arXiv subjects

J. E. Drew

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

At least 91 records · Page 5Linked to original sources

arXiv2007

Newly Discovered Cataclysmic Variables from the INT/WFC Photometric H alpha Survey of the Northern Galactic Plane

We report the discovery of 11 new cataclysmic variable (CV) candidates by the Isaac Newton Telescope (INT) Photometric H alpha Survey of the northern Galactic plane (IPHAS). Three of the systems have been the subject of further follow-up observations. For the CV candidates IPHAS J013031.90+622132.4 and IPHAS J051814.34+294113.2, time-resolved optical spectroscopy has been obtained and radial-velocity measurements of the H alpha emission-line have been used to estimate their orbital periods. A third CV candidate (IPHAS J062746.41+ 014811.3) was observed photometrically and found to be eclipsing. All three systems have orbital periods above the CV period-gap of 2-3 h. We also highlight one other system, IPHAS J025827.88+635234.9, whose spectrum distinguishes it as a likely high luminosity object with unusual C and N abundances.

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arXiv2007

The enigma of the oldest `nova': the central star and nebula of CK Vul

CK Vul is classified as, amongst others, the slowest known nova, a hibernating nova, or a very late thermal pulse object. Following its eruption in AD 1670, the star remained visible for 2 years. A 15-arcsec nebula was discovered in the 1980's, but the star itself has not been detected since the eruption. We here present radio images which reveal an 0.1-arcsec radio source with a flux of 1.5 mJy at 5 GHz. Deep Halpha images show a bipolar nebula with a longest extension of 70 arcsec, with the previously known compact nebula at its waist. The emission-line ratios show that the gas is shock-ionized, at velocities >100 km/s. Dust emission yields an envelope mass of ~0.05 Msun. Echelle spectra indicate outflow velocities up to 360 km/s. From a comparison of images obtained in 1991 and 2004 we find evidence for expansion of the nebula, consistent with an origin in the 1670 explosion; the measured expansion is centred on the radio source. No optical or infrared counterpart is found at the position of the radio source. The radio emission is interpreted as thermal free-free emission from gas with Tel ~ 10000 K. The radio source may be due to a remnant circumbinary disk, similar to those seen in some binary post-AGB stars. We discuss possible classifications of this unique outburst, including that of a sub-Chandrasekhar mass supernova, a nova eruption on a cool, low-mass white dwarf, or a thermal pulse induced by accretion from a circumbinary disk.

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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.

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arXiv2006

The Properties of Cataclysmic Variables In Photometric Halpha Surveys

We report on the properties of 71 known cataclysmic variables (CVs) in photometric Halpha emission line surveys. Our study is motivated by the fact that the Isaac Newton Telescope (INT) Photometric Halpha Survey of the northern galactic plane (IPHAS) will soon provide r', i' and narrow-band Halpha measurements down to r' \simeq 20 for all northern objects between -5 degrees < b < +5 degrees. IPHAS thus provides a unique resource, both for studying the emission line properties of known CVs and for constructing a new CV sample selected solely on the basis of Halpha excess. Our goal here is to carry out the first task and prepare the way for the second. In order to achieve this, we analyze data on 19 CVs already contained in the IPHAS data base and supplement this with identical observations of 52 CVs outside the galactic plane. Our key results are as follows: (i) the recovery rate of known CVs as Halpha emitters in a survey like IPHAS is \simeq 70 per cent; (ii) of the \simeq 30 per cent of CVs which were not recovered \simeq 75 per cent were clearly detected but did not exhibit a significant Halpha excess at the time of our observations; (iii) the recovery rate depends only weakly on CV type; (iv) the recovery rate depends only weakly on orbital period; (v) short-period dwarf novae tend to have the strongest Halpha lines. These results imply that photometric emission line searches provide an efficient way of constructing CV samples that are not biased against detection of intrinsically faint, short-period systems.

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arXiv2005

The shaping of planetary nebula Sh 2-188 through interaction with the interstellar medium

Sh 2-188 is an example of strong interaction between a planetary nebula (PN) and the interstellar medium (ISM). Its structure is postulated to be the result of motion through the ISM. We present new H$α$ images from the Isaac Newton Telescope Photometric H$α$ Survey of the Northern Galactic Plane which reveal new structure. The nebula extends 15 arcmin on the sky in total. We have developed a `triple-wind' hydrodynamical model, comprising of the initial `slow' asymptotic giant branch (AGB) wind and the later `fast' stellar wind plus a third wind reflecting the motion through the ISM. Simulations at various velocities of the central star relative to the ISM indicate that a high velocity of 125 kms is required to reproduce the observed structure. We find most of the structure already forms during the AGB phase. The closure of the ring arises from the slow--fast wind interaction. Most of the mass lost on the AGB has been swept downstream, providing a potential explanation of the missing mass problem in PNe. We report a proper motion for the central star of 30 mas yr^-1 in the direction of the bright limb, implying a distance to the nebula of 850^{+500}_{-420} pc, consistent with a spectroscopic distances. Expansion velocities measured from spectroscopic data are consistent with velocities measured from the simulation. The model shows that the size of the PN was already set during the AGB phase.

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arXiv2005

Near-infrared line spectropolarimetry of hot massive stars

In order to study the inner parts of the circumstellar material around optically faint, infrared bright objects, we present the first medium-resolution spectropolarimetric data taken in the near-infrared. In this paper we discuss Pa beta line data of GL 490, a well-known embedded massive young stellar object, and of MWC 349A and MWC 342, two optically faint stars that are proposed to be in the pre-main sequence phase of evolution. As a check on the method, the classical Be star zeta Tau, known to display line polarization changes at optical wavelengths, was observed as well. Three of our targets show a ``line effect'' across Pa beta. For zeta Tau and MWC 349A this line effect is due to depolarisation by a circumstellar electron-scattering disk. In both cases, the position angle of the polarisation is consistent with that of the larger scale disks imaged at other wavelengths, validating infrared spectropolarimetry as a means to detect flattening on small scales. The tentative detection of a rotation in the polarization position angle at Pa beta in the embedded massive young stellar object GL 490 suggests the presence of a small scale rotating accretion disk with an inner hole - similar to those recently discovered at optical wavelengths in Herbig Ae and T Tauri stars.

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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.

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arXiv2005

2-D Monte Carlo simulations of H I line formation in massive YSO disk winds

Massive young stellar objects (YSOs) are powerful infrared H I line emitters. It has been suggested that these lines form in a outflow from a disk surrounding the YSO. Here, new two-dimensional Monte Carlo radiative transfer calculations are described which test this hypothesis. Infrared spectra are synthesised for a YSO disk wind model based on earlier hydrodynamical calculations. The model spectra are in qualitative agreement with the observed spectra from massive YSOs, and therefore provide support for a disk wind explanation for the H I lines. However, there are some significant differences: the models tend to overpredict the Br alpha/Br gamma ratio of equivalent-widths and produce line profiles which are slightly too broad and, in contrast to typical observations, are double-peaked. The interpretation of these differences within the context of the disk wind picture and suggestions for their resolution via modifications to the assumed disk and outflow structure are discussed.

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arXiv2005

Spiral waves and the secondary in the novalike variable, V3885 Sgr

We present seven nights' blue spectroscopy of the novalike variable star, V3885 Sgr. The line spectrum shows a typical combination of broad absorption and emission in H gamma and H beta and He I, which is associated with the accretion disk. We also observe anti-phased narrow emission, which we attribute to irradiation of the secondary star. The He II 4686 and N III--C III--C IV emission lines are devoid of structure and are most likely formed in an outflow. We measure radial velocity shifts in the absorption and emission lines, from which we fit an orbital period of 4.97126+/-0.00036h. From the velocity semi-amplitudes of the disk and companion star, we are able to constrain the binary mass ratio to q>0.7. The phase-folded spectra provide dense coverage of the entire orbital cycle. Doppler tomograms of the hydrogen and He I lines reveal spiral structure in the accretion disk and the irradiated donor star. We believe this is the first unambiguous detection of spiral waves in a novalike variable.

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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.

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arXiv2005

Sh2-188: a model for a speedy PN

Sh2-188 is thought to be an ancient planetary nebula in the galactic disk. It appears to be one-sided with recent observations revealing structure behind the filamentary limb. We postulate that Sh2-188 is interacting with the ISM and simulate it in terms of a ``triple-wind'' model comprising of the usual ``fast'' and ``slow'' interacting stellar winds plus the wind due to motion through the ISM. We have run simulations at various velocities of the central star relative to the ISM and find that a high velocity of 125 km/s best approximates the observed structure. We also suggest that Sh2-188 is younger than previously thought and that much of the mass lost on the AGB has been swept downstream.

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arXiv2004

Linear line polarimetry modelling of pre-main sequence stars

We present emission line polarimetry data and modelling relevant to the circumstellar geometry and kinematics around pre-main sequence stars. For a sample of both Herbig Ae/Be stars and T Tauri stars, we find that most show polarization changes across Halpha, implying that flattened structures are common on the smallest scales -- and over a range of stellar masses. We also present Monte Carlo calculations of spectral line profiles scattered in rotating accretion disks. We consider both the case of a central star that emits line photons uniformly, as well as via hot spots. Intriguingly, the switch between a uniform point source and a finite-sized star results in a marked difference in the position angle variation across the line. Our models demonstrate the diagnostic potential of line polarimetry in determining the disk inclination and the size of the inner hole -- a spatial scale no other technique currently accesses.

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arXiv2003

The discovery of low-mass pre main sequence stars in Cepheus OB3b

We report the discovery of low-mass PMS stars in the younger subgroup of the Cepheus OB3 association, Cep OB3b, using {\it UBVI} CCD photometry and spectroscopy. The location of a PMS is well defined in a V versus (V-I) colour-magnitude diagram (CMD). Multi-fibre spectroscopy results of optically-selected PMS candidates confirm the T Tauri nature of 10 objects, with equal numbers of classical and weak-line TTS. There are 6 other objects which we classify as possible PMS stars. The newly discovered TTS have masses in the range 0.9 - 3.0 Msun and ages from <1 to nearly 10 Myr, based on the Siess et al.(2000) isochrones. Their location close to the O and B Their location close to the O and B stars of the association demonstrates that low-mass star formation is possible in this hostile environment dominated by early-type stars and that the latter must have been less effective in eroding the circumstellar discs of their lower mass siblings compared to other OB associations (e.g. lambda Ori). We attribute this to the nature of the local environment, speculating that the bulk of molecular material, which shielded low-mass stars from the ionising radiation of their early-type siblings, has only recently been removed (abridged).

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arXiv2002

Stellar wind signatures in sdB stars?

Subdwarf B (sdB) stars form the blue end of the horizonal branch. Their peculiar atmospheric abundance patterns are due to diffusion processes. However, diffusion models fail to explain these anomalies quantitatively. From a NLTE model atmosphere analysis of 40 sdB stars, we found that the more luminous (i.e. more evolved) stars have anomalous H alpha and HeI 6678Ang line profiles, i.e, the lines are too broad and shallow and may even show some emission. We interpret these anomalies as the signatures of a stellar wind, the first such detection in this class of star (if confirmed). Mass loss may also explain the peculiar abundance patterns seen in sdB stars. High-quality UV spectra are needed to confirm that these stars do have stellar winds.

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arXiv2002

The Component Star Masses in RW Tri

We use time-resolved spectra of the cataclysmic variable RW Tri in the I and K-band to determine the orbital velocity of the secondary star using skew mapping and cross correlation techniques respectively. We find radial velocity amplitudes of 250+/-47km/s in the I-band, and 221+/-29km/s in the K-band. We also determine the rotational velocity of the secondary star using the K-band data and find a V(rot)sini of 120+/-20km/s. A combination of these results coupled with an estimate of the effect of heating on the secondary star suggests a mass ratio M_2/M_1 in the range 0.6-1.1; the mass ratio range with no correction for heating is 0.5-0.8. These lead to most likely estimates of the primary and secondary star masses in the range 0.4-0.7 solar mass and 0.3-0.4 solar mass respectively. Further refinement of the stellar masses is hampered by uncertain knowledge of the white dwarf orbital velocity, and we discuss evidence that at least some estimates of the white dwarf velocity are contaminated by non-orbital components.

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arXiv2002

QU Car: a very high luminosity nova-like binary with a carbon-enriched companion

QU Car is listed in cataclysmic variable star catalogues as a nova-like variable. This little-studied, yet bright interacting binary is re-appraised here in the light of new high-quality ultraviolet (UV) interstellar line data obtained with STIS on board the Hubble Space Telescope. The detection of a component of interstellar absorption at a mean LSR velocity of $-$14 km s$^{-1}$ indicates that the distance to QU Car may be $\sim$2 kpc or more -- a considerable increase on the previous lower-limiting distance of 500 pc. If so, the bolometric luminosity of QU Car could exceed $10^{37}$ ergs s$^{-1}$. This would place this binary in the luminosity domain occupied by known compact-binary supersoft X-ray sources. Even at a 500 pc, QU Car appears to be the most luminous nova-like variable known. New intermediate dispersion optical spectroscopy of QU Car spanning 3800--7000 Åis presented. These data yield the discovery that C{\sc iv} $λλ$5801,12 is present as an unusually prominent emission line in an otherwise low-contrast line spectrum. Using measurements of this and other lines in a recombination line analysis, it is shown that the C/He abundance as proxied by the n(C$^{4+}$)/n(He$^{2+}$) ratio may be as high as 0.06 (an order of magnitude higher than the solar ratio). Furthermore, the C/O abundance ratio is estimated to be greater than 1. These findings suggest that the companion in QU Car is a carbon star. If so, it would be the first example of a carbon star in such a binary. An early-type R star best matches the required abundance pattern and could escape detection at optical wavelengths provided the distance to QU Car is $\sim$2 kpc or more.

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arXiv2002

Time-resolved ultraviolet spectroscopy of the compact interacting binary QU Car

We present HST/STIS (1160--1700A) echelle spectra of the cataclysmic variable (CV) star, QU Car, observed in time-tag mode at three epochs. In catalogues this binary is classified as a nova-like variable. We find evidence of a high-state non-magnetic CV at low inclination, with unusually high ionisation. We observed narrow absorption lines (few hundred km/s wide) in N V1240, O V1371 and Si IV1398, as well as broader (HWZI ~1000km/s) emission in C III1176, C IV1549 and He II1640, all with a superposed absorption component. High ionisation is indicated by the unusually string He II emission and the relative strength of the O V absorption line. The dereddened UV SED of, on average, -2.3 suggests that disc accretion dominates the spectral energy distribution. In two observations velocity shifting is noted in the absorption lines on a timescale long enough not to repeat within the ~2600-sec exposures. The absorption superposed on the C IV emission line moves coherently with the N V and Si IV absorption, suggesting the same origin for all absorption lines -- most likely to be in the accretion disc atmosphere. Weak blueshifted absorption in NV and C\IV provides evidence of an outflow component and we estimate a maximum outflow velocity of ~2000km/s. This may be linked to a wind launched from further out in the disc than is typically seen in those high-state non-magnetic CV whose wind speeds are observed to reach to >4000km/s. Unusually, three ionisation stages of carbon -- C II, C III and C IV -- are present in emission, with line width increasing with higher ionisation. The presence of C II in emission and the positive line-width/ionisation correlation is most easily reconciled with an origin in a disc chromosphere, beyond the influence of the EUV-emitting inner disc.

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arXiv2002

Resonance line-profile calculations based on hydrodynamical models of cataclysmic variable winds

We present synthetic line profiles as predicted by the models of 2-D line- driven disk winds due to Proga, Stone & Drew. We compare the model line profiles with HST observations of the cataclysmic variable IX Vel. The model wind consists of a slow outflow that is bounded on the polar side by a fast stream. We find that these two components of the wind produce distinct spectral features. The fast stream produces profiles which show features consistent with observations. These include the appearance of the P-Cygni shape for a range of inclinations, the location of the maximum depth of the absorption component at velocities less than the terminal velocity, and the transition from absorption to emission with increasing inclination. However the model profiles have too little absorption or emission equivalent width. This quantitative difference between our models and observations is not a surprise because the line-driven wind models predict a mass loss rate that is lower than the rate required by the observations. We note that the model profiles exhibit a double-humped structure near the line center which is not echoed in observations. We identify this structure with a non-negligible redshifted absorption which is formed in the slow component of the wind where the rotational velocity dominates over expansion velocity. We conclude that the next generation of disk wind models, developed for application to CVs, needs to yield stronger wind driving out to larger disk radii than do the present models.

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