Using near‐IR spectroscopy to classify substellar candidates in the Trapezium Cluster

Abstract

Abstract.We discuss the use of near-IR spectroscopy to confirm young substellar candidates that were selected by photometry. We first review near-IR spectroscopic methods used to classify young brown dwarf candidates. In a subsequent part, we present ISAAC/VLT photometric and spectroscopic data of substellar candidates in the Trapezium Cluster. These data will be used to derive the effective temperature and reddening of the objects. We create a grid of synthetic spectra from Allard et al. (2000) with different degrees of reddening and compare those with our spectra, assuming a gravity of log g = [3.5, 4.0], which is typical for young objects. The best fitting reddened synthetic spectrum gives us the most likely effective temperature and extinction for our sources. Next, we compare the temperature derived from dereddening the objects towards a 1 Myr isochrone in a colour-magnitude diagram with the one obtained by fitting synthetic atmosphere models to the spectra, and show what extend the differences have when deriving the masses of the objects (under the assumption of an age of 1 Myr).

Infrared spectroscopy and analysis of brown dwarf and planetary mass objects in the Orion nebula cluster

“…In recent years deep near-infrared studies of young clusters have led to the detection of large numbers of brown dwarf and planetary mass candidates (Comeron et al 1993;Williams et al 1995;Lucas & Roche 2000;Lucas, Roche & Tamura 2005). The luminosity and colour criteria (see Section 2 for more details) used for differentiating between sub-stellar and higher mass cluster members have proven to be successful, with spectroscopic follow-up confirming the existence of significant numbers of brown dwarfs in Orion and other star-forming regions (Lucas et al 2001;Luhman et al 2003;Meeus & McCaughrean 2005).…”

Visual Binaries in the Orion Nebula Cluster

“…COUP 1061. This very close system (∼ 100 AU) has a combined spectral type M9-L0 according to Meeus & McCaughrean (2005), who did not resolve it, and since the components have virtually the same brightness, this is therefore a bona fide brown dwarf -brown dwarf binary with a projected separation of 100 AU.…”

“…It is likely that there are several brown dwarfbrown dwarf binaries in our binary sample, but the only one that we are certain of is COUP 1061. Infrared spectroscopy of this source indicates a spectral type of M9-L0 (Meeus & McCaughrean 2005). We have resolved this object into two components with almost equal brightness and a projected separation of 100 AU.…”

Near-infrared cross-dispersed spectroscopy of brown dwarf candidates in the Upper Sco association★

“…The agreement between the old field dwarfs and the young USco members suggests that our spectral classification is quite reasonable. Starting with the M8 and M9 USco dwarfs for which optical classification is available from the literature (Martín et al 2004; Slesnick et al 2006), the main difference resides in the triangular shape of the H band (Lucas et al 2001; Luhman 2004b; Slesnick et al 2004; Meeus & McCaughrean 2005; Allers et al 2007). Additionally, the spectra of young objects appears slightly flatter around 1.3 μm.…”

“…Secondly, Luhman (1999) proposed a T eff versus spectral‐type relation for young dwarfs, that relation later being revised by Luhman et al (2003) and extended by Allers et al (2007). Finally, the direct comparison of observed spectra with theoretical models (Allard, Hauschildt & Schweitzer 2000) allows an estimate of T eff , gravity and masses (Lucas et al 2001; Meeus & McCaughrean 2005).…”