P. Leisy

The metallicity gradient of M 33: chemical abundances of H ii regions

Context. We present spectroscopic observations of a sample of 72 emission-line objects, including mainly H ii regions, in the spiral galaxy M 33. Spectra were obtained with the multi-object, wide field spectrograph AF2/WYFFOS at the 4.2 m WHT telescope. Line intensities, extinction, and electron density were determined for the whole sample of objects. Aims. The aim of the present work was to derive chemical and physical parameters of a set of H ii regions, and from them the metallicity gradient. Methods. Electron temperatures and chemical abundances were derived for the 14 H ii regions where both [O ii ]a nd [Oiii ]e mission line fluxes were measured, including the electron temperature sensitive emission line [O iii] 436.3 nm and in a few cases [N ii] 575.5 nm. The ionization correction factor (ICF) method was used to derive the total chemical abundances. Results. The presence of abundance gradients was inferred from the radial behaviour of several emission-line ratios, and accurately measured from chemical abundances directly derived in 14 H ii regions. The oxygen abundances of our H ii regions, located in the radial region from ∼ 2t o∼7.2 kpc, gave an oxygen gradient −0.054 ± 0.011 dex kpc −1 Conclusions. The overall oxygen gradient for M 33 obtained using ours and previous oxygen determinations in a large number of H ii regions with direct electron temperature determination as well as abundance in young stars presented a two slope shape: −0.19 dex kpc −1 for the central regions (R < 3 kpc), and −0.038 dex kpc −1 for the outer regions (R ≥ 3 kpc).

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 H uf769uf769 regions in these two dwarf irregular galaxies are presented. The extended spectral coverage, from 320.0 to 1000.0 nm, 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 diagnostic [O uf769uf769uf769] line at 436.3 nm was measured in all six PNe and in several H uf769uf769 regions 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 electron temperature is obtained. In addition, all PNe and H uf769uf769 regions were also modelled using the photoionization code CLOUDY (Ferland et al. 1998, PASP, 110, 761). The physico-chemical properties of PNe and H uf769uf769 regions are presented and discussed. A small dispersion in the oxygen abundance of H uf769uf769 regions was found in both galaxies: 12 + log (O/H) = 7.6 ± 0. 2i n Sextans A, and 7.8 ± 0.2 in Sextans B. For the five PNe of Sextans B, we find that 12 + log (O/H) = 8.0 ± 0.3, with a mean abundance consistent with that of H uf769uf769 regions. The only PN known in Sextans A 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 H uf769uf769 regions, 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.

The Local Group Census: Planetary nebulae in IC 10, Leo A and Sextans A

In the framework of our narrow-band survey of the Local Group galaxies, we present the results of the search for planetary nebulae (PNe) in the dwarf irregular galaxies IC 10, Leo A and Sextans A. Using the standard on-band/off-band technique, sixteen new candidate PNe have been discovered in the closest starburst galaxy, IC 10. The optical size of this galaxy is estimated to be much larger than previously thought, considering the location of the new PNe in an area of 3.6 kpc × 2.7 kpc. We also confirm the results of previous studies for the other two dwarf irregular galaxies, with the detection of one candidate PN in Leo A and another one in Sextans A. We review the number of planetary nebulae discovered in the Local Group to date and their behaviour with metallicity. We suggest a possible fall in the observed number of PNe when (Fe/H) � -1.0, which might indicate that below this point the formation rate of PNe is much lower than for stellar populations of near Solar abundances. We also find non-negligible metallicity effects on the (O uf769uf769uf769) luminosity of the brightest PN of a galaxy.

The chemical content of nearby galaxies from planetary nebulae: NGC 147

We report the results of spectroscopic observations, obtained with the Gemini Multi-Object Spectrograph, of eight planetary nebulae (PNe) in the dwarf spheroidal (dSph) galaxy NGC 147, a companion of M31. The physico-chemical properties of the six brightest PNe were derived using both the empirical ICF method and photoionization modelling with CLOUDY. Different aspects of the evolution of low- and intermediate-mass stars in a low-metallicity environment are analysed using relationships between chemical abundances. In addition, certain features of the chemical evolution of NGC 147 were examined. In particular, the mean metallicity of PNe, O/H = 8.06 +0.09 −0.12 (corresponding to [Fe/H]PNe ∼− 0.97), is close to the metallicity of the old stellar population, [Fe/H] =− 1.0, suggesting a negligible chemical enrichment during a substantial amount of time. Finally, the luminosity‐metallicity relationship for the dwarf galaxies of the Local Group is discussed. The location in the luminosity‐metallicity diagram of dSphs does not exclude their formation from old dwarf irregular (dIr) galaxies, but it does exclude their formation from the present time dIrs, since the differences between their metallicities are already present in their older populations. The offset in the luminosity‐ metallicity relationship indicates a faster enrichment of dSphs and, together with the different average abundance ratio [O/Fe ]demonstrates the different star formation histories for these two types of galaxies.

Eclipse of the B3V companion and flaring of emission lines in V838 Monocerotis

After four years during which only the spectacular light echo was showing continuous and rapid evolution while the central star was nearly constant, in autumn 2006 V838 Mon began a sequence of events which profoundly altered its spectroscopic and photometric behavior: (a) an eclipse of the B3V companion, characterized by the disappearance and reappearance of the B3V companion from optical spectra, and an eclipse-like lightcurve of ∼70 day duration and ∆B ∼ 1.15 mag, ∆V ∼ 0.55 mag, ∆RC ∼ 0.10 mag maximum depth; (b) a large increase in intensity of the [FeII] and FeII emission lines, and the appearance in emission for the first time since the 2002 outburst of Hα and higher Balmer series lines. While the [FeII] and FeII lines maintained a very sharp and unresolved profile, the Hα developed into a wide and structured profile, characterized by a sharp central reversal at the same velocity as one of the CO radio emission components. The disappearance of the B3V companion is equally well explained by a grazing eclipse from the outbursting L-type supergiant or by an eclipse from a dust cloud characterized by EB−V = 0.55 and RV = 3.1. We believe the flaring of the emission lines occurred at a similar time as the B3V eclipse just by chance.

The Local Group Census: searching for planetary nebulae in IC 1613, WLM and GR8

In the framework of the Local Group Census (LGC), a survey of the Local Group (LG) galaxies above Dec =− 30 ◦ aimed at surveying the populations that have strong emission lines, we have searched for planetary nebulae (PNe) in the low-metallicity dwarf irregular galaxies IC 1613, WLM, GR 8. Two new candidate PNe have been found in IC 1613, one in WLM and none in GR 8. The observations presented in this paper, together with the previous results from the LGC, represent the first step in the study of the PN population in low-metallicity, dwarf irregular galaxies of the Local Group. These observations will be followed by deep spectroscopy to confirm the nature of these objects and to study their physical-chemical properties. We use the observed number of PNe in each LG galaxy to estimate a lower limit to the mass of the intermediate-age population, which is compared with the star formation rate (SFR) of LG dwarf galaxies. These results are in agreement with those from accurate star formation history (SFH) analyses for these small galaxy systems.

XMMU J134736.6+173403: an eclipsing LMXB in quiescence or a peculiar AGN? (Research Note)

Aims. We report the discovery of a peculiar object observed serendipitously with XMM-Newton. We present its timing and spectral properties and investigate its optical counterpart. Methods. The light curve of the X-ray source, its spectrum, and the spectrum of the best optical counterpart are presented and analyzed. Results. The X-ray flux decreases by a factor of 6.5 within 1 h and stays in a low state for at least 10 h, thereby suggesting the presence of an eclipse. The spectrum is very soft, a power law with a slope of Γ ∼ 2.8, and does not change significantly before and after the flux drop. The source is spatially coincident within few arc-seconds with a Seyfert 2 galaxy belonging to a galaxy pair. Conclusions. Although the background AGN seems the best counterpart, neither the temporal nor the spectral properties of the X-ray source are compatible with it. We investigate the possibility of having a foreground low-mass X-ray binary in quiescence, where the companion is not detected in the optical wavelength.

Spectroscopy of Planetary Nebulae in Sextans A and Sextans B

Sextans A and Sextans B are two dIr galaxies situated in the outskirts of the Local Group (LG), in which both PNe and H II regions have been detected (Jacoby & Lesser (5), Magrini et al. (6), (7)). We present spectroscopic observations of PNe and HII regions in these two galaxies obtained with the VLT. Preliminary results on the PNe physico-chemical properties are presented. 1 The Galaxies: Sextans A and Sextans B Sextans A and Sextans B are both dwarf Irregular galaxies (Ir V and Ir IV-V morphological types, respectively, cf. van den Bergh (11), hereafter vdB00) with approximately the same V luminosity, belonging to the outer fringes of the Local Group. Their distances from the barycenter of the LG are quite similar (1.60 and 1.72 Mpc, see vdB00) and their separation on the sky is relatively small (∼ 10 degrees), which corresponds to about 280 kpc. Moreover their velocity difference is only 23 ± 6k m s −1 . These results support the hypothesis of a common for- mation of these two galaxies, probably together with NGC 3109 and the Antlia galaxy. Considering the mean distance of the four galaxies from the barycenter of the LG, 1.7 Mpc, this sub-group is located beyond the zero velocity surface of the LG (cf. vdB00) and thus it can be considered the nearest external group of galaxies. As said by Mateo ((9)) No two Local Group dwarfs have the same star-formation history. This is true also when comparing very similar galaxies. In fact, in spite of a probable common formation, Sextans A and Sextans B show a different star formation history as indicated by the different amounts of stars in the various evolutionary phases, and also reflected in the different number of PNe and HII regions observed. Sextans A shows a large contribution from an old stellar population, whereas it has modest intermediate (4-10 Gyrs) and recent star formation (1-4 Gyrs ago). On the other hand, Sextans B exhibits very strong recent star formation (1-4 Gyrs), together with a very old population (c.f. the review by Mateo ((9) about the star formation history of the LG dwarfs). In this context, PNe represent an useful tool to trace the chemical enrichment history of galaxies. Moreover, in contrast to chemical abundances derived from H II regions, they are tracers of stellar population over a wide range of ages, from old to intermediate age. L. Magrini et al., Spectroscopy of Planetary Nebulae in Sextans A and Sextans B. In: Planetary

Local Group Galaxies: Abundances in NGC 3109

We present preliminary results of VLT spectroscopy follow‐up of Planetary Nebulae (PNe) and HII regions in the dwarf Irregular galaxy NGC 3109. In total we have observed 15 PNe (of a total of 18) and about 50 HII: at least for 10 PNe and 10 HII regions the very faint [O III]4363 line is observed allowing to derive accurate abundances.The comparison of the abundances with several other galaxies in the Local Group helps to trace general trends: these dwarf galaxies have low initial metallicities, but also He and N are less enriched compared to what it is observed in our Galaxy, M 33 or in the Magellanic Clouds. As already suspected in the LMC and the SMC, but now also seen at lower metallicities the abundances of O and Ne seems to be affected by nucleosynthesis during the life of the PN progenitor.