197 research outputs found
New candidate planetary nebulae in M81
A 34 x 34 arcmin field centred on the spiral galaxy M81 has been searched for
emission-line objects using the prime focus wide field camera (WFC) of the 2.54
m Isaac Newton Telescope (La Palma, Spain). A total of 171 candidate planetary
nebulae (PNe) are found, 54 of which are in common with the ones detected by
Jacoby et al. (1989). The behaviour of PNe excitation as a function of
galactocentric distance is examined, and no significant variations are found.
The PNe luminosity function is built for the disk and bulge of M81, separately.
A distance modulus of 27.92+-0.23 mag is found for disk PNe, in good agreement
with previous distance measurements for M81 (Jacoby et al. 1989; Huterer et al.
1995).Comment: 7 pages including 2 tables. A&A accepted; also available at
http://www.iac.es/publicaciones/preprints.htm
Absolute Spectrophotometry of Northern Compact Planetary Nebulae
We present medium-dispersion spectra and narrowband images of six northern
compact planetary nebulae (PNe): BoBn 1, DdDm 1, IC 5117, M 1-5, M 1-71, and
NGC 6833. From broad-slit spectra, total absolute fluxes and equivalent widths
were measured for all observable emission lines. High signal-to noise emission
line fluxes of H-alpha, H-beta, [OIII], [NII], and HeI may serve as emission
line flux standards for northern hemisphere observers. From narrow-slit
spectra, we derive systemic radial velocities. For four PNe, available emission
line fluxes were measured with sufficient signal-to-noise to probe the physical
properties of their electron densities, temperatures, and chemical abundances.
BoBn 1 and DdDm 1, both type IV PNe, have an H-beta flux over three sigma away
from previous measurements. We report the first abundance measurements of M
1-71. NGC 6833 measured radial velocity and galactic coordinates suggest that
it is associated with the outer arm or possibly the galactic halo, and its low
abundance ([O/H]=1.3x10E-4) may be indicative of low metallicity within that
region.Comment: 9 pages, 1 figure, accepted in A&A (03/14/2005
Formation and Evolution of Planetary Nebulae: A Radiation Hydrodynamics Study
The formation and evolution of a planetary nebula is based on the occurrence of a strong AGB wind and the rapid evolution of the central star with corresponding changes of its ionizing flux and wind power. We have studied the influence of different mass-loss histories in combination with various central-star properties
The chemistry of planetary nebulae and HII regions in the dwarf galaxies Sextans A and B from deep VLT spectra
Spectroscopic observations obtained with the VLT of one planetary nebula (PN)
in Sextans A and of five PNe in Sextans B and of several HII regions (HII) in
these two dwarf irregular galaxies are presented. The extended spectral
coverage, from 320.0 to 1000.0nm, and the large telescope aperture allowed us
to detect a number of emission lines, covering more than one ionization stage
for several elements (He, O, S, Ar). The electron temperature (Te) diagnostic
[OIII] line at 436.3 nm was measured in all six PNe and in several HII allowing
for an accurate determination of the ionic and total chemical abundances by
means of the Ionization Correction Factors method. For the time being, these
PNe are the farthest ones where such a direct measurement of the Te is
obtained. In addition, all PNe and HII were also modelled using the
photoionization code CLOUDY. The physico-chemical properties of PNe and HII are
presented and discussed. A small dispersion in the oxygen abundance of HII was
found in both galaxies: 12 + (O/H)=7.60.2 in SextansA, and
7.80.2 in SextansB. For the five PNe of SextansA, we find that 12 +
(O/H)=8.00.3, with a mean abundance consistent with that of HII. The
only PN known in SextansA appears to have been produced by a quite massive
progenitor, and has a significant nitrogen overabundance. In addition, its
oxygen abundance is 0.4 dex larger than the mean abundance of HII, possibly
indicating an efficient third dredge-up for massive, low-metallicity PN
progenitors. The metal enrichment of both galaxies is analyzed using these new
data.Comment: 19 pages, 11 figures, Accepted by A&
Chemical Abundances of Planetary Nebulae in M33
Using spectroscopic data presented in Magrini et al. (2003), we have analyzed
with the photoionization code CLOUDY 94.00 (Ferland et al. 1998) 11 Planetary
Nebulae belonging to the spiral galaxy M 33. Central star temperatures and
nebular parameters have been determined. In particular the chemical abundances
of He/H, O/H, N/H, Ar/H, and S/H have been measured and compared with values
obtained via the Ionization Correction Factors (ICFs) method, when available.
Chemical abundance relationships have been investigated; in particular, a
correlation between N/H and N/O similar to the Galactic one (Henry 1989), and a
feeble anti-correlation between O/H and N/O have been found.
A gradient in O/H across the disc of M~33 is indicatively consistent with the
one found from HII regions in this galaxy (Vilchez et al 1988). Further studies
in the more external parts of M~33 are however needed to ascertain this point.
The present result shows that oxygen and helium abundances (with lower accuracy
also nitrogen, argon and sulphur) can be actually estimated from the brightest
PNe of a galaxy, even if the electron temperature cannot be measured. We also
found that the oxygen abundance is quite independent of the absolute magnitude
of the PN and consequently the brightest PNe are representative of the whole PN
population. This represents an important tool to measure the metallicity of
galaxies at the time of the formation of PNe progenitors.Comment: 17 pages, 6 figures, A&A accepte
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