J/MNRAS/452/2606 Deep echelle spectrophotometry of NGC3918 (Garcia-Rojas+, 2015)
s-process enrichment in the planetary nebula NGC 3918. Results from deep
echelle spectrophotometry
Garcia-Rojas J., Madonna S., Luridiana V., Sterling N.C., Morisset C.,
Delgado-Inglada G., Toribio San Cipriano L.
<Mon. Not. R. Astron. Soc., 452, 2606-2640 (2015)>
=2015MNRAS.452.2606G 2015MNRAS.452.2606G (SIMBAD/NED BibCode)
ADC_Keywords: Planetary nebulae ; Interstellar medium ; Spectroscopy ;
Radial velocities
Keywords: stars: AGB and post-AGB - ISM: abundances -
planetary nebulae: individual: NGC 3918
Abstract:
The chemical content of the planetary nebula NGC 3918 is investigated
through deep, high-resolution (R∼40000) UVES (Ultraviolet-Visual
Echelle Spectrograph) at VLT (Very Large Telescope) spectrophotometric
data. We identify and measure more than 750 emission lines, making
ours one of the deepest spectra ever taken for a planetary nebula.
Among these lines we detect very faint lines of several
neutron-capture elements (Se, Kr, Rb, and Xe), which enable us to
compute their chemical abundances with unprecedented accuracy, thus
constraining the efficiency of the s-process and convective dredge-up
in NGC 3918 progenitor star. We find that Kr is strongly enriched in
NGC 3918 and that Se is less enriched than Kr, in agreement with the
results of previous papers and with predicted s-process
nucleosynthesis. We also find that Xe is not as enriched by the
s-process in NGC 3918 as is Kr and, therefore, that neutron exposure
is typical of modestly subsolar metallicity asymptotic giant branch
(AGB) stars. A clear correlation is found when representing [Kr/O]
versus log(C/O) for NGC 3918 and other objects with detection of
multiple ions of Kr in optical data, confirming that carbon is brought
to the surface of AGB stars along with s-processed material during
third dredge-up episodes, as predicted by nucleosynthesis models. We
also detect numerous refractory element lines (Ca, K, Cr, Mn, Fe, Co,
Ni, and Cu) and a large number of metal recombination lines of C, N,
O, and Ne. We compute physical conditions from a large number of
diagnostics, which are highly consistent among themselves assuming a
three-zone ionization scheme. Thanks to the high ionization of NGC
3918 we detect a large number of recombination lines of multiple
ionization stages of C, N, O and Ne. The abundances obtained for these
elements by using recently determined state-of-the-art ionization
correction factor (ICF) schemes or simply adding ionic abundances are
in very good agreement, demonstrating the quality of the recent ICF
scheme for high-ionization planetary nebulae.
Description:
The spectra of NGC 3918 were taken with the Ultraviolet-Visual Echelle
Spectrograph (UVES; D'Odorico et al. 2000SPIE.4005..121D 2000SPIE.4005..121D), attached to
the 8.2-m Kueyen (UT2) Very Large Telescope (VLT) at Cerro Paranal
Observatory (Chile) in service mode on 2013 March 8. The observations
were taken under clear/dark conditions and the seeing remains below
1.5 arcsec during the whole run.
Objects:
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RA (ICRS) DE Designation(s)
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11 50 17.77 -57 10 56.4 NGC 3918 = HD 102854
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 84 755 Observed and reddening corrected line ratios
[F(Hβ)=100] and line identifications
in NGC 3918
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See also:
V/84 : Strasbourg-ESO Catalogue of Galactic Planetary Nebulae
(Acker+, 1992)
J/A+AS/132/13 : Planetary nebulae radial velocities (Durand+ 1998)
J/ApJ/714/1096 : Galactic planetary nebulae (Stanghellini+, 2010)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 8 F8.2 0.1nm lambda0 ? Wavelength λ0 (Å) (1)
10- 17 A8 --- Ion Ion designation
19- 35 A17 --- Mult Ion multiplet name or number
37- 44 F8.2 0.1nm lambda ? Observed wavelength λobs
(Å)
45 A1 --- n_lambda [*] Note on lambda (2)
47- 53 F7.3 km/s RV ? Radial velocity
54 A1 --- n_RV [*] Note on RV (2)
56- 64 F9.4 --- Fl/F(Hbeta) ? F(λ)/F(Hβ) ratio (3)
65 A1 --- n_Fl/F(Hbeta) [*] Note on Fl/F(Hbeta) (2)
67- 75 F9.4 --- Il/I(Hbeta) ? I(λ)/I(Hβ) ratio (4)
76 A1 --- n_Il/I(Hbeta) [*] Note on Il/I(Hbeta) (2)
78- 79 I2 % e_Il/I(Hbeta) ? Uncertainty in Il/I(Hbeta) (5)
80 A1 --- neIl/I(Hbeta) [*:] Note on e_Il/I(Hbeta) (2)
82- 84 A3 --- Note Note(s) (6)
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Note (1): There are 18 lines that could not be identified with the available
sources, amounting to ∼2.5 per cent of the measured lines.
Note (2): Note as follows:
* = Not observed;
: = Indicate errors higher than 40 per cent.
Note (3): Where F is the unreddened flux in units of
100.00=5.543x10-12 erg/cm2/s.
Note (4): Where I is the reddened corrected flux, with c(Hβ)=0.27, in units
of 100.00=1.032x10-11 erg/cm2/s.
Note (5): The final percentile errors (1σ) of the I(λ)/I(Hβ)
ratios were computed taking into account the uncertainties in the
determination of c(Hβ).
Note (6): Note as follows:
c = Blended with an unknown line;
d = Affected by charge transfer;
e = Affected by atmospheric absorption bands;
f = Affected by ghost;
g = Partially blended with other emission line;
h = Affected by interstellar Na I absorption;
i = Affected by telluric emission;
? = Dubious identifications.
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 21-Dec-2017