Projects:

The long-term evolution of FUors

V1647 Ori

The outburst of the eruptive young star OO Serpentis

High-resolution polarimetry of Parsamian 21: revealing the structure of an edge-on FUOri disc

EX Lupi

Figure 1: Spectral energy distribution of the FU Orionis-type star V1057 Cyg. Measurements from 1983 are indicated with blue dots, data taken between 1996 and 2000 are indicated with red dots.

The fading phase after the outburst is well-documented in the optical/near-infrared wavelength regime. Very few data have been available so far at mid- and far-infrared wavelengths where thermal emission of the disk and the circumstellar envelope can be observed. Recently the Infrared Space Observatory (ISO) provided new photometric data on FUors in the 4.8-200 μm range.

We search for systematic brightness variations during the post-outburst phase of seven FUors at mid- and far-infrared wavelengths. We compiled two SEDs for each star: the first one is based on IRAS photometry as well as ground-based observations and is representative of the evolutionary status around 1983. The second SED was compiled from observations taken around 1996-2000 including data from ISOPHOT, the infrared photometer on-board ISO, MSX and 2MASS. The comparison of the two SEDs provides information on the wavelength dependence of the far-infrared flux evolution during a period of 15 years. (See e.g. the SED of V1057 Cyg in Fig. 1.)

Our results indicate that while at shorter wavelengths (< 25 μm) the stars show various behaviour (some brightened, some faded, some did not change), at longer wavelengths (≥ 60 μm) none of the stars changed its brightness within the measurement uncertainties. This result contradicts the predictions of models developed to describe the circumstellar structure of FUors. Via a detailed analysis of the case of V1057 Cyg we suggested three different sources of the far-infrared emission of V1057 Cyg, among which the most likely is an optically thick disk, whose temperature profile is controlled by the ambient radiation field.

The results are published in the following papers:

Title: Long-term evolution of FU Orionis objects at infrared wavelengths

Authors:Ábrahám, P., Kóspál, Á., Csizmadia, Sz., Kun, M., Moór, A., Prusti, T.

Journal: Astronomy & Astrophysics, in press (2004)

Title: The long-term evolution of 7 FU Orionis-type stars at infrared wavelengths

Authors: Kóspál, Á., Ábrahám, P., Csizmadia, Sz., Kun, M., Moór, A., Prusti, T.

Journal: 3rd Workshop of Young Researchers in Astronomy and Astrophysics and British-Hungarian N+N Workshop for Young Researchers, Publications of the Astronomy Department of the Eötvös University, v. 14, p. 119-125 (2004)

Title: Long-term evolution of FU Ori-type stars at infrared wavelengths

Authors: Kóspál, Á., Ábrahám, P., Csizmadia, Sz.

Journal: Baltic Astronomy, v. 13, p. 518-521 (2004)

Title: Long-term evolution of FU Ori-type stars at infrared wavelengths

Authors: Kóspál, Á., Ábrahám, P., Kun, M., Csizmadia, Sz., Verdugo, E.

Journal: Magnetic Fields and Star Formation: Theory Versus Observations, Kluwer Academic Press, Astrophysics and Space Science, 291, vols. 1-4, in press (2004)

On January 23 2004 a new nebula (McNeil's Nebula) was discovered towards the Orion B molecular cloud. The appearence of the nebula is probably connected to the outburst of its illuminating source, V1647 Ori (also known as IRAS 05436-0007). (Fig. 2. shows the Orion Cloud at infrared wavelengths).

Figure 2: High-resolution far-infrared image of the Orion Cloud. (RBG colour composite of 60 μm (R), 25 μm (G) and 12 μm (B) IRAS images.)

Using infrared data from ISO, IRAS, 2MASS and ground-based submm and radio observations we investigated the infared properties of this intriguing new source. We constructed the 1-1300 μm SED of V1647 Ori representative of the quiescent phase. According to this SED V1647 Ori proved to be a flat-spectrum source, which may be the result of az extended envelope around the source. The slope of the SED at the far-infrared also suggests a large amount of cold material. From the location of V1647 Ori in the J-H H-K graph we calculated the extinction towards the star, and integrating over the dereddened SED we determined its infrared-to-submillimetre luminosity. We compared the SED with a representative sample of FUors and EXors, and we found V1647 Ori to be more similar to FUors than to EXors. From its bolometric temperature and luminosity we calculated an approximate age of 400 000 years. In this evolutionary stage an accretion disk is already fully developed, though a circumstellar envelope may also be present.

Related paper:

Title: The infrared properties pf the new outburst star IRAS 05436-0007 in quiescent phase

Authors: Ábrahám, P., Kóspál, Á., Csizmadia, Sz., Moór, A., Kun, M., Stringfellow, G.

Journal: Astronomy & Astrophysics, v. 419, p. L39 (2004)

We studied the brightness and spectral evolution of the young eruptive star V1647 Ori during its recent outburst in the period 2004 February-2006 September. We performed a photometric follow-up in the bands V, RC, IC, J, H, and Ks, as well as visible and near-IR spectroscopy. The main results derived from combining our data with those published by other authors are as follows: the brightness of V1647 Ori stayed more than 4 mag above the preoutburst 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 clumps of nearby nebulosity corresponds to an angle of 61°+/-14° between the axis of the nebula and the line of sight. The overall appearance of the infrared and optical spectra did not change in the period 2004 March-2005 March, although a steady decrease of H I emission-line fluxes could be observed. In 2006 May, in the quiescent phase, the He I 1.083 μm line was observed in emission, contrary to its deep blueshifted absorption observed during the outburst. The J-H and H-Ks color maps of the infrared nebula reveal an envelope around the star whose largest extension is about 18″ (0.03 pc). The color distribution of the infrared nebula suggests reddening of the scattered light inside a thick circumstellar disk. Comparison of the Ks and Hα images of McNeil's Nebula, the conical nebulosity illuminated by V1647 Ori, shows that HH 22A, the Spitzer infrared source, and the bright clump C of the nebula may be unrelated objects. We show that the observed properties of V1647 Ori could be interpreted in the framework of the thermal instability models of Bell and coworkers. V1647 Ori might belong to a new class of young eruptive stars, defined by relatively short timescales, recurrent outbursts, a modest increase in bolometric luminosity and accretion rate, and an evolutionary state earlier than that of typical EXors.

V1647 Ori was also observed with MIDI, the mid-infrared interferometric instrument at the Very Large Telescope Interferometer (VLTI), on March 2, 2005. We present the first spectrally resolved interferometric visibility points for this object. Our results show that (1) the mid-infrared emitting region is extended, having a size of ∴7 AU at 10 μm; (2) no signatures of a close companion can be seen; (3) the 8-13 μm spectrum exhibits no obvious spectral features. Comparison with similar observations of Herbig Ae stars suggests that V1647 Ori probably possesses a disk of moderate flaring. A simple disk model with T∴r^-0.53, Σ∴r^-1.5, M_d=0.05 M_Sun is able to fit both the spectral energy distribution and the observed visibility values simultaneously.

Related papers:

Title: The 2004-2006 Outburst and Environment of V1647 Ori

Authors: Acosta-Pulido, J. A.; Kun, M.; Ábrahám, P.; Kóspál, Á.; Csizmadia, Sz.; Kiss, L. L.; Moór, A.; Szabados, L.; Benkő, J. M.; Delgado, R. Barrena; Charcos-Llorens, M.; Eredics, M.; Kiss, Z. T.; Manchado, A.; Rácz, M.; Almeida, C. Ramos; Székely, P.; Vidal-Nunez, M. J.

Journal: 2007, AJ, 133 2020

Title: First AU-scale observations of V1647 Orionis with VLTI/MIDI

Authors: Ábrahám, P.; Mosoni, L.; Henning, Th.; Kóspál, Á.; Leinert, Ch.; Quanz, S. P.; Ratzka, Th.

Journal: 2006, A&A, 449 13

Figure 3: High-resolution far-infrared image if the Serpens Cloud. (RBG colour composite of 60 μm (R), 25 μm (G) and 12 μm (B) IRAS images.)

OO Serpentis is a deeply embedded pre-main sequence star in the Serpens NW star-forming region. The star went into outburst in 1995 and gradually faded afterwards. In many respects its eruption resembled the well-known FU Orionis-type (FUor) or EX Lupi-type (EXor) outbursts. Since very few such events have ever been documented at infrared wavelengths, our aim is to study the temporal evolution of OO Ser in the infrared. OO Ser was monitored with the Infrared Space Observatory in the 3.6-100 μm wavelength range, starting 4 months after peak brightness and covering a period of 20 months. Eight years later, in 2004-2006 we again observed OO Ser at 2.2 and 12 μm from the ground and complemented this dataset with archival Spitzer observations also from 2004. We analysed these data with special attention to source confusion and constructed light curves at 10 different wavelengths as well as spectral energy distributions. Results: The outburst caused brightening in the whole infrared regime. According to the infrared light curves, OO Ser started a wavelength-independent fading after the peak brightness. Later the flux decay became slower but stayed practically wavelength-independent. The fading is still ongoing, and current fading rates indicate that OO Ser will not return to quiescent state before 2011. The outburst timescale of OO Ser seems to be shorter than that of FUors, but longer than that of EXors. This and the moderate luminosity suggest that OO Ser is different from both FUors and EXors, and shows some similarities to the recently erupted young star V1647 Ori. Based on its SED and bolometric temperature, OO Ser seems to be an early class I object, with an age of <105 yr. As proposed by outburst models, the object is probably surrounded by an accretion disc and a dense envelope. This picture is also supported by the wavelength-independence of the fading. Due to the shorter outburst timescales, models developed for FUors can only work for OO Ser if the viscosity parameter in the circumstellar disc, &alpha, is set to an order of magnitude higher value than usual for FUors.

Related paper:

Title: The outburst of the eruptive young star OO Serpentis between 1995 and 2006

Authors: Kóspál, Á.; Ábrahám, P.; Prusti, T.; Acosta-Pulido, J.; Hony, S.; Moór, A.; Siebenmorgen, R.

Journal: 2007, A&A, 470 211

Parsamian 21 is the central source of a compact, bright cometary nebula in Aquila. This star shows many spectroscopic characteristics of FUors and is likely surrounded by a circumstellar disk. Fig. 4. shows an infrared, red and blue colour composite image of Parsamian 21.

Figure 4: RGB colour composite image of the FU Orionis-type star Parsamian 21 (infrared (R), red (G) and blue (B) POSS2 images).

We presented the first high spatial resolution near-infrared direct and polarimetric observations of Parsamian 21, obtained with the Nasmyth Adaptive Optics System-CONICA instrument at the Very Large Telescope (VLT). We complemented these measurements with archival infrared observations, such as Hubble Space Telescope (HST)/Wide Field Planetary Camera 2 (WFPC2) imaging, HST/Near Infrared Camera and Multi-Object Spectrometer (NICMOS) polarimetry, photometry with the Spitzer Space Telescope's Infrared Array Camera (IRAC) and Multiband Imaging Photometer (MIPS), spectroscopy with Spitzer's Infrared Spectrograph (IRS), as well as Infrared Space Observatory (ISO) photometry. Our main conclusions are as follows: (1) we argue that Parsamian 21 is probably an FUOrionis-type object (FUor); (2) Parsamian 21 is not associated with any rich cluster of young stars; (3) our measurements reveal a circumstellar envelope, a polar cavity and an edge-on disc; the disc seems to be geometrically flat and extends from approximately 48 to 360 au from the star; (4) the spectral energy distribution (SED) can be reproduced with a simple model of a circumstellar disc and an envelope; (5) within the framework of an evolutionary sequence of FUors proposed by Green et al. and Quanz et al., Parsamian 21 can be classified as an intermediate-aged object.

Related paper:

Title: High-resolution polarimetry of Parsamian 21: revealing the structure of an edge-on FUOri disc

Authors: Kóspál, Á.; Ábrahám, P.; Apai, D.; Ardila, D. R.; Grady, C. A.; Henning, Th.; Juhász, A.; Miller, D. W.; Moór, A.

Journal: 2008, MNRAS, 383 1015

Figure 1: Lightcurve of EX Lupi between 2001 July and 2008 January. The young star brightened by almost 5 magnitudes.

In 2008 January the amateur astronomer A. Jones announced that EX Lupi, the prototype of the EXor class of pre-main sequence eruptive variables, had brightened significantly, and this outburst period lasted until September 2008 (AAVSO International Database) EX Lup is an M0V star in the Lupus 3 star forming region. Its quiescent phase brightness is V ∼13 mag, which increases during its unpredictable brightenings by 1-5 mag and stay there for several months. In the last decades EX Lup produced a number of flare-ups, the last one in 2002. During its current outburst it reached a peak luminosity of 8 mag in January, shining brighter than ever before.

In quiescence at optical and near-infrared wavelengths EX Lup cannot be distinguished from normal T Tau stars (Herbig 2007). Here we investigate whether it is the circumstellar environment which makes EX Lup an atypical Class II object. In 2008 EX Lupi had one of its highest known eruptions, and its circumstellar structure might have temporarily changed during the outburst. Our characterization of the quiescent disk structure of EX Lup serves as a reference to study the physical changes related to the eruption. 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. A mineralogical decomposition of the 10 μm silicate emission feature as well as the description of the optical and near-infrared spectra were performed. In the quiescent phase data low level variability was clearly detected in the whole optical-infrared domain. The shape of the SED is in general similar to that of a typical T Tauri star SED, with an excess above 25 μm. A modestly flaring disk model reaching out to 150 AU and with a total mass of 0.025 M_Sun was able to reproduce the observed SED. The inner radius at 0.2 AU is considerably larger the sublimation radius. We derived an age and luminosity of the system to be approximately 1.4 x 10^6 year and 0.7 L_Sun respectively. The 10 μm silicate profile could be fitted by a mixture mostly consisting of amorphous silicate and carbon, no crystalline silicates were found.

Related paper:

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EX Lupi in extreme outburst

We performed photometric and spectroscopic observations, that prove that EX Lup is in outburst, exhibiting the highest peak brightness ever observed. The spectra of the present outburst differ significantly from the previous ones in several aspects: the lack of the Hγ and He lines, and the extremely strong metallic features. The increased brightness of the system is probably due to increased accretion. Increased accretion, and consequently increased stellar wind, can also explain the wealth of metallic lines coming from infalling or ejected hot gas, similarly to the case of DR Tau (Beristain et al., 1998).
We observed EX Lupi with several instruments... blabla

On going....

Related paper:

Title: The Extreme Outburst of EX Lup in 2008: Optical Spectra and Light Curve

Authors: Kóspál, Á.; Németh, P.; Ábrahám, P.; Kun, M.; Henden, A.; Jones, A. F.

Journal: 2008, IBVS, 5819 1