* Astronomy

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RE: EX Lupi

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Title: The 2008 outburst of EX Lup - silicate crystals in motion
Authors: Attila Juhasz, Cornelis Dullemond, Roy van Boekel, Jeroen Bouwman, Peter Abraham, Jose Acosta-Pulido, Thomas Henning, Agnes Kospal, Aurora Sicilia-Aguilar, Albert Jones, Attila Moor, Laszlo Mosoni, Zsolt Regaly, Gyula Szokoly, Nikoletta Sipos

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 modelled the spectral energy distribution of EX Lup in the outburst from optical to millimetre 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 modelling 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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Title: Fundamental Vibrational Transition of CO during the Outburst of EX Lupi in 2008
Authors: M. Goto (1), Zs. Regály (2), C. P. Dullemond (1), M. van den Ancker (3), J. M. Brown (4), A. Carmona (5), K. Pontoppidan (6), P. Ábrahám (2), G. A. Blake (6), D. Fedele (1,7), Th. Henning (1), A. Juhász (1), Á. Kóspál (8), L. Mosoni (1,2), A. Sicilia-Aguilar (1), H. Terada (9), R. van Boekel (1), E. F. van Dishoeck (6,8), T. Usuda (9) ((1) MPIA, (2) Konkoly Observatory, (3) ESO, (4) MPE, (5) University of Geneva, (6) California Institute of Technology, (7) Johns Hopkins University, (8) Leiden Observatory, (9) Subaru Telescope)

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 modelling 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.

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EX Lupi

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Title: EX Lupi in quiescence
Authors: N. Sipos, P. Ábrahám, J. Acosta-Pulido, A. Juhász, Á. Kóspál, M. Kun, A. Moór, J. Setiawan

EX Lup is the prototype of EXors, a subclass of low-mass pre-main sequence stars whose episodic eruptions are attributed to temporarily increased accretion. In quiescence the optical and near-infrared properties of EX Lup cannot be distinguished from those of normal T Tau stars. Here we investigate whether it is the circumstellar disk structure which makes EX Lup an atypical Class II object. During outburst the disk might undergo structural changes. Our characterisation of the quiescent disk is intended to serve as a reference to study the physical changes related to one of EX Lupi's strongest known eruptions in 2008 Jan-Sep. We searched the literature for photometric and spectroscopic observations including ground-based, IRAS, ISO and Spitzer data. After constructing the optical-infrared spectral energy distribution (SED), we compared it with the typical SEDs of other young stellar objects and modelled it using the Monte Carlo radiative transfer code RADMC. A mineralogical decomposition of the 10 micron silicate emission feature and also the description of the optical and near-infrared spectra were performed. The SED is in general similar to that of a typical T Tauri star, though above 7 micron EX Lup emits higher flux. The quiescent phase data suggest low level variability in the optical-mid-infrared domain. Integrating the optical and infrared fluxes we derived a bolometric luminosity of 0.7 L_Sun. The 10 micron silicate profile could be fitted by a mixture consisting of amorphous silicates, no crystalline silicates were found. A modestly flaring disk model with a total mass of 0.025 M_Sun and an outer radius of 150 AU was able to reproduce the observed SED. The derived inner radius of 0.2 AU is larger than the sublimation radius, and this inner gap sets EX Lup aside from typical T Tauri stars.

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Scientists have long wondered how tiny silicate crystals, which need sizzling high temperatures to form, have found their way into frozen comets, born in the deep freeze of the solar system's outer edges. The crystals would have begun as non-crystallized silicate particles, part of the mix of gas and dust from which the solar system developed.
A team of astronomers believes they have found a new explanation for both where and how these crystals may have been created, by using NASA's Spitzer Space Telescope to observe the growing pains of a young, sun-like star. Their study results, which appear in the May 14 issue of Nature, provide new insight into the formation of planets and comets.
The researchers from Germany, Hungary and the Netherlands found that silicate appears to have been transformed into crystalline form by an outburst from a star. They detected the infrared signature of silicate crystals on the disk of dust and gas surrounding the star EX Lupi during one of its frequent flare-ups, or outbursts, seen by Spitzer in April 2008. These crystals were not present in Spitzer's previous observations of the star's disk during one of its quiet periods.

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The Variable star EX Lupi is currently in outburst.
A visual magnitude of 7.9 was reported on Jan 29th 2008.

EX Lupi.kmz
Google Sky File (1 kb, kmz)

Blobrana · L

The T Tau-type, pre main-sequence eruptive variable star, EX Lupi is in outburst.
Albert Jones of New Zealand, observed the star at mag V = 9.5 on the 19th January, 2008.

Position(2000): RA: 16:03:05.494 , Dec: -40:18:25.29

Spectral type: M0

EX Lupi is the prototype of the EXor class, which are pre-main-sequence variables that normally remain at minimum light, but are subject to relatively brief (a few months to a few years) flare-ups of several magnitudes amplitude.
There are two generally recognised types of pre-main-sequence stars that are subject to major increases in brightness: FUors and EXors (sometimes called "subfuors"), named after the prototypes FU Orionis and EX Lupi.

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