Tonny Vanmunster

A TRANSITING PLANET OF A SUN-LIKE STAR

A planet transits an 11th magnitude, G1 V star in the constellation Corona Borealis. We designate the planet XO-1b and the star XO-1, also known as GSC 02041-01657. XO-1 lacks a trigonometric distance; we estimate it to be 200 ± 20 pc. Of the 10 stars currently known to host extrasolar transiting planets, the star XO-1 is the most similar to the Sun in its physical characteristics: its radius is 1.0 ± 0.08 R☉, its mass is 1.0 ± 0.03 M☉, its V sin i < 3 km s-1, and its metallicity [Fe/H] is 0.015 ± 0.04. The orbital period of the planet XO-1b is 3.941534 ± 0.000027 days, one of the longer ones known. The planetary mass is 0.90 ± 0.07MJ, which is marginally larger than that of other transiting planets with periods between 3 and 4 days. Both the planetary radius and the inclination are functions of the spectroscopically determined stellar radius. If the stellar radius is 1.0 ± 0.08 R☉, then the planetary radius is 1.30 ± 0.11RJ and the inclination of the orbit is 877 ± 12. We have demonstrated a productive international collaboration between professional and amateur astronomers that was important to distinguishing this planet from many other similar candidates.

XO-3b: A Massive Planet in an Eccentric Orbit Transiting an F5 V Star

We report the discovery of a massive planet (Mpsin i = 13.02 ± 0.64 MJ; total mass = 13.25 ± 0.64 MJ), large (1.95 ± 0.16 RJ) planet in a transiting, eccentric orbit (e = 0.260 ± 0.017) around a 10th magnitude F5 V star in the constellation Camelopardalis. We designate the planet XO-3b and the star XO-3, also known as GSC 03727–01064. The orbital period of XO-3b is 3.1915426 ± 0.00014 days. XO-3 lacks a trigonometric parallax; we estimate its distance to be 260 ± 23 pc. The radius of XO-3 is 2.13 ± 0.21 R☉, its mass is 1.41 ± 0.08 M☉, its vsin i = 18.54 ± 0.17 km s−1, and its metallicity is [ Fe/H ] = − 0.177 ± 0.027. This system is unusual for a number of reasons. XO-3b is one of the most massive planets discovered around any star for which the orbital period is less than 10 days. The mass is near the deuterium-burning limit of 13 MJ, which is a proposed boundary between planets and brown dwarfs. Although Burrows et al. propose that formation in a disk or formation in the interstellar medium in a manner similar to stars is a more logical way to differentiate planets and brown dwarfs, our current observations are not adequate to address this distinction. XO-3b is also unusual in that its eccentricity is large given its relatively short orbital period. Both the planetary radius and the inclination are functions of the spectroscopically determined stellar radius. Analysis of the transit light curve of XO-3b suggests that the spectroscopically derived parameters may be overestimated. Though relatively noisy, the light curves favor a smaller radius in order to better match the steepness of the ingress and egress. The light curve fits imply a planetary radius of 1.25 ± 0.15 RJ, which would correspond to a mass of 12.03 ± 0.46 MJ. A precise trigonometric parallax measurement or a very accurate light curve is needed to resolve the uncertainty in the planetary mass and radius.

XO-2b: Transiting Hot Jupiter in a Metal-rich Common Proper Motion Binary

We report on a V = 11.2 early K dwarf, XO-2 (GSC 03413-00005), that hosts a Rp = 0.98±0.010.03 RJ, Mp = 0.57 ± 0.06 MJ transiting extrasolar planet, XO-2b, with an orbital period of 2.615857 ± 0.000005 days. XO-2 has high metallicity, [Fe/H ] = 0.45 ± 0.02, high proper motion, μtot = 157 mas yr−1, and a common proper motion stellar companion with 31 separation. The two stars are nearly identical twins, with very similar spectra and apparent magnitudes. Due to the high metallicity, these early K dwarf stars have a mass and radius close to solar, M = 0.98 ± 0.02 M☉ and R = 0.97±0.010.02 R☉. The high proper motion of XO-2 results from an eccentric orbit (Galactic pericenter, Rper < 4 kpc) well confined to the Galactic disk (Zmax ~ 100 pc). In addition, the phase-space position of XO-2 is near the Hercules dynamical stream, which points to an origin of XO-2 in the metal-rich, inner thin disk and subsequent dynamical scattering into the solar neighborhood. We describe an efficient Markov chain Monte Carlo algorithm for calculating the Bayesian posterior probability of the system parameters from a transit light curve.

THE 2001 SUPEROUTBURST OF WZ SAGITTAE

ABSTRACT We report the results of a worldwide campaign to observe WZ Sagittae during its 2001 superoutburst. After a 23 yr slumber at documentclass{aastex} usepackage{amsbsy} usepackage{amsfonts} usepackage{amssymb} usepackage{bm} usepackage{mathrsfs} usepackage{pifont} usepackage{stmaryrd} usepackage{textcomp} usepackage{portland,xspace} usepackage{amsmath,amsxtra} usepackage[OT2,OT1]{fontenc} newcommandcyr{ renewcommandrmdefault{wncyr} renewcommandsfdefault{wncyss} renewcommandencodingdefault{OT2} normalfont selectfont} DeclareTextFontCommand{textcyr}{cyr} pagestyle{empty} DeclareMathSizes{10}{9}{7}{6} begin{document} landscape

A COMPARISON OF OBSERVATIONALLY DETERMINED RADII WITH THEORETICAL RADIUS PREDICTIONS FOR SHORT-PERIOD TRANSITING EXTRASOLAR PLANETS

V=15.5

Superhumps in Cataclysmic Binaries. XV. EG Cancri, King of the Echo Outbursts

end{document} , the star rose within 2 days to a peak brightness of 8.2, and showed a main eruption lasting 25 days. The return to quiescence was punctuated by 12 small eruptions, of ∼1 mag amplitude and 2 day recurrence time; these “echo outbursts” are of uncertain origin, but somewhat resemble the normal outbursts of dwarf novae. After 52 ...

SUPERHUMPS IN CATACLYSMIC BINARIES. XXIV. TWENTY MORE DWARF NOVAE

Two extrasolar planets, HD 209458b and TrES-1, are currently known to transit bright parent stars for which physical properties can be accurately determined. The two transiting planets have very similar masses and periods and hence invite detailed comparisons between their observed and theoretically predicted properties. In this paper, we carry out these comparisons. We first report photometric and spectroscopic follow-up observations of TrES-1, and we use these observations to obtain improved estimates for the planetary radius, Rpl = (1.08 ± 0.05)RJ, and the planetary mass, Mpl = (0.729 ± 0.036)MJ. We also confirm that the inclination estimate of the planetary orbit as i = 882. These values agree with those obtained by Alonso et al. in their discovery paper, but the uncertainty in the planet radius has been improved as a result of both high-cadence photometry of two full transits and from independent radius determinations for the V = 11.8 K0 V parent star. We derive estimates for the TrES-1 stellar parameters of R*/R☉ = 0.83 ± 0.03 (by combining independent estimates from stellar models, high-resolution spectra, and transit light curve fitting) M*/M☉ = 0.87 ± 0.05 (via fitting to evolutionary tracks), Teff = 5214 ± 23 K, [Me/H] = 0.001 ± 0.04, rotational velocity V sin(i) = 1.08 ± 0.3 km s-1, log g = 4.52 ± 0.05 dex, log L*/L☉ = -0.32, d = 157 ± 6 pc, and an age of τ = 4 ± 2 Gyr. These estimates of the physical properties of the system allow us to compute evolutionary models for the planet that result in a predicted radius of Rpl = 1.05RJ for a model that contains an incompressible 20 M⊕ core and a radius Rpl = 1.09RJ for a model without a core. We use our grids of planetary evolution models to show that, with standard assumptions, our code also obtains good agreement with the observed radii of the other recently discovered transiting planets, including OGLE-TR-56b, OGLE-TR-111b, OGLE-TR-113b, and OGLE-TR-132b. We report an updated radius for HD 209458b of Rpl = (1.32 ± 0.05)RJ, based on a new radius estimate of R* = 1.12 R☉ for the parent star. Our theoretical predictions for the radius of HD 209458b are Rpl = 1.05RJ and 1.09RJ for models with and without cores. HD 209458b is therefore the only transiting planet whose radius does not agree well with our theoretical models. We argue that tidal heating stemming from dynamical interaction with a second planet is currently the most viable explanation for its inflated size.

Two Galactic Supersoft X-Ray Binaries: V Sagittae and T Pyxidis

We report photometry and spectroscopy of the dwarf nova EG Cancri in its 1996/1997 episode of eruptions. The main eruption was clearly a superoutburst featuring common superhumps with a period of 0.06036(2) days, establishing the star as a new member of the SU UMa class of dwarf novae. At the end of the main eruption, the superhumps were replaced by another wave of slightly longer period (0.06045 days), which endured for at least another 90 days. The properties of the latter wave suggest identification as a late superhump. The recurrence time for superoutbursts is long, probably in the range 7-20 yr. After the 15 day superoutburst, the star displayed six remarkable surges in light, with an average interval of 7 days; these echo outbursts strongly resemble ordinary dwarf nova eruptions. This suggests that a high accretion rate persisted in the disk for ~40 days after the main superoutburst. By a year after outburst, the star faded to V = 18.7, with most of the continuum light from a white dwarf of T ~ 15,000 K. We estimate a distance of 320 pc and a Mv = +11.5 for accretion light. The extreme faintness, the rarity of eruptions, the enormous duration of superhumps, and the quiescent spectrum together establish membership in the WZ Sge subclass, the most sluggish of dwarf novae. Spectroscopy at quiescence and a transient wave in early outburst establish an orbital period of 0.05997(9) days. This suggests a secondary star with M ~ 0.02 M⊙, yet R ~ 0.08 R⊙. A binary can reach such a state after the secondary is forced to lose mass on a timescale shorter than its Kelvin-Helmholtz timescale.

First detection of the growing humps at the rapidly rising stage of dwarf novae AL Com and WZ Sge

We report precise measures of the orbital and superhump period in 20 more dwarf novae. For 10 stars, we report new and confirmed spectroscopic periods—signifying the orbital period —as well as the P o

Superhumps in Cataclysmic Binaries. XVII. AM Canum Venaticorum

We discuss the nature of V Sagittae and T Pyxidis, two enigmatic blue variable stars commonly classed among the cataclysmic variables. These stars have bolometric luminosities in the range 36 (1-50) # 10 ergs s 1 , far exceeding that of any accretion-powered cataclysmic variable. They also show extremely blue colors ( and after dereddening) and orbital light curves that are quite similar and yet are B V 0.3 U B 1.3 not seen in any normal cataclysmic variable. But in all these respects, as well as in the rich and highly excited emission-line spectrum, the stars provide a good match for the newly discovered class of supersoft X-ray binaries, probably powered by quasi-steady nuclear burning of accreted gas on a white dwarf. Both stars show photometric waves at the orbital period. V Sge also shows a deep minimum, a true eclipse of the accretion disk arising from fairly high binary inclination. T Pyx is nearly face-on (probably ), which results in i ∼ 10 -20 narrow lines and a low amplitude for the orbital signal. T Pyx shows a very stable photometric wave at P days, but interpretation of this is hampered by another transient signal at 0.1098 days. This might be 0.076227 construed as evidence for a magnetic white dwarf.