Shih-Ping Lai 賴詩萍 (National Tsing-Hua University, Taiwan) 清華大學, 台灣

 Magnetic fields are believed to control the formation and evolution of the molecular clouds and core.  Questions:  B Geometry vs. Age  How much magnetic flux will be diffused along the evolutionary stages?  Magnetic fields are believed to control the formation and evolution of the molecular clouds and core.  Questions:  B Geometry vs. Age  How much magnetic flux will be diffused along the evolutionary stages? Image taked from Crutcher (2006), Science

 Zeeman Effect – Very Difficult!!  The only way to measure magnetic field strength B los  Polarized Molecular Line Emission (the Goldreich-Kylafis Effect) – Very Difficult too! P  B p or P ‖ B p  Polarization of Dust Emission: P  B p Absorption: P ‖ B p

(Girart, Rao, & Crutcher 1999)

Crutcher et al. 1999Lai et al. 2003

Polarization map (left) and magnetic field map (right) from Girart, Rao, & Marrone (2006), Science, 313, 812

Girart et al (in prep) Tang, Lai et al. (2009, submitted)

Rao, Lai et al., in prepPmax~5%

VLA1623 (Class 0) L1551 IRS1 (Class I) HL Tau (Class II) Lai et al. (2009, in preparation)

Source Type Peak I (Jy/beam) P% at peak Polarization Angle at peak(deg) Total I (Jy) Total P (%) Total PA (deg) NGC1333 IRAS 4A Class (0.04) 0.77 (0.17) (6.2) VLA 1623Class (0.04) 1.06 (0.35) (9.5) L1551 IRS 5 Class I2.41 (0.04) 0.51 (0.21) 22 (11) HL TauClass II0.31 (0.04) 0.78 (0.32) 63 (12) 0.3--

 3 targets are observe pole-on…. (very unlikely)  Growth of dust size reduce the magnetic alignment efficiency  Magnetic field evolve from uniform to random during Class 0 stage, and remain random after Class 0 stage  Magnetic field diffuse quickly during Class 0 stage  Ambipolar diffusion time scale ~ 10 5 yrs  Statistical life time for class 0 ~ 10 5 yrs 13

 We have sensitive polarization observations for VLA 1623, L1551 IRS5, and HL Tau (uncertainty in polarization is ~ %)  Compared to the previous NGC 1333 IRAS4A observation, our results show significant weaker polarization.  Our results suggest that the polarization is weaker in the later stage of the evolution Magnetic flux decay quickly after Class 0 stage ALMA is required to measure more cores to support our conclusion

15 ALMA is The Future

 We can do more!  Using ACA+12m to increase sensitivity  7-pointing small mosaic to preserve extended flux  1 hr in each individual field will give σ=0.17 mJy for the mosaic image, enough to detect 1% polarization with S/N=6 for a 0.1 Jy source  10 source * 1hr * 7 pointings = 70 hr

* NGC 1333 IRAS 4A (Lai 2001, BIMA data)

 We can do more!  Using ACA+12m to increase sensitivity  7-pointing small mosaic to preserve extended flux  1 hr in each individual field will give σ=0.17 mJy for the mosaic image, enough to detect 1% polarization with S/N=6 for a 0.1 Jy source  10 source * 1hr * 7 pointings = 70 hr  Choose 5 objects in Oph and 5 in Perseus  Both have abundant YSOs at different stages  YSO content is well study by Enoch et al. (2009) using Spitzer + Bolocam data

NAMECLASST bol (K)L bol (L ⊙ )M env (L ⊙ ) HH NGC IRAS 4A NGC IRAS 2A SVS 13AI NGC IRAS 6 I

NAMECLASST bol (K)L bol (L ⊙ )M env (L ⊙ ) IRAS IRAS B VLA GSS 30I EL 29/GY214I

 Dual Polarization – probably ready  Wave plates – still needed!  Calibration : “An ongoing program to better understand the polarization performance of the array, and potential routes to modify receiver optics to increase polarization accuracy and sensitivity to further this goal is desirable.”  What should we see from different models?

October 8, 2008ALMA Band 1 Workshop24 –WVR upgrades: phase correction is better understood a next generation WVR sytem may be desirable –polarimetry: developing a dedicated deployable polarimetry system with rotating waveplates –correlator data retention: correlator has very high time resolution but raw data can’t presently be kept –software upgrades: improve data taking efficiency, new algorithms and heuristics, ??? Restoring ALMA Capabilities