1 / 18

Stellar content of visibly obscured HII Regions

Stellar content of visibly obscured HII Regions. W31. G23.96+0.15. Paul Crowther (Sheffield) James Furness (Sheffield), Pat Morris (CalTech), Peter Conti (JILA), Bob Blum (NOAO), Augusto Damineli (IAG-USP), Cassio Barbosa (UNIVAP), Schuyler van Dyk (CalTech). Outline.

kathie
Download Presentation

Stellar content of visibly obscured HII Regions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Stellar content of visibly obscured HII Regions W31 G23.96+0.15 Paul Crowther (Sheffield) James Furness (Sheffield), Pat Morris (CalTech), Peter Conti (JILA), Bob Blum (NOAO), Augusto Damineli (IAG-USP), Cassio Barbosa (UNIVAP), Schuyler van Dyk (CalTech)

  2. Outline • Direct & indirect stellar signatures in obscured compact HII regions • Role of mid-IR fine structure lines • G23.96+0.15 (UCHII) & W31 (giant HII) • Calibration of UCHII regions? • Relevance to starbursts

  3. Conti & Frost 1977 If AV~20-30 mag, near-IR spectral lines may be used instead, e.g. HeII 1.692 m/HeI 1.700m (Hanson et al. 1998; Lenorzer et al. 2004) Direct stellar signatures If AV~few, O star spectral types (Teff) are obtained from blue visual spectra e.g. HeI 4471/HeII 4542 (Walborn 1971) Fit to dwarfs () from Hanson et al. (2005) Conti & Alschuler 1971

  4. Indirect stellar signatures • For high AV, need to rely upon indirect methods using the ionized gas, e.g. thermal bremsstrahlung emission • Radio continuum flux provides estimate of N(LyC), yet without any information on the hardness (Teff) of the EUV radiation field. • Reliable, unless dust absorbs a significant fraction of Lyman continuum photons, and/or free-free emission is not optically thin at observed . • Mid-IR fine structure lines (e.g. [NeII] 12.8m/[NeIII] 15.5m) together with photo- ionization models (CLOUDY) should allow estimate of Teff for the ionizing star(s).

  5. U Metal poor Simon-Diaz & Stasinska 2008 Teff Metal rich 30kK 35kK 40kK Ne+ S2+ Martin-Hernandez et al. 2002 Problems? • ne or U (= NLyC/(4RS2nec)); Predicted nebular fine-structure line ratios depend sensitively upon Teff and…. • metallicity; • stellar atmosphere models.

  6. 30 Dor Metal-poor; high ionization Orion GC Metal-rich; low ionization Metallicity dependence Martin-Hernandez et al. 2002

  7. Teff=41  2 kK (O4-5V) from an analysis of near-IR spectrum (Hanson et al. 2005 IAUS 227), feasible since AK~2 mag G29.96-0.02 (UCHII) Teff=32-35kK (late O) from CMFGEN + nebular analysis of ([NeIII]/[NeII]; Martin- Hernandez et al. 2002; Morisset et al. 2002) Need more cases, but typically compact clusters lie within HII regions. Ionizing stars of UCHII regions rarely seen in near-IR.

  8. ISAAC 2.2m Hanson et al. 2005 (atlas) 2’=3pc@5kpc 10” (0.25 pc @ 5kpc) G23.96+0.15 (UCHII) 2MASS JHK One exception is G23.96+0.15 (UCHII). VLT ISAAC spectroscopy reveals T~38  1 kK (O7.5V) confirming subtype from low res data (Hanson et al. 2002).

  9. Stellar Cluster W31 (GHII) K-band spectroscopy from Blum, Damineli & Conti (2001) revealed a young stellar cluster within W31 (G10.2-0.3) at d~3kpc, comprising “naked” O stars & massive YSO’s Ghosh et al. (1989) also identify a number of UCHII regions. 1 arcmin (1 pc @ 3.3 kpc)

  10. Near- & mid-IR spectroscopy • Refined spectral types for 5 W31 cluster members from VLT/ISAAC • O3-5.5V for 4 “naked” O stars (~30-55 Mo) with ~1.5 Myr, plus O6V for a massive YSO (source 26). • Spitzer/IRS reveals highest [NeIII]/[NeII] ratios for “naked” stars (highest mass, quickest to shed dust cocoon?) • Greatly expanded sample with mid-IR nebular plus near-IR stellar datasets.

  11. U Teff If ne known, Mid-IR diagnostics U dependence separated from Teff using Significant differences between empirical mid-IR line ratios & metal-rich CMFGEN + CLOUDY models predictions

  12. Calibration of UCHII regions? Ground-based mid-IR spectroscopy limited to [SIV]/[NeII]. In this case, systematic offset between observation and prediction. For metal-rich HII regions calibration may be possible.

  13. [SIV]/[NeII]~0.5 OKYM2 W51d1 [SIV]/[NeII]~0.1 IRS2W IRS 2E G49.49-0.37 (W51A) • N-band imaging of ~30 UCHII regions often reveals multiple (dust) continuum sources • Spectral types of individual stars may be extracted from [SIV]/[NeII] ratios • First attempted in this context by Okamoto et al. (2003) for G70.29+1.60 Gemini Michelle 8 arcsec = 0.2 pc (@ 5.5kpc)

  14. Extragalactic HII regions Relevant to interpretation of mid-IR data for starburst regions e.g. IC4662 (Gilbert & Vacca 2008)

  15. Starbursts [NeIII]/[NeII] ratio is used to deduce stellar content/IMF/age of starbursts (e.g. Thornley et al. 2000). Essential to ensure photoionization models are well calibrated.

  16. Summary • In principle, ratios of mid-IR fine structure lines offer means of establishing Sp Types (Teff) of ionizing stars in obscured HII regions; • We provide an increased sample of HII regions, associated with individual O stars, for which both mid-IR nebular diagnostics & spectral types are known (G23.96+0.15, W31); • In practice, disappointing agreement between observed [NeII-III], [SIII-IV] ratios & expectations from photo-ionization models; • Nevertheless, [SIV]/[NeII] ratio does have the potential to serve as a diagnostic for HII regions within the inner Milky Way.

  17. Mid-IR diagnostics Unfortunately agreement is lost for solar grid, once U has its usual definition NLyC/(4RS2nec). Simon-Diaz & Stasinska (2008) appeared to (nearly) resolve stellar/nebular discrepancy for G29.96-0.02 35 40 45 -1 -2 -3 U=NLyC/(4R02nec).

  18. Stellar atmosphere models? From comparison with ISO observations of HII regions, Morisset et al (2004) concluded: -CoStar too hard at high energies (approximate treatment of blanketing) -TLUSTY & Kurucz too soft at high energies (due to neglect of stellar winds) -CMFGEN & WM-basic in “reasonable agreement” with observations (although they fared no better than a blackbody! SED)

More Related