Abstract
Flux variability is a common feature of Young Stellar Objects (YSOs), which is often related to intermittent events of disk accretion (EXors events in case of 3–4 magnitudes variations). Recently, thanks to the surveys carried out by the space missions Spitzer and WISE, it has become possible to perform statistical studies on the mid-IR variability on large samples of YSOs. As a follow-up of our recent statistical study on five star forming regions (Antoniucci et al., Astrophys. J. 782:51, 2014), we present the 3–5 μm variability study of the YSOs population of the Vela-D star forming region. We have compared the 3.6 μm and 4.5 μm Spitzer-IRAC fluxes of 181 YSOs in Vela-D with their WISE fluxes at 3.4 μm and 4.6 μm and selected those objects simultaneously varying in both bands. We have identified a robust sample of 34 variables. On the base of the infrared excess of the Spectral Energy Distribution (SED) and the magnitude vs. color variations, we select 5 EXors candidates, which will be systematically monitored to firmly ascertain their nature. The selected 34 variables represent ∼18 % of the YSOs detected with Spitzer and WISE, a percentage higher than that of other young star forming regions. Conversely, the percentage of candidate EXors (2.7 %) is quite similar to that measured in Perseus, Ophiuchus and Serpens, and also equals that found in Vela-D on the base of Spitzer variability (Giannini et al., Astrophys. J. 704:606, 2009). Consistently with our finding presented in Antoniucci et al. (2014), this fraction equals the probability of observing the source once in burst and once in quiescence, under the hypothesis that the time elapsed between the two events is of about 0.5–1 year. Of the 5 selected EXors candidates, 3 are Class I sources, and 2 are flat-spectrum sources, a circumstance that suggests that accretion-driven variability is a common phenomenon during the earlier phases of the protostellar evolution. In the light of the new WISE data, we also re-examine a sample of 10 variables, which we had already selected in Giannini et al. (2009). From the inspection of their light curves, we select two flat-spectrum sources as the best EXors candidates.
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Notes
Unfortunately Vela-D was not observed in the 3-Band Cryo phase (August–September 2010).
Namely those whose slope between two subsequent photometric data (both in B1 and B2) has always the same sign (Fig. 3).
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Acknowledgements
This work is based on the data products of the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. It makes use also of the observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.
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Giannini, T., Lorenzetti, D., Antoniucci, S. et al. On the 3–5 μm variability of young variables in Vela-D through Spitzer-WISE observations. Astrophys Space Sci 352, 691–698 (2014). https://doi.org/10.1007/s10509-014-1971-2
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DOI: https://doi.org/10.1007/s10509-014-1971-2