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

Spectroscopy of planetary nebulae in M33

Spectroscopic observations of 48 emission-line objects of M33 have been obtained with the multi-object, wide field, fibre spectrograph AF2/WYFFOS at the 4.2m WHT telescope (La Palma, Spain). Line intensities and logarithmic extinction, cbeta, are presented for 42 objects. Their location in the Sabbadin & D'Odorico diagnostic diagram (Halpha/[SII] vs Hlapha/[NII]) suggests that >70% of the candidates are Planetary Nebulae (PNe). Chemical abundances and nebular physical parameters have been derived for the three of the six PNe where the 4363A [OIII] emission line was measurable. These are disc PNe, located within a galactocentric distance of 4.1 kpc, and, to date, they are the farthest PNe with a direct chemical abundance determination. No discrepancy in the Helium, Oxygen and Argon abundances has been found in comparison with corresponding abundances of PNe in our Galaxy. Only a lower limit to the sulphur abundance has been obtained since we could not detect any [SIII] line. N/H appears to be lower than the Galactic value; some possible explanations for this under-abundance are discussed.Comment: 18 pages, 1 JPEG figure and 3 Postscript figures, Accepted for publication in A&

Facilitating an Ethical Disposition (Hexis) as “Care of the Soul” in a Unique Ontological Vision of Socratic Education

This essay adopts a Continental philosophical approach to reading Plato’s Socrates in terms of a “third way” that cuts a middle path between doctrinal and esoteric readings of the dialogues. It presents a portrait of Socratic education that is at odds with contemporary views in education and curriculum that view Plato’s Socrates as either the teacher of a truth-finding method or proto-fascist authoritarian. It argues that the crucial issue of attempting to foster an ethical disposition (hexis) is a unique form of education, in terms of “care of the soul,” that unfolds only within the context of sustained dialectic interrogation. Education is a “difficult” process that entails the “turning” of the soul back to itself in an enlightened form, which is bound up with an ontological relationship of distance to the so-called “truth” of the virtues that appear in limited and dissembling ways to Socrates and the interlocutors. Ultimately, it is shown that “care of the soul” is grounded in the attunement (a pathos and deinon) that locates the human being in the world in such a way that “not-knowing” is the most original way in which our Being-in-the-world unfolds, and to embrace this “difficult” truth is to at once set oneself on the arduous but rewarding educative path toward the potential development of an ethical disposition (hexis)

Distribution dynamics: a spatial perspective

It is quite common in cross-sectional convergence analyses that data exhibit spatial dependence. Within the literature adopting the distribution dynamics approach, authors typically opt for spatial prefiltering. We follow an alternative route and propose a procedure based on an estimate of the mean function of a conditional density for which we develop a two-stage non-parametric estimator that allows for spatial dependence estimated via a spline estimator of the spatial correlation function. The finite sample performance of this estimator is assessed via Monte Carlo simulations. We apply the procedure that incorporates the proposed spatial non-parametric estimator to data on per capita personal income in US states and metropolitan statistical areas

The S2N2 metallicity calibrator and the abundance gradient of M 33

We introduce the log(Ha/[SII]6717+6731) vs. log(Ha/[NII]6583) (S2N2) diagnostic diagram as metallicity and ionisation parameter indicator for HII regions in external galaxies. The location of HII regions in the S2N2 diagram was studied both empirically and theoretically. We found that, for a wide range of metallicities, the S2N2 diagram gives single valued results in the metallicity-ionisation parameter plane. We demonstrate that the S2N2 diagram is a powerful tool to estimate metallicities of high-redshift (z ~ 2) HII galaxies. Finally, we derive the metallicity for 76 HII regions in M33 from the S2N2 diagram and calculate an O/H abundance gradient for this galaxy of -0.05 (+-0.01) dex kpc^-1.Comment: 10 pages, 3 figures and 2 tables. Accepted for publication in MNRA

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 + $\log$(O/H)=7.6$\pm$0.2 in SextansA, and 7.8$\pm$0.2 in SextansB. For the five PNe of SextansA, we find that 12 + $\log$(O/H)=8.0$\pm$0.3, 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&