25 research outputs found
Recommended from our members
False Positives and Shallow Eclipsing Binaries in Transiting Exoplanet Surveys
PLATO (PLAnetary Transits and Oscillations of stars), ESA’s M3 mission, is due to launch in 2026. It will aim to detect transits by exoplanets around bright nearby stars and, where possible, to characterise those stars using asteroseismology.
With 24 cameras arranged in four overlapping groups, PLATO will have an excellent signal to noise ratio, making the detection of an Earth-like planet in an Earth-like orbit around a Sun-like star a real possibility. However, the pixel size is large: at 15", there is an increased risk of blends with background eclipsing binaries. This work aims to quantify that risk.
Data from Kepler has been used to calibrate the distribution of planets and eclipsing binaries detectable in a transiting exoplanet survey using the population synthesis code, BiSEPS. The calibrated synthetic populations have then been used to predict the numbers of exoplanets and eclipsing binaries mimicking planets that PLATO is likely to detect. Other forms of false positive, such as instrumental effects and stellar variability, are beyond the current scope of this project.
My work offers insights into short period (P < 10 day) eclipsing binaries detectable in transiting exoplanet surveys, both in terms of initial mass ratio distribution and initial period distribution.
From confirmed Kepler planets in Kepler Data Release 25, I derive two intrinsic exoplanet distributions which bracket the likely true distribution. These distributions converge at planet radius 0 < log R/R⊕ < 0.2.
For the two proposed Long Look fields from Rauer et al. (2014), I find that more exoplanets are likely to be detected in the Southern field, while more blended eclipsing binaries are likely to contaminate observations of the Northern field.
My methods can be extended to other transiting exoplanet surveys, by incorporating the detection parameters of the relevant observatory into the code
Recommended from our members
Workshop talk: False positives and shallow eclipsing binaries in transiting exoplanet services, PLATO Week, Porto, October 2017
Using the population synthesis code BiSEPS, we estimate the likely contamination from background eclipsing binaries in the forthcoming PLATO mission
TIC 278956474: Two Close Binaries in One Young Quadruple System Identified by TESS
We have identified a quadruple system with two close eclipsing binaries in Transiting Exoplanet Survey Satellite (TESS) data. The object is unresolved in Gaia and appears as a single source at parallax 1.08 ± 0.01 mas. Both binaries have observable primary and secondary eclipses and were monitored throughout TESS Cycle 1 (sectors 1-13), falling within the TESS Continuous Viewing Zone. In one eclipsing binary (P = 5.488 days), the smaller star is completely occluded by the larger star during the secondary eclipse; in the other (P = 5.674 days) both eclipses are grazing. Using these data, spectroscopy, speckle photometry, spectral energy distribution analysis, and evolutionary stellar tracks, we have constrained the masses and radii of the four stars in the two eclipsing binaries. The Li I equivalent width indicates an age of 10-50 Myr and, with an outer period of ?--> days, our analysis indicates this is one of the most compact young 2 + 2 quadruple systems known
A Habitable-zone Earth-sized Planet Rescued from False Positive Status
We report the discovery of an Earth-sized planet in the habitable zone of a
low-mass star called Kepler-1649. The planet, Kepler-1649 c, is
1.06 times the size of Earth and transits its 0.1977 +/-
0.0051 Msun mid M-dwarf host star every 19.5 days. It receives 74 +/- 3 % the
incident flux of Earth, giving it an equilibrium temperature of 234 +/- 20K and
placing it firmly inside the circumstellar habitable zone. Kepler-1649 also
hosts a previously-known inner planet that orbits every 8.7 days and is roughly
equivalent to Venus in size and incident flux. Kepler-1649 c was originally
classified as a false positive by the Kepler pipeline, but was rescued as part
of a systematic visual inspection of all automatically dispositioned Kepler
false positives. This discovery highlights the value of human inspection of
planet candidates even as automated techniques improve, and hints that
terrestrial planets around mid to late M-dwarfs may be more common than those
around more massive stars.Comment: 11 pages, 3 figures, 1 table. Accepted for publication in ApJ
TOI 540 b: A Planet Smaller than Earth Orbiting a Nearby Rapidly Rotating Low-mass Star
We present the discovery of TOI 540 b, a hot planet slightly smaller than
Earth orbiting the low-mass star 2MASS J05051443-4756154. The planet has an
orbital period of days ( 170 ms) and a radius of , and is likely terrestrial based on the observed
mass-radius distribution of small exoplanets at similar insolations. The star
is 14.008 pc away and we estimate its mass and radius to be and , respectively. The
star is distinctive in its very short rotational period of hours and correspondingly small Rossby number of 0.007 as
well as its high X-ray-to-bolometric luminosity ratio of based on a serendipitous XMM-Newton detection during a slew operation.
This is consistent with the X-ray emission being observed at a maximum value of
as predicted for the most rapidly rotating M
dwarfs. TOI 540 b may be an alluring target to study atmospheric erosion due to
the strong stellar X-ray emission. It is also among the most accessible targets
for transmission and emission spectroscopy and eclipse photometry with JWST,
and may permit Doppler tomography with high-resolution spectroscopy during
transit. This discovery is based on precise photometric data from TESS and
ground-based follow-up observations by the MEarth team.Comment: 18 pages, 7 figures. Accepted for publication in The Astronomical
Journa
Validation of TOI-1221 b: A warm sub-Neptune exhibiting TTVs around a Sun-like star
We present a validation of the long-period (
days) transiting sub-Neptune planet TOI-1221 b (TIC 349095149.01) around a
Sun-like (m=10.5) star. This is one of the few known exoplanets with
period >50 days, and belongs to the even smaller subset of which have bright
enough hosts for detailed spectroscopic follow-up. We combine TESS light curves
and ground-based time-series photometry from PEST (0.3~m) and LCOGT (1.0~m) to
analyze the transit signals and rule out nearby stars as potential false
positive sources. High-contrast imaging from SOAR and Gemini/Zorro rule out
nearby stellar contaminants. Reconnaissance spectroscopy from CHIRON sets a
planetary scale upper mass limit on the transiting object (1.1 and 3.5 M at 1 and 3, respectively) and shows no sign of a
spectroscopic binary companion. We determine a planetary radius of , placing it in the sub-Neptune regime. With a
stellar insolation of , we calculate a
moderate equilibrium temperature of 440 K, assuming no albedo
and perfect heat redistribution. We find a false positive probability from
TRICERATOPS of FPP as well as other qualitative and
quantitative evidence to support the statistical validation of TOI-1221 b. We
find significant evidence (>) of oscillatory transit timing
variations, likely indicative of an additional non-transiting planet.Comment: 17 pages, 9 figures, 4 table
Hot, rocky and warm, puffy super-Earths orbiting TOI-402 (HD 15337)
Context: The Transiting Exoplanet Survey Satellite (TESS) is revolutionising the search for planets orbiting bright and nearby stars. In sectors 3 and 4, TESS observed TOI-402 (TIC-120896927), a bright V = 9.1 K1 dwarf also known as HD 15337, and found two transiting signals with periods of 4.76 and 17.18 days and radii of 1.90 and 2.21 R⊕, respectively. This star was observed prior to the TESS detection as part of the radial-velocity (RV) search for planets using the HARPS spectrometer, and 85 precise RV measurements were obtained before the launch of TESS over a period of 14 yr.
Aims: In this paper, we analyse the HARPS RV measurements in hand to confirm the planetary nature of these two signals.
Methods: HD 15337 happens to present a stellar activity level similar to the Sun, with a magnetic cycle of similar amplitude and RV measurements that are affected by stellar activity. By modelling this stellar activity in the HARPS radial velocities using a linear dependence with the calcium activity index log(RHK′), we are able, with a periodogram approach, to confirm the periods and the planetary nature of TOI-402.01 and TOI-402.02. We then derive robust estimates from the HARPS RVs for the orbital parameters of these two planets by modelling stellar activity with a Gaussian process and using the marginalised posterior probability density functions obtained from our analysis of TESS photometry for the orbital period and time of transit.
Results: By modelling TESS photometry and the stellar host characteristics, we find that TOI-402.01 and TOI-402.02 have periods of 4.75642 ± 0.00021 and 17.1784 ± 0.0016 days and radii of 1.70 ± 0.06 and 2.52 ± 0.11 R⊕ (precision 3.6 and 4.2%), respectively. By analysing the HARPS RV measurements, we find that those planets are both super-Earths with masses of 7.20 ± 0.81 and 8.79 ± 1.68 M⊕ (precision 11.3 and 19.1%), and small eccentricities compatible with zero at 2σ.
Conclusions: Although having rather similar masses, the radii of these two planets are very different, putting them on different sides of the radius gap. By studying the temporal evolution under X-ray and UV (XUV) driven atmospheric escape of the TOI-402 planetary system, we confirm, under the given assumptions, that photo-evaporation is a plausible explanation for this radius difference. Those two planets, being in the same system and therefore being in the same irradiation environment are therefore extremely useful for comparative exoplanetology across the evaporation valley and thus bring constraints on the mechanisms responsible for the radius gap
TOI-733 b -- a planet in the small-planet radius valley orbiting a Sun-like star
We report the discovery of a hot ( 1055 K) planet in
the small planet radius valley transiting the Sun-like star TOI-733, as part of
the KESPRINT follow-up program of TESS planets carried out with the HARPS
spectrograph. TESS photometry from sectors 9 and 36 yields an orbital period of
= days and a radius of
= .
Multi-dimensional Gaussian process modelling of the radial velocity
measurements from HARPS and activity indicators, gives a semi-amplitude of
= m s, translating into a planet mass of
= . These
parameters imply that the planet is of moderate density ( =
g cm) and place it in the transition
region between rocky and volatile-rich planets with H/He-dominated envelopes on
the mass-radius diagram. Combining these with stellar parameters and
abundances, we calculate planet interior and atmosphere models, which in turn
suggest that TOI-733 b has a volatile-enriched, most likely secondary outer
envelope, and may represent a highly irradiated ocean world - one of only a few
such planets around G-type stars that are well-characterised.Comment: Accepted for publication in A&
A low-eccentricity migration pathway for a 13-h-period Earth analogue in a four-planet system
It is commonly accepted that exoplanets with orbital periods shorter than one day, also known as ultra-short-period (USP) planets, formed further out within their natal protoplanetary disks before migrating to their current-day orbits via dynamical interactions. One of the most accepted theories suggests a violent scenario involving high-eccentricity migration followed by tidal circularization. Here we present the discovery of a four-planet system orbiting the bright (V = 10.5) K6 dwarf star TOI-500. The innermost planet is a transiting, Earth-sized USP planet with an orbital period of ~13 hours, a mass of 1.42 \ub1 0.18 M⊕, a radius of 1.166−0.058+0.061R⊕ and a mean density of 4.89−0.88+1.03gcm−3. Via Doppler spectroscopy, we discovered that the system hosts 3 outer planets on nearly circular orbits with periods of 6.6, 26.2 and 61.3 days and minimum masses of 5.03 \ub1 0.41 M⊕, 33.12 \ub1 0.88 M⊕ and 15.05−1.11+1.12M⊕, respectively. The presence of both a USP planet and a low-mass object on a 6.6-day orbit indicates that the architecture of this system can be explained via a scenario in which the planets started on low-eccentricity orbits then moved inwards through a quasi-static secular migration. Our numerical simulations show that this migration channel can bring TOI-500 b to its current location in 2 Gyr, starting from an initial orbit of 0.02 au. TOI-500 is the first four-planet system known to host a USP Earth analogue whose current architecture can be explained via a non-violent migration scenario
The Transiting Multi-planet System HD15337: Two Nearly Equal-mass Planets Straddling the Radius Gap
We report the discovery of a super-Earth and a sub-Neptune transiting the star HD 15337 (TOI-402, TIC 120896927), a bright (V = 9) K1 dwarf observed by the Transiting Exoplanet Survey Satellite (TESS) in Sectors 3 and 4. We combine the TESS photometry with archival High Accuracy Radial velocity Planet Searcher spectra to confirm the planetary nature of the transit signals and derive the masses of the two transiting planets. With an orbital period of 4.8 days, a mass of and a radius of 1.64 ± 0.06 R ⊕, HD 15337 b joins the growing group of short-period super-Earths known to have a rocky terrestrial composition. The sub-Neptune HD 15337 c has an orbital period of 17.2 days, a mass of , and a radius of 2.39 ± 0.12 R ⊕, suggesting that the planet might be surrounded by a thick atmospheric envelope. The two planets have similar masses and lie on opposite sides of the radius gap, and are thus an excellent testbed for planet formation and evolution theories. Assuming that HD 15337 c hosts a hydrogen-dominated envelope, we employ a recently developed planet atmospheric evolution algorithm in a Bayesian framework to estimate the history of the high-energy (extreme ultraviolet and X-ray) emission of the host star. We find that at an age of 150 Myr, the star possessed on average between 3.7 and 127 times the high-energy luminosity of the current Sun