Massive star formation via masers

Radio Astronomy-3
Dr. Khaled Edris
Department of Astronomy and Meteorology
Al-Azhar University
Cairo, Egypt
khedres@azhar.edu.eg

Astronomical
Masers
Messenger of Star forming Regions

High Mass Star formation
….. What are
massive stars?

• High mass
≥ 8 𝑀⊙⊙⊙⊙⊙⊙⊙⊙
• O and B stars
30 April 2018 ISYA Egypt 2018 4

….. Are they
important?

Importance:
• Play a vital role in the dynamics and evolution of galaxy
• Produce powerful stellar winds which deposit momentum and
mechanical energy into the interstellar medium
• Heat surrounding molecular clouds and supply energy for chemical
reactions.
High mass star formation

Importance:
• At the end of their lifetime (of the order of 106 yrs), they violently
explode as supernova,
Which:
• enriching the region with heavy elements,
• producing violent shocks,
• trigger star-formation in neighboring molecular clouds.

….. What are the
difficulties?

Difficulties:
• Distant
• Rare
• Form in short timescale relative to low mass.
• Deeply embedded in natal cloud
• Form in clusters

Difficulties:
They should not be formed !!!
….. The problem of
Accretion
Vis
Radiation pressure!!!

….. How do they
form?

The simple answer
….. We do not know
!!!

….. Where are
they?

Where are the star forming regions?
• IRAS Point Source catalogue
• Infrared observations at 12, 25, 60 and 100 𝜇𝑚 (10−6
𝑚)
• ~ 250,000 infrared point source detected.

• Richards et al. 1987
• 39 IRAS sources based on color index selection criterion.
• Without known HII regions.
• Study Compact Molecular Clouds (CMCs)
• 𝐻𝐶𝑂+ observations which required high densities (≥ 105 𝑐𝑚−3) for
excitation

• Wood & Churchwell 1989
• Study UCHII through radio continuum emission at 2 and 6 cm
• They correlate between their detected UCHII regions and their color
index in the IRAS catalogue.
• They suggested a selection criterion for the infrared colors and fluxes
of UCHII regions.

• Palla et al. 1991
• Apply the two criteria of Richards et al and Wood & Churchwell:
• Galactic latitude ≤ 10 𝑜;
• FIR colors: 0.61 ≤ 60 − 25 ≤ 1.74, 𝑎𝑛𝑑 0.087 ≤ 100 − 60 ≤ 0.52;
• No upper limit for flux at 25, 60, and 100 𝜇𝑚;
• No HII regions
• 𝐹60 ≥ 100 𝐽𝑦;
• 𝛿 ≧ −30 𝑜

• 260 IRAS sources high mass
star forming candidates
• Outside box = Sources that
satisfy only the criteria of
Richards et al. 1987 for
CMCs.
• Box (125 sources) = sources
satisfy the criteria of Wood
& Churchwell 1989 for UCHII
regions

• Search them for water
maser which trace
massive star forming
regions.
• Detected water maser
towards 17%.

• Molinari et al. 1996
• 163 of Palla et al. 260-
sample
• Call them High and Low
• Search them for 𝑁𝐻3
which trace dense cores.

• Full dots = detected
sources;
(45% Low, 80% High)
• Empty dots = non-
detected
• Small dots = not
observed

• Sridharan et al. 2002
• A sample of 69 candidate
of High Mass Protostellar
Objects (HMPOs)
• Satisfy the criteria of
Wood and Churchwell
1989 = high sources.

The Answer:
• Sridharan et al. 2002 (S02)
• 69 sources => candidates
for High Mass Protostellar
Objects (HMPOs)
• = High sub-sample
• 163 sources =>
candidates for pre-UCHII
regions
• Divided into High and
Low sub-samples
217 HMPOs candidates
83 Low sub-sample
65 High sub-sample
61 S02 sub-sample
8 common S02/High

What is the best/missing tool to study high
mass star formation?

What is the best/missing tool to study high
mass star formation?
Astronomical Masers

MASER properties:
• Very small, in the scale of milliarcsecond,
• Narrow, fraction of a km/s.
Let us measures velocity and position with great accuracy
• Its flux intensity > 1 Jy and in some cases reach 1000 Jy.
• Trace a specific range of physical condition.
Astronomical Masers

Astronomical Masers
https://www.cv.nrao.edu/course/astr534/HILine.html Water masers, IRAS20126+4104, Edris et al. 2005

• Water (𝐻2 𝑂) masers:
• at 22 GHz (1.3 mm, K band)
• The brightest of all known masers
• Star forming regions ➔ Molecular outflow mostly
• Galaxies
• Late-type stars
Common observed maser species:

Methanol (𝐶𝐻3 𝑂𝐻) Masers,
Two classes
• Class I, collisionally pumped, e.g. at 44 and 95 GHz
• Offset from HII regions
• Class II, radiatively pumped, e.g. at 6.7 GHz
• Only observed towards star forming region
• Closely associated with HII regions, OH, and water masers

• Hydroxyl (OH) masers (18 cm, L band):
• Main lines, at 1665 and 1667 MHz => Star forming Regions
• Satellite lines at 1612 MHz => Late-type stars,
and 1720 MHz => Supernova remnants
• Associated with HII regions
• Some papers related it to earlier stage before the appearance of HII regions
• Good probe for polarization and magnetic field

What evolutionary stage dose OH maser trace?
• HII regions
HII region
OH masers

• Circumstellar disks
What evolutionary stage dose OH maser trace?

OH maser survey towards High Mass
Protostellar Objects (HMPOs)
• 217 HMPOs were
surveyed for OH masers
using
• Nançay Radio telescope
• At 18 cm the Nançay
radio telescope has a
half-power beam-width
of 3.5 arcmin in right
ascension and 19 arcmin
in declination

• GBT Radio telescope
• Observe sources have
not observed by Nancay
• Re-observe detected OH
masers to:
• higher spectral resolution
• decrease the
contamination (8 arcmin)
• make small maps

The survey observations detected 63 OH maser sources out of 217
IRAS sources; 46 sources of them are confirmed by GBT maps.
Of these 37 are new detections.
Edris et al. (2007)

What are the correlations between maser species
associated with HMPOs?

What are the correlations between maser
species associated with HMPOs?

What are the fluxes of OH maser associated
with HMPOs?

What are the masers trace?
• MERLIN Interferometer
• 𝜃 = 1.22
𝜆
Β
= 1.22
0.18
217000
⇒
𝜃 = 0.2 𝑎𝑟𝑐𝑠𝑒𝑐𝑜𝑛𝑑
• IRAS 20126+4104

What are the masers trace towards IRAS 20126+4104?
• OH masers and CH3OH
masers trace the disk while
H2O masers trace the
outflow
• Maser spots of OH, water,
and Methanol.
• Edris et al. (2005)

outflow
• OH maser - 2.2 𝝁𝒎

outflow
• OH and Methanol masers –
Keplerian motion

What are the OH masers trace towards IRAS 19092+0841?
• OH masers
Circumstellar
material.
• Edris et al. (2017)
• OH masers – 850
𝜇𝑚

http://web.science.mq.edu.au/~cpurcell/public/images/sequence_new.png

Low Mass Star formation
http://web.science.mq.edu.au/~cpurcell/public/images/sequence_new.png

Image Credits:
• http://www.livingbliss.me/learning-intuition/light-or-heavy/
• http://proposito.co.uk/2017/06/retirement/
• https://www.radioevangelobari.it/rubriche/meditazioni-bibliche/costruire-la-propria-casa/
• https://www.nichepursuits.com/search-volume-and-cpc-criteria-of-a-winning-keyword/
• https://depositphotos.com/109606492/stock-illustration-very-important-stamp.html
• https://lamerkhav.wordpress.com/
• http://www.clker.com/clipart-right-mark.html
• https://market.ionicframework.com/starters/facebook-messenger-clone
• http://comet.sai.msu.ru/~gmr/masers.htm
• https://www.aanda.org/articles/aa/full_html/2010/09/aa14234-10/aa14234-10.html

Massive star formation via masers

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