Supernova 1987A has been a prime target for the Hubble Space Telescope since its launch, and it will remain so throughout the lifetime of HST. Here I review the observations of SN1987A, paying particular attention to the rapidly developing impact of the blast wave with the circumstellar matter as observed by HST and the Chandra Observatory.

Introduction

If there was ever a match made in heaven, it is the combination of SN1987A and the Hubble Space Telescope. Although the HST was not available to witness the first three years after outburst, it has been the primary instrument to observe SN1987A since then.

SN1987A in the Large Magellanic Cloud is the brightest supernova to be observed since SN1604 (Kepler), the first to be observed in every band of the electromagnetic spectrum, and the first to be detected through its initial burst of neutrinos. Although the bolometric luminosity of SN1987A today is ≈ 10-6 of its value at maximum light (Lmax ≈ 2.5 × 108 L⊙), it will remain bright enough to be observed for many decades in the radio, infrared, optical, UV, and X-ray bands.

SN1987A is classified as a Type II supernova (SNeII) by virtue of the strong hydrogen lines in its spectrum. It was atypical of SNeII in that its light curve did not reach maximum until three months after outburst and its maximum luminosity was about 1/10 the mean maximum luminosity of SNeII.

The Space Telescope Science Institute Symposium on “A Decade of HST Science” took place during 11–14 April 2000.

There is no doubt that the Hubble Space Telescope (HST) in its first decade of operation has had a profound impact on astronomical research. But HST did much more than that. It literally brought a glimpse of the wonders of the universe into millions of homes worldwide, thereby inspiring an unprecedented public curiosity and interest in science.

HST has seen farther and sharper than any optical/UV/IR telescope before it. Unlike astronomical experiments that were dedicated to a single, very specific goal, HST's achievements are generally not of the type of singular discoveries. More often, HST has taken what were existing hints and suspicions from ground-based observations and has turned them into certainty.

In other cases, the level of detail that HST has provided forced theorists to re-think previous broad-brush models, and to construct new ones that would be consistent with the superior emerging data. In a few instances, the availability of HST's razor-sharp vision at critical events provided unique insights into individual phenomena.

These proceedings represent a part of the invited talks that were presented at the symposium, in order of presentation. We thank the contributing authors for preparing their papers.

It is rare in astronomy to have a purely physics-based technique for studying the distant universe. Rooted in General Relativity, the image distortion and time delay of light from distant objects caused by foreground gravitational lenses offers such a window on the universe. Using only combinations of measured redshifts, angles, and arrival times of source intensity fluctuations, lensing observations can probe the mass distribution of the lens, the rate of expansion of the universe (the Hubble constant), the acceleration of expansion (dark energy), and the total amount of matter in the universe. The HST has made and will continue to make unique contributions to this new window on the universe.

Introduction

The universe is not as it seems: distant galaxies and quasars are in the wrong places. Their apparent positions on the sky have moved relative to where they would normally appear, and the culprit is mass-energy. Specifically, a massive object (a star, a galaxy, a cluster of galaxies) will warp space-time around it, causing light rays to bend as they pass by. If a mass concentration lies between us and a distant source, that source will appear in an altered location. The effect is called gravitational lensing, and it also systematically distorts the images of resolved sources like galaxies.

The high spectral resolution and high signal to noise capabilities of the Goddard High Resolution Spectrograph (GHRS) have permitted very accurate measurements of the gas phase abundances and physical conditions in interstellar clouds found in the Galactic disk and low halo and of the matter in several Galactic high velocity clouds. The interstellar gas phase abundances provide important clues about the composition of dust grain mantles and cores, and about the origins of intermediate and high velocity gas in the Galactic disk and halo. The processes that circulate gas from the disk into the low halo do not destroy dust grain cores. The gas in Complex C in the direction of Mrk 290 has a metallicity of 0.089 ± 0.024 solar, which implies the accretion of low metallicity gas by the Milky Way at a rate per unit area sufficient to solve the long standing Galactic G-dwarf problem. GHRS studies of interstellar Si IV, C IV, and N V absorption toward stars and AGNs have yielded measures of the 3 to 5 kpc extension of hot gas into the halo of the Milky Way. The GHRS results coupled with new measurements from the Far-Ultraviolet Spectroscopic Explorer (FUSE) satellite of O VI absorption by hot halo gas permit a study of the physical conditions in the hot Galactic Corona originally envisioned by Lyman Spitzer in his classic 1956 paper “On a Possible Interstellar Galactic Corona.”

HST observed Mars during all 5 oppositions between 1990 and 1999, providing unique new observations of the planet's atmosphere and surface during seasons which are typically poorly-observed telescopically and in wavelength regions or at spatial scales that are not at all observed by spacecraft. HST observations also filled a crucial gap in synoptic observations of Mars prior to 1998, during a time when no spacecraft were observing the planet. HST data have provided important new insights and understanding of the Martian atmosphere, surface, and satellites, and they continue to fulfill important spacecraft mission support functions, including atmospheric aerosol characterization, dust storm monitoring, and instrument cross-calibration.

Introduction

Mars has been the subject of intense telescopic observations for centuries (see, for example, reviews by Martin et al. 1992 and Sheehan 1988). Interest in the red planet stems partly from its prominent appearance in the night sky as a bright extended object roughly every 26 months, and also from historic telescopic observations and more recent spacecraft encounters that have revealed many similarities between Mars and the Earth in terms of surface and atmospheric characteristics and climatic histories. While cold and arid today and probably inhospitable to most forms of life, evidence exists indicating that Mars once may have had a much more clement climate, during a postulated “warm and wet” epoch early in solar system history (e.g. Pollack et al. 1987; Carr, 1998).

The Galactic Center has been the subject of a variety of HST observing programs, mainly since the installation of NICMOS. The observational strengths of NICMOS lie with its sensitivity and very stable point spread function which enables a variety of studies including sensitive searches for variable sources and accurate colors across the 1 to 2.5 µm region. The emission line filters in NICMOS enable studies of the interstellar medium and a search for [SiVI] emission as a ‘smoking gun’ for gas clouds near a black hole powered accretion disk.

Introduction

The center of the Milky Way is of course the closest galaxy nucleus and is a natural area to choose to study in detail. The discovery of a peculiar radio source, SgrA*, and the subsequent demonstration that it is a black hole has only heightened interest in the center. Figure 1 shows a contour plot at 1.04 µm compared to a NICMOS image at 1.45 µm which clearly shows why the Galactic Center requires use of infrared instrument like NICMOS with Av ∼ 30 while AK ∼ 3.3.

The Galactic Center has been studied with HST from the first observing cycle using WFPC proposed in an era where the nature of many of the stars was not understood, and the existence of a cluster in very close proximity to the black hole, SgrA*, was unknown.

This review aims to give an overview of the contribution of the Hubble Space Telescope to our understanding of the detailed properties of Local Group dwarf galaxies and their older stellar populations. The exquisite stable high spatial resolution combined with photometric accuracy of images from the Hubble Space Telescope have allowed us to probe further back into the history of star formation of a large variety of different galaxy types with widely differing star formation properties. It has allowed us to extend our studies out to the edges of the Local Group and beyond with greater accuracy than ever before. We have learned several important things about dwarf galaxy evolution from these studies. Firstly we have found that no two galaxies have identical star formation histories; some galaxies may superficially look the same today, but they have invariably followed different paths to this point. Now that we have managed to probe deep into the star formation history of dwarf irregular galaxies in the Local Group it is obvious that there are a number of similarities with the global properties of dwarf elliptical/spheroidal type galaxies, which were previously thought to be quite distinct. The elliptical/spheroidals tend to have one or more discrete episodes of star formation through-out their history and dwarf irregulars are characterized by quasi-continuous star-formation.

The angular resolution of HST has provided stunning images of star forming regions, circumstellar disks, protostellar jets, and outflows from young stars. HST has resolved the cooling layers behind shocks, and enabled the determination of outflow proper motions on time scales less than the post-shock coolingtime. Observations of the best studied region of star formation, the Orion Nebula, has produced many surprises. HST's superior resolution led to the identification of many new outflow systems based on their proper motions, the discovery of dozens of microjets from young stars, and the detection of wide-angle wind-wind collision fronts. HST has also produced spectacular images of circumstellar disks which have led to a rethinking of some aspects of planet formation. It now appears that most stars in the sky are born in environments similar to the Orion Nebula where within a few hundred thousand years after their formation, proto-planetary disks are subjected to the intense radiation fields of nearby massive stars. As a result, Orion's disks are rapidly evaporating. But at the same time their dust grains appear to be growing. Multi-wavelength images indicate that most of the solid mass in these disks may already be in large grains, possibly larger than a millimeter in size. The formation frequency of planets and the architectures of planetary systems will be determined by the competition between grain growth and photo-evaporation.

Globular clusters represent only a small fraction of the total mass in their parent galaxy, but provide a vast array of tests for stellar physics, dynamics, and galaxy formation. This review discusses the prominent accomplishments of HST-based programs:

1. The definition of precise fiducial sequences in the HR diagram, extending down to the hydrogen-burning limit,

2. Discovery of the upper white dwarf cooling sequence in several clusters,

3. Discovery of a highly consistent IMF on the lower main sequence,

4. Definitive age measurements for the oldest clusters in the outermost halo of the Milky Way, the Magellanic Clouds, and the dwarf elliptical satellites of the Milky Way,

5. Elucidation of the innermost structure of M15 and other core-collapsed clusters,

6. Discovery of surprisingly large “anomalous” populations of stars within dense cluster cores: extended blue horizontal-branch stars, blue stragglers, and others,

7. The first reliable color-magnitude studies for globular clusters in M31, M33, and other outlying Local Group members,

8. Discovery of massive young clusters in starburst galaxies with ages as small as 1 Myr,

9. Measurement of metallicity distribution functions among globular cluster systems in many giant E galaxies—bimodality is common, but details differ strongly, and

10. Deep imaging of cluster luminosity distributions in gE galaxies in Virgo, Fornax, and other Abell clusters as distant as Coma.

A decade of observing with HST also coincides with the completion of the last of the initial three Key Projects for HST, the measurement of the Hubble constant, H0. Here we present the final results of the Hubble Space Telescope (HST) Key Project to measure the Hubble constant, summarizing our method, the results and the uncertainties. The Key Project results are based on a Cepheid calibration of several secondary distance methods applied over the range of about 60 to 400 Mpc. Based on the Key Project Cepheid calibration and its application to five secondary methods (type Ia supernovae, the Tully-Fisher relation, surface brightness fluctuations, type II supernovae, and the fundamental plane for elliptical galaxies), a combined value of H0 = 72 ± 8 km/sec/Mpc is obtained. An age conflict is avoided for current estimates of globular clusters and H0 if we live in A-dominated (or other form of dark energy) universe.

Introduction

When planning HST, pinning down H0 was one of the scientific programs that drove the design and construction of the telescope. Although the original plans for a Large Space Telescope were scaled down during the mid-1970s, one of the primary arguments for an aperture of at least 2.4m was to enable the detection of Cepheid variables in the Virgo cluster (Smith 1989), a goal that was achieved within months of the corrective optics being installed in HST in December, 1993.

One of the brightest and most variable UV emissions in the solar system comes from Jupiter's UV aurora. The auroras have been imaged with each camera on HST, starting with the pre-COSTAR FOC and continuing with increasing sensitivity to the present with STIS. This paper presents a short overview of the scientific results on Jupiter's aurora obtained from HST UV images and spectra, plus a short discussion of Saturn's aurora.

The Earth's aurora: Present understanding

With a long history of ground-based and spacecraft measurements, we now have some understanding of the physics of the Earth's auroral processes. A general picture of the nature of auroral activity on the Earth has evolved, without a complete understanding of the many details. In general, auroral emissions are produced by high energy charged particles precipitating into the Earth's upper atmosphere from the magnetosphere (the region of space where the motions of particles are governed by the Earth's magnetic field). It is well established that the Earth's auroral activity is related to solar activity, and more specifically to conditions in the solar wind reaching the Earth. The precipitating charged particles are accelerated to high energies in the Earth's magnetosphere, with some acceleration occurring in the magnetotail region and some occurring by fieldaligned potentials in the topside ionosphere.

Welcome to amateur astronomy! If you are new to this field, and especially if you have never owned a telescope before, this chapter is for you. Otherwise, feel free to skip ahead. I've tried to write a book that I'll actually use while observing. Parts of it are quite specialized; take what suits you and save the rest for later.

Amateur astronomy, like other hobbies, is something you can go for a little or a lot. Computerized telescopes make casual stargazing easier than ever before, since you don't have to gather up star maps and look up planet positions before going out under the sky. At the other end of the spectrum, the advanced amateur with a busy, semi-professional observing program will find that a computerized telescope is a real time-saver. Both approaches to amateur astronomy are respectable, and so is everything in between.

The key to enjoyment is to have realistic expectations and continue building your knowledge and skill. Looking through a telescope is a very different experience from looking at photographs in books, and it may take some getting used to. If you don't already have a telescope, get some experience looking through other people's telescopes before buying one of your own. Contact a local astronomy club if possible.

Using a telescope

Newcomers are sometimes surprised to find that spectacular objects such as the Horsehead Nebula are not normally visible in telescopes at all – the eye cannot accumulate light the way the camera does.

Chasing eclipses

The proverb that lightning never strikes twice in the same place is, in fact, false. The proverb is truer of an eclipse. It has been calculated that, on average, a total eclipse of the Sun can be seen from the same spot only once every 410 years. So, if you really want to see one, you must take Rebecca Joslin's advice and go '… on the chase'. If you set your heart on seeing one, sooner or later, you will see an eclipse; and you may find, as many have before you, that no sooner have you seen it, than you start planning to see the next one. Part of the attraction is that solar eclipses don't occur very often. On average there is one every 18 months. But, even if they were more common, people would still go out of their way to see them: they are spectacular events, arguably the most breathtaking that the sky has to offer.