One aim of modern astronomy is to detect temperate, Earth-like exoplanets that are well suited for atmospheric characterization. Recently, three Earth-sized planets were detected that transit (that ...is, pass in front of) a star with a mass just eight per cent that of the Sun, located 12 parsecs away. The transiting configuration of these planets, combined with the Jupiter-like size of their host star-named TRAPPIST-1-makes possible in-depth studies of their atmospheric properties with present-day and future astronomical facilities. Here we report the results of a photometric monitoring campaign of that star from the ground and space. Our observations reveal that at least seven planets with sizes and masses similar to those of Earth revolve around TRAPPIST-1. The six inner planets form a near-resonant chain, such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small integers. This architecture suggests that the planets formed farther from the star and migrated inwards. Moreover, the seven planets have equilibrium temperatures low enough to make possible the presence of liquid water on their surfaces.
Abstract Time-resolved SALT spectra of the short-period, dipping X-ray transient, Swift J1357.2−0933, during its 2017 outburst has revealed broad Balmer and He ii λ4686 absorption features, ...blueshifted by ∼600 km s−1. Remarkably these features are also variable on the ∼500 s dipping period, indicating their likely association with structure in the inner accretion disc. We interpret this as arising in a dense, hot (≳30 000 K) outflowing wind seen at very high inclination, and draw comparisons with other accretion disc corona sources. We argue against previous distance estimates of 1.5 kpc and favour a value ≳6 kpc, implying an X-ray luminosity LX ≳ 4 × 1036 erg s−1. Hence it is not a very faint X-ray transient. Our preliminary 1D Monte Carlo radiative transfer and photoionization calculations support this interpretation, as they imply a high intrinsic LX, a column density NH ≳ 1024 cm−2, and a low covering factor for the wind. Our study shows that Swift J1357.2−0933 is truly remarkable amongst the cohort of luminous, Galactic X-ray binaries, showing the first example of He ii λ4686 absorption, the first (and only) variable dip period and is possibly the first black hole ‘accretion disc corona’ candidate.
The last decade has seen a significant gain in both space and ground-based monitoring capabilities, producing vastly better coverage of BH X-ray binaries during their (rare) transient events. This ...interval included two of the three brightest X-ray outbursts ever observed, namely V404 Cyg in 2015, and MAXI J1820+070 in 2018, as well as the outburst of Swift J1357.2-0933, the first such system to show variable period optical dipping. There are now superb multi-wavelength archives of these outbursts, both photometric and spectroscopic, that show substantial outflows in the form of jets and disc winds, and X-ray spectroscopy/timing that reveals how the inner accretion disc evolves. The ground-based AAVSO optical monitoring of the MAXI J1820+070 event was the most extensive ever obtained, revealing periodic variations that evolved as it approached its state transition. These modulations were of an amplitude never seen before, and suggested the development of an irradiation-driven disc warp that persisted through the transition. All these results have demonstrated the power of extensive multi-wavelength photometric and spectroscopic monitoring on all time-scales.
Time-resolved SALT spectra of the short-period, dipping X-ray transient, Swift J1357.2-0933, during its 2017 outburst has revealed broad Balmer and HeII4686 absorption features, blue-shifted by ~600 ...km/s. Remarkably these features are also variable on the ~500s dipping period, indicating their likely association with structure in the inner accretion disc. We interpret this as arising in a dense, hot (>~30,000K) outflowing wind seen at very high inclination, and draw comparisons with other accretion disc corona sources. We argue against previous distance estimates of 1.5 kpc and favour a value >~6 kpc, implying an X-ray luminosity L_X>~4x10^{36} erg/s$. Hence it is not a very faint X-ray transient. Our preliminary 1D Monte-Carlo radiative transfer and photoionization calculations support this interpretation, as they imply a high intrinsic L_X, a column density N_H>~10^{24} cm^{-2} and a low covering factor for the wind. Our study shows that Swift J1357.2-0933 is truly remarkable amongst the cohort of luminous, galactic X-ray binaries, showing the first example of He II absorption, the first (and only) variable dip period and is possibly the first black hole 'accretion disc corona' candidate.
We present preliminary results from our investigation into using an 'inside-out' velocity space for creating a Doppler tomogram. The aim is to transpose the inverted appearance of the Cartesian ...velocity space used in normal Doppler tomography. In a comparison between normal and inside-out Doppler tomograms of cataclysmic variables, we show that the inside-out velocity space has the potential to produce new insights into the accretion dynamics in these systems.
We present the results of applying our inside-out velocity projection and flux modulation mapping techniques to the Doppler tomography of magnetic cataclysmic variables. The inside-out tomogram is ...constructed by directly projecting phase-resolved spectra onto the inside-out framework. In addition, our flux modulation mapping technique extracts any information related to the modulation of the line flux by utilising consecutive half-phase tomograms. We apply this to both the standard and the inside-out techniques. Our test cases, the polars HU Aqr and V834 Cen, and the intermediate polar PQ Gem, were chosen because of their known accretion characteristics, namely ballistic, magnetic and curtain dominated accretion, respectively. In all three cases the inside-out tomogram better exposes low-velocity emission details which are overly compacted in the standard tomogram. This is especially apparent for the mid-inclination V834 Cen where the almost blob-like blended lower velocity emission in the standard tomogram is more exposed in the inside-out tomogram, making it easier to distinguish between the ballistic and magnetically confined accretion flows that are evident in the trailed spectra. Similarly, the inside-out tomogram enhances high velocity emission details which are washed out in the standard tomogram. This is particularly effective in revealing the high velocity magnetic accretion flows in the polars HU Aqr and V834 Cen. The addition of our flux modulation technique gives a significant improvement in reproducing the trailed input spectra adding more confidence to the interpretation of the Doppler maps. Furthermore, amplitude and phase maps are constructed that further reveal amplitude and phasing characteristics of the emission components in the three test cases.
Doppler tomography has revolutionised the interpretation of phase-resolved spectra of interacting binaries. The standard technique extracts emission and kinematic information contained in such ...spectra and projects it onto a two-dimensional velocity coordinate frame. This thesis describes my investigation of constructing Doppler tomograms in 'inside-out' coordinates by reversing the velocity axis. The aim was to determine if the emission distribution in the inside-out tomogram is more intuitive to interpret than the standard tomogram, and if it reveals indiscernible or enhances less discernible details. The inside-out tomogram is constructed by projecting the spectra onto the inside-out coordinate frame with zero velocity transposed to the outer circumference and the maximum velocities to the centre of the tomogram. In addition, this thesis describes a new flux modulation mapping technique applied to the standard and inside-out Doppler tomography of magnetic cataclysmic variables. I developed this technique with the aim to obtain more information from their observed spectra and present it in a useful format. It extracts the flux modulation from consecutive half-phase tomograms and constructs maps of the amplitude and phasing characteristics of the modulation in these systems. My investigation, involving the spectra of non-magnetic and magnetic cataclysmic variables, shows that the inside-out projection redistributes the relative contrast levels in and amongst the emission components. The inside-out projection exposes low-velocity emission details which are overly compacted and enhances high-velocity emission details which are overly tenuous in the standard projection. In addition, the flux modulation mapping technique gives a significant improvement in reproducing the input spectra adding more confidence in the interpretation of the modulation maps. Notable results were obtained for the polars where the blob-like low-velocity emission in their standard tomograms is more exposed in their inside-out tomograms, making it easier to distinguish between the ballistic and magnetic accretion flows that are evident in their trailed spectra. Also, for all the polars investigated the high-velocity magnetic accretion flows not seen in their standard tomograms are revealed in their inside-out tomograms. This extra information is extremely valuable to form a more complete picture of the emission components, broadening our knowledge of the accretion dynamics in these systems.
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