The circumstellar imager: Direct detection of extra-solar planetary systems

The Astrometric Imaging Telescope (AIT) is designed to probe the circumstellar environment by both direct imaging and indirect astrometric measurements. The Circumstellar Imager (CI) is a coronagraphic camera and is the direct imaging component of the AIT. The CI is designed to obtain high-sensitivity images of the circumstellar region. It provides crucial non-inferential information relating to the frequency, origin, and evolution of planetary systems and all forms of circumstellar matter. Such imaging is usually limited by the scattered and diffracted light halos of the star itself, which are greatly suppressed in the CI by mating a novel high-efficiency coronagraph with a phasecompensated optical system. For faint point sources in the circumstellar region, the CI will have a sensitivity in excess of 5 magnitudes fainter than the as-designed Hubble Space Telescope (HST). Laboratory data are shown for the coronagraph, which, in a diffraction-limited environment, is capable of suppressing the stellar diffraction sidelobes by several orders of magnitude without significant sacrifice of field of view. In order to realize the high rejection levels inherent in the coronagraph design, it is necessary to limit scatter in the optical systems, imposing a mid-spatial frequency figure error requirement an order of magnitude smaller than that of the HST. Experimental data directed toward meeting this requirement are also shown.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

The Astrometric Telescope Facility

Summary The Astrometric Telescope Facility (ATF) proposed for use on NASA's planned Space Station is similar in form and data output to ground-based long focus astrometric instruments. With a focal plane scale of 12.7 arc seconds/mm, the strawman design has a field size of 10 arc min square and a limiting visual magnitude fainter than 16. Output from an observation includes the X and Y coordinates of each star and its relative brightness. The targeted precision for the AFT is 0.00001 arc seconds.Portions of the observing program will be made available to members of the astronomical community.     

The Next Generation Space Telescope

The design life time of the Hubble Space Telescope will nominally end in 2005. Even though it might be possible to extend the operational life beyond that date it is evident that a successor to Hubble must be planned for now. Based on the report ‘HST and Beyond’ (Dressler 1996)) and aligned with the NASA ‘Origins’ program a study has been initiated to explore options for a telescope with an aperture of larger than 4 meters and possibly as large as 8 meters, optimized for the near infrared (≈ 1-5 micron) to be placed in an orbit far from Earth. The study started in December 1995 and has been proceeding with considerable momentum. At the current time three studies have been completed (NASA in-house, TRW, and Lockheed), which are being used to explore technological and programmatic challenges. The studies are to be merged. It is impressive to see what can be done with existing technology and within the capabilities of existing organizational arrangements. The goal is to complete the study within one year with the goal of entering into phase A as soon as possible. Formal agreements between ESA and NASA will have to be negotiated if Europe is to play a meaningful role in this exercise. Without such agreements, it is clear that European astronomers will not have access to the NGST in the way that they currently enjoy the opportunities provided by the HST. This revised version was published online in July 2006 with corrections to the Cover Date.     

Major prospects of exoplanet astronomy with the World Space Observatory–UltraViolet mission

The success of the International Ultraviolet Explorer (IUE) first and then of the STIS and COS spectrographs on-board the Hubble Space Telescope (HST) demonstrate the impact that observations at UV wavelengths had and are having on modern astronomy. Several discoveries in the exoplanet field have been done at UV wavelengths. Nevertheless, the amount of data collected in this band is still limited both in terms of observed targets and time spent on each of them. For the next decade, the post-HST era, the only large (2-m class) space telescope capable of UV observations will be the World Space Observatory–UltraViolet (WSO–UV). In its characteristics, the WSO–UV mission is similar to that of HST, but all observing time will be dedicated to UV astronomy. In this work, we briefly outline the major prospects of the WSO–UV mission in terms of exoplanet studies. To the limits of the data and tools currently available, here we also compare the quality of key exoplanet data obtained in the far-UV and near-UV with HST (STIS and COS) to that expected to obtain with WSO–UV.     

超轻量镜面系统的研制

空间望远镜的研制一直要求系统的轻量化,美国宇航局（NASA）最近研制的韦伯太空望远镜,其主镜系统面密度相对于哈勃空间望远镜已大幅减轻。在韦伯望远镜主镜系统的研制过程中,NASA开展了一系列关于超轻量镜面系统的验证计划,多家机构拿出多个方案参与竞标。本文选取几个比较典型的方案,介绍这些镜面系统的设计思想、结构、材料、加工以及相关测试结果,期望能对国内相关方面的工作提供参考。     

“Spektr-UF” project

The “Spektr-UF” project is intended for the design and development of a large space observatory operating in the ultraviolet (UV) band of the spectrum inaccessible for survey from the surface of the Earth. The main observatory instrument is a space telescope T-170M with a primary mirror 1.7 m in diameter; it will be equipped with high and low resolution spectrographs and cameras for high-quality UV imaging. In respect of capabilities, the project is similar to the American Hubble Space Telescope (HST), and exceeds the latter in some parameters. The project is included in the Russian Federal Space Program for the period 2006–2015. The launch is planned for 2016. The project is under development by the Lavochkin Association in cooperation with the Institute of Astronomy, Russian Academy of Sciences.     

A Cyclone on Mars: Observations in 1999

Observations of a cyclone in the Martian northern hemisphere from April 24 to April 27, 1999, are reported. The cyclone was revealed by the Hubble Space Telescope (HST), but later it was identified in CCD images obtained earlier by the author from April 24 to April 26 with the 0.6-m telescope of the Astrophysical Institute Observatory. The cyclone was situated close to the dawn limb at about 65° north latitude. As in the HST images, the cyclone was seen distinctly only at short (<550 nm) wavelengths. The cyclone drifted in the direction of the Martian rotation. The average drift velocity is estimated to be 19 km/h.     

Project HIPPARCOS

The HIPPARCOS satellite project of the European Space Agency is described in detail. The paper focusses on the basic rationale, on the performance of the scientific instrumentation and on an explanation of how scientific objectives can be achieved. The purpose is to provide quantitative visibility of basic project features to astronomers and astrophysicists not familiar with astrometric techniques by exploiting updated technical information on project parameters not generally available in the open literature.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846).     

Unusual comets (?) as observed from the Hubble Space Telescope

In separate projects, the Hubble Space Telescope has been used to assess the nature of 3 unusual objects: Chiron, Pholus and P/Shoemaker-Levy 9. This paper will compare these objects and discuss how the unique capabilities of the HST may be used to address the issue of cometary activity in each. Chiron, which has exhibited obvious cometary characteristics for several years, might have a bound dust coma that is unresolvable from the ground. In an attempt to directly observe this bound coma, we have obtained a series of images of Chiron with the HST Planetary Camera. Inner coma structure out to 0.″2 has been detected. From these observations we infer a low bulk nucleus density for Chiron. Both HST and ground-based images of 5145 Pholus have been obtained to search for evidence of activity. The ground-based data give the most sensitive limits; however, it is shown that the WFPC-2 on HST can give limits 2–3 orders of magnitude more sensitive than conventional ground-based limits. Finally, as part of a collaborative effort, we have been obtaining HST observations of SL9 in order to determine the fragment sizes and to assess their nature (i.e., cometary vs. asteroid). Both ground-based observations from the UH 2.2m telescope on Mauna Kea and HST observations show that the near-nucleus dust is redder than the sun. While FOS spectra did not detect OH emission, the WFPC-2 HST data show that the inner coma remained very circular from July 1993 up until 2 weeks prior to impact, implying continued production of dust.     

A study of the astrometric motion of Barnard's star

The Astrometric technique is unique in that it allows us to do a systematic search of each nearby star to determine whether or not it is the primary star of a planetary system. Both positive and negative results may be expressed with a well defined statistical certainty. Perhaps the best known astrometric study is that of Barnard's star by van de Kamp (1963). That detection was later discounted by Gatewood and Eichhorn (1973) but neither study attempted to specify what types (in mass and orbital period) of planets do not orbit Barnard's star. In the following pages we will relate the results of an ongoing study of that object, qualifying what types of bodies are unlikely to orbit Barnard's star, and showing what we believe to be the first step by step illustration of the various astrometric motions that must be analyzed in this study.     

The cosmic origins spectrograph: capabilities and prelaunch performance

The Cosmic Origins Spectrograph (COS) is an ultraviolet spectrograph scheduled for installation in the Hubble Space Telescope (HST) during HST Servicing Mission 4, currently planned to occur in August 2008. COS was designed to maximize sensitivity to faint point sources, and will provide limiting sensitivities at moderate spectral resolutions (R～20,000) that are a factor of 2 to >10 times better than those provided by previous ultraviolet spectrographs on HST. Here, we present an overview of the some of the science areas that will be addressed by COS observations and provide a summary of the capabilities of COS and the expected on-orbit performance.     

Unusual comets (?) as observed from the Hubble Space Telescope

In separate projects, the Hubble Space Telescope has been used to assess the nature of 3 unusual objects: Chiron, Pholus and P/Shoemaker-Levy 9. This paper will compare these objects and discuss how the unique capabilities of the HST may be used to address the issue of cometary activity in each. Chiron, which has exhibited obvious cometary characteristics for several years, might have a bound dust coma that is unresolvable from the ground. In an attempt to directly observe this bound coma, we have obtained a series of images of Chiron with the HST Planetary Camera. Inner coma structure out to 0.2 has been detected. From these observations we infer a low bulk nucleus density for Chiron. Both HST and ground-based images of 5145 Pholus have been obtained to search for evidence of activity. The ground-based data give the most sensitive limits; however, it is shown that the WFPC-2 on HST can give limits 2–3 orders of magnitude more sensitive than conventional ground-based limits. Finally, as part of a collaborative effort, we have been obtaining HST observations of SL9 in order to determine the fragment sizes and to assess their nature (i.e., cometary vs. asteroid). Both ground-based observations from the UH 2.2m telescope on Mauna Kea and HST observations show that the near-nucleus dust is redder than the sun. While FOS spectra did not detect OH emission, the WFPC-2 HST data show that the inner coma remained very circular from July 1993 up until 2 weeks prior to impact, implying continued production of dust.     

A concept for providing warning of earth impacts by small asteroids

The atmospheric detonation of a 17 m-asteroid above Chelyabinsk, Russia on 2013 February 15 shows that even small asteroids can cause extensive damage. Earth-based telescopes have found smaller harmless objects, such as 2008 TC3, a 4 m-asteroid that was discovered 20h before it exploded over northeastern Sudan (Jenniskens, 2009). 2008 TC3 remains the only asteroid discovered before it hit Earth because it approached Earth from the night side, where it was observed by large telescopes searching for near-Earth objects (NEO’s). The larger object that exploded over Chelyabinsk approached Earth from the day side, from too close to the Sun to be detected from Earth. A sizeable telescope in an orbit about the Sun-Earth L1 (SE-L1) libration point could find objects like the “Chelyabinsk” asteroid approaching approximately from the line of sight to the Sun about a day before Earth closest approach. Such a system would have the astrometric accuracy needed to determine the time and impact zone for a NEO on a collision course. This would give at least several hours, and usually 2–4 days, to take protective measures, rather than the approximately two-minute interval between the flash and shock wave arrival that occurred in Chelyabinsk. A perhaps even more important reason for providing warning of these events, even smaller harmless ones that explode high in the atmosphere with the force of an atomic bomb, is to prevent mistaking such an event for a nuclear attack that could trigger a devastating nuclear war. A concept using a space telescope similar to that needed for an SE-L1 monitoring satellite, is already conceived by the B612 Foundation, whose planned Sentinel Space Telescope could find nearly all 140 m and larger NEO’s, including those in orbits mostly inside the Earth’s orbit that are hard to find with Earth-based telescopes, from a Venus-like orbit (Lu, 2013). Few modifications would be needed to the Sentinel Space Telescope to operate in a SE-L1 orbit, 0.01 AU from Earth towards the Sun, to find most asteroids larger than about 5 meters that approach the Earth from the solar direction. The spacecraft would scan 165 square degrees of the sky around the Earth every hour, finding asteroids when they are brightest (small phase angle) as they approach Earth. We will undertake Monte Carlo studies to see what fraction of asteroids 5 m and larger approaching from the Sun might be found by such a mission, and how much warning time might typically be expected. Also, we will check the overall coverage for all Earth-approaching NEO’s, including ground-based observations and observations by the recently-launched NEOSSat, which may best fill any gaps in coverage between that provided by an SE-L1 telescope and ground-based surveys. Many of the objects as large as 50 m, like the one that created Meteor Crater in Arizona, will not be found by current NEO surveys, while they would usually be seen by this possible mission even if they approached from the direction of the Sun. We should give better warning for future “Bolts out of the blue.”     

The mass of the Andromeda galaxy

This paper argues that the Milky Way galaxy is probably the largest member of the Local Group. The evidence comes from estimates of the total mass of the Andromeda galaxy (M31) derived from the three-dimensional positions and radial velocities of its satellite galaxies, as well as the projected positions and radial velocities of its distant globular clusters and planetary nebulae. The available data set comprises 10 satellite galaxies, 17 distant globular clusters and nine halo planetary nebulae with radial velocities. We find that the halo of Andromeda has a mass of together with a scalelength of 90 kpc and a predominantly isotropic velocity distribution. For comparison, our earlier estimate for the Milky Way halo is Although the error bars are admittedly large, this suggests that the total mass of M31 is probably less than that of the Milky Way . We verify the robustness of our results to changes in the modelling assumptions and to errors caused by the small size and incompleteness of the data set.
Our surprising claim can be checked in several ways in the near future. The numbers of satellite galaxies, planetary nebulae and globular clusters with radial velocities can be increased by ground-based spectroscopy, while the proper motions of the companion galaxies and the unresolved cores of the globular clusters can be measured using the astrometric satellites Space Interferometry Mission ( SIM ) and Global Astrometric Interferometer for Astrophysics ( GAIA ). Using 100 globular clusters at projected radii 20 R 50 kpc with both radial velocities and proper motions, it will be possible to estimate the mass within 50 kpc to an accuracy of 20 per cent. Measuring the proper motions of the companion galaxies with SIM and GAIA will reduce the uncertainty in the total mass caused by the small size of the data set to 22 per cent.     

Understanding physical processes in the diffuse ISM using high-resolution UV spectroscopy

Our understanding of the important physical processes operating in the diffuse interstellar medium (ISM) has advanced in recent years from the analysis of high-resolution ultraviolet (UV) spectra obtained with the Hubble Space Telescope (HST) and the Far-Ultraviolet Spectrograph Explorer (FUSE) and from high-fidelity simulations of the kinematics and energetics of the ISM. Nevertheless, much remains to be learned from observations with the Space Telescope Imaging Spectrograph (STIS) instrument on HST and spectrographs on the World Space Observatory (WSO). I will describe several major unanswered questions and suggest how future UV observations can answer these questions. I will also summarize the instrument requirements needed for a future UV spectroscopic mission and recommend how to achieve a successful mission.     

A globular cluster in the dwarf galaxy Sextans B

We present spectroscopic observations of a massive globular cluster in the dwarf irregular galaxy Sextans B, discovered by us on the Hubble Space Telescope Wide Field and Planetary Camera 2 (HST WFPC2) images. Long-slit spectra were obtained with the SCORPIO spectrograph on the 6-m telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences. We determine the age, metallicity and alpha-element abundance ratio for the globular cluster to be 2 ± 1 Gyr, ?1.35 ±0.25 dex, and 0.1 ± 0.1 dex, respectively. Main photometric and structural parameters of it were determined using our surface photometry on the HST images. The mass (～10⁵ M⊙), luminosity and structural parameters appear to be typical of the globular clusters in our own Galaxy. Our findings shed new light on the evolutionary history of Sextans B.     

Scientific Research using the Electronic Archive of the Hubble Space Telescope

The Hubble Space Telescope (HST), a collaborative project between the US National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) has been operating since 1990. The European HST Science Data Archive, operated at the Space Telescope European Coordinating Facility(ST-ECF) in Garching, Germany, contains all data taken with the scienceinstruments of the HST. The services of the Archive include data browsing,preview, retrieval and re-calibration. Access to the Archive is providedthrough the World Wide Web, data distribution is through the Internet oron bulk media.This paper describes the data products, access to theArchive services, and the procedures for the use of the HST Science DataArchive by qualified scientists from remote locations. The Archive providestools implemented as Java Applets which can be used over the Net. For moresophisticated operations access to a suitable data analysis system isrequired; such software can be downloaded from our site.     

Hipparcos astrometric binaries

The Input Catalogue of some 100000 stars that is presently prepared for observation by the astrometric satellite HIPPARCOS, will contain many double and multiple systems. Because of the Hipparcos observation technique, these systems have to be divided in a few particular categories that are described and discussed. Each of them leads to specific considerations concerning the contribution of the Hipparcos observations. The category of very close pairs to which Hipparcos will certainly add many systems newly discovered during the mission, is compared to that of the few astrometric pairs that have been discovered by groundbased techniques.Hipparcos appears finally as a very important tool in double star astronomy research and especially in the field of very close systems.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846).     

The astrometric signal of microlensing events caused by free floating planets

Astrometric observations of microlensing events can be used to obtain important information about lenses. During these events, the shift of the position of the multiple image centroid with respect to the source star location can be measured. This effect, which is expected to occur on scales from micro-arcseconds to milli-arcseconds, depends on the lens-source-observer system physical parameters. Here, we consider the astrometric and photometric observations by space and ground-based telescopes of microlensing events towards the Galactic bulge caused by free floating planets (FFPs). We show that the efficiency of astrometric signal on photometrically detected microlensing events tends to increase for higher FFP masses in our Galaxy. In addition, we estimate that during five years of the Gaia observations, about a dozen of microlensing events caused by FFPs are expected to be detectable.