* denotes topic related to individual topics
91.2nm
(Lyman edge) –320nm (Earth’s Atmosphere)
*Hot stars emit most of their light
in the UV
AGN’s ‘blue-bump’
* Many important resonance lines are in the UV
Mg h+k, NV, CIV, Si IV, Lyman a, Fe of all
sorts, etc.
* Circumstellar material
Binary mass exchange/loss – *CVs, LMXBs
Winds *O,B stars, *WR stars, PN, SNR, etc
White dwarf companions, VV Cep stars,
Chromospheres, Accretion disks, *Winds
*AGNs
Dust feature at 217.5nm reddening
Gas line absorption in the resonance lines
Lyman a 121.6nm and Lyman edge
91.2nm redshifted
HST was launched: 1990-04-25 at 12:33:51 UTC. It is a 2.4 m, f/24 Ritchey-Chretien. It has a wide array of instruments for imaging and spectroscopy
Space telescope Imaging Spectrograph STIS
Spatially resolved, long-slit (or slitless) spectroscopy from the ultraviolet to the near infrared (1150-10,300 Å) at low to medium spectral resolution (R ~ 500-17,000) in first order.
Echelle spectroscopy at medium to high spectral resolution (R ~ 30,000-110,000), covering a broad simultaneous spectral range ( ~ 800 or 200 Å, respectively) in the ultraviolet (1150-3100 Å).
In addition to these two prime capabilities, STIS also provides:
Imaging capability using the solar-blind far-ultraviolet MAMA detector (1150-1700 Å), the solar-insensitive near-ultraviolet MAMA detector (1150-3100 Å), and the optical CCD (2000-10,300 Å), through a small complement of narrowband and broadband filters.
Objective-prism spectroscopy (R ~500-10) in the ultraviolet (1150-3100 Å).
High-time-resolution ( = 125 microseconds) imaging and spectroscopy in the ultraviolet (1150-3100 Å) and moderate-time-resolution ( ~20 -seconds) CCD imaging and spectroscopy in the near UV, optical, and near IR (2000-10,300 Å).
Coronographic imaging in the near UV, optical, and near IR (2000-10,300 Å) and bar-occulted spectroscopy over the entire spectral range (1150-10,300 Å).
A more detailed description is by Woodgate, et al PASP 110, 1183
INDIVIDUAL TOPICS
How can the Ultraviolet be used to investigate astronomical objects?
Most AGN have a black hole in the center with a disk (and
sometimes jets) that powers an ionization region around it, such as in Seyfert
Galaxies.
Here is a nice introduction. You don’t have to read the whole paper
There are two regions of emission lines
1. Broad emission lines close to the AGN very hot region
2. Narrow lines further from the AGN cooler ejected gas
There may be separate clouds in each of these regions
The very broad wind lines of C IV, Si IV, and of course Lyman a, come from the ‘broad line’ regions
The narrower N V, Ni II, Si II, and Si IV lines come from the narrow line region
Here is a Seyfert spectra which includes FUSE data with the STIS
This is in contrast to LINERS Low-Ionization Nuclear Emission Region Galaxies
A possible energy source for Liners is clusters of hot stars, so sometimes their spectra look like hot star spectra (see below)
Hot O and B stars as well as Wolf-Rayet stars eject a great deal of mass and so wind lines such as N V 1240, Si IV 1400 and C IV 1550 dominate their spectra. The P Cygni profiles show decreasing wind effect as one goes from hot to cooler types. Other photospheric lines are C III 1176, O IV 1339, 1343, and He II 1640. Here are two W-R stars and an O star.
An excellent introduction is at http://www.usm.uni-muenchen.de/people/adi/wind.html
These hot stars are in a star cluster in a Low Luminosity AGN galaxy. The star cluster provides more UV radiation than the low luminosity black hole/accretion disk. Since you are looking at the entire cluster the spectrum is a summation of all the hot stars (but the hottest dominate the brightness.)
If you look at the emission regions around the hot objects rather than the hot objects themselves [OB Stars, central stars of Planetary nebula] and look at the planetary nebula, emission nebula, supernova remnant, nova remnant, you see bright emission lines many of them forbidden lines.
These are from a very low-density gas heated by the central source. This example is a around Eta Carinae
This shows up in two ways:
1. The interstellar lines. These crop up everywhere. Sometime they are due to the ISM in the emitting galaxy. Asterisks mark the ISM lines in these hot stars at N I 1198, 199,1200, Si II 1260, O I+Si II 1302+1306, C II 1334 1335, Si II 1526,.
Since the ISM is cooler than the star, galaxy, AGN, etc. that provides the continuum radiation the ISM lines are narrower than absorption lines in the continuum provider. They are also at the radial velocity of the ISM cloud. In the case of highly redshifted AGNs and quasars this is at a lower redshift than the source.
2. The dust. This is a general absorption and reddening throughout the optical extending into the UV and the far UV. The reddening is very pronounced in the UV. In addition there is a significant wide feature at 220nm. This can actually be used to deredden spectra.
Accretion disks exist in many systems ranging from AGN to Algol binaries. When they are caused by mass transfer from one component of a binary system onto a white dwarf they are called cataclysmic variables, CVs. CVs show lines from the disk in emission and absorption. In the ‘high state’ the UV luminosity from the CV comes from the disk. If the white dwarf has a very strong magnetic field then the field disrupts the disk and matter streams along the field onto the white dwarf. These systems are called polars or intermediate polars. If the disk is very thin as in the case with polars and intermediate polars or if the CV in in the low state you can see the white dwarf. The cool companion can only be seen at much longer wavelengths (if at all.)
The changing nature of the lines with time can act as diagnostics to changes in the disk with during the binary orbit, the amount of mass transferred from the companion star, the heating or cooling of the white dwarf, the dynamics of the disk, etc.
