Физико-химическая структура областей образования массивных звезд И.И. Зинченко Институт прикладной физики РАН

Problems I Difficult to form massive starsDifficult to form massive stars –Require high accretion rates ≥ M o / yr –Generally in dense cluster cores »Not much room for proto-massive star –Radiation pressure on dust grains »Reverses infall once M > M o »Sets (low) upper mass limit? Yorke 1993, Wolfire & Casinelli 1986Yorke 1993, Wolfire & Casinelli 1986 »Eddington limit ~ 100 M o Electron scatteringElectron scattering J. Bally Bonnell, 2005

Radiation pressure: Solutions Disc Accretion Yorke & Sonnhalter 2002Disc Accretion Yorke & Sonnhalter 2002 –Mass accretion through disc »Partially shielded –Stellar Radiation beamed away from disc »Due to rapid rotation High accretion > M o /yr McKee & Tan 2003High accretion > M o /yr McKee & Tan 2003 –Overwhelm radiation pressure –Need very dense initial conditions Rayleigh-Taylor Instabilities Krumholz et al 2005Rayleigh-Taylor Instabilities Krumholz et al 2005 –Locally increase accretion rate Bonnell, 2005

Radiation pressure: Solutions II Destroy dust in accretion flow Keto 2003Destroy dust in accretion flow Keto 2003 –Hyper-compact HII region –Dust destroyed (just) before radiation pressure imparts momentum Stellar Collisions Bonnell, Bate & Zinnecker 1998Stellar Collisions Bonnell, Bate & Zinnecker 1998 –Dense stellar cluster: n > 10 8 stars /pc 3 –Intermediate mass stars hit and merge »No problem with radiation pressure –Binaries: tidal capture –Ultra dense cluster due to accretion Bally & Zinnecker 2005 Bonnell, 2005

Star Formation - ИНАСАН Multi-line observations of selected objects: S mm

Star Formation - ИНАСАН Химическая дифференциация при образовании звезд малой массы Tafalla et al. 2002

Star Formation - ИНАСАН CS, N 2 H + и пыль G – типичный пример (звездочка – точечный источник IRAS). Распределения интенсивностей CS и пыли обычно очень похожи и отличаются от N 2 H +, в отличие от областей образования звезд малой массы.

Star Formation - ИНАСАН CS/dust and N 2 H + /dust ratios (G as an example) r is the projected distance from the CS/dust peak

Star Formation - ИНАСАН Возможная интерпретация  Эффекты насыщения линий Оптическая толща в линиях N 2 H + невелика, как следует из анализа сверхтонкой структуры, а в CS(5- 4) эти эффекты незаметны.Оптическая толща в линиях N 2 H + невелика, как следует из анализа сверхтонкой структуры, а в CS(5- 4) эти эффекты незаметны.  Эффекты возбуждения молекул ИК накачка для CS и N 2 H + может быть существенна на расстояниях r < 0.05 пк от звезды, что значительно меньше типичного размера областей, где наблюдаются данные эффекты.ИК накачка для CS и N 2 H + может быть существенна на расстояниях r < 0.05 пк от звезды, что значительно меньше типичного размера областей, где наблюдаются данные эффекты. Наблюдаемую величину вариаций невозможно объяснить только эффектами возбуждения.Наблюдаемую величину вариаций невозможно объяснить только эффектами возбуждения.  Вариации химического состава Наиболее приемлемое объяснение наблюдаемых вариаций интенсивности – это уменьшение содержания N 2 H + в центре.Наиболее приемлемое объяснение наблюдаемых вариаций интенсивности – это уменьшение содержания N 2 H + в центре.

Star Formation - ИНАСАН Temperatures from CH 3 CCH observations CH 3 CCH J = 6–5 transitions were observed in 2002 at Onsala towards “CS” and “N 2 H + ” peaks in several sources. J=13-12 transitions were observed in 2004 at IRAM 30m. An example of CH3CCH J = spectrum in S140

Star Formation - ИНАСАН SourcePeak T kin 6-5 T kin W3W3W3W3 “CS” 52.6 ± ± 1.5 “N 2 H + ” 30.7 ± ± 2.2 DR21(NH 3 ) “CS” 33.3 ± ± 1.4 “N 2 H + ” 28.8 ± ± 1.1 S140 “CS” 30.6 ± ± 1.0 “N 2 H + ” 27.8 ± ± 2.2 S255 “CS” 34.5 ± ± 0.9 “N 2 H + ” 34.9 ± ± 0.4 Only in W3 a significant temperature difference between the CS and N 2 H + peaks was found. However, in general the N 2 H + peaks are somewhat colder than the CS ones.

Star Formation - ИНАСАН Estimates of S255 parameters from CH 3 OH 2-1 and 5-4 series of transitions (S. Salii et al.) An example of LVG density estimates (in G ) based on CS J=5-4 and J=2-1 data. The yellow contours represent the CS(5-4) map.

Star Formation - ИНАСАН Accelerated collapse model Evolution of the ratio of CS to N 2 H + abundances during collapse. Once a critical number density of 10 5 cm -3 was achieved, three of the four runs shown incorporated a collapse accelerated by the factor shown (2, 3 or 4 times the free-fall velocity). The effect of an enhanced collapse rate should be that high gas densities would be achieved rapidly, before the effects of freeze-out dominate the chemistry. These densities would be reached before molecules that are important as N 2 H + removal agents (such as CO) are significantly depleted in the gas phase. Then N 2 H + abundances should be reduced in such circumstances, while the higher gas density promotes gas phase chemistry producing, in particular, CS. Lintott et al. 2005

Star Formation - ИНАСАН Диссоциативная рекомбинация N 2 H + Geppert et al Вероятно, эта реакция может приводить к уменьшению содержания N 2 H + в областях повышенной ионизации.

Star Formation - ИНАСАН Пример: S76E The 2MASS Ks image with the 0.87 mm continuum map (contours) overlaid. The positions of IRAS, MSX and 2MASS-IRS1 are indicated by a plus, an asterisk and a cross signs, respectively, while the triangles mark the three water masers observed by Migenes et al

Star Formation - ИНАСАН Large scale distribution of molecular gas: CO CO(1-0) mosaic map and spectra at different positions. (29´,-15´)

Star Formation - ИНАСАН Large scale distribution of molecular gas: C 18 O Left: C 18 O(2-1) maps in 1 km/s velocity bins (the central velocity is indicated in the upper left corner). Right: C 18 O (1-0) and (2-1) spectra.

Star Formation - ИНАСАН Large scale distribution of molecular gas: other molecules In CS, SO, HCO +, NH 3 and N 2 H + the emission at V LSR ~ km/s dominates, though a weak component at V LSR ~ 28 km/s can be seen in SO and NH 3. The main component peaks in CS, SO and NH 3 are displaced by 10˝-20˝ to SW or W from S76E nominal position and are rather compact (< 1´) while the emission peak of the secondary component is shifted by ~1.5-2´ to SW. CS(5-4) integrated intensity (grey- scale) as well as red- and blue- shifted parts of the spectrum.

Star Formation - ИНАСАН NMA results: CS J=2-1 and J=3-2

Star Formation - ИНАСАН

Star Formation - ИНАСАН

01/06/2015Star Formation - ИНАСАН  Massive and dense cores in different early evolutionary stages: Stage Observed signatures Comments mm FIR radio early late Pre-UCHII    Large scale infall motions HMPO    Accretion + jet + bipolar outflow Warm    Embedded luminous energy source; T ~ 32 K; UCHII phase Cold    No internal luminous energy source; T < 15 K Garay, 2005

Star Formation - ИНАСАН Basic physical properties of HMSF cores On the basis of the CS survey and ammonia observations the basic physical properties of the cores have been derived and their statistical distributions have been constructed.  The average size is ~ 1 pc.  The average temperature is ~ K.  The mean densities are ~ 10 4 cm -3 which is much lower than densities derived from excitation analysis.  The slope of the mass spectrum is ~  The velocity dispersion is highly supersonic.  The IR luminosity to mass ratio peaks at ~ 10 (in solar units).  The cores are close to gravitational equilibrium. Zinchenko, Pirogov & Toriseva 1998

01/06/2015Star Formation - ИНАСАН Fontani et al. (2002) sample of 12 Clumps

Star Formation - ИНАСАН Radial density profiles from dust continuum Results for 2D power law function and gaussian beam convolution fit to the observational data. The mean power law index is ~ 1.0 for cores with IRAS sources and ~0.6 for cores without IRAS sources. This implies the power law index for radial density dependence ~1.6 (assuming the index for the radial temperature dependence of 0.4).

01/06/2015Star Formation - ИНАСАН n H 2  R -2.6 ClumpHMC Fontani et al. (2002)

Star Formation - ИНАСАН

Star Formation - ИНАСАН Temperature distributions from IRAM CH 3 CCH(13-12) data

Star Formation - ИНАСАН Sourceγβ S (04)0.42(06) S76E0.26(03)0.36(05) DR210.25(04)0.35(06) W30.27(08)0.38(12) S (02)0.32(03)

Star Formation - ИНАСАН Radial dependence of velocity dispersion The enhancement of line widths in the central regions cannot be explained by optical depth effects alone. A plausible explanation could be found in a higher degree of dynamical activity of gas in central regions of HMSF cores, including differential rotation, infall motions and turbulence due to winds and outflows from massive stars.

Star Formation - ИНАСАН Velocity gradients There is a correlation between direction angle of total velocity gradient and elongation angle. The average ratio of rotational to gravitational energy is ~ Therefore, rotation does not play a significant role in core dynamics.

Star Formation - ИНАСАН Радиальные движения  Некоторые особенности профилей линий могут указывать на наличие систематических радиальных движений в облаке.

Star Formation - ИНАСАН Massive protostars? Maps of W3 area in the N 2 H + and HCO + lines. HCO + lines frequently show signs of infall motions.

01/06/2015Star Formation - ИНАСАН Example: IRAS Garay et al. (2002) 8 μm MSX 1.2 mm emission SIMBA Massive IR-dark cloud Isolated massive dense cores: Ideal places to investigate the process of massive star formation 1 pc  Few appear as isolated structures ~10 % M ~ 2x10 3 M ๏  Most within large molecular clouds (GMCs) ~90 % Where are massive dense cores found?

Egan et al G IRDCs = compact objects seen against the bright mid-infrared emission from the Galactic plane. dark between 7 and 100  m ~2000 clouds in a 1  180  scan along the Galactic equator Menten, 2005

Star Formation - ИНАСАН Наблюдения молекул в темных ИК облаках

Star Formation - ИНАСАН Statistics of high velocity outflows in HMSF regions Questions:  Frequency of occurrence (important for understanding the formation mechanism of high mass stars)  Basic physical properties in dependence on IR luminosity

Star Formation - ИНАСАН Indeed, around the BN/KL region there is the well known outflow with an age of about 1000 years. It is possible that the outflow and the ejection of BN and I were result of the same phenomenon. Energy in outflow is of order 4X10 47 ergs, perhaps produced by formation of close binary or merger. H 2 image with NH 3 contours (Shuping et al. 2004; Wilson et al. 2000) Luis F. Rodríguez, 2005

Star Formation - ИНАСАН Identification of high-velocity outflows SO C 18 O residual C 18 O The outflow detection rate is ≥ 40 %

Star Formation - ИНАСАН Outflow properties  There are good correlations between mass, momentum and kinetic energy on the one hand and IR luminosity on the other hand.  From the comparison with mass loss rate, “force” and “mechanical luminosity” the average “dynamical age” is ~ 10 4 years. The scatter in this age is small.

Star Formation - ИНАСАН

(Beuther et al. 2002) Outflow Energetics PfPf. L bol M f vs L bol correlation appears to be upper limit M f is a function of the entrainment efficiency.. MfMf. L acc L ZAMS L bol P f E f  L bol 0.6 for L bol = 0.3 to 10 5 L sun Similar correlations hold for mass accretion rate, ionized mass outflow rate, & core mass.  strong link between accretion & outflow for most L bol... MfMf F = L bol /c (Wu et al. 2004) e.g. Cabrit & Bertout 1992, Shepherd & Churchwell 1996, Anglada et al. 1996, Henning et al. 2000, Beuther et al. 2002, Wu et al Shepherd, 2005

Star Formation - ИНАСАН Correlations between core parameters from CS from N2H+ Garay, 2005

Star Formation - ИНАСАН Small scale clumpiness in HMSF cores Optical depth broadening of CS lines Search for “ripples” in line profiles

Star Formation - ИНАСАН Сверхтонкая структура линий, как индикатор фрагментарности Pirogov 1999

Possible Roles of Magnetic Fields formation of GMCs fragmentation to form cores support against collapse transport of angular momentum from central regions of cores, enabling star formation Crutcher, 2005

Mass to Magnetic Flux Ratios mass/flux ratio ( )  gravitational collapse /magnetic support Crutcher, 2005

Star Formation - ИНАСАН Galactic gradients of the physical properties of HMSF cores The mean density drops exponentially with R (the scale length is ~ 3 kpc)

Star Formation - ИНАСАН HCN and HCO + emission in the disk of M 31 “When investigating the variation with the galactic radius in the M 31 disk, we find that the I(HCN)/I(CO) and I(HCO + )/I(CO) ratios are higher in the inner arm than in the outer arm. This weak trend, if real, is not supposed to come from the abundance gradient but from excitation effects.” (Brouillet et al. 2005)

Star Formation - ИНАСАН Свойства плотных ядер в областях образования звезд большой и малой массы

01/06/2015Star Formation - ИНАСАН A possible scenario for high-mass SF Unstable clump: t ff =10 5 yr Clump n  R -2 M clump > M virial Cesaroni, 2005

01/06/2015Star Formation - ИНАСАН A possible scenario for high-mass SF Unstable clump: t ff =10 5 yr Inside-out collapse: dM accr /dt=M clump /t ff =10 -2 M O /yr infalling Clump n  R -3/2 n  R -2 Cesaroni, 2005

01/06/2015Star Formation - ИНАСАН A possible scenario for high-mass SF Unstable clump: t ff =10 5 yr Inside-out collapse: dM accr /dt=M clump /t ff =10 -2 M O /yr Rotation of core with rotation period=10 5 yr infalling Clump n  R -3/2 n  R -2 rotating Core Cesaroni, 2005

01/06/2015Star Formation - ИНАСАН A possible scenario for high-mass SF Unstable clump: t ff =10 5 yr Inside-out collapse: dM accr /dt=M clump /t ff =10 -2 M O /yr Rotation of core with rotation period=10 5 yr Fragmentation over R centrifugal =R HMC /5=0.01 pc infalling Clump n  R -3/2 n  R -2 rotating Core rotating disks Cesaroni, 2005

01/06/2015Star Formation - ИНАСАН A possible scenario for high-mass SF Unstable clump: t ff =10 5 yr Inside-out collapse: dM accr /dt=M clump /t ff =10 -2 M O /yr Rotation of core with rotation period=10 5 yr Fragmentation over R centrifugal =R HMC /5=0.01 pc Formation of HMC with 5 3 ∼ 100 stars (dM accr /dt) star = M O /yr /100 = = M O /yr over t SF =t ff =10 5 yr infalling Clump n  R -3/2 n  R -2 rotating HMC circumstellar disks Cesaroni, 2005

Star Formation - ИНАСАН Заключение  Химическая дифференциация молекул в областях образования массивных звезд радикально отличается от той, что имеет место в темных холодных облаках, где образуются звезды малой массы. Содержание молекул N 2 H + здесь уменьшается в центре облака, в направлении ИК источников. Причины этого пока не вполне понятны.  Радиальные профили плотности в сгустках, где образуются массивные звезды, соответствуют «стандартной» модели звездообразования.  Зависимость температуры от радиуса близка к ожидаемой для центрального источника нагрева в оптически тонкой среде.  Дисперсия скоростей газа либо постоянна, либо уменьшается от центра к краю облака.  Отношение энергии вращения к гравитационной мало.  В ряде случаев особенности профилей линий указывают на сжатие облаков.  Имеются признаки мелкомасштабной фрагментарности, которая, однако, не проявляется в виде «изрезанности» профилей линий.