Correcting for Activity Effects on the Temperatures, Radii, and Estimated Masses of Low-Mass Stars and Brown Dwarfs

We present empirical relations for determining the amount by which the effective temperatures and radii---and therefore the estimated masses---of low-mass stars and brown dwarfs are altered due to chromospheric activity. Accurate estimates of stellar radii are especially important in the context of searches for transiting exoplanets, which rely upon the assumed stellar radius/density to infer the planet radius/density. Our relations are based on a large set of well studied low-mass stars in the field and on a set of benchmark low-mass eclipsing binaries. The relations link the amount by which an active object's temperature is suppressed, and its radius inflated, to the strength of its Halpha emission. These relations are found to approximately preserve bolometric luminosity. We apply these relations to the peculiar brown-dwarf eclipsing binary 2M0535-05, in which the active, higher-mass brown dwarf has a cooler temperature than its inactive, lower-mass companion. The relations correctly reproduce the observed temperatures and radii of 2M0535-05 after accounting for the Halpha emission; 2M0535-05 would be in precise agreement with theoretical isochrones were it inactive. The relations that we present are applicable to brown dwarfs and low-mass stars with masses below 0.8 Msun and for which the activity, as measured by Halpha, is in the range -4.6 < log Lha/Lbol < -3.3. We expect these relations to be most useful for correcting radius and mass estimates of low-mass stars and brown dwarfs over their active lifetimes (few Gyr). We also discuss the implications of this work for determinations of young cluster IMFs.Comment: To appear in Cool Stars 17 proceeding

OBIA for combining LiDAR and multispectral data to characterize forested areas and land cover in a tropical region

International audiencePrioritizing and designing forest restoration strategies requires an adequate survey to inform on the status (degraded or not) of forest types and the human disturbances over a territory. Very High Spatial Resolution (VHSR) remotely sensed data offers valuable information for performing such survey. We present in this study an OBIA methodology for mapping forest types at risk and land cover in a tropical context (Mayotte Island) combining LiDAR data (1 m pixel), VHSR multispectral images (Spot 5 XS 10 m pixel and orthophotos 0.5 m pixel) and ancillary data (existing thematic information). A Digital Canopy Model (DCM) was derived from LiDAR data and additional information was built from the DCM in order to better take into account the horizontal variability of canopy height: max and high Pass filters (3m x 3m kernel size) and Haralick variance texture image (51m x 51m kernel size). OBIA emerges as a suitable framework for exploiting multisource information during segmentation as well as during the classification process. A precise map (84% total accuracy) was obtained informing on (i) surfaces of forest types (defined according to their structure, i.e. canopy height of forest patches for specific type); (ii) degradation (identified in the heterogeneity of canopy height and presence of eroded areas) and (iii) human disturbances. Improvements can be made when discriminating forest types according to their composition (deciduous, evergreen or mixed), in particular by exploiting a more radiometrically homogenous VHSR multispectral image

Rotational Velocities of Individual Components in Very Low Mass Binaries

We present rotational velocities for individual components of 11 very low mass (VLM) binaries with spectral types between M7 and L7.5. These results are based on observations taken with the near-infrared spectrograph, NIRSPEC, and the Keck II laser guide star adaptive optics system. We find that the observed sources tend to be rapid rotators (v sin i > 10 km s^(–1)), consistent with previous seeing-limited measurements of VLM objects. The two sources with the largest v sin i, LP 349–25B and HD 130948C, are rotating at ~30% of their break-up speed, and are among the most rapidly rotating VLM objects known. Furthermore, five binary systems, all with orbital semimajor axes ≾3.5 AU, have component v sin i values that differ by greater than 3σ. To bring the binary components with discrepant rotational velocities into agreement would require the rotational axes to be inclined with respect to each other, and that at least one component is inclined with respect to the orbital plane. Alternatively, each component could be rotating at a different rate, even though they have similar spectral types. Both differing rotational velocities and inclinations have implications for binary star formation and evolution. We also investigate possible dynamical evolution in the triple system HD 130948A–BC. The close binary brown dwarfs B and C have significantly different v sin i values. We demonstrate that components B and C could have been torqued into misalignment by the primary star, A, via orbital precession. Such a scenario can also be applied to another triple system in our sample, GJ 569A–Bab. Interactions such as these may play an important role in the dynamical evolution of VLM binaries. Finally, we note that two of the binaries with large differences in component v sin i, LP 349–25AB and 2MASS 0746+20AB, are also known radio sources

The Impact of Chromospheric Activity on Observed Initial Mass Functions

Using recently established empirical calibrations for the impact of chromospheric activity on the radii, effective temperatures, and estimated masses of active low-mass stars and brown dwarfs, we reassess the shape of the initial mass function (IMF) across the stellar/substellar boundary in the Upper Sco star-forming region (age 5-10 Myr). We adjust the observed effective temperatures to warmer values using the observed strength of the chromospheric H$\alpha$ emission, and redetermine the estimated masses of objects using pre--main-sequence evolutionary tracks in the H-R diagram. The effect of the activity-adjusted temperatures is to shift the objects to higher masses by 3-100%. While the slope of the resulting IMF at substellar masses is not strongly changed, the peak of the IMF does shift from ~0.06 to ~0.11 Msun. Moreover, for objects with masses <~0.2 Msun, the ratio of brown dwarfs to stars changes from ~80% to ~33%. These results suggest that activity corrections are essential for studies of the substellar mass function, if the masses are estimated from spectral types or from effective temperatures.Comment: Accepted by ApJ, 9 pages, 2 figures. This version corrects a minor typo in the abstrac

Limits on the Mass and Initial Entropy of 51 Eri b from Gaia EDR3 Astrometry

51 Eri b is one of the only young planets consistent with a wide range of possible initial entropy states, including the cold-start scenario associated with some models of planet formation by core accretion. The most direct way to constrain the initial entropy of a planet is by measuring its luminosity and mass at a sufficiently young age that the initial conditions still matter. We present the tightest upper limit on 51 Eri b's mass yet (M < 11 Mjup at 2$\sigma$) using a cross-calibration of Hipparcos and Gaia EDR3 astrometry and the orbit-fitting code orvara. We also reassess its luminosity using a direct, photometric approach, finding log(Lbol/Lsun) = -5.5$\pm$0.2 dex. Combining this luminosity with the 24$\pm$3 Myr age of the $\beta$ Pic moving group, of which 51 Eri is a member, we derive mass distributions from a grid of evolutionary models that spans a wide range of initial entropies. We find that 51 Eri b is inconsistent with the coldest-start scenarios, requiring an initial entropy of >8 $k_B$/baryon at 97% confidence. This result represents the first observational constraint on the initial entropy of a potentially cold-start planet, and it continues the trend of dynamical masses for directly imaged planets pointing to warm- or hot-start formation scenarios.Comment: Accepted for publication in MNRAS (9 pages, 6 figures

Visible Discrimination of Broadband Infrared Light by Dye-Enhanced Upconversion in Lanthanide-Doped Nanocrystals

Optical upconversion of near infrared light to visible light is an attractive way to capture the optical energy or optical information contained in low-energy photons that is otherwise lost to the human eye or to certain photodetectors and solar cells. Until the recent application of broadband absorbing optical antennas, upconversion efficiency in lanthanide-doped nanocrystals was limited by the weak, narrow atomic absorption of a handful of sensitizer elements. In this work, we extend the role of the optical antenna to provide false-color, visible discrimination between bands of infrared radiation. By pairing different optical antenna dyes to specific nanoparticle compositions, unique visible emission is associated with different bands of infrared excitation. In one material set, the peak emission was increased 10-fold, and the width of the spectral response was increased more than 10-fold

Équidiens

Terme désignant une phase tardive de l’art rupestre nord-africain et saharien. Il fut proposé en 1952 par l’Abbé H. Breuil dans son mémoire intitulé Les roches peintes du Tassili n’Ajjer, publié dans les Actes du IIe Congrès panafricain de Préhistoire (Paris, A.M.G., 1955). Cette désignation s’appliquait aux auteurs de gravures et de peintures représentant des chevaux domestiques. Un an plus tôt, en 1951, Th. Monod s’interrogeait sur la nécessité d’établir la séquence suivante dans les œuvres..

Core level photoelectron spectroscopy of heterogeneous reactions at liquid-vapor interfaces: Current status, challenges, and prospects

Liquid–vapor interfaces, particularly those between aqueous solutions and air, drive numerous important chemical and physical processes in the atmosphere and in the environment. X-ray photoelectron spectroscopy is an excellent method for the investigation of these interfaces due to its surface sensitivity, elemental and chemical specificity, and the possibility to obtain information on the depth distribution of solute and solvent species in the interfacial region. In this Perspective, we review the progress that was made in this field over the past decades and discuss the challenges that need to be overcome for investigations of heterogeneous reactions at liquid–vapor interfaces under close-torealistic environmental conditions. We close with an outlook on where some of the most exciting and promising developments might lie in this fiel

Chronic dermatomycoses of the foot as risk factors for acute bacterial cellulitis of the leg: A case-control study

Objective: To assess the role of foot dermatomycosis ( tinea pedis and onychomycosis) and other candidate risk factors in the development of acute bacterial cellulitis of the leg. Methods: A case-control study, including 243 patients ( cases) with acute bacterial cellulitis of the leg and 467 controls, 2 per case, individually matched for gender, age (+/-5 years), hospital and admission date (+/-2 months). Results: Overall, mycology-proven foot dermatomycosis was a significant risk factor for acute bacterial cellulitis (odds ratio, OR: 2.4; p < 0.001), as were tinea pedis interdigitalis (OR: 3.2; p < 0.001), tinea pedis plantaris (OR: 1.7; p = 0.005) and onychomycosis (OR: 2.2; p < 0.001) individually. Other risk factors included: disruption of the cutaneous barrier, history of bacterial cellulitis, chronic venous insufficiency and leg oedema. Conclusions: Tinea pedis and onychomycosis were found to be significant risk factors for acute bacterial cellulitis of the leg that are readily amenable to treatment with effective pharmacological therapy. Copyright (C) 2004 S. Karger AG, Basel