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Papers by A. Aungwerojwit

Research paper thumbnail of Post common envelope binaries from SDSS

Astronomy and Astrophysics, Dec 1, 2011

Context. The complexity of the common-envelope phase and of magnetic stellar wind braking current... more Context. The complexity of the common-envelope phase and of magnetic stellar wind braking currently limits our understanding of close binary evolution. Because of their intrinsically simple structure, observational population studies of white dwarf plus main sequence (WDMS) binaries can potentially test theoretical models and constrain their parameters. Aims. The Sloan Digital Sky Survey (SDSS) has provided a large and homogeneously selected sample of WDMS binaries, which we characterise in terms of orbital and stellar parameters. Methods. We have obtained radial velocity information for 385 WDMS binaries from follow-up spectroscopy and for an additional 861 systems from the SDSS subspectra. Radial velocity variations identify 191 of these WDMS binaries as post common-envelope binaries (PCEBs). Orbital periods of 58 PCEBs were subsequently measured, predominantly from time-resolved spectroscopy, bringing the total number of SDSS PCEBs with orbital parameters to 79. Observational biases inherent to this PCEB sample were evaluated through extensive Monte Carlo simulations. Results. We find that 21-24% of all SDSS WDMS binaries have undergone common-envelope evolution, which is in good agreement with published binary population models and high-resolution HST imaging of WDMS binaries unresolved from the ground. The bias-corrected orbital period distribution of PCEBs ranges from 1.9 h to 4.3 d and approximately follows a normal distribution in log(P orb), peaking at ∼10.3 h. There is no observational evidence for a significant population of PCEBs with periods in the range of days to weeks. Conclusions. The large and homogeneous sample of SDSS WDMS binaries provides the means to test fundamental predictions of binary population models, hence to observationally constrain the evolution of all close compact binaries.

Research paper thumbnail of A Hot Spot Model for GR Tauri

A Hot Spot Model for GR Tauri

Astrophysics and Space Science Library, 2003

ABSTRACT

Research paper thumbnail of Optical polarization of OJ 287 in 2005-2009 (Villforth+, 2010)

Optical polarization of OJ 287 in 2005-2009 (Villforth+, 2010)

These files present the observational data of the paper. There are 7 files : 6 for photometry (BV... more These files present the observational data of the paper. There are 7 files : 6 for photometry (BVRIri) and one for polarimetry. Details of the reduction procedures and the telescopes involved can be found in the paper. (7 data files).

Research paper thumbnail of The UV-Excess survey of the northern Galactic plane

Monthly Notices of the Royal Astronomical Society, 2009

The UV-Excess survey of the northern Galactic plane images a 10 • × 185 • wide band, centred on t... more The UV-Excess survey of the northern Galactic plane images a 10 • × 185 • wide band, centred on the Galactic equator using the 2.5-m Isaac Newton Telescope in four bands (U, g, r, He I 5875) down to ∼21-22 mag (∼20 in He I 5875). 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 Canum Venaticorum stars are made, including the effects of reddening. A first look at the data of the survey (currently 30 per cent complete) is given.

Research paper thumbnail of Iphas J062746.41+014811.3: A Deeply Eclipsing Intermediate Polar

Iphas J062746.41+014811.3: A Deeply Eclipsing Intermediate Polar

The Astrophysical Journal, 2012

ABSTRACT We present time-resolved photometry of a cataclysmic variable discovered in the Isaac Ne... more ABSTRACT We present time-resolved photometry of a cataclysmic variable discovered in the Isaac Newton Telescope Photometric Halpha Survey of the northern galactic plane, IPHAS J062746.41+014811.3 and classify the system as the fourth deeply eclipsing intermediate polar known with an orbital period of Porb=8.16 h, and spin period of Pspin=2210 s. The system shows mild variations of its brightness, that appear to be accompanied by a change in the amplitude of the spin modulation at optical wavelengths, and a change in the morphology of the eclipse profile. The inferred magnetic moment of the white dwarf is mu_wd = 6-7 x 10^33 Gcm^3, and in this case IPHAS J0627 will either evolve into a short-period EX Hya-like intermediate polar with a large Pspin\Porb ratio, or, perhaps more likely, into a synchronised polar. Swift observations show that the system is an ultraviolet and X-ray source, with a hard X-ray spectrum that is consistent with those seen in other intermediate polars. The ultraviolet light curve shows orbital modulation and an eclipse, while the low signal-to-noise ratio X-ray light curve does not show a significant modulation on the spin period. The measured X-ray flux is about an order of magnitude lower than would be expected from scaling by the optical fluxes of well-known X-ray selected intermediate polars.

Research paper thumbnail of Discovery of Two New Accreting Pulsating White Dwarf Stars

The Astrophysical Journal, 2007

We report the discovery of two new accreting pulsating white dwarf stars amongst the cataclysmic ... more We report the discovery of two new accreting pulsating white dwarf stars amongst the cataclysmic variables of the Sloan Digital Sky Survey: SDSS J074531.91+453829.5 and SDSS J091945.10+085710.0. We observe high amplitude non-sinusoidal variations of 4.5-7% at a period close to 1230 s in the optical light curves of SDSS J074531.91+453829.5 and a low amplitude variation of 0.7-1.6% near 260 s in the light curves of SDSS J091945.10+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 260 s period could be the spin period of the accreting white dwarf SDSS J091945.10+085710.0. We also uncovered a non-variable SDSS J171145.08+301320.0 during our search; our two observing runs exclude any pulsation related periodicities in the range of 85-1400 s with an amplitude ≥0.5%. This discovery paper brings the total number of known accreting white dwarf pulsators to eleven.

Research paper thumbnail of MULTI-SITE OBSERVATIONS OF PULSATION IN THE ACCRETING WHITE DWARF SDSS J161033.64–010223.3 (V386 Ser)

The Astrophysical Journal, 2010

Nonradial pulsations in the primary white dwarfs of cataclysmic variables can now potentially all... more Nonradial pulsations in the primary white dwarfs of cataclysmic variables can now potentially allow us to explore the stellar interior of these accretors using stellar seismology. In this context, we conducted a multi-site campaign on the accreting pulsator SDSS J161033.64-010223.3 (V386 Ser) using seven observatories located around the world in May 2007 over a duration of 11 days. We report the best fit periodicities here, which were also previously observed in 2004, suggesting their underlying stability. Although we did not uncover a sufficient number of independent pulsation modes for a unique seismological fit, our campaign revealed that the dominant pulsation mode at 609 s is an evenly spaced triplet. The even nature of the triplet is suggestive of rotational splitting, implying an enigmatic rotation period of about 4.8 days. There are two viable alternatives assuming the triplet is real: either the period of 4.8 days is representative of the rotation period of the entire star with implications for the angular momentum evolution of these systems, or it is perhaps an indication of differential rotation with a fast rotating exterior and slow rotation deeper in the star. Investigating the possibility that a changing period could mimic a triplet suggests that this scenario is improbable, but not impossible.

Research paper thumbnail of Enigmatic Recurrent Pulsational Variability of the Accreting White Dwarf Eq Lyn (SDSS J074531.92+453829.6)

Enigmatic Recurrent Pulsational Variability of the Accreting White Dwarf Eq Lyn (SDSS J074531.92+453829.6)

The Astronomical Journal, 2013

Research paper thumbnail of HS 2325 + 8205 —An Ideal Laboratory for Accretion Disk Physics

Publications of the Astronomical Society of the Pacific, 2012

We identify HS 2325+8205 as an eclipsing, frequently outbursting dwarf nova with an orbital perio... more We identify HS 2325+8205 as an eclipsing, frequently outbursting dwarf nova with an orbital period of P orb = 279.841731(5) min. Spectroscopic observations are used to derive the radial velocity curve of the secondary star from absorption features and also from the Hα emission lines, originating from the accretion disc, yielding K sec = K abs = 237 ± 28 km s −1 and K em = 145 ± 9 km s −1 respectively. The distance to the system is calculated to be 400(+200, −140) pc. A photometric monitoring campaign reveals an outburst recurrence time of ∼ 12 − 14 d. The combination of magnitude range (17 − 14 mag), high declination, eclipsing nature and frequency of outbursts makes HS 2325+8205 the ideal system for "real-time" studies of the accretion disc evolution and behaviour in dwarf nova outbursts.

Research paper thumbnail of Discovery of Two New Accreting ZZ Ceti Stars

Discovery of Two New Accreting ZZ Ceti Stars

We report two new accreting ZZ Ceti stars amongst the cataclysmic variables of the Sloan Digital ... more We report two new accreting ZZ Ceti stars amongst the cataclysmic variables of the Sloan Digital Sky Survey: SDSS J074531.92+453829.5 and SDSS J091945.11+085710.0. We observe high amplitude non-sinusoidal variations of 4.5--7% at a period close to 1230 s in the optical light curves of SDSS J074531.92+453829.5 and a low amplitude variation of 0.7--1% near 260 s in the light curves of SDSS J091945.11+085710.0. We infer that these optical variations are a consequence of non-radial g-mode pulsations in the accreting primary white dwarfs of these cataclysmic variables. This discovery paper brings the total number of known accreting white dwarf pulsators to ten. We determine an orbital period of 86.3 ± 2.0 min for SDSS J074531.92+453829.5 and 93.5 ± 8.5 min for SDSS J091945.11+085710.0.

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

Monthly Notices of the Royal Astronomical Society, 2009

We discuss the properties of 137 cataclysmic variables (CVs) which are included in the Sloan Digi... more 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 Xray 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 < M g >= 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.

Research paper thumbnail of The IPHAS-POSS-I proper motion survey of the Galactic plane

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

Monthly Notices of the Royal Astronomical Society, 2009

... Deacon, NR, Groot, PJ, Drew, JE, Greimel, R., Hambly, NC, Irwin, MJ, Aungwerojwit, A., Drake,... more ... Deacon, NR, Groot, PJ, Drew, JE, Greimel, R., Hambly, NC, Irwin, MJ, Aungwerojwit, A., Drake, J. and Steeghs, D. (2009), The IPHAS-POSS-I proper motion survey ... Isaac Newton Group of Telescopes, Apartado de correos 321, E38700 Santa Cruz de La Palma, Tenerife, Spain. 4 ...

Research paper thumbnail of Newly discovered cataclysmic variables from the INT/WFC photometric Hα survey of the northern Galactic plane

Monthly Notices of the Royal Astronomical Society, 2007

We report the discovery of 11 new cataclysmic variable (CV) candidates by the Isaac Newton Telesc... more We report the discovery of 11 new cataclysmic variable (CV) candidates by the Isaac Newton Telescope (INT) Photometric Hα Survey of the northern Galactic plane (IPHAS). Three of the systems have been the subject of further followup 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 Hα 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.

Research paper thumbnail of Post-common envelope binaries from SDSS - III. Seven new orbital periods

Monthly Notices of the Royal Astronomical Society, 2008

We present follow-up spectroscopy and photometry of 11 post common envelope binary (PCEB) candida... more 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 Na I λλ 8183.27,8194.81 absorption doublet were performed for nine of these systems and provided measurements of six orbital periods in the range P orb = 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 P orb 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 sec . So far, we have published nine SDSS PCEBs orbital periods, all of them P orb < 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 P orb ∼ 1 − 10 days. Consequently, our results suggest that the number of PCEBs decreases considerably for P orb > 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.

Research paper thumbnail of The properties of cataclysmic variables in photometric Hα surveys

Monthly Notices of the Royal Astronomical Society, 2006

We report on the properties of 71 known cataclysmic variables (CVs) in photometric Hα emission li... more We report on the properties of 71 known cataclysmic variables (CVs) in photometric Hα emission line surveys. Our study is motivated by the fact that the Isaac Newton Telescope (INT) Photometric Hα Survey of the northern galactic plane (IPHAS) will soon provide r ′ , i ′ and narrow-band Hα measurements down to r ′ ≃ 20 for all northern objects between −5 o < b < +5 o . 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 Hα 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.

Research paper thumbnail of A ZZ Ceti white dwarf in SDSS J133941.11+484727.5

Monthly Notices of the Royal Astronomical Society, 2006

We present time-resolved spectroscopy and photometry of the cataclysmic variable (CV) SDSS J13394... more We present time-resolved spectroscopy and photometry of the cataclysmic variable (CV) SDSS J133941.11+484727.5 (SDSS 1339) 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 SDSS 1339 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 T wd = 12 500 K for a fixed log g = 8.0, d = 170 pc, 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, ≃ 1.7 × 10 −13 M ⊙ yr −1 . Optical photometry reveals a coherent variability at 641 s with an amplitude of 0.025 mag, which we interpret as non-radial pulsations of the white dwarf. In addition, a long-period photometric variation with a period of either 320 min or 344 min and an amplitude of 0.025 mag 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 SDSS J123813.73-033933.0, SDSS J204817.85-061044.8, GW Lib and FS Aur, but so far no working model for this behaviour is available.

Research paper thumbnail of Post-common-envelope binaries from SDSS - V. Four eclipsing white dwarf main-sequence binaries

Monthly Notices of the Royal Astronomical Society, 2009

We identify SDSS 011009.09+132616.1, SDSS 030308.35+005444.1, SDSS 143547.87+373338.5 and SDSS 15... more We identify SDSS 011009.09+132616.1, SDSS 030308.35+005444.1, SDSS 143547.87+373338.5 and SDSS 154846.00+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. SDSS 0110+1326, SDSS 1435+3733 and SDSS 1548+4057 contain DA white dwarfs, while SDSS 0303+0054 contains a cool DC white dwarf. Orbital periods and ephemerides have been established from multiseason photometry. SDSS 1435+3733, with P orb = 3 h has the shortest orbital period of all known eclipsing WDMS binaries. As for the other systems, SDSS 0110+1326 has P orb = 8 h, SDSS 0303+0054 has P orb = 3.2 h and SDSS 1548+4057 has P orb = 4.4 h. Time-resolved spectroscopic observations have been obtained and the Hα and Ca II λλ 8498.02,8542.09,8662.14 triplet emission lines, as well as the Na I λλ 8183.27,8194.81 absorption doublet were used to measure the radial velocities of the secondary stars in all four systems. A spectral decomposition/fitting technique was then employed to isolate the contribution of each of the components to the total spectrum, and 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 modelling code for close binary systems to fit the eclipse profiles and the ellipsoidal modulation/reflection effect in the light curves, to further constrain the masses and radii of the components in all systems. All three DA white dwarfs have masses of M WD ∼ 0.4 − 0.6 M ⊙ , in line with the expectations from close binary evolution. The DC white dwarf in SDSS 0303+0054 has a mass of M WD 0.85 M ⊙ , making it unusually massive for a post-common envelope system. The companion stars in all four systems are M-dwarfs of spectral type M4 and later. 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 < M WD >= 0.57 ± 0.16 M ⊙ , only slightly lower than the average mass of single white dwarfs. The majority of all eclipsing WDMS binaries contain low-mass (< 0.6 M ⊙ ) 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.

Research paper thumbnail of Cataclysmic variables from a ROSAT/2MASS selection -- I. Four new intermediate polars

Monthly Notices of the Royal Astronomical Society, 2005

We report the first results from a new search for cataclysmic variables (CVs) using a combined X-... more We report the first results from a new search for cataclysmic variables (CVs) using a combined X-ray (ROSAT) / infrared (2MASS) target selection that discriminates against background AGN. Identification spectra were obtained at the Isaac Newton Telescope for a total of 174 targets, leading to the discovery of 12 new CVs. Initially devised to find short-period low-mass-transfer CVs, this selection scheme has been very successful in identifying new intermediate polars. Photometric and spectroscopic follow-up observations identify four of the new CVs as intermediate polars: 1RXS J063631.9+353537 (P orb ≃ 201 min, P spin = 1008.3408 s or 930.5829 s), 1RXS J070407.9+262501 (P orb ≃ 250 min, P spin = 480.708 s), 1RXS J173021.5-055933 (P orb = 925.27 min, P spin = 128.0 s), and 1RXS J180340.0+401214 (P orb = 160.21 min, P spin = 1520.51 s). RX J1730, also a moderately bright hard X-ray source in the IN-TEGRAL/IBIS Galactic plane survey, resembles the enigmatic AE Aqr. It is likely that its white dwarf is not rotating at the spin equilibrium period, and the system may represent a short-lived phase in CV evolution.

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

Monthly Notices of the Royal Astronomical Society, 2007

Intermediate polars (IPs) are cataclysmic variables which contain magnetic white dwarfs with a ro... more 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 hr 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 µ WD ≈ 2 × 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.

Research paper thumbnail of Three eclipsing white dwarf plus main sequence binaries from SDSS

Three eclipsing white dwarf plus main sequence binaries from SDSS

Journal of Physics: Conference Series, 2009

We identify SDSS 0110+1326, SDSS 0303+0054 and SDSS 1435+3733 as three eclipsing white dwarf plus... more We identify SDSS 0110+1326, SDSS 0303+0054 and SDSS 1435+3733 as three eclipsing white dwarf plus main sequence binaries from the Sloan Digital Sky Survey, and report on their follow-up observations. Orbital periods for the three systems are established through multi-season photometry. Time-resolved spectroscopic observations lead to the determination of the radial velocities of the secondary stars. A decomposition technique of

Research paper thumbnail of Post common envelope binaries from SDSS

Astronomy and Astrophysics, Dec 1, 2011

Context. The complexity of the common-envelope phase and of magnetic stellar wind braking current... more Context. The complexity of the common-envelope phase and of magnetic stellar wind braking currently limits our understanding of close binary evolution. Because of their intrinsically simple structure, observational population studies of white dwarf plus main sequence (WDMS) binaries can potentially test theoretical models and constrain their parameters. Aims. The Sloan Digital Sky Survey (SDSS) has provided a large and homogeneously selected sample of WDMS binaries, which we characterise in terms of orbital and stellar parameters. Methods. We have obtained radial velocity information for 385 WDMS binaries from follow-up spectroscopy and for an additional 861 systems from the SDSS subspectra. Radial velocity variations identify 191 of these WDMS binaries as post common-envelope binaries (PCEBs). Orbital periods of 58 PCEBs were subsequently measured, predominantly from time-resolved spectroscopy, bringing the total number of SDSS PCEBs with orbital parameters to 79. Observational biases inherent to this PCEB sample were evaluated through extensive Monte Carlo simulations. Results. We find that 21-24% of all SDSS WDMS binaries have undergone common-envelope evolution, which is in good agreement with published binary population models and high-resolution HST imaging of WDMS binaries unresolved from the ground. The bias-corrected orbital period distribution of PCEBs ranges from 1.9 h to 4.3 d and approximately follows a normal distribution in log(P orb), peaking at ∼10.3 h. There is no observational evidence for a significant population of PCEBs with periods in the range of days to weeks. Conclusions. The large and homogeneous sample of SDSS WDMS binaries provides the means to test fundamental predictions of binary population models, hence to observationally constrain the evolution of all close compact binaries.

Research paper thumbnail of A Hot Spot Model for GR Tauri

A Hot Spot Model for GR Tauri

Astrophysics and Space Science Library, 2003

ABSTRACT

Research paper thumbnail of Optical polarization of OJ 287 in 2005-2009 (Villforth+, 2010)

Optical polarization of OJ 287 in 2005-2009 (Villforth+, 2010)

These files present the observational data of the paper. There are 7 files : 6 for photometry (BV... more These files present the observational data of the paper. There are 7 files : 6 for photometry (BVRIri) and one for polarimetry. Details of the reduction procedures and the telescopes involved can be found in the paper. (7 data files).

Research paper thumbnail of The UV-Excess survey of the northern Galactic plane

Monthly Notices of the Royal Astronomical Society, 2009

The UV-Excess survey of the northern Galactic plane images a 10 • × 185 • wide band, centred on t... more The UV-Excess survey of the northern Galactic plane images a 10 • × 185 • wide band, centred on the Galactic equator using the 2.5-m Isaac Newton Telescope in four bands (U, g, r, He I 5875) down to ∼21-22 mag (∼20 in He I 5875). 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 Canum Venaticorum stars are made, including the effects of reddening. A first look at the data of the survey (currently 30 per cent complete) is given.

Research paper thumbnail of Iphas J062746.41+014811.3: A Deeply Eclipsing Intermediate Polar

Iphas J062746.41+014811.3: A Deeply Eclipsing Intermediate Polar

The Astrophysical Journal, 2012

ABSTRACT We present time-resolved photometry of a cataclysmic variable discovered in the Isaac Ne... more ABSTRACT We present time-resolved photometry of a cataclysmic variable discovered in the Isaac Newton Telescope Photometric Halpha Survey of the northern galactic plane, IPHAS J062746.41+014811.3 and classify the system as the fourth deeply eclipsing intermediate polar known with an orbital period of Porb=8.16 h, and spin period of Pspin=2210 s. The system shows mild variations of its brightness, that appear to be accompanied by a change in the amplitude of the spin modulation at optical wavelengths, and a change in the morphology of the eclipse profile. The inferred magnetic moment of the white dwarf is mu_wd = 6-7 x 10^33 Gcm^3, and in this case IPHAS J0627 will either evolve into a short-period EX Hya-like intermediate polar with a large Pspin\Porb ratio, or, perhaps more likely, into a synchronised polar. Swift observations show that the system is an ultraviolet and X-ray source, with a hard X-ray spectrum that is consistent with those seen in other intermediate polars. The ultraviolet light curve shows orbital modulation and an eclipse, while the low signal-to-noise ratio X-ray light curve does not show a significant modulation on the spin period. The measured X-ray flux is about an order of magnitude lower than would be expected from scaling by the optical fluxes of well-known X-ray selected intermediate polars.

Research paper thumbnail of Discovery of Two New Accreting Pulsating White Dwarf Stars

The Astrophysical Journal, 2007

We report the discovery of two new accreting pulsating white dwarf stars amongst the cataclysmic ... more We report the discovery of two new accreting pulsating white dwarf stars amongst the cataclysmic variables of the Sloan Digital Sky Survey: SDSS J074531.91+453829.5 and SDSS J091945.10+085710.0. We observe high amplitude non-sinusoidal variations of 4.5-7% at a period close to 1230 s in the optical light curves of SDSS J074531.91+453829.5 and a low amplitude variation of 0.7-1.6% near 260 s in the light curves of SDSS J091945.10+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 260 s period could be the spin period of the accreting white dwarf SDSS J091945.10+085710.0. We also uncovered a non-variable SDSS J171145.08+301320.0 during our search; our two observing runs exclude any pulsation related periodicities in the range of 85-1400 s with an amplitude ≥0.5%. This discovery paper brings the total number of known accreting white dwarf pulsators to eleven.

Research paper thumbnail of MULTI-SITE OBSERVATIONS OF PULSATION IN THE ACCRETING WHITE DWARF SDSS J161033.64–010223.3 (V386 Ser)

The Astrophysical Journal, 2010

Nonradial pulsations in the primary white dwarfs of cataclysmic variables can now potentially all... more Nonradial pulsations in the primary white dwarfs of cataclysmic variables can now potentially allow us to explore the stellar interior of these accretors using stellar seismology. In this context, we conducted a multi-site campaign on the accreting pulsator SDSS J161033.64-010223.3 (V386 Ser) using seven observatories located around the world in May 2007 over a duration of 11 days. We report the best fit periodicities here, which were also previously observed in 2004, suggesting their underlying stability. Although we did not uncover a sufficient number of independent pulsation modes for a unique seismological fit, our campaign revealed that the dominant pulsation mode at 609 s is an evenly spaced triplet. The even nature of the triplet is suggestive of rotational splitting, implying an enigmatic rotation period of about 4.8 days. There are two viable alternatives assuming the triplet is real: either the period of 4.8 days is representative of the rotation period of the entire star with implications for the angular momentum evolution of these systems, or it is perhaps an indication of differential rotation with a fast rotating exterior and slow rotation deeper in the star. Investigating the possibility that a changing period could mimic a triplet suggests that this scenario is improbable, but not impossible.

Research paper thumbnail of Enigmatic Recurrent Pulsational Variability of the Accreting White Dwarf Eq Lyn (SDSS J074531.92+453829.6)

Enigmatic Recurrent Pulsational Variability of the Accreting White Dwarf Eq Lyn (SDSS J074531.92+453829.6)

The Astronomical Journal, 2013

Research paper thumbnail of HS 2325 + 8205 —An Ideal Laboratory for Accretion Disk Physics

Publications of the Astronomical Society of the Pacific, 2012

We identify HS 2325+8205 as an eclipsing, frequently outbursting dwarf nova with an orbital perio... more We identify HS 2325+8205 as an eclipsing, frequently outbursting dwarf nova with an orbital period of P orb = 279.841731(5) min. Spectroscopic observations are used to derive the radial velocity curve of the secondary star from absorption features and also from the Hα emission lines, originating from the accretion disc, yielding K sec = K abs = 237 ± 28 km s −1 and K em = 145 ± 9 km s −1 respectively. The distance to the system is calculated to be 400(+200, −140) pc. A photometric monitoring campaign reveals an outburst recurrence time of ∼ 12 − 14 d. The combination of magnitude range (17 − 14 mag), high declination, eclipsing nature and frequency of outbursts makes HS 2325+8205 the ideal system for "real-time" studies of the accretion disc evolution and behaviour in dwarf nova outbursts.

Research paper thumbnail of Discovery of Two New Accreting ZZ Ceti Stars

Discovery of Two New Accreting ZZ Ceti Stars

We report two new accreting ZZ Ceti stars amongst the cataclysmic variables of the Sloan Digital ... more We report two new accreting ZZ Ceti stars amongst the cataclysmic variables of the Sloan Digital Sky Survey: SDSS J074531.92+453829.5 and SDSS J091945.11+085710.0. We observe high amplitude non-sinusoidal variations of 4.5--7% at a period close to 1230 s in the optical light curves of SDSS J074531.92+453829.5 and a low amplitude variation of 0.7--1% near 260 s in the light curves of SDSS J091945.11+085710.0. We infer that these optical variations are a consequence of non-radial g-mode pulsations in the accreting primary white dwarfs of these cataclysmic variables. This discovery paper brings the total number of known accreting white dwarf pulsators to ten. We determine an orbital period of 86.3 ± 2.0 min for SDSS J074531.92+453829.5 and 93.5 ± 8.5 min for SDSS J091945.11+085710.0.

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

Monthly Notices of the Royal Astronomical Society, 2009

We discuss the properties of 137 cataclysmic variables (CVs) which are included in the Sloan Digi... more 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 Xray 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 < M g >= 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.

Research paper thumbnail of The IPHAS-POSS-I proper motion survey of the Galactic plane

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

Monthly Notices of the Royal Astronomical Society, 2009

... Deacon, NR, Groot, PJ, Drew, JE, Greimel, R., Hambly, NC, Irwin, MJ, Aungwerojwit, A., Drake,... more ... Deacon, NR, Groot, PJ, Drew, JE, Greimel, R., Hambly, NC, Irwin, MJ, Aungwerojwit, A., Drake, J. and Steeghs, D. (2009), The IPHAS-POSS-I proper motion survey ... Isaac Newton Group of Telescopes, Apartado de correos 321, E38700 Santa Cruz de La Palma, Tenerife, Spain. 4 ...

Research paper thumbnail of Newly discovered cataclysmic variables from the INT/WFC photometric Hα survey of the northern Galactic plane

Monthly Notices of the Royal Astronomical Society, 2007

We report the discovery of 11 new cataclysmic variable (CV) candidates by the Isaac Newton Telesc... more We report the discovery of 11 new cataclysmic variable (CV) candidates by the Isaac Newton Telescope (INT) Photometric Hα Survey of the northern Galactic plane (IPHAS). Three of the systems have been the subject of further followup 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 Hα 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.

Research paper thumbnail of Post-common envelope binaries from SDSS - III. Seven new orbital periods

Monthly Notices of the Royal Astronomical Society, 2008

We present follow-up spectroscopy and photometry of 11 post common envelope binary (PCEB) candida... more 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 Na I λλ 8183.27,8194.81 absorption doublet were performed for nine of these systems and provided measurements of six orbital periods in the range P orb = 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 P orb 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 sec . So far, we have published nine SDSS PCEBs orbital periods, all of them P orb < 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 P orb ∼ 1 − 10 days. Consequently, our results suggest that the number of PCEBs decreases considerably for P orb > 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.

Research paper thumbnail of The properties of cataclysmic variables in photometric Hα surveys

Monthly Notices of the Royal Astronomical Society, 2006

We report on the properties of 71 known cataclysmic variables (CVs) in photometric Hα emission li... more We report on the properties of 71 known cataclysmic variables (CVs) in photometric Hα emission line surveys. Our study is motivated by the fact that the Isaac Newton Telescope (INT) Photometric Hα Survey of the northern galactic plane (IPHAS) will soon provide r ′ , i ′ and narrow-band Hα measurements down to r ′ ≃ 20 for all northern objects between −5 o < b < +5 o . 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 Hα 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.

Research paper thumbnail of A ZZ Ceti white dwarf in SDSS J133941.11+484727.5

Monthly Notices of the Royal Astronomical Society, 2006

We present time-resolved spectroscopy and photometry of the cataclysmic variable (CV) SDSS J13394... more We present time-resolved spectroscopy and photometry of the cataclysmic variable (CV) SDSS J133941.11+484727.5 (SDSS 1339) 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 SDSS 1339 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 T wd = 12 500 K for a fixed log g = 8.0, d = 170 pc, 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, ≃ 1.7 × 10 −13 M ⊙ yr −1 . Optical photometry reveals a coherent variability at 641 s with an amplitude of 0.025 mag, which we interpret as non-radial pulsations of the white dwarf. In addition, a long-period photometric variation with a period of either 320 min or 344 min and an amplitude of 0.025 mag 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 SDSS J123813.73-033933.0, SDSS J204817.85-061044.8, GW Lib and FS Aur, but so far no working model for this behaviour is available.

Research paper thumbnail of Post-common-envelope binaries from SDSS - V. Four eclipsing white dwarf main-sequence binaries

Monthly Notices of the Royal Astronomical Society, 2009

We identify SDSS 011009.09+132616.1, SDSS 030308.35+005444.1, SDSS 143547.87+373338.5 and SDSS 15... more We identify SDSS 011009.09+132616.1, SDSS 030308.35+005444.1, SDSS 143547.87+373338.5 and SDSS 154846.00+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. SDSS 0110+1326, SDSS 1435+3733 and SDSS 1548+4057 contain DA white dwarfs, while SDSS 0303+0054 contains a cool DC white dwarf. Orbital periods and ephemerides have been established from multiseason photometry. SDSS 1435+3733, with P orb = 3 h has the shortest orbital period of all known eclipsing WDMS binaries. As for the other systems, SDSS 0110+1326 has P orb = 8 h, SDSS 0303+0054 has P orb = 3.2 h and SDSS 1548+4057 has P orb = 4.4 h. Time-resolved spectroscopic observations have been obtained and the Hα and Ca II λλ 8498.02,8542.09,8662.14 triplet emission lines, as well as the Na I λλ 8183.27,8194.81 absorption doublet were used to measure the radial velocities of the secondary stars in all four systems. A spectral decomposition/fitting technique was then employed to isolate the contribution of each of the components to the total spectrum, and 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 modelling code for close binary systems to fit the eclipse profiles and the ellipsoidal modulation/reflection effect in the light curves, to further constrain the masses and radii of the components in all systems. All three DA white dwarfs have masses of M WD ∼ 0.4 − 0.6 M ⊙ , in line with the expectations from close binary evolution. The DC white dwarf in SDSS 0303+0054 has a mass of M WD 0.85 M ⊙ , making it unusually massive for a post-common envelope system. The companion stars in all four systems are M-dwarfs of spectral type M4 and later. 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 < M WD >= 0.57 ± 0.16 M ⊙ , only slightly lower than the average mass of single white dwarfs. The majority of all eclipsing WDMS binaries contain low-mass (< 0.6 M ⊙ ) 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.

Research paper thumbnail of Cataclysmic variables from a ROSAT/2MASS selection -- I. Four new intermediate polars

Monthly Notices of the Royal Astronomical Society, 2005

We report the first results from a new search for cataclysmic variables (CVs) using a combined X-... more We report the first results from a new search for cataclysmic variables (CVs) using a combined X-ray (ROSAT) / infrared (2MASS) target selection that discriminates against background AGN. Identification spectra were obtained at the Isaac Newton Telescope for a total of 174 targets, leading to the discovery of 12 new CVs. Initially devised to find short-period low-mass-transfer CVs, this selection scheme has been very successful in identifying new intermediate polars. Photometric and spectroscopic follow-up observations identify four of the new CVs as intermediate polars: 1RXS J063631.9+353537 (P orb ≃ 201 min, P spin = 1008.3408 s or 930.5829 s), 1RXS J070407.9+262501 (P orb ≃ 250 min, P spin = 480.708 s), 1RXS J173021.5-055933 (P orb = 925.27 min, P spin = 128.0 s), and 1RXS J180340.0+401214 (P orb = 160.21 min, P spin = 1520.51 s). RX J1730, also a moderately bright hard X-ray source in the IN-TEGRAL/IBIS Galactic plane survey, resembles the enigmatic AE Aqr. It is likely that its white dwarf is not rotating at the spin equilibrium period, and the system may represent a short-lived phase in CV evolution.

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

Monthly Notices of the Royal Astronomical Society, 2007

Intermediate polars (IPs) are cataclysmic variables which contain magnetic white dwarfs with a ro... more 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 hr 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 µ WD ≈ 2 × 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.

Research paper thumbnail of Three eclipsing white dwarf plus main sequence binaries from SDSS

Three eclipsing white dwarf plus main sequence binaries from SDSS

Journal of Physics: Conference Series, 2009

We identify SDSS 0110+1326, SDSS 0303+0054 and SDSS 1435+3733 as three eclipsing white dwarf plus... more We identify SDSS 0110+1326, SDSS 0303+0054 and SDSS 1435+3733 as three eclipsing white dwarf plus main sequence binaries from the Sloan Digital Sky Survey, and report on their follow-up observations. Orbital periods for the three systems are established through multi-season photometry. Time-resolved spectroscopic observations lead to the determination of the radial velocities of the secondary stars. A decomposition technique of