Casassus, S., & Carcamo, M. (2022). Variable structure in the PDS 70 disc and uncertainties in radio-interferometric image restoration. Mon. Not. Roy. Astron. Soc., 513(4), 5790–5798.
Abstract: The compact mm-wavelength signal in the central cavity of the PDS 70 disc, revealed by deep ALMA observations, is aligned with unresolved H alpha emission, and is thought to stem from a circumplanetary disc (CPD) around PDS 70c. We revisit the available ALMA data on PDS 70c with alternative imaging strategies, and with special attention to uncertainties and to the impact of the so-called 'JvM correction', which is thought to improve the dynamic range of restored images. We also propose a procedure for the alignment and joint imaging of multi-epoch visibility data. We find that the JvM correction exaggerates the peak signal-to-noise of the data, by up to a factor of 10. In the case of PDS 70, we recover the detection of PDS 70c from the 2019 July data, but only at 8 sigma. However, its non-detection in 2017 Dec. suggests that PDS 70c is variable by at least 42 per cent +/- 13 per cent over a 1.75 yr time-span, so similar to models of the H alpha variability. We also pick up fine structure in the inner disc, such that its peak is offset by similar to 0 ''.04 from the disc centre. The inner disc is variable too, which we tentatively ascribe to Keplerian rotation as well as intrinsic morphological changes.
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Jones, M. I., Wittenmyer, R., Aguilera-Gomez, C., Soto, M. G., Torres, P., Trifonov, T., et al. (2021). Four Jovian planets around low-luminosity giant stars observed by the EXPRESS and PPPS. Astron. Astrophys., 646, A131.
Abstract: We report the discovery of planetary companions orbiting four low-luminosity giant stars with M-star between 1.04 and 1.39 M-circle dot. All four host stars have been independently observed by the EXoPlanets aRound Evolved StarS (EXPRESS) program and the Pan-Pacific Planet Search (PPPS). The companion signals were revealed by multi-epoch precision radial velocities obtained in nearly a decade. The planetary companions exhibit orbital periods between similar to 1.2 and 7.1 yr, minimum masses of m(p)sin i similar to 1.8-3.7 M-J, and eccentricities between 0.08 and 0.42. With these four new systems, we have detected planetary companions to 11 out of the 37 giant stars that are common targets in the EXPRESS and PPPS. After excluding four compact binaries from the common sample, we obtained a fraction of giant planets (m(p) greater than or similar to 1- 2 M-J) orbiting within 5 AU from their parent star of f = 33.3(-7.1)(+9.0)%. This fraction is slightly higher than but consistent at the 1 sigma level with previous results obtained by different radial velocity surveys. Finally, this value is substantially higher than the fraction predicted by planet formation models of gas giants around stars more massive than the Sun.
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Kaye, L., Vissapragada, S., Gunther, M. N., Aigrain, S., Mikal-Evans, T., Jensen, E. L. N., et al. (2022). Transit timings variations in the three-planet system: TOI-270. Mon. Not. Roy. Astron. Soc., 510(4), 5464–5485.
Abstract: We present ground- and space-based photometric observations of TOI-270 (L231-32), a system of three transiting planets consisting of one super-Earth and two sub-Neptunes discovered by TESS around a bright (K-mag = 8.25) M3V dwarf. The planets orbit near low-order mean-motion resonances (5:3 and 2:1) and are thus expected to exhibit large transit timing variations (TTVs). Following an extensive observing campaign using eight different observatories between 2018 and 2020, we now report a clear detection of TTVs for planets c and d, with amplitudes of similar to 10 min and a super-period of similar to 3 yr, as well as significantly refined estimates of the radii and mean orbital periods of all three planets. Dynamical modelling of the TTVs alone puts strong constraints on the mass ratio of planets c and d and on their eccentricities. When incorporating recently published constraints from radial velocity observations, we obtain masses of M-b = 1.48 +/- 0.18 M-circle plus, M-c = 6.20 +/- 0.31 M-circle plus, and M-d = 4.20 +/- 0.16 M-circle plus for planets b, c, and d, respectively. We also detect small but significant eccentricities for all three planets : e(b) = 0.0167 +/- 0.0084, e(c) = 0.0044 +/- 0.0006, and e(d) = 0.0066 +/- 0.0020. Our findings imply an Earth-like rocky composition for the inner planet, and Earth-like cores with an additional He/H2O atmosphere for the outer two. TOI-270 is now one of the best constrained systems of small transiting planets, and it remains an excellent target for atmospheric characterization.
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