Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLimits on the Spin-Orbit Angle and Atmospheric Escape for the 22 Myr-old Planet AU Mic b
336
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We obtained spectra of the pre-main sequence star AU Microscopii during a transit of its Neptune-sized planet to investigate its orbit and atmosphere. We used the high-dispersion near-infrared spectrograph IRD on the Subaru telescope to detect the Doppler shadow from the planet and constrain the projected stellar obliquity. Modeling of the observed planetary Doppler shadow suggests a spin-orbit alignment of the system ($lambda=-4.7_{-6.4}^{+6.8}$ degrees), but additional observations are needed to confirm this finding. We use both the IRD data and spectra obtained with NIRSPEC on Keck-II to search for absorption in the 1083 nm line of metastable triplet He I by the planets atmosphere and place an upper limit for the equivalent width of 3.7 mAA at 99 $%$ confidence. With this limit and a Parker wind model we constrain the escape rate from the atmosphere to $<0.15-0.45, M_{oplus}$ Gyr$^{-1}$, comparable to the rates predicted by an XUV energy-limited escape calculation and hydrodynamic models, but refinement of the planet mass is needed for rigorous tests.
rate research
Read More
Here, we study the dichotomy of the escaping atmosphere of the newly discovered close-in exoplanet AU Mic b. On one hand, the high EUV stellar flux is expected to cause a strong atmospheric escape in AU Mic b. On the other hand, the wind of this young star is believed to be very strong, which could reduce or even inhibit the planets atmospheric escape. AU Mic is thought to have a wind mass-loss rate that is up to $1000$ times larger than the solar wind mass-loss rate ($dot{M}_odot$). To investigate this dichotomy, we perform 3D hydrodynamics simulations of the stellar wind--planetary atmosphere interactions in the AU Mic system and predict the synthetic Ly-$alpha$ transits of AU Mic b. We systematically vary the stellar wind mass-loss rate from a `no wind scenario to up to a stellar wind with a mass-loss rate of $1000~dot{M}_odot$. We find that, as the stellar wind becomes stronger, the planetary evaporation rate decreases from $6.5times 10^{10}$ g/s to half this value. With a stronger stellar wind, the atmosphere is forced to occupy a smaller volume, affecting transit signatures. Our predicted Ly-$alpha$ absorption drops from $sim 20%$, in the case of `no wind to barely any Ly-$alpha$ absorption in the extreme stellar wind scenario. Future Ly-$alpha$ transits could therefore place constraints not only on the evaporation rate of AU Mic b, but also on the mass-loss rate of its host star.
We report measurements of the sky-projected spin-orbit angle for AU,Mic,b, a Neptune-size planet orbiting a very young ($sim20$,Myr) nearby pre-main sequence M dwarf star which also hosts a bright, edge-on, debris disk. The planet was recently discovered from preliminary analysis of radial velocity observations and confirmed to be transiting its host star from photometric data from the NASAs textit{TESS} mission. We obtained radial velocity measurements of AU,Mic over the course of two partially observable transits and one full transit of planet b from high-resolution spectroscopic observations made with the {textsc{Minerva}}-Australis telescope array. Only a marginal detection of the Rossiter--McLaughlin effect signal was obtained from the radial velocities, in part due to AU Mic being an extremely active star and the lack of full transit coverage plus sufficient out-of-transit baseline. As such, a precise determination of the obliquity for AU,Mic,b is not possible in this study and we find a sky-projected spin-orbit angle of $lambda = 47{^{+26}_{-54}}^{circ}$. This result is consistent with both the planets orbit being aligned or highly misaligned with the spin-axis of its host star. Our measurement independently agrees with, but is far less precise than observations carried out on other instruments around the same time that measure a low obliquity orbit for the planet. AU,Mic is the youngest exoplanetary system for which the projected spin-orbit angle has been measured, making it a key data point in the study of the formation and migration of exoplanets -- particularly given that the system is also host to a bright debris disk.
HIP 67522 b is a 17 Myr old, close-in ($P_{orb} = 6.96$ d), Jupiter-sized ($R = 10,R_{oplus}$) transiting planet orbiting a Sun like star in the Sco-Cen OB association. We present our measurement of the systems projected orbital obliquity via two spectroscopic transit observations using the CHIRON spectroscopic facility. We present a global model that accounts for large surface brightness features typical of such young stars during spectroscopic transit observations. With a value of $|lambda| = 5.1^{+2.5,circ}_{-3.7}$ degree, we demonstrate that this well-aligned system cannot be the result of a high eccentricity driven migration history. By being the youngest planet with a known obliquity, HIP 67522 b holds a special place in contributing to our understanding of giant planet formation and evolution. Our analysis shows the feasibility of such measurements for young and very active stars.
AU Mic is a young planetary system with a resolved debris disc showing signs of planet formation and two transiting warm Neptunes near mean-motion resonances. Here we analyse three transits of AU Mic b observed with the CHaracterising ExOPlanet Satellite (CHEOPS), supplemented with sector 1 and 27 Transiting Exoplanet Survey Satellite (TESS) photometry, and the All-Sky Automated Survey (ASAS) from the ground. The refined orbital period of AU Mic b is 8.462995 pm 0.000003 d, whereas the stellar rotational period is P_{rot}=4.8367 pm 0.0006 d. The two periods indicate a 7:4 spin--orbit commensurability at a precision of 0.1%. Therefore, all transits are observed in front of one of the four possible stellar central longitudes. This is strongly supported by the observation that the same complex star-spot pattern is seen in the second and third CHEOPS visits that were separated by four orbits (and seven stellar rotations). Using a bootstrap analysis we find that flares and star spots reduce the accuracy of transit parameters by up to 10% in the planet-to-star radius ratio and the accuracy on transit time by 3-4 minutes. Nevertheless, occulted stellar spot features independently confirm the presence of transit timing variations (TTVs) with an amplitude of at least 4 minutes. We find that the outer companion, AU Mic c may cause the observed TTVs.
DS Tuc Ab is a Neptune-sized planet that orbits around a member of the 45 Myr old Tucana-Horologium moving group. Here, we report the measurement of the sky-projected angle between the stellar spin axis and the planets orbital axis, based on the observation of the Rossiter-McLaughlin effect during three separate planetary transits. The orbit appears to be well aligned with the equator of the host star, with a projected obliquity of lambda = 2.5 +1.0/-0.9 deg. In addition to the distortions in the stellar absorption lines due to the transiting planet, we observed variations that we attribute to large starspots, with angular sizes of tens of degrees. The technique we have developed for simultaneous modeling of starspots and the planet-induced distortions may be useful in other observations of planets around active stars.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
