Mária Kun

EX Lupi in quiescence

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,

Long-term evolution of FU Orionis objects at infrared wavelengths

We investigate the brightness evolution of seven FU Orionis systems in the 1−100 µm wavelength range using data from the Infrared Space Observatory (ISO). The ISO measurements were supplemented by 2MASS and MSX observations performed in the same years as the ISO mission (1995−98). The spectral energy distributions (SEDs) based on these data points were compared with earlier ones derived from the IRAS photometry as well as from ground-based observations carried out around the epoch 1983. In three cases (Z CMa, Parsamian 21, V1331 Cyg) no difference between the two epochs was seen within the measurement uncertainties. V1057 Cyg, V1515 Cyg and V1735 Cyg have become fainter at near-infrared wavelengths while V346 Nor has become slightly brighter. V1057 Cyg exhibits a similar flux change in the mid-infrared. At λ ≥ 60 µ mm ost of the sources remained constant; only V346 Nor seems to fade. Our data on the long-term evolution of V1057 Cyg agree with the model predictions of Kenyon & Hartmann (1991) and Turner et al. (1997) at near- and mid-infrared wavelengths, but disagree at λ> 25 µm. We discuss if this observational result at far-infrared wavelengths could be understood in the framework of the existing models.

The Rapid Outbursting Star GM Cep: An EXor in Tr 37?

We present optical, IR, and millimeter observations of the solar-type star 13-277, also known as GM Cep, in the 4 Myr old cluster Tr 37. GM Cep experiences rapid magnitude variations of more than 2 mag at optical wavelengths. We explore the causes of the variability, which seem to be dominated by strong increases in the accretion, being similar to EXor episodes. The star shows high, variable accretion rates (up to ~10−6 M☉ yr−1) and signs of powerful winds, and it is a very fast rotator (Vsin i ~ 43 km s−1). Its strong mid-IR excesses reveal a very flared disk and/or a remnant envelope, most likely out of hydrostatic equilibrium. The 1.3 mm fluxes suggest a relatively massive disk (MD ~ 0.1 M☉). Nevertheless, the millimeter mass is not enough to sustain increased accretion episodes over large timescales, unless the mass is underestimated due to significant grain growth. We finally explore the possibility of GM Cep having a binary companion, which could trigger disk instabilities producing the enhanced accretion episodes.

Star Formation in the L1333 Molecular Cloud in Cassiopeia

?????Radio and optical observations have been made in order to examine star formation in the dark cloud L1333 [?(1950) = 2h210, ?(1950) = 75?15]. A study of the cumulative distribution of field star distance moduli yields a distance value close to 180 pc for the L1333 molecular cloud. 13CO observations revealed two filamentary molecular clouds with distinct velocities of VLSR ~ -2 and 3 km s-1, respectively. Thirteen C18O cores, characterized by an average molecular mass (MLTE) of ~9 M? and a mean density of ~1.4 ? 104 cm-3, are embedded in the two 13CO clouds. We have detected 18 H? emission-line stars projected within or near the 13CO clouds on objective-prism plates. They can be regarded as candidate pre?main-sequence stars formed in the clouds. Five IRAS sources with flux density distributions characteristic of young stellar objects (YSOs) are found in the area of the cloud. Three of the IRAS sources coincide with H? emission-line stars, the others with faint stars without detected H? emission. One of the latter sources is associated with a C18O core and exhibits a protostar-type infrared spectrum. The IRAS source exhibits a winglike feature of ~1.6 km s-1 (full width at zero intensity) in C18O, which may indicate that the YSO has an outflow. We note that the C18O core has the smallest ratio of virial mass (Mvir) to MLTE among the C18O cores in L1333, suggesting that star formation occurs preferentially in a core whose internal kinetic energy is low compared with the self-gravitational energy. A possible scenario for the past star formation activity is discussed.

The Disappearing Act of KH 15D: Photometric Results from 1995 to 2004

We present results from the most recent (2002–2004) observing campaigns of the eclipsing system KH 15D, in addition to rereduced data obtained at Van Vleck Observatory (VVO) between 1995 and 2000. Phasing 9 yr of photometric data shows substantial evolution in the width and depth of the eclipses. The most recent data indicate that the eclipses are now approximately 24 days in length, or half the orbital period. These results are interpreted and discussed in the context of the recent models for this system put forward by Winn and coworkers and Chiang & Murray-Clay. A periodogram of the entire data set yields a highly significant peak at 48.37 ± 0.01 days, which is in accord with the spectroscopic period of 48.38 ± 0.01 days determined by Johnson and coworkers. Another significant peak, at 9.6 days, was found in the periodogram of the out-of-eclipse data at two different epochs. We interpret this as the rotation period of the visible star and argue that it may be tidally locked in pseudosynchronism with its orbital motion. If so, application of Huts theory implies that the eccentricity of the orbit is e = 0.65 ± 0.01. Analysis of the Ultraviolet and Visual Echelle Spectrograph VLT spectra obtained by Hamilton and coworkers shows that the v sin i of the visible star in this system is 6.9 ± 0.3 km s-1. Using this value of v sin i and the measured rotation period of the star, we calculate the lower limit on the radius to be R = (1.3 ± 0.1) R⊙, which concurs with the value obtained by Hamilton and coworkers from its luminosity and effective temperature. Here we assume that i = 90°, since it is likely that the spin and orbital angular momenta vectors are nearly aligned. One unusually bright data point obtained in the 1995/1996 observing season at VVO is interpreted as the point in time when the currently hidden star B made its last appearance. Based on this datum, we show that star B is 0.46 ± 0.03 mag brighter than the currently visible star A, which is entirely consistent with the historical light curve. Finally, well-sampled VJ and IJ data obtained at the Cerro Tololo Inter-American Observatory Yale 1 m telescope during 2001/2002 show an entirely new feature: the system becomes bluer by a small but significant amount in very steady fashion as it enters eclipse and shows an analogous reddening as it emerges from eclipse. This suggests an extended zone of hot gas located close to but above the photosphere of the currently visible star. The persistence of the bluing of the light curve shows that its length scale is comparable to a stellar radius.

Search for new T Tauri stars in the Cepheus-Cassiopeia region

The Cepheus-Cassiopeia star-forming region has been searched for new T Tauri stars (TTSs) based on the ROSAT all sky survey (RASS). Optical spectroscopic observations were carried out toward 45 GSC stellar counterparts of RASS sources looking for the Li absorption line (6708 A), a sign of youth. The detection of this line resulted in finding 11 to 16 new TTSs in this region. Using follow-up optical photometric observations and evolutionary models these Li-rich stars are revealed to be young low-mass stars. The most of the young stars are separated from the

Long-Term Evolution of FU Ori-Type Stars at Infrared Wavelengths

element[][13]{CO}

Star Formation in L 1199

molecular clouds by ~10 pc, significantly more than in Chamaeleon. A group of the new TTSs are isolated from the CO clouds and distributed inside the previously determined CO void. Possible formation scenarios including the interaction with the supernova shock for the isolated TTSs are discussed.

Study of Molecular Clouds and Star Formation in the Region of IC 2118

We investigated the brightness evolution of 5 FU Ori systems in the 1–200 μm wavelength range using observations from the Infrared Space Observatory, 2MASS and MSX data. The SEDs were compared with earlier ones derived from the IRAS photometry and ground-based observations around the epoch 1983. In three cases no difference was seen, in one object the near- and mid-infrared part of the spectrum became fainter by a factor of 2, and in the fifth case a marginal fading was observed. We study in detail the case of V1057 Cyg.

Study of L 688/L 694/L 700: a Complex of Dark Clouds in Aquila

Lynds 1199 is an extended dark cloud of moderate opacity in the upper Cepheus region. The B3V type star HD206135 illuminating the reflection nebula DG 175 is associated with this cloud. In this paper the nature of the cloud and its associated young stellar objects is studied on the basis of13CO data obtained with the 4 m millimeter wave telescope of Nagoya University, photographic observations taken with the 60/90 cm Schmidt telescope of Konkoly Observatory, as well as IRAS data.