NTT and VLT diffraction limited imaging of Trumpler 14: revealing a massive core-halo cluster

Abstract

Aims. We present the deepest and highest resolution near-infrared imaging to date of cluster Trumpler 14 in Carina. Our goal is to identify and characterise the young stellar population of this massive cluster. Methods. We made use of deep and wide-field NIR images from NTT and VLT observations, that were sensitive enough to detect substellar sources at the distance to this cluster, and at high enough resolution (VLT diffraction limited) to fully resolve the core of the cluster crowded with O stars. Results. We find that Tr14 has a well-defined core-halo structure, where less than 30% of the cluster's members reside in the core. The core is well characterised by a King function with a core radius of 0. 17 (0.14 pc at the adopted distance) and a constant baseline, the halo, of 125 sources/pc 2 . Despite the unusually large number of OB stars, the central number density at zero radius is ∼7.3 × 10 3 pc −3 , which is loose in comparison with similar clusters. We find a normal reddening law towards the cluster and derive a global reddening of A v = 2.6 ± 0.3 mag. We find convincing evidence of a sparse foreground population (∼5 sources/arcmin 2 ) reddened by about A v = 1.4 mag, which we suggest is not associated with Tr14 but is most likely an older population produced in the nearby young clusters of this complex. The colour-magnitude diagrams are compatible with ages between "zero" and ∼5 Myr, although the sources from the core of the cluster appear to concentrate on the youngest isochrones, suggesting that the halo population is, on average, slightly older than the core population. Using a set of simplistic, fixed-age, mass-luminosity relations, we derive a mass of 10 4 M for the cluster. From the NACO JHK s L data, we estimate a fraction of infrared-excess sources of 35%, although this is likely to be an underestimate given the bright completeness limits of the L band. Finally, we argue that the formerly identified proplyd candidates that fall inside our survey are not proplyds but remnants of the disrupted molecular cloud that surround the cluster. We also find a series of interesting objects in our field that are worthy of future attention: a candidate photoionised proplyd best seen in the L band, a compact nebula surrounding an early type star, and a tentative proplyd/small shock associated with a faint source.

A MAD view of Trumpler 14

“…The PSF of each individual image was generated with a PENNY function that had a quadratic dependence on position in the frame, using a selected list of well isolated stars. The calibration of the instrumental H and K S MAD data was done by direct comparison with the JHK S calibrated SOFI catalogue of Ascenso et al (2007). Of particular importance is the absence of (i) any colour term between the two photometric systems over a six-magnitude range (Fig.…”

“…Adopting the cluster centre as defined by Ascenso et al (2007), we computed the radial profile of the star surface density (Fig. 10).…”

“…However, the photometry used A&A 515, A26 (2010) by these authors barely reached the turn-on point of the pre-main sequence (PMS), while they extrapolated the mass assuming a Salpeter initial mass function (IMF). More recently, Ascenso et al (2007) used much deeper IR photometry, which revealed the very rich PMS population and provided a more robust mass estimate of 9000 M . Vazquez et al (1996) reported a core radius of 4.2 pc, while Ascenso et al (2007) revised it to 1.14 pc, and detected for the first time a core-halo structure, which is typical of these young clusters (e.g., Baume et al 2004).…”

Star formation in Cometary Globule 1: the second generation

“…The magnitude zero points of the summed data were fixed using the standard star measurements. The instrumental magnitudes were first converted to the Persson et al (1998) photometric system and then to the 2MASS photometric system as described in Ascenso et al (2007). The magnitude scale was checked by comparing the SOFI photometry of stars in common with 2MASS that have high quality 2MASS photometry.…”

VLT/NACO detection of a proplyd/jet candidate in the core of Trumpler 14

“…The proplyd/jet candidate was discovered during a VLT/NACO JHKsL Brα survey of the core of Trumpler 14 (Vicente et al 2010, Ascenso et al 2007), a young cluster in the Carina Nebula (NGC 3372), and is similar in size and morphology to the numerous proplyds found in the Trapezium cluster (Bally et al 2000, Vicente & Alves 2005. Archival HST/ACS/HRC optical images, together with the adaptive optics near-IR images and existing photoevaporation theories, were used to investigate the morphology of the object and the possible scenarios for its nature, origin and expected lifetime.…”