The Hubble Space Telescope and Next Generation Space

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. 4 m primary operating at f/24. It is in a cyclindrical shape 13. 1 x 4. 3 m. 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 1 st Service mission (inc WFPC 2) 2 nd Service mission (inc STIS, NICMOS) 3 rd Service mission (inc Gyros) Total to date 2, 000 500 600 400 3, 500 Two more missions are planned to install the ACS (2001) and COS (2003). Running costs are around $US 20 m/yr.

Liftoff of the Space Shuttle Discovery On the 24 th 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. • WFPC 1 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 WFPC 1 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 160 x 160 sq. arcsecs and 64 x 64 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 22 x 22 sq. arcsecs and 0. 043 arcsec pixels f/96 with 11 x 11 sq. arcsecs and 0. 022 arcsec pixels f/288 with 3. 6 x 3. 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 170 nm and the other from 115 to 320 nm. The GHRS had 3 resolution modes – low, medium and high. If studying the spectrum around 120 nm, 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.

STS 61 Lasting almost 11 days, STS 61 (launched 2 nd 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 WFPC 2 for WFPC 1, and fix the malfunctioning solar arrays. HST in the cargo bay of Endeavour

Wide Field Planetary Camera 2 Although similar to WFPC 1, the new WFPC 2 had several improvements (including internal corrective optics), such as better CCD detectors and new filters. WFPC 2 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 75 x 75 sq. arcsec fieldof-view. The PC has 0. 045 arcsec pixels and 34 x 34 sq. arcsec fov. This L shape layout was chosen to save money. Schematic layout of the four WFPC 2 CCDs.

Before and After Below is an image of M 100 taken with WFPC 1. Lets see how it looks with WFPC 2, and its improved optics.

Astronomy with WFPC 2 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 WFPC 2 image showing a cluster of galaxies and several gravitational arcs.

STS 82 On the 11 th 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 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 50 x 50 sq. arcsec and both MAMAs have 25 x 25 sq arcsec.

Astronomy with 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 M 84. 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 Hg. Cd. Te 256 x 256 pixel arrays. These three arrays have different effective pixel scales, giving a field-of-view of 11 x 11, 19 x 19 and 51 x 51 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 WFPC 2 (left) and NICMOS (right).

Future Instrumentation Future HST servicing missions are planned for late 2001 (STS 109) 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 (WFC 3). It is hoped that HST will remain active and have at least a few years overlap with the planned 8 m 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 WFPC 2. 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. 5 x 12. 5 sq arcsecs fov and 0. 02 arcsec pixels giving 50 x 50 sq arcsec fov. UV–red mode will have 0. 024 arcsec pixels giving 50 x 50 sq arcsec fov and 200 x 200 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 WFPC 2 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%. H 0 = 73 +/-2 random +/- 7 systematic km/s/Mpc

The Hubble Deep Field In 1995, WFPC 2 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 1987 A The brightest supernova visible from Earth since Kepler’s Star of 1604, SN 1987 A 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: 8 m Cost: $1 billion ? Wavelengths: 0. 6 to 30 microns Orbit: L 2 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