Some useful astronomical links
Preprints and Papers
Currently one of the best ways to stay up to date on what is being submitted is to consult the ApJ's yellow pages. This is a reactive activity. It is easier to receive a daily message from the preprint database at the Los Alamos National Laboratory (http://xxx.lanl.gov/archive/astro-ph). It is important to remember though that the documents in the database were not yet refereed and they are just preprints subject (sometimes) to major reviews. The archive has several mirrors and it is best to select the closer one for retrieval. The Scuola Internazionale Superiore di Studi Avanzati in Triestre is one of them.
Actual papers can be obtained from NASA's Astrophysical Data Service, ADS (at http://adswww.harvard.edu/) and its mirror sites in France (http://cdsads.u-strasbg.fr) and Japan (http://ads.noa.ac.jp/). The ESIS Bibliographic Service is another option in Europe (http://www.esrin.esa.it/htdocs/esis/esisbib.html).
Personal and institutional subscribers to the ApJ can read on-line or download accepted papers (http://www.journals.uchicago.edu/ApJ/journal/). A mirror site also exists in Europe (http://cdsaas.u-strasbg.fr:2001/ApJ/journal). The list of the papers submitted to several journals, what used to be called the astronomical yellow pages can be read on-line (http://www.noao.edu/apj/ypages/yp.html). To complete the electronic library, Astronomy and Astrophysics main journal (http://link.springer.de) and Astronomy and Astrophysics Supplement (http://www.ed-phys.fr/docinfos/OnlineAetA.html) are also on-line.
Planetary science papers published on Icarus are also on-line (http://astrosun.tn.cornell.edu/Icarus/).
Pages with references and documents in Spanish can be reading the electronic journal Astronomía Latino Americana (http://www.inaoep.mx/~ala).
Pretty pictures and articles for interest to amateurs are available in the on-line version of Sky and Telescope (http://www.skypub.com/), Astronomy magazine(http://www.astronomy.com) or the Astronomical Society of the Pacific (http://www.aspsky.org).
Nature also publishes an electronic edition (http://www.nature.com).
NASA Extragalactic Database (NED)
NED (http://nedwww.ipac.caltech.edu/; telnet ned.ipac.caltech.edu username: ned) contains information about 800,000 extragalactic objects which includes 1.3M names and almost a million bibliographic references (since 1983), abstracts (since 1988) and notes on the sources. NED is the place to start on a project that includes extragalactic sources and is freely available to any person with an Internet account.
NED includes an object-based database, it organizes all information around individual extragalactic objects not by catalogs (Helou et al 1995).
The master list was culled from around 40 major astronomical catalogs plus several lists from the literature (PG quasars or compact groups of galaxies, for example). NED team members continuously produce the cross identification of each source in the list.
The information for each of the sources (if available) includes:
NED also includes abstracts of dissertations devoted to extragalactic studies defended since 1980. Dissertation titles and authors only are available for theses since 1909.
It is very easy to search for information in NED. Little information is needed about the object as the query can be started by name, near a position (in equatorial, ecliptic, galactic or super-galactic) IAU formatted name, near the position or by object type. The list can be created also in such a way that object types are excluded from those retrieved inside a searching radius.
If the list is long, a batch job request can be submitted. The user will send an e-mail message to email@example.com and NED will reply with the desired information in one or more messages. NED can also be run in a client mode, making it possible to access the database from within user programs.
To complete the search an image of the object (or the region) can be obtained. NED can produce images from the Digitized Sky Survey, infrared images from the IRAS survey and radio maps.
Thousand and one catalogs in Strasbourg: CDS
The first attempt at a systematic collection of information about astronomical objects and query them in an easy way was done at the Centre des Donneés Astronomiques de Strasbourg (CDS)
(http://cdsweb.u-starsbg.fr/CDS.html). Since 1983 the CDS is embarking in a project to "collect, homogenize, distribute and preserve [on-line] astronomical information" (F. Genova, personal communication). The information is not raw data but metadatabases created from observing logs, catalogs, papers and images.
The services available at the CDS include:
SIMBAD (Set of Identifications, Measurements, and Bibliography for Astronomical Data) can be accessed from the WWW (at the CDS --
http://cdsweb.u-strasbg.fr/simbad.html or at the US node http://www.cfa.harvard.edu/simbad), via telnet or e-mail. SIMBAD has 5,000 individual user accounts in 55 countries. An IP control password will be available soon that will allow institutional access to the service. As it is necessary to have an account, prospective users in the US (charges assumed by NASA) should send a request to firstname.lastname@example.org. Others (European charges are covered by ESO and ESA) should enquire at their libraries or email@example.com.
SIMBAD contains more than 1.5M objects, more than 4.3M identifiers and more than 95k references from 90 journals (since 1950 for stars and since 1983 for extragalactic objects). The data included in SIMBAD evolves constantly as the measurements are updated and more references included daily (in 1994 there were 500 new entries per month).
Its most important characteristic is the cross-identification of the objects. SIMBAD contains a cross-index to several hundred astronomical catalogs and logs of space observatories.
It can be queried by name, coordinates or reference code. SIMBAD is the result of a cooperative effort among several institutions. The bibliography is compiled by the Institute d'Astrophysique in Paris and the Bordeaux Observatory; the catalogs by the Observatoire du Midi Pyrenées, the Paris and Besançon Observatories, Astronomisches Recehen-Institut (Heidel berg) and Institute for Astronomy of the Russian Academy of Sciences; correction to the databases are made by the Montpellier Observatory.
As was the case with NED, SIMBAD can also be used in a client/server mode to retrieve essential information on objects to be included in other programs.
What started with SIMBAD was continued with an impressive collection of browsers and catalogs, a true Astronomer's Bazaar
VizieR (http://cdsweb.u-strasbg.fr/cgi-bin/VizieR) is a collection of around 2400 catalogs (1800 already available on-line) that can be queried either by the specific entry on it, by author name, by keywords, wavelen gth of interest and the mission or through a map based on a neural network analysis of the keywords associated to the catalogs. With Hipparcos on line since May 1997 the use of VizieR has increased exponentially.
VizieR is a cooperative endeavor among the CDS, the Astronomical Data Center in the US, Russian Academy of Sciences Institute for Astronomy (INASAN), National Astronomical Observatory of Japan, the Beijing Observatory in China and the Indian Inter-University Centre for Astronomy and Astrophysics (IUCAA). The CDS created a standard that is followed by these data centers and (most importantly!) by the journals in the publication, presentation and distribution of the data.
Future enhancements include links to SIMBAD and other external archives.
Aladin is an interactive sky atlas that includes images from the Digitized Sky Survey, and for some regions (the LMC, SMC and galactic plane for example) special images with 1" resolution. It also includes a cross identification tool of the objects in the image. Aladin is only available via and X-term version, a WWW port is being developed at the moment.
Dictionary of Nomenclature of Astronomical Objects
The Dictionary of Nomenclature of Astronomical Objects, an up-to date electronic version of the "Second reference dictionary of the nomenclature of celestial objects" (Lortet et al. 1994)
(http://simbad.u-stasbg.fr/cgi-bin/Dic)is a SIMBAD by-product.
Information & On-line Data in Astronomy
At the CDS there is an on-line version of the book "Information & On-line Data in Astronomy" (http://cdsweb.u-strasbg.fr/data-online.html) (Egret & Albrecht 1995). Each section of the book has links to most of the archives and centers of interest.
StarPages (http://vizier.u-strasbg.fr/starpages.html) a collection of directories, dictionaries and astronomical databases:
- Starheads (http://vizier.u-strasbg.fr/starheads.html) list with around 4000 astronomers world wide
- StarWorlds (http://vizier.u-strasbg.fr/starworlds.html): lists more than 6000 organizations world wide
- StarBits ( http://vizier.u-strasbg.fr/starbits.html): lists of around 115,000 acronyms and abbreviations .
The National Space Science Data Center (NSSDC) provides access and distributes a wide variety of data obtained with several NASA missions. Not only astronomical images and spectra are included, but also space plasma data and Earth and space photographs. It is one of the largest astronomical archives.
The Lyon-Meudon Extragalactic Data Base, LEDA (telnet leda.univ lyon1.fr; login: leda) includes on-line versions of the Principal Galaxies Catalog (more than 73,000 objects), the Third Reference Catalog of Bright Galaxies (more than 23,000 objects), HI catalogs and the Catalog of individual optical velocity measurements (OVC). Around 70 parameters are included for each of the more then 95,000 objects. Among them, the position, flux at different wavelength and colors, redshift or radial velocity and surface brightness. The references for all listed measurements are also included. All the parameters are listed in a homogeneous way, calculations are made only from accepted models.
Images of many of the galaxies can be retrieved as well as a map of the region listing all the objects with their PGC number. The output figures can be drawn with or without the stars in the field.
If the list of objects is long, a query can be made by e-mail to firstname.lastname@example.org
The very useful Handbook of Space Astronomy and Astrophysics by M.V. Zombeck is available on-line thanks to Cambridge University Press.
Other useful information on astrophysical objects is stored at the CDS web (http://cdsweb.u-strasbg.fr/data-online.html)
Other images, lists and catalogs
Among the billions and billions of bits in the Web, some other useful lists and archives are:
Catalog of Non-Stellar Objects (http://adac.mtk.nao.ac.jp/prt7.html)
Catalog of Messier objects (http://www.seds.org/messier)
NGC images (http://maxwell.sfsu.edu/asp/ngc.html)
Information on extra-solar planets (http://www.obspm.fr/department/darc/planets/encycl.html)
The Digital Sky Survey
As part of the activities leading to the Guide Star Catalog (GSC) photographic plates covering the whole sky where scanned. For the northern hemisphere, a new set of shorter exposure plates (the Quick-V plates) were obtained. For the south the ESO/SERC Southern J plates were used. In addition some regions were covered by special plates. In parallel with the scanning, the original Palomar Observatory Sky Survey (POSS-I) XE plates were scanned. The latter and the southern plates constitute the Digitized Sky Survey (DSS). A detailed description of the GSC, its contents and the plates used can be found in Lasker et al. (1990),
Russell et al. (1990) and Jenkner et al. (1990).
Once these scans were finished the two PDS machines at STScI were completely refurbished. After an agreement with the Palomar Observatory, the plates that constitute the POSS-II are being scanned. All these scans are available on-line (http://archive.stsci.edu/dss/).
The original scans were made with a pixel size of 25µ, resulting in a 14,000 x 14,000 pixel image with a scale of 1.67"/pix. A 512x512 image covered then an area of 14.3'x14.3'. The new scans are done with a pixel size of just 15µ resulting in a raster of 23,000x23,000 pixels.
Please note that to provide coordinates for targets to be observed with the Hubble Space Telescope it is necessary to use only the plates used to create the GSC and not the ones from the POSS-I.
The Digitized Sky Survey is a set of CD-ROMs containing the POSS-I XE and SERC J scanned plates compressed 10X. It covers the whole sky. A 100X compressed version, called RealSky is presently available only for the northern sky, with the southern part to be released soon. Both sets are sold by the Astronomical Society of the Pacific.
These new scans will be used to construct the GSC-II. This updated version will include 2 x109 objects (100 times more than GSC-I), at least 2 epochs and 2 bands; proper motions will be calculated with an error less than 4.0 mas/yr and a magnitude error between 0.1 and 0.2mag (GSC-I did not contain proper motion information and the magnitude error is 0.4mag).
Automatic Plate Scanner
The University of Minnesota created the Automatic Plate Scanner Catalog (APS) from the scans of the POSS-I O and E plates with |b| > 20o. The catalog consists of a list of classified objects found on both plates using a neural network algorithm to separate the stellar and non-stellar objects. The two catalogs (one for each band) are available on-line (http://aps.umn.edu), they contain coordinates, magnitudes, colors and other parameters. They provides information on 108 stars and around 107 galaxies up to a limiting magnitude of less than 21 in the blue.
The Institute of Astronomy of the Bulgarian Academy of Sciences maintains a database of Wide-Field Plates (http://www.wfpa.acad.bg). The information is standardize and lists the object name, emulsion and filter, J2000 coordinates and UT.
Optical and UV surveys
A list of optical and UV surveys was generated after IAU's Symposium 179 (http://www-gsss.stsci.edu/iauwg/survey_url.home). Among them
The Sloan Digital Sky Survey (SDSS) (http://www-sdss.fnal.gov:8000/) will be a complete survey of ¼ steradians using 30 2048x2048 CCDs in five bands and two fiber optics spectrographs. It will consist of a photometric catalog of 108 galaxies, 108 stars and 106 quasars; a spectroscopic catalog including emission and absorption lines, images in five bands and 1-d spectra of 106 galaxies, 105 stars, 105 quasars and 104 clusters. As the size of the SDSS will probably exceed 1010 bytes, maintaining, distributing and querying it will be quite a challenge.
ESO slice project (http://boas5.bo.astro.it/~cappi/esokp.html) is a galaxy redshift covering 30 square degrees near the South Galactic Pole, complete up to bJ=19.4. It includes the redshifts of 3,000 galaxies.
Two degree Field (2dF) QSO redshift survey: will determine the large scale tridimensional structure of the universe up to z~0.1 by measuring the redshift of 250,000 galaxies. In addition, spectra of 30,000 quasars will be obtained (http://www.aao.gov.au/local/www/rs/qso_surv.html) A mirror site exists in Great Britain (http://www.ast.cam.ac.uk/AAO/www/rs/qso_surv.html)
FOCA (http://www.astrsp-mrs.fr/~xbig/foca/node2.html) was a small airborne telescope that surveyed 70 square degrees at 2000Å with an angular resolution of 12" and 20", the generated catalog includes galaxy counts and color distributions for sources between 15 and 18.5mag
Alexis (http://alexis-www.lanl.gov) is an EUV/X-ray satellite surveying the sky to map the diffuse soft X-ray background, to study flaring stars and make observations of EUV sources. Any object detected found is immediately compared with lists of known objects to determine its possible nature
Several institutions provide on-line facilities that create maps of the sky at
one or more wavelengths. Among them,
The Hipparcos catalog contains 118,218 astrometric entries (milliarcsecond position, parallax and proper motion) with a median error of 1mas. The Tycho catalog on the other hand includes more than a million objects with a median error of 7mas for the brighter sources and 25mas for the fainter ones. More than 100 epochs were acquired for the photometry of the objects in the Hipparcos catalog. The photometric error is between 0.0004 and 0.0007mag for the brighter stars.
These catalogs are now the astrometry standards. The catalog epoch is J1991.25; the equinox J2000.0
The European Space Agency distributes theses catalogs as a series of 16 books and several CD-ROMs. The catalogs can also be queried in the WWW
Simulated data is useful, among other things, to, for example test algorithms, check photometry results, predict exposure times or optimize an observation using deconvolution techniques.
Tiny TIM (http://scivax.stsci.edu/~krist/tinytim.html) creates HST point spread functions. A PSF can be generated for any instrument with any configuration, any wavelength and position. Tiny Tim runs on VAX/VMS, UNIX and Linux
The STSDAS (http://ra.stsci.edu/STSDAS.html) synphot package simulates photometric data and spectra as they are observed with the Hubble Space Telescope. Its output is used also in the exposure time calculators that users query to determine the number of orbits needed for their projects. Synphot can be used to estimate count rates obtained by other telescopes by changing the components lookup tables and instrument graph. A manual is available on-line.
All instruments currently on board the Hubble Space Telecope have Exposure Time Calculators to estimate either the signal to noise or the exposure time of observations with them.
Other Meta Databases
allows the user to retrieve information from several sites using one single
query form. The user only needs to specify a position (or a name that will be
resolved into a position), a search radius and a list of the services (as
available from different organizations) that can be accessed. At the moment
only a prototype exists on-line
Another listing of software packages and utilities is provided by SEDS. (http://www.seds.org/billa/astrosoftware.html)
Selected packages are available on-line at the Starlink Software Store (http://star-www.rl.ac.uk). The distribution method is changing as the primary method will be by CD-ROM instead.
The latest software developments are usually presented at the Astronomical Data Analysis Software and Systems (ADASS) conferences. Its proceedings are published by the ASP. Another series were the ESO ST-ECF Data Analysis conferences whose proceedings were published by ESO.
The Interactive Data Language (IDL) developed by RSI (http://www.rsinc.com) is widely used for reduction and analysis. It is a commercial package with ports to many systems from laptops to workstations.
Linux for astronomy
The Random Factory (http://home.earthlink.net/~rfactory/lfa.html) publishes a CD-ROM with a collection of the most popular reduction and analysis astronomical software that run under the Linux operating system.
The packages include:
Some basic statistics computations are available in the STSDAS' ttools and statistics packages. More serious techniques, like multivariate analysis can be found in the Statistical Consulting Center for Astronomy
(http://www/stat.psu.edu/scca). This site, besides being the portal to a service for statistical queries includes also links to code (http://www/stat.psu.edu/statcodes)
There are several "tours" of the solar system. The most popular ones are:
How am I going to remember this?
Fortunately there are on-line compilations of most of the information presented in this section. In particular the AstroWeb consortium is probably one of the best places to start surfing. There are several versions of AstroWeb at
- STScI's AstroWeb (http://www.stsci.edu/science/net resources.html)
- NRAO's AstroWeb (http://fits.cv.nrao.edu/www/astronomy.html)
- CDS' AstroWeb (http://cdsweb.u-strasbg.fr/astroweb.html)
- MSSSO's AstroWeb (http://msowww.anu.edu/anton/astronomy.html)
- VILSPA's AstroWeb (http://www.vilspa.esa.es/astroweb/astronomy.html)
All of them validate the links daily and report on those that are not accessible.
Finally the web crawlers and cyber-robots that mine the information superhighway are very helpful to find obscure links, some are:
- Altavista (http://www.altavista.com)
- Yahoo (http://www.yahoo.com)
- Lycos (http://www.lycos.com)