42 research outputs found
A Low-Mass Pre-Main-Sequence Eclipsing Binary in Lower Centaurus Crux Discovered with TESS
We report the discovery of 2M1222-57 as a low-mass, pre-main-sequence (PMS)
eclipsing binary (EB) in the Lower Centaurus Crux (LCC) association for which,
using Gaia parallaxes and proper motions with a neural-net age estimator, we
determine an age of 16.22.2 Myr. The broadband spectral energy
distribution (SED) shows clear excess at ~10 um indicative of a circumbinary
disk, and new speckle-imaging observations reveal a faint, tertiary companion
separated by ~100 AU. H-alpha emission is modulated on the orbital period,
consistent with theoretical models of orbitally pulsed accretion streams
reaching from the inner disk edge to the central stars. From a joint analysis
of spectroscopically determined radial velocities and TESS light curves,
together with additional tight constraints provided by the SED and the Gaia
parallax, we measure masses for the eclipsing stars of 0.74 Msun and 0.67 Msun;
radii of 0.98 Rsun and 0.94 Rsun; and effective temperatures of 3750 K and 3645
K. The masses and radii of both stars are measured to an accuracy of ~1%. The
measured radii are inflated, and the temperatures suppressed, relative to
predictions of standard PMS evolutionary models at the age of LCC; also, the Li
abundances are ~2 dex less depleted than predicted by those models. However,
models that account for the global and internal effects of surface magnetic
fields are able to simultaneously reproduce the measured radii, temperatures,
and Li abundances at an age of 17.00.5 Myr. Altogether, the 2M1222-57
system presents very strong evidence that magnetic activity in young stars
alters both their global properties and the physics of their interiors.Comment: 23 pages, 19 figures, accepted by Ap
Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event
We report the lens mass and distance measurements of the nearby microlensing
event TCP J05074264+2447555. We measure the microlens parallax vector
using Spitzer and ground-based light curves with constraints on
the direction of lens-source relative proper motion derived from Very Large
Telescope Interferometer (VLTI) GRAVITY observations. Combining this
determination with the angular Einstein radius
measured by VLTI GRAVITY observations, we find that the lens is a star with
mass at a distance . We find that the blended light basically all comes from the lens.
The lens-source proper motion is , so with currently available adaptive-optics (AO) instruments,
the lens and source can be resolved in 2021. This is the first microlensing
event whose lens mass is unambiguously measured by interferometry + satellite
parallax observations, which opens a new window for mass measurements of
isolated objects such as stellar-mass black holes.Comment: 3 Figures and 6 Tables Submitted to AAS Journa
Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event
We report the lens mass and distance measurements of the nearby microlensing event TCP J05074264+2447555 (Kojima-1). We measure the microlens parallax vector Ï_E using Spitzer and ground-based light curves with constraints on the direction of lens-source relative proper motion derived from Very Large Telescope Interferometer (VLTI) GRAVITY observations. Combining this Ï_E determination with the angular Einstein radius Ξ_E measured by VLTI-GRAVITY observations, we find that the lens is a star with mass M_L = 0.495±0.063 Mâ at a distance D_L = 429 ± 21 pc. We find that the blended light basically all comes from the lens. The lens-source proper motion is Î_(rel,hel) = 26.55±0.36 mas yrâ»Âč, so with currently available adaptive-optics instruments, the lens and source can be resolved in 2021. This is the first microlensing event whose lens mass is unambiguously measured by interferometry + satellite-parallax observations, which opens a new window for mass measurements of isolated objects such as stellar-mass black holes
Validating AU Microscopii d with Transit Timing Variations
AU Mic is a young (22 Myr) nearby exoplanetary system that exhibits excess
TTVs that cannot be accounted for by the two known transiting planets nor
stellar activity. We present the statistical "validation" of the tentative
planet AU Mic d (even though there are examples of "confirmed" planets with
ambiguous orbital periods). We add 18 new transits and nine midpoint times in
an updated TTV analysis to prior work. We perform the joint modeling of transit
light curves using EXOFASTv2 and extract the transit midpoint times. Next, we
construct an O-C diagram and use Exo-Striker to model the TTVs. We generate TTV
log-likelihood periodograms to explore possible solutions for the period of
planet d and then follow those up with detailed TTV and RV MCMC modeling and
stability tests. We find several candidate periods for AU Mic d, all of which
are near resonances with AU Mic b and c of varying order. Based on our model
comparisons, the most-favored orbital period of AU Mic d is 12.73596+/-0.00793
days (T_{C,d}=2458340.55781+/-0.11641 BJD), which puts the three planets near a
4:6:9 mean-motion orbital resonance. The mass for d is 1.053+/-0.511 M_E,
making this planet Earth-like in mass. If confirmed, AU Mic d would be the
first known Earth-mass planet orbiting a young star and would provide a
valuable opportunity in probing a young terrestrial planet's atmosphere.
Additional TTV observation of the AU Mic system are needed to further constrain
the planetary masses, search for possible transits of AU Mic d, and detect
possible additional planets beyond AU Mic c.Comment: 89 pages, 35 figures, 34 tables. Redid EXOFASTv2 transit modeling to
recover more reasonable stellar posteriors, so redid Exo-Striker TTV modeling
for consistency. Despite these changes, the overall results remain unchanged:
the 12-7-day case is still the most favored. Submitted to AAS Journals on
2023 Feb 9t
KELT-22Ab: A Massive, Short-Period Hot Jupiter Transiting a Near-solar Twin
We present the discovery of KELT-22Ab, a hot Jupiter from the KELT-South survey. KELT-22Ab transits the moderately bright (V ⌠11.1) Sun-like G2V star TYC 7518-468-1. The planet has an orbital period of days, a radius of , and a relatively large mass of . The star has , , K, (cgs), and [m/H] = ; thus other than its slightly super-solar metallicity, it appears to be a near-solar twin. Surprisingly, KELT-22A exhibits kinematics and a Galactic orbit that are somewhat atypical for thin-disk stars. Nevertheless, the star is rotating rapidly for its estimated age, and shows evidence of chromospheric activity. Imaging reveals a slightly fainter companion to KELT-22A that is likely bound, with a projected separation of 6âł (âŒ1400 au). In addition to the orbital motion caused by the transiting planet, we detect a possible linear trend in the radial velocity of KELT-22A, suggesting the presence of another relatively nearby body that is perhaps non-stellar. KELT-22Ab is highly irradiated (as a consequence of the small semimajor axis of ), and is mildly inflated. At such small separations, tidal forces become significant. The configuration of this system is optimal for measuring the rate of tidal dissipation within the host star. Our models predict that, due to tidal forces, the semimajor axis is decreasing rapidly, and KELT-22Ab is predicted to spiral into the star within the next Gyr
Twinkle -- a small satellite spectroscopy mission for the next phase of exoplanet science
With a focus on off-the-shelf components, Twinkle is the first in a series of
cost competitive small satellites managed and financed by Blue Skies Space Ltd.
The satellite is based on a high-heritage Airbus platform that will carry a
0.45 m telescope and a spectrometer which will provide simultaneous wavelength
coverage from 0.5-4.5 . The spacecraft prime is Airbus Stevenage
while the telescope is being developed by Airbus Toulouse and the spectrometer
by ABB Canada. Scheduled to begin scientific operations in 2025, Twinkle will
sit in a thermally-stable, sun-synchronous, low-Earth orbit. The mission has a
designed operation lifetime of at least seven years and, during the first three
years of operation, will conduct two large-scale survey programmes: one focused
on Solar System objects and the other dedicated to extrasolar targets. Here we
present an overview of the architecture of the mission, refinements in the
design approach, and some of the key science themes of the extrasolar survey.Comment: Presented at SPIE Astronomical Telescopes & Instrumentation 202
Validating AU Microscopii d with Transit Timing Variations
AU Mic is a young (22 Myr), nearby exoplanetary system that exhibits excess transit timing variations (TTVs) that cannot be accounted for by the two known transiting planets nor stellar activity. We present the statistical âvalidationâ of the tentative planet AU Mic d (even though there are examples of âconfirmedâ planets with ambiguous orbital periods). We add 18 new transits and nine midpoint times in an updated TTV analysis to prior work. We perform the joint modeling of transit light curves using EXOFASTv2 and extract the transit midpoint times. Next, we construct an O â C diagram and use Exo-Striker to model the TTVs. We generate TTV log-likelihood periodograms to explore possible solutions for dâs period, then follow those up with detailed TTV and radial velocity Markov Chain Monte Carlo modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, the most-favored orbital period of AU Mic d is 12.73596 ± 0.00793 days ( T _C _,d = 2458340.55781 ± 0.11641 BJD), which puts the three planets near 4:6:9 mean-motion resonance. The mass for d is 1.053 ± 0.511 M _â , making this planet Earth-like in mass. If confirmed, AU Mic d would be the first known Earth-mass planet orbiting a young star and would provide a valuable opportunity in probing a young terrestrial planetâs atmosphere. Additional TTV observations of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c