378 research outputs found
TESS Spots a Compact System of Super-Earths around the Naked-eye Star HR 858
Transiting Exoplanet Survey Satellite (TESS) observations have revealed a compact multiplanet system around the sixth-magnitude star HR 858 (TIC 178155732, TOI 396), located 32 pc away. Three planets, each about twice the size of Earth, transit this slightly evolved, late F-type star, which is also a member of a visual binary. Two of the planets may be in mean motion resonance. We analyze the TESS observations, using novel methods to model and remove instrumental systematic errors, and combine these data with follow-up observations taken from a suite of ground-based telescopes to characterize the planetary system. The HR 858 planets are enticing targets for precise radial velocity observations, secondary eclipse spectroscopy, and measurements of the Rossiter–McLaughlin effect
Extracting Radial Velocities of A- and B-type Stars from Echelle Spectrograph Calibration Spectra
We present a technique to extract radial velocity measurements from echelle
spectrograph observations of rapidly rotating stars ( km
s). This type of measurement is difficult because the line widths of
such stars are often comparable to the width of a single echelle order. To
compensate for the scarcity of lines and Doppler information content, we have
developed a process that forward-models the observations, fitting the radial
velocity shift of the star for all echelle orders simultaneously with the
echelle blaze function. We use our technique to extract radial velocity
measurements from a sample of rapidly rotating A- and B-type stars used as
calibrator stars observed by the California Planet Survey observations. We
measure absolute radial velocities with a precision ranging from 0.5-2.0 km
s per epoch for more than 100 A- and B-type stars. In our sample of 10
well-sampled stars with radial velocity scatter in excess of their measurement
uncertainties, three of these are single-lined binaries with long observational
baselines. From this subsample, we present detections of two previously unknown
spectroscopic binaries and one known astrometric system. Our technique will be
useful in measuring or placing upper limits on the masses of sub-stellar
companions discovered by wide-field transit surveys, and conducting future
spectroscopic binarity surveys and Galactic space-motion studies of massive
and/or young, rapidly-rotating stars.Comment: Accepted to ApJ
Reassessing the Evidence for Time Variability in the Atmosphere of the Exoplanet HAT-P-7 b
We reassess the claimed detection of variability in the atmosphere of the hot
Jupiter HAT-P-7 b, reported by Armstrong et al. (2016). Although astronomers
expect hot Jupiters to have changing atmospheres, variability is challenging to
detect. We looked for time variation in the phase curves of HAT-P-7 b in Kepler
data using similar methods to Armstrong et al. (2016), and identified
apparently significant variations similar to what they found. Numerous tests
show the variations to be mostly robust to different analysis strategies.
However, when we injected unchanging phase curve signals into the light curves
of other stars and searched for variability, we often saw similar levels of
variations as in the HAT-P-7 light curve. Fourier analysis of the HAT-P-7 light
curve revealed background red noise from stellar supergranulation on timescales
similar to the planet's orbital period. Tests of simulated light curves with
the same level of noise as HAT-P-7's supergranulation show that this effect
alone can cause the amplitude and phase offset variability we detect for
HAT-P-7 b. Therefore, the apparent variations in HAT-P-7 b's atmosphere could
instead be caused by non-planetary sources, most likely photometric variability
due to supergranulation on the host star.Comment: 27 pages, 18 figures, accepted for publication in the Astronomical
Journa
Detecting Exomoons Via Doppler Monitoring of Directly Imaged Exoplanets
Recently, Teachey, Kipping, and Schmitt (2018) reported the detection of a
candidate exomoon, tentatively designated Kepler-1625b I, around a giant planet
in the Kepler field. The candidate exomoon would be about the size and mass of
Neptune, considerably larger than any moon in our Solar System, and if
confirmed, would be the first in a new class of giant moons or binary planets.
Motivated by the large mass ratio in the Kepler-1625b planet and satellite
system, we investigate the detectability of similarly massive exomoons around
directly imaged exoplanets via Doppler spectroscopy. The candidate moon around
Kepler-1625b would induce a radial velocity signal of about 200 m/s on its host
planet, large enough that similar moons around directly imaged planets orbiting
bright, nearby stars might be detected with current or next generation
instrumentation. In addition to searching for exomoons, a radial velocity
survey of directly imaged planets could reveal the orientations of the planets'
spin axes, making it possible to identify Uranus analogs.Comment: 15 pages, 8 figures, 2 tables. Accepted for publication in A
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