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Aungwerojwit A. | Aungwerojwit A | Aungwerojwit Amornrat

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A Volume Limited Sample of Cataclysmic Variables from $\mathit{Gaia}$ DR2: Space Density and Population Properties

Pala A. F., , Breedt E., Knigge C., Hermes J. J., Fusillo N. P. Gentile, Hollands M. A., Naylor T., Pelisoli I., Schreiber M. R.
30 Jul 2019 astro-ph.SR arxiv.org/abs/1907.13152

We present the first volume-limited sample of cataclysmic variables (CVs), selected using the accurate parallaxes provided by the second data release (DR2) of the ESA $\mathit{Gaia}$ space mission. The sample is composed of 42 CVs within $150\,$pc, including two new systems discovered using the $\mathit{Gaia}$ data, and is $(77 \pm 10)\,$per cent complete. We use this sample to study the intrinsic properties of the Galactic CV population. In particular, the CV space density we derive, $\rho=(4.8^{+0.6}{-0.8}) \times10^{-6}\,\mathrm{pc}^{-3}$, is lower than predicted by most binary population synthesis studies. We also find a low fraction of period bounce CVs, seven per cent, and an average white dwarf mass of $\langle M\mathrm{WD} \rangle = (0.83 \pm 0.17)\,\mathrm{M}_\odot$. Both findings confirm previous results, ruling out the presence of observational biases affecting these measurements, as has been suggested in the past. The observed fraction of period bounce CVs falls well below theoretical predictions, by at least a factor of five, and remains one of the open problems in the current understanding of CV evolution. Conversely, the average white dwarf mass supports the presence of additional mechanisms of angular momentum loss that have been accounted for in the latest evolutionary models. The fraction of magnetic CVs in the $150\,$pc sample is remarkably high at $36\,$per cent. This is in striking contrast with the absence of magnetic white dwarfs in the detached population of CV progenitors, and underlines that the evolution of magnetic systems has to be included in the next generation of population models.

Evidence for mass accretion driven by spiral shocks onto the white dwarf in SDSS J123813.73-033933.0

Pala A. F., , Marsh T. R., Breedt E., Hermes J. J., Landstreet J. D., Schreiber M. R., Townsley D. M., Wang L., Aungwerojwit A.
14 Nov 2018 astro-ph.SR arxiv.org/abs/1811.05981

We present high-time-resolution photometry and phase-resolved spectroscopy of the short-period ($P_\mathrm{orb} = 80.52\,\mathrm{min}$) cataclysmic variable SDSS J123813.73-033933.0, observed with the $\mathit{Hubble}$ $\mathit{Space}$ $\mathit{Telescope}$ $\mathit{(HST)}$, the $\mathit{Kepler/K2}$ mission and the Very Large Telescope (VLT). We also report observations of the first detected super-outburst. SDSS J1238-0339 shows two types of variability: quasi-regular brightenings recurring every $\simeq 8.5$ h during which the system increases in brightness by $\simeq 0.5$mag, and a double hump quasi-sinusoidal modulation at the orbital period. The detailed $\mathit{K2}$ light curve reveals that the amplitude of the double-humps increases during the brightenings and that their phase undergoes a $\simeq 90^{\circ}$ phase shift with respect to the quiescent intervals. The $\mathit{HST}$ data unambiguously demonstrate that these phenomena both arise from the heating and cooling of two relatively large regions on the white dwarf. We suggest that the double-hump modulation is related to spiral shocks in the accretion disc resulting in an enhanced accretion rate heating two localised regions on the white dwarf, with the structure of the shocks fixed in the binary frame explaining the period of the double humps. The physical origin of the 8.5 h brightenings is less clear. However, the correlation between the observed variations of the amplitude and phase of the double-humps with the occurrence of the brightenings is supportive of an origin in thermal instabilities in the accretion disc.

New Photometric Investigation of the Low-Mass-Ratio Contact Binary Star V1853 Orionis

He Jia-Jia, Qian Sheng-Bang, Soonthornthum B., Aungwerojwit A., Liu Niang-Ping, Sarotsakulchai T.
04 Nov 2018 astro-ph.SR arxiv.org/abs/1811.01485

Four-color charge-coupled device (CCD) light curves in $B$, $V$, $Rc$ and $Ic$ bands of the total-eclipsing binary system, V1853 Ori, are presented. By comparing our light curves with those published by previous investigators, it is detected that the O'Connell effect on the light curves is disappeared. By analyzing those multi-color light curves with the Wilson-Devinney code (W-D code), it is discovered that V1853 Ori is an A-type intermediate-contact binary with a degree of contact factor of $f=33.3\%(3.7\%)$ and a mass ratio of $q=0.1896(0.0013)$. Combining our 10 new determined times of light minima together with the others published in the literature, the period changes of the system is investigated. We found that the general trend of the observed-calculated $(O-C)$ curve shows a downward parabolic variation that corresponds to a long-term decrease in the orbital period with a rate of $dP/dt=-1.96(0.46)\times{10^{-7}}$ d yr$^{-1}$. The long-term period decrease could be explained by mass transfer from the more-massive component to the less-massive one. By combining our photometric solutions with the Gaia DR 2 data, absolute parameters were derived as $M_{1}$ = 1.20 M${\odot}$, $M{2}$ = 0.23 M${\odot}$, $R{1}$ = 1.36 R${\odot}$, and $R{2}$ = 0.66 R$_{\odot}$. The long-term period decrease and the intermediate-contact configuration suggest that V1853 Ori will evolve into a high fill-out overcontact binary.

The physical properties of AM CVn stars: new insights from Gaia DR2

Ramsay G., Green M. J., Marsh T. R., Kupfer T., Breedt E., Korol V., Groot P. J., Knigge C., Nelemans G., Steeghs D.
15 Oct 2018 astro-ph.SR arxiv.org/abs/1810.06548

AM CVn binaries are hydrogen deficient compact binaries with an orbital period in the 5-65 min range and are predicted to be strong sources of persistent gravitational wave radiation. Using Gaia Data Release 2, we present the parallaxes and proper motions of 41 out of the 56 known systems. Compared to the parallax determined using the HST Fine Guidance Sensor we find that the archetype star, AM CVn, is significantly closer than previously thought. This resolves the high luminosity and mass accretion rate which models had difficulty in explaining. Using Pan-STARRS1 data we determine the absolute magnitude of the AM CVn stars. There is some evidence that donor stars have a higher mass and radius than expected for white dwarfs or that the donors are not white dwarfs. Using the distances to the known AM CVn stars we find strong evidence that a large population of AM CVn stars have still to be discovered. As this value sets the background to the gravitational wave signal of LISA, this is of wide interest. We determine the mass transfer rate for 15 AM CVn stars and find that the majority have a rate significantly greater than expected from standard models. This is further evidence that the donor star has a greater size than expected.

A radio pulsing white dwarf binary star

Marsh T. R., , , Hambsch F. -J., Bernhard K., Lloyd C., Breedt E., Stanway E. R., Steeghs D. T., Parsons S. G.
27 Jul 2016 astro-ph.SR astro-ph.HE arxiv.org/abs/1607.08265

White dwarfs are compact stars, similar in size to Earth but ~200,000 times more massive. Isolated white dwarfs emit most of their power from ultraviolet to near-infrared wavelengths, but when in close orbits with less dense stars, white dwarfs can strip material from their companions, and the resulting mass transfer can generate atomic line and X-ray emission, as well as near- and mid-infrared radiation if the white dwarf is magnetic. However, even in binaries, white dwarfs are rarely detected at far-infrared or radio frequencies. Here we report the discovery of a white dwarf / cool star binary that emits from X-ray to radio wavelengths. The star, AR Scorpii (henceforth AR Sco), was classified in the early 1970s as a delta-Scuti star, a common variety of periodic variable star. Our observations reveal instead a 3.56 hr period close binary, pulsing in brightness on a period of 1.97 min. The pulses are so intense that AR Sco's optical flux can increase by a factor of four within 30 s, and they are detectable at radio frequencies, the first such detection for any white dwarf system. They reflect the spin of a magnetic white dwarf which we find to be slowing down on a 10^7 yr timescale. The spin-down power is an order of magnitude larger than that seen in electromagnetic radiation, which, together with an absence of obvious signs of accretion, suggests that AR Sco is primarily spin-powered. Although the pulsations are driven by the white dwarf's spin, they originate in large part from the cool star. AR Sco's broad-band spectrum is characteristic of synchrotron radiation, requiring relativistic electrons. These must either originate from near the white dwarf or be generated in situ at the M star through direct interaction with the white dwarf's magnetosphere.

High-speed photometry of the disintegrating planetesimals at WD1145+017: evidence for rapid dynamical evolution

Gaensicke B. T., Aungwerojwit A., Marsh T. R., Dhillon V. S., Sahman D. I., Veras Dimitri, Farihi J., Chote P., Ashley R., Arjyotha S.
30 Dec 2015 astro-ph.EP astro-ph.SR arxiv.org/abs/1512.09150

We obtained high-speed photometry of the disintegrating planetesimals orbiting the white dwarf WD1145+017, spanning a period of four weeks. The light curves show a dramatic evolution of the system since the first observations obtained about seven months ago. Multiple transit events are detected in every light curve, which have varying durations(~3-12min) and depths (~10-60%). The time-averaged extinction is ~11%, much higher than at the time of the Kepler observations. The shortest-duration transits require that the occulting cloud of debris has a few times the size of the white dwarf, longer events are often resolved into the superposition of several individual transits. The transits evolve on time scales of days, both in shape and in depth, with most of them gradually appearing and disappearing over the course of the observing campaign. Several transits can be tracked across multiple nights, all of them recur on periods of ~4.49h, indicating multiple planetary debris fragments on nearly identical orbits. Identifying the specific origin of these bodies within this planetary system, and the evolution leading to their current orbits remains a challenging problem.

The Second Data Release of the INT Photometric H-Alpha Survey of the Northern Galactic Plane (IPHAS DR2)

Barentsen Geert, Farnhill H. J., Drew J. E., , Greimel R., Irwin M. J., Miszalski B., Ruhland C., Groot P., Mampaso A.
18 Jun 2014 astro-ph.SR astro-ph.IM arxiv.org/abs/1406.4862

The INT/WFC Photometric H-Alpha Survey of the Northern Galactic Plane (IPHAS) is a 1800 square degrees imaging survey covering Galactic latitudes |b| < 5 deg and longitudes l = 30 to 215 deg in the r, i and H-alpha filters using the Wide Field Camera (WFC) on the 2.5-metre Isaac Newton Telescope (INT) in La Palma. We present the first quality-controlled and globally-calibrated source catalogue derived from the survey, providing single-epoch photometry for 219 million unique sources across 92% of the footprint. The observations were carried out between 2003 and 2012 at a median seeing of 1.1 arcsec (sampled at 0.33 arcsec/pixel) and to a mean 5\sigma-depth of 21.2 (r), 20.0 (i) and 20.3 (H-alpha) in the Vega magnitude system. We explain the data reduction and quality control procedures, describe and test the global re-calibration, and detail the construction of the new catalogue. We show that the new calibration is accurate to 0.03 mag (rms) and recommend a series of quality criteria to select the most reliable data from the catalogue. Finally, we demonstrate the ability of the catalogue's unique (r-Halpha, r-i) diagram to (1) characterise stellar populations and extinction regimes towards different Galactic sightlines and (2) select H-alpha emission-line objects. IPHAS is the first survey to offer comprehensive CCD photometry of point sources across the Galactic Plane at visible wavelengths, providing the much-needed counterpart to recent infrared surveys.

IPHAS J062746.41+014811.3: a deeply eclipsing intermediate polar

Aungwerojwit A., , Wheatley P. J., Pyrzas S., Staels B., Krajci T.,
04 Sep 2012 astro-ph.SR arxiv.org/abs/1209.0719

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.

Post common envelope binaries from SDSS. XII: The orbital period distribution

, , Schreiber M. R., Rebassa-Mansergas A., Schwope A. D., Southworth J., Aungwerojwit A., Bothe M., Davis P. J., Kolb U.
29 Sep 2011 astro-ph.SR arxiv.org/abs/1109.6662

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 hold the potential to test theoretical models and constrain their parameters. The Sloan Digital Sky Survey (SDSS) has provided a large and homogeneously selected sample of WDMS binaries, which we are characterising in terms of orbital and stellar parameters. We have obtained radial velocity information for 385 WDMS binaries from follow-up spectroscopy, and for an additional 861 systems from the SDSS sub-spectra. 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. 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 follows approximately a normal distribution in log(Porb), 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. The large and homogeneous sample of SDSS WDMS binaries provides the means to test fundamental predictions of binary population models, and hence to observationally constrain the evolution of all close compact binaries.

Multi-site Observations of Pulsation in the Accreting White Dwarf SDSS J161033.64-010223.3 (V386 Ser)

Mukadam Anjum S., Townsley D. M., Gaensicke B. T., Szkody P., Marsh T. R., Robinson E. L., Bildsten L., Aungwerojwit A., Schreiber M. R., Southworth J.
29 Mar 2010 astro-ph.SR arxiv.org/abs/1003.5703

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 609s 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. Using time-series spectra acquired in May 2009, we determine the orbital period of SDSS J161033.64-010223.3 to be 83.8 +/- 2.9 min. Three of the observed photometric frequencies from our May 2007 campaign appear to be linear combinations of the 609s pulsation mode with the first harmonic of the orbital period at 41.5min. This is the first discovery of a linear combination between nonradial pulsation and orbital motion for a variable white dwarf.