Electromagnetic radiation - acceleration of charged particles
Definition of a wavelength
Radiation spans a great range of wavelengths most of it invisible to the human eye
Radio waves - from wavelengths under 1mm to several meters

Radio Astronomy tutorial
http://www.jpl.nasa.gov/radioastronomy
http://www.aoc.nrao.edu/intro/faq.html

All kinds of sources in the universe emit radio waves. Radio emission can be thermal or non-thermal. Sources of thermal radio emission are usually very cold. Non-thermal radio emission comes mainly from the synchrotron process where charged particles are relativistically accelerated around magnetic field lines. Molecular emission at radio wavelengths arises mostly from the rotation of the molecular species.

- radio: VLA 1.4 GHz 26 Sep 1981
- optical: NASA image from NY Times Science Section
- radio+Xrays: Nobeyama Radio Heliograph

http://seds.lpl.arizona.edu/nineplanets/nineplanets/sol.html
http://www.nytimes.com/library/national/science/sun-index.html

The closest star, a ball of mainly hydrogen and some helium gas, which produces titanic eruptions, a giant solar wind, and is absolutely required to support life on Earth.

Average type of star, middle-aged, type "G2" on the main sequence
Mean Distance from Earth = 93 million miles, 150 million km (1 AU)
Distance from Milky Way Center = 8,000 pc = 26,000 light years (l.y.).y.
Equatorial Diameter = 870,000 miles = 1.392 million km = 109.2 Earth diameters
Equatorial Radius = 435,000 miles = 696,000 km = 109.2 Earth radii
Largest massive object in the solar system
Rotation Period = 25.5 days at 16 deg latitude(?) 25.4 days at equator, <=36 days near the poles (called differential rotation, just like the 4 gas planets). Core rotation is much more like that of a solid body - core is inner 25% of radius.
Mass = 1.989 E30 kg, 99.8% of Solar System Mass (Jupiter has majority of rest)
Luminosity = 3.846 E26 Watts
Core Temperature = 15.7 MK
Core Pressure = 250 billion atmospheres!
Surface Gravity = 28 times g
Average Density = 1,408 kg/m^3 = 1.408 times water density
Surface (Photospheric) Temperature = 5,800K = 5,527C = 9,981F
Surface Sunspot Temperature = 3800 K (thermally cooler in comparison)
Color = visible, peak in between yellow and green, 550 nm
Solar luminosity = 3.86 E26 Watts = 3.86 billion billion Megawatts
Energy Source = Thermonuclear fusion reactions (H->He) at 700 million tons/sec
>Energy transport via radiative degradation of central gamma rays, then convective in outer 20% of radius, and then emerging as (mainly) visible light waves
Number of satellites (planets) = 9 so far, Jupiter is largest
Solar Lifetime = 10 billion years
Solar Age = 5 billion years; half hydrogen fuel is left.
>Will double its brightness in mean time, and then expand and lose its outer layers near its death, as a PLANETARY NEBULA.
Composition: 75% hydrogen, 25% helium by mass;
92.1% hydrogen, 7.8% helium by number (0.1% "metals")
Space Probes: Ulysses, Wind, ACE, SOHO
Features: sunspots, flares, magnetized loops, corona, solar wind
Photosphere, Chromosphere, Corona
Coronal temperatures exceed 1 MK

INTERESTING:-
Greeks named it Helios; Romans named it Sol
Solar Eclipes - can see optical light from corona
Solar Wind goes out past the solar system, and causes comet tails when they approach the solar system
Solar Magnetosphere very strong, extends well beyond Pluto!
Solar Cycle - 11 years, cause disruptive magnetic storms in the Earth's atmosphere (RFI, power line surges, aurora borealis)
Solar Wind can interact with comets, spacecraft, e.g. causing a long tail
Spectacular Loops and Prominences
Effect of Sun on Earth's climate ? e.g. Solar Cycle, Little Ice Age
What heats the Corona up to >200 times the photosphere ? Corona generates non-thermal emission
Solar Neutrino Problem

OPTICAL - NASA image (HST?) shows complex cell structure, and magnificent flares and prominences coming out of the surface (Presumably some sunspots). Sunspots are at 3800 K, and being "cooler" look dark, but in fact are quite bright !

RADIO+XRAY - soft Xray disk comes from 5800 K thermal radiation.
Radio spots and flares show charged particles being accelerated along field lines - complex, beautiful magnetic fields thread the surface of the Sun.
The radio emission shows up non-thermal processes that have large numbers of charged particles being forced to stop/start/spiral (accelerate. The 3 loops are the flares at successive times.

RADIO - VLA 1.4 GHz image from 26 Sep 1981: relatively cool thermal emission from disk, interrupted by hot, non-thermal motions of charged particles in the equatorial spots.

RADIO IMAGING is necessary to highlight regions where charged particles are being accelerated, i.e. in flares, prominences. Radio imaging also shows up from thermal sources, usually at much lower intensity - thermal emission is always given off since no object can be completely cooled down to absolute zero.

http://www.nytimes.com/library/national/science/saturn-index.html

The second largest planet in the Solar system, and the 7th furthest away from the Sun (Earth is the 3rd planet from the Sun). It is, like all the outer planets except for Pluto, a gas giant (gases are poisonous, like methane and ammonia). Its dominant feature is the set of giant rings in orbit around its equator. These rings are incredibly flat, just 1-2 km in height.

Average Distance from Sun = 888 million miles = 1427 million km (9.5 AU)
Orbital Semi-major Axis = 9.53 AU
Orbital Period = 29.46 Earth years
Orbital Eccentricity = 0.056
Rotation Period = 0.436 Earth days = 10.46 hours
Average Radius = 36,400 miles = 58,232 km = 9.1 Earth radii (10% oblateness)
Mass = 5.69 E26 kg = 95.2 Earth masses
Luminosity = ?
Core Temperature = 12,000 K = 11,727 C = 11,761 F
Surface Gravity = 1.16 times g
Average Density = 690 kg/m^3 = 0.69 times water density
Average Surface Temperature = 134K = -139C = -219F
Color = mixed; yellow, tan, light brown
Energy Source = Kelvin-Helmholtz contraction generates some heat, and an additional unknown mechanism(s) is required
Number of satellites = 18, Titan is largest
Lifetime = ? (< 10 billion years)
Age = ? (< 5 billion years)
Space Probes:
Cassini launched 1997, Earth gravity assist, Saturn rendezvous in 2004. Cassini is an international project, with $3.4 billion price tag (12 countries, including NASA, ESA, Italian Space Agency). Cassini has nuclear-fueled electric generators, running on plutonium.
Voyager 1, 1980 flyby
Voyager 2, 1981 flyby

FEATURES:
Gas giant with a rocky core
>Above the core is a liquid metallic hydrogen layer, then a molecular hydrogen layer - Saturn's interior is similar to Jupiter's
Saturn is the most oblate (flattened) of all the planets, due to its rapid rotation
Giant ring system
The prominent rings visible from Earth are called A and B
The gap in between them is the Cassini Division, probably swept out by the satellite Mimas
The ring particles are made of water ice, or rocks with icy coatings
18 satellites
Titan is largest satellite, with thick nitrogen atmosphere, and an ocean of liquid ethane and methane, and probably other hydrocarbon chemicals
Titan is also the largest moon in the Solar System.
ESA decided to explore Titan for life (1988), using a probe called Huygens, which would split off from the main Cassini probe in 2004.

INTERESTING:
"Saturn" is the Roman God of Agriculture, or the associated Greek god of Cronus
Saturn is the root of the English word "Saturday"
First seen by Galileo with his optical telescope, in 1610
Extreme flatness of ring plane, caused by the many collisions of ring particles in the past - 250,000 km in diameter, only 1.5 km thick
Some moons cause ring disturbances
There are many gaps in the rings, possibly caused by moons. In fact, EVERY ONE of the 4 gas giants has rings, but not as prominently developed as in Saturn !
Auroral displays at both poles, due to SOLAR wind

OPTICAL: ring plane very thin ! reflected light from the sun, it is not a star

INFRARED: generates its own heat, just like Jupiter (nobody knows how)

ULTRAVIOLET: auroral storms at poles where charged particles come crashing down towards the magnetic poles - mainly reflected sunlight ?

RADIO: Prob. an early VLA image
Very Low-frequency Burst radiation similar to Earth & Jupiter (500 kHz)
400-4000 MHz radiation is prob. synchrotron from spiralling trapped particles in magnetosphere
Above about 4 GHz, radiation is almost certainly all thermal BB radiation
The rings are COOLER than the planet ! (see image)

Location: centre of the sword of Orion, beneath (south of) the belt, diffuse luminous patch, emission nebula, 1 degree across
M43 is a small northern part of M42

Composition: complex region of ionized HII associated with Orion GMC (OMC-1)
Distance: 400 parsec = 1300 l.y.
Radius = 7 parsecs = 23 l.y.
Trapezium cluster - four hot young stars that excite and ionize the nebula,
produce both radio and optical radiation, luminosity = 300,000 Lsolar
OMC-1 has about 500 solar masses

RADIO: ionized hydrogen electrons giving braking radiation

INFRARED: dusty regions surrounding stars being born, trap heat, emit IR waves

OPTICAL: reflection from dust of intense radiation from young massive stars, especially Trapezium cluster

XRAY: some young stars emit strongly in Xray, prob. due to some violent activity happening when stars form for the first time
>jets and outflows have been seen
Very hot gas will emit Xrays (1 keV = 10 million K), so if gas is above 10^6 K will emit soft Xrays

- radio: VLA
- optical: HST
- Xray: Chandra

Name: Messier 1, NGC 1952, Crab Nebula SNR
Object Type: Supernova Remnant (NSR)
Remnant is filled, or a plerion
Supernova: 4 July, 1054 ("Guest Star" appearance, according to Chinese records, it was visible even in broad daylight at mag -5 for 3 weeks) Also observed by Japanese
Supernova Type: probably Type II
SNR Age: almost 946 years old at year 2000
SNR Radius: 4 parsecs diameter, 7.3 l.y. across diameter
Distance: about 2 kpc
Remnant ! PULSAR - optical and radio, period 0.0331 seconds, is the power house of the Crab Nebula (electrons lost by pulsar to nebula)
Total energy loss = 10E30/10E31 Watt (3,000 to 30,000 times Lsolar)

Prob. a VLA image.

RADIO: syncrotron radiation at ALL wavelengths

OPTICAL: synchrotron, lots of filaments and excited gas

XRAY: very hot gas pierced by a central bipolar het structure

- radio: VLA image
- Xray: Chandra

Most (apparently) intense extrasolar radio source known at low radio frequency
Radio Flux = 8800 Jy at 178 MHz
Radio Spectral Index is steep (-0.77)
Distance = 2.9 kpc = 9500 l.y.
Flux decrease by 1 percent per year!
Age: about 300 years old at year 2000
Supernova: NEVER RECORDED, about 1700 judging from the size and speed of the expanding shell, obviously too far away to be seen by astronomers on Earth at the time
Progenitor: about 50 Msun supergiant star, core collapsed
Type: Type II, hydrogen-poor spectrum, hydrogen all used up and turned into helium, before the core collapse
Radius: ring like structure is 4 arcmin in diameter, 3.4 pc in diameter, or 1.7 pc in radius (5.5 l.y. in radius, 11 l.y. in diameter)

A VLA image.

RADIO: Shell emits synchrotron emission due to shock acceleration of charged particles.
Expansion velocity is now about 2300 km/s
Lots of shocked filaments NOT visible in optical
Can study magnetic field structure, not visible in other frequencies

INFRARED: hot gas and filaments emit heat, hotter in the shell (< 1000 K gas and dust)

OPTICAL: see optical emission only from the recently shocked gas, it quickly dies away (1000-10000K gas)

XRAY: soft Xrays emitted by gas > 1MK - see lots of filaments in addition to the shell

- radio: VLA
- optical: HST

Distance: to Center of Galaxy is about 8 kpc = 26,000 l.y.
Mass of Object about > 2 million solar masses !
It is an MDO, nobody knows exactly what it is. but it could be a massive black hole !
If it is a MBH, the event horizon radius is 6 million km = 9 times the size of the Sun. (By the way, R_sch of the Earth is = 9mm = 1cm - Polo Mint !
Density is 1E28 times that of water = 10 billion billion billion)
Lies in the Galactic plane, hidden behind dust.
It could have been a low-power quasar or radio galaxy in its youth, now the MBH monster eats much less than before !
Very complicated region surrounds the MBH, swirling gas, magnetic fields, charged particles, synchro radiation, IR star clusters, strong Xray and gamma ray radiation like AGN, but on smaller scale
Complex of radio sources - central one is Sgr A*, smaller than 10 AU (inside Jupiter's orbit)
Ring of gas and dust in Sgr A West can reach 250 km/s = almost 1/1000 light speed - material is both circling and falling in streams
6 million solar masses in center ; perhaps half in IR bright stars, and other half in MDO

Devil's Advocate: vigorous star formation going on at present time, dynamics dominated by the central cluster of stars going around the dynamical center of the Milky Way Galaxy

IMAGE:-VLA image.

RADIO: syncrotron radiation in strong magnetic fields

OPTICAL: obscured by dust

- radio: new VLA image
- optical: HST montage

Virgo A = 3C274 - is the nearest CURRENTLY ACTIVE GALAXY to us, and it is radio-bright. It is in the closest big cluster of galaxies, the Virgo cluster.

D = 16 Mpc = 52 million l.y. away
Flux = 198 Jy at 20 cm
Host = gE giant elliptical galaxy in center of Virgo cluster
Mass of GE must be large enough to bind the Xray emitting gas in the cluster, so infer 1E13 solar masses = 100 Milky Ways ! It is a GALACTIC CANNIBAL !!!
Finding out that it has too little light to account for this mass, it has a very serious DARK MATTER problem - it must have a MASSIVE DARK HALO made of who knows what.
BEEHIVE of GLOBULAR CLUSTERS - more than 100,000 !, each contains 100,000 to 1 million stars !
Optical jet visible with big telescopes from ground, and exquisitely with HST.
Jet and core are sources of non-thermal synchrotron radio and Xray emission, just like other AGN
M = few hundred million 3E8 Msun
R_sch = 900 million km = 6AU, is about the orbit of Jupiter !

IMAGE:-Ground optical image (AAT?) - overexposed, cannot see jet, but see the BEEHIVE of globular clusters

HST image. - see the optical jet coming out of the core

VLA image. - see the core, jets and balloon lobes

VLBA image. - get closer in to the core with Halca/VSOP, radio astronomers using antenna on a satellite.

A list of molecules found in the interstellar medium. This is an incomplete list since molecules are still being discovered.

The orion nebula is a rich source of molecular emission. This shows a Hubble telescope image of the nebula overlaid with spectra of various species taken with the Haystack 37-m telescope. The structure of the spectral lines is caused by different effects - the numerous lines in the H2O maser spectrum are caused by maser spots at different velocities. High spatial resolution observations of such masers can give a detailed picture of the velocity field in the region. The wings in the CO and CS spectra are most probably caused by outflowing molecular material. The structure in the NH3 and N2H+ spectra however, is due to the hyperfine splitting in the molecules energy levels.

In the early days of radio astronomy most of the work done with molecules was the detection of new species. Larger and more complex species began to be detected after the original detections of molecules such as OH, H2O and H2CO. Most of the stronger molecular species have now been identified. New species are still being detected such as the latest detection of glycoaldehyde (a sugar). There is also work being done in detecting known molecular species toward highly redshifted galaxies.

However, most of effort is being done in using molecular emission to probe the physical conditions toward sources such as the temperature, density, the chemistry and kinematics. A few examples follow. Symmetric top molecules such as ammonia (NH3) and CH3CCH are good probes of the kinetic temperature in molecular clouds. Obtaining information from several J transitions of long chain hydrocarbons such as HC3N allows a detailed statistical equilibrium model of level populations which in turn can give a handle on the molecular hydrogen density in clouds (molecular hydrogen cannot be observed directly since it has no dipole moment and in order to observe the rotation of molecules they need to have a dipole moment).

The data show observations toward a dense molecular ridge in the Taurus molecular cloud (TMC-1). The observations were part of a detailed study of the physics and chemistry in the source (see reference). Three transitions of HC3N were observed and a detailed statistical equilibrium analysis was done to obtain molecular hydrogen densities toward the cloud. These numbers were then used in a detailed analysis of the chemistry at all the points in the cloud.

Pratap, Dickens, Snell, Miralles, Bergin, Irvine and Schloerb, 1997, ApJ, 486, 862.

The spectra show the CH3CCH (methyl acetylene) spectra toward three positions in TMC-1. The components in the spectra are the K components (projection of the total angular momentum on the symmetry axis) of the J=6-5 transition. The ratios of the components are used in a statistical equilibrium analysis with an LVG approximation for the radiative trapping to obtain temperatures (see paper for details). The predicted ratios from the model are compared to the observed ratio (as shown in the second figure) to obtain temperatures.

Pratap, Dickens, Snell, Miralles, Bergin, Irvine and Schloerb, 1997,ApJ, 486, 862.

Here is a wonderful example of how molecular emission can give information about the kinematics of the gas around an active galactic nucleus. The picture is an artists conception of the rotation of H2O masers around the center of NGC4258. The complete spectrum is shown as an inset - there are highly blue and red shifted features. VLBI observations show that these doppler shifted features appear to come from a (model) warped, rotating disk around the center. The acceleration of the maser features fit a keplerian model and the central mass required for the observed kinematics corresponds to a supermassive black hole.

Nakai, Inoue and Miyoshi, 1993, Nature, 361, 45
Greenhill et al. 1995, ApJ, 440, 619

Radio telescopes are mainly either prime focus or Cassegrain reflectors. However, the radio telescope looks very different from the optical telescope; radio telescopes are much larger than optical telescopes. The reason for this is that the angular resolution (or the angular area of the sky from which the telescope can collect emission) of a telescope is proportional to the wavelength divided by its diameter. So in order for a radio telescope to be able to detect the same angular resolution as an optical telescope the radio telescope has to be much larger. In addition, the sensitivity of the telescope or the ability to detect weak emission is also related to the area of the reflecting surface.

There are four basic elements to a radio telescope, the reflector, the subreflector, the feed and transmission line and the receiver. The reflector collects power from astronomical sources. The subreflector is a surface that directs the radiation to the feed at the center of the reflector. Behind the feed is the receiver system (at the cassegrain focus). The receiver amplifies the radio signal, selects the appropriate frequency range that detects the signal.

Radio telescopes use a large metal dish, usually parabolic, to reflect radio waves to the subreflector situated close to the prime focus. The signal from the antenna is sent to an amplifier, which magnifies the faint radio signals. The amplified radio signal is then processed by a computer. The receiver is configured in such a way that throughout the amplification process, the signal remains directly proportional to the strength of the incoming radiation. So the resulting image or spectrum is a true representation of the emission from the astronomical source. The image in the slide is a schematic diagram of a radio telescope.

Resolution defines the smallest structure that can be "seen" with the telescope. Mathematically this is defined as the ratio of the wavelength of observation and the diameter of the telescope. Since radio wavelengths are much longer than optical wavelengths, radio telescopes have to be much larger to get the same resolution as an optical telescope. However, the resolution at optical wavelengths is limited by the atmosphere. Radio astronomers can take advantage of the transparency of the atmosphere at radio wavelengths and obtain extremely high resolution by separating two antennas by a large distance and taking the distance between them as the effective diameter of the antenna.

The process of separating two or more antennas by a certain distance and using them as one effective antenna is called interferometry. This process can be done with the antennas all connected by cables which carry the observed radiation to a processing center (called a correlator) - this is called connected element interferometry. The NRAO Very Large Array is one such instrument (shown in the slide).

VLBI combines observations at multiple radio telescopes to form extremely high resolution images of astronomical radio sources. These telescopes are not connected by cables and can sometimes be on different continents. The data are collected on high density magnetic tapes which are then brought to a central correlator after the experiment is conducted. The results are observations with resolutions of milli and micro arcseconds. VLBI continually challenges the limits of both telescopes and observers, while fostering international collaboration on the frontiers of astronomy. Current Haystack-led VLBI projects study the lives of stars from formation to senescence, and probe the violent physics of Active Galactic Nuclei (AGN).

The image on the left is one of the Crab Nebula made with the Haystack 37-m telescope at a frequency of 41 GHz. The resolution is 45". The image on the right is one made with the Very Large Array and has a resolution of a few arcseconds.

The Orion-KL complex in the Great Nebula of Orion emits an infrared luminosity 100,000 times the total luminosity of the Sun. Orion-KL is suspected to harbor one or more massive stars in the process of formation. The Coordinated mm-VLBI Array (CMVA) project administered by Haystack and the Very Long Baseline Array (VLBA) operated by the National Radio Astronomy Observatory were employed to paint these masers of Orion in space and velocity. Silicon monoxide (SiO) mases at wavelengths of 3 and 7 millimeters in narrow ranges of temperature (1800-3600 Kelvin). The masers' spectral fingerprints may be used as a Doppler tracer for velocity. Orion-KL appears to power a giant outflow where the SiO masers seem to form along the arms of an 'X' with a newly formed star at the center. The upper right arms of the 'X' are red shifted meaning that the masing gas is traveling away from us, while the arms to the lower left are blue shifted towards us. Maser transitions requiring higher energies are found closer to the central star. A promising model for this structure is that we are seeing the edges of a bipolar outflow as it impacts the surrounding gas cloud from which the star formed.

MASER: Microwave Amplification by Stimulated Emission of Radiation

Doeleman, S.S., Lonsdale, C.J., Predmore, C.R., Greenhill, L.J., "A Multi-transition SiO Maser study of the Bipolar Outflow in Orion-KL" submitted to ApJ, 2000

R Cassiopeia is a pulsating red M giant star at the opposite end of its stellar evolutionary track from the young stars in Orion. It shows a nearly complete circumstellar ring of maser spots in this 3mm CMVA image. The red disk has been added to show the location and size of the M giant star. Maser spots are color coded to represent velocity relative to the Earth based observer. R Cas ejects large amounts of stellar material into its nearby environment. By observing it periodically, this project attempts to track a giant stellar wind that varies in strength and velocity over time. The astrophysical mechanisms at work are mass-loss from evolved stars, the recycling of matter into interstellar space, and dredge-up of material from interior nucleosynthesis by the star.

Sivakoff, G.R., Phillips, R.B., Lonsdale, C.J., Doeleman, S.S. "VLBI Imaging of the 3mm SiO Masers Around R Cassiopeia", Bulletin of the American Astronomical Society, 31(5): 1437. 45.09. (1999)

This is a sequence of 8-GHz VLBI images of a supernova in M81 from mid-1993 to late 1997. The images show the radio emission increasing in size and intensity as the supernova expands. It also allows a glimpse of the detailed structure of the remnant on very short timescales.

These are three images with very high resolution of the superluminal quasar 3C454.3. These images were made with the Coordinated Millimeter VLBI Array (CMVA) at a frequency of 86 GHz. The VLBI images at cm wavelengths show relatively high superluminal motions on mas to tens of mas scales. The images at 86 GHz show motions considerably slower motions. The observing beam is about 70 micro-arcsecs and which shows details in the jet at spatial resolution of 0.3 pc. The jet appears to be resolved transversely. The sructures in the jet appear to resemble Kelvin-Helmholtz instabilities in a relativistic hydrodynamical flow. Such structures have been observed in other sources at longer wavelengths and larger scales.

Krichbaum et al.

AGN are beacons from the most distant reaches of the Universe that display a variety of unique attributes. Though the AGN core is only a few light years across, AGN may be as much as forty times more luminous than the brightest galaxies, which are 10,000 times larger. This enormous energy output is from release of gravitational energy as matter falls into a supermassive, rotating black hole. Much of the energy re-emerges in colossal jets of relativistic plasma. VLBI polarimetry offers radio astronomers an opportunity to trace the paths of these jets by observing the motions and strengths of the jet magnetic fields.

1055+018 is an example of a particularly violent, variable class of AGN called blazars. The image of 1055+018 displays a powerful radio jet emanating from the blazar's core in the lower left. Yellow contours draw the source in total intensity; colored regions show the strength of polarized emission, with red representing the strongest magnetic field. Visible is a "spine" of relativistic plasma flowing out of the core and plowing through space, encased by a "sheath" of material present due to boundary-layer interactions between the spine and the surrounding galactic medium.

Attridge, Roberts and Wardle 1999, ApJ, 518, L87