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Register a new userThe 2008 outburst of EX Lup - silicate crystals in motion
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EX Lup is the prototype of the EXor class of eruptive young stars. These objects show optical outbursts which are thought to be related to runaway accretion onto the star. In a previous study we observed in-situ crystal formation in the disk of EX Lup during its latest outburst in 2008, making the object an ideal laboratory to investigate circumstellar crystal formation and transport. This outburst was monitored by a campaign of ground-based and Spitzer Space Telescope observations. Here we modeled the spectral energy distribution of EX Lup in the outburst from optical to millimeter wavelengths with a 2D radiative transfer code. Our results showed that the shape of the SED at optical wavelengths was more consistent with a single temperature blackbody than a temperature distribution. We also found that this single temperature component emitted 80-100 % of the total accretion luminosity. We concluded that a thermal instability, the most widely accepted model of EXor outbursts, was likely not the triggering mechanism of the 2008 outburst of EX Lup. Our mid-infrared Spitzer spectra revealed that the strength of all crystalline bands between 8 and 30 um increased right after the end of the outburst. Six months later, however, the crystallinity in the 10 um silicate feature complex decreased. Our modeling of the mid-infrared spectral evolution of EXLup showed that, although vertical mixing should be stronger during the outburst than in the quiescent phase, fast radial transport of crystals (e.g., by stellar/disk wind) was required to reproduce the observed mid-infrared spectra.
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We report monitoring observations of the T Tauri star EX Lupi during its outburst in 2008 in the CO fundamental band at 4.6-5.0 um. The observations were carried out at the VLT and the Subaru Telescope at six epochs from April to August 2008, covering the plateau of the outburst and the fading phase to a quiescent state. The line flux of CO emission declines with the visual brightness of the star and the continuum flux at 5 um, but composed of two subcomponents that decay with different rates. The narrow line emission (50 km s-1 in FWHM) is near the systemic velocity of EX Lupi. These emission lines appear exclusively in v=1-0. The line widths translate to a characteristic orbiting radius of 0.4 AU. The broad line component (FWZI ~ 150 km s-1) is highly excited upto v<=6. The line flux of the component decreases faster than the narrow line emission. Simple modeling of the line profiles implies that the broad-line emitting gas is orbiting around the star at 0.04-0.4 AU. The excitation state, the decay speed of the line flux, and the line profile, indicate that the broad-line emission component is physically distinct from the narrow-line emission component, and more tightly related to the outburst event.
In mid-January 2008, EX Lup, the prototype of the small class of eruptive variables called EXors, began an extreme outburst that lasted seven months. We observed EX Lup during about 21 h with XMM-Newton, simultaneously in X-rays and UV, on August 10-11, 2008 -- a few days before the end of its 2008 outburst -- when the optical flux of EX Lup remained about 4 times above its pre-outburst level. The observed spectrum of the low-level period is dominated below ~1.5 keV by emission from a relatively cool plasma (~4.7 MK) that is lightly absorbed (NH~3.6E20 cm^-2) and above ~1.5 keV by emission from a plasma that is ~ten times hotter and affected by a photoelectric absorption that is 75 times larger. During the X-ray flare, the emission measure and the intrinsic X-ray luminosity of this absorbed plasma component is five times higher than during the low-level period. The soft X-ray spectral component is most likely associated with accretion shocks, as opposed to jet activity, given the absence of forbidden emission lines of low-excitation species (e.g., [O I]) in optical spectra of EX Lup obtained during outburst. The hard X-ray spectral component, meanwhile, is most likely associated with a smothered stellar corona. The UV emission is reminiscent of accretion events, such as those already observed with the Optical/UV Monitor from other accreting pre-main sequence stars, and is evidently dominated by emission from accretion hot spots. The large photoelectric absorption of the active stellar corona is most likely due to high-density gas above the corona in accretion funnel flows (abridged).
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.
EX Lupi-type objects (EXors) form a sub-class of T Tauri stars, defined by sudden sporadic flare-ups of 1-5 magnitudes at optical wavelengths. These eruptions are attributed to enhanced mass accretion from the circumstellar disk to the star, and may constitute important events in shaping the structure of the inner disk and the forming planetary system. Although disk properties must play a fundamental role in driving the outbursts, they are surprisingly poorly known. In order to characterize the dust and gas components of EXor disks, here we report on observations of the $^{12}$CO J=3-2 and 4-3 lines, and the $^{13}$CO 3-2 line in EX Lup, the prototype of the EXor class. We reproduce the observed line fluxes and profiles with a line radiative transfer model, and compare the obtained parameters with corresponding ones of other T Tauri disks.
V1647 Ori is a young eruptive variable star, illuminating a reflection nebula (McNeils Nebula). It underwent an outburst in 2003 before fading back to its pre-outburst brightness in 2006. In 2008, V1647 Ori underwent a new outburst. The observed properties of the 2003-2006 event are different in several respects from both the EXor and FUor type outbursts, and suggest that this star might represent a new class of eruptive young stars, younger and more deeply embedded than EXors, and exhibiting variations on shorter time scales than FUors. In outburst, the star lights up the otherwise invisible McNeils nebular - a conical cloud likely accumulated from previous outbursts. We present follow-up photometric as well as optical and near-IR spectroscopy of the nebula obtainted during the 2008-2009 outburst. We will also present results from contemporaneous X-ray observations. These multi-wavelength observations of V1647 Ori, obtained at this key early stage of the outburst, provide a snapshot of the lighting up of the nebula, probe its evolution through the event, and enable comparison with the 2003-2006 outburst.
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