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Register a new userA new white dwarf companion to the $Deltamu$ star GJ 3346
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Added by
Mariangela Bonavita
Publication date
2020
fields
Physics
and research's language is
English
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We present the discovery of a white dwarf companion at 3.6 from GJ3346, a nearby ($pisim$42 mas) K star observed with SPHERE@VLT as part of an open time survey for faint companions to objects with significant proper motion discrepancies ($Deltamu$) between Gaia DR1 and Tycho-2. Syrius-like systems like GJ3346AB, which include a main sequence star and a white dwarf, can be difficult to detect because of the intrinsic faintness of the latter. They have, however, been found to be common contaminants for direct imaging searches. White dwarfs have in fact similar brightness to sub-stellar companions in the infrared, while being much brighter in the visible bands like those used by Gaia. Combining our observations with Gaia DR2 and with several additional archival data sets, we were able to fully constrain the physical properties of GJ3346B, such as its effective temperature (11$times$10$^3pm$500 K) as well as the cooling age of the system (648$pm$58 Myrs). This allowed us to better understand the system history and to partially explains the discrepancies previously noted in the age indicators for this objects. Although further investigation is still needed, it seems that GJ3346, which was previously classified as young, is in fact most likely to be older than 4 Gyrs. Finally, given that the mass (0.58$pm$0.01$M_{odot}$)} and separation (85 au) of GJ3346B are compatible with the observed $Deltamu$, this discovery represents a further confirmation of the potential of this kind of dynamical signatures as selection methods for direct imaging surveys targeting faint, sub-stellar companions.
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We present L band (3.8 $mu m$) MMT/Clio high-contrast imaging data for the nearby star GJ 758, which was recently reported by Thalmann et al. (2009) to have one -- possibly two-- faint comoving companions (GJ 758B and ``C, respectively). GJ 758B is detected in two distinct datasets. Additionally, we report a textit{possible} detection of the object identified by Thalmann et al as ``GJ 758C in our more sensitive dataset, though it is likely a residual speckle. However, if it is the same object as that reported by Thalmann et al. it cannot be a companion in a bound orbit. GJ 758B has a H-L color redder than nearly all known L--T8 dwarfs. Based on comparisons with the COND evolutionary models, GJ 758B has T$_{e}$ $sim$ 560 K$^{^{+150 K}_{-90K}}$ and a mass ranging from $sim$ 10--20 M$_{J}$ if it is $sim$ 1 Gyr old to $sim$ 25--40 M$_{J}$ if it is 8.7 Gyr old. GJ 758B is likely in a highly eccentric orbit, e $sim$ 0.73$^{^{+0.12}_{-0.21}}$, with a semimajor axis of $sim$ 44 AU$^{^{+32 AU}_{-14 AU}}$. Though GJ 758B is sometimes discussed within the context of exoplanet direct imaging, its mass is likely greater than the deuterium-burning limit and its formation may resemble that of binary stars rather than that of jovian-mass planets.
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