We perform a study of stellar flares for the 24,809 stars observed with 2 minute cadence during the first two months of the TESS mission. Flares may erode exoplanets' atmospheres and impact their ...habitability, but might also trigger the genesis of life around small stars. TESS provides a new sample of bright dwarf stars in our galactic neighborhood, collecting data for thousands of M-dwarfs that might host habitable exoplanets. Here, we use an automated search for flares accompanied by visual inspection. Then, our public allesfitter code robustly selects the appropriate model for potentially complex flares via Bayesian evidence. We identify 1228 flaring stars, 673 of which are M-dwarfs. Among 8695 flares in total, the largest superflare increased the stellar brightness by a factor of 16.1. Bolometric flare energies range from 10^31.0 to 10^36.9 erg, with a median of 10^33.1 erg. Furthermore, we study the flare rate and energy as a function of stellar type and rotation period. We solidify past findings that fast rotating M-dwarfs are the most likely to flare, and that their flare amplitude is independent of the rotation period. Finally, we link our results to criteria for prebiotic chemistry, atmospheric loss through coronal mass ejections, and ozone sterilization. Four of our flaring M dwarfs host exoplanet candidates alerted on by TESS, for which we discuss how these effects can impact life. With upcoming TESS data releases, our flare analysis can be expanded to almost all bright small stars, aiding in defining criteria for exoplanet habitability.
Venusian phosphine: a 'wow!' signal in chemistry? Bains, William; Petkowski, Janusz J.; Seager, Sara ...
Phosphorus, Sulfur, and Silicon and the Related Elements: ICPC-23: 23rd International Conference on Phosphorus Chemistry; Guest Editors:Professor Jozef Drabowicz; Professor Piotr Kiełbasiński and Professor Tomasz Cierpiał,
6/22/2022, Letnik:
197, Številka:
5-6
Report
The potential detection of ppb levels phosphine (PH
3
) in the clouds of Venus through millimeter-wavelength astronomical observations is extremely surprising as PH
3
is an unexpected component of an ...oxidized environment of Venus. A thorough analysis of potential sources suggests that no known process in the consensus model of Venus' atmosphere or geology could produce PH
3
at anywhere near the observed abundance. Therefore, if the presence of PH
3
in Venus' atmosphere is confirmed, it is highly likely to be the result of a process not previously considered plausible for Venusian conditions. The source of atmospheric PH
3
could be unknown geo- or photochemistry, which would imply that the consensus on Venus' chemistry is significantly incomplete. An even more extreme possibility is that strictly aerial microbial biosphere produces PH
3
. This paper summarizes the Venusian PH
3
discovery and the scientific debate that arose since the original candidate detection one year ago.
We report the discovery of TOI 694 b and TIC 220568520 b, two low-mass stellar companions in eccentric orbits around metal-rich Sun-like stars, first detected by the Transiting Exoplanet Survey ...Satellite (TESS). TOI 694 b has an orbital period of 48.05131\(\pm\)0.00019 days and eccentricity of 0.51946\(\pm\)0.00081, and we derive a mass of 89.0\(\pm\)5.3 \(M_J\) (0.0849\(\pm\)0.0051 \(M_\odot\)) and radius of 1.111\(\pm\)0.017 \(R_J\) (0.1142\(\pm\)0.0017 \(R_\odot\)). TIC 220568520 b has an orbital period of 18.55769\(\pm\)0.00039 days and eccentricity of 0.0964\(\pm\)0.0032, and we derive a mass of 107.2\(\pm\)5.2 \(M_J\) (0.1023\(\pm\)0.0050 \(M_\odot\)) and radius of 1.248\(\pm\)0.018 \(R_J\) (0.1282\(\pm\)0.0019 \(R_\odot\)). Both binary companions lie close to and above the Hydrogen burning mass threshold that separates brown dwarfs and the lowest mass stars, with TOI 694 b being 2-\(\sigma\) above the canonical mass threshold of 0.075 \(M_\odot\). The relatively long periods of the systems mean that the magnetic fields of the low-mass companions are not expected to inhibit convection and inflate the radius, which according to one leading theory is common in similar objects residing in short-period tidally-synchronized binary systems. Indeed we do not find radius inflation for these two objects when compared to theoretical isochrones. These two new objects add to the short but growing list of low-mass stars with well-measured masses and radii, and highlight the potential of the TESS mission for detecting such rare objects orbiting bright stars.
We present 2,241 exoplanet candidates identified with data from the Transiting Exoplanet Survey Satellite (TESS) during its two-year prime mission. We list these candidates in the TESS Objects of ...Interest (TOI) Catalog, which includes both new planet candidates found by TESS and previously-known planets recovered by TESS observations. We describe the process used to identify TOIs and investigate the characteristics of the new planet candidates, and discuss some notable TESS planet discoveries. The TOI Catalog includes an unprecedented number of small planet candidates around nearby bright stars, which are well-suited for detailed follow-up observations. The TESS data products for the Prime Mission (Sectors 1-26), including the TOI Catalog, light curves, full-frame images, and target pixel files, are publicly available on the Mikulski Archive for Space Telescopes.
WD 1145+017 is a unique white dwarf system that has a heavily polluted atmosphere, an infrared excess from a dust disk, numerous broad absorption lines from circumstellar gas, and changing transit ...features, likely from fragments of an actively disintegrating asteroid. Here, we present results from a large photometric and spectroscopic campaign with Hubble, Keck , VLT, Spitzer, and many other smaller telescopes from 2015 to 2018. Somewhat surprisingly, but consistent with previous observations in the u' band, the UV transit depths are always shallower than those in the optical. We develop a model that can quantitatively explain the observed "bluing" and the main findings are: I. the transiting objects, circumstellar gas, and white dwarf are all aligned along our line of sight; II. the transiting object is blocking a larger fraction of the circumstellar gas than of the white dwarf itself. Because most circumstellar lines are concentrated in the UV, the UV flux appears to be less blocked compared to the optical during a transit, leading to a shallower UV transit. This scenario is further supported by the strong anti-correlation between optical transit depth and circumstellar line strength. We have yet to detect any wavelength-dependent transits caused by the transiting material around WD 1145+017.
The interiors of giant planets remain poorly understood. Even for the planets in the Solar System, difficulties in observation lead to large uncertainties in the properties of planetary cores. ...Exoplanets that have undergone rare evolutionary processes provide a route to understanding planetary interiors. Planets found in and near the typically barren hot-Neptune 'desert' (a region in mass-radius space that contains few planets) have proved to be particularly valuable in this regard. These planets include HD149026b, which is thought to have an unusually massive core, and recent discoveries such as LTT9779b and NGTS-4b, on which photoevaporation has removed a substantial part of their outer atmospheres. Here we report observations of the planet TOI-849b, which has a radius smaller than Neptune's but an anomalously large mass of \(39.1^{+2.7}_{-2.6}\) Earth masses and a density of \(5.2^{+0.7}_{-0.8}\) grams per cubic centimetre, similar to Earth's. Interior structure models suggest that any gaseous envelope of pure hydrogen and helium consists of no more than \(3.9^{+0.8}_{-0.9}\) per cent of the total planetary mass. The planet could have been a gas giant before undergoing extreme mass loss via thermal self-disruption or giant planet collisions, or it could have avoided substantial gas accretion, perhaps through gap opening or late formation. Although photoevaporation rates cannot account for the mass loss required to reduce a Jupiter-like gas giant, they can remove a small (a few Earth masses) hydrogen and helium envelope on timescales of several billion years, implying that any remaining atmosphere on TOI-849b is likely to be enriched by water or other volatiles from the planetary interior. We conclude that TOI-849b is the remnant core of a giant planet.
We report the discovery of TOI-172 b from the Transiting Exoplanet Survey Satellite (TESS) mission, a massive hot Jupiter transiting a slightly evolved G-star with a 9.48-day orbital period. This is ...the first planet to be confirmed from analysis of only the TESS full frame images, because the host star was not chosen as a two minute cadence target. From a global analysis of the TESS photometry and follow-up observations carried out by the TESS Follow-up Observing Program Working Group, TOI-172 (TIC 29857954) is a slightly evolved star with an effective temperature of \(T_{\rm eff}\) =\(5645\pm50\) K, a mass of \(M_{\star}\) = \(1.128^{+0.065}_{-0.061}\) \(M_{\odot}\), radius of \(R_{\star}\) = \(1.777^{+0.047}_{-0.044}\) \(R_{\odot}\), a surface gravity of \(\log\) \(g_{\star}\) = \(3.993^{+0.027}_{-0.028}\), and an age of \(7.4^{+1.6}_{-1.5}\) Gyr. Its planetary companion (TOI-172 b) has a radius of \(R_{\rm P}\) = \(0.965^{+0.032}_{-0.029}\) \(R_{\rm J}\), a mass of \(M_{\rm P}\) = \(5.42^{+0.22}_{-0.20}\) \(M_{\rm J}\), and is on an eccentric orbit (\(e = 0.3806^{+0.0093}_{-0.0090}\)). TOI-172 b is one of the few known massive giant planets on a highly eccentric short-period orbit. Future study of the atmosphere of this planet and its system architecture offer opportunities to understand the formation and evolution of similar systems.
The future of exoplanet science is bright, as TESS once again demonstrates with the discovery of its longest-period confirmed planet to date. We hereby present HD 21749b (TOI 186.01), a sub-Neptune ...in a 36-day orbit around a bright (V = 8.1) nearby (16 pc) K4.5 dwarf. TESS measures HD21749b to be 2.61\(^{+0.17}_{-0.16}\) \(R_{\oplus}\), and combined archival and follow-up precision radial velocity data put the mass of the planet at \(22.7^{+2.2}_{-1.9}\) \(M_{\oplus}\). HD 21749b contributes to the TESS Level 1 Science Requirement of providing 50 transiting planets smaller than 4 \(R_{\oplus}\) with measured masses. Furthermore, we report the discovery of HD 21749c (TOI 186.02), the first Earth-sized (\(R_p = 0.892^{+0.064}_{-0.058} R_{\oplus}\)) planet from TESS. The HD21749 system is a prime target for comparative studies of planetary composition and architecture in multi-planet systems.
We produce light curves for all ~34,000 targets observed with K2 in Campaign 17 (C17), identifying 34 planet candidates, 184 eclipsing binaries, and 222 other periodic variables. The location of the ...C17 field means follow-up can begin immediately now that the campaign has concluded and interesting targets have been identified. The C17 field has a large overlap with C6, so this latest campaign also offers a rare opportunity to study a large number of targets already observed in a previous K2 campaign. The timing of the C17 data release, shortly before science operations begin with the Transiting Exoplanet Survey Satellite (TESS), also lets us exercise some of the tools and methods developed for identification and dissemination of planet candidates from TESS. We find excellent agreement between these results and those identified using only K2-based tools. Among our planet candidates are several planet candidates with sizes < 4 R_E and orbiting stars with KepMag < 10 (indicating good RV targets of the sort TESS hopes to find) and a Jupiter-sized single-transit event around a star already hosting a 6 d planet candidate.
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