C. Giammanco

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.

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.

Candidate planetary nebulae in the IPHAS photometric catalogue

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 catalogue. 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.

The internal dynamical equilibrium of H II regions: A statistical study

We present an analysis of the integrated Hα emission line profiles for the H  region population of the spiral galaxies NGC 1530, NGC 6951 and NGC 3359. We show that ∼70% of the line profiles show two or three Gaussian components. The relations between the luminosity (log LHα) and non-thermal line width (log σnt )f or the H regions of the three galaxies are studied and compared with the relation found taken all the H  regions of the three galaxies as a single distribution. In all of these distributions we find a lower envelope in log σnt. A clearer envelope in σnt is found when only those H  regions with σnt >σ s(13 km s −1 ) are considered, where σs is a canonical estimate of the sound speed in the interestellar medium. The linear fit for the envelope is log LHα = (36.8 ± 0.7) + (2.0 ± 0.5) log σnt where the Hα luminosity of the region is taken directly from a photometric H  region catalogue. When the Hα luminosity used instead is that fraction of the H  region luminosity, corresponding to the principal velocity component, i.e. to the turbulent non-expanding contribution, the linear fit is log LHα = (36.8 ± 0.6) + (2.0 ± 0.5) log σnt, i.e. unchanged but slightly tighter. The masses of the H  regions on the envelope using the virial theorem and the mass estimates from the Hα luminosity are comparable, which offers evidence that the H  regions on the envelope are virialized systems, while the remaining regions, the majority, are not in virial equilibrium.

IPHAS extinction distances to planetary nebulae

Aims. The determination of reliable distances to planetary nebulae (PNe) is a major difficulty in the study of this class of objects in the Galaxy. The availability of new photometric surveys such as IPHAS (the INT/WFC photometric Hα survey of the northern Galactic plane) covering large portions of the sky provide an opportunity to apply the so-called extinction method to determine the distances of a large number of objects. Methods. The technique is applied to a sample of 137 PNe located between −5 and 5 degrees in Galactic latitude, and between 29.52 and 215.49 degrees in longitude. The characteristics of the distance-extinction method and the main sources of errors are carefully discussed. Results. The data on the extinction of the PNe available in the literature, complemented by new observations, allow us to determine extinction distances for 70 PNe. A comparison with statistical distance scales from different authors is presented.

New young planetary nebulae in IPHAS

Aims. We search for very small-diameter galactic planetary nebulae (PNe) representing the earliest phases of PN evolution. The IPHAS catalogue of Hα-emitting stars provides a useful basis for this study since all sources present in this catalogue must be of small angular diameter. Methods. The PN candidates are selected based on their location in two colour−colour diagrams: IPHAS (r � − Hα )v s. (r � − i � ), and 2MASS (J − H )v s. (H − Ks). Spectroscopic follow-up was carried out on a sample of candidates to confirm their nature. Results. 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 close to 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 2 kpc and 6 kpc. From the data in hand, we conclude that four of the discovered objects are probably young PNe.

A new planetary nebula in the outer reaches of the galaxy

Aims. 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. Methods. 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. Results. The newly discovered planetary nebula turned out to be located at a very large galactocentric distance (DGC = 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.

Temperature fluctuations in HII regions : Ionization by cosmic rays as a key mechanism

We present a detailed model capable of explaining quantitatively the temperature fluctuations observed in luminous, large H II regions. The model is based on two assumptions which we justify on the basis of observations: that the major fraction of the hydrogen in the clouds that form the H II regions is not photoionized and is essentially H I, this H I is lightly ionized by fluxes of low energy cosmic rays (CR) produced by processes originating in the hot stars which illuminate the regions.

The kinematics of the quadrupolar nebula M 1-75 and the identification of its central star

Context. The link between the shaping of bipolar planetary nebulae and their central stars is still poorly understood. Aims. The kinematics and shaping of the multipolar nebula M 1-75 are hereby investigated, and the location and nature of its central star are briefly discussed. Methods. Fabry-Perot data from GHFAS on the WHT sampling the Doppler shift of the (Nii) 658.3 nm line are used to study the dynamics of the nebula, by means of a detailed 3-D spatio-kinematical model. Multi-wavelength images and spectra from the WFC and IDS on the INT, and from ACAM on the WHT, allowed us to constrain the parameters of the central star. Results. The two pairs of lobes, angularly separated by� 22 � , were ejected simultaneously approx.� 3500-5000 years ago, at the adopted distance range from 3.5 to 5.0 kpc. The larger lobes show evidence of a slight degree of point symmetry. The shaping of the nebula could be explained by wind interaction in a system consisting of a post-AGB star surrounded by a disc warped by radiative instabilities. This requires the system to be a close binary or a single star which engulfed a planet as it died. On the other hand, we present broad- and narrow-band images and a low S/N optical spectrum of the highly-reddened, previously unnoticed star which is likely the nebular progenitor. Its estimated V− I colour allows us to derive a rough estimate of the parameters and nature of the central star.

K 3–22: a D-type symbiotic star

A goal of the IPHAS survey is to determine the frequency and nature of emission-line sources in the Galactic plane. According to our selection criteria, K 3-22 is a candidate symbiotic star, but it was previously classified as a planetary nebula. To determine its nature, we acquired a low-resolution optical spectrum of K 3-22. Our analysis of our spectroscopy demonstrates that K 3-22 is indeed a D-type symbiotic star, because of its high excitation nebular spectrum and the simultaneous presence of Raman-scattered O VI emission at 6825 and 7082 angstrom, which is detected primarily in symbiotic stars.