分类： 天文学 >> 天文学 提交时间： 2023-02-19
A. J. Maas
E. Ilin
M. Oshagh
E. Pallé
H. Parviainen
K. Molaverdikhani
A. Quirrenbach
E. Esparza-Borges
F. Murgas
V. J. S. Béjar
N. Narita
A. Fukui
C. -L. Lin
M. Mori
P. Klagyivik
摘要： Although high energetic radiation from flares is a potential threat to exoplanet atmospheres and may lead to surface sterilization, it might also provide the extra energy for low-mass stars needed to trigger and sustain prebiotic chemistry. We investigate two flares on TRAPPIST-1, an ultra-cool dwarf star that hosts seven exoplanets of which three lie within its habitable zone. The flares are detected in all four passbands of the MuSCAT2 allowing a determination of their temperatures and bolometric energies. We analyzed the light curves of the MuSCAT1 and MuSCAT2 instruments obtained between 2016 and 2021 in $g,r,i,z_\mathrm{s}$-filters. We conducted an automated flare search and visually confirmed possible flare events. We studied the temperature evolution, the global temperature, and the peak temperature of both flares. For the first time we infer effective black body temperatures of flares that occurred on TRAPPIST-1. The black body temperatures for the two TRAPPIST-1 flares derived from the SED are consistent with $T_\mathrm{SED} = 7940_{-390}^{+430}$K and $T_\mathrm{SED} = 6030_{-270}^{+300}$K. The flare black body temperatures at the peak are also calculated from the peak SED yielding $T_\mathrm{SEDp} = 13620_{-1220}^{1520}$K and $T_\mathrm{SEDp} = 8290_{-550}^{+660}$K. We show that for the ultra-cool M-dwarf TRAPPIST-1 the flare black body temperatures associated with the total continuum emission are lower and not consistent with the usually adopted assumption of 9000-10000 K. This could imply different and faster cooling mechanisms. Further multi-color observations are needed to investigate whether or not our observations are a general characteristic of ultra-cool M-dwarfs. This would have significant implications for the habitability of exoplanets around these stars because the UV surface flux is likely to be overestimated by the models with higher flare temperatures.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
D. Specht
R. Poleski
M. T. Penny
E. Kerins
I. McDonald
Chung-Uk Lee
A. Udalski
I. A. Bond
Y. Shvartzvald
Weicheng Zang
R. A. Street
D. W. Hogg
B. S. Gaudi
T. Barclay
G. Barentsen
S. B. Howell
F. Mullally
C. B. Henderson
S. T. Bryson
D. A. Caldwell
摘要： We present K2-2016-BLG-0005Lb, a densely sampled, planetary binary caustic-crossing microlensing event found from a blind search of data gathered from Campaign 9 of the Kepler K2 mission (K2C9). K2-2016-BLG-0005Lb is the first bound microlensing exoplanet discovered from space-based data. The event has caustic entry and exit points that are resolved in the K2C9 data, enabling the lens--source relative proper motion to be measured. We have fitted a binary microlens model to the Kepler data, and to simultaneous observations from multiple ground-based surveys. Whilst the ground-based data only sparsely sample the binary caustic, they provide a clear detection of parallax that allows us to break completely the microlensing mass--position--velocity degeneracy and measure the planet's mass directly. We find a host mass of $0.58\pm0.04 ~{\rm M}_\odot$ and a planetary mass of $1.1\pm0.1 ~{\rm M_J}$. The system lies at a distance of $5.2\pm0.2~$kpc from Earth towards the Galactic bulge, more than twice the distance of the previous most distant planet found by Kepler. The sky-projected separation of the planet from its host is found to be $4.2\pm0.3~$au which, for circular orbits, deprojects to a host separation $a = 4.4^{+1.9}_{-0.4}~$au and orbital period $P = 13^{+9}_{-2}~$yr. This makes K2-2016-BLG-0005Lb a close Jupiter analogue orbiting a low-mass host star. According to current planet formation models, this system is very close to the host mass threshold below which Jupiters are not expected to form. Upcoming space-based exoplanet microlensing surveys by NASA's Nancy Grace Roman Space Telescope and, possibly, ESA's Euclid mission, will provide demanding tests of current planet formation models.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
F. Murgas
G. Nowak
T. Masseron
H. Parviainen
R. Luque
E. Pallé
Judith Korth
I. Carleo
Sz. Csizmadia
E. Esparza-Borges
Ahlam Alqasim
William D. Cochran
Fei Dai
Hans J. Deeg
D. Gandolfi
Elisa Goffo
Petr Kabáth
K. W. F. Lam
John Livingston
Alexandra Muresan
摘要： We used TESS light curves and HARPS-N spectrograph radial velocity measurements to establish the physical properties of the transiting exoplanet candidate found around the star HD 20329 (TOI-4524). We performed a joint fit of the light curves and radial velocity time series to measure the mass, radius, and orbital parameters of the candidate. We confirm and characterize HD 20329b, an ultra-short-period (USP) planet transiting a solar-type star. The host star (HD 20329, $V = 8.74$ mag, $J = 7.5$ mag) is characterized by its G5 spectral type with $\mathrm{M}_\star= 0.90 \pm 0.05$ M$_\odot$, $\mathrm{R}_\star = 1.13 \pm 0.02$ R$_\odot$, and $\mathrm{T}_{\mathrm{eff}} = 5596 \pm 50$ K; it is located at a distance $d= 63.68 \pm 0.29$ pc. By jointly fitting the available TESS transit light curves and follow-up radial velocity measurements, we find an orbital period of $0.9261 \pm (0.5\times 10^{-4})$ days, a planetary radius of $1.72 \pm 0.07$ $\mathrm{R}_\oplus$, and a mass of $7.42 \pm 1.09$ $\mathrm{M}_\oplus$, implying a mean density of $\rho_\mathrm{p} = 8.06 \pm 1.53$ g cm$^{-3}$. HD 20329b joins the $\sim$30 currently known USP planets with radius and Doppler mass measurements.
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