re to 0.02 dex/Re. These conversions provide the most accurate method of converting metallicity gradients when key emission lines are unavailable. We find that diagnostics that share common sets of emission line ratios agree best, and that diagnostics calibrated through the electron temperature provide more consistent results compared to those calibrated through photoionization models.

Dissecting quasars with the J-PAS narrow-band photometric survey

2019 ◽  
Vol 15 (S356) ◽  
pp. 12-16
Author(s):  
Silvia Bonoli ◽  
Giorgio Calderone ◽  
Raul Abramo ◽  
Jailson Alcaniz ◽  
Narciso Benitez ◽  
...  
Keyword(s):  
Emission Line ◽  
Wavelength Range ◽  
Software Package ◽  
Narrow Band ◽  
Active Galaxies ◽  
Emission Lines ◽  
Low Resolution ◽  
Strong Emission ◽  
Optical Wavelength ◽  
Quasar Spectra

AbstractThe J-PAS survey will soon start observing thousands of square degrees of the Northern Sky with its unique set of 56 narrow band filters covering the entire optical wavelength range, providing, effectively, a low resolution spectra for every object detected. Active galaxies and quasars, thanks to their strong emission lines, can be easily identified and characterized with J-PAS data. A variety of studies can be performed, from IFU-like analysis of local AGN, to clustering of high-z quasars. We also expect to be able to extract intrinsic physical quasar properties from the J-PAS pseudo-spectra, including continuum slope and emission line luminosities. Here we show the first attempts of using the QSFit software package to derive the properties for 22 quasars at 0.8 < z < 2 observed by the miniJPAS survey, the first deg2 of J-PAS data obtained with an interim camera. Results are compared with the ones obtained by applying the same software to SDSS quasar spectra.

scholarly journals IUE Spectra of The by Dra/Flare Star AU Mic

1983 ◽  
Vol 71 ◽  
pp. 249-250
Author(s):  
C.J. Butler ◽  
A.D. Andrews ◽  
J.G. Doyle ◽  
P.B. Byrne ◽  
J.L. Linsky ◽  
...  
Keyword(s):  
Light Curve ◽  
Emission Line ◽  
Flare Star ◽  
Emission Lines ◽  
Spectral Variation ◽  
Strong Emission ◽  
Line Intensities ◽  
The Mean ◽  
Phase Interval

A coordinated series of ground-based optical and IUE observations of BY Dra variables was undertaken to follow the spectral variation of these stars over one cycle. In the first series 20 LWR and 19 SWP trailed spectra were taken of AU Mic over a three day period 4-6 August 1980 .In Figure 1 we show the mean integrated fluxes for the strong emission lines in the SWP spectra of AU Mic over the observed phase interval of 0.14 to 0.8 together with an approximate V light curve determined by the FES on IUE. From comparison of the emission line intensities and FES magnitudes in Figure 1 several points emerge.

scholarly journals The Statistical Equilibrium of H and He and the H/He Ratio in WR Stars

1984 ◽  
Vol 86 ◽  
pp. 88-91
Author(s):  
A.B. Underhill ◽  
A.K. Bhatia
Keyword(s):  
Electron Temperature ◽  
Statistical Equilibrium ◽  
Emission Lines ◽  
General Distribution ◽  
Strong Emission ◽  
B Stars ◽  
Effective Temperatures ◽  
The Masses ◽  
Selection Of ◽  
Made In

The mixed selection of strong emission lines present in the spectra of WR stars suggests that we are observing plasma with an electron temperature of the order of 105 K somewhere in the atmospheres of these rare stars. In the spectra of some WR stars emission lines of H are detected; this suggests that plasma with an electron temperature of the order of 104 K may be present also. Since the observations made in the last 30 years show that the masses, luminosities, effective temperatures, and general distribution in space of WR stars are similar to those of stars with spectral types in the range from about B2 to O9, a prime question is why are the spectra of WR stars so different from those of the B stars with which they are associated.

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