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Profiling Young Massive Stars Tracey Hill
Leiden Observatory, Leiden University Thesis work - UNSW with M Burton, M Cunningham, V Minier


IAUs 242: Masers, Alice Springs

Massive Star Formation
T T T T T Study is hindered ­ recall talk by de Buizer Optically obscured prior to main sequence evolution. Difficult to pinpoint individual stages of evolution. Low mass SF models? IR excellent tracer:
Z Stars emit bulk of radiation at wavelengths shorter than Lymann continuum limit Z Circumstellar dust envelope absorbs radiation and re-emits in the infrared.

Tracey Hill Tuesday 13th March 07

T Massive stars associated with infrared radiation (IRAS & MSX), UC HII regions, maser sources, millimetre & submillimetre emission. T Do maser species trace different evolutionary stages?
Z Walsh et al (1998): Masers are the first readily detectable tracer of MSF


IAUs 242: Masers, Alice Springs

A Range of MSF Cores
1.2mm Continuum, SEST/SIMBA

Ionized Core (UC HII region) Hot Molecular Core

Tracey Hill

hanol

Tuesday 13th March 07

Cold Core (Reverse) Evolutionary Order??
Minier, Hill et al, 2005


So what happens before the onset of maser emission?


IAUs 242: Masers, Alice Springs

SEST/SIMBA
TSearch for cold cores that mark the earliest stages of MSF TSEST: Targeted positions of known methanol maser & UC HII sources (131) TSIMBA: large F.O.V (240'' x 480'') T405 sources detected (3-s) TGenerally, tracer position correlates with mm peak TEvidence of star formation devoid of methanol masers and UC HII regions
("mm-only cores")

Tuesday 13th March 07

Tracey Hill


Tuesday 13th March 07

Tracey Hill IAUs 242: Masers, Alice Springs

SIMBA maps


IAUs 242: Masers, Alice Springs Tracey Hill

Introducing the `mm-only' core
T~ 60% sources (255/405) detected have no maser &/or UC HII (mm-emission only). mmonly core T~ 45 % do not have mid-IR MSX emission. [lower limit] or are devoid of a mid-IR source. TWhat is their story?
ZYounger? Deeply embedded? ZIntermediate mass? combination?

Tuesday 13th March 07


IAUs 242: Masers, Alice Springs

Profiling Young massive Stars
TUsing: SIMBA, SCUBA, MSX, sometimes IRAS TAssuming b=2 (Hill et al. 2006) TLevenberg-Marquardt least squares fit
Z162 sources (of 405)

Tracey Hill

TFit results in 6 parameters:
ZTemperature, luminosity, mass, H2 number density, surface density, Lum/Mass

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T8 parameters known TAnalysis =>

(+ radius, distance)


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Tracey Hill IAUs 242: Masers, Alice Springs

Example SED mm-only core


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Tracey Hill IAUs 242: Masers, Alice Springs

Mass


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Tracey Hill IAUs 242: Masers, Alice Springs

Luminosity


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Tracey Hill IAUs 242: Masers, Alice Springs

Temperature


Tuesday 13th March 07

Tracey Hill IAUs 242: Masers, Alice Springs

Correlation plots


So what's up with the mmonly core?


IAUs 242: Masers, Alice Springs

Results: mm-only core
TComparable mass to sources with methanol maser &/or UC HII T But:
ZSmaller , Less luminous, Smaller L/M Zand cooler ZMore dense (H2 and surface)

Tracey Hill Tuesday 13th March 07

than sources with methanol maser/radio continuum. TKS test: distinctly different for luminosity, temperature, and L/M TAn earlier stage of massive star evolution? TBimodal temperature population!


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Tracey Hill IAUs 242: Masers, Alice Springs

Examining the Bimodal Nature of the mm-only Core


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Tracey Hill IAUs 242: Masers, Alice Springs

Bimodal mm-only Population


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Tracey Hill IAUs 242: Masers, Alice Springs

Analysis cont....


IAUs 242: Masers, Alice Springs

Analysis revealed....
~ Little distinction between warm-mm & sources with methanol maser and/or radio continuum source for all parameters tested. ~ Cool-mm sources are distinctly different from the warm-mm sources, methanol maser and/or radio continuum source for all parameters tested bar for mass and radius

Tracey Hill Tuesday 13th March 07

~Cool-mm: less luminous, lower L/M, higher H2 number and surface densities (S). They have smaller radii than those sources with an UC HII region. ~The warm-mm display similar characteristics to those known to be forming massive stars (those with methanol maser &/or UC HII).


IAUs 242: Masers, Alice Springs

TIndications: mm-only cores are younger examples of massive star formation Tmm-only comprised of two populations

mm-only core:example of evolution?

ZPrior to the onset of methanol maser emission ZDistinguished by temperature ZPopulations distinct from each other

Tracey Hill Tuesday 13th March 07

TWarm-mm sources examples of young massive stars ­ hot cores? TCool-mm sources examples of failed/starless cores? (e.g. Vasquez-Semadeni et al. 2005)