arXiv subjects

Q. A. Parker

Publications and source records attributed to Q. A. Parker.

At least 127 records · Page 7Linked to original sources

arXiv2007

MASH-II: More Planetary Nebulae from the AAO/UKST HαSurvey

We present a supplement to the Macquarie/AAO/Strasbourg H$α$ planetary nebulae (PNe) catalogue (MASH), which we denote MASH-II. The supplement consists of over 300 true, likely and possible new Galactic PNe found after re-examination of the entire AAO/UKST H$α$ survey of the southern Galactic Plane in digital form. We have spectroscopically confirmed over 240 of these new candidates as bona-fide PNe and we include other high quality candidates awaiting spectroscopic confirmation as possible PNe. These latest discoveries largely comprise two distinct groups: small, star-like or moderately resolved PNe at one end and mostly large, extremely low surface brightness PNe at the other. Neither group were easy to discover from simple visual scrutiny of the original survey exposures as for MASH but were relatively straightforward to uncover from the digital images via application of semi-automated discovery techniques. We suspect the few PNe still hidden in the H$α$ survey will lie outside our search criteria or be difficult to find.

astro-ph↗

arXiv2007

Is the sky falling? Searching for stellar streams in the local Milky Way disc in the CORAVEL and RAVE surveys

We have searched for in-falling stellar streams on to the local Milky Way disc in the CORAVEL and RAVE surveys. The CORAVEL survey consists of local dwarf stars (Nordstrom et al. Geneva-Copenhagen survey) and local Famaey et al. giant stars. We select RAVE stars with radial velocities that are sensitive to the Galactic vertical space velocity (Galactic latitude b < -45 deg). Kuiper statistics have been employed to test the symmetry of the Galactic vertical velocity distribution functions in these samples for evidence of a net vertical flow that could be associated with a (tidal?) stream of stars with vertically coherent kinematics. In contrast to the `Field of Streams' found in the outer halo, we find that the local volumes of the solar neighbourhood sampled by the CORAVEL dwarfs (complete within ~3 x 10^-4 kpc^3), CORAVEL giants (complete within ~5 x 10^-2 kpc^3) and RAVE (5-15% complete within ~8 kpc^3) are devoid of any vertically coherent streams containing hundreds of stars. This is sufficiently sensitive to allow our RAVE sample to rule out the passing of the tidal stream of the disrupting Sagittarius (Sgr) dwarf galaxy through the solar neighbourhood. This agrees with the most recent determination of its orbit and dissociates it from the Helmi et al. halo stream. Our constraints on the absence of the Sgr stream near the Sun could prove a useful tool for discriminating between Galactic potential models. The lack of a net vertical flow through the solar neighbourhood in the CORAVEL giants and RAVE samples argues against the Virgo overdensity crossing the disc near the Sun. There are no vertical streams in the CORAVEL giants and RAVE samples with stellar densities >1.6 x 10^4 and 1.5 x 10^3 stars kpc^-3 respectively and therefore no evidence for locally enhanced dark matter.

astro-ph↗

arXiv2007

Multi-wavelength study of a new Galactic SNR G332.5-5.6

We present compelling evidence for confirmation of a Galactic supernova remnant (SNR) candidate, G332.5-5.6, based initially on identification of new, filamentary, optical emission line nebulosity seen in the arcsecond resolution images from the AAO/UKST HAlpha survey. The extant radio observations and X-ray data which we have independently re-reduced, together with new optical spectroscopy of the large-scale fragmented nebulosity, confirms the identification. Optical spectra, taken across five different, widely separated nebula regions of the remnant as seen on the HAlpha images, show average ratios of [NII]/HAlpha =2.42, [SII]/HAlpha = 2.10, and [SII] 6717/6731 = 1.23, as well as strong [OI] 6300, 6364A and [OII] 3727A emission. These ratios are firmly within those typical of SNRs. Here, we also present the radio-continuum detection of the SNR at 20/13cm from observations with the Australia Telescope Compact Array (ATCA). Radio emission is also seen at 4850 MHz, in the PMN survey (Griffith and Wright 1993) and at 843 MHz from the SUMSS survey (Bock, Large and Sadler 1999). We estimate an angular diameter of ~30 arcmin and obtain an average radio spectral index of alpha = -0.6 +- 0.1 which indicates the non-thermal nature of G332.5-5.6. Fresh analysis of existing ROSAT X-ray data in the vicinity also confirms the existence of the SNR. The distance to G332.5-5.6 has been independently estimated by Reynoso and Green (2007) as 3.4 kpc based on measurements of the HI lambda21 cm line seen in absorption against the continuum emission. Our cruder estimates via assumptions on the height of the dust layer (3.1 kpc) and using the Sigma-D relation (4 kpc) are in good agreement.

astro-ph↗

arXiv2007

The RAVE Survey: Constraining the Local Galactic Escape Speed

We report new constraints on the local escape speed of our Galaxy. Our analysis is based on a sample of high velocity stars from the RAVE survey and two previously published datasets. We use cosmological simulations of disk galaxy formation to motivate our assumptions on the shape of the velocity distribution, allowing for a significantly more precise measurement of the escape velocity compared to previous studies. We find that the escape velocity lies within the range $498\kms < \ve < 608 \kms$ (90 per cent confidence), with a median likelihood of $544\kms$. The fact that $\ve^2$ is significantly greater than $2\vc^2$ (where $\vc=220\kms$ is the local circular velocity) implies that there must be a significant amount of mass exterior to the Solar circle, i.e. this convincingly demonstrates the presence of a dark halo in the Galaxy. For a simple isothermal halo, one can calculate that the minimum radial extent is $\sim58$ kpc. We use our constraints on $\ve$ to determine the mass of the Milky Way halo for three halo profiles. For example, an adiabatically contracted NFW halo model results in a virial mass of $1.42^{+1.14}_{-0.54}\times10^{12}M_\odot$ and virial radius of $305^{+66}_{-45}$ kpc (90 per cent confidence). For this model the circular velocity at the virial radius is $142^{+31}_{-21}\kms$. Although our halo masses are model dependent, we find that they are in good agreement with each other.

astro-ph↗

arXiv2007

Multi-frequency Study of the LMC Supernova Remnant (SNR) B0513-692 and New SNR Candidate J051327-6911

We present a new multi-wavelength study of supernova remnant (SNR) B0513-692 in the Large Magellanic Cloud (LMC). The remnant also has a strong, superposed, essentially unresolved, but unrelated radio source at its north-western edge, J051324-691049. This is identified as a likely compact HII region based on related optical imaging and spectroscopy. We use the Australia Telescope Compact Array (ATCA) at 4790 and 8640 MHz to determine the large scale morphology, spectral index and polarization characteristics of B0513-692 for the first time. We detect a strongly polarized region (49%) in the remnant's southern edge. Interestingly we also detect a small (~40 arcsec) moderately bright, but distinct optical, circular shell in our Halpha imagery which is adjacent to the compact HII region and just within the borders of the NE edge of B0513-692. We suggest this is a separate new SNR candidate based on its apparently distinct character in terms of optical morphology in 3 imaged emission lines and indicative SNR optical spectroscopy (including enhanced optical [SII] emission relative to Halpha).

astro-ph↗

arXiv2007

A Statistical Study of Galactic SNRs using the PMN Survey

The Parkes-MIT-NRAO (PMN) radio survey has been used to generate a quasi all-sky study of Galactic Supernova Remnants (SNRs) at a common frequency of 4.85 GHz. We present flux densities estimated for the sample of 110 Southern Galactic SNRs (up to Dec = - 65 deg.) observed with the Parkes 64-m radio telescope and an additional sample of 54 from the Northern PMN (up to Dec = +64 deg.) survey undertaken with the Green Bank 43-m (20 SNRs) and 91-m (34 SNRs) radio telescopes. Out of this total sample of 164 selected SNRs (representing 71% of the 231 known SNRs in the Green catalogue) we consider 138 to provide reliable estimates of flux density and surface brightness distribution. This sub-sample represents those SNRs which fall within carefully chosen selection criteria which minimises the effects of the known problems in establishing reliable fluxes from the PMN survey data. Our selection criteria are based on a judicious restriction of source angular size and telescope beam together with careful evaluation of fluxes on a case by case basis. This gives confidence in the newly derived PMN fluxes when the selection criteria are respected. We find a sharp drop off in the flux densities for Galactic SNRs beyond 4 Jy and then a fairly flat distribution from 5-9 Jy, a slight decline and a further flat distribution from 9-20 Jy though the numbers of SNR in each Jy bin are low. We also re-visit the contentious Sigma-D relation to determine a new power law index for a sub-sample of shell type SNRs which yields beta= -2.2 +/- 0.6. This new evaluation of the Sigma-D relation, applied to the restricted sample, provides new distance estimates and their Galactic scale height distribution. We find a peak in the SNR distribution between 7-11 kpc with most restricted to +/- 100 pc Galactic scale height.

astro-ph↗

arXiv2006

G315.1+2.7: a new Galactic SNR from the AAO/UKST HAlpha survey

New narrow-band HAlpha imaging and subsequent optical spectra confirm G315.1+2.7, a previously identified candidate supernova remnant (SNR), as a bona-fide Galactic SNR. Present observations are based on independent discovery of filamentary optical emission nebulosity on images of the AAO/UKST HAlpha survey of the southern Galactic plane which were found to co-incide with existing multi-frequency radio detections. Separate medium and high dispersion spectra were taken across two locations of this 11 arcmin N-S aligned optical filament. The resulting spectral signatures were found to strongly confirm the SNR identification based on standard emission line ratio discriminators which characterise emission from shock heated gas. The average observed ratios of [SII]/HAlpha=1.13, [NII]/HAlpha=1.43 and [SII] 6717/6731=1.46, together with the simultaneous detection of [OII] at 3727A, [OIII] 5007A and [OI] 6300A, all point to an SNR origin of the observed optical emission. Careful scrutiny of the low-resolution but high sensitivity SHASSA HAlpha survey also revealed a low-level but distinct optical emission arc. This arc precisely correlates with the large, 2.5 degree, north-south angular extent of the proposed new SNR also seen as a fractured structure in the extant radio data. G315.1+2.7 was detected previously at 2400 and 4800 MHz and at 408 and 1420 MHz. We also identified associated radio emission at 843 MHz from the now publicly available SUMSS survey. On the basis of optical imaging and spectra and radio observations at five frequencies, we identify G315.1+2.7 as a new Galactic SNR. The large projected angular extent of the new remnant, together with the distance estimate of ~1.7 kpc and diameter of ~80pc, make G315.1+2.7 one of the largest remnants known.

astro-ph↗

arXiv2006

The "Principes de Asturias" nebula: a new quadrupolar planetary nebula from the IPHAS survey

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.

astro-ph↗

arXiv2006

The Radial Velocity Experiment (RAVE): first data release

We present the first data release of the Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity) of up to one million stars using the 6dF multi-object spectrograph on the 1.2-m UK Schmidt Telescope of the Anglo-Australian Observatory (AAO). The RAVE program started in 2003, obtaining medium resolution spectra (median R=7,500) in the Ca-triplet region ($λλ$ 8,410--8,795 Å) for southern hemisphere stars drawn from the Tycho-2 and SuperCOSMOS catalogs, in the magnitude range 9<I<12. The first data release is described in this paper and contains radial velocities for 24,748 individual stars (25,274 measurements when including re-observations). Those data were obtained on 67 nights between 11 April 2003 to 03 April 2004. The total sky coverage within this data release is $\sim$4,760 square degrees. The average signal to noise ratio of the observed spectra is 29.5, and 80% of the radial velocities have uncertainties better than 3.4 km/s. Combining internal errors and zero-point errors, the mode is found to be 2 km/s. Repeat observations are used to assess the stability of our radial velocity solution, resulting in a variance of 2.8 km/s. We demonstrate that the radial velocities derived for the first data set do not show any systematic trend with color or signal to noise. The RAVE radial velocities are complemented in the data release with proper motions from Starnet 2.0, Tycho-2 and SuperCOSMOS, in addition to photometric data from the major optical and infrared catalogs (Tycho-2, USNO-B, DENIS and 2MASS). The data release can be accessed via the RAVE webpage: http://www.rave-survey.org.

astro-ph↗

arXiv2006

An Optical Emission Line Survey of Large Planetary Nebulae

Accurate emission line fluxes from planetary nebulae (PNe) provide important constraints on the nature of the final phases of stellar evolution. Large, evolved PNe may trace the latest stages of PN evolution, where material from the AGB wind is returned to the interstellar medium. However, the low surface brightness and spatially extended emission of large PNe have made accurate measurements of line fluxes difficult with traditional long-slit spectroscopic techniques. Furthermore, distinguishing these nebulae from HII regions, supernova remnants, or interstellar gas ionized by a hot, evolved stellar core can be challenging. Here, we report on an ongoing survey of large Galactic PNe (r > 5') with the Wisconsin H-Alpha Mapper (WHAM), a Fabry-Perot spectrograph designed to detect faint diffuse optical emission lines with high sensitivity and spectral resolution. Our sample includes newly revealed H-alpha enhancements from the AAO/UKST and WHAM H-alpha surveys of Parker et al. and Haffner et al. We present accurate emission line fluxes of H-alpha, [NII], and [OIII], and compare our data to other measurements. We use the emission line ratios and kinematics of the ionized gas to assess, or in some cases reassess, the identification of some nebulae.

astro-ph↗

arXiv2005

Discovery of Ultra-Compact Dwarf Galaxies in the Virgo Cluster

We have discovered nine ultra-compact dwarf galaxies (UCDs) in the Virgo Cluster, extending samples of these objects outside the Fornax Cluster. Using the 2dF multi-fiber spectrograph on the Anglo-Australian Telescope, the new Virgo members were found among 1500 color-selected, star-like targets with 16.0 < b_j < 20.2 in a two-degree diameter field centered on M87 (NGC4486). The newly-found UCDs are comparable to the UCDs in the Fornax Cluster, with sizes <~ 100 pc, -12.9 < M_B < -10.7, and exhibiting red, absorption-line spectra, indicative of an older stellar population. The properties of these objects remain consistent with the tidal threshing model for the origin of UCDs from the surviving nuclei of nucleated dwarf ellipticals disrupted in the cluster core, but can also be explained as objects that were formed by mergers of star clusters created in galaxy interactions. The discovery that UCDs exist in Virgo shows that this galaxy type is probably a ubiquitous phenomenon in clusters of galaxies; coupled with their possible origin by tidal threshing, the UCD population is a potential indicator and probe of the formation history of a given cluster. We also describe one additional bright UCD with M_B = -12.0 in the core of the Fornax Cluster. We find no further UCDs in our Fornax Cluster Spectroscopic Survey down to b_j = 19.5 in two additional 2dF fields extending as far as 3 degrees from the center of the cluster. All six Fornax bright UCDs identified with 2dF lie within 0.5 degree (projected distance of 170 kpc) of the central elliptical galaxy NGC1399.

astro-ph↗

arXiv2005

Five WC9 stars discovered in the AAO/UKST H-alpha Survey

We report the discovery of 5 massive Wolf-Rayet (WR) stars resulting from a programme of follow-up spectroscopy of candidate emission line stars in the AAO/UKST Southern Galactic Plane H-alpha survey. The 6195-6775 angstrom spectra of the stars are presented and discussed. A WC9 class is assigned to all 5 stars through comparison of their spectra with those of known late-type WC stars, bringing the known total number of Galactic WC9 stars to 44. Whilst three of the five WC9 stars exhibit near infrared (NIR) excesses characteristic of hot dust emission -- as seen in the great majority of known WC9 stars -- we find that two of the stars show no discernible evidence of such excesses. This increases the number of known WC9 stars without NIR excesses to 7. Reddenings and distances for all 5 stars are estimated.

astro-ph↗

arXiv2005

The Aao/Ukst Supercosmos H-alpha Survey (SHS)

The UK Schmidt Telescope (UKST) of the Anglo-Australian Observatory completed a narrow-band H-alpha plus [NII] 6548, 6584A survey of the Southern Galactic Plane and Magellanic Clouds in late 2003. The survey, which was the last UKST wide-field photographic survey, and the only one undertaken in a narrow band, is now an on-line digital data product of the Wide-Field Astronomy Unit of the Royal Observatory Edinburgh (ROE). The survey utilised a high specification, monolithic H-alpha interference band-pass filter of exceptional quality. In conjunction with the fine grained Tech-Pan film as a detector it has produced a survey with a powerful combination of area coverage (4000 square degrees), resolution (~1 arcsecond) and sensitivity (<=5 Rayleighs), reaching a depth for continuum point sources of R~20.5. The main survey consists of 233 individual fields on a grid of centres separated by 4 degrees at declinations below +2 degrees and covers a swathe approximately 20 degrees wide about the Southern Galactic Plane. The original survey films were scanned by the SuperCOSMOS measuring machine at the Royal Observatory, Edinburgh to provide the on-line digital atlas called the SuperCOSMOS H-alpha Survey (SHS). We present the background to the survey, the key survey characteristics, details and examples of the data product, calibration process, comparison with other surveys and a brief description of its potential for scientific exploitation.

astro-ph↗

arXiv2004

The cosmological significance of Low Surface Brightness galaxies found in a deep blind neutral-hydrogen survey

We have placed limits on the cosmological significance of gas-rich low surface-brightness (LSB) galaxies as a proportion of the total population of gas-rich galaxies by carrying out a very deep survey (HIDEEP) for neutral hydrogen (HI) with the Parkes multibeam system. Such a survey avoids the surface-brightness selection effects that limit the usefulness of optical surveys for finding LSB galaxies. To complement the HIDEEP survey we have digitally stacked eight 1-hour R-band Tech Pan films from the UK Schmidt Telescope covering 36 square degrees of the survey area to reach a very deep isophotal limit of 26.5 R mag/sq. arcsec. At this level, we find that all of the 129 HI sources within this area have optical counterparts and that 107 of them can be identified with individual galaxies. We have used the properties of the galaxies identified as the optical counterparts of the HI sources to estimate the significance of LSB galaxies (defined to be those at least 1.5 magnitudes dimmer in effective surface-brightness than the peak in the observed distribution seen in optical surveys). We calculate the contribution of LSB galaxies to the total number, neutral hydrogen density, luminosity density, baryonic mass density, dynamical mass density and cross-sectional area of gas-rich galaxies. We do not find any `Crouching Giant' LSB galaxies such as Malin 1, nor do we find a population of extremely low surface-brightness galaxies not previously found by optical surveys. Such objects must either be rare, gas-poor or outside the survey detection limits.

astro-ph↗

arXiv2004

PFP 1: A Large Annular Planetary Nebula Caught in the First Stages of ISM Interaction

This paper presents (H-alpha + [NII]) imaging and spectroscopy of a previously unknown, highly evolved planetary nebula of low excitation. It was discovered serendipitously from AAO/UKST H-alpha Survey images as part of a project to exploit the survey data and has evaded detection by previous surveys due to very low surface brightness. It is a remarkably annular planetary nebula, some 19' across, making it one of the largest examples of its type. We estimate a radius of 1.5 pc and a distance of 550pc as derived from a new H-alpha surface brightness - radius relation. PFP 1 has near perfect circular symmetry, broken only at the NW edge which is coupled with significantly increased (H-alpha + [NII]) intensity. This indicates an early stage of an interaction with the interstellar medium. A blue central star candidate has been identified from the SuperCOSMOS Sky Survey data.

astro-ph↗

arXiv2004

Discovery of a WO star in the Scutum-Crux arm of the inner Galaxy

We report the discovery of only the fourth massive WO star to be found in the Milky Way, and only the seventh identified within the Local Group. This has resulted from the first observations made in a programme of follow-up spectroscopy of candidate emission line stars from the AAO/UK Schmidt Southern Galactic Plane H-alpha Survey. The optical spectrum of this star, to become WR 93b in the Catalogue of Galactic Wolf-Rayet stars, is presented and described. WR 93b is classified as WO3 and is shown to be highly reddened (E(B-V) = 2.1 pm 0.1). A recombination line analysis of the emission lines yields the abundance ratios C/He = 0.95 and O/He = 0.13 (by number). Comparisons at near infrared wavelengths of reddening corrected photometry between WR 93b and both of Sand 2 (WO3, D = 49 kpc) and Sand 5 (WO2, D = 1.75 kpc) yields a consistent distance to WR 93b of 3.4 kpc. Positioned at Galactic co-ordinates l = 353.27, b = -0.85, the star is most likely located in the Scutum-Crux Arm of the inner Milky Way. We note that none of the four Galactic WO stars lies significantly beyond the Solar Circle (with two well inside). Estimation of the wind terminal velocity in WR 93b at 5750 km/s makes this star the current wind speed record holder among all non-degenerate stars.

astro-ph↗

arXiv2004

The Large Scale Distribution of Galaxies in the Shapley Supercluster

We present new results of our wide-field redshift survey of galaxies in a 182 square degree region of the Shapley Supercluster (SSC) based on observations with the FLAIR-II spectrograph on the UK Schmidt Telescope. We present new measurements to give a total sample of redshifts for 710 bright (R<16.6) galaxies, of which 464 are members of the SSC (8000<v<18000 kms). Our data reveal that the main plane of the SSC extends further than previously realised, filling the whole extent of our survey region of 10 degrees by 20 degrees on the sky (35 Mpc by 70 Mpc). There is also a significant structure associated with the slightly nearer Abell 3571 cluster complex with a caustic structure evident out to a radius of 6 Mpc. These galaxies seem to link two previously identified sheets of galaxies and establish a connection with a third one at v=15000 kms. They also tend to fill the gap of galaxies between the foreground Hydra-Centaurus region and the more distant SSC. We calculate galaxy overdensities of 5.0+/-0.1 over the 182 square degree region surveyed and 3.3+/-0.1 in a 159 square degree region excluding rich clusters.

astro-ph↗

arXiv2003

HIDEEP - An extragalactic blind survey for very low column-density neutral hydrogen

We have carried out an extremely long integration-time (9000 s/beam) 21-cm blind survey of 60 square degrees in Centaurus using the Parkes multibeam system. We find that the noise continues to fall as sqrt(t) throughout, enabling us to reach an HI column-density limit of 4.2 x 10^18 cm^-2 for galaxies with a velocity width of 200 km/s in the central 32 square degree region, making this the deepest survey to date in terms of column density sensitivity. The HI data are complemented by very deep optical observations from digital stacking of multi-exposure UK Schmidt Telescope R-band films, which reach an isophotal level of 26.5 R mag arcsec^-2 (~27.5 B mag arcsec^-2). 173 HI sources have been found, 96 of which have been uniquely identified with optical counterparts in the overlap area. There is not a single source without an optical counterpart. Although we have not measured the column-densities directly, we have inferred them from the optical sizes of their counterparts. All appear to have a column-density of N_HI = 10^(20.65 +/- 0.38). This is at least an order of magnitude above our sensitivity limit, with a scatter only marginally larger than the errors on N_HI. This needs explaining. If confirmed it means that HI surveys will only find low surface brightness (LSB) galaxies with high M_HI/L_B. Gas-rich LSB galaxies with lower HI mass to light ratios do not exist. The paucity of low column-density galaxies also implies that no significant population will be missed by the all-sky HI surveys being carried out at Parkes and Jodrell Bank.

astro-ph↗