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811. XO-4b 3yr observations with DEMONEX
ID:
ivo://CDS.VizieR/J/ApJ/820/87
Title:
XO-4b 3yr observations with DEMONEX
Short Name:
J/ApJ/820/87
Date:
21 Oct 2021
Publisher:
CDS
Description:
The DEdicated MONitor of EXotransits (DEMONEX) was a 20-inch robotic and automated telescope to monitor bright stars hosting transiting exoplanets to discover new planets and improve constraints on the properties of known transiting planetary systems. We present results for the misaligned hot Jupiter XO-4b containing seven new transits from the DEMONEX telescope, including three full and four partial transits. We combine these data with archival light curves and archival radial velocity measurements to derive the host star mass M_{star}_=1.293_-0.029_^+0.030^M_{sun}_ and radius R_{star}_=1.554_-0.030_^+0.042^R_{sun}_, the planet mass M_P_=1.615_-0.099_^+0.10^M_J_ and radius R_P_=1.317_-0.029_^+0.040^R_J_, and a refined ephemeris of P=4.1250687+/-0.0000024days and T_0_=2454758.18978+/-0.00024BJD_TDB_. We include archival Rossiter-McLaughlin measurements of XO-4 to infer the stellar spin-planetary orbit alignment of {lambda}=-40.0_-7.5_^+8.8^deg. We test the effects of including various detrend parameters, theoretical and empirical mass-radius relations, and Rossiter-McLaughlin models. We infer that detrending against CCD position and time or airmass can improve data quality but can have significant effects on the inferred values of many parameters--most significantly R_p_/R_{star}_ and the observed central transit times T_C_. In the case of R_p_/R_{star}_ we find that the systematic uncertainty due to detrending can be three times that of the quoted statistical uncertainties. The choice of mass-radius relation has little effect on our inferred values of the system parameters. The choice of Rossiter-McLaughlin models can have significant effects on the inferred values of vsinI_{star}_ and the stellar spin-planet orbit angle {lambda}.
812. XO-2N and XO-2S spectra
ID:
ivo://CDS.VizieR/J/A+A/583/A135
Title:
XO-2N and XO-2S spectra
Short Name:
J/A+A/583/A135
Date:
21 Oct 2021
Publisher:
CDS
Description:
Binary stars hosting exoplanets are a unique laboratory where chemical tagging can be performed to measure with high accuracy the elemental abundances of both stellar components, with the aim to investigate the formation of planets and their subsequent evolution. Here, we present a high-precision differential abundance analysis of the XO-2 wide stellar binary based on high resolution HARPS-N@TNG spectra. Both components are very similar K-dwarfs and host planets. Since they formed presumably within the same molecular cloud, we expect they should possess the same initial elemental abundances. We investigate if the presence of planets can cause some chemical imprints in the stellar atmospheric abundances. We measure abundances of 25 elements for both stars with a range of condensation temperature T_C_=40-1741K, achieving typical precisions of ~0.07dex. The North component shows abundances in all elements higher by +0.067+/-0.032dex on average, with a mean difference of +0.078dex for elements with T_C_>800K. The significance of the XO-2N abundance difference relative to XO-2S is at the 2{sigma} level for almost all elements. We discuss the possibility that this result could be interpreted as the signature of the ingestion of material by XO-2N or depletion in XO-2S due to locking of heavy elements by the planetary companions. We estimate a mass of several tens of M_{earth}_ in heavy elements. The difference in abundances between XO-2N and XO-2S shows a positive correlation with the condensation temperatures of the elements, with a slope of (4.7+/-0.9)x10^-5^dex/K, which could mean that both components have not formed terrestrial planets, but that first experienced the accretion of rocky core interior to the subsequent giant planets.
813. X-ray-age relation and exoplanet evaporation
ID:
ivo://CDS.VizieR/J/MNRAS/422/2024
Title:
X-ray-age relation and exoplanet evaporation
Short Name:
J/MNRAS/422/2024
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the relationship between coronal X-ray emission and stellar age for late-type stars, and the variation of this relationship with spectral type. We select 717 stars from 13 open clusters and find that the ratio of X-ray to bolometric luminosity during the saturated phase of coronal emission decreases from 10^-3.1^ for late K-dwarfs to 10^-4.3^ for early F-type stars (across the range 0.29<(B-V)_0_<1.41). Our determined saturation timescales vary between 10^7.6^ and 10^8.3^ years, though with no clear trend across the whole FGK range. We apply our X-ray emission - age relations to the investigation of the evaporation history of 121 known transiting exoplanets using a simple energy -limited model of evaporation and taking into consideration Roche lobe effects and different heating/evaporation efficiencies. We confirm that a linear cut-off of the planet distribution in the M^2^/R^3^ versus a^-2^ plane is an expected result of population modification by evaporation and that the known transiting exoplanets display such a cut-off. We find that for an evaporation efficiency of 25 percent we expect around 1 in 5 of the known transiting exoplanets to have lost >10 percent of their mass since formation. In addition we provide estimates of the minimum formation mass for which a planet could be expected to survive for 4Gyrs for a range of stellar and planetary parameters. We emphasise the importance of the earliest periods of a planet's life for its evaporation history with 75 percent expect to occur within the first Gyr. This raises the possibility of using evaporation histories to distinguish different migration mechanisms. For planets with spin-orbit angles available from measurements of the Rossiter-McLaughlin effect no difference is found between the distributions of planets with misaligned orbits and those with aligned orbits. This suggests that dynamical effects accounting for misalignment occur early in the life of a planetary system, although additional data is required to test this.
814. YZ Ceti radial velocity curve
ID:
ivo://CDS.VizieR/J/A+A/605/L11
Title:
YZ Ceti radial velocity curve
Short Name:
J/A+A/605/L11
Date:
21 Oct 2021
Publisher:
CDS
Description:
Exoplanet surveys have shown that systems with multiple low-mass planets on compact orbits are common. Except for a few cases, however, the masses of these planets are generally unknown. At the very end of the main sequence, host stars have the lowest mass and hence offer the largest reflect motion for a given planet. In this context, we monitored the low-mass (0.13M_{sun}_) M dwarf YZ Cet (GJ 54.1, HIP 5643) intensively and obtained radial velocities and stellar-activity indicators derived from spectroscopy and photometry, respectively. We find strong evidence that it is orbited by at least three planets in compact orbits (Porb=1.97, 3.06, 4.66 days), with the inner two near a 2:3 mean-motion resonance. The minimum masses are comparable to the mass of Earth (Msini=0.75+/-0.13, 0.98+/-0.14, and 1.14+/-0.17M_{earth}_), and they are also the lowest masses measured by radial velocity so far. We note the possibility for a fourth planet with an even lower mass of Msini=0.472+/-0.096 Mearth at Porb=1.04-days. An n-body dynamical model is used to place further constraints on the system parameters. At 3.6 parsecs, YZ Cet is the nearest multi-planet system detected to date.

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