353 research outputs found
Non-detection of Contamination by Stellar Activity in the Spitzer Transit Light Curves of TRAPPIST-1
We apply the transit light curve self-contamination technique of Morris et
al. (2018) to search for the effect of stellar activity on the transits of the
ultracool dwarf TRAPPIST-1 with 2018 Spitzer photometry. The self-contamination
method fits the transit light curves of planets orbiting spotted stars,
allowing the host star to be a source of contaminating positive or negative
flux which influences the transit depths but not the ingress/egress durations.
We find that none of the planets show statistically significant evidence for
self-contamination by bright or dark regions of the stellar photosphere.
However, we show that small-scale magnetic activity, analogous in size to the
smallest sunspots, could still be lurking in the transit photometry undetected.Comment: Accepted for publication in ApJ
WISE J072003.20-084651.2: An Old and Active M9.5 + T5 Spectral Binary 6 pc from the Sun
[Abridged] We report observations of the recently discovered, nearby late-M
dwarf WISE J072003.20-084651.2. Astrometric measurements obtained with TRAPPIST
improve the distance measurement to 6.01.0 pc and confirm the low
tangential velocity (3.50.6 km/s) reported by Scholz. Low-resolution
optical spectroscopy indicates a spectral type of M9.5 and prominent H
emission ( = -4.680.06), but no evidence of subsolar
metallicity or Li I absorption. Near-infrared spectroscopy reveals subtle
peculiarities indicating the presence of a T5 binary companion, and
high-resolution laser guide star adaptive optics imaging reveals a faint
(H = 4.1) candidate source 0"14 (0.8 AU) from the primary. We measure a
stable radial velocity of +83.80.3 km/s, indicative of old disk kinematics
and consistent with the angular separation of the possible companion. We
measure a projected rotational velocity of v sin i = 8.00.5 km/s, and find
evidence of low-level variability (~1.5%) in a 13-day TRAPPIST lightcurve, but
cannot robustly constrain the rotational period. We also observe episodic
changes in brightness (1-2%) and occasional flare bursts (4-8%) with a 0.8%
duty cycle, and order-of-magnitude variations in H line strength.
Combined, these observations reveal WISE J0720-0846 to be an old, very low-mass
binary whose components straddle the hydrogen burning minimum mass, and whose
primary is a relatively rapid rotator and magnetically active. It is one of
only two known binaries among late M dwarfs within 10 pc of the Sun, both
harboring a mid T-type brown dwarf companion. While this specific configuration
is rare (1.4% probability), roughly 25% of binary companions to late-type M
dwarfs in the local population are likely low-temperature T or Y brown dwarfs.Comment: 18 pages, 23 figures; accepted for publication in A
A Monitoring Campaign for Luhman 16AB. I. Detection of Resolved Near-Infrared Spectroscopic Variability
[abbreviated] We report resolved near-infrared spectroscopic monitoring of
the nearby L dwarf/T dwarf binary WISE J104915.57-531906.1AB (Luhman 16AB), as
part of a broader campaign to characterize the spectral energy distribution and
temporal variability of this system. A continuous 45-minute sequence of
low-resolution IRTF/SpeX data spanning 0.8-2.4 micron were obtained, concurrent
with combined-light optical photometry with ESO/TRAPPIST. Our spectral
observations confirm the flux reversal of this binary, and we detect a
wavelength-dependent decline in the relative spectral fluxes of the two
components coincident with a decline in the combined-light optical brightness
of the system over the course of the observation. These data are successfully
modeled as a combination of brightness and color variability in the T0.5 Luhman
16B, consistent cloud variations; and no significant variability in L7.5 Luhman
16A. We estimate a peak-to-peak amplitude of 13.5% at 1.25 micron over the full
lightcurve. Using a two-spot brightness temperature model, we infer an average
cloud covering fraction of ~30-55% for Luhman 16B, varying by 15-30% over a
rotation period. A Rhines scale interpretation for the size of the variable
features explains an apparent correlation between period and amplitude for
three highly variable T dwarfs, and predicts relatively fast winds (1-3 km/s)
for Luhman 16B consistent with lightcurve evolution on an advective time scale
(1-3 rotation periods). Our observations support the model of a patchy
disruption of the mineral cloud layer as a universal feature of the L dwarf/T
dwarf transition.Comment: 11 pages, 7 figures; accepted for publication in Astrophysical
Journa
Ground-based follow-up observations of TRAPPIST-1 transits in the near-infrared
The TRAPPIST-1 planetary system is a favorable target for the atmospheric
characterization of temperate earth-sized exoplanets by means of transmission
spectroscopy with the forthcoming James Webb Space Telescope (JWST). A possible
obstacle to this technique could come from the photospheric heterogeneity of
the host star that could affect planetary signatures in the transit
transmission spectra. To constrain further this possibility, we gathered an
extensive photometric data set of 25 TRAPPIST-1 transits observed in the
near-IR J band (1.2 m) with the UKIRT and the AAT, and in the NB2090 band
(2.1 m) with the VLT during the period 2015-2018. In our analysis of these
data, we used a special strategy aiming to ensure uniformity in our
measurements and robustness in our conclusions. We reach a photometric
precision of (RMS of the residuals), and we detect no significant
temporal variations of transit depths of TRAPPIST-1 b, c, e, and g over the
period of three years. The few transit depths measured for planets d and f hint
towards some level of variability, but more measurements will be required for
confirmation. Our depth measurements for planets b and c disagree with the
stellar contamination spectra originating from the possible existence of bright
spots of temperature 4500 K. We report updated transmission spectra for the six
inner planets of the system which are globally flat for planets b and g and
some structures are seen for planets c, d, e, and f.Comment: accepted for publication in MNRA
A low-density hot Jupiter in a near-aligned, 4.5-day orbit around a = 10.8, F5V star
We report the independent discovery and characterisation of a hot Jupiter in
a 4.5-d, transiting orbit around the star TYC 7282-1298-1 ( = 10.8, F5V).
The planet has been pursued by the NGTS team as NGTS-2b and by ourselves as
WASP-179b. We characterised the system using a combination of photometry from
WASP-South and TRAPPIST-South, and spectra from CORALIE (around the orbit) and
HARPS (through the transit). We find the planet's orbit to be nearly aligned
with its star's spin. From a detection of the Rossiter-McLaughlin effect, we
measure a projected stellar obliquity of . From
line-profile tomography of the same spectra, we measure . We find the planet to have a low density ( = 0.67
0.09 , = 1.54 0.06 ), which, along
with its moderately bright host star, makes it a good target for transmission
spectroscopy. We find a lower stellar mass ( = )
than reported by the NGTS team ( = ), though the
difference is only .Comment: Submitted to AJ. 9 pages, 6 figures, 5 table
Transiting hot Jupiters from WASP-South, Euler and TRAPPIST : WASP-95b to WASP-101b
We report the discovery of the transiting exoplanets WASP-95b, WASP-96b, WASP-97b, WASP-98b, WASP-99b, WASP-100b andWASP-101b. All are hot Jupiters with orbital periods in the range 2.1-5.7 d, masses of 0.5-2.8 MJup and radii of 1.1-1.4 RJup. The orbits of all the planets are compatible with zero eccentricity. WASP-99b produces the shallowest transit yet found by WASP-South, at 0.4 per cent. The host stars are of spectral type F2-G8. Five have metallicities of [Fe/H] from -0.03 to +0.23, while WASP-98 has a metallicity of -0.60, exceptionally low for a star with a transiting exoplanet. Five of the host stars are brighter than V = 10.8, which significantly extends the number of bright transiting systems available for follow-up studies. WASP-95 shows a possible rotational modulation at a period of 20.7 d. We discuss the completeness of WASP survey techniques by comparing to the HATnet project.Publisher PDFPeer reviewe
A full transit of v2 Lupi d and the search for an exomoon in its Hill sphere with CHEOPS
The planetary system around the naked-eye star v2 Lupi (HD 136352; TOI-2011) is composed of three exoplanets with masses of 4.7, 11.2, and 8.6 Earth masses (M⊕). The TESS and CHEOPS missions revealed that all three planets are transiting and have radii straddling the radius gap separating volatile-rich and volatile-poor super-earths. Only a partial transit of planet d had been covered so we re-observed an inferior conjunction of the long-period 8.6 M⊕ exoplanet v2 Lup d with the CHEOPS space telescope. We confirmed its transiting nature by covering its whole 9.1 h transit for the first time. We refined the planet transit ephemeris to P = 107.1361−0.0022+0.0019 days and Tc = 2459009.7759−0.0096+0.0101 BJDTDB, improving by ~40 times on the previously reported transit timing uncertainty. This refined ephemeris will enable further follow-up of this outstanding long-period transiting planet to search for atmospheric signatures or explore the planet’s Hill sphere in search for an exomoon. In fact, the CHEOPS observations also cover the transit of a large fraction of the planet’s Hill sphere, which is as large as the Earth’s, opening the tantalising possibility of catching transiting exomoons. We conducted a search for exomoon signals in this single-epoch light curve but found no conclusive photometric signature of additional transiting bodies larger than Mars. Yet, only a sustained follow-up of v2 Lup d transits will warrant a comprehensive search for a moon around this outstanding exoplanet
WASP-157b, a Transiting Hot Jupiter Observed with K2
We announce the discovery of the transiting hot Jupiter WASP-157b in a 3.95-d
orbit around a V = 12.9 G2 main-sequence star. This moderately inflated planet
has a Saturn-like density with a mass of M and a
radius of R. We do not detect any rotational or
phase-curve modulations, nor the secondary eclipse, with conservative
semi-amplitude upper limits of 250 and 20 ppm, respectively.Comment: 6 pages, 5 figures and 4 tables. Accepted for publication in PAS
- …