Isochronal age-mass discrepancy of young stars: SCExAO/CHARIS integral field spectroscopy of the HIP 79124 triple system

Abstract

We present SCExAO/CHARIS 1.1-2.4 µm integral field direct spectroscopy of the young HIP 79124 triple system. HIP 79124 is a member of the Scorpius-Centaurus association, consisting of an A0V primary with two low-mass companions at a projected separation of <1 . Thanks to the high quality wavefront corrections provided by SCExAO, both companions are decisively detected without the employment of any PSF-subtraction algorithm to eliminate quasi-static noise. The spectrum of the outer C object is very well matched by Upper Scorpius M4 ± 0.5 standard spectra, with a T eff = 2945 ± 100 K and a mass of ∼ 350 M Jup . HIP 79124 B is detected at a separation of only 180 mas in a highly-correlated noise regime, and it falls in the spectral range M6 ± 0.5 with T eff = 2840 ± 190 K and ∼ 100 M Jup . Previous studies of stellar populations in Sco-Cen have highlighted a discrepancy in isochronal ages between the lower-mass and higher-mass populations. This could be explained either by an age spread in the region, or by conventional isochronal models failing to reproduce the evolution of low-mass stars. The HIP 79124 system should be coeval, and therefore it provides an ideal laboratory to test these scenarios. We place the three components in a color-magnitude diagram and find that the models predict a younger age for the two low-mass companions (∼ 3 Myr) than for the primary star (∼ 6 Myr). These results imply that the omission of magnetic effects in conventional isochronal models inhibit them from reproducing early low-mass stellar evolution, which is further supported by the fact that new models that include such effects provide more consistent ages in the HIP 79124 system.

VLT/SPHERE exploration of the young multiplanetary system PDS70

“…PDS70_v2 We have estimated the mass of PDS 70 c by comparing the photometric values reported in Table 2 with the AMES-DUSTY models (Allard et al 2001) assuming the system age of 5.4±1.0 Myr. The error bars on the age could be underestimated for late-type Scorpius-Centaurus stars due to the fact that the effects of the magnetic activity are not taken properly into account as found by Asensio-Torres et al (2019) for the case of HIP 79124. The results of this procedure are listed in Table 5.…”

Perturbers: SPHERE detection limits to planetary-mass companions in protoplanetary disks

“…We note here that the derived isochronal parameters for young PMS stars carry a moderate uncertainty. Stellar age is the most critical parameter to estimate reliable sensitivities to planet mass; deviations in L/T eff values, the use of different evolutionary tracks, the effect of magnetic fields, and the initial position of the star at t = 0 can all contribute to dubious estimations of individual ages (e.g., Asensio-Torres et al 2019). Our approach allows us to obtain a homogeneous and consistent classification of the different PPDs, while the adopted ages (Table 1) also tend to agree, within error bars, with other individual studies.…”

Characterization of very wide companion candidates to young stars with planets and disks

“…According to our analysis, this target is a highly probable wide companion of HIP 74865 with an estimated age of 7-8 Myr -younger than the UCL subassociation (15 ± 3 Myr) in which the object is located. This age discrepancy has been addressed previously (Feiden 2016;Asensio-Torres et al 2019) as theoretical isochrones failing to reproduce the correct age of K and M stars by a factor of two (due to neglecting magnetic fields in the models). However, this issue has only been flagged up for 2MASS J1517-3028, and not for 2MASS J1324-5129 or 2MASS J1457-3543, although these latter two are also late-type M-dwarfs, albeit later in type in comparison with 2MASS J1517-3028.…”

“…Feiden (2016) also pointed out that cooler K and M stars located in young stellar associations are reported to be younger than hotter A, F, or G stars belonging to the same association by a factor of two. This problem is probably due to neglect of the magnetic fields in stellar evolution isochrones which in turn fail to reproduce the age of low-mass PMS stars accurately (Asensio- Torres et al 2019;Feiden 2016). Therefore, by adopting the most appropriate stellar evolution models tailored for ages beyond 10 Myr, we expect 2MASS J1517-3028 to have an age consistent with UCL.…”