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Star Formation Regions (SFR):
 | Summary of the properties of clouds and other regions found in the interstellar medium.
(from Duley & Williams, 1984, Interstellar Chemistry, Harcourt Brace Jovanovich,
publishers, chapter 1.3)
[N: T = kinetic temperature; n = number of H atoms cm-3 in all forms;
M = mass; r = radius.]
 | Intercloud medium: T=10^4 K. Dominant atom H. Dominant ion C+. All atoms with ionization potential < 13.6 eV ionized. n~0.1 cm-3. No molecules. |
| Diffuse clouds: T=100 K. Partially convertion of H into H2. Dominant ion C+. Other atoms partially neutral. n~100 cm-3. Molecules CO, H2CO, and some others observed. |
| Dark clouds: T=10-20 K. Most H converted into H2. Large optical depth in visible and ultraviolet. n~10^4 cm-3. Little internal motion. M=10^2-10^4 Msun. r~5pc. Many molecules observed. |
| Molecular clouds: T = 50 K. Associated with regions of excitation. Large optical depth. Often emitters in infrared of thermal radiation. n<10^6 cm-3. M<10^6 Msun. r<30pc. Many molecules observed but much turbulent motion produces wide lines. |
| Giant molecular clouds: T = 10 K. Relatively low density n~600 cm-3. Very large mass M~5x10^5 Msun. Diameter 40-100 pc. |
| Circumstellar shells: T = 100-1000 K. Associated with late type stars with low surface temperatures. Molecules and dust seen. Oxygen-rich stars show silicates, SiO. Carbon-rich stars show carbon, C2H2. |
| Compact H II regions: T = 100-1000 K. Hot stars in dense clouds of gas and dust. Infrared and radio emission of gas and dust including molecules. Maser sources SiO, H2O, OH. n~10^3-10^4 cm-3. |
| H II region: T=10^4 K. Dominant ion H+, but C+, N+, and O+ also present. n~10^2-10^3 cm-3. r~1-10pc. Line and continuum radiaion emitted. |
| Coronal gas: T = 10^5-10^6 K. n=10^-2 cm-3. Atoms highly ionized, e.g., O VI observed. May occupy ~20% of interstellar medium. |
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| Representative sources of each class of interstellar clouds:
(from Duley & Williams, 1984, Interstellar Chemistry, Harcourt Brace Jovanovich,
publishers, chapter 1.3)
| zita Oph -- diffuse
cloud. It is an early type star at a distance of 130 pc and obscured by a diffuse cloud. Mainly composed of H2, also some H atoms. Dust grains produce H2 and surply shielding for several other molecules. |
| IRC +10216 -- circumstellar shell. A carbon rich AGB star at around 150 pc. |
| TMC-1 -- dark
cloud. at 115 pc in Taurus. Narrow linewidth <1 km/s. |
| Sgr B2 -- a unique molecular cloud
at the center of the Galaxy. With the largest number of detected molecular species. The largest and most massive molecular cloud yet detected. |
| W3 -- a compact H II region among the H II region complex in the Perseus arm of the Galaxy. It shows strong IR absorption of cold dust and gas. |
| rho Ophiuchi -- a vast molecular cloud near the star rho Oph and showing
both dark cloud and molecular cloud
characteristics. |
| Giant molecular clouds -- 3000-4000 of them between 4-9 kpc in our Galaxy. 10^2-10^3 H cm-3. 10K. size 100 pc. 1-2x10^5 Msun. long lived (lifetime of 3x10^8 yr).
Places of star formation. |
|
| Triggered star formation in Per
OB1 (from the lunch box talk by Dr. Hsu-Tai Lee at ASIAA on Nov. 19,
2007)
| The star cluster Per OB1
shows spatial and velocity distribution agreeing to the H1 observation
of a super buble created by SN near the
galatic plane. This is a good example of triggered
star formation activity. |
|
| ASTE Observations of Star
Formation Regions ( From Kamegai Kazuhisa's lunch box talk in ASIAA on Apr. 16,
2007):
| C I 3P1-3P0 emission line
is a good tracer of hot core in SFR. |
| Complex molecules such as HCOOCH3 (methyl formate) and CH3OOCH3
(dimethyl ether) are also good tracers of hot cores. |
| Examples of hot cores: L1688, L1689, L1709, HD 47889, and some
globules in Cha II (e.g., DC 303.8-14.2, corresponding to
IRAS 13036-7644). |
|
| Detection of negative ion in L1527 (from the
colloquium talk by Ms. Nami Sakai at ASIAA on 26 Jun. 2007) L1527 is a low
mass protostar. Up to now, positive ions such as H3+,
HCO+,, He+, H+, etc. have been detected in the star formation
regions, some negative ions such as electron, PAH
grain are also known, but the detection of
molecular anion are still rare. Appearance of abundant
anion in L1527 indicates low ionization degree,
because, otherwise, the anion will be eaten up by ion through fast chemical
reactions. |
| Molecular line survey of massive clumps assiciated
with infrared dark cloud (from the colloquium talk by Dr. Takeshi
Sakai at ASIAA on 26 June, 2007) massive clumps of cool molecular gas might be connected with the formation of massive stars. Those massive clumps associated with infrared
dark clouds (IRDCs) are most possible candidates of massive stars.
Chemistry signpost of star formation stages: Dense
core (CCS -> N2H+) => SFR (CH3OH,H2CO,NH3 ->
CH3CN,C2H5,CN,HCOOCH3)
=> H2O maser. |
| Circumstellar disk around hyper massive protostellar
objects (HMPOs). (From the lunch talk by Dr. Pravankara Manoj in
ASIAA on 25 Jun, 2007) Only stars with main sequence mass lower than 8 Msun
has observable protostellar object stage. More massive stars evolve fast and
enter main sequence before the dissipation of circumstellar matter. The
evolutionary path of low mass star is: class 0
objects => class 1 objects => protostar => MS star.
The evolutionary path of massive star is: HMPOs
=> HCH => UCH
=> HII => Herbig Be
star => MS star. Here, UCH refers to
ultra-compact H II region. Up to now, there are only two HMPOs with clear
detection of IR emission: MWC 297 and R Mon. They are the best candidates of HMPOs with
circumstellar disk. |
| Infall and outflow in HH object (from Dr.
Chin-Fei Lee's talk in star formation group meeting in ASIAA on 26 Jun,
2007) HH 212 is a HH objects with very strong and well collimated bipolar
outflows. Interferometry observations of C18O, 13CO and SO using the SMA
reveal a infalling disk around the central
star, oriented perpendicular to the bipolar outflow. The P-V diagram that shows a stronger and broader blue
half and a weaker and narrower red half is reproduced by a optically
thick infalling disk with slow rotation. The different opacity
effects to the blue and red half of the disk is eccential to
reproduce the P-V diagram. |
| Massive star formation (from colloquium talk
by Dr. Luis F. Rodriguez at ASIAA on 2007, July 24)
| Although low mass star can be formed by accretion of matter, high mass
star can not be formed this way, because for protostars with mass >
10 Msun, the radiation pressure will overtake
gravity and so blow away surrounded material. (Fgrav
= GMm/r2, Frad = L sig
/ 4 pi r2C). There are two ways to form
massive stars: 1) decrease the efficiency of gas pressure sig, e.g.,
accrete gas via accretion disk or fast accrete in a short time; 2) merge two low mass stars to form a massive star. |
| Although narrow jets or disk are frequently seen around low mass
protostars, massive star protostars do not show jets or disk,
instead they show broad outflows. The reason could be the difference
between the dynamic timescale of outflow
and the Kelvin-Helmhertz timescale of jets or disk. For low mass protostars,
dynamical timescase of outflow is about 104 yr, while K-H
timescase is around 106 yr. Oppositely, for massive
protostars, the dynamic timescale of outflow is about 105 yr,
while the K-H timescale is around 104 yr. |
| Examples of massive protostars: L1551 IRS5,
HH1-2(VLA 1), HH8081,
IRAS 16547-4247 (O star, distance is 2.9
kpc, 6.2x104 Lsun), BNKL 1 (multiple
system). |
|
| Radio astrometry of young stars (from the
colloquium talk by Dr. Luis F., Rodriguez at ASIAA on 2007, July 23) Continuum emission from young stars can be used to do
astrometry through interferometry. There are
three kinds of continuum emission from young stars: free-free
emission or dust emission from extended structures around the massive
young stars is suitable for observations by VLA;
gyarosynchrotron emission from the small
magnitosphere of the young star is suitable for observations by VLBA. Several examples observed by them: YLW15, L1527, L1551 IRS5, T Tauri. |
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