# A TGAS/Gaia DR1 parallactic distance to the sigma Orionis cluster

## TL;DR

This paper uses Gaia DR1 data to determine a precise distance to the sigma Orionis cluster, resolving a long-standing debate and refining cluster membership with implications for star formation studies.

## Contribution

It provides the first Gaia-based parallactic distance to sigma Orionis, clarifies cluster membership, and identifies interlopers, enhancing understanding of the cluster's structure and stellar population.

## Key findings

- Distance to sigma Orionis is 360^{+44}_{-35} pc.
- Discrepancies in previous distance estimates are resolved.
- Identification of interlopers refines cluster membership.

## Abstract

With the new Tycho-Gaia Astrometric Solution, I derive a new parallactic distance to the young sigma Orionis open cluster, which is a cornerstone region for studying the formation and evolution of stars and substellar objects from tens of solar masses to a few Jupiter masses. I started with the list of the 46 brightest cluster stars of Caballero (2007). After identifying the 24 TGAS stars in the 30 arcmin-radius survey area and accounting for 11 FGKM-type dwarfs and giants in the fore- and background, I got a list of 13 cluster members and candidates with new parallaxes. Of them, I discarded five cluster member candidates with questionable features of youth and/or discordant parallaxes and proper motions, including a distant Herbig Ae/Be star, and proceeded with the remaining eight stars. The sigma Orionis mean heliocentric distance is d =360^{+44}_{-35} pc, which is consistent with a contemporaneous interferometric determination that concludes a two-decade dispute on the cluster distance. As a by-product, the re-classification of those five cluster member candidates, now interlopers, shows a manifest deficit of cluster stars between 1.2 and 2.1 Msol, which leaves the door open to new astrometric membership analyses with the next Gaia data releases.