Transcript AAO Techniques Workshop (April 2001) 12 Mbytes

The Hubble Space Telescope
and
Next Generation Space
Telescope
Duncan A. Forbes
Centre for Astrophysics & Supercomputing,
Swinburne University
Why a Space Telescope ?
Putting a telescope in orbit above most of the
atmosphere has two main advantages:
1. It is unaffected by `seeing’ (atmospheric turbulence)
which tends to smear out the detail in astronomical
objects.
2. It can observe at wavelengths which are absorbed by
the Earth’s atmosphere e.g. UV and infrared
wavelengths.
Hubble Space Telescope Description
The HST has a 2.4m primary operating at f/24. It is in a
cyclindrical shape 13.1x4.3m.
The instruments
are located in
bays behind the
primary mirror.
Telescope
movement
comes from
internal gyros.
HST Schematic
How much does it cost ?
The Hubble Space Telescope was 85% paid for NASA and
15% by ESA. Below is a `guesstimate’ how much HST cost
to develop and maintain.
$USmillion
Initial Research and Development
1st Service mission (inc WFPC2)
2nd Service mission (inc STIS, NICMOS)
3rd Service mission (inc Gyros)
2,000
500
600
400
Total to date
3,500
Two more missions are planned to install the ACS (2001)
and COS (2003). Running costs are around $US20m/yr.
Liftoff of the Space Shuttle Discovery
On the 24th April 1990, the Space Shuttle Discovery
blasted off from Cape Canaveral with HST onboard.
At an altitude of 600 km (then a
record height for the Shuttle),
HST was placed into orbit. The
event was recorded with IMAX
cameras. After an initial systems
check the Shuttle returned to
Earth. The first images would be
taken later.
Discovery enroute to orbit.
The Initial Instruments
HST was launched with 5 instruments.
• WFPC1 Wide Field Planetary Camera 1
• FOC Faint Object Camera
• GHRS Goddard High Resolution Spectrograph
• FOS Faint Object Spectrograph
• HSP High Speed Photometer
HST also included the FGS (Fine Guidance
Sensors) necessary for the acquisition and
locking-on to guide stars.
Wide Field Planetary Camera 1
The WFPC1 was designed to be the main imaging
camera on the HST. It took images over the wavelength
range 300 to 1000 nm with four CCD detectors. Over
time the UV sensitivity dropped off due to the build-up on
contaminants on the CCDs.
It could operate in two focal modes – f/12.9 or Wide
Field Camera mode, and f/30 Planetary Camera mode.
The resulting pixel scales were 0.1 and 0.043 arcsecs.
These were chosen to roughly match the diffraction
limit of the telescope.The total field-of-views of are
160x160 sq. arcsecs and 64x64 sq. arcsecs
respectively.
Faint Object Camera
The FOC was built by the European Space Agency. Its
photocathode and 3-stage intensifier was designed to
image faint objects.
It had three different focal ratios and therefore field-ofviews and resolution, ie
f/48 with 22x22 sq. arcsecs and 0.043 arcsec pixels
f/96 with 11x11 sq. arcsecs and 0.022 arcsec pixels
f/288 with 3.6x3.6 sq. arcsecs and 0.0072 arcsec pixels.
Goddard High Resolution Spectrograph
Built at Goddard Space Flight Center, the GHRS
provided high spectral resolution at UV wavelengths. It
consisted of two 521-channel Digicon electronic light
detectors. One detector was sensitive to light from 105 to
170nm and the other from 115 to 320nm.
The GHRS had 3 resolution modes – low, medium and
high. If studying the spectrum around 120nm, GHRS
could distinguish two lines that were only 0.06, 0.006
and 0.0012 nm apart for the three modes respectively.
Faint Object Spectrograph
The FOS could obtain spectra of objects that were fainter
than those possible with the GHRS and over a much
larger wavelength range (ie 115 to 800 nm). It consisted
of a `blue’ tube sensitive from 115 to 550 nm and a `red’
tube covering 180 to 800 nm. The detectors were two
512-element Digicon light intensifiers.
The FOS had various apertures to let the light through,
ranging from 0.1 to 1.0 arcsecs. It had two spectral
resolution modes. It also included an occulting device to
block out the light from the centre of an object. This was
used to block out the light from a quasar and study the
surrounding host galaxy for example.
High Speed Photometer
The HSP was designed to obtain high time resolution
photometry of astronomical objects, for example variable
stars, supernovae, active galactic nuclei.
As it was the least used of the original instruments
and it was removed when space was required for
the corrective optics (COSTAR). It was returned to
Earth in December 1993.
STS61
Lasting almost 11 days, STS61 (launched 2nd Dec. 1993)
was one of the most ambitious shuttle missions to be flown.
The astronaunts, which
included an astronomer, had to
carefully remove the HSP
replace it with the corrective
optics (COSTAR), swap
WFPC2 for WFPC1, and fix the
malfunctioning solar arrays.
HST in the cargo bay of Endeavour
Wide Field Planetary Camera 2
Although similar to WFPC1, the new WFPC2 had several
improvements (including internal corrective optics), such
as better CCD detectors and new filters.
WFPC2 consists of 4 separate
CCDs. Three (WF CCDs) are
arranged in an L shape with the
fourth (PC) in the bend of the L.
The WF CCDs have 0.1 arcsec
pixels and 75x75 sq. arcsec fieldof-view. The PC has 0.045 arcsec
pixels and 34x34 sq. arcsec fov.
This L shape layout was chosen
to save money.
Schematic layout of the
four WFPC2 CCDs.
Before and After
Below is an image of M100 taken with WFPC1.
Lets see how
it looks with
WFPC2, and
its improved
optics.
Astronomy with WFPC2
WFPC2 is the workhorse imaging camera on HST. Its
relatively large field-of-view (by HST standards),
photometric accuracy and spatial resolution has made it
ideal for imaging distant galaxies, gravitational lenses,
quasar hosts, globular clusters, cepheid variables and
planetary nebulae to name a few.
Example of a
WFPC2 image
showing a cluster
of galaxies and
several
gravitational arcs.
STS82
On the 11th Nov. 1997 the Space Shuttle Discovery
blasted off bound for the HST.
The crew swapped the
GHRS and FOC for two
new instruments – STIS
and NICMOS. They also
replaced a failed FGS,
updated the data recorder
and improved the thermal
insulation.
Night launch of Discovery
STIS
The Space Telescope Imaging Spectrograph can obtain
2-dimensional spectra thus it can record spectra from
many locations in an object simultaneously.
It has three detectors – a CCD and two MAMAs
(Multi-Anode Mircochannel Arrays). The CCD
operates from 305 to 1000 nm, and the MAMAs from
115 to 170 nm and 165 to 310 nm. The CCD has a
field-of-view of 50x50 sq. arcsec and both MAMAs
have 25x25 sq arcsec.
Astronomy with STIS
STIS provides a long slit capability for the first time on
HST. This has been put to use in studying nearby Black
Holes in other galaxies. STIS can obtain spectra and
hence velocities either side of the central Black Hole.
STIS is also the instrument of choice if the astronomer
wants to observe at UV wavelengths, eg studying young
hot stars.
The right side figure shows the
gas velocities around a central
black hole in M84. Wavelength is
vertical and velocity is horizontal
in this figure. It indicates rapid
rotation about the galaxy
nucleus.
NICMOS
The Near Infrared Camera and Multi-Object Spectrometer
can obtain images and spectra at wavelengths between
0.8 and 2.5 microns, ie in the near infrared. It is
cryogenically cooled using frozen nitrogen.
It consists of three HgCdTe
256x256 pixel arrays. These
three arrays have different
effective pixel scales, giving a
field-of-view of 11x11, 19x19
and 51x51 sq. arcsec.
NICMOS instrument
Astronomy with NICMOS
Operating at near-infrared wavelengths means NICMOS
can penetrate dusty regions. Its main limitations are a
limited cryogenic lifetime and a small field-of-view. Use
has focused on imaging star formation regions, cores of
active galaxies and distant galaxies.
Central region of a
nearby galaxy imaged
by WFPC2 (left) and
NICMOS (right).
Future Instrumentation
Future HST servicing missions are planned for late 2001
(STS109) and 2003. As well as continued maintanance,
these servicing missions will install new instruments.
Scheduled instruments include the Advanced Camera for
Surveys (ACS) in 2001, Cosmic Origins Spectrograph
(COS) in 2003 and possibly the Wide Field Camera 3
(WFC3).
It is hoped that HST will remain active and have at least
a few years overlap with the planned 8m New
Generation Space Telescope due for launch around
2009.
Advanced Camera for Surveys
The ACS will become the main imaging camera on HST,
replacing the WFPC2. It will cover the wavelength range
from 200 to 1000 nm and from 115 to 200 nm each with
two spatial resolutions.
UV mode will have 0.01 arcsec pixels giving
12.5x12.5 sq arcsecs fov and 0.02 arcsec pixels
giving 50x50 sq arcsec fov.
UV–red mode will have 0.024 arcsec pixels giving
50x50 sq arcsec fov and 200x200 sq arcsec fov.
Cosmic Origins Spectrograph
The COS is an ultraviolet spectrograph optimized to
observe faint point-like objects. The scientific focus will
be quasar absorption lines, distant galaxies, horizontal
branch stars in globular clusters, atmospheres of solar
system planets.
The instrument will have two channels. A far-UV
channel operating between 115 and 178 nm and a
near-UV one between 178 and 320 nm.
The Hubble Space Telescope Archive
Since its launch in 1990, HST has made
• 300,000 observations of
• 15,000 different objects, amassing
• 4 Terabytes of data
Essentially all of this data is available to both
professional astronomers and the public alike via the
web-driven interface at http://archive.stsci.edu
HST Archive Products
For any requested dataset, the archive provides:
• raw data files (uncalibrated data)
• calibrated data files (processed using best available bias and
flat field calibration files)
• data quality files (information about positions and
characteristics of bad pixels)
• telescope pointing and jitter files (information about telescope
guiding during observation period)
• list of latest and best calibration reference files
The calibrated data files are generally sufficient for most scientific
applications. The HST data handbook describes the pipeline
process and hints for post-pipeline reduction.
The HST Key Projects
Three Key Projects
• Quasar Absorption Lines
• Hubble Constant
• Medium Deep Survey
Results published as a series of papers in the literature.
HST Imaging Highlights: 1990-2000
Scientific highlights from WFPC2 during its first decade of
operation include:
• the expansion rate of the Universe
• the deep field
• the birth of stars
• the death of a nearby massive star
The Hubble Constant
Using Cepheid
variables the Hubble
constant, and hence
the expansion rate of
the Universe, was
measured to an
accuracy <10%.
H0 = 73 +/-2random +/- 7systematic km/s/Mpc
The Hubble Deep Field
In 1995, WFPC2 spent
10 consecutive days
pointing at a small patch
of sky near the handle of
the Big Dipper.
The resulting image
contains over 1500
galaxies, and represents
the deepest astronomical
image ever taken and is
one of the most important
contributions to
observational cosmology.
A Stellar Nursery
The spectacular pillars of
cool gas and dust in the
Eagle Nebula.
The pillars are being
eroded from above by
ultraviolet radiation from
massive stars. In time,
hidden embryonic stars
within the pillars will
become visible, as the
surrounding gas and dust
continues to erode (i.e.,
photoevaporate).
Stellar Death: Supernova 1987A
The brightest supernova
visible from Earth since
Kepler’s Star of 1604,
SN1987A was the result
of an exploding massive
star in the Large
Magellanic Cloud.
HST has allowed
astronomers to study the
early evolution of a SN at
sub-light year scales, for
the first time.
The Next Generation Space Telescope
Launch: 2009 ?
Size: 8m
Cost: $1billion ?
Wavelengths: 0.6 to 30 microns
Orbit: L2
Web: www.ngst.stsci.edu/science
Science Drivers: Origins
Structure of the Universe
Origin and Evolution of Galaxies
History of the Milky Way
Birth and Formation of Stars
Origin of Planetary Systems
Wide-field, diffraction limited imaging in near-infrared
Mid-infrared imaging
Spectrograph(s)
Sensitivity
Factor of 1000
gain over
imaging with
HST+NICMOS,
factor of 100
gain over
Gemini+NIRI