The Low‐Mass Initial Mass Function in Young Clusters: L1495E

Abstract

We have developed a technique of IR spectral classification in which we use K-band spectra (R ~ 1000) to derive the spectral types and continuum veilings of young, late-type stars (~1 Myr, >G0). We show close agreement between the spectral types derived in this manner and those obtained optically. We complement previous optical spectroscopy with IR spectra of the most heavily embedded members of the young, embedded cluster L1495E. We critically analyze the translation between observable (spectral type, photometry) and theoretical (Teff, Lbol) parameters and use these data to construct an H-R diagram. We find that the evolutionary tracks of D'Antona & Mazzitelli imply a coeval population of ≤1 Myr and a plausible initial mass function (IMF). However, these models may underestimate the masses of objects near and below the hydrogen burning limit. The models of Swenson produce implausibly old ages and the models of Baraffe et al. yield somewhat old ages and an implausible IMF. We use infrared imaging to show that the spectroscopic sample for this cluster may be seriously incomplete below ~0.15 M☉. After applying a completeness correction to the IMF derived with the tracks of D'Antona & Mazzitelli, we find no evidence for a turnover at low masses; the IMF appears roughly flat in logarithmic mass units. Compared to the results of photometric studies of ρ Oph and NGC 2024, the IMF appears roughly invariant among star-forming environments representing a 2 order of magnitude range in the density of young stars. However, the detailed behavior of the IMF from low stellar masses into the substellar regime will remain uncertain until (1) better evolutionary tracks are available and (2) the sources in the photometric completeness correction can be spectroscopically confirmed as low-mass cluster members.