Inferring the parallax of Westerlund 1 from Gaia DR2

Abstract

Westerlund 1 (Wd1) is potentially the largest star cluster in the Galaxy. That designation critically depends upon the distance to the cluster, yet the cluster is highly obscured, making luminosity-based distance estimates difficult. Using {\it Gaia} Data Release 2 (DR2) parallaxes and Bayesian inference, we infer a parallax of $0.35_{-0.06}^{+0.07}$ mas corresponding to a distance of $2.6_{-0.4}^{+0.6}$ kpc. To leverage the combined statistics of all stars in the direction of Wd1, we derive the Bayesian model for a cluster of stars hidden among Galactic field stars; this model includes the parallax zero-point. Previous estimates for the distance to Wd1 ranged from 1.0 to 5.5 kpc, although values around 5 kpc have usually been adopted. The {\it Gaia} DR2 parallaxes reduce the uncertainty from a factor of 3 to 18\% and rules out the most often quoted value of 5 kpc with 99\% confidence. This new distance allows for more accurate mass and age determinations for the stars in Wd1. For example, the previously inferred initial mass at the main-sequence turn-off was around 40 M${}_{\odot }$; the new {\it Gaia} DR2 distance shifts this down to about 22 M${}_{\odot }$. This has important implications for our understanding of the late stages of stellar evolution, including the initial mass of the magnetar and the LBV in Wd1. Similarly, the new distance suggests that the total cluster mass is about four times lower than previously calculated.

arXiv comment14 pages, 10 figures

References in corpus (35)

• emcee: The MCMC Hammer
• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• Gaia Data Release 2: The astrometric solution
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• Mass Loss: Its Effect on the Evolution and Fate of High-Mass Stars
• Rotating Massive Main-Sequence Stars I: Grids of Evolutionary Models and Isochrones
• Milky Way Cepheid Standards for Measuring Cosmic Distances and Application to Gaia DR2: Implications for the Hubble Constant
• Evidence for a systematic offset of -80 micro-arcseconds in the Gaia DR2 parallaxes
• On the massive stellar population of the Super Star Cluster Westerlund 1
• A Neutron Star with a Massive Progenitor in Westerlund 1
• The astrometric core solution for the Gaia mission. Overview of models, algorithms and software implementation
• A census of the Wolf-Rayet content in Westerlund 1 from near-infrared imaging and spectroscopy
• The Missing Luminous Blue Variables and the Bistability Jump
• Confirmation of the $Gaia$ DR2 parallax zero-point offset using asteroseismology and spectroscopy in the $Kepler$ field
• The RMS Survey: Galactic distribution of massive star formation
• The Initial Masses of the Red Supergiant Progenitors to Type-II Supernovae
• Intermediate to low-mass stellar content of Westerlund 1
• Mass Function of the Arches Cluster from Gemini Adaptive Optics Data
• The population of OB supergiants in the starburst cluster Westerlund 1
• Mass segregation and elongation of the starburst cluster Westerlund 1
• N-Body Simulations of Compact Young Clusters near the Galactic Center
• The distance and neutral environment of the massive stellar cluster Westerlund 1
• The Milky Way Spiral Structure Parameters from Data on Masers and Selected Open Clusters
• The Starburst Cluster Westerlund 1: The Initial Mass Function and Mass Segregation
• Extinction law in the range 0.4-4.8 $\mu$m and the 8620 $\mathring{A}$ DIB towards the stellar cluster Westerlund 1
• Spectroscopic monitoring of the luminous blue variable Westerlund1-243 from 2002 to 2009
• Medium resolution 2.3 micron spectroscopy of the massive Galactic open cluster Westerlund 1
• Discrepancies in the ages of young star clusters; evidence for mergers?
• Reconstructing the Arches I: Constraining the Initial Conditions
• A newly identified Luminous Blue Variable in the galactic starburst cluster Westerlund 1
• The Fundamental Parameters of Four Massive Eclipsing Binaries in Westerlund 1
• Fundamental Parameters of four Massive Eclipsing Binaries in Westerlund 1
• An ALMA 3mm continuum census of Westerlund 1
• Detection of additional Wolf-Rayet stars in the starburst cluster Westerlund 1 with SOAR

Cited by in corpus (12)

• X-ray Searches for Axions from Super Star Clusters
• A deep spectromorphological study of the $\gamma$-ray emission surrounding the young massive stellar cluster Westerlund 1
• On the Gaia DR2 distances for Galactic Luminous Blue Variables
• Multiplicity of Galactic Luminous Blue Variable stars
• The Age of Westerlund 1 Revisited
• Unlocking Galactic Wolf-Rayet stars with $\text{Gaia}$ DR2 II: Cluster and Association membership
• Westerlund 1 under the light of Gaia EDR3: Distance, isolation, extent, and a hidden population
• Comparison of Gaia and Hipparcos parallaxes of close visual binary stars and the impact on determinations of their masses
• Distance and age of the massive stellar cluster Westerlund 1. I. Parallax method using Gaia-EDR3
• A systematic aging method I: HII regions D118 and D119 in NGC 300
• Distance and age of the massive stellar cluster Westerlund 1. II. The eclipsing binary W36
• Structure and Dynamics of the Young Massive Star Cluster Westerlund 1