128 research outputs found
Spin-Orbit Alignment of the TrES-4 Transiting Planetary System and Possible Additional Radial Velocity Variation
We report new radial velocities of the TrES-4 transiting planetary system,
including observations of a full transit, with the High Dispersion Spectrograph
of the Subaru 8.2m telescope. Modeling of the Rossiter-McLaughlin effect
indicates that TrES-4b has closely aligned orbital and stellar spin axes, with
. The close spin-orbit alignment angle
of TrES-4b seems to argue against a migration history involving planet-planet
scattering or Kozai cycles, although there are two nearby faint stars that
could be binary companion candidates. Comparison of our out-of-transit data
from 4 different runs suggest that the star exhibits radial velocity
variability of 20 ms^-1 in excess of a single Keplerian orbit. Although
the cause of the excess radial velocity variability is unknown, we discuss
various possibilities including systematic measurement errors, starspots or
other intrinsic motions, and additional companions besides the transiting
planet.Comment: 10 pages, 3 figures, 3 tables, PASJ in pres
A Possible Spin-Orbit Misalignment in the Transiting Eccentric Planet HD 17156b
We present simultaneous photometric and spectroscopic observations of HD
17156b spanning a transit on UT 2007 November 12. This system is of special
interest because of its 21-day period (unusually long for a transiting planet)
and its high orbital eccentricity of 0.67. By modeling the Rossiter-McLaughlin
effect, we find the angle between the sky projections of the orbital axis and
the stellar rotation axis to be . Such a large
spin-orbit misalignment, as well as the large eccentricity, could be explained
as the relic of a previous gravitational interaction with other planets.Comment: 5 pages, 2 figures, 3 tables. Accepted for publication in PASJ
Letters (Vol. 60, No. 2
A Search for H-alpha Absorption in the Exosphere of the Transiting Extrasolar Planet HD 209458b
There is evidence that the transiting planet HD 209458b has a large exosphere
of neutral hydrogen, based on a 15% decrement in Lyman-alpha flux that was
observed by Vidal-Madjar et al. during transits. Here we report upper limits on
H-alpha absorption by the exosphere. The results are based on optical spectra
of the parent star obtained with the Subaru High Dispersion Spectrograph.
Comparison of the spectra taken inside and outside of transit reveals no
exospheric H-alpha signal greater than 0.1% within a 5.1A band (chosen to have
the same Delta_lambda/lambda as the 15% Ly-alpha absorption). The corresponding
limit on the column density of n=2 neutral hydrogen is N_2 <~ 10^9 cm^{-2}.
This limit constrains proposed models involving a hot (~10^4 K) and
hydrodynamically escaping exosphere.Comment: To appear in PASJ [9 pages, 5 figures]. Minor corrections to match
published versio
Subaru HDS Transmission Spectroscopy of the Transiting Extrasolar Planet HD 209458b
We have searched for absorption in several common atomic species due to the
atmosphere or exosphere of the transiting extrasolar planet HD 209458b, using
high precision optical spectra obtained with the Subaru High Dispersion
Spectrograph (HDS). Previously we reported an upper limit on H alpha absorption
of 0.1% (3 sigma) within a 5.1\AA band. Using the same procedure, we now report
upper limits on absorption due to the optical transitions of Na D, Li, H alpha,
H beta, H gamma, Fe, and Ca. The 3 sigma upper limit for each transition is
approximately 1% within a 0.3\AA band (the core of the line), and a few tenths
of a per cent within a 2\AA band (the full line width). The wide-band results
are close to the expected limit due to photon-counting (Poisson) statistics,
although in the narrow-band case we have encountered unexplained systematic
errors at a few times the Poisson level. These results are consistent with all
previously reported detections and upper limits, but are significantly more
sensitive.Comment: 10 pages, 9 figure
Measurement of the Rossiter--McLaughlin Effect in the Transiting Exoplanetary System TrES-1
We report a measurement of the Rossiter--McLaughlin effect in the transiting
extrasolar planetary system TrES-1, via simultaneous spectroscopic and
photometric observations with the Subaru and MAGNUM telescopes. By modeling the
radial velocity anomaly that was observed during a transit, we determine the
sky-projected angle between the stellar spin axis and the planetary orbital
axis to be [deg]. This is the third case for which
has been measured in a transiting exoplanetary system, and the first
demonstration that such measurements are possible for relatively faint host
stars (, as compared to for the other systems). We also
derive a time of mid-transit, constraints on the eccentricity of the TrES-1b
orbit (), and upper limits on the mass of the Trojan
companions (14 ) at the 3 level.Comment: 8 pages, 5 figures, 2 tables. Published in PASJ. Corrected typo
Analytic Description of the Rossiter-McLaughlin Effect for Transiting Exoplanets: Cross-Correlation Method and Comparison with Simulated Data
We obtain analytical expressions for the velocity anomaly due to the
Rossiter- McLaughlin effect, for the case when the anomalous radial velocity is
obtained by cross-correlation with a stellar template spectrum. In the limit of
vanishing width of the stellar absorption lines, our result reduces to the
formula derived by Ohta et al. (2005), which is based on the first moment of
distorted stellar lines. Our new formula contains a term dependent on the
stellar linewidth, which becomes important when rotational line broadening is
appreciable. We generate mock transit spectra for four existing exoplanetary
systems (HD17156, TrES-2, TrES- 4, and HD209458) following the procedure of
Winn et al. (2005), and find that the new formula is in better agreement with
the velocity anomaly extracted from the mock data. Thus, our result provides a
more reliable analytical description of the velocity anomaly due to the
Rossiter-McLaughlin effect, and explains the previously observed dependence of
the velocity anomaly on the stellar rotation velocity.Comment: 31 pages, 9 figures, Astrophysical Journal in pres
Further Observations of the Tilted Planet XO-3: A New Determination of Spin-Orbit Misalignment, and Limits on Differential Rotation
Abstract: We report on observations of the Rossiter-McLaughlin (RM) effect for the XO-3 exoplanetary system. The RM effect for the system was previously measured by two different groups, but their results were statistically inconsistent. To obtain a decisive result we observed two full transits of XO-3b with the Subaru 8.2-m telescope. By modeling these data with a new and more accurate analytic formula for the RM effect, we find the projected spin-orbit angle to be λ=37.3 deg ± 3.0 deg, in good agreement with the previous finding by Winn et al. (2009). In addition, an offset of ~22 m/s[superscript -1] was observed between the two transit datasets. This offset could be a signal of a third body in the XO-3 system, a possibility that should be checked with future observations. We also attempt to search for a possible signature of the stellar differential rotation in the RM data for the first time, and put weak upper limits on the differential rotation parameters.United States. National Aeronautics and Space Administration (NNX11AG85G
Improved Measurement of the Rossiter-McLaughlin Effect in the Exoplanetary System HD 17156
We present an improved measurement of the Rossiter-McLaughlin effect for the
exoplanetary system HD 17156, based on radial-velocity data gathered with the
Subaru 8.2m telescope throughout the planetary transit of UT 2008 November 7.
The data allow for a precise and independent determination of the projected
spin-orbit angle of this system: . This
result supersedes the previous claim of
by Narita et al., which was based on lower-precision data with poor statistics.
Thus the stellar spin and planetary orbital axes of the HD 17156 system are
likely to be well-aligned, despite the planet's large orbital eccentricity
suggesting a history of strong dynamical interactions.Comment: 16 pages, 3 figures, 3 tables, PASJ accepte
Improved modeling of the Rossiter-McLaughlin effect for transiting exoplanets
We present an improved formula for the anomalous radial velocity of the star during planetary transits due to the Rossiter-McLaughlin (RM) effect. The improvement comes from a more realistic description of the stellar absorption line profiles, taking into account stellar rotation, macroturbulence, thermal broadening, pressure broadening, and instrumental broadening. Although the formula is derived for the case in which radial velocities are measured by cross-correlation, we show through numerical simulations that the formula accurately describes the cases where the radial velocities are measured with the iodine absorption-cell technique. The formula relies on prior knowledge of the parameters describing macroturbulence, instrumental broadening, and other broadening mechanisms, but even 30% errors in those parameters do not significantly change the results in typical circumstances. We show that the new analytic formula agrees with previous ones that had been computed on a case-by-case basis via numerical simulations. Finally, as one application of the new formula, we reassess the impact of the differential rotation on the RM velocity anomaly. We show that differential rotation of a rapidly rotating star may have a significant impact on future RM observations.United States. National Aeronautics and Space Administration (Origins program grant NNX11AG85G
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