Young Stellar Objects observed by MOSTMichal Siwak & MOST team

Mount Suhora Observatory, Cracow Pedagogical Universityul. Podchorazych 2, 30-084 Krakow, Poland

Introduction

In the recent years the MOST satellite gathered dozens of high quality lightcurves of Young Stellar Objects (YSO). We present the most interestingresults obtained from the data collected between 2009-2013.

Observations

The optical system of the MOST satellite consists of a Rumak-Maksutovf/6, 15 cm reflecting telescope. The custom broad-band filter covers thespectral range of 350 – 700 nm with the effective wavelength located closeto the Johnson V band (Matthews et al., 2004). All targets listed belowwere observed in the direct-imaging mode of the satellite. For details ofdata processing see Siwak et al. (2010).

◮ Classical T Tauri, FUors and Herbig Stars

stars year of observations

TW Hya 2007, 2008, 2009, 2011RY Tau 2009FU Ori 2010Z CMa 2011RU Lup, IM Lup 2012, 2013AB Aur, SU Aur 2012

◮ Weak-lined T Tauri Stars (WTTS)

stars year of observations

V410 Tau, V987 Tau 2009Lupus 3-14 2009, 2010Lupus 3-48 2009

TW Hya and mysterious ”eclipses”

In contrast to the previous MOST runs the variations observed in 2011 weresurprisingly regular showing roughly equidistant spikes at typical separationof about 4 days. The data reveal also a dozen of well defined dips, whichwe call ”eclipses” (third and fourth panel). We suggest, that these may beeclipses of hot spots created at the footprints of accretion columns causedby ”dusty clumps” orbiting the star on highly inclined orbits.

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TW Hya 2009

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TW Hya 2011

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Figure 1: Differencies between light curves of TW Hya obtained in 2009 and 2011. The darker

points in 2011 data represent single MOST orbits containing ”eclipses” (see third panel). The

fourth panel shows relation between total eclipse duration D and branch duration (D-d)/2.

(Siwak et al., 2011a and Siwak et al., in prep.)

Quasi-periodic oscillations in FU Orionis

The light curve of FU Ori obtained during 28 days reveals two main 9-8 and2.4-2.2 days quasi-periodic features occurring nearly simultaneously. Theirperiods may shorten slowly which may be due to spiralling in of individualplasma parcels toward the inner disc radius, estimated at 4.8±0.2 R⊙ –this value agrees well with the estimates from interferometric observations(Siwak et al., 2013 and references therein).

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FU Ori

Figure 2: Light curve of FU Ori (first panel) and its Morlet-6 wavelet spectra (next two panels).

Differential rotation of Weak-lined T Tauri Stars

The light curves of a few WTTS observed by MOST are modulated by coldspots. A simple model assuming one large polar spot and second smallerlocalized closer to the stellar equator well reproduces the observed lightvariations. Assuming that the spots are invariable in time, differentialrotation can be determined, as in the case of V987 Tau and Lupus 3-14.The two remaining stars seems to rotate rigidly (Siwak et al., 2011b).

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V410 Tau 0.92

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V987 Tau

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Figure 3: Light curves of V410 Tau, V987 Tau, Lup 3-14 and Lup 3-48.

Conclusion

This is just the sample of results obtained for a few YSOs by the smallestspace telescope. The data obtained for SU Aur & AB Aur and RU Lup &IM Lup are currently under analysis. In the near future, we plan tocomplete photometric survey of all Classical T Tauri-type Stars brighterthan V≈11.5 mag and available for the MOST satellite.A longer run, necessary for detailed characterisation of FU Ori quasi -periodic oscillations will take place during the 2013-2014 Winter season.

References

Matthews J., Kusching R., Guenther D., et al., 2004, Nature, 430, 51Siwak M., Rucinski S. M., Matthews J., et al., 2010, MNRAS, 408, 314Siwak M., Rucinski S. M., Matthews J., et al., 2011a, MNRAS, 410, 2725Siwak M., Rucinski S. M., Matthews J., et al., 2011b, MNRAS, 415, 1119Siwak M., Rucinski S. M., Matthews J., et al., 2013, MNRAS, 432, 194

Acknowledgments

MS is immensely grateful for the Polish National Science Centre grant2012/05/E/ST9/03915 and the CSA postdoctoral grant to S.M. Rucinski.

Protostars & Planets VI, 15-20 July 2013, Heidelberg, Germany siwak@astro.as.up.krakow.pl