AGE SPREAD IN W3 MAIN: LARGE BINOCULAR TELESCOPE/LUCI NEAR-INFRARED SPECTROSCOPY OF THE MASSIVE STELLAR CONTENT

Journal Article · Tue Jan 10 04:00:00 EST 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/744/2/87· OSTI ID:22004294

Bik, A; Henning, Th; Brandner, W; Gouliermis, D A; Gennaro, M; Rochau, B; Beuther, H; Kudryavtseva, N ^[1]; Stolte, A ^[2]; Pasquali, A ^[3]; Ageorges, N ^[4]; Seifert, W ^[5]; Wang, Y ^[6]

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1. Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg (Germany)
2. Argelander Institut fuer Astronomie, Auf dem Huegel 71, 53121 Bonn (Germany)
3. Astronomisches Rechen Institut, Moenchhofstrasse 12-14, 69120 Heidelberg (Germany)
4. Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching (Germany)
5. Landessternwarte Koenigstuhl, Zentrum fuer Astronomie Heidelberg, Koenigstuhl 12, 69117 Heidelberg (Germany)
6. Purple Mountain Observatory, Chinese Academy of Sciences, 210008 Nanjing (China)

We present near-infrared multi-object spectroscopy and JHK{sub s} imaging of the massive stellar content of the Galactic star-forming region W3 Main, obtained with LUCI at the Large Binocular Telescope. We confirm 15 OB stars in W3 Main and derive spectral types between O5V and B4V from their absorption line spectra. Three massive young stellar objects are identified by their emission line spectra and near-infrared excess. The color-color diagram of the detected sources allows a detailed investigation of the slope of the near-infrared extinction law toward W3 Main. Analysis of the Hertzsprung-Russell diagram suggests that the Nishiyama extinction law fits the stellar population of W3 Main best (E(J - H)/E(H - K{sub s}) = 1.76 and R{sub K{sub s}} = 1.44). From our spectrophotometric analysis of the massive stars and the nature of their surrounding H II regions, we derive the evolutionary sequence of W3 Main and we find evidence of an age spread of at least 2-3 Myr. While the most massive star (IRS2) is already evolved, indications for high-mass pre-main-sequence evolution are found for another star (IRS N1), deeply embedded in an ultracompact H II (UCH II) region, in line with the different evolutionary phases observed in the corresponding H II regions. We derive a stellar mass of W3 Main of (4 {+-} 1) Multiplication-Sign 10{sup 3} M{sub Sun} by extrapolating from the number of OB stars using a Kroupa initial mass function and correcting for our spectroscopic incompleteness. We have detected the photospheres of OB stars from the more evolved diffuse H II region to the much younger UCH II regions, suggesting that these stars have finished their formation and cleared away their circumstellar disks very fast. Only in the hyper-compact H II region (IRS5) do the early-type stars seem to be still surrounded by circumstellar material.

• OSTI ID: 22004294
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 744; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
ABSORPTION SPECTROSCOPY
COLOR
HERTZSPRUNG-RUSSELL DIAGRAM
INFRARED SPECTRA
MASS
PHOTOSPHERE
SPECTROPHOTOMETRY
STAR EVOLUTION
STARS
TELESCOPES