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تسجيل مستخدم جديدA multi-wavelength look at the GJ 9827 system -- No evidence of extended atmospheres in GJ 9827 b and d from HST and CARMENES data
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GJ9827 is a bright star hosting a planetary system with three transiting planets. As a multi-planet system with planets that sprawl within the boundaries of the radius gap between terrestrial and gaseous planets, GJ9827 is an optimal target to study the evolution of the atmospheres of close-in planets with a common evolutionary history and their dependence from stellar irradiation. Here, we report on the Hubble Space Telescope (HST) and CARMENES transit observations of GJ9827 planets b and d. We performed a stellar and interstellar medium characterization from the ultraviolet HST spectra, obtaining fluxes for Ly-alpha and MgII of F(Ly-alpha) = (5.42+0.96-0.75) X 10^{-13} erg cm^{-2} s^{-1} and F(MgII) = (5.64 +- 0.24) X 10^{-14} erg cm^{-2} s^{-1}. We also investigated a possible absorption signature in Ly-alpha in the atmosphere of GJ9827b during a transit event from HST spectra, as well as H-alpha and HeI signature for the atmosphere of GJ9827b and d from CARMENES spectra. We found no evidence of an extended atmosphere in either of the planets. This result is also supported by our analytical estimations of mass-loss based on the measured radiation fields for all the three planets of this system, which led to a mass-loss rate of 0.4, 0.3, and 0.1 planetary masses per Gyr, for GJ9827b, c, and d respectively. These values indicate that the planets could have lost their volatiles quickly in their evolution and probably do not retain an atmosphere at the current stage.
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HD 106315 and GJ 9827 are two bright, nearby stars that host multiple super-Earths and sub-Neptunes discovered by K2 that are well suited for atmospheric characterization. We refined the planets ephemerides through Spitzer transits, enabling accurate
transit prediction required for future atmospheric characterization through transmission spectroscopy. Through a multi-year high-cadence observing campaign with Keck/HIRES and Magellan/PFS, we improved the planets mass measurements in anticipation of HST transmission spectroscopy. For GJ 9827, we modeled activity-induced radial velocity signals with a Gaussian process informed from the Calcium II H&K lines in order to more accurately model the effect of stellar noise on our data. We found planet masses of M$_b$=$4.87pm 0.37$ M$_oplus$, M$_c$=$1.92pm 0.49$ M$_oplus$, and M$_d$=$3.42pm 0.62$ M$_oplus$. For HD 106315, we found that such activity-radial velocity decorrelation was not effective due to the reduced presence of spots and speculate that this may extend to other hot stars as well (T$_{rm {eff}}>6200$ K). We found planet masses of M$_b$=$10.5pm 3.1$ M$_oplus$ and M$_c$=$12.0pm 3.8$ M$_oplus$. We investigated all of the planets compositions through comparing their masses and radii to a range of interior models. GJ 9827 b and GJ 9827 c are both consistent with an Earth-like rocky composition, GJ 9827 d and HD 106315 b both require additional volatiles and are consistent with moderate amounts of water or hydrogen/helium, and HD 106315 c is consistent with 10% hydrogen/helium surrounding an Earth-like rock and iron core.
We report on the discovery of three transiting planets around GJ~9827. The planets have radii of 1.75$_{-0.12}^{+0.11 }$, 1.36$_{- 0.09 }^{+ 0.09}$, and 2.10$_{- 0.15 }^{+ 0.15 }$~R$_{oplus}$, and periods of 1.20896, 3.6480, and 6.2014 days, respecti
vely. The detection was made in Campaign 12 observations as part of our K2 survey of nearby stars. GJ~9827 is a $V = 10.39$~mag K6V star at distance of 30.3 parsecs and the nearest star to be found hosting planets by Kepler and K2. The radial velocity follow-up, high resolution imaging, and detection of multiple transiting objects near commensurability drastically reduce the false positive probability. The orbital periods of GJ~9827~b, c and d planets are very close to the 1:3:5 mean motion resonance. Our preliminary analysis shows that GJ~9827 planets are excellent candidates for atmospheric observations. Besides, the planetary radii span both sides of the rocky and gaseous divide, hence the system will be an asset in expanding our understanding of the threshold.
We present a study on the spatially scanned spectroscopic observations of the transit of GJ 1132 b, a warm ($sim$500 K) Super-Earth (1.13 R$_oplus$) that was obtained with the G141 grism (1.125 - 1.650 $mu$m) of the Wide Field Camera 3 (WFC3) onboard
the Hubble Space Telescope. We used the publicly available Iraclis pipeline to extract the planetary transmission spectra from the five visits and produce a precise transmission spectrum. We analysed the spectrum using the TauREx3 atmospheric retrieval code with which we show that the measurements do not contain molecular signatures in the investigated wavelength range and are best-fit with a flat-line model. Our results suggest that the planet does not have a clear primordial, hydrogen-dominated atmosphere. Instead, GJ 1132 b could have a cloudy hydrogen-dominated envelope, a very enriched secondary atmosphere, be airless, or have a tenuous atmosphere that has not been detected. Due to the narrow wavelength coverage of WFC3, these scenarios cannot be distinguished yet but the James Webb Space Telescope may be capable of detecting atmospheric features, although several observations may be required to provide useful constraints.
Aims. GJ 9827 (K2-135) has recently been found to host a tightly packed system consisting of three transiting small planets whose orbital periods of 1.2, 3.6, and 6.2 days are near the 1:3:5 ratio. GJ 9827 hosts the nearest planetary system (d = $30.
32pm1.62$ pc) detected by Kepler and K2 . Its brightness (V = 10.35 mag) makes the star an ideal target for detailed studies of the properties of its planets. Results. We find that GJ 9827 b has a mass of $M_mathrm{b}=3.74^{+0.50}_{-0.48}$ $M_oplus$ and a radius of $R_mathrm{b}=1.62^{+0.17}_{-0.16}$ $R_oplus$, yielding a mean density of $rho_mathrm{b} = 4.81^{+1.97}_{-1.33}$ g cm$^{-3}$. GJ 9827 c has a mass of $M_mathrm{c}=1.47^{+0.59}_{-0.58}$ $M_oplus$, radius of $R_mathrm{c}=1.27^{+0.13}_{-0.13}$ $R_oplus$, and a mean density of $rho_mathrm{c}= 3.87^{+2.38}_{-1.71}$ g cm$^{-3}$. For GJ 9827 d we derive $M_mathrm{d}=2.38^{+0.71}_{-0.69}$ $M_oplus$, $R_mathrm{d}=2.09^{+0.22}_{-0.21}$ $R_oplus$, and $rho_mathrm{d}= 1.42^{+0.75}_{-0.52}$ g cm$^{-3}$. Conclusions. GJ 9827 is one of the few known transiting planetary systems for which the masses of all planets have been determined with a precision better than 30%. This system is particularly interesting because all three planets are close to the limit between super-Earths and mini-Neptunes. We also find that the planetary bulk compositions are compatible with a scenario where all three planets formed with similar core/atmosphere compositions, and we speculate that while GJ 9827 b and GJ 9827 c lost their atmospheric envelopes, GJ 9827 d maintained its atmosphere, owing to the much lower stellar irradiation. This makes GJ 9827 one of the very few systems where the dynamical evolution and the atmospheric escape can be studied in detail for all planets, helping us to understand how compact systems form and evolve.
Super-Earths belong to a class of planet not found in the Solar System, but which appear common in the Galaxy. Given that some super-Earths are rocky, while others retain substantial atmospheres, their study can provide clues as to the formation of b
oth rocky planets and gaseous planets, and - in particular - they can help to constrain the role of photo-evaporation in sculpting the exoplanet population. GJ 9827 is a system already known to host 3 super-Earths with orbital periods of 1.2, 3.6 and 6.2 days. Here we use new HARPS-N radial velocity measurements, together with previously published radial velocities, to better constrain the properties of the GJ 9827 planets. Our analysis cant place a strong constraint on the mass of GJ 9827 c, but does indicate that GJ 9827 b is rocky with a composition that is probably similar to that of the Earth, while GJ 9827 d almost certainly retains a volatile envelope. Therefore, GJ 9827 hosts planets on either side of the radius gap that appears to divide super-Earths into pre-dominantly rocky ones that have radii below $sim 1.5 R_oplus$, and ones that still retain a substantial atmosphere and/or volatile components, and have radii above $sim 2 R_oplus$. That the less heavily irradiated of the 3 planets still retains an atmosphere, may indicate that photoevaporation has played a key role in the evolution of the planets in this system.
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