Annual Parallax Measurements of an Infrared Dark Cloud MSXDC G034.43+00.24 with VERA

TL;DR

This study precisely measured the distance to an infrared dark cloud using VLBI astrometry, leading to revised core mass estimates and spectral classifications, and revealed significant peculiar motion.

Contribution

First direct parallax measurement of MSXDC G034.43+00.24, refining its distance and physical properties, and highlighting the importance of accurate astrometry in star formation studies.

Findings

Distance to the cloud is 1.56 kpc, less than previous estimates.

Core masses are revised down to hundreds of solar masses.

The spectral type of the associated star is B1, still massive.

Abstract

We have measured the annual parallax of the H2O maser source associated with an infrared dark cloud MSXDC G034.43+00.24 from the observations with VERA (VLBI Exploration of Radio Astrometry). The parallax is 0.643 +/- 0.049 mas, corresponding to the distance of 1.56 +0.12/-0.11 kpc. This value is less than the half of the previous kinematic distance of 3.7 kpc. We revise the core mass estimates of MSXDC G034.43+00.24, based on virial masses, LTE masses and dust masses and show that the core masses decrease from the previous estimations of ~1000 Mo to hundreds of Mo. The spectral type derived from the luminosity also changes from O9.5 to B1 in the case of MM1. This spectral type is still consistent with that of the massive star. The radial velocity derived from the flat rotation model is smaller than the observed velocity, which corresponds to the peculiar motion of ~40 km/s in the line-of-sight direction.