19 research outputs found
Evidence for SpinâOrbit Alignment in the TRAPPIST-1 System
In an effort to measure the RossiterâMcLaughlin effect for the TRAPPIST-1 system, we performed high-resolution spectroscopy during transits of planets e, f, and b. The spectra were obtained with the InfraRed Doppler spectrograph on the Subaru 8.2 m telescope, and were supplemented with simultaneous photometry obtained with a 1 m telescope of the Las Cumbres Observatory Global Telescope. By analyzing the anomalous radial velocities, we found the projected stellar obliquity to be λ = 1 ± 28° under the assumption that the three planets have coplanar orbits, although we caution that the radial-velocity data show correlated noise of unknown origin. We also sought evidence for the expected deformations of the stellar absorption lines, and thereby detected the "Doppler shadow" of planet b with a false-alarm probability of 1.7%. The joint analysis of the observed residual cross-correlation map including the three transits gave λ = 19_(-15)^(+13)°. These results indicate that the the TRAPPIST-1 star is not strongly misaligned with the common orbital plane of the planets, although further observations are encouraged to verify this conclusion
Planet(esimal)s Around Stars with TESS (PAST) III: A Search for Triplet He I in the Atmospheres of Two 200 Myr-old Planets
We report a search for excess absorption in the 1083.2 nm line of ortho
(triplet) helium during transits of TOI-1807b and TOI-2076b, 1.25 and
2.5R planets on 0.55- and 10.4-day orbits around nearby
200~Myr-old K dwarf stars. We limit the equivalent width of any
transit-associated absorption to 4 and 8 mA, respectively. We limit the
escape of solar-composition atmospheres from TOI-1807b and TOI-2076b to
1 and 0.1M Gyr, respectively,
depending on wind temperature. The absence of a H/He signature for TOI-1807b is
consistent with a measurement of mass indicating a rocky body and the
prediction by a hydrodynamic model that any H-dominated atmosphere would be
unstable and already have been lost. Differential spectra obtained during the
transit of TOI-2076b contain a He I-like feature, but this closely resembles
the stellar line and extends beyond the transit interval. Until additional
transits are observed, we suspect this to be the result of variation in the
stellar He I line produced by rotation of active regions and/or flaring on the
young, active host star. Non-detection of escape could mean that TOI-2076b is
more massive than expected, the star is less EUV-luminous, the models
overestimate escape, or the planet has a H/He-poor atmosphere that is primarily
molecules such as HO. Photochemical models of planetary winds predict a
semi-major axis at which triplet He I observations are most sensitive to mass
loss: TOI-2076b orbits near this optimum. Future surveys could use a distance
criterion to increase the yield of detections.Comment: Accepted to MNRA
Limits on the Spin-Orbit Angle and Atmospheric Escape for the 22 Myr-old Planet AU Mic b
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 ( 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 planet's atmosphere and
place an upper limit for the equivalent width of 3.7 m\AA at 99
confidence. With this limit and a Parker wind model we constrain the escape
rate from the atmosphere to Gyr, 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.Comment: 10 pages, 5 figures, accepted for publication in ApJ Letter
Absence of extended atmospheres in low-mass star radius-gap planets GJ 9827 b, GJ 9827 d and TOI-1235 b
\textit{Kepler} showed a paucity of planets with radii of 1.5 - 2 around solar mass stars but this radius-gap has not been well
studied for low-mass star planets. Energy-driven escape models like
photoevaporation and core-powered mass-loss predict opposing transition regimes
between rocky and non-rocky planets when compared to models depicting planets
forming in gas-poor environments. Here we present transit observations of three
super-Earth sized planets in the radius-gap around low-mass stars using
high-dispersion InfraRed Doppler (IRD) spectrograph on the Subaru 8.2m
telescope. The planets GJ 9827 b and d orbit around a K6V star and TOI-1235 b
orbits a M0.5 star. We limit any planet-related absorption in the 1083.3 nm
lines of triplet He I by placing an upper-limit on the equivalent width of
14.71 m{\AA}, 18.39 m{\AA}, and 1.44 m{\AA}, for GJ 9827 b (99% confidence), GJ
9827 d (99% confidence) and TOI-1235 b (95% confidence) respectively. Using a
Parker wind model, we cap the mass-loss at 0.25
Gyr and 0.2 Gyr for GJ 9827 b and d,
respectively (99% confidence), and 0.05 Gyr for
TOI-1235 b (95\% confidence) for a representative wind temperature of 5000 K.
Our observed results for the three planets are more consistent with the
predictions from photoevaporation and/or core-powered mass-loss models than the
gas-poor formation models. However, more planets in the radius-gap regime
around the low-mass stars are needed to robustly predict the atmospheric
evolution in planets around low-mass stars.Comment: Accepted for MNRAS. 12 pages, 15 figure
Direct Imaging Explorations for Companions around Mid-Late M Stars from the Subaru/IRD Strategic Program
The Subaru telescope is currently performing a strategic program (SSP) using
the high-precision near-infrared (NIR) spectrometer IRD to search for
exoplanets around nearby mid/late-M~dwarfs via radial velocity (RV) monitoring.
As part of the observing strategy for the exoplanet survey, signatures of
massive companions such as RV trends are used to reduce the priority of those
stars. However, this RV information remains useful for studying the stellar
multiplicity of nearby M~dwarfs. To search for companions around such
``deprioritized" M~dwarfs, we observed 14 IRD-SSP targets using Keck/NIRC2
observations with pyramid wavefront sensing at NIR wavelengths, leading to high
sensitivity to substellar-mass companions within a few arcseconds. We detected
two new companions (LSPM~J1002+1459~B and LSPM~J2204+1505~B) and two new
candidates that are likely companions (LSPM~J0825+6902~B and LSPM~J1645+0444~B)
as well as one known companion. Including two known companions resolved by the
IRD fiber injection module camera, we detected seven (four new) companions at
projected separations between ~au in total. A comparison of the
colors with the spectral library suggests that LSPM~J2204+1505~B and
LSPM~J0825+6902~B are located at the boundary between late-M and early-L
spectral types. Our deep high-contrast imaging for targets where no bright
companions were resolved did not reveal any additional companion candidates.
The NIRC2 detection limits could constrain potential substellar-mass companions
() at 10~au or further. The failure with Keck/NIRC2
around the IRD-SSP stars having significant RV trends makes these objects
promising targets for further RV monitoring or deeper imaging with JWST to
search for smaller-mass companions below the NIRC2 detection limits.Comment: 16 pages, 8 figures, accepted for publication in A
The mass determination of TOI-519 b: a close-in giant planet transiting a metal-rich mid-M dwarf
We report the mass determination of TOI-519 b, a transiting substellar object
around a mid-M dwarf. We carried out radial velocity measurements using Subaru
/ InfraRed Doppler (IRD), revealing that TOI-519 b is a planet with a mass of
. We also find that the host star is metal
rich ( dex) and has the lowest effective
temperature ( K) among all stars hosting known
close-in giant planets based on the IRD spectra and mid-resolution infrared
spectra obtained with NASA Infrared Telescope Facility / SpeX. The core mass of
TOI-519 b inferred from a thermal evolution model ranges from to
, which can be explained by both the core accretion and disk
instability models as the formation origins of this planet. However, TOI-519 is
in line with the emerging trend that M dwarfs with close-in giant planets tend
to have high metallicity, which may indicate that they formed in the core
accretion model. The system is also consistent with the potential trend that
close-in giant planets around M dwarfs tend to be less massive than those
around FGK dwarfs.Comment: 10 pages, 5 figures. Accepted for publication in PAS
Non-detection of Helium in the upper atmospheres of TRAPPIST-1b, e and f
We obtained high-resolution spectra of the ultra-cool M-dwarf TRAPPIST-1
during the transit of its planet `b' using two high dispersion near-infrared
spectrographs, IRD instrument on the Subaru 8.2m telescope and HPF instrument
on the 10m Hobby-Eberly Telescope. These spectroscopic observations are
complemented by a photometric transit observation for planet `b' using the
APO/ARCTIC, which assisted us to capture the correct transit times for our
transit spectroscopy. Using the data obtained by the new IRD and HPF
observations, as well as the prior transit observations of planets `b', `e' and
`f' from IRD, we attempt to constrain the atmospheric escape of the planet
using the He I triplet 10830 {\AA} absorption line. We do not detect evidence
for any primordial extended H-He atmospheres in all three planets. To limit any
planet related absorption, we place an upper limit on the equivalent widths of
<7.754 m{\AA} for planet `b', <10.458 m{\AA} for planet `e', and <4.143 m{\AA}
for planet `f' at 95% confidence from the IRD data, and <3.467 m{\AA} for
planet `b' at 95% confidence from HPF data. Using these limits along with a
solar-like composition isothermal Parker wind model, we attempt to constrain
the mass-loss rates for the three planets. For TRAPPIST-1b, our models exclude
the highest possible energy-limited rate for a wind temperature <5000 K. This
non-detection of extended atmospheres having low mean-molecular weight in all
three planets aids in further constraining their atmospheric composition by
steering the focus towards the search of high molecular weight species in their
atmospheres.Comment: 11 pages; 4 figures; Accepted for publication in A
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January 2019. Revised November 2019