ALMA Measurements of Circumstellar Material in the GQ Lup System
Authors:
MacGregor et al
Abstract:
We present ALMA observations of the GQ Lup system, a young Sun-like star with
a substellar mass companion in a wide-separation orbit. These observations of
870 μm continuum and CO J=3-2 line emission with beam size ∼0.3″
(∼45 AU) resolve the disk of dust and gas surrounding the primary star, GQ
Lup A, and provide deep limits on any circumplanetary disk surrounding the
companion, GQ Lup b. The circumprimary dust disk is compact with a FWHM of
59±12 AU, while the gas has a larger extent with a characteristic radius of
46.5±1.8 AU. By forward-modeling the velocity field of the circumprimary
disk based on the CO emission, we constrain the mass of GQ Lup A to be M∗=(1.03±0.05)∗(d/156 pc) M⊙, where d is a known distance, and
determine that we view the disk at an inclination angle of
60.5∘±0.5∘ and a position angle of 346∘±1∘. The
3σ upper limit on the 870 μm flux density of any circumplanetary
disk associated with GQ Lup b of <0.15 mJy implies an upper limit on the dust
disk mass of <0.04 M⊕ for standard assumptions about optically thin
emission. We discuss proposed mechanisms for the formation of wide-separation
substellar companions given the non-detection of circumplanetary disks around
GQ Lup b and other similar systems.
Magnetic activity and hot Jupiters of young Suns: the weak-line T Tauri stars V819 Tau and V830 Tau
Authors:
Donati et al
Abstract:
We report results of a spectropolarimetric and photometric monitoring of the weak-line T Tauri stars (wTTSs) V819 Tau and V830 Tau within the MaTYSSE programme, involving the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope. At ~3 Myr, both stars dissipated their discs recently and are interesting objects for probing star and planet formation. Profile distortions and Zeeman signatures are detected in the unpolarized and circularly-polarized lines, whose rotational modulation we modelled using tomographic imaging, yielding brightness and magnetic maps for both stars.
We find that the large-scale magnetic fields of V819 Tau and V830 Tau are mostly poloidal and can be approximated at large radii by 350-400 G dipoles tilted at ~30 degrees to the rotation axis. They are significantly weaker than the field of GQ Lup, an accreting classical T Tauri star (cTTS) with similar mass and age which can be used to compare the magnetic properties of wTTSs and cTTSs. The reconstructed brightness maps of both stars include cool spots and warm plages. Surface differential rotation is small, typically ~4.4x smaller than on the Sun, in agreement with previous results on wTTSs.
Using our Doppler images to model the activity jitter and filter it out from the radial velocity (RV) curves, we obtain RV residuals with dispersions of 0.033 and 0.104 km/s for V819 Tau and V830 Tau respectively. RV residuals suggest that a hot Jupiter may be orbiting V830 Tau, though additional data are needed to confirm this preliminary result. We find no evidence for close-in giant planet around V819 Tau.
Astrometric follow-up observations of directly imaged sub-stellar companions to young stars and brown dwarfs
Authors:
Ginski et al
Abstract:
The formation of massive planetary or brown dwarf companions at large projected separations from their host star is not yet well understood. In order to put constraints on formation scenarios we search for signatures in the orbit dynamics of the systems. We are specifically interested in the eccentricities and inclinations since those parameters might tell us about the dynamic history of the systems and where to look for additional low-mass sub-stellar companions. For this purpose we utilized VLT/NACO to take several well calibrated high resolution images of 6 target systems and analyze them together with available literature data points of those systems as well as Hubble Space Telescope archival data. We used a statistical Least-Squares Monte-Carlo approach to constrain the orbit elements of all systems that showed significant differential motion of the primary star and companion. We show for the first time that the GQ Lup system shows significant change in both separation and position angle. Our analysis yields best fitting orbits for this system, which are eccentric (e between 0.21 and 0.69), but can not rule out circular orbits at high inclinations. Given our astrometry we discuss formation scenarios of the GQ Lup system. In addition, we detected an even fainter new companion candidate to GQ Lup, which is most likely a background object. We also updated the orbit constraints of the PZ Tel system, confirming that the companion is on a highly eccentric orbit with e greater than 0.62. Finally we show with a high significance, that there is no orbital motion observed in the cases of the DH Tau, HD 203030 and 1RXS J160929.1-210524 systems and give the most precise relative astrometric measurement of the UScoCTIO 108 system to date.
