​​G. Cugno (1), S. P. Quanz (1), S. Hunziker (1), T. Stolker (1), H. M. Schmid (1), H. Avenhaus (2), P. Baudoz (3), A. J. Bohn (4), M. Bonnefoy (5), E. Buenzli (1), G. Chauvin (5 and 6), A. Cheetham (7), S. Desidera (8), C. Dominik (9), P. Feautrier (5), M. Feldt (2), C. Ginski (4), J. H. Girard (10), R. Gratton (8), J. Hagelberg (1), E. Hugot (11), M. Janson (12), A.-M. Lagrange (5), M. Langlois (11 and 13), Y. Magnard (5), A.-L. Maire (2), F. Menard (5 and 14), M. Meyer (15 and 1), J. Milli (10), C. Mordasini (16), C. Pinte (17 and 5), J. Pragt (18), R. Roelfsema (18), F. Rigal (18), J. Szulágyi (19), R. van Boekel (2), G. van der Plas (5), A. Vigan (11), Z. Wahhaj (10), A. Zurlo (11 and 20) ((1) ETH Zürich, (2) Max Planck Institute Heidelberg, (3) LESIA, (4) Leiden Observatory, (5) Univ. Grenoble, (6) Universidad de Chile, (7) Geneva Observatory, (8) Osservatorio Astronomico di Padova, (9) University of Amsterdam, (10) ESO Santiago de Chile, (11) Marseille Université, (12) Stockholm University, (13) CNRS Lyon, (14) CNRS Grenoble, (15) University of Michigan, (16) Universität Bern, (17) Monash University, (18) NOVA, (19) University of Zürich, (20) Universidad Diego Portales)
http://arxiv.org/abs/1812.06993
Aims: We want to detect and quantify observables related to accretion processes occurring locally in circumstellar disks, which could be attributed to young forming planets. We focus on objects known to host protoplanet candidates and/or disk structures thought to be the result of interactions with planets. Methods: We analyzed observations of 6 young stars (age 3.5−103.5−10 Myr) and their surrounding environments with the SPHERE/ZIMPOL instrument on the VLT in the Hαα filter (656 nm) and a nearby continuum filter (644.9 nm). Results: We re-detect the known accreting M-star companion HD142527 B with the highest published signal to noise to date in both Hαα and the continuum. We derive new astrometry (r=62.8+2.1−2.7r=62.8−2.7+2.1 mas and PA=(98.7±1.8)∘PA=(98.7±1.8)∘) and photometry (ΔΔN_Ha=6.3+0.2−0.36.3−0.3+0.2 mag, ΔΔB_Ha=6.7±0.26.7±0.2 mag and ΔΔCnt_Ha=7.3+0.3−0.27.3−0.2+0.3 mag) for the companion in agreement with previous studies, and estimate its mass accretion rate (M˙≈1−2×10−10M⊙ yr−1M˙≈1−2×10−10M⊙ yr−1). A faint point-like source around HD135344 B (SAO206462) is also investigated, but a second deeper observation is required to reveal its nature. No other companions are detected. In the framework of our assumptions we estimate detection limits at the locations of companion candidates around HD100546, HD169142 and MWC758 and calculate that processes involving Hαα fluxes larger than ∼8×10−14−10−15erg/s/cm2∼8×10−14−10−15erg/s/cm2 (M˙>10−10−10−12M⊙ yr−1M˙>10−10−10−12M⊙ yr−1) can be excluded. Furthermore, flux upper limits of ∼10−14−10−15erg/s/cm2∼10−14−10−15erg/s/cm2 (M˙<10−11−10−12M⊙ yr−1M˙<10−11−10−12M⊙ yr−1) are estimated within the gaps identified in the disks surrounding HD135344B and TW Hya.

​
Dynamical masses of M-dwarf binaries in young moving groups: II - Toward empirical mass-luminosity isochrones.
Markus Janson, Stephen Durkan, Mickael Bonnefoy, Laetitia Rodet, Rainer Kohler, Sylvestre Lacour, Wolfgang Brandner, Thomas Henning, Julien Girard
http://arxiv.org/abs/1811.11802
Low-mass stars exhibit substantial pre-main sequence evolution during the first ~100 Myrs of their lives. Thus, young M-type stars are prime targets for isochronal dating, especially in young moving groups (YMGs), which contain large amounts of stars in this mass and age range. If the mass and luminosity of a star can both be directly determined, this allows for a particularly robust isochronal analysis. This motivates in-depth studies of low-mass binaries with spatially resolvable orbits, where dynamical masses can be derived. Here we present the results of an observing campaign dedicated to orbital monitoring of AB Dor Ba/Bb, which is a close M-dwarf pair within the quadruple AB Dor system. We have acquired eight astrometric epochs with the SPHERE/ZIMPOL and NACO instruments, which we combine with literature data to improve the robustness and precision for the orbital characterization of the pair. We find a system mass 0.66+/-0.12 Msun and bolometric luminosities in log(L/Lsun) of -2.02+/-0.02 and -2.11 +/- 0.02 for AB Dor Ba and Bb, respectively. These measurements are combined with other YMG pairs in the literature to start building a framework of empirical isochrones in mass-luminosity space. This can be used to calibrate theoretical isochrones and to provide a model-free basis for assessing relative stellar ages. We note a tentative emerging trend where the youngest moving group members are largely consistent with theoretical expectations, while stars in older associations such as the AB Dor moving group appear to be systematically underluminous relative to isochronal expectations.