arXiv subjects

A. Aungwerojwit

Publications and source records attributed to A. Aungwerojwit.

At least 37 records · Page 2Linked to original sources

arXiv2009

The UV-Excess Survey of the Northern Galactic Plane (UVEX)

The UV-Excess Survey of the Northern Galactic Plane images a 10x185 degree wide band, centered on the Galactic Equator using the 2.5m Isaac Newton Telescope in four bands (U,g,r,HeI5875) down to ~21st-22nd magnitude (~20th in HeI5875). The setup and data reduction procedures are described. Simulations of the colours of main-sequence stars, giant, supergiants, DA and DB white dwarfs and AM CVn stars are made, including the effects of reddening. A first look at the data of the survey (currently 30% complete) is given.

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arXiv2009

SDSS unveils a population of intrinsically faint cataclysmic variables at the minimum orbital period

We discuss the properties of 137 cataclysmic variables (CVs) which are included in the Sloan Digital Sky Survey (SDSS) spectroscopic data base, and for which accurate orbital periods have been measured. 92 of these systems are new discoveries from SDSS and were followed-up in more detail over the past few years. 45 systems were previously identified as CVs because of the detection of optical outbursts and/or X-ray emission, and subsequently re-identified from the SDSS spectroscopy. The period distribution of the SDSS CVs differs dramatically from that of all the previously known CVs, in particular it contains a significant accumulation of systems in the orbital period range 80--86 min. We identify this feature as the elusive "period minimum spike" predicted by CV population models, which resolves a long-standing discrepancy between compact binary evolution theory and observations. We show that this spike is almost entirely due to the large number of CVs with very low accretion activity identified by SDSS. The optical spectra of these systems are dominated by emission from the white dwarf photosphere, and display little or no spectroscopic signature from the donor stars, suggesting very low-mass companion stars. We determine the average absolute magnitude of these low-luminosity CVs at the period minimum to be =11.6+-0.7. Comparison of the SDSS CV sample to the CVs found in the Hamburg Quasar Survey and the Palomar Green Survey suggests that the depth of SDSS is the key ingredient resulting in the discovery of a large number of intrinsically faint short-period systems.

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arXiv2009

The IPHAS-POSS-I proper motion survey of the Galactic Plane

We present a proper motion survey of the Galactic plane, using IPHAS data and POSS-I Schmidt plate data as a first epoch, that probes down to proper motions below 50 milliarcseconds per year. The IPHAS survey covers the northern plane ($|b| < 5^{\circ}$) with CCD photometry in the $r$, $i$ and H$α$ passbands. We examine roughly 1400 sq. deg. of the IPHAS survey area and draw up a catalogue containing 103058 objects with significant proper motions below 150 millarcseconds per year in the magnitude range 13.5$< r' <$19. Our survey sample contains large samples of white dwarfs and subdwarfs which can be identified using a reduced proper motion diagram. We also found several objects with IPHAS colours suggesting H$α$ emission and significant proper motions. One is the known cataclysmic variable GD552; two are known DB white dwarfs and five others are found to be non-DA (DB and DC) white dwarfs, which were included in the H$α$ emission line catalogue due to their lack of absorption in the H$α$ narrow-band.

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arXiv2008

Post Common Envelope Binaries from SDSS. V: Four eclipsing white dwarf main sequence binaries

We identify SDSS011009.09+132616.1, SDSS030308.35+005444.1, SDSS143547.87+373338.5 and SDSS154846.00+405728.8 as four eclipsing white dwarf plus main sequence (WDMS) binaries from the Sloan Digital Sky Survey, and report on follow-up observations of these systems. Orbital periods and ephemerides have been established from multi-season photometry. SDSS1435+3733, with Porb=3h has the shortest orbital period of all known eclipsing WDMS binaries. Time-resolved spectroscopic observations have been obtained and the radial velocities of the secondary stars in all four systems were measured. A spectral decomposition/fitting technique was then employed to determine the white dwarf effective temperatures and surface gravities, as well as the spectral types of the companion stars. We used a light curve modeling code to further constrain the masses and radii of the components in all systems. All three DA white dwarfs have masses of Mwd~0.4-0.6Msun, in line with the expectations from close binary evolution. The DC white dwarf in SDSS0303+0054 has a mass of Mwd>0.85Msun, making it unusually massive for a post-common envelope system. Our new additions raise the number of known eclipsing WDMS binaries to fourteen, and we find that the average white dwarf mass in this sample is =0.57+/-0.16Msun, only slightly lower than the average mass of single white dwarfs. The majority of all eclipsing WDMS binaries contain low-mass (<0.6Msun) secondary stars, and will eventually provide valuable observational input for the calibration of the mass-radius relations of low-mass main sequence stars and of white dwarfs.

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arXiv2008

Post Common Envelope Binaries from SDSS - III. Seven new orbital periods

We present follow-up spectroscopy and photometry of 11 post common envelope binary (PCEB) candidates identified from multiple Sloan Digital Sky Survey (SDSS) spectroscopy in an earlier paper. Radial velocity measurements using the \Lines{Na}{I}{8183.27,8194.81} absorption doublet were performed for nine of these systems and provided measurements of six orbital periods in the range $\Porb= 2.7-17.4$ h. Three PCEB candidates did not show significant radial velocity variations in the follow-up data, and we discuss the implications for the use of SDSS spectroscopy alone to identify PCEBs. Differential photometry confirmed one of our spectroscopic orbital periods and provided one additional \Porb measurement. Binary parameters are estimated for the seven objects for which we have measured the orbital period and the radial velocity amplitude of the low-mass companion star, $K_\mathrm{sec}$. So far, we have published nine SDSS PCEBs orbital periods, all of them $\Porb<1$ d. We perform Monte-Carlo simulations and show that $3σ$ SDSS radial velocity variations should still be detectable for systems in the orbital period range of $\Porb\sim1-10$ days. Consequently, our results suggest that the number of PCEBs decreases considerably for $\Porb>1$ day, and that during the common envelope phase the orbital energy of the binary star is maybe less efficiently used to expell the envelope than frequently assumed.

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arXiv2008

Initial Data Release from the INT Photometric H-alpha Survey of the Northern Galactic Plane (IPHAS)

The INT/WFC Photometric H-alpha Survey of the Northern Galactic Plane (IPHAS) is an imaging survey being carried out in H-alpha, r' and i' filters, with the Wide Field Camera (WFC) on the 2.5-metre Isaac Newton Telescope (INT) to a depth of r'=20 (10 sigma). The survey is aimed at revealing large scale structure in our local galaxy, and also the properties of key early and late populations making up the Milky Way. Mapping emission line objects enables a particular focus on objects in the young and old stages of stellar evolution ranging from early T-Tauri stars to late planetary nebulae. In this paper we present the IPHAS Initial Data Release, primarily a photometric catalogue of about 200 million unique objects, coupled with associated image data covering about 1600 square degrees in three passbands. We note how access to the primary data products has been implemented through use of standard virtual observatory publishing interfaces. Simple traditional web access is provided to the main IPHAS photometric catalogue, in addition to a number of common catalogues (such as 2MASS) which are of immediate relevance. Access through the AstroGrid VO Desktop opens up the full range of analysis options, and allows full integration with the wider range of data and services available through the Virtual Observatory. The IDR represents the largest dataset published primarily through VO interfaces to date, and so stands as an examplar of the future of survey data mining. Examples of data access are given, including a cross-matching of IPHAS photometry with sources in the UKIDSS Galactic Plane Survey that validates the existing calibration of the best data.

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arXiv2008

Orbital periods of cataclysmic variables identified by the SDSS. III. Time-series photometry obtained during the 2004/5 International Time Project on La Palma

We present time resolved CCD photometry of 15 cataclysmic variables (CVs) identified by the Sloan Digital Sky Survey (SDSS). The data were obtained as part of the 2004/05 International Time Programme on La Palma. We discuss the morphology of the light curves and the CV subtypes and give accurate orbital periods for 11 systems. Nine systems are found below the 2-3h orbital period gap, of which five have periods within a few minutes of the ~80min minimum orbital period. One system each is found within and above the gap. This confirms the previously noted trend for a large fraction of short-period systems among the SDSS CVs. Objects of particular interest are SDSSJ0901+4809 and SDSSJ1250+6655 which are deeply eclipsing. SDSSJ0854+3905 is a polar with an extremely modulated light curve, which is likely due to a mixture of cyclotron beaming and eclipses of the accretion region by the white dwarf. One out of five systems with white-dwarf dominated optical spectra exhibits non-radial pulsations.

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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 pre-cataclysmic variable, LTT560

System parameters of the object LTT560 are determined in order to clarify its nature and evolutionary status. We apply time-series photometry to reveal orbital modulations of the light curve, time-series spectroscopy to measure radial velocities of features from both the primary and the secondary star, and flux-calibrated spectroscopy to derive temperatures of both components. We find that LTT560 is composed of a low temperature T~7500K DA white dwarf as the primary and an M5.5+-1 main-sequence star as the secondary component. The current orbital period is Porb=3.54(07)h. We derive a mass ratio Msec/Mwd = 0.36(03) and estimate the distance to d=25-40pc. Long-term variation of the orbital light curve and an additional H-alpha emission component on the white dwarf indicate activity in the system, probably in the form of flaring and/or accretion events.

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arXiv2007

Orbital periods of cataclysmic variables identified by the SDSS. II. Measurements for six objects, including two eclipsing systems

Continuing our work from Paper I (Southworth et al., 2006) we present medium-resolution spectroscopy and broad-band photometry of seven cataclysmic variables (CVs) discovered by the SDSS. For six of these objects we derive accurate orbital periods, all which are measured for the first time. For SDSS J013132.39+090122.2, which contains a non-radially pulsating white dwarf, we find an orbital period of 81.54 +/- 0.13 min and a low radial velocity variation amplitude indicative of an extreme mass ratio. For SDSS J205914.87+061220.4, we find a period of 107.52 +/- 0.14 min. This object is a dwarf nova and was fading from its first recorded outburst throughout our observations. INT photometry of SDSS J155531.99-001055.0 shows that this system undergoes total eclipses which are 1.5 mag deep and occur on a period of 113.54 +/- 0.03 min. A NOT light curve of SDSS J075443.01+500729.2 shows that this system is also eclipsing, on a period of 205.965 +/- 0.014 min, but here the eclipses are V-shaped and only 0.5 mag deep. Its low emission-line strengths, orbital period and V-shaped eclipse unambiguously mark it as a novalike object. WHT photometry of SDSS J005050.88+000912.6 and SDSS J210449.94+010545.8 yields periods of 80.3 +/- 2.2 and 103.62 +/- 0.12 min, respectively. Photometry of the seventh and final system, SDSS J165658.12+212139.3, shows only flickering. Our results strengthen the conclusion that the faint magnitude limit of the SDSS spectroscopic database implies that the sample of CVs contained in it has quite different characteristics to previously studied samples of these objects. Five of the six orbital periods measured here are shorter than the observed 2-3 hr CV period gap. Two systems have periods very close to the minimum orbital period for hydrogen-rich CVs.

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arXiv2007

Discovery of two new accreting pulsating white dwarf stars

We report the discovery of two new accreting pulsating white dwarf stars amongst the cataclysmic variables of the Sloan Digital Sky Survey: SDSSJ074531.91+453829.5 and SDSSJ091945.10+085710.0. We observe high amplitude non-sinusoidal variations of 4.5-7% at a period close to 1230s in the optical light curves of SDSSJ074531.91+453829.5 and a low amplitude variation of 0.7-1.6% near 260s in the light curves of SDSSJ091945.10+085710.0. We infer that these optical variations are a consequence of nonradial g-mode pulsations in the accreting primary white dwarfs of these cataclysmic variables. However we cannot rule out the remote possibility that the 260s period could be the spin period of the accreting white dwarf SDSSJ091945.10+085710.0. We also uncovered a non-variable SDSSJ171145.08+301320.0 during our search; our two observing runs exclude any pulsation related periodicities in the range of 85-1400s with an amplitude greater than or equal to 0.5%. This discovery paper brings the total number of known accreting white dwarf pulsators to eleven.

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arXiv2007

HS1857+5144: A hot and young pre-cataclysmic variable

We report the discovery of a new white dwarf/M dwarf binary, HS1857+5144, identified in the Hamburg Quasar Survey (HQS). Time-resolved optical spectroscopy and photometry were carried out to determine the properties of this new cataclysmic variable progenitor pre-CV). The light curves of HS1857+5144 display a sinusoidal variation with a period of Porb=383.52 min and peak-to-peak amplitudes of 0.7 mag and 1.1 mag in the B-band and R-band, respectively. The large amplitude of the brightness variation results from a reflection effect on the heated inner hemisphere of the companion star, suggesting a very high temperature of the white dwarf. Our radial velocity study confirms the photometric period as the orbital period of the system. A model atmosphere fit to the spectrum of the white dwarf obtained at minimum light provides limits to its mass and temperature of Mwd=~0.6-1.0 Msun and Twd=~70000-100000 K, respectively. The detection of HeII 4686 absorption classifies the primary star of HS1857+5144 as a DAO white dwarf. Combining the results from our spectroscopy and photometry, we estimate the mass of the companion star and the binary inclination to be Msec=~0.15-0.30 Msun and i=~45-55 deg, respectively. We classify HS1857+5144 as one of the youngest pre-CV known to date. The cooling age of the white dwarf suggests that the present system has just emerged from a common envelope phase ~10^5 yr ago. HS1857+5144 will start mass transfer within or below the 2-3h period gap.

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arXiv2007

SW Sextantis stars: the dominant population of CVs with orbital periods between 3-4 hours

[Abridged] We present time-series optical photometry of five new CVs identified by the Hamburg Quasar Survey. The eclipses observed in HS 0129+2933, HS 0220+0603, and HS 0455+8315 provided very accurate orbital periods of 3.35129827(65), 3.58098501(34), and 3.56937674(26) h, respectively. HS 0805+3822 shows grazing eclipses and has a likely orbital period of 3.2169(2) h. Time-resolved optical spectroscopy of the new CVs (with the exception of HS 0805+3822) is also presented. Radial velocity studies provided an orbital period of 3.55 h for HS 1813+6122, which allowed us to identify the observed photometric signal at 3.39 h as a negative superhump wave. The spectroscopic behaviour clearly identifies these new CVs as new SW Sextantis stars. These new additions increase the number of known SW Sex stars to 35. Almost 40 per cent of the total SW Sex population do not show eclipses, invalidating the requirement of eclipses as a defining characteristic of the class and the models based on a high orbital inclination geometry alone. On the other hand, the predominance of orbital periods in the narrow 3-4.5 h range is becoming more pronounced. In fact, almost half the CVs which populate the 3-4.5 h period interval are definite members of the class. These statistics are confirmed by our results from the Hamburg Quasar Survey CVs. Remarkably, 54 per cent of the Hamburg nova-like variables have been identified as SW Sex stars with orbital periods in the 3-4.5 h range. The observation of this pile-up of systems close to the upper boundary of the period gap is difficult to reconcile with the standard theory of CV evolution, as the SW Sex stars are believed to have the highest mass transfer rates among CVs. Finally, we review the full range of common properties that the SW Sex stars exhibit.

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arXiv2007

SDSS J233325.92+152222.1 and the evolution of intermediate polars

Intermediate polars (IPs) are cataclysmic variables which contain magnetic white dwarfs with a rotational period shorter than the binary orbital period. Evolutionary theory predicts that IPs with long orbital periods evolve through the 2-3 hour period gap, but it is very uncertain what the properties of the resulting objects are. Whilst a relatively large number of long-period IPs are known, very few of these have short orbital periods. We present phase-resolved spectroscopy and photometry of SDSS J233325.92+152222.1 and classify it as the IP with the shortest known orbital period (83.12 +/- 0.09 min), which contains a white dwarf with a relatively long spin period (41.66 +/- 0.13 min). We estimate the white dwarf's magnetic moment to be mu(WD) \approx 2 x 10^33 G cm^3, which is not only similar to three of the other four confirmed short-period IPs but also to those of many of the long-period IPs. We suggest that long-period IPs conserve their magnetic moment as they evolve towards shorter orbital periods. Therefore the dominant population of long-period IPs, which have white dwarf spin periods roughly ten times shorter than their orbital periods, will likely end up as short-period IPs like SDSS J2333, with spin periods a large fraction of their orbital periods.

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arXiv2006

Dwarf novae in the Hamburg Quasar Survey: Rarer than expected

We report the discovery of five new dwarf novae from the Hamburg Quasar Survey (HQS), and discuss the properties of the sample of dwarf novae in the HQS. The orbital periods of the new dwarf novae are ~105.1 min or ~109.9 min, 114.3+-2.7 min, 92.66+-0.17 min, 272.317+-0.001 min, 258.02+-0.56 min for HS0417+7445, HS1016+3412, HS1340+1524, HS1857+7127, and HS2214+2845, respectively. HS1857+7127 is found to be partially eclipsing. In HS2214+2845 the secondary star of spectral type M3+-1 is clearly detected, and we estimate the distance to the system to be d=390+-40 pc. We recorded one superoutburst of the SU UMa system HS0417+7445. HS1016+3412 and HS1340+1524 have rare outbursts, and their subtype is yet undetermined. HS1857+7127 frequently varies in brightness and may be a Z Cam-type dwarf nova. HS2214+2845 is a U Gem-type dwarf nova with a most likely cycle length of 71 d. To date, 14 new dwarf novae have been identified in the HQS. The ratio of short-period (<3 h) to long-period (>3 h) systems of this sample is 1.3, much smaller compared to the ratio of 2.7 found for all known dwarf novae. The HQS dwarf novae display typically infrequent or low-amplitude outburst activity, underlining the strength of spectroscopic selection in identifying new CVs independently of their variability. The spectroscopic properties of short-period CVs in the HQS suggest that most of them are still evolving towards the minimum period. Their total number agrees with the predictions of population models within an order of magnitude. However, the bulk of all CVs is predicted to have evolved past the minimum period, and those systems remain unidentified. Those post-bounce systems may have markedly weaker Hbeta emission lines compared to the average known short-period CVs, and probably undergo no or extremely rare outbursts.

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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

A ZZ Ceti white dwarf in SDSS J133941.11+484727.5

We present time-resolved spectroscopy and photometry of the cataclysmic variable (CV) SDSSJ133941.11+484727.5 (SDSS1339) which has been discovered in the Sloan Digital Sky Survey Data Release 4. The orbital period determined from radial velocity studies is 82.524(24)min, close to the observed period minimum. The optical spectrum of SDSS1339 is dominated to 90% by emission from the white dwarf. The spectrum can be successfully reproduced by a three-component model (white dwarf, disc, secondary) with Twd=12500K for a fixed log g=8.0, d=170pc, and a spectral type of the secondary later than M8. The mass transfer rate corresponding to the optical luminosity of the accretion disc is very low,~1.7x10^-13Msun/yr. Optical photometry reveals a coherent variability at 641s with an amplitude of 0.025mag, which we interpret as non-radial pulsations of the white dwarf. In addition, a long-period photometric variation with a period of either 320min or 344min and an amplitude of 0.025mag is detected, which bears no apparent relation with the orbital period of the system. Similar long-period photometric signals have been found in the CVs SDSSJ123813.73-033933.0, SDSSJ204817.85-061044.8, GW Lib and FS Aur, but so far no working model for this behaviour is available.

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arXiv2005

HS0139+0559, HS0229+8016, HS0506+7725 and HS0642+5049: Four new long-period cataclysmic variables

We present time-resolved optical spectroscopy and photometry of four relatively bright (V~14.0-15.5) long-period cataclysmic variables (CVs) discovered in the Hamburg Quasar Survey: HS0139+0559, HS0229+8016, HS0506+7725 and HS0642+5049. Their respective orbital periods, 243.69+-0.49min, 232.550+-0.049min, 212.7+-0.2min and 225.90+-0.23min are determined from radial velocity and photometric variability studies. HS0506+7725 is characterised by strong Balmer and He emission lines, short-period (~10-20min) flickering and weak X-ray emission in the ROSAT All Sky Survey. The detection of a deep low state (~18.5) identifies HS0506+7725 as a member of the VY Scl stars. HS0139+0559, HS0229+8016 and HS0642+5049 display thick-disc like spectra and no or only weak flickering activity. HS0139+0559 and HS0229+8016 exhibit clean quasi-sinusoidal radial velocity varations of their emission lines but no or very little orbital photometric variability. In contrast, we detect no radial velocity variation in HS0642+5049 but a noticeable orbital brightness variation. We identify all three systems either as UX UMa-type novalike variables or as Z Cam-type dwarf novae. Our identification of these four new systems underlines that the currently known sample of CVs is rather incomplete even for bright objects. The four new systems add to the clustering of orbital periods in the 3-4h range found in the sample of HQS selected CVs, and we discuss the large incidence of magnetic CVs and VY Scl/SW Sex stars found in this period range among the known population of CVs.

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