A. Mampaso

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 VST Photometric Hα Survey of the Southern Galactic Plane and Bulge (VPHAS

The VST Photometric HSurvey of the Southern Galactic Plane and Bulge (VPHAS+) is surveying the southern Milky Way in u,g,r,i and Hat �1 arcsec angular resolution. Its footprint spans the Galactic latitude range 5 o < b < +5 o at all longitudes south of the celestial equator. Extensions around the Galactic Centre to Galactic latitudes ±10 ◦ bring in much of the Galactic Bulge. This ESO public sur- vey, begun on 28th December 2011, reaches down to �20th magnitude (10�) and will provide single-epoch digital optical photometry for �300 million stars. The observing strategy and data pipelining is described, and an appraisal of the segmented narrow- band Hfilter in use is presented. Using model atmospheres and library spectra, we compute main-sequence (u g), (g r), (r i) and (r H�) stellar colours in the Vega system. We report on a preliminary validation of the photometry using test data obtained from two pointings overlapping the Sloan Digital Sky Survey. An example of the (u g,g r) and (r H�,r i) diagrams for a full VPHAS+ survey field is given. Attention is drawn to the opportunities for studies of compact nebulae and nebular morphologies that arise from the image quality being achieved. The value of the u band as the means to identify planetary-nebula central stars is demonstrated by the discovery of the central star of NGC 2899 in survey data. Thanks to its excellent imaging performance, the VST/OmegaCam combination used by this survey is a per- fect vehicle for automated searches for reddened early-type stars, and will allow the discovery and analysis of compact binaries, white dwarfs and transient sources.

Low-Ionization Structures in Planetary Nebulae: Confronting Models with Observations

Around 50 planetary nebulae (PNs) are presently known to possess small-scale low-ionization structures (LISs) located inside or outside their main nebular bodies. We consider here the different kinds of LISs (jets, jetlike systems, symmetrical and nonsymmetrical knots) and present a detailed comparison of the existing model predictions with the observational morphological and kinematical properties. We find that nebulae with LISs appear indistinctly spread among all morphological classes of PNs, indicating that the processes leading to the formation of LISs are not necessarily related to those responsible for the asphericity of the large-scale morphological components of PNs. We show that both the observed velocities and locations of most nonsymmetrical systems of LISs can be reasonably well reproduced assuming either fossil condensations originated in the asymptotic giant branch (AGB) wind or in situ instabilities. The jet models proposed to date (hydrodynamical and magnetohydrodynamical interacting winds or accretion disk collimated winds) appear unable to account simultaneously for several key characteristics of the observed high-velocity jets, such as their kinematical ages and the angle between the jet and the symmetry axes of the nebulae. The linear increase in velocity observed in several jets favors magnetohydrodynamical confinement compared to pure hydrodynamical interacting wind models. On the other hand, we find that the formation of jetlike systems characterized by relatively low expansion velocities (similar to those of the main shells of PNs) cannot be explained by any of the existing models. Finally, the knots that appear in symmetrical and opposite pairs of low velocity could be understood as the survival of fossil (symmetrical) condensations formed during the AGB phase or as structures that have experienced substantial slowing down by the ambient medium.

The Necklace : equatorial and polar outflows from the binary central star of the new planetary nebula IPHASX J194359.5+170901

IPHASXJ194359.5+170901 is a new high-excitation planetary nebula with remark- able characteristics. It consists of a knotty ring expanding at a speed of 28 kms 1 , and a fast collimated outflow in the form of faint lobes and caps along the direction perpendicular to the ring. The expansion speed of the polar caps is �100 kms 1 , and their kinematical age is twice as large as the age of the ring. Time-resolved photometry of the central star of IPHASXJ194359.5+170901 re- veals a sinusoidal modulation with a period of 1.16 days. This is interpreted as evi- dence for binarity of the central star, the brightness variations being related to the orbital motion of an irradiated companion. This is supported by the spectrum of the central star in the visible range, which appears to be dominated by emission from the irradiated zone, consisting of a warm (6000-7000 K) continuum, narrow C III, C IV, and N III emission lines, and broader lines from a flat H I Balmer sequence in emission. IPHASXJ194359.5+170901 helps to clarify the role of (close) binaries in the for- mation and shaping of planetary nebulae. The output of the common-envelope evolu- tion of the system is a strongly flattened circumstellar mass deposition, a feature that seems to be distinctive of this kind of binary system. Also, IPHASXJ194359.5+170901 is among the first post-CE PNe for which the existence of a high-velocity polar out- flow has been demonstrated. Its kinematical age might indicate that the polar outflow is formed before the common-envelope phase. This points to mass transfer onto the secondary as the origin, but alternative explanations are also considered.

The second data release of the INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS DR2)

The INT/WFC Photometric Hα Survey of the Northern Galactic Plane (IPHAS) is a 1800 deg2 imaging survey covering Galactic latitudes |b| < 5° and longitudes l = 30°–215° in the r, i, and Hα filters using the Wide Field Camera (WFC) on the 2.5-m Isaac Newton Telescope (INT) in La Palma. We present the first quality-controlled and globally calibrated source catalogue derived from the survey, providing single-epoch photometry for 219 million unique sources across 92 per cent of the footprint. The observations were carried out between 2003 and 2012 at a median seeing of 1.1 arcsec (sampled at 0.33 arcsec pixel−1) and to a mean 5σ depth of 21.2 (r), 20.0 (i), and 20.3 (Hα) in the Vega magnitude system. We explain the data reduction and quality control procedures, describe and test the global re-calibration, and detail the construction of the new catalogue. We show that the new calibration is accurate to 0.03 mag (root mean square) and recommend a series of quality criteria to select accurate data from the catalogue. Finally, we demonstrate the ability of the catalogues unique (r − Hα, r − i) diagram to (i) characterize stellar populations and extinction regimes towards different Galactic sightlines and (ii) select and quantify Hα emission-line objects. IPHAS is the first survey to offer comprehensive CCD photometry of point sources across the Galactic plane at visible wavelengths, providing the much-needed counterpart to recent infrared surveys.

High Spatial Resolution Galactic 3D Extinction Mapping with IPHAS

We present an algorithm (MEAD, for ‘Mapping Extinction Against Distance’) which will determine intrinsic (r ′ −i ′ ) colour, extinction, and distance for early-A to K4 stars ex tracted from the IPHAS r ′ /i ′ /Hα photometric database. These data can be binned up to map extinction in three dimensions across the northern Galactic Plane. The large size of the IPHAS database (∼ 200 million unique objects), the accuracy of the digital photometry it contains and its faint limiting magnitude (r ′ ∼ 20) allow extinction to be mapped with fine angular ( ∼ 10 arcmin) and distance (∼ 0.1 kpc) resolution to distances of up to 10 kpc, outside the Solar Circle. High reddening within the Solar Circle on occasion brings this range down to ∼ 2 kpc. The resolution achieved, both in angle and depth, greatly exceeds that of previous empirical 3D extinction maps, enabling the structure of the Galactic Pla ne to be studied in increased detail. MEAD accounts for the effect of the survey magnitude limits, photometric errors, unresolved ISM substructure, and binarity. The impact of metallicity variations, within the range typical of the Galactic disc is small. The accuracy and reliability o f MEAD are tested through the use of simulated photometry created with Monte-Carlo sampling techniques. The success of this algorithm is demonstrated on a selection of fields and th e results are compared to the literature.

IPHAS and the symbiotic stars I. Selection method and first discoveries

Context. The study of symbiotic stars is essential to understand important aspects of stellar evolution in interacting binaries. Their observed population in the Galaxy is however poorly known, and is one to three orders of magnitudes smaller than the predicted population size. Aims. IPHAS, the INT Photometric Ha survey of the Northern Galactic plane, gives us the opportunity to make a systematic, complete search for symbiotic stars in a magnitude-limited volume, and discover a significant number of new systems. Methods. A method of selecting candidate symbiotic stars by combining IPHAS and near-IR (2MASS) colours is presented. It allows us to distinguish symbiotic binaries from normal stars and most of the other types of Ha emission line stars in the Galaxy. The only exception are T Tauri stars, which can however be recognized because of their concentration in star forming regions. Results. Using these selection criteria, we discuss the classification of a list of 4338 IPHAS stars with Ha in emission. 1500 to 2000 of them are likely to be Be stars. Among the remaining objects, 1183 fulfill our photometric constraints to be considered candidate symbiotic stars. The spectroscopic confirmation of three of these objects, which are the first new symbiotic stars discovered by IPHAS, proves the potential of the survey and selection method.

IPHAS and the symbiotic stars. II. New discoveries and a sample of the most common mimics

Context. Knowledge of the total population of symbiotic stars in the Galaxy is important for understanding basic aspects of stellar evolution in interacting binaries and the relevance of this class of objects in the formation of supernovae of type Ia. Aims. In a previous paper, we presented the selection criteria needed to search for symbiotic stars in IPHAS, the INT Hα survey of the Northern Galactic plane. IPHAS gives us the opportunity to make a systematic, complete search for symbiotic stars in a magnitude-limited volume. Methods. Follow-up spectroscopy at different telescopes worldwide of a sample of sixty two symbiotic star candidates is presented. Results. Seven out of nineteen S-type candidates observed spectroscopically are confirmed to be genuine symbiotic stars. The spectral type of their red giant components, as well as reddening and distance, were computed by modelling the spectra. Only one new D-type symbiotic system, out of forty-three candidates observed, was found. This was as expected (see discussion in our paper on the selection criteria). The object shows evidence for a high density outflow expanding at a speed ≥65 km s −1 . Most of the other candidates are lightly reddened classical T Tauri stars and more highly reddened young stellar objects that may be either more massive young stars of HAeBe type or classical Be stars. In addition, a few notable objects have been found, such as three new Wolf-Rayet stars and two relatively high-luminosity evolved massive stars. We also found a helium-rich source, possibly a dense ejecta hiding a WR star, which is surrounded by a large ionized nebula. Conclusions. These spectroscopic data allow us to refine the selection criteria for symbiotic stars in the IPHAS survey and, more generally, to better understand the behaviour of different Hα emitters in the IPHAS and 2MASS colour-colour diagrams.

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  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 ] line at 436.3 nm was measured in all six PNe and in several H  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  regions were also modelled using the photoionization code CLOUDY (Ferland et al. 1998, PASP, 110, 761). The physico-chemical properties of PNe and H  regions are presented and discussed. A small dispersion in the oxygen abundance of H  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  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  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 UV-excess survey of the northern galactic plane

The UV-Excess survey of the northern Galactic plane images a 10 ◦ × 185 ◦ wide band, centred on the Galactic equator using the 2.5-m Isaac Newton Telescope in four bands ( U, g, r,He I 5875) down to ∼21-22 mag (∼20 in He I 5875). The setup and data reduction procedures are described. Simulations of the colours of main-sequence stars, giant, supergiants, DA and DB white dwarfs and AM Canum Venaticorum stars are made, including the effects of reddening. A first look at the data of the survey (currently 30 per cent complete) is given.