scholarly journals Quantitative classification of [WC] nuclei of Planetary Nebulae

1997 ◽  
Vol 180 ◽  
pp. 18-18 ◽  
Author(s):  
A. Acker ◽  
M. Parthasarathy ◽  
W. Leindecker ◽  
J. Koeppen ◽  
B. Stenholm
Keyword(s):  
Emission Line ◽  
Spectral Characteristics ◽  
Planetary Nebulae ◽  
Emission Lines ◽  
High Signal ◽  
Absorption Feature ◽  
Total Strength ◽  
Central Stars ◽  
Stellar Emission

We have carried out spectral classification of 65 [WC] stars, using spectra obtained at ESO in 1994-1995 with a spectral resolution of 1500 and high signal to noise ratio. We quantify the visual classification, by using the line ratios of CIII, CIV, OV, OVI in the 530-580 nm range, correlated with the blue CIII - IV lines. We measured the total strength of the above emission lines and derived the ratios of the emission line strengths. Using the stellar emission line ratios we classified about 32 CSPN as [WC] and about 30 as WELS which show only relatively weak CIV 5806 and CIV 4650 and He II 4686 stellar emission lines. The presence of CIV 5806 and the absence of CIII 5696 the WELS appear to belong to the [WC3] type. However the OV lines are very weak or absent. Some stars are reclassified, and 4 stars are found in the [WC5-7] gap. We classified 34 CSPN as [WC]. The [WC2] CSPN NGC 2867 and PB 6 show narrow and weak He II 5412 absorption feature. Based on the relative strengths of the stellar emission features NGC 2867 [WC 2], PB 6 [WC2] and M1-61 [WC4] appear to be related to WELS (Weak Emission Line Central Stars of Planetary Nebulae). The observed spectral characteristics of the central stars of these PN suggest that they are related to [WC] - PG 1159 type of objects.

scholarly journals The Weak Emission Line Stars

2003 ◽  
Vol 209 ◽  
pp. 235-236
Author(s):  
Jeffrey Fogel ◽  
Orsola De Marco ◽  
George Jacoby
Keyword(s):  
Emission Line ◽  
Absorption Line ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Emission Lines ◽  
Type I ◽  
Evolutionary Sequence ◽  
Lower Mass ◽  
Stellar Temperatures ◽  
Central Stars

In this paper, we study the evolution of the weak emission line central stars of planetary nebula (WELS), which are similar to the H-deficient Wolf-Rayet central stars except for systematically weaker emission lines. Our attempts at finding an evolutionary sequence for the WELS similar to what was established for Wolf-Rayet central stars, were unsuccessful. No correlation was found between any of the analysed quantities: emission and absorption line fluxes or stellar and nebular parameters from the literature. It does appear, however, that WELS have intermediate stellar temperatures (30–80 kK), and do not reside in the middle of Type I planetary nebulae, possibly indicating lower mass precursors.

scholarly journals Optical Histories of Some Possible Embryonic Planetary Nebulae

1978 ◽  
Vol 76 ◽  
pp. 326-327
Author(s):  
P.A. Feldman ◽  
C.R. Purton
Keyword(s):  
Emission Line ◽  
Planetary Nebulae ◽  
Mass Outflow ◽  
Central Stars ◽  
Stellar Emission

From the list of stellar emission-line objects which exhibit radio spectra characteristic of uniform radial mass outflow, we have selected those objects which might be considered possible embryonic planetary nebulae. Our criterion was to choose those mass outflow objects with exciting stars of the types'characteristic of central stars of non-stellar (i.e., normal) planetary nebulae. These objects are Hb 12, Hen 1044, HD 167362, and possible M2-9, Vy 2-2, and Hl-23.

scholarly journals Weak emission line central stars of planetary nebulae

2011 ◽  
Vol 7 (S283) ◽  
pp. 510-511
Author(s):  
Helga Todt ◽  
Miriam Peña ◽  
Julia Zühlke ◽  
Lida Oskinova ◽  
Wolf-Rainer Hamann ◽  
...  
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
Hydrogen Content ◽  
Planetary Nebulae ◽  
Emission Lines ◽  
Detailed Knowledge ◽  
Spectral Classification ◽  
Balmer Lines ◽  
Formation And Evolution ◽  
Central Stars

AbstractTo understand the evolution and morphology of planetary nebulae, a detailed knowledge of their central stars is required. Central stars that exhibit emission lines in their spectra, indicating stellar mass-loss allow to study the evolution of planetary nebulae in action. Emission line central stars constitute about 10 % of all central stars. Half of them are practically hydrogen-free Wolf-Rayet type central stars of the carbon sequence, [WC], that show strong emission lines of carbon and oxygen in their spectra. In this contribution we address the weak emission-lines central stars (wels). These stars are poorly analyzed and their hydrogen content is mostly unknown. We obtained optical spectra, that include the important Balmer lines of hydrogen, for four weak emission line central stars. We present the results of our analysis, provide spectral classification and discuss possible explanations for their formation and evolution.

scholarly journals The Ionization of Planetary Nebulae

1968 ◽  
Vol 34 ◽  
pp. 190-204 ◽  
Author(s):  
Robert E. Williams
Keyword(s):  
Ionizing Radiation ◽  
Emission Line ◽  
Radiation Field ◽  
Planetary Nebulae ◽  
Model Atmosphere ◽  
Evolutionary Sequence ◽  
Lyman Continuum ◽  
The Mean ◽  
Central Stars

The ionization of the most abundant elements in planetary nebulae has been determined for a number of models of nebulae at different epochs in their expansion. The values used for the temperatures and radii of the central stars and the sizes and densities of the shells have come from Seaton's evolutionary sequence. The ionizing radiation field has been taken from model atmosphere calculations of the central stars by Gebbie and Seaton, and Böhm and Deinzer. Emission-line fluxes have been calculated for the models and compared with observations of planetary nebulae by O'Dell, Osterbrock's group, and Aller and his collaborators. Results indicate that the central stars have strong He+ Lyman continuum excesses, similar to those predicted by Gebbie and Seaton. The mean abundance determinations for the nebulae made by Aller are confirmed, with the exception of nitrogen, which appears to be 3 or 4 times more abundant than his value. It is also seen that the electron temperatures of the nebulae are higher than previous theoretical determinations, providing better agreement with empirically derived values.

scholarly journals SDSS-IV MaNGA: the spectroscopic discovery of strongly lensed galaxies

2018 ◽  
Vol 477 (1) ◽  
pp. 195-209 ◽  
Author(s):  
Michael S Talbot ◽  
Joel R Brownstein ◽  
Adam S Bolton ◽  
Kevin Bundy ◽  
Brett H Andrews ◽  
...  
Keyword(s):  
Emission Line ◽  
Narrow Band ◽  
Signal To Noise Ratio ◽  
Gravitational Lens ◽  
Emission Lines ◽  
High Signal ◽  
Common Source ◽  
Narrow Band Image ◽  
Background Emission ◽  
Field Unit

Abstract We present a catalogue of 38 spectroscopically detected strong galaxy–galaxy gravitational lens candidates identified in the Sloan Digital Sky Survey IV (SDSS-IV). We were able to simulate narrow-band images for eight of them demonstrating evidence of multiple images. Two of our systems are compound lens candidates, each with two background source-planes. One of these compound systems shows clear lensing features in the narrow-band image. Our sample is based on 2812 galaxies observed by the Mapping Nearby Galaxies at APO (MaNGA) integral field unit (IFU). This Spectroscopic Identification of Lensing Objects (SILO) survey extends the methodology of the Sloan Lens ACS Survey (SLACS) and BOSS Emission-Line Survey (BELLS) to lower redshift and multiple IFU spectra. We searched ∼1.5 million spectra, of which 3065 contained multiple high signal-to-noise ratio background emission-lines or a resolved [O ii] doublet, that are included in this catalogue. Upon manual inspection, we discovered regions with multiple spectra containing background emission-lines at the same redshift, providing evidence of a common source-plane geometry which was not possible in previous SLACS and BELLS discovery programs. We estimate more than half of our candidates have an Einstein radius ≳ 1.7 arcsec, which is significantly greater than seen in SLACS and BELLS. These larger Einstein radii produce more extended images of the background galaxy increasing the probability that a background emission-line will enter one of the IFU spectroscopic fibres, making detection more likely.

scholarly journals Spectral analyses of late–type [WC] central stars: element abundances of N, Ne and Si

1997 ◽  
Vol 180 ◽  
pp. 119-119
Author(s):  
U. Leuenhagen
Keyword(s):  
Wind Velocity ◽  
Optical Spectra ◽  
Emission Lines ◽  
Late Type ◽  
Spectral Analyses ◽  
Element Abundances ◽  
Type Object ◽  
Central Stars ◽  
Stellar Emission

The optical spectra of [WC] central stars of the latest subtypes ([WC11], [WC12]) exhibit not only stellar emission lines of hydrogen (in some cases), helium, carbon and oxygen, but also features of nitrogen (N ii, N iii), neon (Ne i), magnesium (Mg ii), aluminium (Al iii), silicon (Si iii, Si iv) and iron (Fe iii). Some of these features are also visible in the peculiar [WC9]–type object SwSt 1 which has a lower final wind velocity and a smaller wind density than normal [WC9] stars.

scholarly journals Non-LTE analysis of central stars∗

1984 ◽  
Vol 105 ◽  
pp. 205-208
Author(s):  
R.P. Kudritzki ◽  
R.H. Méndez ◽  
K.P. Simon
Keyword(s):  
Emission Line ◽  
Planetary Nebulae ◽  
Present Knowledge ◽  
Indirect Methods ◽  
Central Stars

Most of our present knowledge about central stars of planetary nebulae (CPN) is obtained by indirect methods using the emission line spectra of the surrounding nebula. These methods, which apply the beautiful recombination theory, can provide us with information about temperature, distance and radius of the CPN. However, we know that these methods are subject to severe problems, which then lead to strong discrepancies in the parameters of the CPN.

scholarly journals Comments on the Detection and Classification of Compact Emission-Line Galaxies

1979 ◽  
Vol 47 ◽  
pp. 151-153
Author(s):  
T. D. Kinman
Keyword(s):  
Emission Line ◽  
Emission Lines ◽  
Ultraviolet Excess ◽  
Strong Emission ◽  
The Galaxy ◽  
Objective Prism ◽  
Emission Line Galaxies

Four methods for finding emission-line galaxies have been compared. Method (a) uses the ultraviolet excess, as found either by filter photography (Haro 1956) or by objective prism spectra (Markarian 1967). glanco (1974) introduced a thin prism with the CTIO Schmidt (1740 Å mm-1 at Hβ) which with IIIa-J plates [Method (b)] gave enough resolution for Smith (1975) and MacAlpine et al. (1977a, 1977b) to detect and classify galaxies by strong emission lines. Following a suggestion by McCarthy that even higher dispersion might be useful, I have used the CTIO Schmidt with [Method (c)] the 4° prism, a GGl+55 filter and IIIa-J emulsion and with [Method (d)] the 10° prism, an RG630 filter and IIIa-F emulsion. These latter give about 400 Å mm-1 at Hβ and Hα respectively which improves the visibility of emission lines against the galaxy continuum so that [0111] 5007 and 4959 and Hβ can be seen on the green plates and Hα and [SII] 6725 can be seen on the red plates.

scholarly journals Spectra of Wolf-Rayet type central stars and their analysis

1997 ◽  
Vol 180 ◽  
pp. 91-96 ◽  
Author(s):  
W.-R Hamann
Keyword(s):  
Planetary Nebulae ◽  
Emission Lines ◽  
Considerable Fraction ◽  
Broad Emission ◽  
Central Stars

Wolf-Rayet (short: WR) stars are characterized by the bright and broad emission lines which dominate their spectra. This class was originally established for Pop. I stars, distinguishing a nitrogen (WN) and carbon (WC) sequence according to the dominating lines. Wolf-Rayet (specifically, WC) type spectra are also shown by a considerable fraction of central stars of planetary nebulae.

scholarly journals Excitation Class of Nebulae as an Evolution Criterion

1993 ◽  
Vol 155 ◽  
pp. 481-481
Author(s):  
G.A. Gurzadyan ◽  
A.G. Egikyan
Keyword(s):  
Empirical Relationship ◽  
Planetary Nebulae ◽  
Emission Lines ◽  
Independent Parameter ◽  
The Mean ◽  
Evolutionary Interpretation

A principally new, quantitative system of the classification of spectra of planetary nebulae is proposed. The excitation class of a nebula, p, is determined according to the relative intensities of emission lines, N1+N2/4686 HeII and N1+N2/Hβ. The excitation classes are obtained for 177 PN with known distances and sizes of all classes – low (p=1–3), middle (p=4–8) and high (p=9–12+). An empirical relationship between the excitation class p and the mean radius of the nebulae Rn is discovered – the largest sizes occur for highly excited nebulae, and the smallest for low excitation ones. This relationship as well as excitation class p, as an independent parameter admit an evolutionary interpretation (Gurzadyan, Egikyan 1991).

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