The relationship between luminosity and mass is of fundamental importance for direct imaging studies of brown dwarf and planetary companions to stars. In principle this can be inferred from ...theoretical mass-luminosity models; however, these relations have not yet been thoroughly calibrated, since there is a lack of substellar companions for which both the brightness and mass have been directly measured. One notable exception is GJ 758 B, a brown dwarf companion in a ~20 AU orbit around a nearby Sun-like star, which has been both directly imaged and dynamically detected through a radial velocity trend in the primary. This has enabled a mass constraint for GJ 758 B of 42+19−7 MJup 42 − 7 + 19 M Jup $ 42_{-7}^{+19}M_\mathrm{Jup} $ . Here, we note that Gaia is ideally suited for further constraining the mass of intermediate-separation companions such as GJ 758 B. A study of the differential proper motion, Δμ, with regards to HIPPARCOS is particularly useful in this context, as it provides a long time baseline for orbital curvature to occur. By exploiting already determined orbital parameters, we show that the dynamical mass can be further constrained to 42.4+5.6−5.0 MJup 42.4 − 5.0 + 5.6 M Jup $ 42.4_{-5.0}^{+5.6}M_\mathrm{Jup} $ through the Gaia-HIPPARCOS Δμ motion. We compare the new dynamical mass estimate with substellar evolutionary models and confirm previous indications that there is significant tension between the isochronal ages of the star and companion, with a preferred stellar age of ≤5 Gyr while the companion is only consistent with very old ages of ≥8 Gyr.
Abstract
The determination of the astrophysical properties of stars remains challenging and frequently relies on the application of stellar models. Stellar sequences in nearby open clusters provide ...some of the best means to test and calibrate stellar evolutionary models and isochrones and to use these models to assign astrophysical properties consistently to a large sample of stars. We aim at updating the single-star sequence of the members of the Hyades cluster, identifying the best-fitting isochrones, and determining the astrophysical properties of the stars. The Gaia Catalog of Nearby Stars provides a comprehensive sample of high-probability members of the Hyades cluster. We apply a multistep method to flag photometric outliers and to identify bona fide single stars and likely binary and multiple systems. The single stars define a tight sequence, which in the mass range 0.12–2.2
M
⊙
is well fitted by PARSEC isochrones for a supersolar metallicity of M/H = +0.18 ± 0.03 and an age of 775 ± 25 Myr. The isochrones enable us to assign mass, effective temperature, luminosity, and surface gravity to each of the 600 bona fide single main-sequence stars. The observed sequence validates the PARSEC isochrones. The derived stellar properties can serve as benchmarks for atmospheric and evolutionary models and for all-sky catalogs of stellar astrophysical properties. The stellar properties are also relevant for studies of exoplanet properties among Hyades exoplanet hosts.
ABSTRACT If advanced extraterrestrial civilizations choose to construct vast numbers of Dyson spheres to harvest radiation energy, this could affect the characteristics of their host galaxies. ...Potential signatures of such astroengineering projects include reduced optical luminosity, boosted infrared luminosity, and morphological anomalies. Here, we apply a technique pioneered by Annis to search for Kardashev type III civilizations in disk galaxies, based on the predicted offset of these galaxies from the optical Tully-Fisher (TF) relation. By analyzing a sample of 1359 disk galaxies, we are able to set a conservative upper limit of on the fraction of local disks subject to Dysonian astroengineering on galaxy-wide scales. However, the available data suggests that a small subset of disk galaxies actually may be underluminous with respect to the TF relation in the way expected for Kardashev type III objects. Based on the optical morphologies and infrared-to-optical luminosity ratios of such galaxies in our sample, we conclude that none of them stand out as strong Kardashev type III candidates and that their inferred properties likely have mundane explanations. This allows us to set a tentative upper limit at on the fraction of Karashev type III disk galaxies in the local universe.
Abstract
High-contrast imaging of debris disk systems permits us to assess the composition and size distribution of circumstellar dust, to probe recent dynamical histories, and to directly detect and ...characterize embedded exoplanets. Observations of these systems in the infrared beyond 2–3
μ
m promise access to both extremely favorable planet contrasts and numerous scattered-light spectral features—but have typically been inhibited by the brightness of the sky at these wavelengths. We present coronagraphy of the AU Microscopii (AU Mic) system using JWST’s Near Infrared Camera (NIRCam) in two filters spanning 3–5
μ
m. These data provide the first images of the system’s famous debris disk at these wavelengths and permit additional constraints on its properties and morphology. Conducting a deep search for companions in these data, we do not identify any compelling candidates. However, with sensitivity sufficient to recover planets as small as ∼0.1 Jupiter masses beyond ∼2″ (∼20 au) with 5
σ
confidence, these data place significant constraints on any massive companions that might still remain at large separations and provide additional context for the compact, multiplanet system orbiting very close-in. The observations presented here highlight NIRCam’s unique capabilities for probing similar disks in this largely unexplored wavelength range, and they provide the deepest direct imaging constraints on wide-orbit giant planets in this very well-studied benchmark system.
Abstract
The detection of emission lines associated with accretion processes is a direct method for studying how and where gas giant planets form, how young planets interact with their natal ...protoplanetary disk, and how volatile delivery to their atmosphere takes place. H
α
(
λ
= 0.656
μ
m) is expected to be the strongest accretion line observable from the ground with adaptive optics systems, and is therefore the target of specific high-contrast imaging campaigns. We present MagAO-X and Hubble Space Telescope (HST) data obtained to search for H
α
emission from the previously detected protoplanet candidate orbiting AS209, identified through Atacama Large Millimeter/submillimeter Array observations. No signal was detected at the location of the candidate, and we provide limits on its accretion. Our data would have detected an H
α
emission with
F
H
α
> 2.5 ± 0.3 × 10
−16
erg s
−1
cm
−2
, a factor 6.5 lower than the HST flux measured for PDS70 b. The flux limit indicates that if the protoplanet is currently accreting it is likely that local extinction from circumstellar and circumplanetary material strongly attenuates its emission at optical wavelengths. In addition, the data reveal the first image of the jet north of the star as expected from previous detections of forbidden lines. Finally, this work demonstrates that current ground-based observations with extreme adaptive optics systems can be more sensitive than space-based observations, paving the way to the hunt for small planets in reflected light with extremely large telescopes.
Abstract Observations of debris disks offer important insights into the formation and evolution of planetary systems. Though M dwarfs make up approximately 80% of nearby stars, very few M dwarf ...debris disks have been studied in detail—making it unclear how or if the information gleaned from studying debris disks around more massive stars extends to the more abundant M dwarf systems. We report the first scattered-light detection of the debris disk around the M4 star Fomalhaut C using JWST's Near Infrared Camera (NIRCam; 3.6 and 4.4 μ m). This result adds to the prior sample of only four M dwarf debris disks with detections in scattered light and marks the latest spectral type and oldest star among them. The size and orientation of the disk in these data are generally consistent with the prior Atacama Large Millimeter/submillimeter Array submillimeter detection. Though no companions are identified, these data provide strong constraints on their presence—with sensitivity sufficient to recover sub-Saturn mass objects in the vicinity of the disk. This result illustrates the unique capability of JWST to uncover elusive M dwarf debris disks in scattered light and lays the groundwork for deeper studies of such objects in the 2–5 μ m regime.
Abstract
Based on GAIA Early Data Release 3 (EDR3), we revisit and update our sample of bonafide single stars in the Hyades open cluster. The small observational uncertainties in parallax and ...photometry of EDR3 result in a tightly defined stellar sequence, which is ideal for the testing and calibration of theoretical stellar evolutionary tracks and isochrones. We benchmark the solar-scaled mesa evolutionary models against the single star sequence. We find that the non-rotating mesa models for Fe/H = +0.25 provide a good fit for stars with masses above 0.85, and very low mass stars below 0.25 M⊙. For stars with masses between 0.25 and 0.85 M⊙, the models systematically under predict the observed stellar luminosity. One potential limitation of the models for partially convective stars more massive than 0.35 M⊙ is the prescription of (superadiabatic) convection with the mixing-length theory parameter αML tuned to match the Solar model. Below 0.35 M⊙, the increased scatter in the stellar sequence might be a manifestation of the convective kissing instability, which is driven by variations in the 3He nuclear energy production rate due to instabilities at the convective core to envelope boundary. For a Hyades-like stellar population, the application of solar-scaled models to subsolar mass stars could result in a significant underestimate of the age, or an overestimate of the metallicity. We suggest that future grids of solar-scaled evolutionary stellar models could be complemented by Hyades-scaled models in the mass range 0.25 to 0.85 M⊙.
Context.
The
Gaia
astrophysical parameters inference system (Apsis) provides astrophysical parameter estimates for several to hundreds of millions of stars.
Aims.
We aim to benchmark
Gaia
DR3 Apsis.
...Methods.
We compiled approximately 1500 bona fide single stars in the Hyades and Pleiades open clusters for validation of PARSEC isochrones, and for comparison with Apsis estimates. PARSEC stellar isochrones in the
Gaia
photometric system enable us to assign average ages and metallicities to the clusters, and mass, effective temperature, luminosity, and surface gravity to the individual stars.
Results.
Apsis does not recover the single-age, single-metallicity characteristic of the cluster populations. Ages assigned to cluster members seemingly follow the input template for Galactic populations, with earlier-type stars being systematically assigned younger ages than later-type stars. Cluster metallicities are underestimated by 0.10–0.2 dex. Effective temperature estimates are in general reliable. Surface gravity estimates reveal strong systematic errors for specific ranges of the
Gaia
BP
−
RP
colours.
Conclusions.
We caution that
Gaia
DR3 Apsis estimates can be subject to significant systematic uncertainties. Some of the Apsis estimates, such as metallicity, might only be meaningful for statistical studies of the time-averaged Galactic stellar population, but are not recommended to be used for individual stars.
Context. Brown dwarfs in the spectral range L9–T3.5, within the so called L/T transition, have been shown to be variable at higher amplitudes and with greater frequency than other field dwarfs. This ...strong variability allows for the probing of their atmospheric structure in 3D through multi-wavelength observations for studying the underlying physical mechanisms responsible for the variability. The few known strongly variable dwarfs in this range have been extensively studied. Now, more variables such as these need to be discovered and studied to better constrain atmospheric models. This is also critical to better understand giant exoplanets and to shed light on a number of possible correlations between brown dwarf characteristics and variability. Aims. Previous studies suggest an occurrence rate for strong variability (peak-to-peak amplitudes > 2%) of up to ∼39% among brown dwarfs within the L/T transition. In this work, we aim to discover new strong variables in this spectral range by targeting ten previously unsurveyed brown dwarfs. Methods. We used the NOTCam at the Nordic Optical Telescope to observe 11 targets, with spectral types ranging from L9.5 to T3.5, in the J-band during October 2017 and September 2018. Using differential aperture photometry, we then analysed the light curves for significant variability using Lomb-Scargle periodogram algorithms and least squares fitting. Results. We report first discoveries of strong and significant variability in four out of the ten targets (false alarm probability < 0.1%), measuring peak-to-peak amplitudes up to 10.7 ± 0.4% in J for the T1 dwarf 2MASS J22153705+2110554, for which we observe significant light curve evolution between the 2017 and 2018 epochs. We also report a marginally significant detection of strong variability, and confirm that the well known 2MASS J01365662+0933473 is still strongly variable three years after the last reported epoch. Finally, we present an extensive multi-epoch catalogue of strong variables reported in the literature and discuss possible correlations that are identifiable from the catalogue. Conclusions. We significantly add to the number of known strong variables, and through Poisson statistics infer an occurrence rate for strong variability among L9–T3.5 brown dwarfs of 40 +32−19 40 − 19 + 32 $ {40}^{+32}_{-19} $ %, which is in agreement with previous estimates. The new variables identified in this work are also excellently suited for extensive multi-wavelength observations dedicated to probing the 3D structure of brown dwarf atmospheres.
ABSTRACT
We search for additional companions in the GJ 367 exoplanet system and aim to better constrain its age and evolutionary status. We analyse high-contrast direct imaging observations obtained ...with HST/NICMOS, VLT/NACO, and VLT/SPHERE. We investigate and critically discuss conflicting age indicators based on theoretical isochrones and models for Galactic dynamics. A comparison of GAIA EDR3 parallax and photometric measurements with theoretical isochrones suggests a young age ≤60 Myr for GJ 367. The star’s Galactic kinematics exclude membership to any nearby young moving group or stellar stream. Its highly eccentric Galactic orbit, however, is atypical for a young star. Age estimates considering Galactic dynamical evolution are most consistent with an age of 1–8 Gyr. We find no evidence for a significant mid-infrared excess in the WISE bands, suggesting the absence of warm dust in the GJ 367 system. The direct imaging data provide significantly improved detection limits compared to previous studies. At 530 mas (5 au) separation, the SPHERE data achieve a 5σ contrast of 2.6 × 10−6. The data exclude the presence of a stellar companion at projected separations ≥0.4 au. At projected separations ≥5 au we can exclude substellar companions with a mass ≥1.5 MJup for an age of 50 Myr, and ≥20 MJup for an age of 5 Gyr. By applying the stellar parameters corresponding to the 50 Myr isochrone, we derive a bulk density of ρplanet = 6.2 g cm−3 for GJ 367 b, which is 25 per cent smaller than a previous estimate.
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