The 1993–1994 Activity of EX Lupi

Herbig, G. H.; Aspin, C.; Gilmore, A. C.; Imhoff, C. L.; Jones, A. F.

doi:10.1086/324420

Cited by 62 publications

(86 citation statements)

References 17 publications

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“…However, the value of the optical extinction of EX Lup, although not well known, is very likely much lower, and generally assumed to be 0 or 1 mag in the literature (e.g., Herbig et al 2001;Gras-Velázquez & Ray 2005;Sipos et al 2009). Herbig et al (2001) noticed that the near-IR colors of EX Lup obtained in March 1992 (Hughes et al 1994) are redder than those of normal M0 dwarfs. We found here that the reddened color of EX Lup in the near-IR is consistent with the intrinsic near-IR excesses of classical T Tauri stars (CTTSs), which are caused by direct emission of near-IR flux from disks and not by the reddening of photospheric emission by dust.…”

Section: The Origin Of the Hard X-ray Component Of Ex Lupmentioning

confidence: 99%

“…4.2, the optical extinction is negligible in EX Lup, therefore, we could consider this value to be the intrinsic UV flux. We assumed for the hot spot a black-body spectrum of temperature 13 000 K, as measured from an IUE spectrum obtained during the 1994 outburst, when EX Lup was at V = 12.1 mag (Herbig et al 2001), i.e., 3.3 times fainter than during our observation. We found a surface filling factor of 0.9% for the hot spot.…”

Section: The Origin Of the Uv Emission Of Ex Lupmentioning

confidence: 99%

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A few days before the end of the 2008 extreme outburst of EX Lupi: accretion shocks and a smothered stellar corona unveiled by XMM-Newton

Grosso

Hamaguchi

Kastner

et al. 2010

A&A

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Context. EX Lup is a pre-main sequence star that exhibits repetitive and irregular optical outbursts driven by an increase in the mass accretion rate in its circumstellar disk. 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. Aims. We attempt to characterize the X-ray and UV emission of EX Lup during this outburst. Methods. 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. Results. We detected EX Lup in X-rays with an observed flux in the 0.2-10 keV energy range of 5.4 × 10 −14 erg s −1 cm −2 during a low-level period. This observed flux increased by a factor of four during a flaring period that lasted about 2 h. 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 (N H 3.6 × 10 20 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. The intrinsic X-ray luminosity of the relatively cool plasma is ∼4 × 10 28 erg s −1 . The intrinsic X-ray luminosity of EX Lup, ∼3.4 × 10 29 erg s −1 , is hence dominated by emission from the hot plasma. 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. We detected UV variability on timescales ranging from less than one hour up to about four hours. We show from simulated light curves that the power spectral density of the UV light curve can be modeled with a red-noise spectrum with a power-law index of 1.39 ± 0.06. None of the UV events observed on August 10-11, 2008 correlate unambiguously with simultaneous X-ray peaks. Conclusions. 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.

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Section: The Origin Of the Hard X-ray Component Of Ex Lupmentioning

confidence: 99%

Section: The Origin Of the Uv Emission Of Ex Lupmentioning

confidence: 99%

A few days before the end of the 2008 extreme outburst of EX Lupi: accretion shocks and a smothered stellar corona unveiled by XMM-Newton

Grosso

Hamaguchi

Kastner

et al. 2010

A&A

View full text Add to dashboard Cite

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“…This fact has already been mentioned by Gras-Velázquez & Ray (2005), who could not derive a positive extinction value from the E B−V and E R−I colors. Similarly, Herbig et al (2001) claim it is unknown as well. An infrared excess above the photosphere is detectable longwards of the K-band.…”

Section: The Optical-infrared Sedmentioning

confidence: 99%

“…During its unpredictable flare-ups, its brightness may increase by 1−5 mag for a period of several months (Herbig 1977). In past decades EX Lup produced a number of eruptions, the last one in 2002 (Herbig 1977;Herbig et al 2001;Herbig 2007). During the present outburst, which lasted until 2008 September (AAVSO International Database 1 ), EX Lup reached a peak brightness of 8 mag in 2008 January, brighter than ever before.…”

Section: Introductionmentioning

confidence: 99%

EX Lupi in quiescence

Sipos

Ábrahám

Acosta–Pulido

et al. 2009

A&A

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Aims. EX Lupi 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 that makes EX Lup an atypical Class II object. During outburst the disk might undergo structural changes. Our characterization of the quiescent disk is intended to serve as a reference for studying the physical changes related to one of EX Lupi's strongest known eruptions in 2008 Jan-Sep. Methods. 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 modeled it using the Monte Carlo radiative transfer code RADMC. We determined the mineralogical composition of the 10 μm silicate emission feature and also gave a description of the optical and near-infrared spectra. Results. The SED is similar to that of a typical T Tauri star in most aspects, though EX Lup emits higher flux above 7 μm. The quiescent phase data suggest low-level variability in the optical-mid-infrared domain. By integrating the optical and infrared fluxes, we derived a bolometric luminosity of 0.7 L . The 10 μm silicate profile could be fitted by a mixture consisting of amorphous silicates, but no crystalline silicates were found. A modestly flaring disk model with a total mass of 0.025 M 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 apart from typical T Tauri stars.

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“…In November 2003 a young, low-mass star deeply embedded in the Lynds 1630 dark cloud, which is located in the M78 (NGC 2068) star formation region in Orion, brightened suddenly [13,14] in a manner that is reminiscent of optical outbursts associated with certain, less cloud-obscured, pre-main sequence (pre-MS) stars [16][17][18].…”

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confidence: 99%