Methanol Masers Around Young Massive Stars

Bright young things, lasers and alcohol

Spitzer mid-IR image of the DR21 region in the Cygnus-X molecular complex

Image Credit: NASA, Spitzer Space Telescope.

Aims of the project

To test our best models of methanol masers

To observe massive star formation at its earliest stages

Methanol MasersEnergy Levels of E-methanol (Cragg et al, 2005).

J, K rotational quantum numbers, vt and vCO vibrational

6.7GHz transition is the first astrophysical methanol maser to switch on in massive star-forming regions:

51 – 60 A+

Notation: JK – J’K’ Asgn(p)

Energy levels of A-methanol, with decay paths to astrophysical maser population inversions illustrated with arrows. (Cragg et al, 1992).

Cragg et al, 2005 Not strongly dependent

on gas temperature, pumped by radiation from dust

Sharp switch on at ~110 K dust temperature, and after that, not strongly dependent

Switch off over 108 cm-3 gas number density due to thermal quenching

Amplification along line of sight for specific column density 1011-1014 cm-3 s.

Cygnus-X Molecular Complex

Left: MAMBO contour map of DR21Right: MAMBO contour map with 8μm map overlaid

Image Credit: Motte et al, 2007.

Cygnus-X is a giant molecular complex in the Cygnus constellation, a star forming region with about 13 times the mass of the Orion nebula. DR21 is a cloud in the north of Cygnus-X in which we found masers. We selected targets identified by stellar signposts such as SiO outflows in Motte et al, 2007.

MERLIN Multi-Element Radio Linked Interferometer

Network Mark II (Jodrell Bank, pictured), Cambridge,

Defford, Knockin, Darnhall, Pickmere

Image Credit: Jodrell Bank Observatory.

217 km

Data Reduction in AIPS

Pictured: Spectrum of DR21-N53 centred on 6.668GHz, produced with AIPS.

Calibration:

Bandpass to correct for differences in sensitivity across the spectrum.

Amplitude and phase calibrations for varying conditions and forming the image.

Split peak corresponding to a single maser

Single peak corresponding to a different maser

Singlet and doublet as yet not located

Results

Two known masers confirmed and one to three distinct new masers discovered

Null results on other targets: why?

Gas density sufficient in all targets: must be temperature

Masers were detected in massive cores with strong SiO outflows from their poles, as measured by ∫TSiOdv.

SiO OutflowsSiO outflows from the poles were an indicator of stellar activity we used to select our targets.

Left: spectra of the six strongest SiO outflows.

Two to four of the targets to the left have methanol masers, and no others in the sample of 17. N12 and N40 have much lower mass than the maser candidates.

Hypothesis: only those protostellar cores with the strongest SiO outflows have methanol masers.Image Credit: Motte et al, 2007.

Maser

Maser

Maser?

Maser?Maser?

No Maser

Bri

gh

tness t

em

pera

ture

(K

)

Velocity (kms-1)

Future Work

Improve phase calibration and image the masers, i.e. are they in disks?

Map velocity distribution in the masers: what are the characteristics of the disk?

Confirm SiO – methanol correlation with larger samples and greater sensitivity

Extend to mid-IR sources

Acknowledgement

Thank you to Dr Lisa Harvey-Smith for her encouragement, ideas, endless debugging and giving me the opportunity to do the project in the first place!