A near-infrared variability campaign of TMR-1: New light on the nature of the candidate protoplanet TMR-1C

Abstract : We present a near-infrared (NIR) photometric variability study of the TMR-1 system, a Class I protobinary located in the Taurus molecular cloud. Our aim is to confirm NIR variability for the candidate protoplanet, TMR-1C, located at a separation of about 10″ (~1000 AU) from the protobinary. We conducted a photometric monitoring campaign between October 2011 and January 2012 using the CFHT/WIRCam imager. We were able to obtain 44 epochs of observations in each of the H and K_s filters, resulting in high-quality photometry with uncertainties of less than one-tenth of a magnitude. The shortest time difference between two epochs is ~14 min, and the longest is ~4 months. Based on the final accuracy of our observations, we do not find any strong evidence of short-term NIR variability at amplitudes of ≥0.15-0.2 mag for TMR-1C or TMR-1AB. Our present observations, however, have reconfirmed the large-amplitude long-term variations in the NIR emission for TMR-1C, which were observed between 1998 and 2002, and have also shown that no particular correlation exists between the brightness and the color changes. The object TMR-1C became brighter in the H band by ~1.8 mag between 1998 and 2002, and then fainter again by ~0.7 mag between 2002 and 2011. In contrast, TMR-1C became continually brighter in the K_s band in the period between 1998 and 2011. The (H - K_s) color for TMR-1C shows large variations, from a red value of 1.3 ± 0.07 and 1.6 ± 0.05 mag in 1998 and 2000, to a much bluer color of -0.1 ± 0.5 mag in 2002, and then again a red color of 1.1 ± 0.08 mag in 2011. The difference in the variability trends observed in the H and K_s bands suggests the presence of more than one origin for the observed variations. The observed variability from 1998 to 2011 suggests that TMR-1C becomes fainter when it gets redder, as expected from variable extinction, while the brightening observed in the K_s band could be due to physical variations in the inner disk structure of TMR-1C. We have argued in favor of TMR-1C being a young stellar object (YSO), rather than a faint background star passing behind some foreground material. There may exist short-term NIR variations at an amplitude level lower than our detection limit (~0.2 mag), which would be consistent with the YSO hypothesis. If the observed long-term variability is due to foreground extinction, then we would expect simultaneous brightening/dimming in the H and K_s bands, which we do not find to be the case. Variable foreground extinction is also expected to occur over a large spatial scale; we monitored several other objects within 4'× 4' of the TMR-1 system, and found only two objects which show long-term variations, indicating that this is not a large-scale effect. The NIR colors for TMR-1C obtained using the high-precision photometry from 1998, 2000, and 2011 observations are similar to the protostars in Taurus, suggesting that it could be a faint dusty Class I source. This object is thus a strong candidate YSO, but final confirmation as a protoplanet remains elusive and requires further investigation. Our study has also revealed two new variable sources in the vicinity of TMR-1AB that show long-term variations of ~1-2 mag in the NIR colors between 2002 and 2011. The proper motions measured for TMR-1AB and TMR-1C are -40,+58 mas/yr and -22,+5 mas/yr, respectively, with an uncertainty of ~31 mas/yr. A larger baseline of 20 years or more is required to confidently confirm the physical association of TMR-1AB and C.

Tables 1-4 are available in electronic form at http://www.aanda.org