1 / 14

Masers observations of Magnetic fields during Massive Star Formation

Masers observations of Magnetic fields during Massive Star Formation. Wouter Vlemmings (Argelander-Institut für Astronomie, Bonn) with Gabriele Surcis, Rosy Torres, Ramiro Franco (Bonn) Kalle Torstensson, Huib Jan van Langevelde (Leiden/JIVE, Netherlands), Richard Dodson (ICRAR, Australia).

alfonso-gomez
Télécharger la présentation

Masers observations of Magnetic fields during Massive Star Formation

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. Masers observations of Magnetic fields during Massive Star Formation • Wouter Vlemmings(Argelander-Institut für Astronomie, Bonn) • with Gabriele Surcis, Rosy Torres, Ramiro Franco (Bonn) Kalle Torstensson, Huib Jan van Langevelde (Leiden/JIVE, Netherlands), Richard Dodson (ICRAR, Australia)

  2. Pudritz & Banerjee 2005 MSF Magnetic Fields • Role relative to turbulence and gravity? • B launches outflows, stabilize accretion disks, facilitate enhanced accretion rate? • B suppresses fragmentation? • Need B-field probes at high densities and small scales • complement larger scale dust • Zeeman splitting of masers and other spectral lines!

  3. Zeeman Splitting • “splitting of a spectral line into several components in the presence of a static magnetic field” B=0 B≠0 • Circular polarization, V∝dI/dv • Not not for all masers!

  4. SF Masers • Maser polarization observed from: • OH (1.6 and 6 GHz) • Faraday rotation • H2O (22 GHz) • Shocks • SiO (43 and 86 GHz) • rare, polarization interpretation • CH3OH (methanol, 6.7, 12.2, 36 GHz) • Common MSF maser, strong Poster I.24, Green et al. & II.32 Torres et al. Poster II.26, Surcis et al. Poster II.26, Surcis et al.

  5. Methanol Masers • Non-paramagnetic: • Zeeman splitting << doppler line-width • Using g-Landé factor from 25 GHz laboratory measurements (Jen 1951): • Vz = 49 m/s G-1 for 6.7 GHz methanol • Circular polarization ~0.1-0.3% for mG B-fields • Linear polarization weak (Ellingsen 2002; Vlemmings et al. 2006; Dodson 2008) • Typical 2-3% for 6.7 and 12.2 GHz masers • Occasionally as high as 8-10% • Depends on e.g. maser saturation • Analysis requires maser radiative transfer

  6. Effelsberg survey • Detection of Zeeman splitting requires high SNR • SNR~3000 needed to detect 1 mG • Strong masers (>50Jy) • Effelsberg 100m telescope: • 51 hr; ~50 strong Northern methanol maser regions • Southern sources done with Parkes MB system • Stability problem, scan-to-scan Right-Left CP variability • Still simultaneous 6 GHz OH (poster II.32, Torres et al.)

  7. Results (I) Cepheus A

  8. Survey Results (II) • Significant Zeeman splitting detected in 35/47 6.7 GHz methanol maser sources associated with high-mass star formation • Corresponds to |B|=23 ± 5 mG in the methanol region (nH2~107-109 cm-3) • Larger than Bcrit~12 mG ⇒ dynamically important • Average field ~6 times higher than average 1.6 GHz OH maser field • Line-of-sight direction consistent with OH maser measurements • Probes overall Galactic field direction?

  9. Further observations • High resolution follow-up (EVN; Surcis poster II.26) • confirmed field • indicate connection to larger scale structure • 6 GHz OH Effelsberg survey • B vs. density relation 1000 AU W75N (Surcis et al. 2010)

  10. The case of Cepheus A • Cepheus A HW2 ~20 M☉ @ 700 pc (Jiménez-Serra et al. 2007; Moscadelli et al. 2009) • Thermal radio jet, ionized gas at ~500 km/s (Curiel et al. 2006) • Rotating dust (R~330 AU) and molecular gas (R~580 AU) disk structure ⊥ to outflow (Patel et al. 2005, Jiménez-Serra et al. 2007, Torrelles et al. 2007) • made up of at least 3 YSOs (e.g. Comito et al. 2007) • Flattened 6.7 GHz methanol maser structure near disk plane (R~650 AU, h~300 AU) • infall at ~1.7 km/s (Torstensson et al. 2007, 2010)

  11. MERLIN image of the polarization of methanol masers around the outflow Cepheus A HW2 750 AU Cepheus A results

  12. Cepheus A B-field Vlemmings et al. 2010

  13. e-MERLIN MSF legacy project • Upgrade to MERLIN array • 4 GHz bandwidth, L,C and K-band, ~1 μJy sensitivity, 10-150 mas resolution • ‘Feedback during Massive Star Formation’ • 450 hrs allocated at C-band (5-7 GHz) • simultaneous map radio continuum emission and the 3D magnetic field from methanol/OH masers e-MERLIN beam NGC 7538 IRS1 and associated masers (VLA, Galván-Madrid et al. 2010)

  14. Conclusions • Significant Zeeman splitting detected in 35/47 6.7 GHz methanol maser sources associated with high-mass star formation • Corresponds to |B|=23 ± 5 mG in the methanol region (nH2~107-109 cm-3) • Larger than Bcrit~12 mG ⇒ dynamically important • Average field ~6 times higher than average 1.6 GHz OH maser field • High-resolution studies show relation with large scale fields • Cepheus A: magnetic field regulated infall

More Related