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Register a new userALMA Measurements of Circumstellar Material in the GQ Lup System
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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 $mu$m continuum and CO J=3-2 line emission with beam size $sim0.3$ ($sim45$ 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 $59pm12$ AU, while the gas has a larger extent with a characteristic radius of $46.5pm1.8$ 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 $M_* = (1.03pm0.05)*(d/156text{ pc})$ $M_odot$, where $d$ is a known distance, and determine that we view the disk at an inclination angle of $60.5^circpm0.5^circ$ and a position angle of $346^circ pm1^circ$. The $3sigma$ upper limit on the 870 $mu$m 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 $<0.04$ $M_oplus$ 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.
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Substellar companions at wide separation around stars hosting planets or brown dwarfs (BDs) yet close enough for their formation in the circumstellar disc are of special interest. In this letter we report the discovery of a wide (projected separation $sim$16.0arcsec, or 2400 AU, and position angle 114.61$^circ$) companion of the GQ Lup A-B system, most likely gravitationally bound to it. A VLT/X-Shooter spectrum shows that this star, 2MASS J15491331-3539118, is a bonafide low-mass ($sim$0.15 M$_odot$) young stellar object (YSO) with stellar and accretion/ejection properties typical of Lupus YSOs of similar mass, and with kinematics consistent with that of the GQ Lup A-B system. A possible scenario for the formation of the triple system is that GQ Lup A and 2MASS J15491331-3539118 formed by fragmentation of a turbulent core in the Lup I filament, while GQ Lup B, the BD companion of GQ Lup A at 0.7arcsec, formed in situ by the fragmentation of the circumprimary disc. The recent discoveries that stars form along cloud filaments would favour the scenario of turbulent fragmentation for the formation of GQ Lup A and 2MASS J15491331-3539118.
Very recently, a second companion on wider orbit has been discovered around GQ Lup. This is a low-mass accreting star partially obscured by a disk seen at high inclination. If detected, this disk may be compared to the known disk around the primary. We detected this disk on archive HST and WISE data. The extended spectral energy distribution provided by these data confirms the presence of accretion from Halpha emission and UV excess, and shows an IR excess attributable to a warm disk. In addition, we resolved the disk on the HST images. This is found to be roughly aligned with the disk of the primary. Both of them are roughly aligned with the Lupus I dust filament containing GQ Lup.
EX Lup is a well-studied T Tauri star that represents the prototype of young eruptive stars EXors. In this paper we analyze new adaptive optics imaging and spectroscopic observations of EX Lup and its circumstellar environment in near-infrared in its quiescent phase. We observed EX Lup with the high contrast imager SPHERE/IRDIS in the dual-beam polarimetric imaging mode to resolve the circumstellar environment in near-infrared scattered light. We complemented these data with earlier SINFONI spectroscopy. We resolve for the first time in scattered light a compact feature around EX Lup azimuthally extending from 280deg to 360deg, and radially extending from 0.3arcsec to 0.55arcsec in the plane of the disk. We explore two different scenarios for the detected emission. One accounting for the emission as coming from the brightened walls of the cavity excavated by the outflow whose presence was suggested by ALMA observations in the J=3-2 line of 12CO. The other accounts for the emission as coming from an inclined disk. We detect for the first time a more extended circumstellar disk in scattered light, which shows that a region between 10 and 30 au is depleted of mum-size grains. We compare the J-, H- and K-band spectra obtained with SINFONI in quiescence with the spectra taken during the outburst, showing that all the emission lines were due to the episodic accretion event. Conclusions. Based on the morphology analysis we favour the scenario in which the scattered light is coming from a circumstellar disk rather than the outflow around EX Lup. We analyze the origin of the observed feature either as coming from a continuous circumstellar disk with a cavity, or from the illuminated wall of the outer disk or from a shadowed disk. Moreover, we discuss what is the origin of the mum-size grains depleted region, exploring the possibility that a sub-stellar companion may be the cause of it.
We present 870 $mu$m ALMA observations of polarized dust emission toward the Class II protoplanetary disk IM Lup. We find that the orientation of the polarized emission is along the minor axis of the disk, and that the value of the polarization fraction increases steadily toward the center of the disk, reaching a peak value of ~1.1%. All of these characteristics are consistent with models of self-scattering of submillimeter-wave emission from an optically thin inclined disk. The distribution of the polarization position angles across the disk reveals that while the average orientation is along the minor axis, the polarization orientations show a significant spread in angles; this can also be explained by models of pure scattering. We compare the polarization with that of the Class I/II source HL Tau. A comparison of cuts of the polarization fraction across the major and minor axes of both sources reveals that IM Lup has a substantially higher polarization fraction than HL Tau toward the center of the disk. This enhanced polarization fraction could be due a number of factors, including higher optical depth in HL Tau, or scattering by larger dust grains in the more evolved IM Lup disk. However, models yield similar maximum grain sizes for both HL Tau (72 $mu$m) and IM Lup (61 $mu$m, this work). This reveals continued tension between grain-size estimates from scattering models and from models of the dust emission spectrum, which find that the bulk of the (unpolarized) emission in disks is most likely due to millimeter (or even centimeter) sized grains.
In this paper we present simulated observations of massive self-gravitating circumstellar discs using the Atacama Large Millimetre/sub-millimetre Array (ALMA). Using a smoothed particle hydrodynamics model of a $0.2M_{odot}$ disc orbiting a $1M_{odot}$ protostar, with a cooling model appropriate for discs at temperatures below $sim 160$K and representative dust opacities, we have constructed maps of the expected emission at sub-mm wavelengths. We have then used the CASA ALMA simulator to generate simulated images and visibilities with various array configurations and observation frequencies, taking into account the expected thermal noise and atmospheric opacities. We find that at 345 GHz (870 $mu$m) spiral structures at a resolution of a few AU should be readily detectable in approximately face-on discs out to distances of the Taurus-Auriga star-forming complex.
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