The massive star forming complex W33 –Closer than expected?

Trigonometric parallax observations of water masers

Katharina Immer

Max-Planck-Institut fur Radioastronomie, Bonn, Germany

05.12.2012

Collaborators: K. Menten & A. Brunthaler (MPIfR), M. Reid (CfA)

Introduction Observations Results Summary

Massive Star Formation

Although massive stars have a strong impact on theUniverse, their formation is still poorly understood.

Study star forming regions in detail

distance dObserved quantity Physical parameter

Physical size ∝ dLuminosity }Mass ∝ d2

Spectral types

Introduction Observations Results Summary

Kinematic Distances

Commonly used method to determine distances

Needed:

Measurement of radial velocity fromDoppler shifts

Galactic circular rotation curve (e.g.from CO observations, Burton & Gor-don 1978)

Illustration Credit:Robert Hurt, IPAC

Problems:

Near-far distance ambiguity

Peculiar motions: local velocity deviations due to shocks, out-flows...

Introduction Observations Results Summary

Trigonometric parallaxes

Definition

Parallax: apparent movement of a source relative to a distant back-ground due to the movement of the Earth around the Sun

Parallax signature with time

Introduction Observations Results Summary

Trigonometric parallaxes

Parallax values in µas – mas range ⇒ high astrometricprecision needed

Requires at least one year of observations to well samplethe Right Ascension parallax signature

Bonus: Linear proper motions of the source

Maser sources used as targets for parallax observations

Introduction Observations Results Summary

The Massive Star Forming Complex W33

Typical star forming regions along evolutionary sequence,from quiescent to highly active clouds

Dust emission at 870 µm (ATLASGAL survey, Schuller et al. 2009)

Introduction Observations Results Summary

The Massive Star Forming Complex W33

Peculiar kinematic structure: two different velocity componentsfrom W33 A to W33 Main at 36 km/s and in W33 B at 58 km/s

One connected star forming complex with large internal motionsat a near-kinematic distance of 3.7 kpcOR

Superposition of several independent star forming regions ar-ranged along the line of sight

Introduction Observations Results Summary

The Massive Star Forming Complex W33

Physical parameters

Size 16 pcLuminosity L ∼ 2 · 106 L� (Stier et al. 1984)Mass M ∼ (0.2–2)·106 M� (Goldsmith & Mao 1983)Spectral types O6 – B0 (Haschick & Ho 1983)

Introduction Observations Results Summary

BeSSeL survey

Observations part of BeSSeL survey

BeSSeL survey will determine accurate distances and propermotions of up to 400 high mass star forming regions andreliably locate the spiral arms in the Milky Way

Introduction Observations Results Summary

Observations

Observation of four watermasers in W33 at 22 GHzwith the VLBA

Eight epochs from 2010October to 2012 Januarytotal observing time perepoch: ∼ 7 h

Observation of two back-ground quasars as positionreference

Masers in W33 Main andW33 A phase-referencedto maser in W33 B,yielding relative parallaxes

Introduction Observations Results Summary

Parallax Determination

Images of water masers and backgroundquasars for each epoch

Absolute position of strongest maser spot inW33 B relative to both background quasars

Fit of positions with a sinusoidal parallax sig-nature + linear proper motions in each coor-dinate

Absolute positions of the strongest maserspots in W33 A and W33 Main masers= relative position to W33 B + position ofW33 B relative to both background quasars

Introduction Observations Results Summary

Parallax Determination

Images of water masers and backgroundquasars for each epoch

Absolute position of strongest maser spot inW33 B relative to both background quasars

Fit of positions with a sinusoidal parallax sig-nature + linear proper motions in each coor-dinate

Absolute positions of the strongest maserspots in W33 A and W33 Main masers= relative position to W33 B + position ofW33 B relative to both background quasars

Introduction Observations Results Summary

Parallax Determination

Images of water masers and backgroundquasars for each epoch

Absolute position of strongest maser spot inW33 B relative to both background quasars

Fit of positions with a sinusoidal parallax sig-nature + linear proper motions in each coor-dinate

Absolute positions of the strongest maserspots in W33 A and W33 Main masers= relative position to W33 B + position ofW33 B relative to both background quasars

Introduction Observations Results Summary

Parallax of W33B

Introduction Observations Results Summary

Parallax of W33B

Paralla

x π= (0.4

16± 0.0

28)ma

s

Introduction Observations Results Summary

Parallaxes of W33A and W33Main

Introduction Observations Results Summary

Parallaxes of W33A and W33Main

π = (0.343

± 0.037)

mas

Introduction Observations Results Summary

Parallaxes of W33A and W33Main

π = (0.343

± 0.037)

mas

π = (0.408

± 0.025)

mas

Introduction Observations Results Summary

Parallaxes of W33A and W33Main

π = (0.343

± 0.037)

mas

π = (0.408

± 0.025)

mas

π = (0.396

± 0.032)

mas

Introduction Observations Results Summary

Distance to W33 – Summary

All parallaxes consistent with parallax of 0.416 mas within 2 σ

⇒ Distance d to W33 = 2.4 kpc ( 23 of near-kinematic distance)

⇒ W33 is one connected star forming complex!

W33 located in the Scutum spiral arm

Physical parameters overestimated

Revised values

Size 10 pcLuminosity L ∼ 8·105 L�Mass M ∼ (0.8–8)·105 M�Spectral types O7.5 – B1.5

Introduction Observations Results Summary

Distance to W33 – Summary

Introduction Observations Results Summary

Distance to W33 – Summary

All parallaxes consistent with parallax of 0.416 mas within 2 σ

⇒ Distance d to W33 = 2.4 kpc ( 23 of near-kinematic distance)

⇒ W33 is one connected star forming complex!

W33 located in the Scutum spiral arm

Physical parameters overestimated

Revised values

Size 10 pcLuminosity L ∼ 8·105 L�Mass M ∼ (0.8–8)·105 M�Spectral types O7.5 – B1.5

Introduction Observations Results Summary

Outlook - Multi-wavelength observations of W33

Submillimeter Array : 8 GHz spectra of five clouds in W33 at230 GHz

Atacama Pathfinder Experiment Telescope: 8 GHz spectra ofsix clouds in W33 at 280 GHz

Karl G. Jansky Very Large Array : Radio continuum and H2O,CH3OH, and NH3 spectral line observations of W33 Main at22 GHz

IRAM 30 m Telescope: 13CO and C18O observations of W33Main at 220 GHz

Additional: Spitzer (3.6 – 24 µm), Herschel (60–600 µm),ATLASGAL (870 µm), and 330 MHz maps

THANK YOU FOR YOURATTENTION!

Internal Motions in W33

Determination of proper motions for all maser spots in eachW33 maser

Average of proper motions ⇒ one proper motion per maser

Subtraction of overall motion of W33 complex ⇒ internalmotions of W33 clouds

Internal Motions in W33