38 research outputs found
Detecting Solar System Analogs through Joint Radial Velocity/Astrometric Surveys
Earth-mass exoplanets on year-long orbits and cool gas giants (CGG) on
decade-long orbits lie at the edge of current detection limits. The Terra
Hunting Experiment (THE) will take nightly radial velocity (RV) observations on
HARPS3 of at least 40 bright nearby G and K dwarfs for 10 years, with a target
1 measurement error of 0.3 m/s, in search of exoplanets that are
Earth-like in mass and temperature. However, RV observations can only provide
minimum mass estimates, due to the mass-inclination degeneracy. Astrometric
observations of these same stars, with sufficient precision, could break this
degeneracy. Gaia will soon release 100-200 astrometric observations of
the THE stars with a 10 year baseline and 34.2 as 1
along-scan measurement error. The Nancy Grace Roman Space Telescope will be
capable of precision astrometry using its wide field imager (target 5-20
as 1 measurement error for bright stars) and could extend the
astrometric observational baseline to 25 years. We simulate and model an
observing program that combines data from these three telescopes. We find that
(1) THE RVs and Gaia astrometry can detect Earth-like and CGG-like exoplanets
around bright Sun-like stars at 10 parsecs and that (2) adding Roman astrometry
improves the detection precision for CGG masses and periods by a factor up to
10 and 4, respectively. Such a survey could provide insight into
the prevalence of Solar System analogs, exoplanet architectures reminiscent of
the mass and orbital separation hierarchy of our Solar System, for the nearest
Sun-like stars.Comment: 21 pages, 10 figures. Revised based on comments from anonymous
reviewer at AAS Journals. Code available at
https://github.com/dyahalomi/rv_and_astrometr
The Mass of the White Dwarf Companion in the Self-Lensing Binary KOI-3278: Einstein vs. Newton
KOI-3278 is a self-lensing stellar binary consisting of a white-dwarf
secondary orbiting a Sun-like primary star. Kruse and Agol (2014) noticed small
periodic brightenings every 88.18 days in the Kepler photometry and interpreted
these as the result of microlensing by a white dwarf with about 63 of the
mass of the Sun. We obtained two sets of spectra for the primary that allowed
us to derive three sets of spectroscopic estimates for its effective
temperature, surface gravity, and metallicity for the first time. We used these
values to update the Kruse and Agol (2014) Einsteinian microlensing model,
resulting in a revised mass for the white dwarf of . The spectra also allowed us to determine radial velocities and
derive orbital solutions, with good agreement between the two independent data
sets. An independent Newtonian dynamical MCMC model of the combined velocities
yielded a mass for the white dwarf of . The nominal uncertainty for the Newtonian mass is about four times
better than for the Einsteinian, vs. and the difference
between the two mass determinations is . We then present a joint
Einsteinian microlensing and Newtonian radial velocity model for KOI-3278,
which yielded a mass for the white dwarf of . This joint model does not rely on any white dwarf evolutionary
models or assumptions on the white dwarf mass-radius relation. We discuss the
benefits of a joint model of self-lensing binaries, and how future studies of
these systems can provide insight into the mass-radius relation of white
dwarfs.Comment: ApJ Accepted; 22 Pages, 8 Figures, 6 Tables and 4 Supplementary
Table
A Reply to: Large Exomoons unlikely around Kepler-1625 b and Kepler-1708 b
Recently, Heller & Hippke argued that the exomoon candidates Kepler-1625 b-i
and Kepler-1708 b-i were allegedly 'refuted'. In this Matters Arising, we
address these claims. For Kepler-1625 b, we show that their Hubble light curve
is identical to that previously published by the same lead author, in which the
moon-like dip was recovered. Indeed, our fits of their data again recover the
moon-like dip with improved residuals than that obtained by Heller & Hippke.
Their fits therefore appear to have somehow missed this deeper likelihood
maximum, as well producing apparently unconverged posteriors. Consequently,
their best-fitting moon is the same radius as the planet, Kepler-1625 b; a
radically different signal from that which was originally claimed. The authors
then inject this solution into the Kepler data and remark, as a point of
concern, how retrievals obtain much higher significances than originally
reported. However, this issue stems from the injection of a fundamentally
different signal. We demonstrate that their Hubble light curve exhibits ~20%
higher noise and discards 11% of the useful data, which compromises its ability
to recover the subtle signal of Kepler-1625 b-i. For Kepler-1708 b-i it was
claimed that the exomoon model's Bayes factor is highly sensitive to detrending
choices, yielding reduced evidence with a biweight filter versus the original
claim. We use their own i) detrended light curve and ii) biweight filter code
to investigate these claims. For both, we recover the original moon signal, to
even higher confidence than before. The discrepancy is explained by comparing
to their quoted fit metrics, where we again demonstrate that the Heller &
Hippke regression definitively missed the deeper likelihood maximum
corresponding to Kepler-1708 b-i. We conclude that both candidates remain
viable but certainly demand further observations.Comment: Under consideration by Nature Astronomy as Matters Arisin
Securing the legacy of TESS through the care and maintenance of TESS planet ephemerides
Much of the science from the exoplanets detected by the TESS mission relies
on precisely predicted transit times that are needed for many follow-up
characterization studies. We investigate ephemeris deterioration for simulated
TESS planets and find that the ephemerides of 81% of those will have expired
(i.e. 1 mid-transit time uncertainties greater than 30 minutes) one
year after their TESS observations. We verify these results using a sample of
TESS planet candidates as well. In particular, of the simulated planets that
would be recommended as JWST targets by Kempton et al. (2018), 80% will
have mid-transit time uncertainties 30 minutes by the earliest time JWST
would observe them. This rapid deterioration is driven primarily by the
relatively short time baseline of TESS observations. We describe strategies for
maintaining TESS ephemerides fresh through follow-up transit observations. We
find that the longer the baseline between the TESS and the follow-up
observations, the longer the ephemerides stay fresh, and that 51% of simulated
primary mission TESS planets will require space-based observations. The
recently-approved extension to the TESS mission will rescue the ephemerides of
most (though not all) primary mission planets, but the benefits of these new
observations can only be reaped two years after the primary mission
observations. Moreover, the ephemerides of most primary mission TESS planets
(as well as those newly discovered during the extended mission) will again have
expired by the time future facilities such as the ELTs, Ariel and the possible
LUVOIR/OST missions come online, unless maintenance follow-up observations are
obtained.Comment: 16 pages, 10 figures, accepted to AJ; main changes are cross-checking
results against the sample of real TOIs, and addressing the impact of the
TESS extended missio
Not So Fast Kepler-1513: A Perturbing Planetary Interloper in the Exomoon Corridor
Transit Timing Variations (TTVs) can be induced by a range of physical
phenomena, including planet-planet interactions, planet-moon interactions, and
stellar activity. Recent work has shown that roughly half of moons would induce
fast TTVs with a short period in the range of two-to-four orbits of its host
planet around the star. An investigation of the Kepler TTV data in this period
range identified one primary target of interest, Kepler-1513 b. Kepler-1513 b
is a planet orbiting a late G-type dwarf at
AU. Using Kepler photometry, this initial analysis
showed that Kepler-1513 b's TTVs were consistent with a moon. Here, we report
photometric observations of two additional transits nearly a decade after the
last Kepler transit using both ground-based observations and space-based
photometry with TESS. These new transit observations introduce a previously
undetected long period TTV, in addition to the original short period TTV
signal. Using the complete transit dataset, we investigate whether a
non-transiting planet, a moon, or stellar activity could induce the observed
TTVs. We find that only a non-transiting perturbing planet can reproduce the
observed TTVs. We additionally perform transit origami on the Kepler
photometry, which independently applies pressure against a moon hypothesis.
Specifically, we find that Kepler-1513 b's TTVs are consistent with an exterior
non-transiting Saturn mass planet, Kepler-1513 c, on a wide orbit,
5 outside a 5:1 period ratio with Kepler-1513 b. This example
introduces a previously unidentified cause for planetary interlopers in the
exomoon corridor, namely an insufficient baseline of observations.Comment: 20 pages, 13 figures. Accepted to MNRAS. Code available at
https://github.com/dyahalomi/Kepler151
Securing the Legacy of TESS through the Care and Maintenance of TESS Planet Ephemerides
Much of the science from the exoplanets detected by the Transiting Exoplanet Survey Satellite (TESS) mission relies on precisely predicted transit times that are needed for many follow-up characterization studies. We investigate ephemeris deterioration for simulated TESS planets and find that the ephemerides of 81% of those will have expired (i.e., 1σ mid-transit time uncertainties greater than 30 minutes) 1 yr after their TESS observations. We verify these results using a sample of TESS planet candidates as well. In particular, of the simulated planets that would be recommended as James Webb Space Telescope (JWST) targets by Kempton et al., ~80% will have mid-transit time uncertainties >30 minutes by the earliest time JWST would observe them. This rapid deterioration is driven primarily by the relatively short time baseline of TESS observations. We describe strategies for maintaining TESS ephemerides fresh through follow-up transit observations. We find that the longer the baseline between the TESS and the follow-up observations, the longer the ephemerides stay fresh, and that 51% of simulated primary mission TESS planets will require space-based observations. The recently approved extension to the TESS mission will rescue the ephemerides of most (though not all) primary mission planets, but the benefits of these new observations can only be reaped 2 yr after the primary mission observations. Moreover, the ephemerides of most primary mission TESS planets (as well as those newly discovered during the extended mission) will again have expired by the time future facilities such as the ELTs, Ariel, and the possible LUVOIR/Origins Space Telescope missions come online, unless maintenance follow-up observations are obtained
Exploring the Atmospheric Dynamics of the Extreme Ultrahot Jupiter KELT-9b Using TESS Photometry
We carry out a phase-curve analysis of the KELT-9 system using photometric observations from NASA's Transiting Exoplanet Survey Satellite (TESS). The measured secondary eclipse depth and peak-to-peak atmospheric brightness modulation are 650⁺¹⁴₋₁₅ and 566 ± 16 ppm, respectively. The planet's brightness variation reaches maximum 31 ± 5 minutes before the midpoint of the secondary eclipse, indicating a 5.°2 ± 0.°9 eastward shift in the dayside hot spot from the substellar point. We also detect stellar pulsations on KELT-9 with a period of 7.58695 ± 0.00091 hr. The dayside emission of KELT-9b in the TESS bandpass is consistent with a blackbody brightness temperature of 4600 ± 100 K. The corresponding nightside brightness temperature is 3040 ± 100 K, comparable to the dayside temperatures of the hottest known exoplanets. In addition, we detect a significant phase-curve signal at the first harmonic of the orbital frequency and a marginal signal at the second harmonic. While the amplitude of the first harmonic component is consistent with the predicted ellipsoidal distortion modulation assuming equilibrium tides, the phase of this photometric variation is shifted relative to the expectation. Placing KELT-9b in the context of other exoplanets with phase-curve observations, we find that the elevated nightside temperature and relatively low day–night temperature contrast agree with the predictions of atmospheric models that include H₂ dissociation and recombination. The nightside temperature of KELT-9b implies an atmospheric composition containing about 50% molecular and 50% atomic hydrogen at 0.1 bar, a nightside emission spectrum that deviates significantly from a blackbody, and a 0.5–2.0 μm transmission spectrum that is featureless at low resolution