Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.atnf.csiro.au/research/masermeeting/web_papers/1105_Reid.pdf Äàòà èçìåíåíèÿ: Mon Apr 30 04:23:51 2007 Äàòà èíäåêñèðîâàíèÿ: Sun Dec 23 09:44:23 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: europe

IAU Symp. 242: Summary
· Progress since 2001 meeting in Brazil · What do we think we understand? · What don't we understand?


Masers: Complexity
· Chemistry (Temp, dens, ionization, evaporation, dissociation, ...) · Amplification (limited by clumping or Vel/B-field gradients, saturation, beaming, pumping)
Pump: concept of single pump path naÎve:10-100s routes contribute to OH Ampl.: OH line wing variability ~103 s puzzling Polarization: pure components (100% linear) not seen! Why? OH stimulation of by radiation in aligned clouds

· Lifetimes (dynamic cloud formation) · Projections (3-D observed as 2-D) · Extinction (eg, visible, IR images)

OH masers in H2O outflow

Synchrotron Emission !

Thermal Bremsstrahlung


Interstellar Masers: Characteristics
· H2O
Power-law position correlations...no clustering scale...fractal/turbulence outer scale ~ injection of energy via jet wind (~1017 cm) inner scale ~ dissipation of energy at maser spot scale (~1013 cm)

·OH
OH: strong clustering scale (not power-laws like H2O) ~ 100 AU Both form lines/arcs on sky & worms in P-V space Are maser "worms" Strelnitski's cascading vorticity?

·CH3OH (unknown)
Class II: expect similar to OH Class I: perhaps like H2O


Interstellar Masers: Variability
· CH3OH Periodic Variability
Clear quasi-sinusoidal variations in ~10% surveyed VLBA maps show spot "pulsation", nothing else changing Periods between 133 to 504 days...similar to Miras While chance meeting of MSF cloud & Mira variable very low... embedded pulsating PMS star (eg, lower mass VY CMa) intriguing => pulsation lifetime ~ 10% of maser lifetime


· SiO · H2O

Masers Pumps

Collisions and/or radiation

Collisional: doesn't correlate well with IR; but does with outflows/shocks

· CH3OH
Class-I collisional: shocks at interface of MC Class-II radiative: associated with IR dark clouds and hot molec cores of MSFRs

· OH
Radiative: OH correlates well with MIR; not with fast outflow

· H2CO
Radio Continuum and IR pumps probably doesn't work; by default (possibly e- if nH~103) collisions if nH~106

Does intrinsic complexity of the pumping or ignorance of atomic/molecular cross-sections dominate?


Mm/submm Masers
· Lots of new mm/submm masers,
Even though (as Strelnitski pointed out at the last meeting), it is harder for Nature to invert populations at higher frequencies


Interstellar Masers: YSO disk/jets
· Fast outflows: H2O · Slow outflows: H2O, CH3OH, SiO · Disks: ? (H-recomb masers in MWC349) disk hard differentiate from bipolar jets often rely on other jet indicators: H2 2.1 um thermal SiO radio continuum, but not always... · HII expansion: OH, CH3OH Class II · Shocks: CH3OH Class I, OH/SNRs


Interstellar Masers: B-fields
· OH
typically 1 ­ 10 mG...but up to 40 mG seen! Always ordered: either 0 or 1 reversal across source

· H2O
typically 10 ­ 100 mG

· B ~ n(H2)

0.5

suggests n(H2O) only ~100 x n(OH)... but uncomfortable for B(OH) > B(H2O)


Interstellar Masers: Age Sequence

OH in H2O outflow Class I very young, but will form star? H2O first gen/Class II 2nd generation H2O 2x OH...longer lived or lower mass star mm-only cores - - - - - - - - - - - - - - - - - - > ? (Keto) NH3-only cores

Other dimensions: stellar mass, external ionization & shocks, etc.


AGB Masers: Standard Model

Ti + O <> TiO H <> p + e "Hard place" "Rock"

Note: asymmetry in radio photospheres (green)


AGB Masers: Standard Model


Stellar Masers: Magnetic Fields
Maser B(Zeeman) (G) 0.001 0.1 10. R (cm) 6x10 5x10 B2/8 nkT v2 -------- dynes/cm2 -----10-7 10
-3

OH H2O SiO

14 14

4x10 1x10

-7 -5

10

-5

3x10

6x10

10-3 10-2

13

10+1

-3


Stellar Masers: Magnetic Fields
Maser B(Zeeman) (G) 0.003 0.03 3. 0.5 3. R (cm) 6x10 B2/8 nkT v2 -------- dynes/cm2 -----4x10 4x10 4x10-7 6x10 1x10
-5

OH H2O SiO Radio/Molec Star

14 14

-7 -5

10

-5

2x10

4x10

10-3 10-2 4x10
-1

6x1013 5x10 2x10
13

-1

-3

2x10

-2 -1

3x10

-1 0

13

4x10

5x10

5x10+1

Assume B ~ 1/R2

20 km/s shocks


Stellar Masers: Post AGB Stars
Synchrotron emission

Eg, SiO "disk" + fast H2O "outflow"

Cat's Eye PN (HST)


Stellar Masers: Super & Hypergiant Stars
· VY CMa
In SF region, but has no Li, so post-main-seq star L ~ 5 x 105 Lsun (D/1.5 kpc)2 ~ maximum allowed L parallax needed! Losing mass extremely rapidly over past 103 yr Complex asymmetric structures seen, but an axis at PA~50 deg seen in OH,H2O,SiO,IR

· S Per
H2O projected to same R as main-line OH: problem. co-spatial or projection effect (H2O f-b caps)? OH main-line Zeeman B-field 3 mG, H2O B-field 150 mG suggests not co-spatial "Onion model dead" ...too early to claim this.


· Spiral Structure

Galactic Structure

Parallaxes are here, parallaxes are here! ~10 MSFRs &10 evolved stars (~25 Pulsars also) Large kinematic anomalies found VERA and VLBA will soon provide ~100 mapping spiral arms (finally) determining (dark) mass distribution of M.W. measuring o & Ro (+/-few%)

· Inner Galaxy
Surveys of evolved stars tracing the Bar

· Magnetic Field
Some tantalizing correlations of Pulsar RM B-fields with OH maser B-field...definitive results must await many parallaxes


H2O AGN Masers
· Sub-pc scale disks and jets
Clear understanding that masers populate both disk and jets types: thin disks, thick disks, jets, winds Learning details of accretion disks (warps, B-fields, n, T, M NGC 4258: archetypal AGN maser Thin, warped, accretion disk well established Periodicity in high vel data real disk thinness ~ 5 µas ~ ~10 AU measured => hydrostatic equil T=600 K accel vs Vsys changes may be caused by spiral arms
BH,

, spiral arms...)


H2O AGN Masers
·Precision Cosmology
Maser Cosmology Project: GBT + VLBA direct, geometric distance + redshift goal: H0 accurate to 3% Eq. of state of dark energy ... Cosmological constant vs. quintessence UGC3789 excellent "NGC4258-like" candidate


OH Megamasers
Associated with star bursts (result of major mergers)... not associated with the AGNs, but... 183 GHz AGN H2O masers found in Arp220 (which doesn't have 22 GHz!) Very dense gas is key: specifically n(H2) ~ 105.6 cm-3, but if large B-fields measured are correct, might imply n(H2) >106Associated, but weak, H2CO and 1720 MHz OH "megamasers" Why 1667 MHz compact & 1665 MHz extended? Torus filled with clouds (each with low gain); chance alignments (both along l.o.s. and in Vel) can give high gain spots Aligned, well-separated clumps produces high beaming...unsaturated Origin of arcs with V-gradients unclear: M ~ r V2 / G > 105 Msun if gravitational
7


Next Meeting?
· Ho measured to 3% accuracy...w=1
(and the Universe will end)

· Constancy of Fundamental "Constants" further tested · mm/submm maser observations will be as common as cm-wave masers · Blind surveys (of at least the Plane) will be completed for all major classes of molecular masers · Milky Way mapped with ~200 parallaxes/proper motions · H-recombination line maser from EOR ·...


Where Should the Next Meeting be?
Washington DC (North America) Rio de Janeiro (South America) Alice Springs (Australia) ? (Europe, Asia, or Africa)
7'th meeting would logically be in the Antarctic in ~2030 !