spitzer mid-ir image of the dr21 region in the cygnus-x molecular complex image credit: nasa,...
Post on 19-Dec-2015
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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
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