Mass accretion rates from multi-band photometry in the Carina Nebula: the case of Trumpler 14

TL;DR

This study investigates mass accretion rates of pre-Main Sequence stars in Trumpler 14 using multi-band photometry, revealing active accretion in stars up to 10 million years old and evidence of gas-rich transitional discs in older stars.

Contribution

It provides new measurements of accretion rates and ages for PMS stars in Trumpler 14, highlighting the presence of gas in older transitional discs, challenging previous assumptions.

Findings

Most PMS stars are younger than 10 Myr with median age ~3 Myr.

Approximately 20% of accreting stars are older than 10 Myr.

Spectral energy distributions indicate the presence of gas-rich transitional discs in older stars.

Abstract

We present a study of the mass accretion rates of pre-Main Sequence (PMS) stars in the cluster Trumpler 14 (Tr14) in the Carina Nebula. Using optical multi-band photometry we were able to identify 356 PMS stars showing H-alpha excess emission with equivalent width EW(H-alpha)>20\AA. We interpret this observational feature as indication that these objects are still actively accreting gas from their circumstellar medium. From a comparison of the HR diagram with PMS evolutionary models we derive ages and masses of the PMS stars. We find that most of the PMS objects are younger than 10 Myr with a median age of ~3 Myr. Surprisingly, we also find that ~20% of the mass accreting objects are older than 10 Myr. For each PMS star in Trumpler 14 we determine the mass accretion rate ($\dot{M}_{acc}$) and discuss its dependence on mass and age. We finally combine the optical photometry with near-IR observations to build the spectral energy distribution (SED) for each PMS star in Tr14. The analysis of the SEDs suggests the presence of transitional discs in which a large amount of gas is still present and sustains accretion onto the PMS object at ages older than 10 Myr. Our results, discussed in light of recent recent discoveries with Herschel of transitional discs containing a massive gas component around the relatively old PSM stars TW Hydrae, 49 Ceti, and HD 95086, support a new scenario in which old and evolved debris discs still host a significant amount of gas.