The Evolution of the Multiplicity of Embedded Protostars I: Sample Properties and Binary Detections

TL;DR

This study conducts a near-infrared survey of Class I protostars to analyze their binary separation distribution from 100 to 5000 AU, providing new data on young stellar object multiplicity.

Contribution

It presents the first extensive, unbiased near-infrared survey of Class I protostars across the sky, detecting 89 companions including 73 new discoveries, and refines binary detection methods at L'-band.

Findings

Detected 89 binary companions, 73 of which are new.

Established detection limits and minimized contamination in binary identification.

Provided positional and photometric data for the surveyed protostars.

Abstract

We present the observational results of a near-infrared survey of a large sample of Class I protostars designed to determine the Class I binary separation distribution from ~100 AU to ~5000 AU. We have selected targets from a new sample of 267 nearby candidate Class I objects. This sample is well understood, consists of mostly Class I young stellar objects (YSOs) within 1 kpc, has targets selected from the whole sky, and is not biased by previous studies of star formation. We have observed 189 Class I YSOs north of -40 degrees declination at H, K and L'-bands, with a median angular resolution of 0.33" at L'. We determine our detection limit for close binary companions by observing artificial binaries. We choose a contrast limit and an outer detection limit to minimize contamination and to ensure that a candidate companion is gravitationally bound. Our survey uses observations at L' rather than K-band for the detection of binary companions since there is less scattered light and better seeing at L'. This paper presents the positions of our targets, the near-IR photometry of sources detected in our fields at L', as well as the observed properties of the 89 detected companions (73 of which are newly discovered). Although we have chosen contrast and separation limits to minimize contamination, we expect that there are ~6 stars identified as binary companions that are due to contamination. Finder charts at L' for each field are shown to facilitate future studies of these objects.