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Register a new userMulti-Wavelength Study of the 2008-2009 Outburst of V1647 Ori
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David Garcia-Alvarez
Publication date
2011
fields
Physics
and research's language is
English
Authors
D. Garcia-Alvarez
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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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We present new high-resolution infrared echelle spectra of V1647 Ori, the young star that illuminates McNeils nebula. From the start, V1647 Ori has been an enigmatic source that has defied classification, in some ways resembling eruptive stars of the FUor class and in other respects the EXor variables. V1647 Ori underwent an outburst in 2003 before fading back to its pre-outburst brightness in 2006. In 2008, it underwent a new outburst. In this paper we present high-resolution K-band and M-band spectra from the W. M. Keck Observatory that were acquired during the 2008 outburst. We compare the spectra to spectra acquired during the previous outburst and quiescent phases. We find that the luminosity and full width at half maximum power of Br-gamma increased as the star has brightened and decreased when the star faded indicating that these phases are driven by variations in the accretion rate. We also show that the temperature of the CO emission has varied with the stellar accretion rate confirming suggestions from modeling of the heating mechanisms of the inner disk (e.g. Glassgold et al. 2004). Finally we find that the lowest energy blue-shifted CO absorption lines originally reported in 2007 are no longer detected. The absence of these lines confirms the short-lived nature of the outflow launched at the start of the quiescent phase in 2006.
(Abridged) We studied the brightness and spectral evolution of the young eruptive star V1647 Ori during its recent outburst in the period 2004 February - 2006 Sep. We performed a photometric follow-up in the bands V, R_C, I_C, J, H, K_s as well as visible and near-IR spectroscopy. The main results are as follows: The brightness of V1647 Ori stayed more than 4 mag above the pre-outburst level until 2005 October when it started a rapid fading. In the high state we found a periodic component in the optical light curves with a period of 56 days. The delay between variations of the star and variations in the brightness of clump of nearby nebulosity corresponds to an angle of 61+/-14 degrees between the axis of the nebula and the line of sight. A steady decrease of HI emission line fluxes could be observed. In 2006 May, in the quiescent phase, the HeI 1.083 line was observed in emission, contrary to its deep blueshifted absorption observed during the outburst. The J-H and H-K_s color maps of the infrared nebula reveal an envelope around the star. The color distribution of the infrared nebula suggests reddening of the scattered light inside a thick circumstellar disk. We show that the observed properties of V1647 Ori could be interpreted in the framework of the thermal instability models of Bell et al. (1995). V1647 Ori might belong to a new class of young eruptive stars, defined by relatively short timescales, recurrent outbursts, modest increase in bolometric luminosity and accretion rate, and an evolutionary state earlier than that of typical EXors.
Context: It is hypothesized that low-mass young stellar objects undergo eruptive phases during their early evolution. The outburst of V1647 Ori between 2003 and 2006 offered a rare opportunity to investigate such an accretion event. Aims: By means of our interferometry observing campaign during this outburst, supplemented by other observations, we investigate the temporal evolution of the inner circumstellar structure of V1647 Ori We also study the role of the changing extinction in the brightening of the object and separate it from the accretional brightening. Methods: We observed V1647 Ori with MIDI/VLTI at two epochs in this outburst. First, during the slowly fading plateau phase (2005 March) and second, just before the rapid fading of the object (2005 September), which ended the outburst. We used the radiative transfer code MC3D to fit the interferometry data and the spectral energy distributions from five different epochs at different stages of the outburst. The comparison of these models allowed us to trace structural changes in the system on AU-scales. We also considered qualitative alternatives for the interpretation of our data. Results: We found that the disk and the envelope are similar to those of non-eruptive young stars and that the accretion rate varied during the outburst. We also found evidence for the increase of the inner radii of the circumstellar disk and envelope at the beginning of the outburst. Furthermore, the change of the interferometric visibilities indicates structural changes in the circumstellar material. We test a few scenarios to interpret these data. We also speculate that the changes are caused by the fading of the central source, which is not immediately followed by the fading of the outer regions. However, if the delay in the fading of the disk is responsible for the changes seen in the MIDI data, the effect should be confirmed by dynamical modeling.
The blazar AO 0235+164 (z = 0.94) has been one of the most active objects observed by Fermi Large Area Telescope (LAT) since its launch in Summer 2008. In addition to the continuous coverage by Fermi, contemporaneous observations were carried out from the radio to {gamma} -ray bands between 2008 September and 2009 February. In this paper, we summarize the rich multi-wavelength data collected during the campaign (including F-GAMMA, GASP- WEBT, Kanata, OVRO, RXTE, SMARTS, Swift, and other instruments), examine the cross-correlation between the light curves measured in the different energy bands, and interpret the resulting spectral energy distributions in the context of well-known blazar emission models. We find that the {gamma} -ray activity is well correlated with a series of near-IR/optical flares, accompanied by an increase in the optical polarization degree. On the other hand, the X-ray light curve shows a distinct 20 day high state of unusually soft spectrum, which does not match the extrapolation of the optical/UV synchrotron spectrum. We tentatively interpret this feature as the bulk Compton emission by cold electrons contained in the jet, which requires an accretion disk corona with an effective covering factor of 19% at a distance of 100 Rg . We model the broadband spectra with a leptonic model with external radiation dominated by the infrared emission from the dusty torus.
Abriged version for astroph: The young late-type star V1118 Orionis was in outburst from 2005 to 2006. We followed the outburst with optical and near-infrared photometry; the X-ray emission was further probed with observations taken with XMM-Newton and Chandra during and after the outburst. In addition, we obtained mid-infrared photometry and spectroscopy with Spitzer at the peak of the outburst and in the post-outburst phase. The spectral energy distribution of V1118 Ori varied significantly over the course of the outburst. The optical flux showed the largest variations, most likely due to enhanced emission by a hot spot. The latter dominated the optical and near-infrared emission at the peak of the outburst, while the disk emission dominated in the mid-infrared. The X-ray flux correlated with the optical and infrared fluxes, indicating that accretion affected the magnetically active corona and the stellar magnetosphere. The thermal structure of the corona was variable with some indication of a cooling of the coronal temperature in the early phase of the outburst with a gradual return to normal values. Color-color diagrams in the optical and infrared showed variations during the outburst, with no obvious signature of reddening due to circumstellar matter. Using MC realizations of star+disk+hotspot models to fit the SED in ``quiescence and at the peak of the outburst, we determined that the mass accretion rate varied from about 2.5E-7 Msun/yr to 1E-6 Msun/yr; in addition the fractional area of the hotspot increased significantly as well. The multi-wavelength study of the V1118 Ori outburst helped us to understand the variations in spectral energy distributions and demonstrated the interplay between the disk and the stellar magnetosphere in a young, strongly accreting star.
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