290 research outputs found
New brown dwarfs in Upper Sco using UKIDSS Galactic Cluster Survey science verification data
No full textIndi Ba, Bb: a detailed study of the nearest known brown dwarfs
No full textThe discovery of ε Indi A, Bb, a binary brown dwarf system very close to the Sun, makes possible a concerted campaign to characterise the physical parameters of two T dwarfs. Recent
observations suggest substellar atmospheric and evolutionary models may be inconsistent with observations, but there have been few conclusive tests to date. We therefore aim to characterise these benchmark brown dwarfs to place constraints on such models. We have obtained high angular resolution optical, near-infrared, and thermal-infrared imaging and medium-resolution (up to R ~ 5000) spectroscopy of ε Indi A, Bb with the ESO VLT and present VRIzJHKL'M' broad-band photometry and 0.63-5.1 spectroscopy of the individual components. The photometry and spectroscopy of the two partially blended sources were extracted
with a custom algorithm. Furthermore, we use deep AO-imaging to place upper limits on the (model-dependent) mass of any further system members. We derive luminosities of log = -4.699 ± 0.017 and -5.232 ± 0.020 for ε Indi A, Bb, respectively, and using the dynamical system mass and COND03 evolutionary models predict a system age of 3.7-4.3 Gyr, in excess of previous estimates and recent predictions from observations of these brown dwarfs. Moreover, the effective temperatures of 1352-1385 K and 976-1011 K predicted from the COND03
evolutionary models, for ε Indi A and Bb respectively, are in disagreement with those derived from the comparison of our data with the BT-Settl atmospheric models where we find effective temperatures of 1300-1340 K and 880-940 K, for ε Indi A and Bb respectively, with surface gravities of log g = 5.25 and 5.50. Finally, we show that spectroscopically determined effective temperatures and surface gravities for ultra-cool dwarfs can lead to underestimated masses even where precise luminosity constraints are available
Brown dwarfs in wide-field surveys
No full textIn this invited talk, I briefly summarise early photometric and proper motion surveys carried out in the nearest and youngest open clusters to introduce the motivation behind the Galactic Cluster component of the UKIRT Infrared Deep Sky Survey. Afterwards, I focus on the latest results that we obtained in the Upper Sco association and in the Pleiades. To finish, I show a comparison of the luminosity and mass functions obtained in the Upper Sco association, the Pleiades cluster, and σ Orionis from the homogeneous set of data publicly available from the Galactic Clusters Survey
TOI-1201 b: A mini-Neptune transiting a bright and moderately young M dwarf
No full textWe present the discovery of a transiting mini-Neptune around TOI-1201, a relatively bright and moderately young early M dwarf ( J ≈ 9.5 mag, ~600–800 Myr) in an equal-mass ~8 arcsecond-wide binary system, using data from the Transiting Exoplanet Survey Satellite, along with follow-up transit observations. With an orbital period of 2.49 d, TOI-1201 b is a warm mini-Neptune with a radius of R b = 2.415 ± 0.090 R ⊕ . This signal is also present in the precise radial velocity measurements from CARMENES, confirming the existence of the planet and providing a planetary mass of M b = 6.28 ± 0.88 M ⊕ and, thus, an estimated bulk density of 2.45 −0.42 +0.48 g cm −3 . The spectroscopic observations additionally show evidence of a signal with a period of 19 d and a long periodic variation of undetermined origin. In combination with ground-based photometric monitoring from WASP-South and ASAS-SN, we attribute the 19 d signal to the stellar rotation period ( P rot = 19–23 d), although we cannot rule out that the variation seen in photometry belongs to the visually close binary companion. We calculate precise stellar parameters for both TOI-1201 and its companion. The transiting planet is anexcellent target for atmosphere characterization (the transmission spectroscopy metric is 97 −16 +21 ) with the upcoming James Webb Space Telescope. It is also feasible to measure its spin-orbit alignment via the Rossiter-McLaughlin effect using current state-of-the-art spectrographs with submeter per second radial velocity precision.We present the discovery of a transiting mini-Neptune around TOI-1201, a relatively bright and moderately young early M dwarf ( J ≈ 9.5 mag, ~600–800 Myr) in an equal-mass ~8 arcsecond-wide binary system, using data from the Transiting Exoplanet Survey Satellite, along with follow-up transit observations. With an orbital period of 2.49 d, TOI-1201 b is a warm mini-Neptune with a radius of R b = 2.415 ± 0.090 R ⊕ . This signal is also present in the precise radial velocity measurements from CARMENES, confirming the existence of the planet and providing a planetary mass of M b = 6.28 ± 0.88 M ⊕ and, thus, an estimated bulk density of 2.45 −0.42 +0.48 g cm −3 . The spectroscopic observations additionally show evidence of a signal with a period of 19 d and a long periodic variation of undetermined origin. In combination with ground-based photometric monitoring from WASP-South and ASAS-SN, we attribute the 19 d signal to the stellar rotation period ( P rot = 19–23 d), although we cannot rule out that the variation seen in photometry belongs to the visually close binary companion. We calculate precise stellar parameters for both TOI-1201 and its companion. The transiting planet is anexcellent target for atmosphere characterization (the transmission spectroscopy metric is 97 −16 +21 ) with the upcoming James Webb Space Telescope. It is also feasible to measure its spin-orbit alignment via the Rossiter-McLaughlin effect using current state-of-the-art spectrographs with submeter per second radial velocity precision
TOI-1801 b: A temperate mini-Neptune around a young M0.5 dwarf
No full textWe report the discovery, mass, and radius determination of TOI-1801 b, a temperate mini-Neptune around a young M dwarf. TOI-1801 b was observed in TESS sectors 22 and 49, and the alert that this was a TESS planet candidate with a period of 21.3 days went out in April 2020. However, ground-based follow-up observations, including seeing-limited photometry in and outside transit together with precise radial velocity (RV) measurements with CARMENES and HIRES revealed that the true period of the planet is 10.6 days. These observations also allowed us to retrieve a mass of 5.74 ± 1.46
M
⊕
, which together with a radius of 2.08 ± 0.12
R
⊕
, means that TOI-1801 b is most probably composed of water and rock, with an upper limit of 2% by mass of H
2
in its atmosphere. The stellar rotation period of 16 days is readily detectable in our RV time series and in the ground-based photometry. We derived a likely age of 600–800 Myr for the parent star TOI-1801, which means that TOI-1801 b is the least massive young mini-Neptune with precise mass and radius determinations. Our results suggest that if TOI-1801 b had a larger atmosphere in the past, it must have been removed by some evolutionary mechanism on timescales shorter than 1 Gyr
Revisiting the dynamical masses of the transiting planets in the young AU Mic system: Potential AU Mic b inflation at ~20 Myr
No full textContext . Understanding planet formation is important in the context of the origin of planetary systems in general and of the Solar System in particular, as well as to predict the likelihood of finding Jupiter, Neptune, and Earth analogues around other stars. Aims . We aim to precisely determine the radii and dynamical masses of transiting planets orbiting the young M star AU Mic using public photometric and spectroscopic datasets. Methods . We performed a joint fit analysis of the TESS and CHEOPS light curves and more than 400 high-resolution spectra collected with several telescopes and instruments. We characterise the stellar activity and physical properties (radius, mass, density) of the transiting planets in the young AU Mic system through joint transit and radial velocity fits with Gaussian processes. Results . We determine a radius of R p b = 4.79 ± 0.29 R ⊕ , a mass of M p b = 9.0 ± 2.7 M ⊕ , and a bulk density of ρ p b = 0.49 ± 0.16 g cm −3 for the innermost transiting planet AU Mic b. For the second known transiting planet, AU Mic c, we infer a radius of R p c = 2.79 ± 0.18 R ⊕ , a mass of M p c = 14.5 ± 3.4 M ⊕ , and a bulk density of ρ p c = 3.90 ± 1.17 g cm −3 . According to theoretical models, AU Mic b may harbour an H 2 envelope larger than 5% by mass, with a fraction of rock and a fraction of water. AU Mic c could be made of rock and/or water and may have an H 2 atmosphere comprising at most 5% of its mass. AU Mic b has retained most of its atmosphere but might lose it over tens of millions of years due to the strong stellar radiation, while AU Mic c likely suffers much less photo-evaporation because it lies at a larger separation from its host. Using all the datasets in hand, we determine a 3σ upper mass limit of M p [d] sin i = 8.6 M ⊕ for the AU Mic’d’ TTV-candidate. In addition, we do not confirm the recently proposed existence of the planet candidate AU Mic ’e’ with an orbital period of 33.4 days. We investigated the level of the radial velocity variations and show that it is lower at longer wavelength with smaller changes from one observational campaign to another
Exploring the lower mass function in the young open cluster IC 4665
No full textWe present a study of the young (30-100 Myr) open cluster IC 4665 with the aim to determine the shape of the mass function well into the brown dwarf regime. We photometrically select 691 low-mass stellar and 94 brown dwarf candidate members over an area of 3.82 square degrees centred on the cluster. K-band follow-up photometry and Two-Micron All-Sky Survey data allow a first filtering of contaminant objects from our catalogues. A second filtering is performed for the brightest stars using proper motion data provided by the Tycho-2 and UCAC2 public catalogues. Contamination by the field population for the lowest mass objects is estimated using same latitude control fields. We fit observed surface densities of various cluster populations with King profiles and find a consistent tidal radius of 1.0°. The presence of possible mass segregation is discussed. In most respects investigated, IC 4665 is similar to other young open clusters at this age: (1) a power law fit to the mass function between 1 and 0.04 M⊙ results in best fit for a slope of -0.6; (2) a cusp in the mass function is noticed at about the substellar boundary with respect to the power law description, the interpretation of which is discussed; (3) a fraction between 10-19% for BDs with M ⪆ 0.03 M⊙ to total members; (4) a best-fit lognormal function to the full mass distribution shows an average member mass of 0.32 M⊙, if IC 4665 has an age of 50 Myr
Dynamical masses of two young transiting sub-Neptunes orbiting HD 63433
No full textContext. Although the number of exoplanets reported in the literature exceeds 5000 so far, only a few dozen of them are young planets (≤900 Myr). However, a complete characterization of these young planets is key to understanding the current properties of the entire population. Hence, it is necessary to constrain the planetary formation processes and the timescales of dynamical evolution by measuring the masses of exoplanets transiting young stars.
Aims. We characterize and measure the masses of two transiting planets orbiting the 400 Myr old solar-type star HD 63433, which is a member of the Ursa Major moving group.
Methods. We analysed precise photometric light curves of five sectors of the TESS mission with a baseline of ~750 days and obtained ~150 precise radial velocity measurements with the visible and infrared arms of the CARMENES instrument at the Calar Alto 3.5 m telescope in two different campaigns of ~500 days. We performed a combined photometric and spectroscopic analysis to retrieve the planetary properties of two young planets. The strong stellar activity signal was modelled by Gaussian regression processes. Results. We have updated the transit parameters of HD 63433 b and c and obtained planet radii of Rpb = 2.140 ± 0.087 R⊕ and Rpc = 2.692 ± 0.108 R⊕. Our analysis allowed us to determine the dynamical mass of the outer planet with a 4σ significance (Mpc = 15.54 ± 3.86 M⊕) and set an upper limit on the mass of the inner planet at 3σ (Mpb < 21.76 M⊕). According to theoretical models, both planets are expected to be sub-Neptunes, whose interiors mostly consist of silicates and water with no dominant composition of iron, and whose gas envelopes are lower than 2% in the case of HD 63433 c. The envelope is unconstrained in HD 63433 b
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