Searching for planetary-mass T-dwarfs in the core of Serpens

Abstract

Context. The knowledge of the present-day mass function of young clusters and the mass of their coolest substellar members is essential to clarify the brown dwarf formation mechanism, which still remains a matter of debate. Aims. We searched for isolated planetary-mass T-dwarfs in the ∼3 Myr old Serpens Core cluster. Methods. We performed a deep imaging survey of the central part of this cluster using the WIRCam camera at the CFHT. Observations were performed through the narrow-band CH 4 off and CH 4 on filters, to identify young T-dwarfs from their 1.6 μm methane absorption bands, and the broad-band JHK S filters, to better characterize the selected candidates. We complemented our WIRCam photometry with optical imaging data from MegaCam at CFHT and Suprime-Cam at the Subaru telescope and mid-infrared flux measurements from the Spitzer "core to disk" (c2d) Legacy Survey. Results. We report four faint T-dwarf candidates in the direction of the Serpens Core with CH 4 on−CH 4 off above 0.2 mag, estimated visual extinction in the range 1−9 mag and spectral type in the range T1−T5 based on their dereddened CH 4 on−CH 4 off colors. Comparisons with T-dwarf spectral models and optical to mid-infrared color-color and color-magnitude diagrams, indicate that two of our candidates (ID 1 and 2) are background contaminants (most likely heavily reddened low-redshift quasars). The properties of the other two candidates (ID 3 and 4) are consistent with them being young members of the Serpens Core cluster, although our analysis can not be considered conclusive. In particular, ID 3 may also be a foreground T-dwarf. It is detected by the Spitzer c2d survey but only flux upper limits are available above 5.8 μm and, hence, we can not assess the presence of a possible disk around this object. However, it presents some similarities with other young T-dwarf candidates (S Ori 70 in the σ Orionis cluster and CFHT_J0344+3206 in the direction of IC 348). If ID 3 and 4 belong to Serpens, they would have a mass of a few Jupiter masses and would be amongst the youngest, lowest mass objects detected in a star-forming region so far.

Characterising the Protostellar Population of the Magellanic Clouds with VLT/SINFONI

“…2 Jacob Ward, Joana Oliveira, Jacco van Loon, Marta Sewilo In general our sample exhibits high Brγ luminosities / K -band magnitude ratios compared with similar objects in the Milky Way from Cooper et al (2013), suggestive of higher accretion rates. This would be consistent with the results of De Marchi et al (2011) and Spezzi et al (2012), finding that low mass pre-main sequence stars exhibit higher accretion rates in the Magellanic Clouds than in the Milky Way. The effects of metallicity on H i emission are expected to be small (Kudritzki 2002) and we see no excess He i emission compared to the Galactic sample.…”

Spectroscopy of brown dwarf candidates in IC 348 and the determination of its substellar IMF down to planetary masses

“…This is the goal of a large programme (P.I. J. Bouvier) we are conducting at the Canada-France-Hawaii Telescope (CFHT), designed to uncover the substellar population of various nearby young clusters and compare their IMF and minimum mass for brown dwarf formation (Burgess et al 2009;Alves de Oliveira et al 2010;Alves de Oliveira et al 2012;Spezzi et al 2012).…”

Probing the Upper Scorpius mass function in the planetary-mass regime★

“…Alves de confirmed spectroscopically the first L dwarfs in the ρ Ophiuchus molecular cloud with masses between 10 and 4 MJup, resulting in a mass function in agreement with other regions (Bastian et al 2010) and the field (Chabrier 2003(Chabrier , 2005. Moreover, Spezzi et al (2012) reported two potential T-type candidates in the core of the Serpens cloud with masses of a few Jupiter masses if true members. Similarly Burgess et al (2009) identified one mid-T-type candidate in IC 348 with a mass between 5 and 1 MJup but spectroscopy is mandatory to confirm their nature.…”