Physics – Optics
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009phdt.........1k&link_type=abstract
PhD Thesis, Eötvös Loránd University, Budapest, Hungary, 120 pages
Physics
Optics
Stars: Pre-Main Sequence, Stars: Circumstellar Matter, Infrared: Stars
Scientific paper
Young eruptive stars (FU Orionis- and EX Lupi-type objects) form a small, but remarkable subgroup of pre-main sequence stars. They are characterized by eruptions which may increase the brightness of the system by as much as a factor of 100. Outbursts probably correspond to increased accretion from the circumstellar disk to the star. In my dissertation I present the detailed analysis of three young eruptive stars using ground-based and space-borne observations at optical and infrared wavelengths.
The outburst of OO Serpentis between 1995 and 2006. OO Ser is a deeply embedded young star that produced an eruption in 1995. Using archival (ISO, Spitzer) and new observations, I constructed the light curves of the star at ten different infrared wavelengths. My results show that the eruption caused brightening in the whole infrared regime, which is followed by a slow, wavelength-independent fading. The fading is still ongoing and the star will probably not return to quiescence before 2011. The timescale of the outburst is shorter than that of typical FU Ori-type objects, but longer than that of EX Lupi-type stars. Based on the spectral energy distribution, OO Ser seems to be an early Class I object with an age of <10^5 yr. In accordance with outburst models, the star is probably surrounded by an accretion disk and a dense envelope. Due to the shorter timescales, outburst models developed for FU Ori-type stars can only work for OO Ser if the viscosity of the circumstellar disk is set to an order of magnitude larger value than usual for FU Ori objects.
The 2004-2006 outburst and environment of V1647 Orionis. V1647 Ori is a pre-main sequence star that suddenly brightened up in less than 4 months, reaching its peak brightness in 2004 February. I participated in a monitoring program, in which we obtained V R_C I_C J H K_s-band observations. After reaching its peak brightness, the star was fading very slowly. Then, in 2005 October it suddenly faded back to its quiescence level. The timescale of the outburst and the moderate increase in bolometric luminosity suggest that V1647 Ori differs both from FU Ori- and EX Lupi-type objects. By calculating the time delay between the brightness variations of the star and a nebular position, I deduced the geometry of the system. The near-infrared color maps of the nebula suggest that the star is surrounded by a disk and an extended nebula.
High-resolution polarimetry of Parsamian 21. Parsamian 21 is an FU Orionis-type object consisting of a central star and an extended reflection nebula. We obtained high spatial resolution adaptive optics assisted near-infrared direct and polarimetric observations with the NACO instrument at ESO's Very Large Telescope. I complemented these measurements with archival Hubble, Spitzer and ISO data. The results revealed that (1) the star is probably indeed an FU Orionis-type object; (2) the star is not associated with any known rich cluster of young stars; (3) the star is surrounded by an edge-on disk, and a circumstellar envelope with a polar cavity; (4) the disk seems to be flat and extends from at least 48 to 360 AU from the star; (5) the spectral energy distribution can be successfully modeled with a circumstellar disk and an envelope; (6) within the framework of an evolutionary sequence of FU Ori-type stars, Parsamian 21 seems to be an intermediate-aged object.
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