Abstract by Marta Sewilo
The Surveying the Agents of a Galaxy's Evolution (SAGE) Spitzer Legacy Programs provide a comprehensive picture of the current star formation activity in the Large (SAGE-LMC, Meixner et al. 2006) and Small (SAGE-SMC, Gordon et al. 2011) Magellanic Clouds which is traced by the IRAC (3.6, 4.5, 5.8, and 8.0 microns) and MIPS (24, 70, and 160 microns) bands. It allowed for the first time a global study of star formation in the Magellanic Clouds (MCs) at high enough resolution to resolve individual cores and protostars at a range of mid-IR wavelengths. The methods for searching and identifying Young Stellar Objects (YSOs) in the MCs will be discussed. These methods involve color-magnitude selections, inspection of the multi-wavelength images, and fitting of the spectral energy distributions of the YSO candidates using the 2D radiative transfer models (Robitaille et al. 2006).
The most recent data from the "HERschel Inventory of the Agents of Galaxy Evolution” (HERITAGE; Meixner et al. 2010) survey provided reliable longwave (100 - 500 microns) SEDs of large samples of Spitzer-identified high-mass YSOs, thus constraining their physical properties and evolutionary stages more precisely than was previously possible. Herschel also discovers the youngest YSOs whose SEDs peak in Herschel bands.
Relevant Papers
"Spitzer Sage Survey of the Large Magellanic Cloud. III. Star Formation and ~1000 New Candidate Young Stellar Objects"
Whitney et al. 2008
"High- and Intermediate-Mass Young Stellar Objects in the Large Magellanic Cloud"
Gruendl and Chu 2009
"The youngest massive protostars in the Large Magellanic Cloud"
Sewilo et al. 2010
Talk Slides
pdf
Nice work. I note that these studies reveal the Stage I and Stage 0 studies. But to get at the Stage III and Stage II objects, we will need HST photometry of these fields. - Margaret Meixner
ReplyDeleteYour plot of the mass functions has a few objects with masses of 20 solar masses and higher. Are these masses reliable? These are potentially very interesting objects because they are so rare. -- Claus
ReplyDeleteWhich isochrones are you using? -- Claus
ReplyDeleteHow well are actual input parameters constrained? You have a combination of parameters, like mass-loss rates, ages, masses, etc., which affect the SED, and which are not independent. What are the best known parameters? -- Claus
ReplyDeleteRegarding the slide showing four sample SEDs: why do two of the SEDs have very strong 10 micron absorption, whereas the other two show no feature at that wavelength? -- Claus
ReplyDeleteQuantitative analyses remain to be done, but the most luminous IR sources in 30 Dor likely have high masses (AJ 116, 1708; 117, 225; 124, 1601). Alternatively, Brandner et al., AJ 122, 858 suggested some might be "overluminous" HAeBe objects. But at least some of them are likely O stars, because the "newborns" visible optically in the adjacent Knots 1, 2, 3 are (refs. above).
ReplyDeleteWhite et al. (A&A 342, 233) derived masses up to 60 solar for cores in the heads of the M16 pillars. These were subsequently found to be IR sources by VLT and NICMOS.
The stellar evolutionary tracks used are for canonical
ReplyDeletenonaccreting pre-main-sequence stars:
Bernasconi & Maeder (1996) for Mstar >= 9 Msun
Siess et al. (2000) for Mstar <= 7 Msun
a combination of both for 7 Msun < Mstar < 9 Msun
----
The disk affects the spectral energy distribution most
strongly at edge-on inclinations by causing a broad dip at about 10 microns (independent of the silicate
feature) due to high extinction and low scattering
albedo in this wavelength region. The high extinction
in the disk mid-plane blocks thermal radiation from
inner disk+envelope. The low albedo prevents radiation
from scattering out the polar regions.
(Whitney et al. 2003, 598, 1079)
-- Marta