Transmission spectroscopy has been successfully used from both the ground and in space to characterize the atmospheres of transiting exoplanets. This technique is challenging from the ground because ...ground-based spectrographs tend not to be designed to be photometrically stable, and effects such as variable slit losses cause significant systematic uncertainties. An alternative approach is to use simultaneous photometric observations in multiple wavebands to determine wavelength-dependent transit depth differences. We report an application of this technique to one of the hottest known exoplanets, WASP-12b, using the triple-beam camera ULTRACAM. We obtained simultaneous light curves in Sloan u
′, and two narrow-band filters centred on 4169 and 6010 Å, with full widths at half-maximum 52 and 118 Å, respectively. We fit these light curves with a photometric model and determine the planetary radius in the three different bands. Our data show no evidence for a difference in planetary radius over the wavelength range we study, and are consistent with an atmosphere that is dominated by Rayleigh scattering from a high-altitude haze, as well as more complicated atmosphere models which include the effects of molecules such as TiO. Our planetary radius measurements have an average precision of 2.6 per cent, compared to the ∼1.4-2.4 per cent radius differences predicted by the models over this wavelength range. We also find a consistent time of ingress and egress across our three wavebands, in contrast to the early ingress which has been reported for this system at shorter wavelengths.
ABSTRACT
The nova super-remnant (NSR) surrounding M 31N 2008-12a (12a), the annually erupting recurrent nova (RN), is the only known example of this phenomenon. As this structure has grown as a ...result of frequent eruptions from 12a, we might expect to see NSRs around other RNe; this would confirm the RN–NSR association and strengthen the connection between novae and type Ia supernovae (SN Ia) as NSRs centred on SN Ia provide a lasting, unequivocal signpost to the single degenerate progenitor type of that explosion. The only previous NSR simulation used identical eruptions from a static white dwarf (WD). In this Paper, we simulate the growth of NSRs alongside the natural growth/erosion of the central WD, within a range of environments, accretion rates, WD temperatures, and initial WD masses. The subsequent evolving eruptions create dynamic NSRs tens of parsecs in radius comprising a low-density cavity, bordered by a hot ejecta pile-up region, and surrounded by a cool high-density, thin, shell. Higher density environments restrict NSR size, as do higher accretion rates, whereas the WD temperature and initial mass have less impact. NSRs form around growing or eroding WDs, indicating that NSRs also exist around old novae with low-mass WDs. Observables such as X-ray and H α emission from the modelled NSRs are derived to aid searches for more examples; only NSRs around high accretion rate novae will currently be observable. The observed properties of the 12a NSR can be reproduced when considering both the dynamically grown NSR and photoionization by the nova system.
We present high-speed ULTRACAM photometry of the eclipsing post-common-envelope binaries DE CVn, GK Vir, NN Ser, QS Vir, RR Cae, RX J2130.6+4710, SDSS 0110+1326 and SDSS 0303+0054 and use these data ...to measure precise mid-eclipse times in order to detect any period variations. We detect a large (∼250 s) departure from linearity in the eclipse times of QS Vir which Applegate's mechanism fails to reproduce by an order of magnitude. The only mechanism able to drive this period change is a third body in a highly elliptical orbit. However, the planetary/sub-stellar companion previously suggested to exist in this system is ruled out by our data. Our eclipse times show that the period decrease detected in NN Ser is continuing, with magnetic braking or a third body the only mechanisms able to explain this change. The planetary/sub-stellar companion previously suggested to exist in NN Ser is also ruled out by our data. Our precise eclipse times also lead to improved ephemerides for DE CVn and GK Vir. The width of a primary eclipse is directly related to the size of the secondary star and variations in the size of this star could be an indication of Applegate's mechanism or Wilson (starspot) depressions which can cause jitter in the O−C curves. We measure the width of primary eclipses for the systems NN Ser and GK Vir over several years but find no definitive variations in the radii of the secondary stars. However, our data are precise enough (ΔRsec/Rsec < 10−5) to show the effects of Applegate's mechanism in the future. We find no evidence of Wilson depressions in either system. We also find tentative indications that flaring rates of the secondary stars depend on their mass rather than rotation rates.
We present the discovery, classification, and radio-to-X-ray follow-up observations of iPTF17cw, a broad-lined (BL) type Ic supernova (SN) discovered by the intermediate Palomar Transient Factory ...(iPTF). Although it is unrelated to the gravitational wave trigger, this SN was discovered as a happy by-product of the extensive observational campaign dedicated to the follow-up of Advanced LIGO event GW 170104. The spectroscopic properties and inferred peak bolometric luminosity of iPTF17cw are most similar to the gamma-ray-burst (GRB)-associated SN, SN 1998bw, while the shape of the r-band light curve is most similar to that of the relativistic SN, SN 2009bb. Karl G. Jansky Very Large Array (VLA) observations of the iPTF17cw field reveal a radio counterpart 10 times less luminous than SN 1998bw, and with a peak radio luminosity comparable to that of SN 2006aj/GRB 060218 and SN 2010bh/GRB 100316D. Our radio observations of iPTF17cw imply a relativistically expanding outflow. However, further late-time observations with the VLA in its most extended configuration are needed to confirm fading of the iPTF17cw radio counterpart at all frequencies. X-ray observations carried out with Chandra reveal the presence of an X-ray counterpart with a luminosity similar to that of SN 2010bh/GRB 100316D. Searching the Fermi catalog for possible γ-rays reveals that GRB 161228B is spatially and temporally compatible with iPTF17cw. The similarity to SN 1998bw and SN 2009bb, the radio and X-ray detections, and the potential association with GRB 161228B all point to iPTF17cw being a new candidate member of the rare sample of optically discovered engine-driven BL-Ic SNe associated with relativistic ejecta.
We have measured the transmission spectrum of the extremely inflated hot Jupiter WASP-52b using simultaneous photometric observations in Sloan Digital Sky Survey u', g' and a filter centred on the ...sodium doublet (Na I) with the ULTRACAM instrument mounted on the 4.2-m William Herschel Telescope. We find that Rayleigh scattering is not the dominant source of opacity within the planetary atmosphere and find a transmission spectrum more consistent with wavelength-independent opacity such as from clouds. We detect an in-transit anomaly that we attribute to the presence of stellar activity and find that this feature can be more simply modelled as a bright region on the stellar surface akin to solar faculae rather than spots. A spot model requires a significantly larger planet/star radius ratio than that found in previous studies. Our results highlight the precision that can be achieved by ground-based photometry with errors in the scaled planetary radii of less than one atmospheric scale height, comparable to Hubble Space Telescope observations.
We present ground-based high-precision observations of the transit of WASP-17b using the multiband photometer ULTRACAM on ESO's New Technology Telescope (NTT) in the context of performing ...transmission spectrophotometry of this highly inflated exoplanet. Our choice of filters (SDSS u
′, g
′ and r
′ bands) is designed to probe for the presence of opacity sources in the upper atmosphere. We find evidence for a wavelength dependence in the planet radius in the form of enhanced absorption in the SDSS r
′ band, consistent with a previously detected broad sodium feature. We present a new independent measurement of the planetary radius at R
pl = 1.97 ± 0.06R
J
, which confirms this planet as the most inflated exoplanet known to date. Our measurements are most consistent with an atmospheric profile devoid of enhanced TiO opacity, previously predicted to be present for this planet.
We present high-speed ULTRACAM and SOFI photometry and X-shooter spectroscopy of the recently discovered 94-min orbital period eclipsing white dwarf/main-sequence binary SDSS J085746.18+034255.3 (CSS ...03170) and use these observations to measure the system parameters. We detect a shallow secondary eclipse and hence are able to determine an orbital inclination of i = 85
5 ± 0
2. The white dwarf has a mass of 0.51 ± 0.05 M⊙ and a radius of 0.0247 ± 0.0008 R⊙. With a temperature of 35 300 ± 400 K the white dwarf is highly overinflated if it has a carbon-oxygen core; however, if it has a helium core then its mass and radius are consistent with evolutionary models. Therefore, the white dwarf in SDSS J085746.18+034255.3 is most likely a helium core white dwarf with a mass close to the upper limit expected from evolution. The main-sequence star is an M8 dwarf with a mass of 0.09 ± 0.01 M⊙ and a radius of 0.110 ± 0.004 R⊙ placing it close to the hydrogen burning limit. The system emerged from a common envelope ∼20 million years ago and will reach a semidetached configuration in ∼400 million years, becoming a cataclysmic variable with a period of 66 min, below the period minimum.
Abstract
We present time-resolved optical spectroscopy of the dwarf nova CSS100603:112253−111037. Its optical spectrum is rich in helium, with broad, double-peaked emission lines produced in an ...accretion disc. We measure a line flux ratio He i λ5876/Hα = 1.49 ± 0.04, a much higher ratio than is typically observed in dwarf novae. The orbital period, as derived from the radial velocity of the line wings, is 65.233 ± 0.015 min. In combination with the previously measured superhump period, this implies an extreme mass ratio of M
2/M
1 = 0.017 ± 0.004. The Hα and He i λ 6678 emission lines additionally have a narrow central spike, as is often seen in the spectra of AM CVn-type stars. Comparing their properties with cataclysmic variables (CVs), AM CVn systems and hydrogen binaries below the CV period minimum, we argue that CSS100603:112253−111037 is the first compelling example of an AM CVn system forming via the evolved CV channel.
With the addition of this system, evolved CVs now account for 7 per cent of all known semidetached white dwarf binaries with P
orb < 76 min. Two recently discovered binaries may further increase this figure. Although the selection bias of this sample is not yet well defined, these systems support the evolved CV model as a possible formation channel for ultracompact accreting binaries. The orbital periods of the three ultracompact hydrogen accreting binaries overlap with those of the long-period AM CVn stars, but there are currently no known systems in the period range of 67-76 min.
With orbital periods of the order of tens of minutes or less, the AM Canum Venaticorum stars are ultracompact, hydrogen-deficient binaries with the shortest periods of any binary subclass, and are ...expected to be among the strongest gravitational wave sources in the sky. To date, the only known eclipsing source of this type is the P= 28 min binary SDSS J0926+3624. We present multiband, high time resolution light curves of this system, collected with William Herschel Telescope (WHT)/ULTRACAM in 2006 and 2009. We supplement these data with additional observations made with Liverpool Telescope/Rapid Imager to Search for Exoplanets (LT/RISE), XMM-Newton and the Catalina Real-Time Transient Survey. From light curve models we determine the mass ratio to be q=M
2/M
1= 0.041 ± 0.002 and the inclination to be
. We calculate the mass of the primary white dwarf to be 0.85 ± 0.04 M⊙ and the donor to be 0.035 ± 0.003 M⊙, implying a partially degenerate state for this component. We observe superhump variations that are characteristic of an elliptical, precessing accretion disc. Our determination of the superhump period excess is in agreement with the established relationship between this parameter and the mass ratio, and is the most precise calibration of this relationship at low q. We also observe a quasi-periodic oscillation in the 2006 data, and we examine the outbursting behaviour of the system over a 4.5 year period.
We present high-speed, three-colour photometry of the eclipsing cataclysmic variables CTCV J1300−3052, CTCV J2354−4700 and SDSS J115207.00+404947.8. These systems have orbital periods of 128.07, ...94.39 and 97.52 min, respectively, placing all three systems below the observed 'period gap' for cataclysmic variables. For each system we determine the system parameters by fitting a parametrized model to the observed eclipse light curve by χ2 minimization.
We also present an updated analysis of all other eclipsing systems previously analysed by our group. The updated analysis utilizes Markov chain Monte Carlo techniques which enable us to arrive confidently at the best fits for each system with more robust determinations of our errors. A new bright-spot model is also adopted, that allows better modelling of bright-spot dominated systems. In addition, we correct a bug in the old code which resulted in the white dwarf radius being underestimated, and consequently both the white dwarf and donor mass being overestimated. New donor masses are generally between 1σ and 2σ of those originally published, with the exception of SDSS 1502 (−2.9σ, ΔM
r=−0.012 M⊙) and DV UMa (+6.1σ, ΔM
r=+0.039 M⊙). We note that the donor mass of SDSS 1501 has been revised upwards by 0.024 M⊙ (+1.9σ). This system was previously identified as having evolved past the minimum orbital period for cataclysmic variables, but the new mass determination suggests otherwise. Our new analysis confirms that SDSS 1035 and SDSS 1433 have evolved past the period minimum for cataclysmic variables, corroborating our earlier studies.
We find that the radii of donor stars are oversized when compared to theoretical models, by approximately 10 per cent. We show that this can be explained by invoking either enhanced angular momentum loss, or by taking into account the effects of star spots. We are unable to favour one cause over the other, as we lack enough precise mass determinations for systems with orbital periods between 100 and 130 min, where evolutionary tracks begin to diverge significantly.
We also find a strong tendency towards high white dwarf masses within our sample, and no evidence for any He-core white dwarfs. The dominance of high-mass white dwarfs implies that erosion of the white dwarf during the nova outburst must be negligible, or that not all of the mass accreted is ejected during nova cycles, resulting in the white dwarf growing in mass.
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