403 research outputs found
The EBLM Project—From False Positives to Benchmark Stars and Circumbinary Exoplanets
The EBLM project aims to characterise very-low-mass stars that are companions to solar-type stars in eclipsing binaries. We describe the history and motivation for this project, the methodology we use to obtain the precise mass, radius, and effective temperature estimates for very-low-mass M dwarfs, and review the results of the EBLM study and those from related projects. We show that radius inflation in fully convective stars is a more subtle effect than what was previously thought based on less precise measurements, i.e., the mass–radius–effective temperature relations we observe for fully convective stars in single-line eclipsing binaries show reasonable agreement with the theoretical models, particularly if we account for the M-dwarf metallicity, as inferred from the analysis of the primary star spectrum.<br/
The EBLM Project -- From False Positives to Benchmark Stars and Circumbinary Exoplanets
The EBLM project aims to characterise very low-mass stars that are companions
to solar-type stars in eclipsing binaries. We describe the history and
motivation for this project, the methodology we use to obtain precise mass,
radius and effective temperature estimates for very low-mass M-dwarfs, and
review results of the EBLM study and those from related projects. We show that
radius inflation in fully-convective stars is a more subtle effect than was
previously thought based on less precise measurements, i.e. the
mass-radius-effective temperature relations we observe for fully-convective
stars in single-line eclipsing binaries show reasonable agreement with
theoretical models, particularly if we account for the M-dwarf metallicity, as
inferred from the analysis of the primary star spectrum.Comment: Accepted for publication in the journal Universe, special issue The
Royal Road: Eclipsing Binaries and Transiting Exoplanets. 30 pages, 8 figure
The TESS light curve of the eccentric eclipsing binary 1SWASP J011351.29+314909.7 -- no evidence for a very hot M-dwarf companion
A 2014 study of the eclipsing binary star 1SWASPJ011351.29+314909.7
(J0113+31) reported an unexpectedly high effective temperature for the M-dwarf
companion to the 0.95-M primary star. The effective temperature
inferred from the secondary eclipse depth was 600 K higher than the value
predicted from stellar models. Such an anomalous result questions our
understanding of low-mass stars and might indicate a significant uncertainty
when inferring properties of exoplanets orbiting them. We seek to measure the
effective temperature of the M-dwarf companion using the light curve of
J0113+31 recently observed by the Transiting Exoplanet Survey Satellite (TESS).
We use the pycheops modelling software to fit a combined transit and eclipse
model to the TESS light curve. To calculate the secondary effective
temperature, we compare the best-fit eclipse depth to the predicted eclipse
depths from theoretical stellar models. We determined the effective temperature
of the M dwarf to be = 3208 43 K, assuming = 5, [Fe/H] = and no alpha-element enhancement. Varying these
assumptions changes by less than 100 K. These results do
not support a large anomaly between observed and theoretical low-mass star
temperatures.Comment: 5 pages, 3 figures, published in MNRA
The EBLM Project I-Physical and orbital parameters, including spin-orbit angles, of two low-mass eclipsing binaries on opposite sides of the Brown Dwarf limit
This paper introduces a series of papers aiming to study the dozens of low
mass eclipsing binaries (EBLM), with F, G, K primaries, that have been
discovered in the course of the WASP survey. Our objects are mostly single-line
binaries whose eclipses have been detected by WASP and were initially followed
up as potential planetary transit candidates. These have bright primaries,
which facilitates spectroscopic observations during transit and allows the
study of the spin-orbit distribution of F, G, K+M eclipsing binaries through
the Rossiter-McLaughlin effect. Here we report on the spin-orbit angle of
WASP-30b, a transiting brown dwarf, and improve its orbital parameters. We also
present the mass, radius, spin-orbit angle and orbital parameters of a new
eclipsing binary, J1219-39b (1SWAPJ121921.03-395125.6, TYC 7760-484-1), which,
with a mass of 95 +/- 2 Mjup, is close to the limit between brown dwarfs and
stars. We find that both objects orbit in planes that appear aligned with their
primaries' equatorial planes. Neither primaries are synchronous. J1219-39b has
a modestly eccentric orbit and is in agreement with the theoretical
mass--radius relationship, whereas WASP-30b lies above it.Comment: 12 pages, 7 figures, data in appendices, submitted to A&A (taking in
account 1st referee report
The spin-orbit angles of the transiting exoplanets WASP-1b, WASP-24b, WASP-38b and HAT-P-8b from Rossiter-McLaughlin observations
We present observations of the Rossiter-McLaughlin effect for the transiting
exoplanet systems WASP-1, WASP-24, WASP-38 and HAT-P-8, and deduce the
orientations of the planetary orbits with respect to the host stars' rotation
axes. The planets WASP-24b, WASP-38b and HAT-P-8b appear to move in prograde
orbits and be well aligned, having sky-projected spin orbit angles consistent
with zero: {\lambda} = -4.7 \pm 4.0{\deg}, {\lambda} = 15 + 33{\deg}/-43{\deg}
and {\lambda} = -9.7 +9.0{\deg}/-7.7{\deg}, respectively. The host stars have
Teff < 6250 K and conform with the trend of cooler stars having low
obliquities. WASP-38b is a massive planet on a moderately long period,
eccentric orbit so may be expected to have a misaligned orbit given the high
obliquities measured in similar systems. However, we find no evidence for a
large spin-orbit angle. By contrast, WASP-1b joins the growing number of
misaligned systems and has an almost polar orbit, {\lambda} = -79
+4.5{\deg}/-4.3{\deg}. It is neither very massive, eccentric nor orbiting a hot
host star, and therefore does not share the properties of many other misaligned
systems.Comment: Submitted to MNRAS, 13 pages, 8 tables, 6 figures. Includes revised
parameter values for WASP-38 and HAT-P-
WASP-23b: a transiting hot Jupiter around a K dwarf and its Rossiter-McLaughlin effect
We report the discovery of a new transiting planet in the Southern
Hemisphere. It has been found by the WASP-south transit survey and confirmed
photometrically and spectroscopically by the 1.2m Swiss Euler telescope, LCOGT
2m Faulkes South Telescope, the 60 cm TRAPPIST telescope and the ESO 3.6m
telescope. The orbital period of the planet is 2.94 days. We find it is a gas
giant with a mass of 0.88 \pm 0.10 Mj and a radius estimated at 0.96 \pm 0.05
Rj . We have also obtained spectra during transit with the HARPS spectrograph
and detect the Rossiter-McLaughlin effect despite its small amplitude. Because
of the low signal to noise of the effect and of a small impact parameter we
cannot place a constraint on the projected spin-orbit angle. We find two
confiicting values for the stellar rotation. Our determination, via spectral
line broadening gives v sin I = 2.2 \pm 0.3 km/s, while another method, based
on the activity level using the index log R'HK, gives an equatorial rotation
velocity of only v = 1.35 \pm 0.20 km/s. Using these as priors in our analysis,
the planet could either be misaligned or aligned. This should send strong
warnings regarding the use of such priors. There is no evidence for
eccentricity nor of any radial velocity drift with time.Comment: 13 pages, 8 figures, 7 tables, accepted for publication in A&
Doppler tomography of transiting exoplanets: A prograde, low-inclined orbit for the hot Jupiter CoRoT-11b
We report the detection of the Doppler shadow of the transiting hot Jupiter
CoRoT-11b. Our analysis is based on line-profile tomography of time-series,
Keck/HIRES high-resolution spectra acquired during the transit of the planet.
We measured a sky-projected, spin-orbit angle of 0.1 +/- 2.6 degrees, which is
consistent with a very low-inclined orbit with respect to the stellar rotation
axis. We refined the physical parameters of the system using a Markov chain
Monte Carlo simultaneous fitting of the available photometric and spectroscopic
data. An analysis of the tidal evolution of the system shows how the currently
measured obliquity and its uncertainty translate into an initial absolute value
of less than about 10 degrees on the zero-age main sequence, for an expected
average modified tidal quality factor of the star Q'* > 4 x 10^6. This is
indicative of an inward migration scenario that would not have perturbed the
primordial low obliquity of CoRoT-11b. Taking into account the effective
temperature and mass of the planet host star (Teff=6440 K, M*=1.23 MSun), the
system can be considered a new telling exception to the recently proposed
trend, according to which relatively hot and massive stars (Teff>6250 K, M*>1.2
MSun) seem to be preferentially orbited by hot Jupiters with high obliquity.Comment: 5 pages, 4 figures, accepted for publication in A&A Letter
WASP-120b, WASP-122b and WASP-123b: Three newly discovered planets from the WASP-South survey
We present the discovery by the WASP-South survey of three planets transiting
moderately bright stars (V ~ 11). WASP-120b is a massive (5.0MJup) planet in a
3.6-day orbit that we find likely to be eccentric (e = 0.059+0.025-0.018)
around an F5 star. WASP-122b is a hot-Jupiter (1.37MJup, 1.79RJup) in a 1.7-day
orbit about a G4 star. Our predicted transit depth variation cause by the
atmosphere of WASP-122b suggests it is well suited to characterisation.
WASP-123b is a hot-Jupiter (0.92MJup, 1.33RJup) in a 3.0-day orbit around an
old (~ 7 Gyr) G5 star.Comment: 15 pages, 10 figures, 5 table
WASP-29b: A Saturn-sized transiting exoplanet
We report the discovery of a Saturn-sized planet transiting a V = 11.3, K4
dwarf star every 3.9 d. WASP-29b has a mass of 0.24+/-0.02 M_Jup and a radius
of 0.79+/-0.05 R_Jup, making it the smallest planet so far discovered by the
WASP survey, and the exoplanet most similar in mass and radius to Saturn. The
host star WASP-29 has an above-Solar metallicity and fits a possible
correlation for Saturn-mass planets such that planets with higher-metallicity
host stars have higher core masses and thus smaller radii.Comment: 6 pages, submitted to ApJ
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