Publications (19)9.8 Total impact
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Article: A new Planetary Nebula in the outer reaches of the Galaxy
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ABSTRACT: A proper determination of the abundance gradient in the Milky Way requires the observation of objects at large galactiocentric distances. With this aim, we are exploring the planetary nebula population towards the Galactic Anticentre. In this article, the discovery and physico-chemical study of a new planetary nebula towards the Anticentre direction, IPHASX J052531.19+281945.1 (PNG 178.1-04.0), is presented. The planetary nebula was discovered from the IPHAS survey. Long-slit follow-up spectroscopy was carried out to confirm its planetary nebula nature and to calculate its physical and chemical characteristics. The newly discovered planetary nebula turned out to be located at a very large galactocentric distance (D_GC=20.8+-3.8 kpc), larger than any previously known planetary nebula with measured abundances. Its relatively high oxygen abundance (12+log(O/H) = 8.36+-0.03) supports a flattening of the Galactic abundance gradient at large galactocentric distances rather than a linearly decreasing gradient.05/2011; -
Article: The Necklace: equatorial and polar outflows from the binary central star of the new planetary nebula IPHASX J194359.5+170901
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ABSTRACT: ABSTRACTIPHASX J194359.5+170901 is a new high-excitation planetary nebula with remarkable characteristics. It consists of a knotty ring expanding at a speed of 28 km s−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 km s−1, and their kinematical age is twice as large as the age of the ring.Time-resolved photometry of the central star of IPHASX J194359.5+170901 reveals a sinusoidal modulation with a period of 1.16 d. This is interpreted as evidence 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.IPHASX J194359.5+170901 helps to clarify the role of (close) binaries in the formation and shaping of planetary nebulae (PNe). The output of the common-envelope (CE) evolution of the system is a strongly flattened circumstellar mass deposition, a feature that seems to be distinctive of this kind of binary system. Also, IPHASX J194359.5+170901 is among the first post-CE PNe for which the existence of a high-velocity polar outflow has been demonstrated. Its kinematical age might indicate that the polar outflow is formed before the CE phase. This points to mass transfer on to the secondary as the origin, but alternative explanations are also considered.Monthly Notices of the Royal Astronomical Society 01/2011; 410(2):1349 - 1359. · 4.90 Impact Factor -
Article: The Necklace: equatorial and polar outflows from the binary central star of the new planetary nebula IPHASXJ194359.5+170901
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ABSTRACT: IPHASXJ194359.5+170901 is a new high-excitation planetary nebula with remarkable characteristics. It consists of a knotty ring expanding at a speed of 28 km/s, 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 km/s, 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 reveals a sinusoidal modulation with a period of 1.16 days. This is interpreted as evidence 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 formation and shaping of planetary nebulae. The output of the common-envelope evolution 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 outflow 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. Comment: Accepted for publication on MNRAS09/2010; -
Article: IPHAS and the symbiotic stars. II. New discoveries and a sample of the most common mimics
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ABSTRACT: In a previous paper [arXiv:0712.2391], we presented the selection criteria needed to search for symbiotic stars in IPHAS, the INT Halpha 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. Follow-up spectroscopy at different telescopes worldwide of a sample of sixty two symbiotic star candidates is presented. 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 larger than 65 km/s. 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. Comment: Accepted for publication on Astronomy and Astrophysics10/2009; -
Article: Candidate planetary nebulae in the IPHAS photometric catalogue
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ABSTRACT: Context. We have carried out a semi-automated search for planetary nebulae (PNe) in the INT Photometric H-Alpha Survey (IPHAS) catalogue. We present the PN search and the list of selected candidates. We cross correlate the selected candidates with a number of existing infrared galactic surveys in order to gain further insight into the nature of the candidates. Spectroscopy of a subset of objects is used to estimate the number of PNe present in the entire candidate list. Aims. The overall aim of the IPHAS PN project is to carry out a deep census of PNe in the northern Galactic plane, an area where PN detections are clearly lacking. Methods. The PN search is carried out on the IPHAS photometric catalogues. The candidate selection is based on the IPHAS and 2MASS/UKIDSS colours of the objects and the final candidate selection is made visually. Results. From the original list of ~600 million IPHAS detections we have selected a total of 1005 objects. Of these, 224 are known objects, leaving us with 781 PN candidates. Based on the initial follow-up spectroscopy, we expect the list to include very young and proto-PNe in addition to genuine, normal PNe (~16 %) and emission line objects other than PNe. We present additional criteria to select the most probable PN candidates from our candidate list. Comment: 11 pages, 7 figures06/2009; -
Article: New Young Planetary Nebulae in IPHAS
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ABSTRACT: We search for very small-diameter galactic planetary nebulae (PNe) representing the earliest phases of PN evolution. A recently published IPHAS catalogue of Ha-emitting stars provides a useful base for this study as all sources present in this catalogue must be of small angular diameter. The PN candidates are selected based on their location in two colour-colour diagrams: IPHAS (r' - Ha) vs. (r' - i'), and 2MASS (J - H) vs. (H - Ks). Spectroscopic follow-up has been carried out on a sample of candidates in order to confirm their nature. We present a total of 83 PN candidates. We were able to obtain spectra or find the classification from the literature for 35 candidates. Five of these objects are likely to be new PNe, including one large bipolar PN discovered serendipitously near an emission-line star. PN distances deduced from extinction-distance relations based on IPHAS field-star photometry are presented for the first time. These yield distance estimates for our objects in the range from 2 kpc to 6 kpc. From the data to hand, we conclude that four of the discovered objects are very probably young PNe. Comment: 18 pages, 15 figures04/2009; -
Article: A pile of new Planetary Nebulae in the Galactic Plane
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ABSTRACT: and the IPHAS collaboration RESUMEN El cartografiado IPHAS (Isaac Newton Telescope Photometric H-alpha Survey; http://www.iphas.org) está casi terminado. Las imágenes, tomadas en los filtros Hα, r' e i' con un límite de completitud mejor que r'=20 mag, cubren una banda de diez grados a lo largo del plano galáctico, con resolución de 1 segarc. IPHAS está encontrando las nebulosas planetarias (PNe) que faltaban en el plano galáctico; esperamos triplicar el número de PNe conocidas allí. Hemos descubierto cientos de candidatos a PNe, tanto pequeños (<10 arcsec) como extensos; algunos de ellos están situados en regiones clave, como el anticentro. Presentamos aquí un primer estudio de la región entre RA=18 y 20 h , donde las observaciones ya están completas. ABSTRACT The INT photometric H-alpha Survey (IPHAS; http://www.iphas.org) is now near completion. A band of 10 degrees along the Northern Galactic Plane is being imaged in Hα, r' and i' filters with typically 1 arcsec resolution and a completeness limit better than r'=20 mag. IPHAS is filling in the currently existing gap in the Planetary Nebulae (PNe) population of the Plane: we are on course to tripling the number of PNe known in the northern plane. Many hundreds of candidate PNe, both small diameter (<10 arcsec) and extended, have been identified; some are located in areas of particular interest as the Anticenter region. A preliminary analysis of the region from RA=18 to 20 h , where the observations are already complete, is presented.01/2009; 35:103-104. -
Article: The Iron abundance in Galactic Planetary Nebulae
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ABSTRACT: We constrain the iron abundance in a sample of 33 low-ionization Galactic planetary nebulae (PNe) using [Fe III] lines and correcting for the contribution of higher ionization states with ionization correction factors (ICFs) that take into account uncertainties in the atomic data. We find very low iron abundances in all the objects, suggesting that more than 90% of their iron atoms are condensed onto dust grains. This number is based on the solar iron abundance and implies a lower limit on the dust-to-gas mass ratio, due solely to iron, of M_dust/M_gas>1.3x10^{-3} for our sample. The depletion factors of different PNe cover about two orders of magnitude, probably reflecting differences in the formation, growth, or destruction of their dust grains. However, we do not find any systematic difference between the gaseous iron abundances calculated for C-rich and O-rich PNe, suggesting similar iron depletion efficiencies in both environments. The iron abundances of our sample PNe are similar to those derived following the same procedure for a group of 10 Galactic H II regions. These high depletion factors argue for high depletion efficiencies of refractory elements onto dust grains both in molecular clouds and AGB stars, and low dust destruction efficiencies both in interstellar and circumstellar ionized gas.12/2008; -
Article: IPHAS and the symbiotic stars. I. Selection method and first discoveries
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ABSTRACT: 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. IPHAS, the INT Photometric Halpha 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. 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 Halpha 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. Using these selection criteria, we discuss the classification of a list of 4338 IPHAS stars with Halpha 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. Comment: Accepted for publication on Astronomy and Astrophysics. 12 pages, 8 figures12/2007; -
Article: Initial Data Release from the INT Photometric H-alpha Survey of the Northern Galactic Plane (IPHAS)
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ABSTRACT: The INT/WFC Photometric H-alpha Survey of the Northern Galactic Plane (IPHAS) is an imaging survey being carried out in H-alpha, r' and i' filters, with the Wide Field Camera (WFC) on the 2.5-metre Isaac Newton Telescope (INT) to a depth of r'=20 (10 sigma). The survey is aimed at revealing large scale structure in our local galaxy, and also the properties of key early and late populations making up the Milky Way. Mapping emission line objects enables a particular focus on objects in the young and old stages of stellar evolution ranging from early T-Tauri stars to late planetary nebulae. In this paper we present the IPHAS Initial Data Release, primarily a photometric catalogue of about 200 million unique objects, coupled with associated image data covering about 1600 square degrees in three passbands. We note how access to the primary data products has been implemented through use of standard virtual observatory publishing interfaces. Simple traditional web access is provided to the main IPHAS photometric catalogue, in addition to a number of common catalogues (such as 2MASS) which are of immediate relevance. Access through the AstroGrid VO Desktop opens up the full range of analysis options, and allows full integration with the wider range of data and services available through the Virtual Observatory. The IDR represents the largest dataset published primarily through VO interfaces to date, and so stands as an examplar of the future of survey data mining. Examples of data access are given, including a cross-matching of IPHAS photometry with sources in the UKIDSS Galactic Plane Survey that validates the existing calibration of the best data. Comment: 17 pages, 23 figures, MNRAS in press. Version with full-resolution figures can be found at http://casu.ast.cam.ac.uk/surveys-projects/iphas12/2007; -
Article: The S2N2 metallicity calibrator and the abundance gradient of M 33
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ABSTRACT: 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 MNRAS08/2007; -
Article: The "Principes de Asturias" nebula: a new quadrupolar planetary nebula from the IPHAS survey
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ABSTRACT: The Isaac Newton Telescope Photometric H-alpha Survey (IPHAS) is currently mapping the Northern Galactic plane reaching to r'=20 mag with typically 1" resolution. Hundreds of Planetary Nebulae (PNe), both point-like and resolved, are expected to be discovered. We report on the discovery of the first new PN from this survey: it is an unusual object located at a large galactocentric distance and has a very low oxygen abundance. The nebula shows an intricate morphology: there is an inner ring surrounding the central star, bright inner lobes with an enhanced waist, and very faint lobular extensions reaching up to more than 100". We classify it as a quadrupolar PN, a rather unusual class of planetary showing two pairs of misaligned lobes. From long-slit spectroscopy we derive Te[NII] =12800+-1000K, Ne = 390+-40 cm-3, and chemical abundances typical of Peimbert's Type I nebulae (He/H =0.13, N/O =1.8) with an oxygen abundance of 12 + log(O/H)=8.17+-0.15. A kinematic distance of 7.0 kpc is derived, implying an unusually large size of >4 pc for the nebula. The photometry of the central star indicates the presence of a relatively cool companion. This, and the evidence for a dense circumstellar disk and quadrupolar morphology, all of which are rare among PNe, support the hypothesis that this morphology is related to binary interaction. Comment: Accepted by Astronomy and Astrophysics. For better quality images please download the journal pdf file08/2006; -
Article: The INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS)
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ABSTRACT: The Isaac Newton Telescope (INT) Photometric Hα Survey of the Northern Galactic Plane (IPHAS) is a 1800-deg2 CCD survey of the northern Milky Way spanning the latitude range −5° < b < + 5° and reaching down to r′≃ 20 (10σ). Representative observations and an assessment of point-source data from IPHAS, now underway, are presented. The data obtained are Wide Field Camera images in the Hα narrow-band, and Sloan r′ and i′ broad-band filters. We simulate IPHAS (r′−Hα, r′−i′) point-source colours using a spectrophotometric library of stellar spectra and available filter transmission profiles: this defines the expected colour properties of (i) solar metallicity stars, without Hα emission, and (ii) emission-line stars. Comparisons with observations of fields in Aquila show that the simulations of normal star colours reproduce the observations well for all spectral types earlier than M. A further comparison between colours synthesized from long-slit flux-calibrated spectra and IPHAS photometry for six objects in a Taurus field confirms the reliability of the pipeline calibration. Spectroscopic follow-up of a field in Cepheus shows that sources lying above the main stellar locus in the (r′− Hα, r′−i′) plane are confirmed to be emission-line objects with very few failures. In this same field, examples of Hα deficit objects (a white dwarf and a carbon star) are shown to be readily distinguished by their IPHAS colours. The role IPHAS can play in studies of spatially resolved northern Galactic nebulae is discussed briefly and illustrated by a continuum-subtracted mosaic image of Shajn 147 (a supernova remnant, 3° in diameter). The final catalogue of IPHAS point sources will contain photometry on about 80 million objects. Used on its own, or in combination with near-infrared photometric catalogues, IPHAS is a major resource for the study of stellar populations making up the disc of the Milky Way. The eventual yield of new northern emission-line objects from IPHAS is likely to be an order of magnitude increase on the number already known.Monthly Notices of the Royal Astronomical Society 08/2005; 362(3):753 - 776. · 4.90 Impact Factor -
Article: IPHAS: Surveying the North Galactic Plane in H-alpha
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ABSTRACT: H-alpha emission is ubiquitous in our Galaxy. It traces ionised gas of assorted nebulae such as HII regions, planetary nebulae, Wolf-Rayet nebulae, and supernova remnants. It is a strong signature of active stars, interacting binaries, very massive stars (especially supergiants, Luminous Blue Variables and Wolf-Rayet stars), Be stars, post-AGB stars, pre-main-sequence stars and so on. These objects represent important evolutionary phases which are generally short lived, and are hence few in number and difficult to find. Their discovery is therefore well worth the effort of a concerted programme and in August 2003 a major new survey project was started using the Wide Field Camera (WFC) on the Isaac Newton Telescope (INT) to do just that. It is called the INT Photometric H-alpha Survey of the Northern Galactic Plane, or IPHAS for short.The Newsletter of the Isaac Newton Group of Telescopes. 02/2005; 9:3-7. -
Article: IPHAS and the symbiotic stars 1: selection method and first discoveries.
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Article: A Search for New Planetary Nebulae Located at Large Galactocentric Distances.
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Article: The INT Photometric Ha Survey of the Northern Galactic Plane (IPHAS).
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Article: A Search for Symbiotic Stars in the Milky way
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ABSTRACT: We present the search for symbiotic stars in the Northern Galactic Plane within the IPHAS imaging survey. The criterion used to select this class of objects is a combination of the IPHAS r--Hα vs. r--i color-color diagram with the 2MASS J--H vs. H--K diagram. This allows us to distinguish symbiotic stars from other classes of Hα -emitting evolved stars and nebulae. Confusion with young stars in star-forming regions can be also limited by a careful selection of the regions of the Milky Way to be investigated. In this way, more than a thousand new candidate symbiotic stars have been selected so far, and a spectroscopic campaign to determine their real nature is in progress.Baltic Astronomy. 16:73-75. -
Article: IPHAS extinction distances to planetary nebulae
http://dx.doi.org/10.1051/0004-6361/201014464.
Top co-authors
Top Journals
Institutions
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2005–2007
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Instituto de Astrofísica de Canarias
La Laguna, Canary Islands, Spain -
Harvard-Smithsonian Center for Astrophysics
Cambridge, MA, USA
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