ABSTRACT
We present a photometric characterization of 208 ultra-cool dwarfs (UCDs) with spectral types between M4 and L4, from 20-s and 2-min cadence TESS light curves. We determine rotation periods ...for 87 objects ($\sim 42~{{\ \rm per\ cent}}$) and identify 778 flare events in 103 UCDs ($\sim 49.5~{{\ \rm per\ cent}}$). For 777 flaring events (corresponding to 102 objects), we derive bolometric energies between 2.1 × 1030 and $1.1 \times 10^{34}\ \mathrm{erg}$, with 56 superflare events. No transiting planets or eclipsing binaries were identified. We find that the fraction of UCDs with rotation and flaring activity is, at least, 20 per cent higher in M4–M6 spectral types than in later UCDs (M7–L4). For spectral types between M4 and L0, we measure the slope of the flare bolometric energy–duration correlation to be γ = 0.497 ± 0.058, which agrees with that found in previous studies for solar-type and M dwarfs. Moreover, we determine the slope of the flare frequency distribution to be α = −1.75 ± 0.04 for M4–M5 dwarfs, α = −1.69 ± 0.04 and α = −1.72 ± 0.1 for M6–M7 and M8–L0 dwarfs, respectively, which are consistent with previous works that exclusively analysed UCDs. These results support the idea that independently of the physical mechanisms that produce magnetic activity, the characteristics of the rotational modulation and flares are similar for both fully convective UCDs and partially convective solar-type and early-M stars. Based on the measured UCD flare distributions, we find that ultraviolet radiation emitted from flares does not have the potential to start prebiotic chemistry.
Abstract
The transit timing variations method is currently the most successful method to determine dynamical masses and orbital elements for Earth-sized transiting planets. Precise mass determination ...is fundamental to restrict planetary densities and thus infer planetary compositions. In this work, we present
Nauyaca
, a Python package dedicated to finding planetary masses and orbital elements through the fitting of observed midtransit times from an
N
-body approach. The fitting strategy consists of performing a sequence of minimization algorithms (optimizers) that are used to identify high probability regions in the parameter space. These results from optimizers are used for initialization of a Markov chain Monte Carlo method, using an adaptive Parallel-Tempering algorithm. A set of runs are performed in order to obtain posterior distributions of planetary masses and orbital elements. In order to test the tool, we created a mock catalog of synthetic planetary systems with different numbers of planets where all of them transit. We calculate their midtransit times to give them as an input to
Nauyaca
, testing statistically its efficiency in recovering the planetary parameters from the catalog. For the recovered planets, we find typical dispersions around the real values of ∼1–14
M
⊕
for masses, between 10–110 s for periods, and between ∼0.01–0.03 for eccentricities. We also investigate the effects of the signal-to-noise ratio and number of transits on the correct determination of the planetary parameters. Finally, we suggest choices of the parameters that govern the tool for the usage with real planets, according to the complexity of the problem and computational facilities.
The EBLM Project Triaud, Amaury H. M. J.; Martin, David V.; Ségransan, Damien ...
Astronomy and astrophysics (Berlin),
12/2017, Letnik:
608
Journal Article
ABSTRACT
We present the discovery of TOI-2136 b, a sub-Neptune planet transiting a nearby M4.5V-type star every 7.85 d, identified through photometric measurements from the Transiting Exoplanet ...Survey Satellite (TESS) mission. The host star is located 33 pc away with a radius of R* = 0.34 ± 0.02 R⊙, a mass of $0.34\pm 0.02 \, \mathrm{M}_{\odot }$, and an effective temperature of 3342 ± 100 K. We estimate its stellar rotation period to be 75 ± 5 d based on archival long-term photometry. We confirm and characterize the planet based on a series of ground-based multiwavelength photometry, high-angular-resolution imaging observations, and precise radial velocities from Canada–France–Hawaii Telescope (CFHT)/SpectroPolarimètre InfraROUge (SPIRou). Our joint analysis reveals that the planet has a radius of 2.20 ± 0.17 R⊕ and a mass of 6.4 ± 2.4 M⊕. The mass and radius of TOI-2136 b are consistent with a broad range of compositions, from water-ice to gas-dominated worlds. TOI-2136 b falls close to the radius valley for M dwarfs predicted by thermally driven atmospheric mass-loss models, making it an interesting target for future studies of its interior structure and atmospheric properties.
The EBLM project von Boetticher, Alexander; Triaud, Amaury H. M. J.; Queloz, Didier ...
Astronomy and astrophysics (Berlin),
8/2017, Letnik:
604
Journal Article, Web Resource
Recenzirano
Odprti dostop
We report the discovery of an eclipsing binary system with mass-ratio q ˜ 0.07. After identifying a periodic photometric signal received by WASP, we obtained CORALIE spectroscopic radial velocities ...and follow-up light curves with the Euler and TRAPPIST telescopes. From a joint fit of these data we determine that EBLM J0555-57 consists of a sun-like primary star that is eclipsed by a low-mass companion, on a weakly eccentric 7.8-day orbit. Using a mass estimate for the primary star derived from stellar models, we determine a companion mass of 85 ± 4 MSUBJup/SUB (0.081 MSUB⊙/SUB) and a radius of 0.84SUP+ 0.14/SUPSUB-0.04/SUBRSUBJup/SUB (0.084 RSUB⊙/SUB) that is comparable to that of Saturn. EBLM J0555-57Ab has a surface gravity log gSUB2/SUB =5.50SUP+ 0.03/SUPSUB-0.13/SUB and is one of the densest non-stellar-remnant objects currently known. These measurements are consistent with models of low-mass stars. The photometry tables and radial velocities are only available at the CDS and on demand via anonymous ftp to http://cdsarc.u-strasbg.fr ( http://130.79.128.5 ) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/604/L6
Parenago 1802, a member of the ~1 Myr Orion Nebula Cluster, is a double-lined, detached eclipsing binary in a 4.674 day orbit, with equal-mass components. Here we present extensive VICJHKS light ...curves (LCs) spanning ~15 yr, as well as a Keck/High Resolution Echelle Spectrometer (HIRES) optical spectrum. The LCs evince a third light source that is variable with a period of 0.73 days, and is also manifested in the high-resolution spectrum, strongly indicating the presence of a third star in the system, probably a rapidly rotating Classical T Tauri star. We incorporate this third light into our radial velocity and LC modeling of the eclipsing pair, measuring accurate masses, radii, and temperature ratio. We find that tidal heating effects can explain the observed luminosity difference of the eclipsing pair, providing an alternative to the previously suggested age difference.
ABSTRACT
A new generation of observatories is enabling detailed study of exoplanetary atmospheres and the diversity of alien climates, allowing us to seek evidence for extraterrestrial biological and ...geological processes. Now is therefore the time to identify the most unique planets to be characterized with these instruments. In this context, we report on the discovery and validation of TOI-715 b, a $R_{\rm b}=1.55\pm 0.06\rm R_{\oplus }$ planet orbiting its nearby (42 pc) M4 host (TOI-715/TIC 271971130) with a period $P_{\rm b} = 19.288004_{-0.000024}^{+0.000027}$ d. TOI-715 b was first identified by TESS and validated using ground-based photometry, high-resolution imaging and statistical validation. The planet’s orbital period combined with the stellar effective temperature $T_{\rm eff}=3075\pm 75~\rm K$ give this planet an installation $S_{\rm b} = 0.67_{-0.20}^{+0.15}~\rm S_\oplus$, placing it within the most conservative definitions of the habitable zone for rocky planets. TOI-715 b’s radius falls exactly between two measured locations of the M-dwarf radius valley; characterizing its mass and composition will help understand the true nature of the radius valley for low-mass stars. We demonstrate TOI-715 b is amenable for characterization using precise radial velocities and transmission spectroscopy. Additionally, we reveal a second candidate planet in the system, TIC 271971130.02, with a potential orbital period of $P_{02} = 25.60712_{-0.00036}^{+0.00031}$ d and a radius of $R_{02} = 1.066\pm 0.092\, \rm R_{\oplus }$, just inside the outer boundary of the habitable zone, and near a 4:3 orbital period commensurability. Should this second planet be confirmed, it would represent the smallest habitable zone planet discovered by TESS to date.
Close Companions around Young Stars Kounkel, Marina; Covey, Kevin; Moe, Maxwell ...
The Astronomical journal,
05/2019, Letnik:
157, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Multiplicity is a fundamental property that is set early during stellar lifetimes, and it is a stringent probe of the physics of star formation. The distribution of close companions around young ...stars is still poorly constrained by observations. We present an analysis of stellar multiplicity derived from Apache Point Observatory Galactic Evolution Experiment-2 spectra obtained in targeted observations of nearby star-forming regions. This is the largest homogeneously observed sample of high-resolution spectra of young stars. We developed an autonomous method to identify double-lined spectroscopic binaries (SB2s). Out of 5007 sources spanning the mass range of ∼0.05-1.5 M , we find 399 binaries, including both radial velocity (RV) variables and SB2s. The mass ratio distribution of SB2s is consistent with being uniform for q < 0.95 with an excess of twins for q > 0.95. The period distribution is consistent with what has been observed in close binaries (<10 au) in the evolved populations. Three systems are found to have q ∼ 0.1, with a companion located within the brown dwarf desert. There are no strong trends in the multiplicity fraction as a function of cluster age from 1 to 100 Myr. There is a weak dependence on stellar density, with companions being most numerous at * ∼ 30 stars/pc−2 and decreasing in more diffuse regions. Finally, disk-bearing sources are deficient in SB2s (but not RV variables) by a factor of ∼2; this deficit is recovered by the systems without disks. This may indicate a quick dispersal of disk material in short-period equal-mass systems that is less effective in binaries with lower q.
Abstract
The use of high-resolution, high signal-to-noise stellar spectra is essential in order to determine the most accurate and precise stellar atmospheric parameters via spectroscopy. This is ...particularly important for determining the fundamental parameters of exoplanets, which directly depend on the stellar properties. However, different techniques can be implemented when analysing these spectra which will influence the results. These include performing an abundance analysis relative to the solar values in order to negate uncertainties in atomic data, and fixing the surface gravity (log g) to an external value such as those from asteroseismology. The choice of lines used will also influence the results. In this paper, we investigate differential analysis and fixing log g for a set of FGK stars that already have accurate fundamental parameters known from external methods. We find that a differential line list gives slightly more accurate parameters compared to a laboratory line list; however, the laboratory line list still gives robust parameters. We also find that fixing the log g does not improve the spectroscopic parameters. We investigate the effects of line selection on the stellar parameters and find that the choice of lines used can have a significant effect on the parameters. In particular, removal of certain low excitation potential lines can change the T
eff by up to 50 K. For future HoSTS papers we will use the differential line list with a solar microturbulence value of 1 km s−1, and we will not fix the log g to an external value.
Abstract
Wide binary stars with similar components hosting planets provide a favorable opportunity for exploring the star–planet chemical connection. We perform a detailed characterization of the ...solar-type stars in the WASP-160 binary system. No planet has been reported yet around WASP-160A, while WASP-160B is known to host a transiting Saturn-mass planet, WASP-160B b. For this planet, we also derive updated properties from both literature and new observations. Furthermore, using TESS photometry, we constrain the presence of transiting planets around WASP-160A and additional ones around WASP-160B. The stellar characterization includes, for the first time, the computation of high-precision differential atmospheric and chemical abundances of 25 elements based on high-quality Gemini-GRACES spectra. Our analysis reveals evidence of a correlation between the differential abundances and the condensation temperatures of the elements. In particular, we find both a small but significant deficit of volatiles and an enhancement of refractory elements in WASP-160B relative to WASP-160A. After WASP-94, this is the second stellar pair among the shortlist of planet-hosting binaries showing this kind of peculiar chemical pattern. Although we discuss several plausible planet formation and evolution scenarios for WASP-160A and B that could explain the observed chemical pattern, none of them can be conclusively accepted or rejected. Future high-precision photometric and spectroscopic follow-up, as well as high-contrast imaging observations, of WASP-160A and B might provide further constraints on the real origin of the detected chemical differences.
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