We present the first results of our search for new, extended planetary nebulae (PNe) based on careful, systematic, visual scrutiny of the imaging data from the Isaac Newton Telescope Photometric H ...alpha Survey of the Northern Galactic plane (IPHAS). The newly uncovered PNe will help to improve the census of this important population of Galactic objects that serve as key windows into the late-stage evolution of low- to intermediate-mass stars. They will also facilitate study of the faint end of the ensemble Galactic PN luminosity function. The sensitivity and coverage of IPHAS allows PNe to be found in regions of greater extinction in the Galactic plane and/or those PNe in a more advanced evolutionary state and at larger distances compared to the general Galactic PN population. Using a set of newly revised optical diagnostic diagrams in combination with access to a powerful, new, multiwavelength imaging data base, we have identified 159 true, likely and possible PNe for this first catalogue release. The ability of IPHAS to unveil PNe at low Galactic latitudes and towards the Galactic Anticentre, compared to previous surveys, makes this survey an ideal tool to contribute to the improvement of our knowledge of the whole Galactic PN population.
Using a sample of 213 713 stars from the Radial Velocity Experiment (RAVE) survey, limited to a distance of 2 kpc from the Sun and to |z| < 1 kpc, we report the detection of a velocity gradient of ...disc stars in the fourth quadrant, directed radially from the Galactic Centre. In the direction of the Galactic Centre, we apply a simple method independent of stellar proper motions and of Galactic parameters to assess the existence of this gradient in the RAVE data. This velocity gradient corresponds to |K+C| > rsim 3 km s−1 kpc−1, where K and C are the Oort constants measuring the local divergence and radial shear of the velocity field, respectively. In order to illustrate the effect, assuming a zero radial velocity of the local standard of rest we then reconstruct the two-dimensional Galactocentric velocity maps using two different sets of proper motions and photometric distances based either on isochrone fitting or on K-band magnitudes, and considering two sets of values for the Galactocentric radius of the Sun and local circular speed. Further observational confirmation of our finding with line-of-sight velocities of stars at low latitudes, together with further modelling, should help constrain the non-axisymmetric components of the Galactic potential, including the bar, the spiral arms and possibly the ellipticity of the dark halo.
We report the identification of extended tidal debris potentially associated with the globular cluster NGC 3201, using the RAdial Velocity Experiment (RAVE) catalogue. We find the debris stars are ...located at a distance range of 1–7 kpc based on the forthcoming RAVE distance estimates. The derived space velocities and integrals of motion show interesting connections to NGC 3201, modulo uncertainties in the proper motions. Three stars, which are among the four most likely candidates for NGC 3201 tidal debris, are separated by 80° on the sky yet are well matched by the 12 Gyr, Fe/H = −1.5 isochrone appropriate for the cluster. This is the first time tidal debris around this cluster has been reported over such a large spatial extent, with implications for the cluster's origin and dynamical evolution.
We estimate the accretion rates of 235 Classical T Tauri star (CTTS) candidates in the Lagoon Nebula using ugri H α photometry from the VST Photometric H α survey+. Our sample consists of stars ...displaying H α excess, the intensity of which is used to derive accretion rates. For a subset of 87 stars, the intensity of the u-band excess is also used to estimate accretion rates. We find the mean variation in accretion rates measured using H α and u-band intensities to be ∼0.17 dex, agreeing with previous estimates (0.04–0.4 dex) but for a much larger sample. The spatial distribution of CTTS align with the location of protostars and molecular gas suggesting that they retain an imprint of the natal gas fragmentation process. Strong accretors are concentrated spatially, while weak accretors are more distributed. Our results do not support the sequential star-forming processes suggested in the literature.
As part of a systematic search programme of a 10° wide strip of the northern Galactic plane, we present preliminary evidence for the discovery of four (and possibly five) new supernova remnants ...(SNRs). The pilot search area covered the 19-20 h right ascension zone sampling from +20° to +55° in declination using binned mosaic images from the Isaac Newton Telescope Photometric Hα Survey (IPHAS). The optical identification of the candidate SNRs was based mainly on their filamentary and arc-like emission morphologies, their apparently coherent, even if fractured, structure and clear disconnection from any diffuse neighbouring H ii region type nebulosity. Follow-up optical spectroscopy was undertaken, sampling carefully across prominent features of these faint sources. The resulting spectra revealed typical emission-line ratios for shock-excited nebulae which are characteristic of SNRs, which, along with the latest diagnostic diagrams, strongly support the likely SNR nature of these sources: G038.7−1.3 (IPHASX J190640.5+042819), G067.6+0.9 (IPHASX J195744.9+305306), G066.0−0.0 (IPHASX J195749.2+290259) and G065.8−0.5 (IPHASX J195920.4+283740). A fifth possible younger, higher density nebula SNR candidate, G067.8+0.5 (IPHASX J200002.4+305035), was discovered ∼5 arcmin to the west of IPHASX J195744.9+305306, and it warrants further study. A multiwavelength cross-check from available archived data in the regions of these candidates was also performed with a focus on possible radio counterparts. A close positional match between previously unrecognized radio structures at several frequencies and across various components of the Hα optical image data was found for all SNR candidates. This lends further direct support for the SNR nature of these objects. Evolved SNRs may have very weak and/or highly fragmented radio emission which could explain why they had not been previously recognized, but the association becomes clear in combination with the optical emission.
NGC 6334 and NGC 6357 Russeil, D.; Adami, C.; Bouret, J. C. ...
Astronomy and astrophysics (Berlin),
11/2017, Letnik:
607
Journal Article
Recenzirano
Odprti dostop
Aims. The formation of high-mass stars is still debated. For this reason, several projects such as Herschel-HOBYS are focussed on the study of the earliest phases of massive star formation. As a ...result, massive star-forming complexes such as NGC 6334 and NGC 6357 have been observed in the far-infrared to study their massive dense cores where massive stars are expected to form. However, to better characterise the environments of these cores we need to understand the previous massive star formation history. To better characterise the environment of these massive dense cores we study the previous high-mass star formation and how these stars act on their environments. Methods. This study is based on the spectral classification of the OB stars identified towards NGC 6334 and NGC 6357 with spectra taken with the AAOmega spectrograph on the Anglo-Australian Telescope (AAT). From the subsequent spectral classification of 109 stars across these regions we were able to evaluate the following: distance, age, mass, global star-forming efficiency (SFE), and star formation rate (SFR) of the regions. The physical conditions of the ionised gas for both complexes was also derived. Results. We confirm that NGC 6334 and NGC 6357 belong to the Saggitarius-Carina arm which, in this direction, extends from 1 kpc to 2.2 kpc. From the location of the stars in Hertzprung-Russell diagram we show that stars older than ∼10 Myr are broadly spread across these complexes, while younger stars are mainly located in the H ii regions and stellar clusters. Our data also suggests that some of the young stars can be considered runaway stars. We evaluate a SFE of 0.019 +0.008 −0.007 and 0.021 +0.004 −0.003 and a SFR of 1.1 × 10 3 ± 300 M Myr −1 and 1.7 × 10 3 ± 400 M Myr −1 for NGC 6334 and NGC 6357, respectively. We note that 29 OB stars have X-ray counterparts, most of them belonging to NGC 6357. This suggests that molecular clouds in NGC 6357 are more impacted by X-ray flux and stellar winds than in NGC 6334. Finally, from the analysis of nebular lines (Hα, NII, and SII) from spectra from several regions of ionised gas, we confirm that the filaments in NGC 6357 are shock heated.
During a detailed search for optical counterparts of known Galactic supernova remnants (SNRs) using the Anglo-Australian Observatory/United Kingdom Schmidt Telescope (AAO/UKST) Hα survey of the ...southern Galactic plane we have found characteristic optical Hα filaments and associated emission in the area of SNR G213.0−0.6. Although this remnant was previously detected in the radio as a non-thermal source, we also confirm emission at 4850 MHz in the Parkes-MIT-NRAO (PMN) survey and at 1400 MHz in the NRAO/VLA Sky Survey (NVSS). There is an excellent match in morphological structure between the optical (Hα) and radio emission. We subsequently obtained optical spectroscopy of selected Hα filaments using the South African Astronomical Observatory 1.9-m telescope which confirmed shock excitation typical of supernova remnants. Our discovery of Hα emission and the positional match with several radio frequency maps led us to reassign G213.0−0.6 as G213.3−0.4 as these coordinates more accurately reflect the actual centre of the SNR shell and hence the most probable place of the original supernova explosion. Support for this new SNR ID comes from the fact that the X-ray source 1RXS J065049.7−003220 is situated in the centre of this new remnant and could be connected with the supernova explosion.
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