arXiv subjects

J. E. Drew

Publications and source records attributed to J. E. Drew.

At least 19 recordsLinked to original sources

arXiv2026

WEAVE imaging spectroscopy of NGC 6720: an iron bar in the Ring

We present spatially resolved spectroscopic observations of the planetary nebula NGC 6720, the Ring Nebula, taken during the science verification phase of WEAVE, a new instrument mounted on the William Herschel Telescope on La Palma. We use the instrument's Large Integral Field Unit (LIFU) to obtain spectra of the Ring Nebula, covering its entire optically bright inner regions as well as parts of its much fainter outer molecular halo. We report the discovery of emission from [Fe~{\sc v}] and [Fe~{\sc vi}] confined to a narrow ``bar'' extending across the central regions of the nebula. No lines of other elements share this morphology or, at the spectral resolving power used ($R \sim 2500$), the same radial velocity. The extent to which iron in this bar is depleted is presently unclear; comparison with JWST-detected dust continuum emission suggests that some dust grain destruction may be occurring in the region, but there is currently no observational evidence for the $>$ 50~km\,s$^{-1}$ shock waves or $T > 10^6$~K X-ray emitting gas needed to enable this. Where the bar is located along the line of sight through the nebula, and how it was created, are new puzzles to be solved for this iconic planetary nebula.

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arXiv2025

Uniformly-calibrated VPHAS+ photometry in the third quadrant of the Galactic plane

The southern Galactic plane has been mapped at optical wavelengths and at under one-arcsecond angular resolution by the VST Photometric Ha Survey of the Galactic plane and bulge (VPHAS+). Anticipating the release of a uniform photometric calibration of the entire survey, we examine the properties of VPHAS+ ugriHa photometry of r < 19 mag. point sources in the third Galactic quadrant (longitudes 210^o to 260^o). We compare our interim calibration in gri with that of Pan-STARRS, the DECam Plane Survey (DECaPS-2) and Skymapper. We use the comparisons to identify small gri photometric offsets. Corrections to the Ha and u magnitude scales are determined via comparison with synthetic photometry. VPHAS+ and its northern counterpart, the INT Galactic Plane Survey (IGAPS), are shown to closely align, where they overlap across the celestial equator. Aided by Gaia Data Release 3, SIMBAD, and specialist catalogues, we present selections of: A stars; sub-luminous stars; intrinsically-red luminous stars; young stellar objects; emission-line and OB stars. Attention is drawn to stellar variability as a contaminant in selecting emission line objects via (r - Ha) excess. It is argued the (r - i, r - Ha) plane is the better choice for this selection than (g - i, r - Ha). Using A stars to map extinction, we trace the main run of dust obscuration, situated at mainly negative Galactic latitudes. Like the dust, OB and emission line stars are more frequent below the Galactic equator: at heliocentric distances of up to ~7 kpc, these stars' distribution fit in with the known warping of the Galactic plane. An overdensity of B stars, several degrees across and potentially in the Outer Arm, is found around (l,b) = (212.0, -0.6).

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arXiv2024

WEAVE First Light Observations: Origin and Dynamics of the Shock Front in Stephan's Quintet

We present a detailed study of the large-scale shock front in Stephan's Quintet, a byproduct of past and ongoing interactions. Using integral-field spectroscopy from the new William Herschel Telescope Enhanced Area Velocity Explorer (WEAVE), recent 144 MHz observations from the LOFAR Two-metre Sky Survey (LoTSS), and archival data from the Very Large Array and James Webb Space Telescope (JWST), we obtain new measurements of key shock properties and determine its impact on the system. Harnessing the WEAVE large integral field unit's (LIFU) field of view (90 $\times$ 78 arcsec$^{2}$), spectral resolution ($R\sim2500$) and continuous wavelength coverage across the optical band, we perform robust emission line modeling and dynamically locate the shock within the multi-phase intergalactic medium (IGM) with higher precision than previously possible. The shocking of the cold gas phase is hypersonic, and comparisons with shock models show that it can readily account for the observed emission line ratios. In contrast, we demonstrate that the shock is relatively weak in the hot plasma visible in X-rays (with Mach number of $\mathcal{M} \sim 2 - 4$), making it inefficient at producing the relativistic particles needed to explain the observed synchrotron emission. Instead, we propose that it has led to an adiabatic compression of the medium, which has increased the radio luminosity ten-fold. Comparison of the Balmer line-derived extinction map with the molecular gas and hot dust observed with JWST suggests that pre-existing dust may have survived the collision, allowing the condensation of H$_{2}$ - a key channel for dissipating the shock energy.

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arXiv2024

Circumstellar disk accretion across the Lagoon Nebula: the influence of environment and stellar mass

Pre-main sequence disk accretion is pivotal in determining the final stellar properties and the early conditions for close-in planets. We aim to establish the impact of internal (stellar mass) and external (radiation field) parameters on disk evolution in the Lagoon Nebula massive star-forming region. We employ simultaneous $u,g,r,i,Hα$ time series photometry, archival infrared data, and high-precision $K2$ light curves, to derive stellar, disk, and accretion properties for 1012 Lagoon Nebula members. Of all young stars in the Lagoon Nebula, we estimate $34\%-37\%$ have inner disks traceable down to $\sim 12$ $μ$m, while $38\%-41\%$ are actively accreting. We detect disks $\sim$1.5 times more frequently around G/K/M stars than higher-mass stars, which appear to deplete their inner disks on shorter timescales. We find tentative evidence for faster disk evolution in the central regions of the Lagoon Nebula, where the bulk of the O/B population is located. Conversely, disks appear to last longer at its outskirts, where the measured fraction of disk-bearing stars tends to exceed those of accreting and disk-free stars. The derived mass accretion rates show a non-uniform dependence on stellar mass between $\sim 0.2-5$ $M_\odot$. In addition, the typical accretion rates appear to differ across the Lagoon Nebula extension, with values two times lower in the core region than at its periphery. Finally, we detect tentative density gradients in the accretion shocks, with lags in the appearance of brightness features as a function of wavelength that can amount to $\sim7\%-30\%$ of the rotation period.

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arXiv2023

The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementation

WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366$-$959\,nm at $R\sim5000$, or two shorter ranges at $R\sim20\,000$. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for $\sim$3 million stars and detailed abundances for $\sim1.5$ million brighter field and open-cluster stars; (ii) survey $\sim0.4$ million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey $\sim400$ neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in $z<0.5$ cluster galaxies; (vi) survey stellar populations and kinematics in $\sim25\,000$ field galaxies at $0.3\lesssim z \lesssim 0.7$; (vii) study the cosmic evolution of accretion and star formation using $>1$ million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at $z>2$. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator.

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arXiv2023

Gaia-ESO Survey: massive stars in the Carina Nebula. A new census of OB stars

The Gaia-ESO survey sample of massive OB stars in the Carina Nebula consists of 234 stars. The addition of brighter sources from the Galactic O-Star Spectroscopic Survey and additional sources from the literature allows us to create the most complete census of massive OB stars done so far in the region. It contains a total of 316 stars, being 18 of them in the background and four in the foreground. Of the 294 stellar systems in Car OB1, 74 are of O type, 214 are of non-supergiant B type and 6 are of WR or non-O supergiant (II to Ia) spectral class. We identify 20 spectroscopic binary systems with an O-star primary, of which 6 are reported for the first time, and another 18 with a B-star primary, of which 13 are new detections. The average observed double-lined binary fraction of O-type stars in the surveyed region is 0.35, which represents a lower limit. We find a good correlation between the spectroscopic n-qualifier and the projected rotational velocity of the stars. The fraction of candidate runaways among the stars with and without the n-qualifier is 4.4% and 2.4%, respectively, although non resolved double-lined binaries can be contaminating the fast rotators sample.

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arXiv2022

Spectroscopic follow-up of a sub-set of the Gaia/IPHAS catalogue of Hα-excess sources

State-of-the-art techniques to identify Hαemission line sources in narrow-band photometric surveys consist of searching for Hαexcess with reference to nearby objects in the sky (position-based selection). However, while this approach usually yields very few spurious detections, it may fail to select intrinsically faint and/or rare Hα-excess sources. In order to obtain a more complete representation of the heterogeneous emission line populations, we recently developed a technique to find outliers relative to nearby objects in the colour-magnitude diagram (CMD-based selection). By combining position-based and CMD-based selections, we built an updated catalogue of Hα-excess candidates in the northern Galactic Plane. Here we present spectroscopic follow-up observations and classification of 114 objects from this catalogue, that enable us to test our novel selection method. Out of the 70 spectroscopically confirmed Hαemitters in our sample, 15 were identified only by the CMD-based selection, and would have been thus missed by the classic position-based technique. In addition, we explore the distribution of our spectroscopically confirmed emitters in the Gaia CMD. This information can support the classification of emission line sources in large surveys, such as the upcoming WEAVE and 4MOST, especially if augmented with the introduction of other colours.

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arXiv2022

UGPS J194310+183851: an Unusual Optical and X-ray Faint Cataclysmic Variable?

The growing number of multi-epoch optical and infrared sky surveys are uncovering unprecedented numbers of new variable stars, of an increasing number of types. The short interval between observations in adjacent near infrared filters in the UKIDSS Galactic Plane Survey (UGPS) allows for the discovery of variability on the timescale of minutes. We report on the nature of one such object, through the use of optical spectroscopy, time-series photometry and targeted X-ray observations. We propose that UGPS J194310.32+183851.8 is a magnetic cataclysmic variable star of novel character, probably featuring a longer than average spin period and an orbital period likely to be shorter than the period gap (i.e. P$_{\text{orb}}$<2 hours). We reason that the star is likely a member of the short period Intermediate-Polar subclass that exist below this period boundary, but with the additional feature that system's SED is fainter and redder than other members of the group.

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arXiv2021

The Gaia-ESO Survey: Target selection of open cluster stars

The Gaia-ESO Survey (GES) is a public, high-resolution spectroscopic survey with FLAMES@VLT. GES targeted in particular a large sample of open clusters (OCs) of all ages. The different kinds of OCs are useful to reach the main science goals, which are the study of the OC structure and dynamics, the use of OCs to constrain and improve stellar evolution models, and the definition of Galactic disc properties (e.g. metallicity distribution). GES is organised in 19 working groups (WGs). We describe here the work of three of them, WG4 in charge of the selection of the targets within each cluster), WG1 responsible for defining the most probable candidate members, and WG6 in charge of the preparation of the observations. As GES has been conducted before Gaia DR2, we could not make use of the Gaia astrometry to define cluster members. We made use of public and private photometry to select the stars to be observed with FLAMES. Candidate target selection was based on ground-based proper motions, radial velocities, and X-ray properties when appropriate, and it was mostly used to define the position of the clusters' evolutionary sequences in the colour-magnitude diagrams. Targets for GIRAFFE were selected near the sequences in an unbiased way. We used available information on membership only for the few UVES stars. We collected spectra for 62 confirmed OCs (a few more were taken from the ESO archive). Among them are very young clusters, where the main targets are pre-main sequence stars, clusters with very hot and massive stars currently on the main sequence, intermediate-age and old clusters where evolved stars are the main targets. The selection of targets was as inclusive and unbiased as possible and we observed a representative fraction of all possible targets, thus collecting the largest, most accurate, and most homogeneous spectroscopic data set on ever achieved. [abridged]

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arXiv2021

Proper motions of OB stars in the far Carina Arm

In large scale maps of the Galactic disc, the Carina Arm stands out as a clear spiral feature, hosting prominent star clusters and associations rich in massive stars. We study the proper motions of 4199 O and early B most likely in the far Carina Arm, at distances mainly in excess of 4 kpc from the Sun, within the sky region, $282^{\circ} < \ell < 294^{\circ}$ and $-3^{\circ} < b < +1^{\circ}$ (Galactic coordinates). The sample is constructed by extending an existing blue-selected catalogue, and cross-matching with Gaia EDR3 astrometry. The observed pattern of proper motions is modulated into a saw-tooth pattern, with full amplitude approaching 1 mas yr$^{-1}$, recurring roughly every 2--3 degrees of longitude (200--300 pc at the median OB-star distance of 5.8 kpc). Kinematic perturbation of underlying circular rotation is most likely present. The data also reveal a moving group containing $>50$ OB stars at $\ell \sim 286^{\circ}$, $b \sim -1^{\circ}.4$ behind the main run of the far arm. An analysis of relative proper motions is performed that yields an incidence of runaway O stars of at least 10\% (potentially $>20$\% when full space motions become available). To map where runaways have run away from, we set up simulations for the region that assume linear trajectories and test for trajectory impact parameter in order to identify likely ejection hot spots. We find the method currently gives good results for times of flight of up to $\sim$4 Myr. It shows convincingly that only NGC 3603 and Westerlund 2 have ejected OB stars in significant numbers. Indeed, both clusters have experienced intense spells of ejection between 0.6--0.9 and 0.5--0.8 Myr ago, respectively.

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arXiv2021

High resolution H-alpha imaging of the Northern Galactic Plane, and the IGAPS images database

The INT Galactic Plane Survey (IGAPS) is the merger of the optical photometric surveys, IPHAS and UVEX, based on data from the Isaac Newton Telescope (INT) obtained between 2003 and 2018. These capture the entire northern Galactic plane within the Galactic coordinate range, -5<b<+5 deg. and 30<l<215 deg. From the beginning, the incorporation of narrowband H-alpha imaging has been a unique and distinctive feature of this effort. Alongside a focused discussion of the nature and application of the H-alpha data, we present the IGAPS world-accessible database of images for all 5 survey filters, i, r, g, U-RGO and narrowband H-alpha, observed on a pixel scale of 0.33 arcsec and at an effective (median) angular resolution of 1.1 to 1.3 arcsec. The background, noise, and sensitivity characteristics of the narrowband H-alpha filter images are outlined. Typical noise levels in this band correspond to a surface brightness at full one-arcsec resolution of around 2e-16 erg/cm2/s/arcsec2. Illustrative applications of the H-alpha data to planetary nebulae and Herbig-Haro objects are outlined and, as part of a discussion of mosaicking technique, we present a very large background-subtracted narrowband mosaic of the supernova remnant, Simeis 147. Finally we lay out a method that exploits the database via an automated selection of bright ionized diffuse interstellar emission targets for the coming generation of wide-field massive-multiplex spectrographs. Two examples of the diffuse H-alpha maps output from this selection process are presented and compared with previously published data.

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arXiv2021

Population-based identification of Hα-excess sources in the Gaia DR2 and IPHAS catalogues

We present a catalogue of point-like Hα-excess sources in the Northern Galactic Plane. Our catalogue is created using a new technique that leverages astrometric and photomeric information from Gaia to select Hα-bright outliers in the INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS), across the colour-absolute magnitude diagram. To mitigate the selection biases due to stellar population mixing and to extinction, the investigated objects are first partitioned with respect to their positions in the Gaia colour-absolute magnitude space, and in the Galactic coordinates space, respectively. The selection is then performed on both partition types independently. Two significance parameters are assigned to each target, one for each partition type. These represent a quantitative degree of confidence that the given source is a reliable Hα-excess candidate, with reference to the other objects in the corresponding partition. Our catalogue provides two flags for each source, both indicating the significance level of the Hα-excess. By analysing their intensity in the Hα narrow band, 28,496 objects out of 7,474,835 are identified as Hα-excess candidates with a significance higher than 3. The completeness fraction of the Hα outliers selection is between 3% and 5%. The suggested 5σ conservative cut yields a purity fraction of 81.9%.

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arXiv2020

H$α$ fluxes and extinction distances for planetary nebulae in the IPHAS survey of the Northern Galactic Plane

We report H$α$ filter photometry for 197 northern hemisphere planetary nebulae (PNe) obtained using imaging data from the IPHAS survey. H$α$+[N II] fluxes were measured for 46 confirmed or possible PNe discovered by the IPHAS survey and for 151 previously catalogued PNe that fell within the area of the northern Galactic Plane surveyed by IPHAS. After correcting for [N II] emission admitted by the IPHAS H$α$ filter, the resulting H$α$ fluxes were combined with published radio free-free fluxes and H$β$ fluxes, in order to estimate mean optical extinctions to 143 PNe using ratios involving their integrated Balmer line fluxes and their extinction-free radio fluxes. Distances to the PNe were then estimated using three different 3D interstellar dust extinction mapping methods, including the IPHAS-based H-MEAD algorithm of Sale (2014). These methods were used to plot dust extinction versus distance relationships for the lines of sight to the PNe; the intercepts with the derived dust optical extinctions allowed distances to the PNe to be inferred. For 17 of the PNe in our sample reliable Gaia DR2 distances were available and these have been compared with the distances derived using three different extinction mapping algorithms as well as with distances from the nebular radius vs. H$α$ surface brightness relation of Frew et al. (2016). That relation and the H-MEAD extinction mapping algorithm yielded the closest agreement with the Gaia DR2 distances.

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arXiv2020

IGAPS: the merged IPHAS and UVEX optical surveys of theNorthern Galactic Plane

The INT Galactic Plane Survey (IGAPS) is the merger of the optical photometric surveys, IPHAS and UVEX, based on data from the Isaac Newton Telescope (INT) obtained between 2003 and 2018. Here, we present the IGAPS point source catalogue. It contains 295.4 million rows providing photometry in the filters, i, r, narrow-band Halpha, g and U_RGO. The IGAPS footprint fills the Galactic coordinate range, |b| < 5deg and 30deg < l < 215deg. A uniform calibration, referred to the Pan-STARRS system, is applied to g, r and i, while the Halpha calibration is linked to r and then is reconciled via field overlaps. The astrometry in all 5 bands has been recalculated on the Gaia DR2 frame. Down to i ~ 20 mag (Vega system), most stars are also detected in g, r and Halpha. As exposures in the r band were obtained within the IPHAS and UVEX surveys a few years apart, typically, the catalogue includes two distinct r measures, r_I and r_U. The r 10sigma limiting magnitude is ~21, with median seeing 1.1 arcsec. Between ~13th and ~19th magnitudes in all bands, the photometry is internally reproducible to within 0.02 magnitudes. Stars brighter than r=19.5 have been tested for narrow-band Halpha excess signalling line emission, and for variation exceeding |r_I-r_U| = 0.2 mag. We find and flag 8292 candidate emission line stars and over 53000 variables (both at >5sigma confidence). The 174-column catalogue will be available via CDS Strasbourg.

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arXiv2019

The O star hinterland of the Galactic starburst, NGC 3603

The very bright and compact massive young cluster, NGC 3603, has been cited as an example of a starburst in the Milky Way and compared with the much-studied R136/30 Doradus region in the Large Magellanic Cloud. Here we build on the discovery by Mohr-Smith et al. (2017) of a large number of reddened O stars around this cluster. We construct a list of 288 candidate O stars with proper motions, in a region of sky spanning 1.5x1.5 square degrees centered on NGC 3603, by cross-matching the Mohr-Smith et al. (2017) catalogue with Gaia DR2 (Gaia Collaboration et al. 2018). This provides the basis for a first comprehensive examination of the proper motions of these massive stars in the halo of NGC 3603, relative to the much better studied central region. We identify up to 11 likely O star ejections -- 8 of which would have been ejected between 0.60 and 0.95 Myr ago (supporting the age of c.1 Myr that has been attributed to the bright cluster centre). Seven candidate ejections are arranged in a partial ring to the south of the cluster core spanning radii of 9-18 arcmin (18-36 pc if the cluster is 7 kpc away). We also show that the cluster has a halo of a further 100 O stars extending to a radius of at least 5 arcmin, adding to the picture of NGC 3603 as a scaled down version of the R136/30 Dor region.

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arXiv2019

A study of full space motions of outer Galactic disk A and F stars in two deep pencil-beams

A and F stars can be used as probes of outer Galactic disk kinematics: here we extend the work of Harris et al. (2018) by crossmatching their A/F sample with Gaia DR2 to bring in proper motions. These are combined with the already measured radial velocities and spectro-photometric distances to obtain full space motions. We use this sample of 1173 stars, located in two pencil-beam sightlines (l=178deg and l=118deg), to sample the Galactocentric velocity field out to almost R_G=15 kpc. We find there are significant differences in all three (radial, azimuthal and vertical) kinematic components between the two directions. The rotation curve is roughly flat in the anticentre direction, confirming and extending the result of Kawata et al. (2018a) thanks to the greater reach of our spectro-photometric distance scale. However at l=118deg the circular velocity rises outwards from R_G=10.5 kpc and there is a more pronounced gradient in radial motion than is seen at l=178deg. Furthermore, the A star radial motion differs from the F stars by ~10 km/s. We discuss our findings in the context of perturbers potentially responsible for the trends, such as the central bar, spiral arms, the warp and external satellites. Our results at l=178deg are broadly consistent with previous work on K giants in the anticentre, but the kinematics at l=118deg in the Perseus region do not yet reconcile easily with bar or spiral arm perturbation.

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arXiv2019

Disentangling the spatial substructure of Cygnus OB2 from Gaia DR2

For the first time, we have explored the spatial substructure of the Cygnus OB2 association using parallaxes from the recent second Gaia data release. We find significant line-of-sight substructure within the association, which we quantify using a parameterised model that reproduces the observed parallax distribution. This inference approach is necessary due to the non-linearity of the parallax-distance transformation and the asymmetry of the resulting probability distribution. By using a Markov Chain Monte Carlo ensemble sampler and an unbinned maximum likelihood test we identify two different stellar groups superposed on the association. We find the main Cygnus OB2 group at ~1760 pc, further away than recent estimates have envisaged, and a foreground group at ~1350 pc. We also calculate individual membership probabilities and identify outliers as possible non-members of the association.

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arXiv2018

The Gaia/IPHAS and Gaia/KIS Value-Added Catalogues

We present a sub-arcsecond cross-match of Gaia DR2 against the INT Photometric H-alpha Survey of the Northern Galactic Plane Data Release 2 (IPHAS DR2) and the Kepler-INT Survey (KIS). The resulting value-added catalogues (VACs) provide additional precise photometry to the Gaia photometry (r, i and H-alpha for IPHAS, with additional U and g for KIS). In building the catalogue, proper motions given in \gaia\ DR2 are wound back to match the epochs of IPHAS DR2, thus ensuring high proper motion objects are appropriately cross-matched. The catalogues contain 7,927,224 and 791,071 sources for IPHAS and KIS, respectively. The requirement of >5-sigma parallax detection for every included source means that distances out to 1--1.5 kpc are well covered. We define two additional parameters for each catalogued object: (i) $f_c$, a magnitude-dependent tracer of the quality of the Gaia astrometric fit; (ii) $f_{FP}$, the false-positive rate for parallax measurements determined from astrometric fits of a given quality at a given magnitude. Selection cuts based on these parameters can be used to clean colour-magnitude and colour-colour diagrams in a controlled and justified manner. We provide both full and light versions of the VAC, with VAC-light containing only objects that represent our recommended trade-off between purity and completeness. Uses of the catalogues include the identification of new variable stars in the matched data sets, and more complete identification of H-alpha-excess emission objects thanks to separation of high-luminosity stars from the main sequence.

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